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2017 Annual Meeting of
The Pittsburgh‐Cleveland Catalysis Society
May 25th, 2017 120 Auburn Science and Engineering Center (ASEC)
The University of Akron Akron, OH 44325
Sponsors:
Auburn West Tower Rehabilitation
Future site of InfoCision Stadium and Summa Field
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2017 Annual Meeting of the Pittsburgh‐Cleveland Catalysis Society (PCCS) May 25th, 2017
120 Auburn Science and Engineering Center (ASEC), The University of Akron
8:30 AM Registration and breakfast
9:00 AM Invited Talk: Prof. Steven Chuang, University of Akron: Identification of the Structure of Adsorbed Species in CO2 Capture and Utilization Processes by Infrared Spectroscopy
9:40 AM Yasemin Basdogan, University of Pittsburgh: Accurate computational modeling of chemical reactions in polar solvents using cluster‐continuum modeling
10:00 AM Haoran He, Pennsylvania State University: DFT Studies of Intermetallic Gamma‐Brass Crystal Structures for Selective Hydrogenation
10:20 AM Xiaochen Shen, University of Akron: More accurate depiction of adsorption energy on transition metals using work function as one additional descriptor
10:40 AM Stephen D. House, University of Pittsburgh: Computationally Assisted STEM and EXAFS Characterization of Tunable, Rh/Au Bimetallic Nanoparticle Catalysts
11:00 AM Invited Talk: Prof. David W. Flaherty, University of Illinois at Urbana‐Champaign: Direct Synthesis of H2O2: Competing Reaction Pathways Depend Differently on Surface Structure
11:40 AM Lunch and Poster Session (Hallway, 2B level ASEC)
1:20 PM Invited Talk: Prof. Ana C. Alba‐Rubio, University of Toledo: Multifunctional homogeneous‐heterogeneous polymer catalysts for biomass conversion
2:00 PM Irem Sen, Carnegie Mello University: Alloy Catalysis across Composition Space
2:20 PM Hao Chi, University of Pittsburgh: The Impact of Copper Oxidation States on the Reactivity in Partial Oxidation of Methanol
2:40 PM Tuo Ji, University of Akron: Hierarchical Macrotube/Mesopore Carbon Decorated with Mono‐dispersed Ag Nanoparticles as Highly Active Catalyst
3:00 PM: Break
3:20 PM Invited Talk: Prof. James R. McKone, University of Pittsburgh: Binary Ni–Mo electrocatalysts for alkaline hydrogen evolution
4:00 PM Wenbin Yin, University of Akron: Enhancing Performance of a Ni/YSZ anode in CH4 and CH4/CO2 Solid Oxide Fuel Cell with a high active oxidation Pd@CeO2 catalyst
4:20 PM Yuxin Zhai, University of Akron: Photocatalysis Synthesis of L‐pipecolinic Acid from L‐lysine on TiO2 and Ag/TiO2 Catalysts
4:40 PM Judges meet followed by awards
2017 Annual Meeting of the Pittsburgh‐Cleveland Catalysis Society (PCCS) 11:40 AM – 1:20 PM, May 25th, 2017
Hallway, 2B level, Auburn Science and Engineering Center (ASEC), The University of Akron
Poster Session
Yahui Yang, University of Pittsburgh: Impact of Pore Diffusion in Ni@SiO2 Core@Shell Nanocatalysts
Lin Pan, University of Akron: Hydrogenation of phenol to cyclohexanone via tubular nanofiber supported catalyst
Xiaoxiao Yu, Carnegie Mellon University: PdxCu1‐x Phase Transition at Nanoscale
Dominic R. Alfonso, National Energy Technology Laboratory‐DOE: Assessment of Trends in the Catalytic Electroreduction of CO2 on Metal Nanoparticles
GAYATRI SHRIKHANDE, University of Akron: Chemoenzymatic Synthesis and Characterization of Multifunctional Fluoresceins for Breast Cancer Diagnosis
Henry O. Ayoola, University of Pittsburgh: Atomic structure of the Pt/γ‐Al2O3 interface through a combined experiment and theory approach: A model catalyst study
Mudit Dixit, University of Pittsburgh: Understanding the C‐H Activation and
Dehydrogenation Mechanisms of Alkanes on ‐Alumina Ross V. Grieshaber, University of Pittsburgh: Migration and structural evolution of carbon‐
encapsulated Fe nanoparticles via in situ TEM
James Dean, University of Pittsburgh: CO2 Activation on Cu‐based Bimetallic Nanoparticles
Jiawei Liu, The University of Akron: Direct Catalytic Conversion of CO2/CH3OHto Carbonates: an in situ FTIR Study
Yanbo Pan, The University of Akron: Wide Operation Temperature Window for CO PROX on Pt‐Mn Alloy Nanoparticle Catalyst
Gizem Ozbuyukkaya, University of Pittsburgh: New Mechanistic Insights into Oxidative Coupling
of Methane
Matthew T. Curnan, University of Pittsburgh: Connecting O Diffusion along Cu Interfacial Defects with Cu Oxide Nano‐island Nucleation and Growth: A Theoretical and Experimental Study
PRAJAKATTA MULAY, The University of Akron: SYNTHESIS OF DIAMINE‐FUNCTIONALIZED PEGs VIA ENZYME CATALYZED ESTERIFICATION
Wanling Zhu, University of Pittsburgh: Impact of Surface Hydroxylation on Stability and Reactivity of Silica‐Support Metal Nanoparticles: On the Way to Tailor the Catalysts
2017 Annual PCCS Meeting Planning Committee and Officers
President: Zhenmeng Peng Assistant Professor Dept. Chem. & Biomol. Eng. Univ. Akron [email protected] President‐Elect: Giannis Mpourmpakis Assistant Professor Dept. Chem. Eng. Univ. Pittsburgh [email protected] Secretary: Irem Sen Dept. Chem. Eng. Carnegie Mellon Univ. [email protected] Treasurer: Dominic Alfonso Chemist National Energy Technology Lab [email protected] Director: Götz Veser Professor Dept. Chem. Eng. Univ. Pittsburgh [email protected] Corporate Sponsor: Paul Kester Sr. Sales Engineer Micromeritics Instrument Corp. [email protected]
Invited Talk Identification of the Structure of Adsorbed Species in CO2 Capture and Utilization Processes
by Infrared Spectroscopy
Steven S. C. Chuang Department of Polymer Science
The University of Akron, Akron, OH 44325
This presentation will provide an overview of pathways for CO2 capture and conversion processes. This presentation will also discuss the use of infrared (IR) and Raman spectroscopy as well as transient (i.e., dynamic) approaches to study the structure of adsorbed species, the nature of active sites and rate‐determining steps for controlling CO2 capture by amine sorbents and a number of catalytic reactions including CO2/CH4 reactions in solid oxide fuel cells (CO2/CH4‐SOFC) and photocatalytic conversion of CO2/H2O.
Invited Talk Multifunctional homogeneous‐heterogeneous polymer catalysts for biomass conversion
Ana C. Alba‐Rubio Dept. of Chemical Engineering. University of Toledo.
Poly(styrenesulfonic acid) (PSSA) combines the advantages of both homogeneous and heterogeneous catalysis. PSSA is soluble in polar solvents; therefore, all acidic sulfonic groups are readily accessible. In addition, the catalyst cannot be deactivated through coking because there is no surface for the carbonaceous species to be deposited. At the same time, PSSA, due to its high molecular weight, can be easily recovered by ultrafiltration for further utilization. This polymer catalyst can be obtained by sulfonation of polystyrene waste (e.g., yogurt packaging or expanded polystyrene), which is an additional advantage from an environmental point of view.1
The talk will address the effectiveness of this catalyst in several biomass conversion reactions that require Brønsted acid sites: synthesis of biodiesel from vegetable oil,2 dehydration of xylose to furfural,1 furfural oxidation to maleic and succinic acids,1 and synthesis of hydroxymethylfurfural (HMF) from fructose. The addition of Lewis acid functionality to this polymer for a one‐pot synthesis of HMF from glucose will be also discussed.
1. Alonso‐Fagúndez, N.; Laserna, V.; Alba‐Rubio, A.C.; Mengibar, M.; Heras, A.; Mariscal, R.; Granados, M.L., Poly‐(styrene sulphonic acid): An acid catalyst from polystyrene waste for reactions of interest in biomass valorization. Catalysis Today 2014, 234, 285‐294.
2. Granados, M.L.; Alba‐Rubio, A.C.; Sádaba, I.; Mariscal, R.; Mateos‐Aparicio, I.; Heras, Á., Poly (styrenesulphonic) acid: an active and reusable acid catalyst soluble in polar solvents. Green Chemistry 2011, 13 (11), 3203‐3212.
Invited Talk Direct Synthesis of H2O2: Competing Reaction Pathways Depend Differently on Surface
Structure Neil M. Wilson, Pranjali Priyadarshini, David W. Flaherty
University of Illinois at Urbana‐Champaign, Urbana, Illinois 61801 H2O2 is a benign and selective oxidant useful for epoxidations, bleaching, and disinfection, yet, its use is limited because the current H2O2 production method is viable only at very large scales. Direct synthesis of H2O2 (H2 + O2 → H2O2) could enable on‐site, and even in situ, H2O2 production, which motivates searches for highly selective catalysts. H2O2 formation rates and selectivities are known to increase when Au or Sn are added to Pd clusters. However, the reasons for these changes are not understood.
Here, we combine rate measurements on Pd and Pd‐based bimetallic clusters to determine the mechanism of this reaction and to understand the reasons why alloying Pd often increases H2O2 selectivities. The change in H2O2 and H2O formation rates with H2 and O2 pressures are not consistent with a Langmuirian mechanism, but instead suggest O2* species react with a liquid‐phase intermediate. Additionally, H2O2 formation rates in protic solvents are 103 larger than those measured in aprotic liquids. These observations suggest that proton‐electron transfer processes, reminiscent of the two electron oxygen reduction reaction, form H2O2 on metal clusters. Charge conservation requires that these metal clusters must also catalyze both heterolytic hydrogen oxidation (H2 → 2H+ + e‐) and oxygen reduction (O2 + 2e
‐ + 2H+ → H2O2).These reactions occur on surfaces saturated with O2*‐ and OOH*‐intermediates. In parallel, O‐O bonds within chemisorbed intermediates cleave homolytically to form H2O. Consequently, the H2O2 selectivities are determined by competition between heterolytic and homolytic reactions involving O2 at liquid‐solid interface.
Proton‐electron transfer is the dominant pathway for H2O2 formation also on monometallic and bimetallic clusters comprised of Pd and either Au, Zn, or Sn. Incorporating a second metal into Pd clusters does not change the mechanism for H2O2 or H2O formation. These modifications do, however, change barriers for the formation of H2O (significantly) with lesser effects on barriers for steps that lead to H2O2. Comparisons of measured activation enthalpies for the competing reaction pathways to differences in product selectivities on across a series of Pd‐bimetallic catalysts show that that O‐O bond rupture is more sensitive to the electronic structure of the cluster than other elementary steps, and that electronic effects are largely responsible for increased H2O2 selectivities on these catalysts. Ensemble effects that reflect changes in the distribution of active sites are apparent yet to a lesser degree. Both mechanisms can increase H2O2 selectivities significantly. Overall, our work presents a clear mechanism for H2O2 formation on metal clusters and explains the roles of solvent identity and cluster composition in determining H2O2 selectivities. We gratefully acknowledge support from the National Science Foundation and the University of Illinois.
Invited Talk Binary Ni–Mo electrocatalysts for alkaline hydrogen evolution
James R. McKone Assistant professor of chemical engineering, University of Pittburgh
Water electrolysis technologies can be driven with electricity from renewables to provide a clean source of hydrogen as a fuel or chemical feedstock. Commercial electrolyzer systems based on proton‐exchange membranes have advanced considerably in recent years, but they are still constrained by high capital expense. Considerable improvements in system cost can be achieved by transitioning to alkaline environments, but much less work has been done to understand and develop practical alkaline anion exchange membranes and electrolysis catalysts compared to analogous acid‐based components.
We are studying binary Ni–Mo composite catalysts for the hydrogen evolution half‐reaction in water electrolysis. For decades, these materials have been known to give among the highest observed activities (high geometric current density at low overpotential) that have ever been obtained using non‐precious metals. Nevertheless, the intrinsic activity, reaction mechanism, and even surface composition of Ni–Mo composites have been the subject of considerable debate. In this presentation, I will discuss work to develop straightforward synthetic protocols for Ni–Mo electrocatalysts that can be implemented in conventional water electrolyzers and solar‐driven water splitting devices. I will also discuss recent and ongoing work to elucidate composition‐structure‐function relationships in these systems, leading to multiple plausible hypotheses as to why Ni–Mo exhibits higher activity for hydrogen evolution compared to either Ni or Mo alone.
Accurate computational modeling of chemical reactions in polar solvents using cluster-
continuum modeling
Yasemin Basdogan*, John A. Keith
Department of Chemical and Petroleum Engineering,
University of Pittsburgh
3700 O'Hara Street, Pittsburgh, PA 15261
Recent studies have precipitated concerns about reaction mechanisms predicted using
quantum chemistry methods. It remains especially difficult to accurately model mechanisms
having multiple steps in polar solvents. Using the Morita-Bayless-Hillman reaction mechanism
as an example, we have studied how local solvation effects that are not treated by continuum
solvation models can dramatically affect reaction pathways. Our automated procedure uses
global optimization methods (ABCluster) to generate local solvation environments around
reaction intermediates modeled with cluster-continuum modeling. We then model reaction
pathways involving these intermediates using growing string methods. Our approach can
accurately predict the reaction pathway derived by experiment, but surprisingly, calculations
indicate that pathways operate through high energy intermediate states. This approach offers a
practical correction to errors intrinsic to widely used continuum solvation methods and
therefore is a more reliable means to model homogeneous reaction mechanisms.
DFT Studies of Intermetallic Gamma-Brass Crystal Structures for Selective Hydrogenation
Haoran He, Anish Dasgupta, Gaurav Kumar, Robert M. Rioux, and Michael J. Janik
Department of Chemical Engineering, The Pennsylvania State University, University Park, PA 16802, USA
*mjanik@ psu.edu; (814) 863-9366
Bimetallic compounds can offer tunable site electronics and ensemble structure for selective hydrogenation catalysis. In this study, we consider the γ-brass phase (Cu5Zn8 prototype), in order to expose surfaces with controlled Mx nuclearity to control the selectivity for hydrogenation. The γ-brass structure has a 52 atoms unit cell with 4 distinct symmetry sites —outer tetrahedral (OT), inner tetrahedral (IT) octahedral (OH) cuboctahedral (CO) as shown in Figure 1. In particular, the Pd-Zn γ-brass atomic arrangement as well as the substitution pattern of Zn by Pd in the Pd-Zn γ-brass phase (15.4-24%) has been extensively studied by Edstrom and Westman through x-ray diffraction analysis[1]. Surface energy calculations indicated that the most stable Pd8Zn44 facet is (1 -1 0), which exposes only monomers for Pd8, but includes Pd trimers for Pd9-11. We vary the number of Pd atoms per isolated active site and investigate its effect on H2 dissociation and acetylene hydrogenation mechanisms. DFT calculations agreed with experimental results that H2 activation is faster on trimer sites, substantiating the formation of Pd3 trimer sites on Pd9Zn43 catalyst surfaces. The activation barrier for H2 dissociation is nearly identical experimentally on Pd9, Pd10 and Pd11, further substantiating the isolation of the Pd trimer sites. DFT calculations indicate that acetylene binds strongly on both monomer bridge and trimer sites, whereas ethylene binds strongly on monomer atop and trimer side atop sites. At the same time, H2 dissociation and binding adjacent to ethylene is only possible on the trimer sites. DFT calculations showed the apparent barrier of ethylene hydrogenation is higher than the ethylene desorption barrier, which indicates Pd8Zn44 is superior catalyst in selectively hydrogenating acetylene to ethylene. Pd9-11 on the other hand, contains trimers on the surface, which can lower the ethylene hydrogenation barrier, compared with Pd8Zn44. The full path of acetylene hydrogenation on these isolated sites, as well as a microkinetic model for acetylene hydrogenation on these intermetallics, will be presented. The gamma-brass intermetallic structures offer isolated active sites with controlled nuclearity, allowing both the design of active and selective catalysts as well as the elucidation of site requirements.
Figure 1. Illustration of the sites in the γ-brass structure: inner tetrahedral (IT, red); outer
tetrahedral (OT, blue); octahedral (OH, green); and cuboctahedral (CO, orange).
References
1. Edstrom, V.A and S. Westman, X-ray Determination of Structure of Cubic Gamma Pd, Zn Phase. Acta Chemica Scandinavica, 1969. 23 (1): p.279-&.
More accurate depiction of adsorption energy on transition metals using work function as
one additional descriptor
Xiaochen Shen a, Yanbo Pan a, Bin Liu b, Jinlong Yang c, Jie Zeng c,*, Zhenmeng Peng a,*
Reaction mechanism and properties of a catalytic process are primarily determined by the
interactions between reacting species and catalyst. However, the interactions are often
challenging to be experimentally measured, especially for unstable intermediates. Therefore, it
is of significant importance to establish an exact relationship between chemical-catalyst
interaction and catalyst parameters, which will allow calculation of these interactions and thus
advance the mechanistic understanding.
Here, we proposed to use work function as one additional catalyst descriptor to more
accurately describe the adsorption energy on transition metals. By conducting comparative DFT
studies of O, OH, and OOH species adsorption on transition metals including Au, Cu, Pd, Pt, Rh,
Ag and Ni, we divided Eads into E ionic and Ecovalent contributions and discovered their quadratic
and linear correlations to W and εd parameters, respectively. We established a new Eads–(εd, W)
model, which showed a 2D polynomial function of εd and W. The new 2D polynomial model
exhibited significantly improved goodness of fitting compared with the currently used Eads–εd
model. Benefiting from an improved accuracy, the new 2D polynomial model was applicable to
calculate Eads values and predict the catalytic properties, demonstrated with the obtained
volcano plot by correlating the ORR activity of different transition metals and the calculated EO
using the fitting function. The finding that Eads can be more accurately depicted using εd and W
descriptors opens a new era for Eads calculation using measurable catalyst parameters and
helps to better understand the catalytic properties of transition metals
a Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH 44325, United States. E-mail: [email protected] b Department of Chemical Engineering, Kansas State University, Manhattan, KS 66506, United States. c Hefei National Laboratory for Physical Sciences at the Microscale, Key Laboratory of Strongly-Coupled Quantum Matter Physics of Chinese Academy of Sciences, and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China. E-mail: [email protected]
Computationally Assisted STEM and EXAFS Characterization of Tunable, Rh/Au Bimetallic Nanoparticle Catalysts
Stephen D. House1, Cecile S. Bonifacio1, Janis Timoshenko2, Pranaw Kunal3, Haiqin Wan3, Zhiyao Duan3, Hao Li3, Judith C. Yang1, Anatoly I. Frenkel2,4, Simon M. Humphrey3, Richard M. Crooks3,
Graeme A. Henkelman3
1 University of Pittsburgh, Pittsburgh, PA 15261 (USA) 2 Stony Brook University, Stony Brook, NY 11794 (USA) 3 University of Texas at Austin, Austin, TX 78712 (USA)
4 Brookhaven National Laboratory, Upton, NY 11973 (USA) The acceleration of catalyst discovery and design enabled by computational simulations is only practical if the theoretical structures identified can be synthesized and experimentally verified. Of particular interest are bi-functional/bimetallic catalysts, since each part can be tailored for a specific function, and have the potential to exceed the selectivity and efficiency of a single-component system [1]. However, the addition of a second metal greatly increases the complexity of the system; variation in the mixing patterns and reconfiguration of the elements can affect the reaction mechanisms and thus catalytic performance [2]. Most experimental tools for the characterization of nanoparticles (NPs) provide structural data, but not enough to uniquely determine the structure with atomic precision. Here we present our application of a correlative theory-experiment design approach to characterize Rh/Au bimetallic hydrogenation catalysts, which our calculations predict to have performance superior to single-element catalysts while also being tunable [3]. Multiple mixed-metal ratios of Rh/Au alloy nanoparticles were prepared via microwave-assisted synthesis. The samples were then examined using extended X-ray absorption fine structure (EXAFS) spectroscopy using the Stanford synchrotron radiation lightsource (SSRL), scanning transmission electron microscopy (STEM), and energy-dispersive X-ray spectroscopy (EDS). EXAFS samples the local atomic environments of particle ensembles to determine the average coordination number, interatomic distances, and disorder through fitting to a reference structure [4]. The nanoparticle input structures were calculated using the modified embedded atom method (MEAM). S/TEM enables direct, characterization of materials to the atomic scale and can measure the particle size, morphology, and elemental distributions (via EDS) necessary to inform accurate input models for interpreting the EXAFS data [5]. For the Rh/Au material, no simple model adequately reproduced the EXAFS data. Instead, it is a complex, heterogeneous system composed of larger (3-10 nm) Au-rich core-shell-like mixed-metal nanoparticles, small (1-3 nm) unalloyed Rh nanoparticles, and a Rh-rich background of sub-nm clusters and individual atoms. Both the size and relative abundance of particle type, as well as the structural details of the core-shell particles, depended on the stoichiometry. The details of this were only revealed through the combined, correlative effort, granting a understanding not achievable with approach alone. [1] A.K. Singh and Q. Xu, ChemCatChem 5 (2013), p. 4754-4766. [2] R. Ferrando, J. Jellinek, R.L. Johnston, Chem. Rev. 108 (2008), p. 845-910. [3] S. Garcia, et al., ACS Nano 8 (2014), p. 11512-11521. [4] A.I. Frenkel, Chem. Soc. Rev. 41 (2012), p. 8163-8178. [5] J.C. Yang, et al., Chem. Soc. Rev. 41 (2012), p. 8179-8194.
Alloys are known to possess superior catalytic properties than their pure components.
Finding the rational design of new alloy catalysts with optimal catalytic properties for a given
application is the major challenge in multicomponent catalyst design due to the need to perform
many catalyst preparation, characterization and reactivity measurements across composition
space. To accelerate this search Composition Spread Alloy Films (CSAFs), thin multicomponent
films that have composition gradients parallel to their surfaces, AxByC1-x-y with x = 0 → 1 and y =
0 → 1-x, are prepared to be able to span the entire composition space. Many otherwise intractable
fundamental scientific problems in alloy science and catalysis that can be effectively addressed
through use of CSAFs as high throughput materials libraries.
Study of alloy catalysis across composition space using a CSAF requires a multichannel
reactor system that can be used to run steady state catalytic reactions at many different positions
or alloy compositions on the CSAF. We have developed a 100 channel microreactor array that can
sample product distributions from 100 different alloy catalysts of about 10 minutes. CuxAuyPd1-x-
y CSAFs spanning all of binary and ternary composition space have been prepared using a rotating
shadow mask CSAF deposition tool which is designed and developed in our group. CSAF surface
composition and valence electron energy distributions are measured using X-ray Photoemission
Spectroscopy (XPS).
The relationship between alloy catalyst activity and electronic structure has been
investigated experimentally across a broad, continuous span of CuxAuyPd1-x-y composition space.
The CSAF was used as a catalyst library with a multichannel microreactor to measure H2-D2
exchange kinetics at 100 discrete compositions on the CSAFs over a temperature range of 333 –
597 K at atmospheric pressure. H2 conversion was chosen to be the indicator of activity. It was
found that H2-D2 exchange activity varies across the CSAF and it tends to increase with increasing
Pd content. When the activities on AuPd and CuPd binary regions are compared, it was found that
more Pd is needed in CuPd than in AuPd to achieve the same activity.
A microkinetic model that has been validated using a number of single component Cu-Pd
catalysts in a fixed bed reactor was used to estimate the energy barriers to dissociative adsorption
(∆𝐸𝑎𝑑𝑠‡
) and associative desorption (∆𝐸𝑑𝑒𝑠‡
) of H2 as functions of alloy composition, x and y. On
the CuxAuyPd1-x-y CSAF, increasing Pd content from 0 to 1 was found to decrease adsorption
barrier from 0.44 to 0.12 eV. Increasing Pd content from 0.25 to 1 was found to increase desorption
barrier from 0.4 to 0.74 eV which suggests H2-D2 exchange reaction is limited by H2 desorption
step within this Pd content.
Spatially resolved X-ray photoelectron spectra were obtained from the CSAFs and used to
estimate the energy of the valence-band center as a function of alloy composition. The v-band
center shifted monotonically from -3.4 to 5.6 eV across the CuxAuyPd1-x-y CSAF. The barrier to
dissociative adsorption of H2 was found to decrease as the v-band energy increases. This data
provides the first experimental correlation of elementary reaction barriers with valence band
energy across a continuous span of alloy composition space.
PCCS Annual Symposium - Spring 2017 Oral presentation
The Impact of Copper Oxidation States on the Reactivity in Partial Oxidation of Methanol
Hao Chi1, Christopher Andolina1, Jonathan Li2, Matthew Curnan1, Guangwen Zhou2, Götz Veser1 and
Judith Yang1
1University of Pittsburgh, Pittsburgh, PA 15216 (USA) 2State University of New York, Binghamton, NY 13902 (USA)
Abstract:
To mitigate the impact of climate change and pollution, we need to replace our current fossil fuel based energy supply with cleaner energy production methods, such as fuel cells. Methanol is of particular interest due to its relatively high energy density and safe handling. Hence methanol can be used to replace H2 as a storage fuel to power fuel cell directly or indirectly. The partial oxidation of methanol (POM, CH3OH + 0.5O2 → CO2 + 2H2) catalyzed by a copper based catalyst can provide on-board generation of fuel-cell ready H2 streams. Although POM activity of copper-containing catalysts has been studied for decades, the reaction mechanism and the catalytically active sites are still poorly understood. In particular, the chemical nature of the active phase (Cu0, Cu+ or Cu2+) is unclear and their impacts on activity and selectivity of POM are unknown. In the present contribution, we present results from a study of partial oxidation of methanol (POM) catalyzed by Cu/ZnO powder catalysts with the aim to identify correlations between POM reactivity and Cu oxidation state. We prepared a 30wt% Cu/ZnO nanoparticle catalyst by a co-precipitation synthesis. The catalytic performance was measured at different O2 /methanol molar ratios in a home-built micro-reactor. The Cu oxidation state was assessed at different time-points via ex-situ X-ray photoelectron spectroscopy (XPS). We found that the reactivity for POM and the oxidation state of copper changes with reaction time and with O2 to methanol feed ratio. Most importantly, we observed a strong correlation between H2 selectivity and (metallic) Cu0 content of the catalyst. Surprisingly, the CO2 selectivity was not significantly impacted by the oxidation state of the catalyst, but showed a strong correlation with the O2 partial pressure. Based on the observed correlations, we propose a mechanism for POM including different bonding configurations of intermediates between metallic Cu and Cu2O surfaces. We are currently in the process of verifying key reaction steps by first—principle calculations. The knowledge we gain from this study will benefit the optimization of current Cu-based catalysts which may lead us to a promising methanol based energy economy.
Hierarchical Macrotube/Mesopore Carbon Decorated with Mono-dispersed Ag
Nanoparticles as Highly Active Catalyst
Tuo Ji and Jiahua Zhu*
Noble metal nanoparticles have attracted significant interests in catalysis science and
engineering due to their unprecedented activities as heterogeneous catalysts. To
maximize efficiency of these metal nanoparticles, high surface area porous support
are widely used. Even though significant enhancement in catalytic performance has
been achieved by using artificially designed carbon structure, the complicated
manufacturing procedure and involved high cost restrict the practical application in
real industry. Nature provides a feasible way to get out of this dilemma. In this work,
nature wood has been utilized as reductant to synthesize monodispersed Ag
nanoparticles on its surface. Owing to abundant oxygen-containing functional groups
and unique matrix, Ag nanoparticles can be in-situ reduced and embedded into wood
matrix. By further carbonization of Ag/Wood composite, wood is converted to
carbon with embedded mesopore structures. Through the two-step reduction and
carbonization, macro-tube/meso-pore carbon frame with decorated mono-dispersed
silver nanoparticles (Ag/C) is conveniently synthesized. Ag/C shows outstanding
activity in 4-nitrophenol and 2-nitrophenol reduction reactions with much higher
reaction rate than literature reports and no obvious activity degradation is observed
after 10 cycles of durability test. This newly developed synthetic methodology could
serve as a general tool to design and synthesize other metal/carbon nanocomposite
catalysts for a wider range of catalytic applications. More importantly, the utilization
of widely accessible renewable resource provides sustainable feature of this work to
reduce manufacturing cost and environmental impact.
Enhancing Performance of a Ni/YSZ anode in CH4 and CH4/CO2 Solid Oxide Fuel Cell with a
high active oxidation Pd@CeO2 catalyst
Wenbin Yin and Steven S.C. Chuang*
Department of Polymer Science
The University of Akron, Akron, Ohio 44325-3909, United States
Abstract
The Ni/YSZ anode has been extensively studied and used for high temperature solid oxide fuel
cell using hydrogen as a feed (H2-SOFC). Switching the feed from H2 to CH4 led to a rapid
degradation of the Ni/YSZ anode because of the decomposition of CH4 onto the Ni surface and
the growth of carbon filaments. The use of CH4 as a feed to the SOFC (CH4-SOFC) will allow
elimination of reforming and water gas shift reactors in the high temperature natural gas SOFC
system. To overcome the issue of Ni/YSZ degradation, we impregnated a Ni/YSZ anode with a
highly active oxidation Pd@CeO2 catalyst which consists of Pd nanoparticle (<10 nm) as a core
and CeO2 as a shell. CeO2 shell could prevent Pd particles from sintering at 750 - 850℃, a
typical operating temperature range of SOFC.
We found that Pd@CeO2 exhibited an exceptionally higher activity for CO oxidation than
Ni/YSZ. Addition of Pd@CeO2 on the Ni/YSZ anode formed a Pd@CeO2 layer on the top of
Ni/YSZ, resulting in enhancing performance of CH4-SOFC and CH4/CO2-SOFC. The Pd@CeO2
layer inhibited coke formation, decreased the impedance, and increased the current density by
two times in SOFC. In this presentation, the structure of Pd@CeO2 (shown in Figure 1) and
anode as well as their role in catalyzing CH4 and CH4/CO2 conversion and electrochemical
oxidation for electric power generation will be discussed.
Figure1. Pd@CeO2 (A) HRTEM image, (B) Scanning transmission electron microscopy (STEM)
image, and mapping results of the elements (C) Pd, (D) Ce, (E) Typical TEM, (F) the
corresponding EDX spectra for selected locations.
Photocatalysis Synthesis of L-pipecolinic Acid from L-lysine on TiO2 and Ag/TiO2 Catalysts
Yuxin Zhai1 and Steven S.C. Chuang1* 1 Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3009, US
Titania (TiO2) has been extensively studied in photocatalysis because of its chemical stability, long durability,
nontoxicity, and low cost.[1] One promising application of TiO2-photocatalysis is the synthesis of L-pipecolinic
acid (L-PCA), which is an important and expensive intermediate compound for pipetide antibiotics, piperidine
alkaloids, and immune-suppressants.[2],[3] L-PCA can be synthesized via one-step photocatalysis from a cheap and
optically pure L-lysine (L-lys)[4-6], shown in Scheme 1. In this study, we employed the in situ infrared (IR)
spectroscopy (Figure 1 (a)) to investigate the effect of TiO2 and modified TiO2 (Ag/TiO2) on the selectivity and
reaction rate of L-PCA formation. The addition of Ag on TiO2 accelerated the rate of formation L-PCA, shown in
Figure 1 (b). Figure 1 (c) showed the formation of L-PCA from L-lys, as evidenced by the rise of -C=O at 1687
cm-1 and -NH at 3288 cm-1 accompanied by a decrease in the intensity of L-lys’ -NH2 at 3359 cm-1. This
presentation will discuss the photocatalytic pathway for the conversion of L-lysine to L-pipecolic acid. Further
study on the role of Ag and additives in promoting TiO2-photocatalysis could open up a new low-cost route to the
synthesis of amino acid.
Scheme 1. Photocatalytic synthesis of L-pipecolic acid from L-lysine.
Figure 1. (a) Illustration of in situ IR spectroscopy. (b) Formation rate of L-PCA on TiO2 and Ag/TiO2. (c) IR
absorbance spectra of the formation of L-PCA on Ag/TiO2.
Reference [1] K. Nakata; A. Fujishima, Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2012, 13 (3) 169-189.
[2] B.T.A. Ekenstam, C. Bovin, US Patent 4695576 (1987).
[3] Chandren, S.; Ohtani, B., Journal of Photochemistry and Photobiology A: Chemistry 2012, 246, 50-59.
[4] B. Pal, S. Ikeda, H. Kominami, Y. Kera, B. Ohtani, Journal of Catalysis 2003, 217, 152–159. [5] B. Ohtani, S. Tsuru, S. Nishimoto, T. Kagiya, K. Izawa, Journal of Organic Chemistry 1990, 55, 5551–5553.
[6] B. Ohtani, K. Iwai, H. Kominami, T. Matsuura, Y. Kera, S. Nishimoto, Chemical Physics Letters 1995, 242, 315–319.
0 10 20 30 40 50
0
5
10
TiO2
onoff
um
ol
Time (min)
UV on
onoffUV on
2wt% Ag/TiO2
(a) (b)
(c)
4000 3000 2000 1000
16
87
Abso
rban
ce
Wavenumber (cm-1
)
0.5 min
0 min
0.05 min
21
17
33
59
32
88
Ag/TiO2
2017 Pittsburgh Cleveland Catalysis Society Akron, OH, USA
May 25th, 2017
Abstract Submission
Impact of Pore Diffusion in Ni@SiO2 Core@Shell Nanocatalysts
Yahui Yang and Götz Veser Department of Chemical and Petroleum Engineering, University of Pittsburgh, USA
Abstract:
The engineering of materials on the nanoscale enables precise tailoring of materials’ functionality. Core-shell materials are a widely studied class of engineered nanomaterials with application in various technologies. In catalysis, core-shell nanostructures have drawn much attention due to their ability to isolate the nanoparticle cores inside the support and hence alleviate sintering issues. On the other hand, by tailoring the porosity of the shell material, these nanocatalysts can also be considered ‘nano-reactors’ with porous membrane walls for preferential diffusion of molecules, and hence enable tuning of selectivity.
Here, we designed nickel-silica based core-shell nanostructured catalysts (Ni@SiO2), synthesized in a reverse micro-emulsion mediated sol-gel process. The silica shell is microporous with pore diameters of ~0.8-1.2 nm. Diffusion of gases through these porous shells falls into the transition regime from Knudsen diffusion to configurational diffusion, suggesting the possibility of a membrane “sieving effect” in these core-shell structures. Fine control of SiO2 shell thickness with near nanometer precision for Ni@SiO2 can be achieved by adjusting several synthesis parameters, including hydrolysis time and SiO2 precursor concentration, which allows us to control the degree of preferential diffusion and evaluate this effect in a systematic way.
Catalytic performance of Ni@SiO2 with different shell thickness is evaluated in fixed-bed experiments using oxidation of hydrogen and methane as model reactions. We first studied the preferential oxidation of H2 and CH4 gas mixtures over pre-oxidized Ni@SiO2. We observe that H2 conversion indeed precedes methane conversion by 0.3 minutes, confirming the existence of significant preferential diffusion of the lighter molecule (H2). As to CH4/O2 mixtures, we find that at oxygen-rich conditions (CH4:O2 feed ratio=1:5), decreasing shell thickness results in increasingly rapid loss of reactivity of the catalyst. This can be traced back to oxidation of the active Ni phase, i.e. formation of NiO which is known to show low combustion activity. Thicker shells result in delayed diffusion of O2 and hence a less oxygen-rich gas mixture in the central cavity, slowing down the deactivation of the catalyst. Increasing the CH4:O2 feed ratio to the stoichiometric ratio for partial oxidation of CH4 (CH4:O2=2:1), a strong ignition-extinction hysteresis is observed. Again, we find a strong dependence of this hysteresis on shell thickness, with both ignition and extinction occurring at increasingly high temperature with increasing shell thickness.
Hydrogenation of phenol to cyclohexanone via tubular nanofiber supported catalyst
Lin Pan and G. G Chase
Abstract
Cyclohexanone is the key intermediate in the manufacture of nylon-6 and nylon-66. The hydrogenation of
phenol process is commonly used in industry due to the lower temperature requirement and less byproducts
generation compared with the oxidation of cyclohexane1. The hydrogenation process could happen through
two path ways: one step or two step reaction. The one step reaction (Figure 1) is applied here. The
hydrogenation can be conducted either in liquid phase (low temperature) or gas phase (high temperature).
The temperature needed for the one-step reaction is lower than that needed for the two step reaction2.
The liquid phase reaction is preferred in our work because the operation conditions are easier to establish
and control in a laboratory environment. Researchers have evaluated many catalysts for use in liquid phase
phenol hydrogenation. The catalysts have been applied as dispersed particles in the liquid as a pseudo
homogeneous reaction and the catalyst particles have been immobilized on monolithic support structures
for heterogeneous reaction. Each approach has its advantages and disadvantages. In general, hydrogen
bubbles must transport through the liquid phase to the catalyst particles for the reaction to occur. The
transport of individual bubbles to a catalyst particle is somewhat random and challenging to predict. To our
knowledge no previous research has evaluated the performance of catalyst supported on a gas-liquid barrier
membrane. The membrane is in the form of a hollow tube. Hydrogen gas flows through the inside of the
tube and aqueous phenol flows on the outside of the tube. The objective of this work is to the feasibility
and to evaluate the reaction kinetics of a prototype tubular membrane reactor shown in Figure 2. The
membrane is fabricated using electrospinning techniques.
Figure 1. The one step reaction pathway of phenol hydrogenation
Figure 2. Designed reactor of tubular hydrogenation reactor
Reference
1. Liu, Huizhen, et al. "Selective phenol hydrogenation to cyclohexanone over a dual supported Pd–
Lewis acid catalyst." Science 326.5957 (2009): 1250-1252.
2. Shore, Sheldon G., et al. "Vapor phase hydrogenation of phenol over silica supported Pd and Pd-
Yb catalysts." Catalysis Communications 3.2 (2002): 77-84.
Abstract: PdxCu1-x Phase Transition at Nanoscale
One of the most interesting characteristics of alloy nanoparticles (NPs) is that they can have
different phases from those of the bulk. In the bulk phase diagram of PdxCu1-x, there exists a
composition range, 0.35 < 𝑥𝑥 < 0.55, over which a B2 phase (ordered body centered cubic, CsCl
structure) is formed at T < 873 K, in spite of the fact that pure Pd and Cu both have face centered
cubic (FCC) bulk crystal structures. An experimental methodology has been developed for
determining the phase behavior of PdxCu1-x size and composition spread nanoparticle (SCSNP)
libraries. Spatially resolved X-ray photoemission spectroscopy (XPS) was used to map the Cu
2p3/2 core level shifts (CLS) with respect to the value for pure Cu across composition space on the
bulk PdxCu1-x alloy. The result has shown that the Cu 2p3/2 binding energy decreases
monotonically with increasing Pd at.% in the FCC phase. There is additional discontinuous CLS
over the composition range from 0.35 to 0.55 Pd at.%, where the B2 phase forms. Therefore, the
Cu 2p3/2 core level binding energy measured by XPS can be used to distinguish between the
ordered B2 phase and disordered FCC phase. The PdxCu1-x SCSNP library on a Mo substrate was
prepared using a rotatable shadow mask deposition tool previously developed by our group. After
annealing the PdxCu1-x alloy thin film to 700 K, the additional CLS over the composition range,
0.35 < 𝑥𝑥 < 0.55, has been observed at a film thickness > 6 nm, which suggests the formation of B2
phase. However, at a film thickness between 4 – 6 nm, the Cu 2p3/2 binding energy decreases
monotonically across composition space which suggests that only FCC phase exists for alloy films
in this thickness range. Because the FCC phase is more densely packed than the B2 phase, the
surface tension in this thickness regime can drive a conversion from the ordered B2 phase back to
the randomly distributed FCC solid solution. More interestingly, the additional CLS over the
composition range from 0.35 to 0.55 Pd at.% reoccurs at a film thickness < 4 nm, which suggests
the formation of B2 phase. This observation is the result of dewetting of the PdxCu1-x NPs after
heating at 700 K for 30 mins, and the size of dewetting NPs exceeds 6 nm where the close-packed
FCC phase is stabilized. Dewetting of PdxCu1-x NPs is validated by the appearance of the substrate
Mo XPS signal at a film thickness < 4 nm. This comprehensive experimental study of the phase
behavior for PdxCu1-x alloy NPs will be correlated with their catalytic activity across composition
and size spaces to accelerate the development of alloy NPs for catalytic applications.
Assessment of Trends in the Catalytic Electroreduction of CO2 on Metal Nanoparticles
Dominic R. Alfonso and Douglas Kauffman
National Energy Technology Laboratory-DOE, 626 Cochran Mills Rd,
Pittsburgh, PA 15236, USA
Metal nanoparticles are being pursued by the U.S. Department of Energy’s (DOE) CO2
Utilization Technologies program in the quest to develop more active and selective catalyst for
CO2 conversion into higher value products and adding to DOE’s carbon management portfolio.
Though various metal nanoparticle based heterogeneous catalysts have shown promising
electrochemical activities for reduction of CO2, there have been no systematic studies of the
reactive properties of these materials that can guide further experiments. We present large-scale
screening based density functional theory (DFT) calculations to analyze trends in the activity of
Ag, Au, Cu, Ir, Ni, Pd, Pt and Rh nanoparticles for CO2 reduction. We looked at different particle
size (n=13, 55, 147 and 309) to investigate its influence on the activity. Our preliminary results
indicate that the relevant COOH and CHO intermediates exhibit an abnormal adsorption
behavior as their adsorption strengths do not show linear correlation with that of CO. In general,
the adsorption of COOH and CHO is enhanced with respect to that of CO, compared to that on
the packed (111) metal counterparts. The scaling relations also was predicted to vary with system
size. Based on these data, theoretical analysis of the trends in overpotentials for electrocatalytic
CO2 reduction is underway. Experimental efforts are also underway to synthesize and test
variously sized nanoparticles to approximate the DFT models. Experimentally determined CO2
reduction overpotentials and rate-limiting steps will be compared with calculated results.
Chemoenzymatic Synthesis and Characterization of Multifunctional Fluoresceins for Breast Cancer Diagnosis
GAYATRI SHRIKHANDE, SANGHAMITRA SEN, JUDIT E. PUSKAS*
The University of Akron, Department of Chemical and Biomolecular Engineering, Akron, OH, USA. Tel: 330-972-6203, Email: [email protected]
ABSTRACT
Fluorescein exhibits excellent luminescent properties to be used as a diagnostic agent for the detection of malignant cells. This work highlights the synthesis of four tetra-functional flouresceins by very efficient chemo-enzymatic catalysis. First pure fluorescein diacrylate (FL-DA) was prepared with high efficiency. Subsequently tetra-allyl, tetra-ester and tetra-hydroxy fluoresceins were synthesized via Michael addition of the corresponding functional secondary amines, catalyzed by Candida antarctica lipase B. The structure of the products was confirmed using 13C and 1H-NMR. MS (ESI) was used to quantify the purity of the crude products: 100%, 96% and 91% for the tetra-hydroxy, tetra-ester and tetra-allyl fluorescein. These multifunctional fluoresceins are good candidates for the synthesis of imaging agents for a wide variety of applications.
Atomic structure of the Pt/γ-Al2O3 interface through a combined experiment and theory
approach: A model catalyst study
Henry O. Ayoola1, Cecile S. Bonifacio1, Qing Zhu1, Josh Kas2, Kim Kisslinger3, Dong Su3, Eric
A. Stach3, John J. Rehr2, Wissam A. Saidi4 and Judith C. Yang1
1 Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA 2 Department of Physics, University of Washington, Seattle, WA 3 Center for Functional Nanomaterials, Brookhaven National Lab, Upton, NY 4 Department of Mechanical Engineering and Material Science, University of Pittsburgh, Pittsburgh, PA
Abstract: Pt/γ-Al2O3 is an important industrial catalyst-support combination due to its
widespread use in fuel cells, catalytic converters, and petroleum reforming. For supported metal
catalysts, such as Pt/γ-Al2O3, an important area of study is the interaction between catalyst and
support, especially the behavior at the interface. This interaction affects many catalytically
relevant properties of the system, including catalyst dispersion, particle shape, and electronic
structure. To gain an atomic level understanding of this interaction, a combined experiment and
theory approach is necessitated. Commercially available γ-Al2O3 is structurally complex and
thus, it is difficult to directly correlate results from experiments with results from well-defined
systems normally used in theoretical simulations. To bridge this gap, we have synthesized a
model catalyst using Pt nanoparticles of well-defined size and morphology on a single crystal γ-
Al2O3 (111) thin film that enables us to study specific structural and electronic properties of the
system at the nanoscale that can then be directly compared with computational results. By using
electron energy loss spectroscopy (EELS) experiments in combination with EELS simulations—
using the FEFF9 program—we have correlated some of the inter-related electronic and structural
properties of the system. We confirmed the commonly cited monoclinic γ-Al2O3 model [1]—an
approximate but computationally less demanding structure—as sufficiently accurate for EELS
simulation, using this method. Our previous EELS data revealed an unusual feature in the
electronic structure related to the local oxygen coordination that was seen only at the interface
but not in the bulk γ-Al2O3. By creating different models of the Pt/γ-Al2O3 interface and
calculating the near-edge EELS spectra for each model, we have determined that the most
probable interface structure consists of Pt not sitting in an O vacancy and bonded to O adatom(s).
With this approach, we can now move further to study the nanoscale structural dynamics
between the Pt catalyst and the underlying γ-Al2O3 support during reaction through in situ
environmental TEM.
References:
1. Digne, M., et al., Use of DFT to achieve a rational understanding of acid-basic
properties of γ-alumina surfaces. Journal of Catalysis, 2004. 226(1): p. 54-68.
Understanding the C-H Activation and Dehydrogenation Mechanisms of Alkanes on γ-Alumina
Mudit Dixit, and Giannis Mpourmpakis*
Department of Chemical Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA [email protected]
Olefins are important chemical building blocks for the production of a wide range of valuable chemicals
and plastics. A promising route to produce olefins is the non-oxidative dehydrogenation of alkanes on
metal oxides. The Lewis acid-base functionalities of metal oxides play a key role in their catalytic behavior.
However, how these functionalities affect the alkane dehydrogenation behavior and how they can be
rationalized on multisite surfaces of metal oxides, is still elusive. In this work, we provide fundamental
insights into the various mechanisms of alkane dehydrogenation on γ-Al2O3 and identify chemically
intuitive, structure activity relationships, by using Density Functional Theory calculations. The obtained
relationships can be utilized to accelerate the discovery of active dehydrogenation metal-oxide catalysts.
Migration and structural evolution of carbon-encapsulated Fe nanoparticles via in situ TEM Ross V. Grieshaber1, Zhenyu Liu2, Judith Yang1 1. Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA, United States. 2. Kennametal, Inc, Latrobe, PA, United States. Abstract: Catalysts are susceptible to deactivation due to poisoning or the loss of desirable structural features; encapsulation of nanoparticles has been used to inhibit poisoning and to limit the amount of inter-particle interaction. Iron and iron-containing nanoparticle catalysts are of interest as cost-effective replacements for expensive noble metal catalysts. Carbon-encapsulated (Fe@C) nanoparticles allow for investigation into the structural dynamics induced by the reaction environment and the effect of carbonaceous growth on catalyst materials. Here we report the preparation of carbon encapsulated Fe NPs catalysts and their subsequent thermal stability – degradation and coarsening. In situ transmission electron microscopy (TEM) allowed the dynamic behavior of this material to be studied during reaction, at elevated temperatures (up to 650 °C) and extended durations (minutes to hours). Under these conditions, the particles exhibited liquid-like behavior and a release of the Fe nanoparticles from their carbonaceous shells. While this behavior was primarily attributed to the increased temperatures, the energy from the electron beam likely also contributed through compression of the carbonaceous shell material, which has been shown to increase the pressure inside the core-shell considerably. Particle coarsening progressed by both Ostwald ripening and particle coalescence as competing mechanisms in parallel. In situ TEM enabled the size regimes over which ripening or particle coalescence dominated to be determined. A mechanistic understanding of the morphological evolution of the catalyst structure over the course of the reaction was developed. Because the amount of free surface area is typically correlated with activity of a nanoparticle catalyst, these results provide insight into how the activity of the system changes during reaction.
CO2 Activation on Cu-based Bimetallic Nanoparticles
James Dean, Natalie Austin and Giannis Mpourmpakis
Department of Chemical Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261,
United States
Cu nanoparticles (NPs) are promising hydrogenation catalysts for the conversion of carbon dioxide
to useful chemicals (e.g. methanol). We investigate the adsorption and activation of CO2 on Cu
NPs doped with one of the heteroatoms Au, Mn, Mo, Ni, Pd, Rh, Ru, Sc, V, Zn, and Zr, using
Density-Functional Theory calculations. Candidate heteroatoms were selected based on their
preference to occupy a surface site on the NP. Two significant descriptors for CO2 adsorption were
identified: (1) the heteroatom local d-band center must be higher in energy than the Lowest
Unoccupied Molecular Orbital (LUMO) of CO2, and (2) the electropositivity of the heteroatom
must be higher relative to Cu. These criteria lead to an effective charge transfer from the NP to
CO2, which is necessary for CO2 activation. With these descriptors, bimetallic NPs can be rapidly
screened for their ability to chemisorb and activate CO2. We demonstrate that Zr-decorated Cu
NPs can effectively adsorb and activate CO2. Our work highlights the importance of generating
binding sites on a NP surface based on stability and electronic structure properties, which can lead
to the effective design of CO2 conversion catalysts.
Direct Catalytic Conversion of CO2/CH3OH to Carbonates: an in situ FTIR Study
Jiawei Liu1, Long Zhang1, and Steven S.C. Chuang1*
1Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3909
Direct catalytic conversion of CO2/alcohol, as shown in Scheme 1, offers a promising alternative to the
production of organic carbonates – a high value-added intermediate compounds in polymer industry. This
pathway could avoid the use of highly toxic compounds in the synthesis. This poster will discuss the
synthesis involved CO2 and organic carbonate and will report the results from an in situ FTIR study of the
conversion of CO2 with methanol into dimethyl carbonates (DMC).
The reaction of CO2/methanol to form carbonate/water, Scheme 1, is thermodynamically unfavorable.
The removal of water by the hydration reaction of 2-cyanopyridine can shift the equilibrium toward the
product, DMC. The catalytic reaction of CO2/methanol over CeO2 catalyst has been carried out with 2-
cyanopyridine, a reactive dehydrating agent, in a high pressure IR cell under 350 psi and 140 °C. Figure 1
shows the results of IR studies which revealed a number of interesting features: (i) the synthesis of DMC can
be achieved at 350 psi, confirmed by the decrease of the methanol band at 1462 cm-1 and the increase of the
DMC band at 1756 cm-1; (ii) the formation of picolinamide, a product of hydration of 2-cyanopyridine, led
that of DMC. CO2 was found to be adsorbed in the form of bidentate carbonate and monodentate carbonate
on CeO2, while methanol formed methoxy and formate. The relationship between these adsorbed species
and the reaction pathway will be discussed.
Scheme 1. Reaction pathway of catalytic conversion of CO2/Methanol to DMC
Figure 1. FTIR spectra (left) and IR profiles (right) during the methanol/CO2 reaction at 350 psi, 140 °C
Wide Operation Temperature Window for CO PROX on Pt-Mn Alloy Nanoparticle
Catalyst
Yanbo Pan 1, Sang Youp Hwang 1, Xiaochen Shen, Changlin Zhang, Zhenmeng Peng*
Preferential oxidation (PROX) of CO in H2-rich stream has received lots of interests to provide
clean H2 for proton exchange membrane fuel cell (PEMFC). Various types of catalyst have been
intensively studied in the PROX reaction so far. However, most of the PROX catalysts have
apparent limitations such as low activity at low temperature and low PROX selectivity. Pt alloy
nanoparticles have been demonstrated to have both high PROX activity and selectivity. However,
these catalysts have a problem that the PROX selectivity would rapidly decrease above room
temperature due to their narrow operation temperature windows. Therefore, it’s of high desire to
find new catalyst with both excellent property and broadened temperature range.
In this work, density functional theory (DFT) studies were firstly conducted on different Pt alloy
such as Pt-Ni, Pt-Mn and Pt-Cu to obtain their corresponding energy barriers in CO PROX
process. The calculation results showed that Pt-Mn had a relatively low energy barrier for CO
oxidation as well as a relatively high energy barrier for H2 oxidation, which indicated that Pt-Mn
alloy nanoparticles may have a good activity and wider temperature window in CO PROX. Then
Pt-Mn alloy nanoparticles on alumina were synthesized and tested for CO preferential oxidation
(PROX). And Pt-Ni and Pt catalysts were also prepared and tested as a comparison. Results
exhibit that Pt-Mn showed 100% CO selectivity in a wide temperature window from room
temperature to 170°C for CO PROX reaction, which matched well with the calculation results.
The excellent property and extended temperature window for CO PROX on Pt-Mn have been
attributed to the low reducibility of Mn oxide.
1 Yanbo Pan and Sang Youp Hwang contributed equally to this work. * Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH 44325, United States. E-mail: [email protected]
2017 Pittsburgh Cleveland Catalysis Society Pittsburgh, PA, USA
May 25th, 2017
Abstract Submission
New Mechanistic Insights into Oxidative Coupling of Methane
Gizem Ozbuyukkaya and Götz Veser Department of Chemical and Petroleum Engineering, University of Pittsburgh, USA
Abstract:
The recent increase in recoverable natural gas resources has renewed interest in using this resource beyond combustion, in particular via conversion to higher value and easily transportable chemicals. One target process is oxidative coupling of methane (OCM) to ethylene, an important feedstock for the chemical industry. However, achieving high ethylene yields in OCM is challenging since competitive total oxidation is thermodynamically favored at typical reaction temperatures (800-900°C).
We aimed to evaluate the performance of OCM in a “chemical looping” configuration, in which pure streams of methane and oxygen, respectively, are periodically fed to the reactor (rather than a traditional co-feed). In OCM, a metal oxide catalyst provides its lattice oxygen via a Mars-Van Krevelen mechanism to activate methane. In chemical looping, the lattice oxygen is then replenished after the methane activation in a separate oxidation step. Chemical looping thus provides a potential opportunity to suppress gas phase total oxidation reactions since the hydrocarbons and gas phase oxygen are never contacted directly in the reactor.
Supported Mn oxide-based supported catalysts were chosen for reactive testing and were synthesized via simple wet-impregnation. Thermo-gravimetric analysis (TGA) of the metal oxides combined with X-Ray Diffraction (XRD) and Transmission electron microscopy (TEM) gave insight into oxidation states, and reaction rates were evaluated in fixed-bed reactor experiments. We found that although lattice oxygen in unpromoted Mn catalyst is able to activate methane, C2 yields were poor since intermediates and products are quickly oxidized further to CO2 on the carrier surface, i.e. the undesired total oxidation seems to occur on the catalyst surface and removal of gas phase oxygen hence has little impact on selectivity.
The addition of Na2WO4 as a well-known promoter for OCM was further tested to improve reaction selectivity. Although Na2WO4 alone was found to be essentially inactive for OCM, its addition to Mn oxide greatly suppressed CO2 formation and increased C2H4 yield to 14% at 900°C. Remarkably, improvement in C2 selectivity was also observed when separate Mn and Na2WO4 catalysts were physically mixed (rather than being alloyed in a single catalyst formulation). Product distribution and performance of alloy catalysts and the physical mixtures were found to be indistinguishable, in contradiction to the prevailing mechanism in the published literature that requires directly exchange of lattice oxygen between the two oxide phases.
Overall, the present study hence provides new insights into the reaction mechanism and points towards new directions for further process improvements.
Connecting O Diffusion along Cu Interfacial Defects with Cu Oxide Nano-
island Nucleation and Growth: A Theoretical and Experimental Study Dr. Matthew T. Curnan1, Dr. Christopher M. Andolina1, Dr. Qing Zhu1, Dr. Wissam A. Saidi2,
and Dr. Judith C. Yang1,3 1Department of Chemical and Petroleum Engineering, University of Pittsburgh; Pittsburgh, PA, USA
2Department of Mechanical Engineering and Materials Science, University of Pittsburgh; Pittsburgh, PA, USA 3Department of Physics and Astronomy, University of Pittsburgh; Pittsburgh, PA, USA
Determining what enables the energetic favorability of chemisorbed and diffusing adsorbates – such
as O2 – on Cu and Cu-based catalytic systems – such as low-index Cu surfaces and Cu/ZnO/Al2O3 – is
critical to improving interfacial system reactivity in applications that include the chemical vapor
deposition synthesis of graphene and the improvement of oxidation resistance to diminish catalyst
deactivation. Past research has shown that the catalytic activity of Cu-based materials is dependent
on improving the amount of exposed specific Cu surface area available for oxidation or related
processes, which can be accomplished relative to flat Cu surfaces with the introduction of defects
such as surface facets and grain boundaries (GBs). Metal oxidation completed on different surfaces
with distinct facets or GBs is initially controlled by the relative energetics associated with surface
adsorption and diffusion processes in those interfaces. In the cases of Cu surfaces such as Cu(100),
Cu(110), and Cu(111) or low-angle symmetric tilt GBs such as Cu Σ5(210)[001] and adsorbates such
as O2, oxidation can proceed with O2 interfacial adsorption, followed by dissociation of adsorbed O2
and subsequent O interfacial diffusion. Distributions of Cu-O structures formed in these interfaces
during late-stage oxidation can be at least partially determined by matching early-stage, dissociated
O adsorption site energy distributions and their inter-site activation energy barriers. Under particular
reaction conditions, these early-stage and late-stage properties can be linked, forming a predictive
basis for determining which adsorbate properties can be linked to late-stage Cu oxide patterns.
In this study, we improve upon former systematic evaluations of O site and diffusion barrier
energetics over faceted Cu surfaces, which featured variations in facet step height, terrace location,
facet type, and facet intersection or corner type. Beyond the addition of new data within this
paradigm, our study also evaluates relative O site favorability in different GB systems. The Climbing
Image Nudged Elastic Band (CI-NEB) method is implemented in both molecular mechanics and first-
principles density functional theory simulations to comparatively calculate O diffusion barrier
energetics, while initial and final site energy endpoints for CI-NEB calculations are resolved using
corresponding structural relaxation calculations. In surface facet calculations, this study reconciles
the spatial distributions of late-stage Cu oxide nano-islands with early-stage, matching distributions
of diffused O on comparable surfaces. Molecular dynamics simulations are employed to determine
the distributions of O on Cu surfaces during early-stage oxidation, while environmental transmission
electron microscopy experimental methods are used to generate analogous late-stage oxide island
distributions. Through this study, relative O site favorability is linked to local O coordination, defect
type, and reaction conditions – spanning O coverage and thermodynamics – over studied surface
facet and GB systems. In the context of temperature variation, the extent of agreement between
experimental and theoretical techniques fosters a further link between the precedence of particular
reaction mechanisms and thermodynamics, promoting future study of the temperature dependence
of Cu-O bonding in Cu interfacial systems and how changes in bonding character affect reactivity.
SYNTHESIS OF DIAMINE-FUNCTIONALIZED PEGs VIA ENZYME CATALYZED ESTERIFICATION
PRAJAKATTA MULAY, SANGHAMITRA SEN, JUDIT E. PUSKAS*
The University of Akron, Department of Chemical and Biomolecular Engineering, Akron, OH, USA. Tel: 330-972-6203, Email: [email protected]
ABSTRACT
Poly(ethylene glycol) (PEG) is a non-toxic, hydrophilic polymer that is widely used for biomedical applications. In this research diamine-functionalized PEGs were successfully prepared by the enzyme catalyzed esterification of tert-butyloxycarbonyl (tBOC) protected amino acids with PEG using Candida antartica lipase B (CALB) as an enzyme catalyst, followed by de-protection. The esterification reaction is quantitative in 24 hours under mild conditions. 1H and 13C NMR spectroscopy with MALDI-ToF mass spectrometry were used to confirm the structure and purity of the products. This method provides a convenient process to effectively synthesize diamine-functionalized PEGs, to be used for the synthesis of cancer diagnostic and therapeutic agents.
1
Impact of Surface Hydroxylation on Stability and Reactivity of Silica-Support Metal
Nanoparticles: On the Way to Tailor the Catalysts
Wanling Zhu, Yahui Yang and Götz Veser
Chemical Engineering Department, University of Pittsburgh
Metal nanoparticles (NPs) are characterized by a very high surface area to volume ratio, and a
large number of low-coordination sites. However, these properties also strongly destabilize NPs,
making them prone to sintering and hence loss of activity and selectivity. Recent computational
modeling in our group developed an amorphous silica model and found that nanoparticle
adhesion energetics and charge transfer depend on the silica surface hydroxyl density. Since the
hydroxylation is easily tunable by pretreatment temperature, this suggest that both electronic
charge and catalyst stability may be modified via catalyst calcination.
In this work, platinum NPs dispersed on amorphous silica supports were used as model
catalyst. Two silica supports with different hydroxyl density were investigated to explore the
impact of surface hydroxylation on stability and reactivity of the catalysts. We found that the
thermal stability of Pt NPs on fully hydroxylized (rehydroxylized) silica showed better stability
than those on dehydroxylized silica, and concluded there are two phases during particle sintering
which may be dominated by different particle growth mechanisms. Finally, we analyzed the
reactivity of these two catalysts in CO oxidation and found that the ignition temperature of
rehydroxylized catalysts was about 30 °C lower than for dehydroxylized catalysts, which
correlates well with improved thermal stability of this catalyst.
Overall, our results confirm that the degree of surface hydroxylation of silica has strong
impact on both stability and reactivity of the silica-supported metal nanocatalysts.
