Adrian Merritt

1NSF REU program at UIC, 7/29/2010

UICPhysics

I. Research Objectives and Methods

II. Sample Characterization

III. Particle Size Results

IV. Research Conclusion

V. Future Work

NSF REU program at UIC, 7/29/20102

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The core objective is to better understand how the manganese promoter affects the rhodium catalyst performance

Some current possibilities are:• Particle size• Oxide species• Changes to interfacial interaction• Formation of surface oxides

NSF REU program at UIC, 7/29/20103

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Due to the de Broglie wavelength, electron microscopes can have a fundamentally finer resolution than light microscopes

Electrons passing through the sample are scattered by various mechanisms

Spatial, mass/thickness and analytical information is available from the scattered electrons

NSF REU program at UIC, 7/29/20104

Image from Transmission Electron Microscopy, B. Williams and C. Carter, volume IV

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Invented by Franz Fischer and Hans Tropsch

Utilizes syngas to produce hydrocarbon products (methane, ethanol, diesel and gasoline fuels)

Syngas is a mixture of CO and H2, which can be produced from coal gasification, natural gas, or biogas, and is used as the base feedstock for the process

In all cases though, the reaction relies upon the proper catalysts for selectivity and efficiency

NSF REU program at UIC, 7/29/20105

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Rhodium is a useful catalyst for the FT process as it lies at an intermediate mass level and so works to create ethanol for use as an alternative fuel source

Manganese acts as a promoter, which changes the effects of a catalyst without being a catalyst itself

Manganese improves the selectivity and overall efficiency of rhodium catalysts for the FT process

E.g. from T. Feltes: 1% Mn loading on 3% Rh on SiO2 support raises CO conversion ten fold and increases ethanol selectivity from 0.0% to 9.2%

NSF REU program at UIC, 7/29/20106

Image from The Selective Adsorption of a Manganese Promoter Over Supported CO Hydrogenation Catalysts, Theresa E. Feltes, 2010

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Carbon film on copper support grid

d = 3 mm

Allows deposition of catalyst particles and easy viewing

Powdered samples are prepared by dry impregnation (DI) or strong electrostatic adsorption (SEA)

NSF REU program at UIC, 7/29/20107

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Final sample has many medium-sized clusters of silica particles

Best (most useful) clusters are those overhanging an edge (reduces impact of C-film)

NSF REU program at UIC, 7/29/20108

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Rhodium on silica, 3% loading by DI Rhodium on silica, 3% loading by DI with 1% manganese Calcination at 350° C for 4 hours in air Reduction (when applicable) at 300° C for 2 hours under

H2 flow

NSF REU program at UIC, 7/29/20109

Images from The Study of Heterogeneous Catalysts by High-Resolution Transmission Electron Microscopy, A. Datye & D. Smith, Catalyst Review, 1992

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Typical magnification is x300k

Use diffraction contrast imaging to differentiate rhodium particles (crystalline) from the silica support (amorphous)

NSF REU program at UIC, 7/29/201010

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Averages: 3.12 nm vs. 3.08 nmStandard deviations: 0.80 nm vs. 0.83 nmThe same (within experimental limits)!

UICPhysicsNSF REU program at UIC, 7/29/2010

12

Averages: 2.26 nm vs. 2.44 nmStandard deviations: 0.54 nm vs. 0.67 nm

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Averages: 2.55 nm vs. 2.43 nmStandard deviations: 0.91 nm vs. 0.69 nmHeated at 300° C for 2 hours, then allowed to cool

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Sample Average Particle Size (nm)

Standard Deviation (nm)

RhOx (unreduced) 3.12 0.80

Rh 3.08 0.83

Rh+Mn Ox (unreduced)

2.26 0.54

Rh+Mn 2.44 0.67

Rh+Mn (in situ heating)

2.55 0.91

Rh+Mn (after cooling) 2.43 0.67 Averages not different enough to cause all

phenomena observed in catalysts with a promoter

NSF REU program at UIC, 7/29/201014

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Catalyst particle size has been ruled out

Next step is JEOL JEM-2010F work• Better resolution through Z-contrast imaging• EELS setup

EELS allows changes in electronic structure to be characterized

Together, allows better characterization of structure

NSF REU program at UIC, 7/29/201015

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University of Washington ab initio program for simulation EELS spectra

Full multiple scattering simulation

Preparation for JEM-2010F EELS work, distinguishing rhodium oxide species

NSF REU program at UIC, 7/29/201016

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National Science Foundation and Department of Defense for funding, EEC-NSF Grant # 0755115

Professors Takoudis and Jursich as REU organizers

Professor Robert Klie as PI Yuan Zhao as mentor Ke-Bin Low for TEM training and aid The RRC for its support in TEM work

NSF REU program at UIC, 7/29/201017