Bimetallic nanocomposite catalysts fabricated by

area selective atomic layer deposition and applications

Rong Chen, Kun Cao, Yun Lang, Jiaming Cai, Bin Shan

Huazhong University of Science & Technology

2019-04-04

2019 Area Selective Deposition Workshop

Catalyst for Environment and Energy

Q. Jia et al. ACS catal. 2016

W. Wang et al. Adv. Mater.2017S. Zhang et al. JACS. 2014

S. Cao et al. Catal. Sci. Technol.2017

• Energy and Environment

• Huge demand for noble metals

O2

H2

Fuel cell

PGM market report 2018 Feb Pt, Pd, Ru, Rh, Au, Ag

HC,CH,NOx

CO2,H2ON2

Increasing

2015 2016 2017

Pt Pd Rh Pt Pd Rh Pt Pd Rh

100.5 237.0 23.7 102.2 247.1 25.5 103.6 262.0 26.7

15.5 14.1 2.0 16.1 13.3 2.3 16.1 16.4 2.3

243.9 284.4 28.7 255.6 291.6 31.4 255.6 315.8 32.6

185.8 200.8 23.3 189.2 210.3 23.5 189.9 205.2 23.9

demand

supply

Automobile

Chemical

storage

2

Catalyst is designed to be

more active and in lower cost

Core-shell Alloy Monometallic mixture

Catalyst Design is Important

Xie, et al. Nano. Lett. 2014

• Single metal catalyst • Bimetallic catalyst

Alayoglu et al. Nat. Mater. 2008S. Zhang et al. JACS. 2014

3

ALD for Constructing Bimetallic Catalyst

• Composition and thickness control by ALD

J.W. Elam et al, Nano Lett. 2010

• ALD technology: conformality, self-limiting surface

W.M.M. Kessels et al. Chem. Mater. 2012

Nanotechnology 2015 4

5

• Lattice strain

bulkthin

shell

thick

shell

Latt

ice

stra

in

(%)

Alayoglu et al. Nat Mater. 2008

Mikkelsen et al. Chem. Mater.. 2014

Maark et al. J. Phys. Chem.C. 2014

• Ligand effect

MethodsInteraction in Bimetallic Core-shell Catalyst

0 10 20 30 40 50 6070.0

70.2

70.4

70.6

70.8

71.0

71.2

Bin

din

g E

ne

rgy

(eV

)

Au content in PtAu NPs (%)

Pt4f

Interaction between metals

• Chemical state

Nilekar et al. JACS. 2010

ee

• Chemisorption

• The precise structure would lead to better understanding on reaction

mechanism and boost catalytic performance.

Outlines

• Bimetallic nanoparticles for catalysts

• Catalysts for PROX reaction

Pd@Pt Core-shell nanoparticles

Facet selective Pt on Ru nanoparticles

• Catalyst for DRM reaction

Meshed Co coating on Ni nanoparticles

• Summary

7

Pd@Pt : lattice matched, core shell interaction (ligand effect)

Ru@Pt : mismatched crystal constant, lattice strain factor

@Pt

PdRu

@Pt

Lattice strain Ligand effect

PROX: Preferential oxidation of CO

• PROX reaction

• expensive

→ Pt

• high activity

• Catalyst demand

• high selectivity

PROX

1% 10ppm

H2+

CO

H2+

CO2

Catalyst surface

CO CO CO COCO CO

→ M@Pt

ALD recipe Pd Pt Ru

Precursor

Chamber

temperature200 ºC 300 ºC 275 ºC

Plus/purge

time

8

O2

2s 8s 2s 8s

Pd(hfac)2 Formalin

1.6s 8s 2s 8s

MeCpPtMe3 O2

• Growth rate on Si wafer

Nucleation Liner growth

50nm

Pd, Pt and Ru ALD Processes

1.6s 8s 3s 8s

Ru(Etcp)2 O2

O3

0 100 200 300 400

0

3

6

9

12

15

18

Pd Ru

Pt

Film

th

ickn

ess

(n

m)

ALD cycles

50nm

precursors

carrier gasMain chamber

supports

SAMs Approach for Core-shell Structure

Sci. Rep., 2015, 5, 8470

Strategy for fabricating

core shell NPs

• Utilizing SAMs assisted area selective ALD could refine the nucleation of

shell metal on core and obtain core shell NPs with regular ALD recipes.

pinhole

-CH3 endgroup

9

Growth of Pt shell on Pd core

• The size and composition of the core shell NPs can be controlled

precisely by varying the ALD cycles.

Core-shell structure Pt growth process on Pd

QCM

10

Activity and Selectivity for PROX Reaction

PROX: CO+H2+1/2 O2 → CO2+H2 CO-tolerant: CO+H2+1/2 O2 → CO+H2O

Preferential oxidation of CO in H2 (PROX) reaction

ChemCatChem, 2016, 8, 326

• The catalyst with 1 ML Pt shell shows optimal catalytic performance and

minimal Pt loading, lowest Ea of it suggesting lower CO oxidation barrier.

11

d-band Center Comparison between Ru@Pt & Pd@Pt

• For Pd@Pt catalysts, Pt is coherent on Pd thus the

d band center is influenced solely by ligand effect

Pt(111) on Ru (001)

(1.6% mismatch)

Pt(111) on Pd (111)

Lattice strain & Ligand effect Ligand effect

100

120

140

160

180

200

220

240

260

T50

Ru

Pd

Pt

Pd@Pt

Te

mp

ratu

re /

C

Ru@Pt

• Lower d-band center leads to weaker adsorption

of CO, which would reduce the CO poison effect

• For Pt(111)/Ru (001) surface, the lower d band is

the results of both lattice strain and ligand effect

12

Design of Bi-functional Ru-Pt nanoparticles

⚫ The nanoparticles with bi-functional exposed facets shows weaker CO

adsorption (Ru(001)/Pt(111)) and enhanced O2 dissociation(Ru(101)).

13

Surface evolution and electron modification effect

• As the Pt coating layer reaches to 5ML, the Pt coating layer becomes

continuous and the surface properties are similar to pure Pt.

• The 1ML Pt-Ru(001) shows lowest T50：As Ru(101) surface is gradually

covered, the activity starts to decrease.

78 76 74 72 70 68

Inte

nsit

y (

a.u

.)

Binding Energy(eV)

(a) (b)Pt 4f 7/2Ru 3p 3/2

70.9

71.1

71.2

Pt4f 5/2

Al 2p 71.3Pure Pt

1MLPt-Ru001

2MLPt-Ru001

5MLPt@Ru

10MLPt@Ru

Pure Pt

461.6462.7

Pure Ru

462.1

Pure Pt

74.4

2200 2150 2100 2050 2000 1950 1900

Wavenumber (cm-1)

A

dso

rban

ce (

a.u

.)468 466 464 462 460 458

Binding Energy (eV)

Inte

nsit

y (

a.u

.)

(c)2090 cm-1

Pt-CO

2030 cm-1

Ru-CO

1MLPt-Ru001

2MLPt-Ru001

5MLPt@Ru

10MLPt@Ru

1MLPt-Ru001

2MLPt-Ru001

5MLPt@Ru

10MLPt@Ru

FTIR reveals the surface evolution

14Submitted

Outlines

• Bimetallic nanoparticles for catalysts

• Catalysts for PROX reaction

Pd@Pt Core-shell nanoparticles

Facet selective Pt on Ru nanoparticles

• Catalyst for DRM reaction

Meshed Co coating on Ni nanoparticles

• Summary

Meshed coating of Ni nanoparticles

⚫ Single Co component is less active in DRM reaction, the complete coating

of Co on Ni (Co@Ni core shell structure) will decrease the reactivity

⚫ The meshed coated CoNi catalyst is designed to improve activity and

coking inhibition, the Co component effectively enhance CO2 adsorption

and activation, which helps to remove the carbon species on Ni sites

CO2 Reforming of CH4

Challenge: coking and sintering

Heavy coking

ChemSusChem 2015, 8, 3556; Science 2012, 335, 1205

16

Design and Fabrication of meshed coating structure

• First, atomically thin CoOx layers are deposited on Ni with ALD method

• Post reduction of as deposited CoOx layers on Ni, where oxygen release from

CoOx produces a meshed Co coating

J. Catal., 2019 in press17

18

Fabrication method for meshed coating structure

• Oxygen is released from CoOx, which

produces a meshed Co coating

CoOx ALD Reduction

Ni Ni@CoOx Ni@Co

Metallic phase

oxidative phase

Meshed Co coating on Ni

• Metallic Co in Ni catalysts could

stabilize the metallic phase of Ni

component, which is beneficial for

activity enhancement

Chemical state of Co

Catalytic activity and stability

• Excessive amount of Co coating (core shell structure) will cause Ni surface

getting covered, resulting in decrease of activity

• Ni@meshed-Co catalyst has outstanding long-term reaction stability than

the pure Ni-based catalyst

• Co stabilizes the Ni0 content and Co facilitates the adsorption and activation

of CO2, which is beneficial to the activity enhancement

Bare NiCore shell

Meshed coating

Activity Stability

19

The Coking Reduction

• The Ni@meshed-Co catalysts surface are mainly non-graphitic carbon species that

can be activated and eliminated

• The higher CO2 conv. produces much less CO, and meshed coating catalysts produces

less CH* intermediates and are fast removed

TG Raman

20

Summary

Core shell

structure

Facet selective

coated structure

Meshed like

coated structure

• SAMs assisted selective ALD is applied to fabricate Pd@Pt

core shell nanoparticles, Pt coating layer can be controlled

with atomic monolayer precision showing high activity for

PROX reaction

• Facet selective ALD is achieved through lattice mismatch to

fabricate bi-functional Pt@Ru(001) structure, enhancing the

CO activation and O2 dissociation at the same time for

PROX reaction

• ALD with post reduction treatment is developed to

synthesize meshed Co coating Ni nanoparticles, which is

highly active and coking resistant for DRM reaction