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

TEM Study of Rhodium Catalysts with Manganese

PromoterAdrian Merritt

UICPhysicsNSF REU program at UIC, 7/29/2010 2

OutlineI. Research Objectives and Methods

II. Sample Characterization

III. Particle Size Results

IV. Research Conclusion

V. Future Work

UICPhysicsNSF REU program at UIC, 7/29/2010 3

Research Objectives 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

UICPhysicsNSF REU program at UIC, 7/29/2010 4

TEM 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

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

UICPhysicsNSF REU program at UIC, 7/29/2010 5

Fischer-Tropsch (and related) Processes

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

UICPhysicsNSF REU program at UIC, 7/29/2010 6

Rhodium Catalyst, Manganese Promoter

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% Image from The Selective Adsorption of a Manganese

Promoter Over Supported CO Hydrogenation Catalysts, Theresa E. Feltes, 2010

UICPhysicsNSF REU program at UIC, 7/29/2010 7

Holey Carbon Films 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)

UICPhysicsNSF REU program at UIC, 7/29/2010 8

Final Sample Final sample has

many medium-sized clusters of silica particles

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

UICPhysicsNSF REU program at UIC, 7/29/2010 9

Current Samples 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

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

UICPhysicsNSF REU program at UIC, 7/29/2010 10

Imaging Samples Typical magnification

is x300k

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

UICPhysicsNSF REU program at UIC, 7/29/2010 11

Particle Sizes (Unpromoted)

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 >5.50

5

10

15

20

25

RhOx (6.18.2010)

Particle Size (nm)

Freq

uenc

y

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5>5.50

5

10

15

20

25Rh (Reduced) (6.21.2010)

Particle Size (nm)

Freq

uenc

y

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

Particle Sizes (Promoted)

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 >5.50

5

10

15

20

25

30

35

40

45

RhOx + Mn (7.7.2010)

Particle Size (nm)

Freq

uenc

y

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 >5.50

5

10

15

20

25

30

35

40

45

Rh+Mn (Reduced) (7.7.2010)

Particle Size (nm)

Freq

uenc

y

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

UICPhysicsNSF REU program at UIC, 7/29/2010 13

Particle Sizes (Promoted, in situ Heating)

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

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 >5.50

5

10

15

20

25

30

35

Rh+Mn (Heated) (7.19.2010)

Particle Size (nm)

Freq

uenc

y

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 >5.50

5

10

15

20

25

30

35

Rh+Mn (Cooled) (7.9.2010)

Particle Size (nm)

Freq

uenc

y

UICPhysicsNSF REU program at UIC, 7/29/2010 14

SummarySample Average Particle

Size (nm)Standard Deviation (nm)

RhOx (unreduced) 3.12 0.80Rh 3.08 0.83Rh+Mn Ox (unreduced)

2.26 0.54

Rh+Mn 2.44 0.67Rh+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

UICPhysicsNSF REU program at UIC, 7/29/2010 15

Future Work 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

UICPhysicsNSF REU program at UIC, 7/29/2010 16

FEFF University of

Washington ab initio program for simulation EELS spectra

Full multiple scattering simulation

Preparation for JEM-2010F EELS work, distinguishing rhodium oxide species530 535 540 545 550 555 560 565 570 575 580

Experimental vs. Theoretical

Rh2O3 O K-Edge FEFFRhO2 O K-Edge FEFFRh2O3 O K-Edge Gatan

Energy (eV)

Coun

ts (

Arb.

uni

ts)

UICPhysicsNSF REU program at UIC, 7/29/2010 17

Acknowledgements 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