Post on 22-Feb-2016
description
transcript
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