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TEM Study of Rhodium Catalysts with Manganese Promoter. Adrian Merritt. Outline. Research Objectives and Methods Sample Characterization Particle Size Results Research Conclusion Future Work. Research Objectives.
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TEM Study of Rhodium Catalysts with Manganese Promoter Adrian Merritt NSF REU program at UIC, 7/29/2010
Outline Research Objectives and Methods Sample Characterization Particle Size Results Research Conclusion Future Work NSF REU program at UIC, 7/29/2010
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 NSF REU program at UIC, 7/29/2010
TEM Image from Transmission Electron Microscopy, B. Williams and C. Carter, volume IV 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, 7/29/2010
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 NSF REU program at UIC, 7/29/2010
Rhodium Catalyst, Manganese Promoter Image from The Selective Adsorption of a Manganese Promoter Over Supported CO Hydrogenation Catalysts, Theresa E. Feltes, 2010 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, 7/29/2010
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) NSF REU program at UIC, 7/29/2010
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) NSF REU program at UIC, 7/29/2010
Current Samples Images from The Study of Heterogeneous Catalysts by High-Resolution Transmission Electron Microscopy, A. Datye & D. Smith, Catalyst Review, 1992 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, 7/29/2010
Imaging Samples Typical magnification is x300k Use diffraction contrast imaging to differentiate rhodium particles (crystalline) from the silica support (amorphous) NSF REU program at UIC, 7/29/2010
Particle Sizes (Unpromoted) Averages: 3.12 nm vs. 3.08 nm Standard deviations: 0.80 nm vs. 0.83 nm The same (within experimental limits)! NSF REU program at UIC, 7/29/2010
Particle Sizes (Promoted) Averages: 2.26 nm vs. 2.44 nm Standard deviations: 0.54 nm vs. 0.67 nm NSF REU program at UIC, 7/29/2010
Particle Sizes (Promoted, in situ Heating) Averages: 2.55 nm vs. 2.43 nm Standard deviations: 0.91 nm vs. 0.69 nm Heated at 300° C for 2 hours, then allowed to cool NSF REU program at UIC, 7/29/2010
Summary • Averages not different enough to cause all phenomena observed in catalysts with a promoter NSF REU program at UIC, 7/29/2010
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 NSF REU program at UIC, 7/29/2010
FEFF 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, 7/29/2010
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 NSF REU program at UIC, 7/29/2010
