Bimetallic catalysts have long been of scientific interest due to the intriguing possibilities that exist with regard to tuning the properties of the catalyst by varying the composition and creating unique local ensembles (active sites). Norskov and coworkers have greatly contributed to our understanding of catalysis through an analysis of the behavior of d-band transition metals. Norskov et al have shown that simple relationships hold equally for transition metals and their alloys and that the average d-band filling of the metal atoms in surface layer(s) acts a predictor of adsorption strength. However, there are a few catalyst systems of considerable importance (e. g. PtSn catalysts for catalytic reforming) where a d-band transition metal is alloyed with a non-transition metal (a metal with some occupancy in p-orbitals in the valence band) and the simple picture of examining the d-band center as a universal predictor seems insufficient. Therefore, this proposal through a combined theoretical/experimental approach will attempt to develop simple rules which could describe the adsorption behavior of p-d alloys (p-electron metals alloyed with d-band metals) in a similar way as has been previously established by Norskov et al for d-band transition metal alloys.
Intellectual Merit The importance of this work is to extend established correlations which describe d-transition metal alloys to a new class of catalysts: alloys involving a d-band transition metal (e.g Pt) and one involving a main group metal (e.g. Sn or Zn). The work will be performed in a collaborative effort between experiment and theory utilizing multiple techniques. A variety of p-d alloy catalysts will be synthesized, and extensively characterized using EXAFS, in situ-XPS, and STEM-EELS. Following their characterization the catalyst will be tested under realistic operating conditions using a traditional microreactor in an effort to link the composition and structure of our materials to their reactivity (and selectivity) for two reactions of considerable importance: water gas shift and propane dehydrogenation. Density Functional Theory studies will examine the electronic structure of these materials and their stability under reaction conditions. Finally theory will be called upon to improve our understanding of the mechanism and thereby aid our design of new catalysts.
Broader Impact This study is of a very general nature and as such may ultimately lead toward ?rules of thumb? in catalyst design as Norskov?s seminal work regarding d-band theory which this work hopes to augment and emulate. Multiple collaborative investigators will work together with the students on this project, each with a unique research perspective (partially as a product of the institutions with which they are affiliated). Therefore the student will gain an appreciation of research at industrial (Dr. Jeff Miller of BP), governmental (Dr. Jeremy Kropf of Argonne National Laboratory) and academic institutions (Professor Robert Klie and John Regalbuto of the University of Illinois at Chicago; Prof. Fabio Ribeiro of Purdue University). The PI intends to make considerable use general user facilities at the Advanced Photon Source (APS) at Argonne National Lab (for EXAFS) and the Advanced Light Source (ALS) at Lawrence Berkeley Labs (for high pressure XPS) which will expose the students to a large variety of research environments as well as a number of synergistic techniques. This work involves practical examples which illustrate the usefulness of undergraduate level chemical thermodynamics and reaction kinetics which can be incorporated into existing courses taught by the PI. The test reactions of interest for these catalysts involve both traditional hydrocarbon catalysis and hydrogen production, a reaction of increasing potential importance to our energy future. These examples will be integrated in the appropriate context to the department?s new introductory course for first year students in chemical engineering. Finally, it is hoped to extend this even further to high school level through interaction with the Illinois Math and Science Academy.
