The Chemical Catalysis Program of the Chemistry Division of the National Science Foundation will support the research program of Professor Francisco Zaera at the University of California, Riverside. Dr. Zaera and his students will examine the hypothesis that the structure of the metallic catalyst surface affects the selectvitiy of the reaction even for mild catalytic hydrocarbon conversions such as the hydrogenation and isomerization of heavy olefins and the oxidation of glycerol. Kinetic investigations using an in situ nanoliter sized reactor, coupled with infrared spectroscopic investigations of the surface intermediates will be used to probe these ideas. The fundamental understanding obtained from these studies will impact the design and utilization of heterogeneous catalysts for industrial processes. New experimental methodology will be developed in the application of the nanoliter reactor technology. Collaboration with research groups in Latin America will continue, and increased participation by students in underrepresented groups, Hispanics in particular, will be pursued.
Our project provides a basic science understanding for reactions relevant to the heterogeneous catalysis use for the conversion of hydrocarbons, for processes relevant to fuel and food processing, the synthesis of fine chemicals and pharmaceuticals, and other important applications. It is highly desirable to use green processes for this, where the catalytic processes are carried out in a way as to minimize the consumption of input chemicals and the generation of byproducts. The central hypothesis motivating our project has been that the nature of the surface of solid catalysts may affect the selectivity of hydrocarbon conversions such as hydrogenations and isomerizations. Experiments have been carried out by using model systems, both under ultrahigh vacuum (UHV) and using a so-called high-pressure cell, to investigate the surface chemistry of olefins and other relevant intermediates in hydrocarbon conversion catalysis. Additional experiments were performed to check structure sensitivity for specific reactions using supported catalysts. Much has been learned about the surface chemistry of hydrocarbons on relevant transition metals. For instance, we have surveyed the differences in the chemistry of C1 adsorbed species on vanadium versus nickel and platinum single-crystal surfaces. Mechanistic insights from modern surface-studies under ultrahigh vacuum (UHV) were provided to explain reaction selectivities in terms of relative rates for different types of surface elementary steps, namely, hydrogenation, dehydrogenation, coupling, and methylene and oxygen insertions. Early transition metals such as vanadium were found to be quite reactive, but to still be able to promote interesting bond-forming reactions, and could possibly be used to prepare novel catalysis. Other studies were directed at illustrating the versatility of nickel in promoting a variety of surface steps for the conversion of adsorbed hydrocarbons. Examples included the selective hydrogenolysis of styrene to toluene, the migration of carbon-carbon double bonds in cyclopentene and 1-pentene, the ring closure of C5 metallacyclic surface intermediates, the coupling of alkyl groups, and the growth of hydrocarbon chains starting from ethyl and propyl surface intermediates. Additional information was reported on the relative rates of the hydrogenation and dehydrogenation surface steps responsible for multiple H-D exchange steps. The bulk of our work centered on the use of Pt surfaces for hydrocarbon conversions, much of it for the conversion of ethylene, used as a representative of olefins. Also, some studies on structure sensitivity were performed using supported catalysts with well-defined platinum nanoparticles. Concretely, catalysts recently developed in our laboratory based on Pt nanoparticles with tetrahedral and cubic shapes, which expose (111) and (100) facets respectively, are being used for the promotion of the oxidation of glycerol at room temperature and under atmospheric pressures. This follows previous work that looked at the influence of structure in the generation of trans fat, an important issue in the production of food. With glycerol, a byproduct from biofuel processing, it was found that supported tetrahedral Pt and cuboctahedral Pt exhibit different selectivity and kinetic behavior from the regular Pt catalysts. In a broad sense, our work on the development of ways to characterize mechanistic details of surface reactions can be extended to other areas, including the semiconductor industry, to tribological problems, and to solid interfaces of biological interest. We have in the past performed work on the chemistry of chemical vapor deposition processes in connection with the formation of surface coatings, a project that is currently being extended to atomic layer depositions, and a number of members in my group have gone to work on different aspects of semiconductor manufacturing such as protection of computer hard disks and the deposition of metals on silicon. We have also worked in collaboration with other colleagues in our Department to develop molecular memories based on the electrochemical reading and writing of porphyrins supported on solid surfaces. We have trained a number of students and postdocs in the last few years. They have then gone to take prominent academic or industrial positions. The details are provided in the section entitled "Training and Development". We have also exposed undergraduate students to research projects; this has provided incentive for them to decide on continuing on to obtain doctorate degrees and to get involved in research work of their own.
