Heterogeneous catalytic processes form the basis for much of the chemical and petroleum processing industries. Solid catalysts enable reactions to occur at sufficiently high rates to be commercially feasible. In many cases, proper selection of a suitable catalyst also permits reaction pathways and product selectivities to occur that would not be kinetically possible in the absence of the catalyst. In our laboratory, we employ kinetic measurements of selected reactions, in combination with a variety of optical and surface spectroscopic and physical characterization techniques, to investigate the surface properties and detailed modes of operation of zeolites, metal oxides and supported metal catalysts.
Among the more challenging problems in the field of heterogeneous catalysis is that of selectively oxidizing small alkanes to higher hydrocarbons and oxygenates in high yields. We are currently investigating, for example, the catalyzed oxidative coupling of methane to C2hydrocarbon products. We have established that this reaction occurs via a heterogeneous-homogeneous reaction mechanism, in which the first step is homolytic cleavage of a C-H bond in methane at an O-site on the oxide catalyst surface. The resulting methyl radicals then emanate into the gas phase where they either undergo coupling to the desired C2 products or enter into a series of chain branching homogeneous reactions that lead to the formation of undesired COx products. We are employing x-ray photoelectron, FT-IR and in situ Raman spectroscopies to characterize the nature of the active sites on the catalyst surfaces. Additional studies using isotopic labelling and laser-induced fluorescence spectroscopy are providing details about the mechanism of this complex reaction system. Other projects involve studies of the direct selective oxidation of methane to oxygenates, such as formaldehyde and methanol, and to aromatic products.
"Conversion of Methyl Radicals to Methanol and Formaldehyde over Vanadium Oxide Catalysts." S. Pak, C. E. Smith, M. P. Rosynek, and J. H. Lunsford. J. Catal. 165 (1997) 73.
"Characterization of a Mo/ZSM-5 Catalyst for the Conversion of Methane to Benzene." D. Wang, J. H. Lunsford, and M. P. Rosynek. J. Catal.. 169 (1997) 347.
"Decomposition of Nitric Oxide over Barium Supported on Magnesium Oxide. 1. Catalytic Results and in situ Raman Spectroscopic Evidence for a Barium-Nitro Intermediate." S. Xie, G. Mestl, M. P. Rosynek, and J. H. Lunsford. J. Amer. Chem. Soc.. 119 (1997) 10186.
"Catalytic Conversion of Methane into Aromatic Hydrocarbons over Iron Oxide Loaded ZSM-5 Zeolites." B. Weckhuysen, D. Wang, M. P. Rosynek, and J. H. Lunsford. Angew. Chem. Int. Ed. Engl.. 36 (1997) 2374.
"Steady-State Conversion of Methane to Aromatics in High Yields using an Integrated Recycle Reaction System." P. Qiu, J. H. Lunsford, and M. P. Rosynek. Catal. Letts. 48 (1997) 11.