Selective Hydrogenation Reactions on Single Crystal and Bimetallic Surfaces
Esan, Dominic Ayomaria
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Hydrogenation is one of the most common chemical transformations encountered in several synthetic industrial processes. It is often accomplished with the aid of a catalyst which can either be homogeneous (catalyst and reactants in the same phase) or heterogeneous (catalyst and reactant in different phases). Heterogeneous catalysis usually involves reactants in the gaseous phase reacting on a catalyst in the solid phase. Selecting the best catalyst and optimal conditions for a particular hydrogenation process requires proper understanding of the catalytic material, the reacting species, and the reaction itself. This understanding has oftentimes been provided by surface scientists via fundamental studies of these hydrogenation reactions on single metal surfaces in an ultrahigh vacuum (UHV) chamber where the conditions (temperature and pressure) can be properly controlled. However, most industrial catalysis involve solid catalysts with more complex morphologies than single-crystal metal surfaces and the operating conditions, especially pressure, are vastly different from UHV conditions. Thus the results from surface science studies are often difficult to correlate with industrial catalytic processes. These differences are sometimes referred to as the material and pressure gaps. In this thesis, using tools such as reflection absorption infrared spectroscopy (RAIRS), Auger electron spectroscopy (AES), temperature-programmed reaction spectroscopy (TPRS), and low energy electron diffraction (LEED), some of the results acquired from efforts to bridge these gaps are presented. The thesis begins with a presentation of the results obtained from the growth and ambient pressure hydrogenation of p(2×2)–N layer on Pt(111). Thereafter, the results from the adsorption and hydrogenation of acrolein on Ru(001) and the surface chemistry of its hydrogenation products – 2-propenol, propanal, and 1-propanaol – on Ru(001) are discussed in detail. The preparation and characterization of pseudomorphic platinum layers on Ru(001) using a homemade evaporator are fully discussed while the results obtained from the adsorption and selective hydrogenation of acrolein on the resulting Pt/Ru(001) bimetallic surfaces are also presented. The thesis concludes with a discussion of the surface-enhanced infrared response observed on isolated platinum nanostructures grown on single layer graphene on Ru(001).
Ultra High Vacuum
Chemical vapor deposition