Fundamental studies of hydrogen chemisorption on supported monometallic and bimetallic catalysts using microcalorimetry

摘要

Hydrogen serves as a reactant in many important commercial processes catalyzed by supported transition metals. However, little is known about the fundamental interactions of hydrogen with these complex catalyst systems. Hence, the objective of this thesis was to investigate the energetics of hydrogen chemisorption on supported monometallic and bimetallic catalysts using microcalorimetry. Differential heats of hydrogen adsorption on silica supported Ru, Rh, Pt, Ru-Ag, Ru-Cu, K/Ru/SiO{dollar}\sb2{dollar} were investigated.;A home-built Tian-Calvet microcalorimeter was designed, built and used to determine the dependence of differential heats of adsorption on the ratio of hydrogen to surface metal. Comparison of initial heats of adsorption on various catalysts provided information on phenomena, such as electronic effects, which might occur in bimetallic and promoted catalysts. Differential heats of adsorption and amounts of hydrogen adsorbed were determined as a function of pressure and coverage. The ability to probe the energetics of adsorption at high pressures was specifically developed in this work. At high pressures weak hydrogen becomes available and this plays an important role in catalytic reactions. However, little is known about the nature of this weak hydrogen. The microcalorimetric results were complemented with hydrogen mobility information obtained via {dollar}\sp1{dollar}H NMR.;The energetics of hydrogen adsorption on silica supported Ru, Rh and Pt was investigated. The Ru-Cu and Ru-Ag model systems were also investigated with emphasis on probing the energetics of adsorption at high pressure. The influence of K promoter on the chemisorption and kinetics of hydrogen adsorption on Ru/SiO{dollar}\sb2{dollar} were also studied. It is proposed that the chemisorption behavior and the energetics of hydrogen adsorption on supported systems at high pressures cannot be obtained through a simple extrapolation of results obtained from surface science studies on single crystals at low pressures.