TABLE OF CONTENTS Heterogeneous catalysts have been used industrially for well over 100 years. Amongst the first processes was the catalytic hydrogenation of oils and fats to produce margarine using finely divided nickel. It is quite likely that when this process was first operated in the late nineteenth century unhealthy amounts of nickel remained in the product. The issue of leaching and the avoidance of trace catalyst residues are still important aspects of research from both economic and environmental points of view.
There is a whole spectrum of heterogeneous catalysts, but the most common types consist of an inorganic or polymeric support, which may be inert or have acid or basic functionality, together with a bound metal, often Pd, Pt, Ni or Co. Even if the support is inert its structure is of vital importance to the efficiency of the catalytic reaction. Since the reactants are in a different phase to the catalyst both diffusion and adsorption influence the overall rate, these factors to some extent depending on the nature and structure of the support.
Surface area is one of the most important factors in determining throughput (amount of reactant converted per unit time per unit mass of catalyst). Many modern inorganic supports have surface areas of 100 to > 1000 m 2 g -1. The vast majority of this area is due to the presence of internal pores; these pores may be of very narrow size distribution to allow specific molecular sized...
