1 INTRODUCTION

Chemisorption of hydrogen is widely utilised in various experimental techniques to characterise hydrogenation catalysts. Data from conventional static chemisorption, temperature programmed desorption (TPD) and pulse chemisorption together constitute an extensive collection of qualitative and quantitative information. The kinetic analysis of a heterogencously catalysed reaction can be supported by separate studies of adsorption/desotption kinetics of reactants and products. In this sense detailed knowledge of hydrogen chemisorption provides essential information for the kinetics of catalytic hydrogenation reactions.

Static chemisorption gives information on the adsorption capacities and the adsorption equilibrium behaviour. TPD measures either desorption alone or combined desorption and re-adsorption. Re-adsoiption during TPD may even maintain the adsorption equilibrium between surface and gas phase. In this case TPD provides temperature-dependent information on the adsorption equilibrium and may be used to determine the equilibrium parameters.1

TPD experiments can be carried out either in ultra high vacuum or at ambient pressure under flow condition. Thus they can bridge the material and pressure gaps between surface science and heterogeneous catalysis. Despite the popularity of TPD as a catalyst characterisation method its application in kinetic analysis for porous samples is often being discouraged. There are indeed important methodical considerations such as the selection of the reactor model and the intrinsic kinetic model and the evaluation of mass transfer limitations. ^{2 7} Furthermore, experimental data with sufficient information content should be collected in a...