Temperature-programmed desorption as a tool to extract quantitative kinetic or energetic information for porous catalysts

Temperature-programmed desorption (TPD) from high-surface area heterogeneous catalysts was investigated as a transient kinetic tool for studying reaction kinetics of elementary gas–solid interactions. TPD experiments carried out in flow setups have only rarely been used for kinetic purposes. Kinetic analysis of this kind of system requires a description of the extrinsic dynamics of the TPD system (i.e., the reactor flow model and intraparticle mass transfer). These were the focus of this study. In addition, the significance of the readsorption of the adsorbate was assessed. A range of process conditions and experimental parameters typical for a flow TPD setup was defined. Simulations were carried out for a single catalyst particle in TPD assuming infinite external mass transfer. The selection of the flow model for the TPD reactor was considered. Finally, the system was studied with a complete heterogeneous model for TPD consisting of a plug flow reactor model and taking into account intraparticle diffusion and intrinsic adsorption/desorption in the predefined range of parameters. The simulation results were then compared with results of previous studies on the methodology of TPD. It is concluded that the extrinsic dynamics of TPD can be coherently modelled to allow kinetic analysis according to general principles of transient kinetics, and a reappraisal of TPD as a kinetic tool for the study of high-surface area catalysts is in order. TPD may help bridge material and pressure gaps between catalysis studies and surface science studies. TPD experiments combined with kinetic analysis may also serve as a useful tool for studying microkinetics of heterogeneous catalysis.