Characterisation of supported chromium oxide catalysts by kinetic analysis of H2-TPR data

The kinetics of reduction of chromium oxide catalysts was studied by applying nonlinear regression analysis to the temperature-programmed reduction (TPR) data of six different CrOx/Al2O3 samples (1.2-14 wt% Cr). Different kinetic models were tested. Three heating rates were required to discriminate between the different kinetic models. The best-fit kinetic models and the estimated parameters for each sample are reported. The two-dimensional nuclei growth model suitably described the kinetics of reduction of samples with loading close to or beyond the monolayer content (> 5 wt%). The overall reduction mechanism seemed to be the same irrespective of the method of catalyst preparation. The chromium content was important, however. Reducibility increased regularly with chromium loading, supporting the idea of a topochemical reduction mechanism. The sample with low chromium content (similar to1 wt%) was reduced by a different overall mechanism than were the other samples and its reduction behaviour was best described by homogeneous first-order kinetics (random nucleation). Complete line-shape analysis of TPR patterns offers a good means for quantitative characterisation. of alumina-supported chromium oxide catalysts, since it provides information on dynamic redox behaviour of the active sites. (C) 2002 Elsevier Science (USA).