Combining accelerated activity tests and catalyst characterization: a time-saving way to study the deactivation of vinylacetate catalysts Original Research Article

Accelerated deactivation of a commercial Pd,Au/SiO2 catalyst for the production of vinylacetate monomer (VAM) has been performed in an internally back-mixed reactor (Berty) using deactivation–compensation protocols in which the concentration of oxygen was kept constant at the reactor outlet and deactivation rates could be measured directly. The formation rates of VAM and the main side product CO2 were studied as a function of time on stream at three different temperatures (155, 170 and 190 °C) in dependence on oxygen and ethylene concentration in the feed as well as in dependence on the initial gas hourly space velocity (GHSV). It was found that high reaction temperature as well as high oxygen partial pressure favor the deactivation markedly while both ethylene concentration and initial GHSV were of no influence on the deactivation rate. By comprehensive catalyst characterization using TEM, H2 chemisorption, thermal analysis, EPR and FTIR spectroscopy, several changes of the catalyst have been identified that might be responsible for deactivation: (i) sintering of metal particles; (ii) diffusion of Au from the surface into the particle bulk; (iii) decomposition of the potassium acetate promoter; and (iv) formation of deposites on the catalyst surface, in particular, at low reaction temperatures.