On the deactivation of Fe, K/active carbon catalysts in the course of oxidative dehydrogenation of ethylbenzene with carbon dioxide

Highly active and selective Fe2O3-K2O/C-act catalysts for oxidative dehydrogenation of ethylbenzene with CO2 undergo deactivation. The course of deactivation up to a loss of 95% activity is described, and related to the formation of an inactive carbonaceous deposit. The catalysts and deposits were characterized after various times-on-stream (TOS) by textural, structural and chemical analysis, as well as by temperature-programmed decomposition and oxidation. XPS spectra of O 1s and K 2p confirmed the removal of OH and diminishing of carbonyl groups, as well as segregation of K2CO3 onto the surface. Prolonged TOS, at temperatures above 500 degrees C caused removal of heteroatoms from the carbonaceous deposits and even the appearance of graphitized structure in XRD patterns. It was found that the activity depended almost linearly on the amount of and the decrease in surface area. An excess of CO in relation to styrene in the product distribution suggests that the deposit is formed owing to styrene polymerization, and further dehydrogenation, on the catalyst surface.