Effect of precipitation medium on surface acidity and catalytic performance of chromium orthophosphates in cyclohexene skeletal isomerization and cumene conversion

Abstract

The influence of the precipitation medium and thermal treatment of CrPO₄(Cr: P = 1) catalysts on their surface acidity (number and strength distribution) was studied by means of the gas-phase chemisorption of pyridine (PY) and 2,6-dimethylpyridine (DMPY) at 573 and 673 K. In addition, Cyclohexene skeletal Isomerization (CSI) and cumene conversion (CC), were selected as dynamic methods for surface acid characterization. Catalysts obtained in propylene oxide–aqueous ammonia exhibited a higher number and strength of acid sites and, hence, greater activity in CSI and CC processes, than catalysts obtained in propylene oxide or aqueous ammonia exclusively. Moreover, cumene dehydrogenation (to α-methylstyrene) always predominated over cumene dealkylation (to propylene and benzene) and accounted for 100% selectivity of CrP-A and CrP-P catalysts. Furthermore, a correlation between surface acidity and catalytic activity was found.