Effect of steaming on the catalytic performance of ZSM-5 zeolite in the selective oxidation of phenol by nitrous oxide

Abstract

Gas-phase oxidation of phenol to dihydroxybenzenes (DHB) with nitrous oxide was performed over a set of ZSM-5 zeolites steamed at different temperatures in the range from 550 to 750°C. The best of the catalysts demonstrated 70% N2O conversion and a more than 90% selectivity for DHB. However, significant differences were observed in DHB isomer distribution and catalyst deactivation due to changes in the acidity of the zeolites. The steaming procedure reduces the concentration of Bronsted acid sites, thus allowing a decrease in coke loading. Simultaneously, a substantial decline in the molar ratio of hydroquinone to catechol in the reaction products was observed, mainly due to the increased selectivity to the ortho isomer – catechol. These results can be used to control the selectivity for different DHB isomers in the title reaction by varying steaming severity.