The effects of morphology of cerium oxide catalysts for dehydrogenation of ethylbenzene to styrene

Abstract

Ethylbenzene (EB) dehydrogenation in presence and absence of CO2 was investigated over CeO2 catalysts of distinct morphologies: cubes, rods and particles. The presence of CO2 resulted in prolonged catalyst activity and higher initial benzene selectivity compared to the absence of CO2. However, CO2 had no effect on the catalytic activity of ceria catalysts after stabilization. CeO2 cubes exhibited about two times higher activity per m2 compared to rods and particles, independent of presence or absence of CO2. Product distribution and Raman spectroscopy characterization of the spent catalysts suggested that superior catalytic activity of CeO2 cubes originates from the enhanced amount of lattice oxygen species that can be extracted by EB on the (100) crystal planes of ceria cubes, contrary to highly intrinsically stable (111) crystal planes predominantly exposed on rods and particles. We suggest that these O species are consumed in nonselective EB conversion pathways, generating partly-reduced surface sites, which are suggested to act as active sites for selective styrene formation.