Highly active catalysts of mesoporous Ce-Cr-mAl2O3 and reaction mechanism for N2O-assisted oxidative dehydrogenation of ethylbenzene to styrene

Abstract

The mesoporous Cr-mAl2O3 and Ce-Cr-mAl2O3 catalysts were prepared via a one-pot hydrothermal process for the N2O-assisted ethylbenzene (EB) selective oxidation to styrene, which was viewed as both a greenhouse recycling method and a new process for styrene (ST) production. It was found that 7Cr-mAl2O3 provided superior catalytic performance with respect to ST among Cr oxide-doped catalysts and that the Ce modification could further increase the ST yield to 54%. To clarify the promoting effect and mechanism of Ce-Cr species on catalytic performance, numerous types of characterization, particularly in-situ DRIFTS, were used. Results indicated that the favorable reducibility of catalyst was crucial for N2O activation. Carbon deposition was unavoidable during the reaction process, but adding Ce-Cr could reduce the stability of the deposited carbon and relief its detrimental effect on catalytic performance. The suitable surface acidity and high relative content of Cr6+ and Oα could be responsible for the excellent catalytic performance of Ce-7Cr-mAl2O3. In-situ DRIFTS not only identified the coupling effect between EB dehydrogenation and N2O decomposition but also proposed the possible reaction pathway that the adsorbed N2O reacted with the EB molecule, thereby providing a good explanation for the promoting effects of high content of N2O on the activity of Ce-7Cr-mAl2O3.