Vanadium oxide supported on mesoporous MCM-41 as new catalysts for dehydrogenation of ethylbenzene with CO 2

Abstract

A series of MCM-41-supported vanadia catalysts (VO x /MCM-41) with the vanadium loading of 0.5–3.0 mmol/g were studied with respect to their performance in the dehydrogenation of ethylbenzene to styrene in the presence of CO 2. Structural and textural characterizations of the catalysts were performed by means of N 2 adsorption, X-ray diffraction (XRD), UV–vis and Raman spectroscopy, and temperature-programmed reduction (TPR). These catalysts were found to be effective for the dehydrogenation reaction. The dispersity and the nature of the vanadium species depend strongly on the V loading, so does the catalyst activity. It was confirmed that, during the dehydrogenation of ethylbenzene with CO 2 over VO x /MCM-41, two reaction pathways, i.e., direct oxidative dehydrogenation of ethylbenzene with CO 2 (one-step pathway) and reaction coupling of simple dehydrogenation of ethylbenzene with the reverse water–gas shift (two-step pathway) occurred. Forty-one percent of styrene could be produced by the one-step pathway. The promoting effect of CO 2 in ethylbenzene dehydrogenation has been attributed to different reaction pathways in the presence and in the absence of CO 2 as well as a higher concentration of active V 5+ species on the catalyst surface under CO 2 atmosphere. The MCM-41-supported vanadia is more active than the vanadia catalyst supported on conventional amorphous SiO 2.