Effect of Introduction of Trace Amount of Chromium Species in Improving Catalytic Performance of MCM-48 in Oxidative Dehydrogenation of Isobutane

Abstract

The catalytic performance of MCM-48 was greatly improved by the introduction of a small amount of chromium during the oxidative dehydrogenation of isobutane. Various characterization procedures such as XRD, N₂ adsorption–desorption isotherms, TEM, NH₃-TPD, XPS, and XAFS were used to identify the role that chromium played in the improvement, and XPS and XAFS results provided the most valuable information. Both measurements revealed that the chromium species existed as Cr⁶⁺ inside the framework of MCM-48 before oxidative dehydrogenation, but was reduced to Cr³⁺ during the reaction. The characteristic pore nature of MCM-48 also contributed to an enhancement of the selectivity to isobutene via the suppression of consecutive oxidation reactions.