Cr/ZSM-5 for ethane dehydrogenation: Enhanced catalytic activity through surface silanol

Dehydrogenation of ethane to ethylene in the presence of CO2 was investigated over CrOx catalysts supported on ZSM-5 with different crystallite sizes, including nanometer, submicron and micrometer. These catalysts behave differently in the dehydrogenation reaction, but no relationship between the activity and crystallite size of ZSM-5 was found. XPS, UV-vis, laser Raman and HR-TEM studis show that the better activity comes from better CrOx dispersion on ZSM-5 surface. The characterization results of ZSM-5 supports by N-2 adsorption, SEM, XRD, XRF, Al-27 and Si-29 MAS NMR reveal that the difference of the dispersion is associated with their surface properties, not with the textural ones. Silanols on the surface play an important role in dispersing the CrOx active species. Silanol nests are more helpful in efficient CrOx dispersion than terminal silanols, which subsequently result in higher dehydrogenation activity. (C) 2016 Elsevier B.V. All rights reserved.