Different Ethane Dehydrogenation Catalysis of Isolated Ga Hydrides and Reduced Ga Cations in MFI Zeolites

ABSTRACT In nonoxidative alkane dehydrogenation using Ga‐exchanged MFI zeolites (Ga‐MFIs), Ga species isolated at ion‐exchange sites, such as Ga hydrides ([GaH 2 ] + /[GaH] 2+ , denoted as GaH x ) and/or Ga cations (Ga + ), are the active sites. Although a previous theoretical study has shown that the catalytic activity of reduced Ga species for ethane (the simplest alkane) dehydrogenation differs in terms of the highest predicted activation enthalpy, the different catalytic activities of GaH x and Ga + have not been experimentally investigated. In this study, we compared the ethane dehydrogenation catalysis of H 2 ‐treated Ga‐MFI containing GaH x (Ga‐MFI‐GaH x ) and Ar‐treated Ga‐MFI, one possessing mainly Ga + (Ga‐MFI‐Ga + ), using steady‐state activity tests, kinetic studies, and temperature‐programmed surface reactions. The combined results show that Ga‐MFI‐GaH x exhibits higher activity than Ga‐MFI‐Ga + . The involvement of these Ga species in ethane activation was also examined using in situ Fourier‐transform infrared spectroscopy, which revealed that GaH x is formed from Ga + upon introducing ethane. The different local structures of the Ga species in the MFI zeolites treated under different gas conditions were investigated using X‐ray absorption spectroscopy.