Determination of highly active and selective surface for the oxidative dehydrogenation of ethane over phase-pure M1 MoVNbTeOx catalyst

Abstract

The original phase-pure M1 MoVNbTeOx catalyst was mechanically treated with stirring water for several days under ambient conditions to obtain particles with different sizes. The catalytic performance was significantly improved and stabilized after about 7 days of treatment. Among all the catalysts, the sample treated in water for 7 days can obtain 57.6 % ethane conversion and 0.79 kgC2H4/kgcat/h ethylene productivity while the original phase-pure M1 catalyst was only 19.2 % and 0.27 kgC2H4/kgcat/h at reaction temperature of 400 °C and contact time of 18.5 gcat·h/molC2H6. Meanwhile, the catalyst was systematically characterized and the results showed that there was essentially no difference in microstructure between the original and treated catalysts. TEM and SEM morphological characterizations presented that the particle size and aspect ratio of the catalysts changed significantly, in which the particle size of the catalyst become smaller and the proportion of basal surface was enhanced. The activity and selectivity of the catalysts exhibited a correlation with the amount and proportion of basal surface. It can be deducted that the basal surface is the most active and selective surface during oxidative dehydrogenation of ethane (ODHE) process, and the intrinsic activity based on the basal (001) plane of the catalyst remains stable after the mechanical treatment. Samples treated in water for 7 days showed excellent long-term stability in a 200 h stability test at reaction temperature of 440 °C and contact time of 9.3 gcat·h/molC2H6. The present work demonstrated that the differences in the catalytic properties of different M1 samples depend mainly on the amount and proportion of exposed basal surface, and the possibility of enhancing the activity of orthorhombic M1 phase by fragmentation method.