Efficient metal borate catalysts for oxidative dehydrogenation of propane

Boron-based catalysts have attracted attention in recent years, due to their high selectivity for light olefins in the catalytic oxidative dehydrogenation of propane (ODHP). But they still face drawbacks such as low activity at mild reaction temperature and more or less boron leaching from the catalyst surface during the reaction. Hence, it is necessary to exploit more efficient boron-based catalysts with higher stability. In this study, metal borate catalysts (CoB4O7 and Ni3B2O6) were prepared by a co-precipitation method and evaluated for the ODHP. Reaction tests showed that both metal borates could catalyze propane dehydrogenation efficiently at 450-540 degrees C with high selectivity and stability. In particular, the CoB4O7 catalyst, after activation at 490 degrees C for 70 h, exhibited rather high stability with propane conversion of 17.6% and an appreciable selectivity for light olefins of 91.4% during the subsequent reaction run. The structural stability and active sites of the metal borate catalysts were investigated by SEM, TEM, XRD, FTIR, ICP-MS and XPS. The results showed that the morphology and crystal structure of the catalysts as well as the composition of bulk and surface elements changed little after reaction, showing excellent structural stability. Besides, the M-B-O (M = Co, Ni) and B-OH species on the catalysts surface were considered to be the active sites, which gradually increased and reached an abundant content without boron leaching during the induction period of the catalysts, affording the high catalytic activity and selectivity for light olefins.