Selective oxidative dehydrogenation of ethane over SnO2-promoted NiO catalysts

Nisingle bondSnsingle bondO mixed oxides catalysts have been investigated for the oxidative dehydrogenation of ethane. The catalysts were prepared through the evaporation of aqueous solutions of nickel nitrate and tin oxalate and finally calcined in air at 500 °C for 2 h. These materials have been characterized by several techniques (N2-adsorption, X-ray diffraction, High-Resolution Electron Microscopy, temperature programmed reduction, X-Ray Photoelectron Spectroscopy, Fourier Transformed Infrared Spectroscopy of adsorbed CO and 18O/16O isotope exchange). The addition of just a tiny amount of tin highly increases the selectivity to ethylene (from ca. 40% to 80–90%). Thus, high selectivity to ethylene (near to 90%) is observed on samples with high Ni/Sn atomic ratios (3 < Ni/Sn < 50), in which no influence of ethane conversion on selectivity to ethylene is observed (suggesting high stability of ethylene on these catalysts). Additionally, for low Sn-loadings, an increase in the catalytic activity has also been observed. The enhanced catalytic properties have been explained in terms of changes in the nature of Ni species on the catalyst surface, which can be considered as the active sites. The nature of Ni species is related to changes in the crystal size of NiO particles (and surface area) of catalysts as well as to the presence of SnOx crystals. In addition, the role of the presence of acid sites on the catalyst surface on the selectivity to ethylene is also discussed.