Effect of boron addition on the activity and selectivity of hydrotreating CoMo/Al2O3 catalysts Original Research Article

The influence of the incorporation of different amounts of boron (x=0.0, 0.2, 0.8, 1.5 and 2.0 wt.-%B) to CoMo/Al2O3 catalysts on the thiophene hydrodesulfurization catalytic activity and chemical state of the CoMo/Al2O3-B(x) catalysts has been investigated by UV-vis diffuse reflectance spectroscopy, X-ray diffraction spectroscopy, scanning electron microscopy, FT-IR of adsorbed nitric oxide, temperature-programmed reduction and acidity measurements. The results indicate that boria is deposited as a monolayer on the surface of the alumina up to a loading of 0.8% B. The incorporation of boron into the catalyst supports leads to a change in the distribution of the cobalt and molybdenum oxidic species which results in a decrease in the proportion of tetrahedrally coordinated Co2+ and Mo6+ species in strong interaction with the alumina support. As a result of this change in species in the oxidic precursors, the number of cobalt sites probed by nitric oxide in the sulfided catalysts increases with boron contents, while the molybdenum sites remain practically unchanged. The net result is a beneficial effect on the catalytic activity of the thiophene hydrodesulfurization reaction which reaches a maximum at a boron content of 0.8 wt.-% B.