An investigation of the benzofuran hydrodeoxygenation network over sulfided and reduced nickel-molybdenum/aluminum oxide catalysts and comparisons with indole hydrodenitrogenation

The hydrodeoxygenation network of benzofuran was investigated over reduced and sulfided Ni-Mo/γ-Al₂O₃ catalysts. The effect of temperature, pressure, H₂S feed concentration, reduction temperature, pretreatment procedure, and catalyst composition on the product distribution and activity of each catalyst was investigated. The effects of these parameters were explained by a catalyst active site model, differences in the adsorption/desorption behavior of the catalyst, and by differences in the reactivities of intermediate species in the network. Parallels between HDO and hydrodenitrogenation(HDN) were studied by comparing the benzofruan HDO findings with results obtained for indole HDN. Characterization techniques used included BET surface area, X-ray photon spectroscopy, temperature programmed reduction and reaction, and diffuse reflectance infrared spectroscopy.; There are 2 routes responsible for the HDO of benzofuran. One is via the hydrogenolysis of 2,3 dihydrobenzofuran which leads to the formation of 2-ethylphenol. The other route starts with the hydrogenation of 2,3 dihydrobenzofuran which leads to the formation of 2-ethylcyclohexanol. The importance of each route depends on the temperature, pressure, feed H₂S concentration, and on the intrinsic hydrogenation and hydrogenolysis activities of the catalyst. Over sulfided catalysts, only the hydrogenolysis route was observed and hydrocarbon production depended on the reactivity of 2-ethylphenol. The benzene ring of 2-ethylphenol prevents it from directly reacting in a E2 or S_N2 reaction. Over reduced catalysts, the hydrogenation route was observed and hydrocarbon production depended on the reactivity of 2-ethylcyclohexanol which can participate in E2 and S_N2 reactions. Consequently the HDO activity of the reduced catalyst was much greater than the HDO activity of the sulfided catalyst. The formation/desorption temperatures of oxygen containing species in the hydrogenation route are lower than the corresponding temperatures of oxygen species in the hydrogenolysis route. In addition, desorption temperatures are significantly lower for reduced catalysts compared to sulfided catalysts in the absence of H₂S. Hydrogen sulfide promoted hydrogenolysis reactions and inhibited hydrogenation reactions. Reduced catalysts become sulfided at high temperatures, but they are stable at low temperatures and can maintain significant hydrogenation activity. It is possible to increase the hydrogenation activity by increasing the Ni content or reduction temperature.