Fundamental Study of Catalytic Functionalities Involved in Effective C-O Cleavage over Ru-Supported Catalysts

Catalytic hydrodeoxygenation (HDO) has been considered as a promising route for biomass revalorization. The development of active and stable materials has been undertaken over the past decade, and precious metals have displayed high activities. Ru has exhibited an outstanding performance due to its high hydrogenation capacity, among other properties. Rational development of these catalysts requires understanding the contribution of properties like acidity, oxophilicity, reducibility, and capacity to generate oxygen vacancies. However, the fundamental basis for effective C-O cleavage is not well understood, to our knowledge. Therefore, this work aimed to evaluate the effect of support in HDO of ethanol, cyclohexanol, and phenol as oxygenated model molecules for bio-oil on Ru catalysts. A series of 0.6 wt % Ru catalysts were prepared by wet impregnation with Ru(NO)(NO3)(3) solutions. A strong influence of support in HDO activity of different molecules with the Ru catalyst was evidenced. Differences in activity on the catalyst with comparable particle size indicated that reactions involving the C-O cleavage by hydrogenation did not occur only on metallic sites. Rather, the activity took place by a cooperative action between the metallic phase and the support. For the HDO reaction of the studied molecules, Ru/TiO2 and Ru/ZrO2 were the most active solids as compared with Ru/SiO2 and Ru/Al2O3. Ethanol and cyclohexanol dehydration-reformation reactions showed that catalytic functionalities could be tuned with the reaction temperature. It was found that acid properties were more relevant when the temperature was increased (formation of ethylene and diethyl ether). At the same time, the metallic (dehydrogenation) function decreased (formation of acetaldehyde and its reformation to methane and CO). The usage of oxyphilic supports with oxygen vacancies, moderate acid site density, and redox properties in combination with high hydrogenating capacity metals like Ru may be the clue to developing highly active materials for alternative fuel production.