Enhancement of C-O bond cleavage to afford aromatics in the hydrodeoxygenation of anisole over ruthenium-supporting mesoporous metal oxides

Mesoporous TiO2, Al2O3, silica (SBA-15), and nonporous conventional TiO2 (P25) were used as supports for Ru catalysts in the hydrodeoxygenation (HDO) of anisole. The catalytic reaction was performed in a batch reactor at 200 degrees C and 5-30 bar H-2 pressure. It was shown that the selectivity of this catalytic system towards benzene strongly depended on the H-2 pressure, being higher at low pressure. Moreover, significant differences in the product distribution were observed for these catalysts suggesting the strong influence of the nature of supports on controlling the reaction pathway. The SBA-15-supported Ru catalyst (Ru/SBA-15) catalyzed the reaction primarily by the hydrogenation (HYD) pathway. The mesoporous-Al2O3-supported Ru (Ru/nieso-Al2O3) promoted the reaction via the HYD and demethylation pathways simultaneously. Mesoporous-TiO2-supported Ru (Ru/meso-TiO2) and P25-supported Ru (Ru/P25) promoted higher yield of benzene, indicating its high selectivity for the direct deoxygenation (DDO) route. The use of meso-TiO2 facilitated the spillover effect, leading to the formation of numerous Ti3+ defect sites and oxygen vacancies. As a result, Ru/meso-TiO2 with anatase phase exhibited higher selectivity for the DDO pathway compared to nonporous P25 with a mixed rutile and anatase phase. The results indicated that the phase and mesoporous structure of TiO2 plays an important role in promoting its interaction with Ru particles and in selecting the HDO reaction pathway.