Synthesis of Al-Modified SBA-15-Supported Ru Catalysts by Chemical Fluid Deposition for Hydrogenation of Dimethyl Terephthalate in Water

Uniformly dispersed 5 wt % ruthenium catalysts supported on Al_xSBA-15 (x = Si/Al ratio) were prepared by chemical fluid deposition employing supercritical CO₂ as the solvent for hydrogenating dimethyl terephthalate to dimethyl 1,4-cyclohexanedicarboxylate in water. Complete conversion of dimethyl terephthalate was achieved over a Ru₅/Al₂₀SBA-15 catalyst having the highest number of Lewis acid sites at 100 °C and 4.14 MPa H₂ pressure in 1 h. Here, 100% selectivity with a dimethyl 1,4-cyclohexanedicarboxylate yield of 93.4% was observed in 0.5 h due to complete cutoff of hydrocracking byproducts at shorter reaction times. Al modification enhanced selectivity of the catalysts toward dimethyl 1,4-cyclohexanedicarboxylate by governing the distribution of Lewis and Brönsted acid sites in the support. Water as a functional solvent enriched the hydrogenation of dimethyl terephthalate via an on-water mechanism. The Ru₅/Al₂₀SBA-15 catalyst was stable over five cycles. Greener catalyst synthesis, use of water, mild reaction conditions, and high atom economy led the proposed system to be a greener sustainable process.