Synthesis of rhodium-platinum bimetallic catalysts supported on SBA-15 by chemical fluid deposition for the hydrogenation of terephthalic acid in water

In this study, rhodium-platinum bimetallic catalysts supported on mesoporous silica SBA-15 (Rh-Pt/SBA-15) were synthesized by a chemical fluid deposition (CFD) method using supercritical CO₂ as a solvent. Uniformly dispersed Rh-Pt nanoparticles with an average size (~6.1 nm) smaller than the pore size of SBA-15 were obtained. The performance of the prepared catalysts in the hydrogenation of terephthalic acid (TPA) in water was investigated in spite of the poor solubility of TPA in water. The Rh-Pt/SBA-15 bimetallic catalyst synthesized at a 70:30 weight ratio of Rh to Pt (Rh₇₀Pt₃₀/SBA-15) exhibited a better catalytic activity than its monometallic counterparts (Rh/SBA-15 and Pt/SBA-15). A TPA conversion as high as 74.3% was achieved using the Rh₇₀Pt₃₀/SBA-15 bimetallic catalyst at 80 °C and 5 MPa of H₂ in a 2-h reaction, whereas the conversion of TPA over the Rh/SBA-15 catalyst was found to be 24.2%, and no reaction was observed in the presence of Pt/SBA-15 catalyst. The enhanced activity of the Rh-Pt/SBA-15 catalyst was attributed to the synergistic effect of Rh and Pt in the bimetallic alloy. In the Rh-Pt/SBA-15 bimetallic catalysts, it is believed that Pt helped the adsorption of arenes on the active sites and Rh played a key role in the catalytic hydrogenation of TPA. Moreover, a complete conversion of TPA could be achieved at 80 °C and 5 MPa of H₂ by increasing the reaction time to 4 h.