Design of γ-Alumina-Supported Phosphotungstic Acid-Palladium Bifunctional Catalyst for Catalytic Liquid-Phase Citral Hydrogenation

This study primarily addresses the development of dynamic, selective and economical metal–acid (bifunctional) catalysts for one-pot menthol production by citral hydrogenation. Specifically, various metals such as Pd, Pt, Ni, Cs Sn were doped over alumina support. Additionally, bifunctional composite also prepared with impregnation heteropoly acids Pd precursors Analytical techniques (e.g., BET, PXRD, FT-IR, pyridine adsorption amine titration methods) applied characterization most efficient Al2O3 PTA-Cat-I). Similarly, essential operational variables loading rate metal precursor, type acid, temperature, gas pressure reaction time) examined during this study. The experimental data shows that catalyst (PTA-Cat-I) produced 45% at full substrate conversion (r = 0.038 mmoles.min−1) in liquid-phase hydrogenation (at optimized operating conditions: 70 °C, 0.5 MPa 8 h). However, acid-supported PTA-Cat-I, PMA-Cat-I, SMA-Cat-I STA-Cat-I) resulted cracking dehydration isopulegol/menthol generation side products 4-isopropyl-1-methyl, cyclohex-1-ane/ene); therefore, yield was extensively diminished. On other hand, non-acidic Cat-I, Cat-II, Cat-III, Cat-IV Cat-V) readily promoted reactions. optimum occurred due to presence strong Lewis weak Bronsted acid sites. Mass transfer substantially diminished acidity strength, blockage pores catalysts.