Synthesis, characterization and catalytic properties of benzyl sulphonic acid functionalized Zr-TMS catalysts

Mesoporous zirconium hydroxide, Zr-TMS (zirconium hydroxide with mesostructured framework; TMS, transition metal oxide mesoporous molecular sieves) catalyst has been prepared through the sol–gel method and functionalized with benzyl sulphonic acid (BSA) using post-synthesis route without destroying the mesoporous structure. The benzyl group anchored Zr-TMS (B-Zr-TMS/≡Zr–O–CH2–Φ) was achieved by etherification reaction of Zr-TMS with benzyl alcohol at 80 °C using cyclohexane as solvent. Further, B-Zr-TMS was subjected to sulphonation reaction with chlorosulphonic acid (ClSO3H) at 70 °C using chloroform as solvent to yield BSA-Zr-TMS (≡Zr–O–CH2–Φ–SO3H). Maximum sulphonic acid (–SO3H) loading was optimized with respect to time of functionalization and concentration of ClSO3H. Functionalization was carried out by loading the maximum amount of benzyl group over Zr-TMS and varying the concentration of –SO3H. The synthesized materials have been characterized by powder XRD, FT-IR, elemental analysis, N2 adsorption–desorption and TPD of ammonia. The catalytic activity of the synthesized catalyst has been performed in liquid phase benzoylation of diphenyl ether to 4-phenoxybenzophenone (4-PBP) using benzoyl chloride as benzoylating agent at 160 °C under atmospheric pressure. The same reaction was carried out by sulphated zirconia (SO42−/ZrO2) and found very poor activity.