Interfacial Synergy in ZSM-5/TiO2 Heterogeneous Catalysts for Enhanced Stability in Rubber Seed Oil Epoxidation

Abstract

Catalytic epoxidation of vegetable oil commonly possesses a reduction of relative conversion to oxirane (RCO%) over reaction time due to the ring-opening of epoxide groups that can be overcome by controlling pore structure and reactant diffusion control. This research was conducted to tailor heterogeneous catalyst composite surface area by combining ZSM-5 with titanium dioxide (TiO₂) via impregnation method to improve the reaction stability of the catalyst in the epoxidation of rubber seed oil (RSO). Five different ratios of ZSM-5 to TiO₂ were studied to observe the catalyst's efficacy in the epoxidation process by measuring the relative conversion to oxirane (RCO%), surface area (BET), and structural characteristics (XRD). The 1:3 ZSM-5/TiO₂ ratio showed the most constant RCO% during the reaction (20 min) compared to single stage catalyst which RCO% inclined rapidly and decline afterwards, even though the epoxide yield was a little lower (below 15%). Next, the calcination conditions (temperature and time) of the catalyst were studied to improve the RCO%. Catalyst calcined at temperature of 300°C within 6 h produced the highest RCO% of 35% compared to initial RCO% of 15%, the lowest BET surface area and the biggest pore volume. XRD characterization showed that TiO₂ was successfully added to the ZSM-5 framework without changing the way the crystals looked. The hybrid catalyst also maintained catalytic activity throughout the multi-cycle evaluation, with all RCO values remaining comfortably above the 40% threshold. The combination of ZSM-5's microporous structure and TiO₂'s reactive surface managed to suppress the ring-opening of epoxide groups and maintained high RCO% at the longest period during the catalytic rubber seed oil epoxidation. This custom-made composite is an effective alternative catalyst to improve quality of epoxide groups produced from vegetable oil epoxidation for making bio-based materials and green polymers.