Enhancing ethyl lactate synthesis over TiO2-Al2O3 catalysts: Synergistic effects of acid treatment and WO3 promotion

Ethyl lactate can be produced from bio-derived feedstock such as ethanol and lactic acid via a catalytic esterification reaction. Here, TiO 2 -Al 2 O 3 support was employed as a catalyst, synthesized by mixing derived precursor Al (aluminum isopropoxide) and Ti (titanium tetraisopropoxide), and acid treatment (H 2 SO 4 and H 3 PO 4 ), followed by loading of tungsten. The WO 3 supported on H 2 SO 4 or H 3 PO 4 -modified TiO 2 -Al 2 O 3 were then evaluated in terms of improving catalytic performance and durability. The catalysts were characterized by X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET), scanning electron microscopy–energy dispersive X–ray spectroscopy (SEM–EDX), and X-ray photoelectron spectroscopy (XPS). The reaction was carried out at 80 °C for 4 h in a batch system. The findings highlighted in particular that 0.5 M of H 2 SO 4 treated WTA highly enhanced the yield of ethyl lactate (57.15%) and reusability over three cycles. The sulfation leads to higher medium to strong acid sites (332.8 μmol/g cat ) and increased surface area (130.1 m 2 /g), also increasing oxygen vacant sites. The catalyst stability declined upon structural degradation over three cycles, which might be attributed to acid site loss and leaching of W and Al. However, the WO 3 supported on 0.5 M H 2 SO 4 -modified TiO 2 -Al 2 O 3 maintained superior long-term reusability compared with Amberlyst-15. These findings provide crucial insights into catalyst design strategies, optimizing acid functionality and structural stability for esterification reactions.