Catalytic and structural insights into MoPO/TiO₂-ZrO₂ catalysts: optimizing esterification for ethyl levulinate production

Ethyl levulinate, a diesel additive, has garnered significant interest in recent times owing to its capacity to be produced in substantial amounts using cost-effective raw materials such as levulinic acid. Molybdenum phosphate (MoPO) supported on titania-zirconia (TiO₂–ZrO_2, hereafter TZ) catalysts prepared by co-precipitation followed by impregnation process and catalytic activities of these materials were studied on the levulinic acid esterification with ethanol. Various characterization techniques such as X-ray diffraction (XRD), Raman, IR spectroscopy, N₂-sorption, UV–Vis spectroscopy, SEM–EDX, and ammonia temperature programmed desorption (TPD-NH₃) were employed on the prepared catalysts. Catalytic activity of catalysts was studied by changing active component amount on the support, amount of catalyst, initial feed ratio, and time on stream. All the prepared MoPo/TZ catalysts exhibited higher activity during esterification of LA with ethanol; however, the best result was obtained for 20 wt% MoPo/TZ sample with 60% conversion of levulinic acid and 100% selectivity of ethyl levulinate. The XRD results confirm the highly dispersed MoPO phase at lower loadings on TZ support and crystalline phase at higher loadings (50 wt%). The catalytic activity results obtained showed a strong correlation with the catalysts’ acidity due to well-dispersed active phase over TZ and surface area.