Controlling the nanoparticle size and shape of a Pt/TiO2 catalyst for enhanced hydrogenation of furfural to furfuryl alcohol†

Abstract

We report the selective liquid phase hydrogenation of furfural to 2-furfuryl alcohol using a Pt/TiO₂ catalyst prepared by the wet-impregnation method under mild reaction conditions (30 °C and 3 bar H₂ pressure). The effect of heat treatment protocols on the catalyst structures and the resultant catalytic properties of 4.2%Pt/TiO₂ and 0.6%Pt/TiO₂ was investigated. For both Pt loadings, the calcined + reduced catalyst exhibited higher activity compared to the reduced only catalyst, with the difference in activity being more pronounced for 4.2%Pt/TiO₂ than for 0.6%Pt/TiO₂. For the 4.2%Pt/TiO₂ catalyst, the reduced-only sample achieved 25% conversion with 90% selectivity for 2-furfuryl alcohol after 6 hours, while the calcined + reduced sample reached 99% conversion with 59% selectivity under identical reaction conditions. For the 0.6%Pt/TiO₂ catalyst, the reduced-only sample showed 70% conversion with 96% selectivity for 2-furfuryl alcohol, whereas the calcined + reduced sample achieved 97% conversion and 95% selectivity after a 2-h reaction. Characterisation of the samples using X-ray photoelectron spectroscopy, CO chemisorption and scanning transmission electron microscopy revealed that direct high temperature reduction resulted in a mixture of large Pt particles (>5 nm) with irregular shapes, small Pt nanoparticles (ca. 2 nm) and some sub-nm clusters. In contrast, calcination + reduction produced uniformly distributed Pt nanoparticles (ca. 2 nm) for both Pt loadings. Despite the presence of strong metal support interaction (SMSI) in Pt/TiO₂ catalysts, no spectroscopic evidence for such a strong interaction was found in this study. Therefore, the observed difference in catalytic activity is attributed to the variations in the shapes and sizes of the Pt nanoparticles. During the synthesis of Pt/TiO₂ catalysts, the calcination + reduction activation procedure is more beneficial for enhancing both activity and selectivity compared to a reduction only procedure.