Molecular TiO2 Modifications of Supported PPh3-Capped Pd Nanocatalysts for CO2 Hydrogenation into Formates

Abstract

TiO2-supported Pd NPs-based materials were prepared following two distinct approaches: For the first set of materials 1–8, modification of the TiO2 support was performed prior to Pd NPs deposition, while the second set (9–15) was synthesized by deposition of modifiers over pre-synthesized Pd-PPh3/TiO2. These catalysts were applied in the hydrogenation of CO2 to formate, and their performance was compared with that of the unmodified Pd-PPh3/TiO2. Modification of the TiO2 support by organosilanes provided a beneficial effect in catalysis compared with the catalyst containing unmodified TiO2 or TiO2 modified by organophosphonic acids. In contrast, in most cases, the deposition of modifiers over previously synthesized Pd NPs supported on TiO2 was not beneficial to the activity of the catalyst. Interestingly, upon recycling, the first set of catalysts suffered a rapid decrease in activity, while the anchoring of modifiers over previously formed Pd NPs showed an improved stability (TON > 500 after the third recycling).