Correlating the Synthesis, Structure, and Catalytic Performance of Pt–Re/TiO₂ for the Aqueous-Phase Hydrogenation of Carboxylic Acid Derivatives

Pt–Re bimetallic catalysts have many applications, ranging from catalytic reforming to the reduction of carboxylic acid derivatives. However, the exact role of Re in these systems has remained a matter of discussion, partly due to the plethora of suggested synthesis protocols and analysis conditions. This study presents an extensive comparison of such literature protocols and the resulting materials. In detail, characterization by N₂ physisorption, X-ray diffraction, temperature-programmed reduction, CO pulse chemisorption, Fourier-transform infrared spectroscopy of adsorbed CO, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and in situ X-ray photoelectron spectroscopy is combined with catalytic testing to yield synthesis–structure–activity correlations. Accordingly, the investigated catalysts share common features, such as Pt⁰ nanoparticles (1–4 nm) decorated with partially reduced Re species (ReO_x–y). The remaining rhenium oxide is spread over the TiO₂ support and enhances Pt dispersion in sequential impregnation protocols. While differences in the number of active sites (Pt⁰/ReO_x–y) mostly explain catalytic results, small variations in the extent of Re reduction and site composition cause additional modulations. The optimal bimetallic catalyst outperforms Ru/C (previous benchmark) in the reduction of N-(2-hydroxyethyl)­succinimide, an important step in the production of a bio-based polyvinylpyrrolidone polymer.