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

Abstract

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.

Selective hydrogenation of benzoic acid over bimetallic NiCo embedded in N‐doped carbon

“…Higher calcination temperature (>600°C) would lead to the agglomeration of NiCo bimetal during the precursor pyrolysis process, as confirmed by the increased particle size as estimated from the XRD results (Figure S1c). 35 The effect of metal mole ratio was then investigated. The mono‐metal Ni/NC and Co/NC catalysts displayed less than 10% conversion of BA.…”

Making more from bio-based platforms: life cycle assessment and techno-economic analysis of N-vinyl-2-pyrrolidone from succinic acid

“…Lastly, further distinctions between Bio-x-Ex scenarios are caused by the choice of a hydrogenation catalyst, which determines overall NVP yields from succinic acid. While a recent improvement of the commercially available Ru/C catalyst, namely a bimetallic Pt–Re/TiO 2 material, 41 reduces normalized process inputs by about 14% relative, further optimization ( Bio-Id-Ex ) would allow for 26%. For reasons of mass balancing, waste quantities are inversely affected by the implemented hydrogenation catalyst.…”

“…4, n amine / n acid = 1, m water / m acid = 1) is implemented as a batch operation at 200 °C and 200 bar H 2 , with yield and by-product formation depending on catalyst choice. Three alternative simulations are implemented: (1) a commercial benchmark catalyst (Ru/C, 74% yield), 39 (2) a recently described optimized system (Pt–Re/TiO 2 , 83% yield) 41 and (3) a hypothetical future case with much reduced by-product formation (98% yield). To account for uncertainty in the handling of oligomeric hydrogenation by-products in the bio-based process, an alternative HEP separation is also considered supported by experiments (ESI, section 2b + c†): a sequence of (vacuum) distillations is implemented with or without prior removal of oligomers by extraction, resulting in conservative and optimistic process scenarios, respectively.…”

“…39,40 Yields of 70 mol% (succininc acid to NVP) were achieved with commercial hydrogenation catalysts and improved by further material development. 41 Consequently, this reaction sequence seems to be a promising way of obtaining a high-value monomer from a potential biomass platform using two conversion steps. While this value proposition appears intriguing, a detailed evaluation of process inputs and outputs is required to determine the expected merit of the proposed transformation.…”

Rhenium in Heterogeneous Catalysis: A Rising Star for Hydrogenation Reactions

“…Pt nanoparticles in Pt−Re/TiO 2 can be decorated by partially reduced Re species (ReO x−y ), independent of the impregnation sequences of metal precursors. 17 Re species spread over the TiO 2 support and helped to enhance the Pt dispersion. The sequential addition during the synthesis of the Ru−Re system was also reported by researchers.…”