Metal carbonyl clusters as effective precursors in the preparation of heterogeneous catalysts for biomass valorization

In this work, the use of metal carbonyl clusters (MCCs) as precursors for the preparation of heterogeneous catalysts is presented. In particular, their deposition on select supports and their subsequent decomposition is shown to be a viable strategy for the preparation of well-dispersed ultrasmall monometallic and bimetallic nanoparticles (NPs). Pt/Ni-based systems were prepared through the decomposition of heterometallic Ni−Pt Chini-type supported on TiO2, while the Ru-based catalysts were prepared employing the MCC [HRu3(CO)11] supported on different materials. The characterization of the final catalysts showed the formation of well-dispersed NPs with mean diameters around 1 nm. Moreover, both kinds of systems presented enhanced catalytic performances compared to analogous catalysts prepared via the more employed incipient wetness impregnation of metallic salts. The Pt/Ni-based catalysts were found to be active for both model reactions performed: reductive amination of furfural (FUR) and selective oxidation of 5-hydroxymethylfurfural (HMF). Ni insertion in the Pt active phase achieved two important results: in reductive amination of FUR, it led to an increased yield of furfurylamine (FAM) above 90% after one hour of reaction; in HMF oxidation, it improved catalyst stability, allowing five reaction cycles to be performed on the same catalyst. The preparation of Ru-based systems demonstrated the possibility of obtaining small NPs through the MCCs decomposition over different supports, allowing fine-tuning of the properties of the final catalyst. The preparation of Ru nanoparticles supported over basic materials led to improved catalytic performances compared to the use of NaHCO3 to promote HMF oxidation over non-basic catalysts like Ru/TiO2. Employing the materials obtained from the calcination of Mg/Al layer double hydroxides (LDH) as support for the Ru NPs, it was possible to carry out the HMF oxidation obtaining a complete conversion of the reagent and a high FDCA yield of around 90% after 6 hours of reaction.