The construction of novel and efficient hafnium catalysts using naturally existing tannic acid for Meerwein-Ponndorf-Verley reduction

A Novel Tannic Acid-Based Carbon-Supported Cobalt Catalyst for Transfer Hydrogenation of Biomass Derived Ethyl Levulinate

The catalytic conversion of ethyl levulinate (EL) to γ-valerolactone (GVL) is an important intermediate reaction in the conversion and utilization of biomass resources. The development of novel and efficient catalysts is significantly important for this reaction. In this work, using the biomass-derived tannic acid as carbon precursor and the transition metal cobalt as active component, a novel tannic acid carbon supported cobalt catalyst (Co/TAC) was prepared by pyrolysis and subsequent hydrazine hydrate reduction method. The hydrogenation of EL and other carbonyl compounds by hydrogen transfer reaction was used to evaluate the performance of the catalysts. The effects of different preparation and reaction conditions on the performance of the catalysts were investigated, and the structures of the prepared catalysts were characterized in detail. The results showed that the carbonization temperature of the support had a significant effect on the activity of the catalyst for the reaction. Under the optimized conditions, the Co/TAC-900 catalyst obtained the highest GVL yield of 91.3% under relatively mild reaction conditions. Furthermore, the prepared catalyst also showed high efficiency for the hydrogenation of various ketone compounds with different structures. This work provides a new reference for the construction of the catalysts during the conversion of biomass and a potential pathway for the high-value utilization of tannin resource.

Recyclable Zr/Hf-Containing Acid-Base Bifunctional Catalysts for Hydrogen Transfer Upgrading of Biofuranics: A Review

The massive burning of a large amount of fossil energy has caused a lot of serious environmental issues (e.g., air pollution and climate change), urging people to efficiently explore and valorize sustainable alternatives. Biomass is being deemed as the only organic carbon-containing renewable resource for the production of net-zero carbon emission fuels and fine chemicals. Regarding this, the selective transformation of high-oxygen biomass feedstocks by catalytic transfer hydrogenation (CTH) is a very promising strategy to realize the carbon cycle. Among them, the important Meerwein-Ponndorf-Verley (MPV) reaction is believed to be capable of replacing the traditional hydrogenation strategy which generally requires high-pressure H2 and precious metals, aiming to upgrade biomass into downstream biochemical products and fuels. Employing bifunctional heterogeneous catalysts with both acidic and basic sites is needed to catalyze the MPV reaction, which is the key point for domino/cascade reaction in one pot that can eliminate the relevant complicated separation/purification step. Zirconium (Zr) and hafnium (Hf), belonging to transition metals, rich in reserves, can demonstrate similar catalytic efficiency for MPV reaction as that of precious metals. This review introduced the application of recyclable heterogeneous non-noble Zr/Hf-containing catalysts with acid-base bifunctionality for CTH reaction using the safe liquid hydrogen donor. The corresponding catalysts were classified into different types including Zr/Hf-containing metal oxides, supported materials, zeolites, metal-organic frameworks, metal-organic hybrids, and their respective pros and cons were compared and discussed comprehensively. Emphasis was placed on evaluating the bifunctionality of catalytic material and the key role of the active site corresponding to the structure of the catalyst in the MPV reaction. Finally, a concise summary and prospect were also provided centering on the development and suggestion of Zr/Hf-containing acid-base bifunctional catalysts for CTH.

Tailoring Lewis/Brønsted acid properties of MOF nodes via hydrothermal and solvothermal synthesis: simple approach with exceptional catalytic implications

The Lewis/Brønsted catalytic properties of the Metal-Organic Framework (MOF) nodes can be tuned by simply controlling the solvent employed in the synthetic procedure. In this work, we demonstrate that Hf-MOF-808 can be prepared from a material with a higher amount of Brønsted acid sites, via modulated hydrothermal synthesis, to a material with a higher proportion of unsaturated Hf Lewis acid sites, via modulated solvothermal synthesis. The Lewis/Brønsted acid properties of the resultant metallic clusters have been studied by different characterization techniques, including XAS, FTIR and NMR spectroscopies, combined with a DFT study. The different nature of the Hf-MOF-808 materials allows their application as selective catalysts in different target reactions requiring Lewis, Brønsted or Lewis-Brønsted acid pairs.

Zirconium and hafnium polyhedral oligosilsesquioxane complexes – green homogeneous catalysts in the formation of bio-derived ethers via a MPV/etherification reaction cascade

Newly designed POSS supported zirconium and hafnium isopropoxides are robust, durable and selective homogeneous catalysts for the conversion of hydroxymethylfurfural to bis(isopropoxymethyl)furane via MPV/etherification reaction with isopropanol as a green solvent/reagent.