Polymeric organophosphate-hafnium unconventional MOFs nanohybrids enable high-efficiency upgrading of biomass feedstocks via cascade catalytic transfer hydrogenation-dehydration

Abstract

Efficiently selective catalytic conversion of biomass into biofuels and high-value chemicals using robust and porous catalysts is of great significance for valorization of renewable carbon resources. With respect to this, to reduce the supply dependence on natural oils, heterogeneous catalysis provides the opportunity for versatile anethole (AN) synthesis from bio-derived 4′-methoxypropiophenone (4-MOPP) via the one-pot cascade reactions of catalytic transfer hydrogenation (CTH) followed by dehydration, using an alcohol hydrogen donor and a Lewis/Brønsted acid catalyst. Herein, a sustainable and green strategy for catalytic upgrading of 4-MOPP to AN was developed via the cascade CTH-dehydration process, which was remarkably promoted by polymeric organophosphate unconventional MOFs-hafnium nanohybrids (PDVP-Hf) prepared via a simple solvothermal method. Interestingly, Brønsted/Lewis acidity, Lewis basicity, and hydrophobicity of PDVP-Hf could be effectively regulated by simply adjusting the composite components, among which PDVP-Hf-3 having an amorphous and porous inorganic-organic framework structure (with mesopores centered at 6.52 nm), an enhanced acidity of a suitable B/L molar ratio with lower basicity, and a strong hydrophobicity (water contact angle of 113°), was demonstrated to be efficient for selective conversion of 4-MOPP to AN with a maximum yield of 98.9% using 2-pentanol as hydrogen donor. Moreover, this developed catalytic system exhibited broad substrate generality, and could be employed for reductive upgrading of various carbonyl compounds to alcohols, or further coupled with dehydration to afford olefins. The catalyst synergistic roles of L acid-base couple sites (Hf4+-O2−) and B acid species (-OH) contributed to its pronounced performance, while high thermostability and robust hydrophobicity of PDVP-Hf-3 endowed its superior reusability, with no significant decline in reactivity for five consecutive recycles. The involved catalytic mechanisms and reaction pathways were explicitly elucidated by control experiments and theoretical calculations. This work sheds light on the appropriate design of unconventional MOF-polymer nanohybrids by combining both advantages for enhanced biomass upgrading via tough cascade reactions.