Pentacoordinated Al3+ stabilized polyoxometalates for the efficient catalytic valorization of biomass-derived feedstocks

Abstract

The high-loading, good distribution and stable heterogenization of polyoxometalate (POMs) salts with supports, such as oxides, is rather challenging since the structural integrity of POMs is easily destroyed if strong interactions exist. Here, we developed a novel route to achieve the in situ anchoring of high-loading ammonium phosphomolybdate (APMo, with a mass fraction as high as 49%) on alumina with coordinatively unsaturated Al³⁺ sites without the deformation of the Keggin structures of POMs. The anchoring effect of Al³⁺_penta to polyoxometalates originating from the strong APMo–alumina interaction effectively promotes the dispersion and stability of APMo compared to the samples made by impregnation. The remaining heteropoly acid structure and synergistic effect between APMo and alumina make the hybrid materials exhibit superior redox and acid catalytic performances, achieving >99% selectivity of benzaldehyde for benzyl alcohol oxidation and double the yield for fatty acid esterification compared with that of the impregnated catalyst. This work offers an alternative to the trade-off problem for the heterogenization of POM catalysts and provides a green and recyclable catalyst for the efficient valorization of biomass-derived feed blocks into value-added chemicals.