Selective C-C Bond Cleavage in Diols and Lignin Models: High-Throughput Screening of Metal Oxide-Anchored Vanadium in Mesoporous Silica

The development of selective and robust heterogeneous oxidation catalysts is an enabling technology for conversion of biomass-derived platform chemicals. Vanadium active sites were incorporated into the structure of mesoporous silica via an ultra-fast, one-pot synthesis method based on microwave-assisted heating. In addition, Al/Ti/Zr/Ce anchoring ions were introduced in order to minimize vanadium leaching and better control its dispersion. The supported V-(Al/Ti/Zr/Ce)-MCM-41 composite materials were assessed as catalysts for aerobic C-C bond cleavage of simple models for lignin (1,2-diphenyl-2-methoxyethanol) and sugar-derived polyalcohols (meso-hydrobenzoin). The Ti-IV ions proved to be the best anchors to prevent V leaching, while Al-III and Zr-IV ions were the best to improve selective conversion of the substrates. The active sites in these catalysts are shown to be 2D VOx layers stabilized on the anchors. In a screen of twelve solvents, weakly polar solvents like toluene were found to be most suitable for this reaction, as was environmentally friendly ethyl acetate. The above properties, together with the high selectivity for C-C bond cleavage, advocate for a heterogeneous catalytic pathway, intrinsically different from that reported previously for molecular oxovanadium (V) catalysts.

Automated summary

The development of selective and robust heterogeneous oxidation catalysts is crucial for converting biomass-derived platform chemicals. A microwave-assisted synthesis method was used to incorporate vanadium active sites into mesoporous silica, while Al/Ti/Zr/Ce anchoring ions were introduced to minimize vanadium leaching and improve substrate conversion selectivity. The catalysts showed 2D VOx layers stabilized on anchors, with Ti-IV ions proving to be the best for preventing V leaching and Al-III/Zr-IV ions for enhancing substrate conversion selectivity, in the presence of weakly polar solvents like toluene and ethyl acetate as suitable reaction solvents. The high selectivity for C-C bond cleavage suggests a heterogeneous catalytic pathway different from previously reported molecular oxovanadium (V) catalysts.