Zr-based metal-organic frameworks and SBA-15 silica support: a synergistic approach for bio-jet fuel precursors production

The chemical conversion of biomass-derived platform molecules, such as furfural, into sustainable aviation fuel (SAF) is a subject of increasing interest. This work examines the aldol condensation between two biomass-derived platforms, like furfural and methyl isobutyl ketone, to produce the corresponding adduct (FuMe), suitable as a SAF precursor. Zr-modified MOFs are typically efficient catalysts in aldol condensation. However, crystalline MOF catalysts suffer from small pore size and limited reusability, especially when applied to processes involving bulky products. To overcome these limitations, this work provided a series of zirconium MOFs supported on mesoporous SBA-15 silica, aiming at increasing both the stability and the accessibility of the Zr-MOF active phases. The characterization via XRD, TEM-EDX, XPS, ICP-AES, 13C NMR, TGA, and N2 adsorption of the MOF/mesoporous silica hybrid materials demonstrated the successful incorporation of highly dispersed Zr organo-species onto the SBA-15 surface area. As a result, the catalytic performance of the prepared hybrid materials was markedly superior to that of the corresponding free crystalline Zr-MOFs, in terms of higher condensation activity and better selectivity. The best-performing hybrid, UiO-66@SBA-15, achieved 67% furfural conversion vs 3% on the unsupported MOF, accompanied by 100% FuMe selectivity. Furthermore, reducing furfural concentration allowed achieving total conversion (100%) and FuMe selectivity (100%). This is attributed to a synergistic effect between the surface-dispersed Zr-MOF active phase and the mesoporous silica support. In addition to demonstrating enhanced catalytic activity, the synthesised materials also exhibited improved stability during subsequent condensation processes, reinforcing the benefits of supporting Zr-MOF phases onto silica surfaces.