Critical design of heterogeneous catalysts for biomass valorization: current thrust and emerging prospects

Catalysis in the heterogeneous phase plays a crucial role in the valorization of biorenewable substrates with controlled reactivity, efficient mechanical process separation, greater recyclability and minimization of environmental effects. In this minireview, we have critically analyzed the design aspects of catalysts with multifunctional properties in making biomass conversion processes more productive and sustainable. The catalytic systems have been categorized into subgroups such as metal oxides and phosphates, supported metals, functionalized porous materials, acidic and ion-exchange resins, zeolites and carbonaceous materials to discuss their structural features and active sites towards intrinsic reactivity and selectivity in the transformation of biomass intermediates via hydrolysis, dehydration, hydrodeoxygenation and oxidation pathways. Recent advances in photocatalytic materials for the oxidation of biomass-derived small molecules (such as sugars, alcohols, carboxylic acids) and lignin model compounds and the role of different heteroatoms in improving photo-electronic properties are discussed. The synergistic effect of metal nano-particulate sites and acid-base supports of bimetallic catalytic systems in performing multistep cascade processes in one-pot are analyzed.