Research interest in biomass conversion to fuels and chemicals has increased significantly in the last decade as the necessity for a renewable source of carbon has become more evident. Accordingly, many different reactions and processes to convert biomass into high-value products and fuels have been proposed in the literature. Special attention has been given to the conversion of lignocellulosic biomass, which does not compete with food sources and is widely available as a low cost feedstock. In this review, we start with a brief introduction on lignocellulose and the different chemical structures of its components: cellulose, hemicellulose, and lignin. These three components allow for the production of different chemicals after fractionation. After a brief overview of the main reactions involved in biomass conversion, we focus on those where bimetallic catalysts are playing an important role. Although the reactions are similar for cellulose and hemicellulose, which contain C(6) and C(5) sugars, respectively, different products are obtained, and therefore, they have been reviewed separately. The third major fraction of lignocellulose that we address is lignin, which has significant challenges to overcome, as its structure makes catalytic processing more challenging. Bimetallic catalysts offer the possibility of enabling lignocellulosic processing to become a larger part of the biofuels and renewable chemical industry. This review summarizes recent results published in the literature for biomass upgrading reactions using bimetallic catalysts.

Lignocellulosic biomass typically contains more than 50 wt% sugars that can be upgraded to valuable platform molecules, such as levulinic acid (LA) and gamma-valerolactone (GVL). This article focuses on upgrading GVL produced from lignocellulosic biomass to various chemicals and fuels, such as polymers, fuel additives, and jet fuel. We also review the use of GVL as a solvent for biomass processing, which led to significant improvements in product yields and a more simplified process for producing biomassderived chemicals such as LA, furfural, and hydroxymethylfurfural.

Cellulose deconstruction at 428 K was studied in biphasic reaction systems consisting of GVL and aqueous solutions containing HCl (0.1-1.25 M) and a solute, such as salt or sugar. This biphasic system achieves high yields of levulinic and formic acids (e.g., 70%), and leads to complete solubilization of cellulose. The GVL solvent extracts the majority of the levulinic acid (e.g., greater than 75%), which can subsequently be converted to GVL over a carbon-supported Ru-Sn catalyst. This approach for cellulose conversion eliminates the need to separate the final product from the solvent, because the GVL product is the solvent. In addition, this approach eliminates the deposition of solid humin species in the cellulose deconstruction reactor, allowing these species to be collected and used for other processing options.