Strategic Design of Copper Nanoparticles on Modified Clay as Catalyst for Efficient Domino Synthesis of γ-Valerolactone from Furfural via Transfer Hydrogenation

Gamma Valerolactone (GVL) is an important chemical derived from the hemicellulose in biomass whose applications span across the solvent, biofuel and polymer industries. A domino reaction selectively producing GVL from furfural makes it a highly desirable transformation. In this regard, finely dispersed copper nanoparticles immobilized on zirconia-modified montmorillonite K10 clay were synthesized and examined to achieve high selectivity for GVL. The catalysts were well characterized by employing various techniques, such as PXRD, TEM, FESEM, N₂ sorption, NH₃-TPD, TGA, ICP-OES, FTIR, pyridine IR and XPS. A detailed investigation of the co-operative effect of the active sites responsible for achieving the maximum selectivity towards GVL was carried out. An intrinsic interplay between the lower particle size of copper (metal centers), the Lewis acidity (zirconia sites) and the Brönsted acidic (MMT) sites was found. Further active site masking and reaction intermediates were tested to identify and prove the synergistic effect of the active sites in the reaction pathway. To achieve the highest yield, a response surface methodology using a Central Composite Design model was formulated. Under the optimized reaction conditions, the catalyst demonstrated 99.9% furfural conversion and a high GVL selectivity of 98%, the highest obtained so far in the literature. The catalyst remained highly stable over four reaction cycles with a marginal decrease in its activity and was regenerated via an autogenous solvothermal treatment in between each cycle. Spent catalyst characterizations revealed that its structural integrity and physicochemical properties were retained.