Looking into More Eyes Combining in Situ Spectroscopy in Catalytic Biofuel Upgradation with Composition-Graded Ag-Co Core-Shell Nanoalloys

γ-Valerolactone (GVL), which can be generated from levulinic acid (LA), has attained a humongous amount of interest due to its implantation in various fields, which includes fuels and fuel additives. Herein, for the first time, we have sequentially synthesized silver-cobalt core-shell nanoalloy-based catalysts through a simple wet impregnation method for selective conversion of LA to GVL. The highest catalytic proficiency (97.3 LA conversion with 100% GVL selectivity) had been achieved over a composition-graded optimized catalyst, named 5Ag-15Co, under comparatively moderate reaction conditions (150 °C, 1 MPa H2 pressure). The catalyst structure-activity relationship has been established through an extensive range of in situ spectroscopic characterizations, which included in situ X-ray photoelectron spectroscopy (XPS), in situ CO-diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and in situ attenuated total reflection-inferred (ATR-IR) spectroscopy. The extraordinary catalytic activity could be attributed to the modulation of electronic properties, which is mainly due to the synergistic interaction in the core-shell alloy system, as confirmed from in situ XPS studies. The presence of the highest amount of metallic cobalt in the 5Ag-15Co catalyst, which was evidenced by both in situ XPS and in situ CO-DRIFT, could assist the hydrogenation step in hydrodeoxygenation of LA to GVL. This finding also was emphasized by H2 chemisorption analysis, which revealed the presence of the highest active metal surface area in the 5Ag-15Co catalyst. In situ ATR-IR has elucidated that moderate interaction, which was generated between the catalyst and LA, has enhanced the rate of reaction. This finding also has been emphasized by the results obtained from NH3-TPD analysis, which revealed that the presence of high surface density of Lewis/weak acidic sites facilitated the hydrogenation step in the hydrodeoxygenation (HDO) reaction. The detailed kinetic analysis revealed that the 5Ag-15Co catalyst had the lowest activation energy (41.34 kJ) among its counterparts, which accelerated the reaction rate.