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

Abstract

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 H 2 pressure). The catalyst structure−activity relationship has been established through an extensive range of in situ spectroscopic characterizations, which included in situ Xray photoelectron spectroscopy (XPS), in situ CO-diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and in situ attenuated total reflectioninferred (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 H 2 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 NH 3 -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.

Tuning the electronic property of Pd nanoparticles by encapsulation within ZIF-67 shells towards enhanced performance in 1,3-butadiene hydrogenation

“…6, the peaks of three samples are in the range of 1900-2200 cm −1 . According to the literature, the peaks above 2000 cm −1 correspond to different valence states of CO and Co. 40,41 The adsorption band present at 1990 cm −1 was assigned to the bridgebonded adsorption of CO on Pd(100), which is consistent with the TEM results. 42 The bridging-adsorbed CO band at 1940 cm −1 in Pd/ZIF-67 can be ascribed to adsorption on the Pd NC edges.…”

MOF‐derived bimetallic NiCo nanoalloys for the hydrogenation of biomass‐derived levulinic acid to γ‐valerolactone

“…This could be due to the enhanced adsorption at the alloyed NiCo metallic sites that could be responsible for the elevated performance attained by the bimetallic alloyed catalysts. In combination with the analysis of EXAFS (Figure 3) and HAADF‐STEM (Figure 4), NiCo is the main active center and porous carbon support would provide large surface area, whereas Ni likely performs as the main hydrogenation centers and the Co sites are also beneficial for the adsorption of LA 48–50 . Molecular H 2 can be activated on Ni active sites, which can further facilitate the hydrogenation of the adjacent LA molecules adsorbed on the nearby Co sites.…”

“…In combination with the analysis of EXAFS (Figure 3) and HAADF-STEM (Figure 4), NiCo is the main active center and porous carbon support would provide large surface area, whereas Ni likely performs as the main hydrogenation centers and the Co sites are also beneficial for the adsorption of LA. [48][49][50] Molecular H 2 can be activated on Ni active sites, which can further facilitate the hydrogenation of the adjacent LA molecules adsorbed on the nearby Co sites. The desired product GVL will be formed either by dehydrocyclization of 4-hydroxypentanoic acid or the subsequent hydrogenation of angelica lactone.…”

Low Loading of CoRe/TiO2 for Efficient Hydrodeoxygenation of Levulinic Acid to γ-Valerolactone

“…Typically, GVL can be obtained through hydrogenation and subsequent cyclization of levulinic acid (LA) . Many types of monometals, such as Ir, Au, Pt, Re, Pd, Rh, Ru, Ni, Mo, Co, Fe, and Cu, supported on various supports including activated carbon (AC), carbon nanotube (CNT), ordered mesoporous carbon (OMC), SiO 2 , Al 2 O 3 , TiO 2 , ZrO 2 , and zeolites, have been studied as catalysts for this purpose. − Except for monometallic catalysts, more and more heterogeneous bimetallic catalysts have also been developed for the hydrodeoxygenation of LA into GVL in the past few decades. − Although the catalytic mechanism of bimetallic catalysts is far from clear, it is widely believed that the addition of the second metal will form heteroatom bonds that change the electronic environment of the metal surface. Thus, the microgeometry of the metal lattice is altered, which would bring synergistic effects during the catalytic reactions.…”