Nanohydrotalcite Supported Ruthenium Nanoparticles: Highly Efficient Heterogeneous Catalyst for the Oxidative Valorization of Lignin Model Compounds

Abstract

The catalytic transformation of lignocellulosic biomass derived chemicals into value‐added chemicals under mild conditions remains a challenge in the fields of synthetic chemistry and catalysis. Herein, we describe a new heterogeneous catalyst system that efficiently works in the oxidative valorization of lignin model compounds. This new heterogeneous catalyst system comprised of nano‐sized hydrotalcite (n‐HT; Mg6Al2(CO3)(OH)16) supported ruthenium(0) nanoparticles (Ru/n‐HT) was prepared by ion‐exchange of [Ru(OH2)Cl5]2− anions with the extraframework CO32− anions of n‐HT followed by their borohydride reduction (NaBH4) in water at room temperature. The characterization of Ru/n‐HT was done by the combination of various spectroscopic and the sum of their results revealed that the formation of well‐dispersed ruthenium(0) nanoparticles with a mean diameter of 3.2 ± 0.9 nm on the surface of n‐HT structure. The catalytic performance of Ru/n‐HT in terms of activity, selectivity and stability was tested in the aerobic oxidation of cinnamyl, veratryl and vanillyl alcohols, which are important lignin model compounds used to mimic the propyl side chain, the phenolic and non‐phenolic, respectively functional groups of lignin. We found that Ru/n‐HT nanocatalyst displays remarkable activity at high selectivity and almost complete conversion in these catalytic transformations under mild reaction conditions (at 373 K under 3 bar initial O2 pressure).

Catalytic aerobic oxidation of lignin-based vanillyl alcohol under base–free conditions over an efficient and reusable LaFeO3 perovskite for vanillin production

“…As is known, the solvent is a very important metric for green and sustainable measures; 40 the solvents used in the existing methods are mainly organic solvents, such as alcohols, acetonitrile, DMSO, THF, DMF, 1,4-dioxane, acetone, xylene, EtOAc, etc . Although the conversion of vanillyl alcohol and the yield of vanillin were relatively high when acetonitrile, DMSO, THF, DMF, 1,4-dioxane, and acetone were used as solvents, among which acetonitrile was the best (the higher the polarity, the higher the conversion 41 ), they are classified as problematic and/or hazardous in CHEM21, 42 so it is not suitable as a solvent in Green Chemistry. By comparison, our study used alcohols and EtOAc as solvents, which were recommended solvents.…”

Aerobic oxidation of vanillyl alcohol to vanillin catalyzed by air-stable and recyclable copper complex and TEMPO under base-free conditions

“…Various other metal nanoparticles immobilized on a variety of carriers such as metal organic frameworks (MOFs), carbon, titania, and ceria have been also investigated. [59][60][61][62] Photocatalytic oxidations of vanillyl alcohol to vanillin over Ce and Zr oxide supported on biomass-templated titania were also reported by Muñoz-Batista and Luque et al 63 These smart materials showed excellent selectivity (99%) toward vanillin; however, the conversion of vanillyl alcohol was not great (maximum 52%). Similar photocatalytic conversion of vanillyl alcohol to vanillin under mild reaction conditions are reported by other groups.…”

“…Similarly, excellent selectivity could not be achieved using metal nanoparticles. [58][59][60][61][62] Although high selectivity could be achieved using photocatalysts, [63][64][65] poor conversion was a major issue in contrast to complete conversion achieved with the present catalyst. Hence, we can conclude that we have developed a significantly improved catalytic protocols as compared to the existing catalytic system for the aerobic oxidation of vanillyl alcohol to vanillin.…”

Hydrotalcite framework stabilized ruthenium nanoparticles (Ru/HTaL): efficient heterogeneous catalyst for the methanolysis of ammonia-borane

“…To investigate the effect of temperature on the rate of Ru/HTaL (50 mg, 1.12 wt% Ru) catalysed methanolysis of AB (100 mM in 5.0 mL of methanol), the catalytic reaction was performed at different temperatures (25,30,35,40, and 45°C). The initial rates at each temperature were determined from the linear portion of plots (volume of H 2 versus time) and used for the construction of Arrhenius and Eyring plots [41,42] from where activation parameters were determined.…”

“…Hydrotalcite-supported Pt [31], Pd [32][33][34], Ru [35], and Au [36] nanoparticles have been used as catalysts in hydrogenation, oxidation, and coupling reactions. The characterization of Ru/HTaL has been done by using various spectroscopic and visualization techniques including inductively coupled plasma optical emission spectroscopy (ICP-OES), powder X-ray diffraction (P-XRD), Fourier transform infrared spectroscopy (FTIR), 11 B NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), bright field transmission electron microscopy (BFTEM), and high resolution transmission electron microscopy (HRTEM).…”