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Metal–acid nanoplate-supported ultrafine Ru nanoclusters for efficient catalytic fractionation of lignin into aromatic alcohols

Ullah, Naseeb, Odda, Atheer Hameid, Liang, Kuang, Kombo, Miza Ali, Sahar, Shafaq, Ma, Liu-Bo, Fang, Xiao-Xiang, Xu, An-Wu
Green chemistry 2019 v.21 no.10 pp. 2739-2751
Bronsted acids, X-ray photoelectron spectroscopy, alcohols, ammonia, aromatic compounds, biomass, catalysts, chemical bonding, cleavage (chemistry), cost effectiveness, desorption, fractionation, green chemistry, hafnium, hydrogen, ketones, lignin, lignocellulose, nanocomposites, nanoparticles, phosphates, solvents, transmission electron microscopy, vanillin
The catalytic fractionation of lignin in a native lignocellulose matrix is crucial to the comprehensive achievement of sustainable and green chemicals. Herein, we prepared a novel metal–acid bifunctional nanocomposite of finely scattered metallic Ru nanoclusters (NCs) sustained on porous hafnium phosphate nanoplates (α-HfP NPs) to effectively depolymerise lignocellulosic biomass. A native lignin fraction of pine lignocellulose was promptly depolymerised into 19.86 wt% yield (lignin based) of valuable phenolic monomers (with dihydroeugenol as the main compound with high selectivity) and few cyclic ketones through one-pot catalytic reductive fractionation under mild conditions (190 °C, 3.5 MPa H₂). Detailed scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and temperature-programmed desorption ammonia investigation correlated with the obtained results revealed that the metal–acid synergistic influence and the presence of Brønsted acid sites in the support for dehydration and the well-dispersed metallic role of Ru NCs for hydrodeoxygenation were responsible for the cleavage of lignin–carbohydrate (ester and ether linkages) bonds. Moreover, treating commercial lignin as a substrate in an organic solvent generated 4-hydroxy-3-methoxybenzaldehyde (vanillin) in high yield, as well as other functionalised phenolic monomers up to 85% selectivity, illustrating the high susceptibility of Ru/α-HfP NPs towards C–O bond cleavage through reductive fractionation. Multiple recycling tests of the catalyst were performed without any apparent loss of activity. Overall, this report highlighted the potential of the synthesis strategy of the metal–acid supported catalyst to immediately depolymerise untreated biomass and can thus encourage the green, cost-efficient, large-scale production of intermediate chemicals.