Valorization of native birch wood lignin into monomeric phenols over nickel-based catalysts has been studied. High chemoselectivity to aromatic products was achieved by using Ni-based catalysts and common alcohols as solvents. The results show that lignin can be selectively cleaved into propylguaiacol and propylsyringol with total selectivity >90% at a lignin conversion of about 50%. Alcohols, such as methanol, ethanol and ethylene glycol, are suitable solvents for lignin conversion. Analyses with MALDI-TOF and NMR show that birch lignin is first fragmented into smaller lignin species consisting of several benzene rings with a molecular weight of m/z ca. 1100 to ca. 1600 via alcoholysis reaction. The second step involves the hydrogenolysis of the fragments into phenols. The presence of gaseous H 2 has no effect on lignin conversion, indicating that alcohols provide active hydrogen species, which is further confirmed by isotopic tracing experiments. Catalysts are recycled by magnetic separation and can be reused four times without losing activity. The mechanistic insights from this work could be helpful in understanding native lignin conversion and the formation of monomeric phenolics via reductive depolymerization. Broader contextNature efficiently synthesizes aromatic structures and deposits them as lignin in plants. Incorporation of catalytic technologies into lignin conversion is a possible option for valorizing the feedstock as a renewable raw material for aromatic chemical production. Use of heterogeneous catalysts facilitates separation and recycling, and has attracted great attention. However, the detailed chemistry between solid catalysts and solid feedstocks still remains unknown because of mass transfer limitations. Herein we report the valorization of native birch wood lignin into monomeric phenols over nickel-based catalysts. High chemoselectivity to aromatic products was achieved by using Ni-based catalysts and common alcohols as solvents. The results show that lignin can be selectively cleaved into propylguaiacol and propylsyringol with total selectivity >90% at a lignin conversion of about 50%. Analysis results show that birch lignin is rst fragmented into smaller lignin species consisting of several benzene rings with a molecular weight of m/z ca. 1100 to ca. 1600 via alcoholysis reaction. The second step involves the hydrogenolysis of the fragments into phenols. This study will greatly contribute to the understanding of the lignin depolymerization reaction and will be interesting for other biomass conversion.

Noble-metal clusters are important catalysts because of their unique structures and activities, which are associated with their metalÀmetal bonds.[1] Numerous methods have been developed to encapsulate metal clusters within porous materials or polymers to protect the clusters against sintering.[2] A common porous support is zeolite, owing to its intrinsic subnanometer pore diameters, which are similar to the size of the metal clusters and can confine and prevent the clusters from growing into big particles. This confinement allows metal clusters to activate reactants with small molecular sizes that are accessible to the pores. [3] Mesoporous silica provides an ideal support, owing to its large pore diameters, which are suitable for large-sized organic substrates and biomass derivatives.[4] Ligand-stabilized metal precursors are usually used to anchor the clusters within the mesoporous channel with a low loading of the metal.[5] Uniform mesoporous-silica-supported noble-metal clusters cannot be achieved by impregnation of the support in an aqueous solution of the metal salts because the pore diameter of mesoporous silica (> 2 nm) is larger than the size of the metal clusters. The metal clusters are easily grown into big particles with a broad size distribution.[6] The incorporation of heteroelements (Zr, Ti, Al, etc.) into mesoporous silica has been developed to disperse metal species.[7] However, some metal particles still migrate towards the outside of the support during the reduction step with hydrogen, which causes their aggregation into big particles and, hence, the blocking of the entrance to the pore channels. Therefore, substantial challenges remain towards the goal of synthesizing uniform metal clusters that are immobilized within mesoporous silica from the corresponding metal salts.Biomass becomes an increasingly important feedstock to produce fuels and chemicals for a sustainable future.[8] Furan derivatives have been identified as the key building blocks to synthesize valuable chemicals.[9] Besides its nontoxic and nonflammable properties, water is a desirable solvent because the furan derivatives are soluble under aqueous conditions.[10] Several catalysts have been developed for the hydrogenation of furan derivatives in water, but high reaction temperatures or high hydrogen pressures are required to achieve high activities because of the low aqueous solubility of hydrogen. [11] Herein, immobilized ruthenium clusters (50 Ru atoms) in nanosized mesoporous zirconium silica (MSN-Zr) were synthesized by using an impregnation method, starting from an aqueous solution of RuCl 3 . The Ru cluster catalyst showed remarkable activity for hydrogenation of furan derivatives in water at room temperature under 5 bar hydrogen pressure.MSN-Zr-x, which has a uniform hexagonal pore structure, was synthesized by modification of our previously reported two-step procedure, [12] in which x denotes the Si/Zr molar ratio (for the detailed preparation, see the Supporting Information). The morphology and pore structure are sim...