A novel Ni/SiO(2)-catalyzed route for selective cleavage of ether bonds of (lignin-derived) aromatic ethers and hydrogenation of the oxygen-containing intermediates at 120 °C in presence of 6 bar H(2) in the aqueous phase is reported. The C-O bonds of α-O-4 and β-O-4 linkages are cleaved by hydrogenolysis on Ni, while the C-O bond of the 4-O-5 linkage is cleaved via parallel hydrogenolysis and hydrolysis. The difference is attributed to the fact that the C(aliphatic)-OH fragments generated from hydrolysis of α-O-4 and β-O-4 linkages can undergo further hydrogenolysis, while phenol (produced by hydrolysis of the 4-O-5 linkage) is hydrogenated to produce cyclohexanol under conditions investigated. The apparent activation energies, E(a)(α-O-4) < E(a)(β-O-4) < E(a)(4-O-5), vary proportionally with the bond dissociation energies. In the conversion of β-O-4 and 4-O-5 ether bonds, C-O bond cleavage is the rate-determining step, with the reactants competing with hydrogen for active sites, leading to a maximum reaction rate as a function of the H(2) pressure. For the very fast C-O bond cleavage of the α-O-4 linkage, increasing the H(2) pressure increases the rate-determining product desorption under the conditions tested.

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Cellulose-derived tetrahydrofuran-dimethanol (THFDM) can be converted over Pt-WO x /TiO2 catalysts to 1,6-hexanediol (1,6-HDO) with up to 70% yield. This reaction involves ring-opening of THFDM to 1,2,6-hexanetriol (HTO) and then hydrogenolysis of HTO to 1,6-HDO. Hydrogen atoms spill over from Pt sites onto WO x /TiO2 to reduce the WO functional group and create Brønsted acid sites. Similar catalytic activity for THFDM conversion can be been obtained with a physical mixture of Pt/TiO2 and WO x /TiO2 due to hydrogen spillover over spatially separate Pt and WO x when a reducible support (TiO2) is used.

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