Our group has found that ReOx-modified Ir metal (Ir-ReOx) catalyst exhibited unique catalytic properties in the hydrogenolysis of C-O bonds of various biomass-based substrates. The catalysis of Ir-ReOx was influenced by the kinds of the solvents such as water and alkanes. It is suggested that the heterolytic dissociation of H2 molecules on Ir-ReOx to hydride and proton proceeds and the adsorbed hydrogen species can be stabilized in the water solvent. The role of Re species is not acidic one, it makes the interaction between the catalyst surface and OH groups in the substrates. The C-O hydrogenolysis reaction catalysed by Ir-ReOx in the water solvent promoted by the addition of acid cocatalysts. This behavior is interpreted by the promotion of the Re alkoxide formation under acidic atmosphere. As a result, the C-O bond hydrogneolysis proceeds in the  direct mechanism.  On the other hand, the acidic property of the Re species on Ir-ReOx became strong in the alkane solvent, and the mechanism was also changed to the indirect reaction mechanism such as dehydration + hydrogenation and dehydrogenation + dehydration + hydrogenation. At present, the suitable substrates for the hydrogenolysis catalysed by Ir-ReOx in the alkane solvents is very limited, however, the applicability will be wide. Another characteristic of Ir-ReOx is much lower catalytic activity of C-C bond hydrogenolysis than that of C-O bond hydrogenolysis. This property is utilized to the complete C-O bond hydrogenlysis of sugars and sugar alcohols without C-C bond dissociation. The addition of acid cocatalyst such as HZSM-5 promoted the dehydration of 2- and/or 3-alcohols to alkenes, which is converted to alkanes by the hydrogenation on Ir-ReOx. It is expected that the complete C-O bond hydrogenlysis catalysed by Ir-ReOx + acid cocatalysts will be applicable to the conversion of cellulose and hemi-cellulose to n-hexane and n-pentane, which is regarded as the production of bio-naphtha.

Hydrogeneolysis of C-O bonds in biomass-based substrates using Ir-ReO<sub>x</sub>/SiO<sub>2 </sub>catalysts: Role of Re species and acid cocatalysts

248th National Meeting (2014)

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Hydrogeneolysis of C-O bonds in biomass-based substrates using Ir-ReOx/SiO2 catalysts: Role of Re species and acid cocatalysts

Hydrogeneolysis of C-O bonds in biomass-based substrates using Ir-ReO_x/SiO₂catalysts: Role of Re species and acid cocatalysts