Mesoporous mixed CuCo oxides as robust catalysts for liquid-phase furfural hydrogenation

A series of highly ordered mesoporous CuCo oxide catalysts with a controlled composition are successfully synthesized by nanocasting from mesoporous silica, KIT-6 template. Liquid-phase furfural (FAL) hydrogenation is carried out to find the optimal composition of the CuCo oxide catalysts to achieve the best catalytic performance. As-prepared mesoporous mixed CuCo oxides exhibit a high surface area (60‒135 m2 g−1) and a well-defined ordered mesostructure with homogenous dispersion of Cu and Co. Among various compositions of CuxCoy oxides (x = 1-9) studied, the Cu1Co5 oxide catalyst shows the highest conversion in the hydrogenation of FAL, which is superior to those achieved with mesoporous monometallic oxides, CuO and Co3O4. While 2-methylfuran is produced from furfuryl alcohol via aldehyde hydrogenation and subsequent hydrogenolysis, the formation of 2-methylfuran increased with a decrease in the Cu/Co ratio of the CuCo oxide catalyst. The mixed CuCo oxide catalyst is readily reduced under the reaction environment to produce metallic CuCo as the active species. The synergistic interactions between Cu and Co in the mixed CuCo oxide catalysts play an important role in the outstanding catalytic performance for FAL hydrogenation, which could not be achieved with either of the monometallic catalysts or their physical mixtures. The excellent stability and recyclability of mesoporous mixed CuCo oxide catalysts as well as the exceptionally high activity, surpassing those of the monometallic oxides, render them promising as a low-cost and efficient catalyst for the industrial upgrading of biomass-derived FAL

Interfacial effect of Pd supported on mesoporous oxide for catalytic furfural hydrogenation

Highly dispersed Pd is loaded onto different types of mesoporous oxide supports to investigate the synergetic metal-support effect in catalytic furfural (FAL) hydrogenation. Ordered mesoporous Co3O4, MnO2, NiO, CeO2, and Fe2O3 are prepared by the nanocasting and the supported Pd on mesoporous oxide catalysts are obtained by the chemical reduction method. It is revealed that mesoporous oxides play an important role on Pd dispersion as well as the redox behavior of Pd, which determines the final FAL conversion. Among the catalysts used, Pd/ Co3O4 shows the highest conversion in FAL hydrogenation and distinct product selectivity toward 2-methylfuran (MF). While FAL is converted via two distinct pathways to produce either furfuryl alcohol (FA) via aldehyde hydrogenation or MF via hydrogenolysis, MF as a secondary product is derived from FA via the hydrogenolysis of C?O over the Pd/Co3O4 catalyst. It is revealed that FAL is hydrogenated to FA preferentially on the Pd surface; then the secondary hydrogenolysis to MF from FA is further promoted at the interface between Pd and Co3O4. We confirm that the reaction pathway over Pd/Co3O4 is totally different from other catalysts such as Pd/MnO2, which produces FA dominantly. The characteristics of the mesoporous oxides influence the Pd-oxide interfaces, which determine the activity and selectivity in FAL hydrogenation

Cu2O(100) surface as an active site for catalytic furfural hydrogenation

In order to investigate the major active site of Cu-based catalysts in furfural (FAL) hydrogenation, theoretical calculations were combined with empirical analyses. The adsorption of FAL and H-2 on the Cu(111), CuO(100), and Cu2O(100) surfaces was compared based on density functional theory (DFT) calculations. The migration barrier of the dissociatively adsorbed H atoms on different surfaces was also calculated. It is demonstrated that the Cu2O(100) surface has the largest FAL adsorption energy of 1.63 eV and an appropriate Cu-Cu distance for adsorption and preferential dissociation of the H-2 molecule. To correlate the DFT results with catalytic ex-periments, mesoporous copper oxides (m-CuO) were prepared under controlled reduction conditions. The overall activity of the m-CuO catalysts is determined by the concentration of exposed Cu+. The combined results from DFT calculations and experiments show that Cu2O is a major active species promoting the high activity of FAL hydrogenation