Selective conversion of furfural to methylfuran over silica-supported Ni-Fe bimetallic catalysts

The conversion of furfural in H-2 over SiO2-supported Ni and Ni-Fe bimetallic catalysts has been investigated at 1 bar in the 210-250 degrees C temperature range. Over the monometallic Ni catalyst, furfuryl alcohol and furan are primary products resulting from hydrogenation and decarbonylation, respectively. These primary products are further converted in secondary reactions. Furan yields C-4 products (butanal, butanol, and butane) via ring opening, while furfuryl alcohol produces 2-methylfuran via C-O hydrogenolysis. By contrast, 2-methylfuran is not produced to a great extent on pure Ni at any level of overall conversion. But, on Fe Ni bimetallic catalysts, the yield of 2-methylfuran greatly increases while the yields of furan and C-4 products decrease. That is, the addition of Fe suppresses the decarbonylation activity of Ni while promoting the C=O hydrogenation (at low temperatures) and the C-O hydrogenolysis (at high temperatures). DFT analysis of the possible surface species on the mono- and bimetallic surfaces suggests that the differences in selectivity displayed by these catalysts can be attributed to the stability of the eta(2)-(C,O) surface species, which is higher on the Ni Fe than on pure Ni. As a result, this eta(2)-(C,O) species can be readily hydrogenated to furfuryl alcohol and subsequently hydrogenolyzed to 2-methylfuran on the bimetallic alloy due to a strong interaction between the carbonyl O and the oxyphilic Fe atoms. Without Fe, on the pure Ni surface, the eta(2)-(C,O) species can be converted into a surface acyl species, which can be decomposed to produce furan and CO. Detailed XRD and TPR characterization indicate the formation of Fe-Ni alloys in all the bimetallic catalysts. (C) 2011 Elsevier Inc. All rights reserved.