Aqueous phase hydrogenation of furfural on Ni/TiO2 catalysts: nature of the support phase steers the product selectivity

Nickel catalysts supported on six different titania phases (ATA, ATH, P25, ART, RTH and RTS), which differ in phase composition (anatase/rutile), textural characteristics, acidity and nature of metal-support interactions, have been investigated for aqueous phase hydrogenation of furfural. The two phases of titania, anatase and rutile, showed remarkable differences in the activity as well as selectivity for products. Higher conversion of furfural was observed on rutile phase supported catalysts. While both phases showed the formation of furfuryl alcohol, on anatase supported catalysts, the formation of deep hydrogenated products was restricted to cyclopentanone only. On the other hand, on rutile phase supports, further hydrogenated products, like tetrahydrofurfuryl alcohol and cyclopentanol, were observed. Activity/selectivity patterns are rationalized on the basis of metal-support interactions based on XPS, DFT, H-2-TPR and acidity data. The results showed that the reducibility of the support depends on the titania crystal phase, which affects active sites at the interface and the metal surface charge redistribution and blockage of reactive sites. The higher reducibility of the anatase phase was found to be detrimental to hydrogenation activity. This investigation paves the way for designing catalysts for selective catalytic transformations of bio-renewable raw materials, like furfural.