Catalytic Conversion Furfuryl Alcohol to Tetrahydrofurfuryl Alcohol and 2-Methylfuran at Terrace, Step, and Corner Sites on Ni

The surface structures at catalytic sites are critical factors for determining catalytic selectivity. Here, we use periodic density functional theory and microkinetic modeling to systematically investigate the effect of surface structures on the conversion of furfuryl alcohol (FA). We consider nine surface terminations of Ni with various coordination numbers representing terrace, step, and corner sites. We study three reaction paths for FA conversion on various surfaces and find that the surface structure impacts the adsorption configuration and causes significant differences in selectivity. Barrier height analysis shows that terrace sites favor hydrogenation to tetrahydrofurfuryl alcohol (THFA), whereas corner sites favor C-OH bond scission to produce 2-methylfuran (2-MF); step sites show similar barriers for the two reactions. We explain this by identifying three characteristics of the reactant adsorption structures that have a significant effect on selectivity, namely, that a shorter distance between the adsorbed hydrogen atom and the C3 carbon of FA favors hydrogenation to produce THFA, and more negative charge transfer to O-al(co)hol and a longer C-O-al(co)hol bond length favor C-O-al(co)hol bond scission to produce 2-MF. Since the reactions have similar barriers at a step site, microkinetic calculations are employed to calculate the product selectivity on a step site under experimental conditions. At lower temperatures and hiller generalized coordination number ((CN) over bar), THFA is the most favorable product, while the selectivity to 2-MF is higher at lower (CN) over bar and at higher temperature. This work provides guidance for the rational design catalysts to control the product distribution of FA conversion.