Dual-Site-Mediated Hydrogenation Catalysis on Pd/NiO: Selective Biomass Transformation and Maintenance of Catalytic Activity at Low Pd Loading

Abstract

Creating a new chemical ecosystem based on platform chemicals derived from waste biomass has significant challenges: catalysts need to be able to convert these highly functionalized molecules to specific target chemicals and they need to be economical - not relying on large quantities of precious metals - and maintain activity over many cycles. Herein, we demonstrate how Pd/NiO is able to direct the selectivity of furfural hydrogenation and maintain performance at low Pd loading by a unique dual-site mechanism. Sol-immobilization was used to prepare 1 wt % Pd nanoparticles supported on NiO and TiO2, with the Pd/NiO catalyst showing enhanced activity with a significantly different selectivity profile; Pd/NiO favors tetrahydrofurfuryl alcohol (72%), whereas Pd/TiO2 produces furfuryl alcohol as the major product (68%). Density functional theory studies evidenced significant differences on the adsorption of furfural on both NiO and Pd surfaces. On the basis of this observation we hypothesized that the role of Pd was to dissociate hydrogen, with the NiO surface adsorbing furfural. This dual-site hydrogenation mechanism was supported by comparing the performance of 0.1 wt % Pd/NiO and 0.1 wt % Pd/TiO2. In this study, the 0.1 and 1 wt % Pd/NiO catalysts had comparable activities, whereas there was a 10-fold reduction in performance for 0.1 wt % Pd/TiO2. When TiO2 is used as the support, the Pd nanoparticles are responsible for both hydrogen dissociation and furfural adsorption and the activity is strongly correlated with the effective metal surface area. This work has significant implications for the upgrading of bioderived feedstocks, suggesting alternative ways for promoting selective transformations and reducing the reliance on precious metals.