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 TiO 2 , with the Pd/NiO catalyst showing enhanced activity with a significantly different selectivity profile; Pd/NiO favors tetrahydrofurfuryl alcohol (72%), whereas Pd/TiO 2 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/TiO 2 . In this study, the 0.1 and 1 wt % Pd/NiO catalysts had comparable activities, whereas there was a 10fold reduction in performance for 0.1 wt % Pd/TiO 2 . When TiO 2 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.

Furfural Adsorption and Hydrogenation at the Oxide‐Metal Interface: Evidence of the Support Influence on the Selectivity of Iridium‐Based Catalysts

“…From product distribution plots as a function of reaction time or conversion (Figure 2 and Figure S.3) it appears clear that the FF is preferentially hydrogenated to THFA over Ir/NiO at all time points and at each FF conversion value, thus indicating that a different pathway is followed over this catalyst compared to Ir/CeO 2 and Ir/TiO 2 . Furthermore, the peculiar behaviour of Ir/NiO is in line with what has been already observed over NiO and Pd/NiO [34] …”

“…The reason behind the peculiar selectivity of Ir/NiO could be a result of the unique capacity of the NiO support to adsorb and activate the furfural molecule, as already reported for Pd/NiO catalysts [34] …”

“…Moreover, in some cases, cooperative catalysis between metal nanoparticles and the support surface has been reported for furfural hydrogenation [28–33] . In this regard, we have recently demonstrated that furfural hydrogenation proceeds with enhanced selectivity to tetrahydrofurfuryl alcohol via a dual‐site mediated mechanism over a Pd/NiO catalyst: the Pd centre is responsible for the dissociation of hydrogen, which subsequently spills over onto the NiO support, where furfural is adsorbed and activated [34] …”

Controlling the Production of Acid Catalyzed Products of Furfural Hydrogenation by Pd/TiO2

“…The conversion to acetals requires Brønsted acid sites on the TiO 2 surface [61,62] . We recently published an article on Pd/NiO catalysts and were able to demonstrate a dual‐site hydrogenation mechanism, where spillover of hydrogen onto the NiO support was a significant part of the reaction pathway [63] . For TiO 2 , hydrogen spillover creates surface hydroxyls that are able to act as Brønsted acid sites required for ether formation [64,65] .…”

Recent progress in use and observation of surface hydrogen migration over metal oxides

“…Campisi et al reported that Pd/NiO can catalyze the selective conversion of furfural to tetrahydrofurfuryl alcohol (72%), although Pd/TiO 2 favours furfuryl alcohol (68%). 2 Furfural is regarded as a promising platform molecule to various products in a biorefinery. Its selective conversion using tailored catalysts is desired.…”