Coverage-Induced Conformational Effects on Activity and Selectivity: Hydrogenation and Decarbonylation of Furfural on Pd(111)

Abstract

Adsorption, hydrogenation, and decarbonylation of furfural on hydrogen-covered Pd(111) was investigated using density functional theory calculations. It was found that both the energy and the conformation of adsorbed furfural vary with increasing coverage of hydrogen or furfural. Furfural lies flat at low coverage but becomes tilted on crowded surfaces. The energy profiles of hydrogenation and decarbonylation reactions on a hydrogen-covered Pd(111) change profoundly compared to those on bare Pd(111). The energy span theory shows that the furfural hydrogenation and decarbonylation effective barriers exhibit a maximum with increasing hydrogen coverage. In contrast, the selectivity to hydrogenation toward furfuryl alcohol over decarbonylation is favored with increasing hydrogen coverage. Microkinetic modeling suggests that the conformation change with increasing H coverage has a significant effect on reaction rates (up to orders of magnitude) and induces a selectivity reversal from furan as the main product (low-H coverage limit) to furfuryl alcohol (high-H coverage limit). Our results may rationalize different selectivity trends seen experimentally under typical reactor and UHV conditions. Importantly, this study underscores the potential importance of operating conditions on hydrodeoxygenation activity and selectivity due to conformational changes of multifunctional biomass derivatives.

Insights into the mechanism of nitrobenzene reduction to aniline over Pt catalyst and the significance of the adsorption of phenyl group on kinetics

“…To model the mechanism of nitrobenzene reduction, there are two significant problems to overcome. The first challenge is associated with the large size of nitrobenzene molecule, because a larger molecule would considerably increase the number of possible adsorption configurations [21][22][23][24][25][26][27][28][29][30][31][32], therefore, a significantly more adsorption configurations should be carefully tested in the calculations of nitrobenzene, in contrast to the much fewer adsorption configurations of other smaller organic molecules such as formic acid or methanol. In addition, an increase in adsorption configurations would also lead to an increase in the numbers of possible transition states, which again makes the calculations more complicated and time-consuming [21,22].…”

“…Only a few pioneering works have been made in the study of these large molecules [21,22,[26][27][28][29][30][31][32]. Saeys et al calculated benzene adsorption and hydrogenation to cyclohexane on Pt(111) [21,22].…”

“…With respect to some other large molecules in heterogeneous catalysis, Lu et al systematically calculated the hydrogenation of guaiacol over Ru(0001) and Pt(111) surfaces involving the C-O bond dissociation [28,29]. Wang et al studied the activity and selectivity between hydrogenation and decarbonylation of furan and its derivatives on Pd(111) [30,31]. These studies have provided some initial insights into the surface chemistry of large molecules in heterogeneous catalysis.…”

Shaping the selectivity in heterogeneous hydrogenation by using molecular modification strategies: Experiment and theory

“…However, high activity catalysts usually lead to poor selectivity such that these metals could not be employed alone in most cases. To achieve high selectivity, the active centers should be dilute through alloying or isolated by inorganic species (such as CO, H and S) [24][25][26][27][28][29][30] and/or organic compounds (such as amines and thiol) [22,[31][32][33][34][35][36][37]. The most famous catalyst developed for this purpose is Lindlar catalyst (Pd-Pb/CaCO 3 ), which is commercially used for the selective hydrogenation of alkynes to alkenes [38,39].…”

“…To prevent the deeper hydrogenation, quinoline or octanediol would be added to deactivate the activity of Pd sites, while CO would be mixed in the feed streams to further poison the catalysts [30]. Recently, the influence of surface/subsurface hydrogen on the selectivity has been emphasized, especially for Pd and Pt catalysts [24][25][26][27][28][29]40]. In these cases, H atoms could be better viewed as surface modifiers, which significantly change the electronic states as well as the accessibility http://dx.doi.org/10.1016/j.cattod.2016.05.017 0920-5861/© 2016 Elsevier B.V. All rights reserved.…”