Theoretical Investigation of the Reaction Mechanism of the Guaiacol Hydrogenation over a Pt(111) Catalyst

Abstract

The reaction mechanism of the mild hydrogenation of guaiacol over Pt(111) has been investigated by density functional theory calculations and microkinetic modeling.Our model suggests that at 573 K catechol is the preferred reaction product and that any deoxygenation to, e.g., phenol or benzene is at least four orders of magnitude slower than the production of catechol.Slow deoxygenation of guaiacol can occur by decarbonylation and possibly by hydrogenation of the phenyl ring followed by C-OH bond cleavage. Direct -OH removal without activation of the phenyl ring is found to be at least five orders of magnitude slower. Overall, this study suggests that Pt (111) sites are not active deoxygenation sites and that the experimentally observed deoxygenation activity of Pt catalysts originates likely from the involvement of the catalyst support or Pt step and corner sites.

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].…”

“…Mahata et al reported the mechanism of nitrobenzene reduction over Ni(111) via direct or indirect mechanisms [26]. 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].…”

Conceptual Process Design and Techno-Economic Assessment of Ex Situ Catalytic Fast Pyrolysis of Biomass: A Fixed Bed Reactor Implementation Scenario for Future Feasibility

“…However, hydrogenation reactions are generally exothermic and are therefore favored at lower temperatures. For example, the hydrogenation of the phenyl ring in catechol, phenol, and benzene (products derived from the pyrolysis of lignin) is thermodynamically unfavorable at temperatures above 300°C [16]. Accordingly, the extent of hydrogen incorporation in these fixed bed systems will be limited by thermodynamic equilibrium, with greater hydrogen incorporation achieved in fixed bed reactor #2 due to its lower operating temperature.…”

Aromatic molecules on low-index coinage metal surfaces: Many-body dispersion effects

“…CO, can decompose the closest-packed Cu(111) surface into disordered structures and enhance the reactivity of surface for water dissociation. In this regard, a complete understanding of the interaction of molecules with more open, and even “imperfect” structures, such as steps, kinks, impurities, and defects, is highly demanded for practical uses17181920. However, due to the complex local atomic structure, which is accompanied by the highly corrugated potential-energy surface13, it remains a tremendous task to reliably predict the structure and energetics for molecules on non-closest-packed surfaces.…”