Structure–Activity Relationships in Alkane Dehydrogenation on γ-Al₂O₃: Site-Dependent Reactions

Abstract

A promising route to produce olefins, the building blocks for plastics and chemicals, is the nonoxidative dehydrogenation of alkanes on metal oxides, taking advantage of the Lewis acid−base surface functionalities of the oxides. However, how alkane dehydrogenation activity depends on the strength of surface acid−base site pairs is still elusive. In this work, we provide fundamental insights into the reaction mechanisms of propane dehydrogenation on different facets of γ-Al 2 O 3 and develop structure−activity relationships, using density functional theory calculations and first-principles molecular dynamics simulations. We identified the binding energy of dissociated H 2 as an activity descriptor for alkane dehydrogenation. Interestingly, a volcano relationship between catalytic activity and dissociative H 2 binding energy was discovered for propane dehydrogenation, unraveling a sitedependent catalytic behavior on γ-Al 2 O 3 , with a concerted surface mechanism being energetically preferred to a sequential one on the most active sites. We demonstrated that although surface hydration, in general, blocks strong Lewis acid−base pairs on the (110) γ-Al 2 O 3 surface, the presence of hydroxyl groups (on neighboring to strong Lewis sites) can enhance the propane dehydrogenation activity of a "defect site pair" (Al III −O III ) of the metastable surface. Moreover, we performed ab initio metadynamics simulations of the most active site on γ-Al 2 O 3 to examine the hydrogen formation and surface dynamics under dehydrogenation reaction conditions. Metadynamics simulations demonstrated that the poisoning of active sites by hydrogen adsorption is unlikely under experimental conditions. The developed relationships can be utilized to screen metal oxide surfaces and accelerate the discovery of active catalysts for alkane conversion to olefins.

Dual‐function catalysis in propane dehydrogenation over Pt1–Ga2O3 catalyst: Insights from a microkinetic analysis

“…It is clear that propane and H 2 are weakly physisorbed on the surface without bond formation. Furthermore, the calculated adsorption energies fall within the typical ranges of the physisorption energies of propane and H 2 (−0.2 ~ −0.4 eV and − 0.05 ~ −0.2 eV for propane and H 2 , respectively), as has been observed on metal surfaces 68‐70 and other oxide surfaces 12,17 …”

“…Metal‐oxide surfaces usually have a high degree of site heterogeneity, 17 which provides an opportunity for understanding site‐dependent catalysis and designing optimal catalysts under the guidance of structure–activity relationships 64 . On the outermost layer of the pristine Ga 2 O 3 (100) surface, there exist three distinct types of ions, namely, octahedrally coordinated Ga(o), tetrahedrally coordinated Ga(t), and threefold coordinated O, as shown in Figure 1a.…”

Facile synthesis of ordered mesoporous zinc alumina catalysts and their dehydrogenation behavior

“…In addition, it is well-known that the amount of different acidic sites of catalyst are the key to affect catalytic activity in alkane dehydrogenation reaction. 37 The isobutane conversion rate vs. the number of different acidic sites on the basis of Table 2 were plotted (Fig. 10).…”

Cobalt‐Based Catalyst Supported on Different Morphologies of Alumina for Non‐oxidative Propane Dehydrogenation: Effect of Metal Support Interaction and Lewis Acidic Sites

“…Alumina can be obtained in both amorphous and crystalline form, and increasing the crystallinity improves thermal stability. [12] It was found that nano-shape morphology enhances the metal dispersion, thus improving the interaction with the support. The modification of physical and chemical properties affects the interaction of metal as well as interaction of reactants and products.…”

“…[11] Recently another study showed the structureactivity relationship on gamma-alumina. [12] It was found that nano-shape morphology enhances the metal dispersion, thus improving the interaction with the support. For dehydrogenation reaction, the morphology effect has also been studied to understand the structure-activity relationship.…”