Decomposition of ethylene on transition metal surfaces M(111). A comparative DFT study of model reactions for M=Pd, Pt, Rh, Ni

Effect of point defects on acetylene hydrogenation reaction over Ni(111) surface: a density functional theory study

Density functional theory (DFT) calculations are carried out to investigate the effect of point defects on acetylene hydrogenation reaction over Ni(111) surface with three different defect concentrations (DC = 0.0500, 0.0625, and 0.0833), compared with the perfect Ni(111) surface. The adsorptions of C₂ species and H atoms and the mechanism of acetylene hydrogenation via the ethylene pathway are systematically analyzed. The results indicate that the existence of defects will make C₂ species and H atoms more inclined to adsorb near the defects. Introducing an appropriate amount of point defect concentration can enhance the catalytic activity and ethylene selectivity of Ni. In this work, DC = 0.0625 Ni(111) surface has the highest catalytic activity and selectivity of ethylene. This work provides useful theoretical information on the effect of defects on acetylene hydrogenation and is helpful for the design of Ni and related metal catalysts with defects.

Approaching complexity of alkyl hydrogenation on Pd via density-functional modelling

Pd is widely used to catalyse hydrogenation and dehydrogenation reactions. One of them is the hydrogenation of ethylene, which includes the transformation of ethyl species to ethane. Herein, by means of density-functional calculations we address several still insufficiently understood factors affecting the latter process. In particular, we shed light on the following aspects of hydrogenation of alkyls on Pd: (i) the mechanistic details of how subsurface H accelerates the reaction on a (111) surface; (ii) the role of nanoparticle edges; and (iii) the influence of a common spectator ethylidyne, [triple bond, length as m-dash]C-CH₃. These factors are identified as significant for the height of the ethyl hydrogenation barrier on Pd. Moreover, we show that butyl hydrogenation on Pd is also governed by very similar interactions, which suggests a broader applicability of our conclusions. This study highlights the complexity of alkyl hydrogenation and analyses the factors that need to be taken into account for a more realistic description of the hydrogenation processes on metal surfaces.

Mechanistic Insights into Ethylene Transformations on Ir(111) by Density Functional Calculations and Microkinetic Modeling

Ethylidyne, ethane, and carbon monomer formations from ethylene over Ir(111) at different coverages are investigated using density functional theory methods. Two possible reaction mechanisms for ethylidyne formation are investigated. The calculations show that vinyl prefers the dehydrogenation to yield vinylidene (M2) over the hydrogenation to produce ethylidene (M1) kinetically and thermodynamically at 1/9 (1/3) ML. Ethylidyne formation could be a competitive side reaction of ethylene hydrogenation, however, the ethylidyne species does not directly participate in the ethylene hydrogenation mechanism. The mechanism for C monomer formation is also studied. Microkinetic modeling shows that the ethylene hydrogenation reactivity decreases in the sequence Ir(111)>Rh(111)>Pd(111)>Pt(111) under typical hydrogenation conditions. The catalytic activity of ethylene hydrogenation decreases with increased stability of ethylene adsorption and reaction barrier of the rate-limiting step.

Surface restructuring of Cu-based single-atom alloy catalysts under reaction conditions: the essential role of adsorbates

The stabilities and catalytic performances of single-atom alloy (SAA) structures under the reaction conditions of acetylene hydrogenation are thoroughly examined utilizing density functional theory (DFT) calculations.

Elucidation of the higher coking resistance of small versus large nickel nanoparticles in methane dry reforming via computational modeling

Monoatomic C species remain separated in the subsurface regions of small Ni nanoparticles, while in larger particles, carbon chains are formed, which can be considered as precursors for coke or graphene formation.

Carbon dissolution and segregation in platinum

Density functional studies at show the feasibility of C subsurface incorporation in Platinum occupying tetrahedral sites. A comparative with Ni and Pd highlights that surface relaxation is critical in C dissolution, specially at low-coordinated sites of Pt nanoparticles. Results explain phenomena such as C dissolution and segregation to form graphene from below, and may serve to tune the Pt surface chemical reactivity.

Acetylene adsorption on δ-MoC(001), TiC(001) and ZrC(001) surfaces: a comprehensive periodic DFT study

Molybdenum, titanium, and zirconium carbide surfaces are explored theoretically as potential catalysts for selective hydrogenation from acetylene to ethylene.

Adsorption and transformations of ethene on hydrogenated rhodium clusters in faujasite-type zeolite. A computational study

Phase diagrams from DFT modeling suggest that zeolite-supported Rh₄ clusters may be appropriate for the catalytic hydrogenation of ethene to ethane, whereas Rh₃ clusters favor the formation of the stable adsorbed ethylidyne species, preventing further hydrogenation.

Ethylene decomposition on Ir(111): initial path to graphene formation

The complete mechanism behind the thermal decomposition of ethylene (C₂H₄) on Ir(111), which is the first step of graphene growth, is established for the first time employing a combination of experimental and theoretical methods.

Preparation of improved Ag–Pd/TiO2 catalysts using the combined strong electrostatic adsorption and electroless deposition methods for the selective hydrogenation of acetylene

Ag–Pd/TiO₂ catalysts prepared by the strong electrostatic adsorption and electroless deposition with θ_Ag 0–0.92.

Surface carbon species formation from ethylene decomposition on Pd(100): a first-principles-based kinetic Monte Carlo study

Based on the activation barriers and reaction energies from periodic density functional calculations, we conducted kinetic Monte Carlo (kMC) simulations of surface carbon species formation from ethylene decomposition on a Pd(100) surface.

Molecular understandings on the activation of light hydrocarbons over heterogeneous catalysts

Due to the depletion of petroleum and the recent shale gas revolution, the dropping of the price for light alkanes makes alkanes an attractive feedstock for the production of light alkenes and other valuable chemicals. Understanding the mechanism for the activation of C-H bonds in hydrocarbons provides fundamental insights into this process and a guideline for the optimization of catalysts used for the processing of light alkanes. In the last two decades, density functional theory (DFT) has become a powerful tool to explore elementary steps and mechanisms of many heterogeneously catalyzed processes at the atomic scale. This review describes recent progress on computational understanding of heterogeneous catalytic dehydrogenation reactions of light alkanes. We start with a short description on basic concepts and principles of DFT as well as its application in heterogeneous catalysis. The activation of C-H bonds over transition metal and alloy surfaces are then discussed in detail, followed by C-H activation over oxides, zeolites and catalysts with single atoms as active sites. The origins of coking formation are also discussed followed by a perspective on directions of future research.