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

Abstract

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-CH. 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.

Constructing Bridges between Computational Tools in Heterogeneous and Homogeneous Catalysis

“…Aleksandrov et al investigated alkyl hydrogenation on Pd (111) surfaces and on Pd nanoparticles (Figure 12). 79 The activation energy barrier was decomposed as in eq 8:…”

“…Scheme used to analyze ethyl hydrogenation promoted by Pd catalysts. 79 E Coads accounts for the interaction energy between the ethyl group and the hydrogen, while E Int accounts for the interaction between the Pd catalyst and the reacting fragments. suggesting that surface deformation energy is another important factor in determining the reactivity of alloys, besides the well-known shift of the d-band center upon alloying.…”

“…Scheme used to analyze ethyl hydrogenation promoted by Pd catalysts. 79 E Coads accounts for the interaction energy between the ethyl group and the hydrogen, while E Int accounts for the interaction between the Pd catalyst and the reacting fragments. When the content of hydrogen increases and subsurface hydrogen begins to be present in the nanoparticle, the catalyst-adsorbate interaction becomes weaker in the starting material, leading to a reduction of approximately 20 kJ/mol in the overall barrier.…”

“…Nevertheless, implementation of better algorithms for transition-state localization, together with more easily available computational power, is making localization of transition state geometries in heterogeneous catalysis more common, which has stimulated the use of ASM to rationalize activation barriers of reactions involving heterogeneous catalysts. Aleksandrov et al investigated alkyl hydrogenation on Pd (111) surfaces and on Pd nanoparticles(Figure 12) 79.…”

CO Dimerization on Cu Nanoparticles under High CO Coverage

“…The amount of surface species depends on the reaction temperature and pressure and may vary significantly between high- and low-pressure industrial processes and relatively low-pressure laboratory studies. The concentration of surface species is known to remarkably affect the properties of the catalyst in certain reactions, , which implies possible differences between the properties exhibited by catalysts in laboratory and industrial settings. Moreover, most transition metals in heterogeneous catalysts are present in the form of highly dispersed nanoparticles, whose size may strongly affect the catalyst properties. , The high surface-to-bulk ratio in nanostructured catalysts may further exacerbate the dependency of the catalyst properties on the coverage of surface species …”