DFT Study on the Complex Reaction Networks in the Conversion of Ethylene to Ethylidyne on Flat and Stepped Pd

Abstract

Adsorption and conversion of ethylene to ethylidyne on flat (111) and stepped Pd surfaces have been studied with the aim to unravel the complex chemistry of small organic molecules on Pd. These processes are crucial to understanding many experimental observations on Pd catalysts involved in selective hydrogenations, steam reforming, polymerization, and several other chemical processes. Our results provide a view on the complex chemistry of olefins on the surface, where several competitive processes take place simultaneously and where a hierarchy among different bond activations can be established. For Pd, the C-H bonds of the olefins are the most labile on the surface, followed by C-C and last isomerization processes. From the picture above not always the most straightforward reaction mechanism is necessarily the one taking place on the surface. Scrambling of H atoms on the organic moieties is the most effective way to generate certain (even long lasting) isomers on the surfaces.

Shape-Dependence of Pd Nanocrystal Carburization during Acetylene Hydrogenation

“…In the absence of H 2 , acetylene converts to vinylidene, 46 whereas in the presence of hydrogen, acetylene hydrogenates to ethylene or ethylidyne probably via vinyl, 47 the former being much less reactive than the latter. 48 However, when an excess of hydrogen is present in the system, the hydrogenation reaction is probably favored with respect to CC scission and carbide formation, as was also recently demonstrated by DFT calculations. 49 In order to better understand this phenomenon, we performed DFT calculations on a Pd 36 cluster, containing both Pd(111) and Pd(100) faces, and on Pd 36 C n derivatives, n being 1, 2, or 6.…”

First-principles calculations of the initial incorporation of carbon into flat and stepped Pd surfaces

“…It is also larger than any barrier in ethylene decomposition process, where highest barriers in processes ͑CH, CCH, and C 2 decomposition͒ forming atomic carbons are around 1.5 eV. 17,32 We note that in the measurements carbon coverage is high whereas our calculations are mainly done at low coverage. The case study shows that the presence of preadsorbed carbon increases the diffusion barrier to the first interlayer.…”

“…17 This raises the question of the role of the steps in the adsorption and the diffusion of carbon on the surface and selvedge of Pd. Here the systematic study of carbon adsorption and initial corporation on flat and stepped Pd is presented.…”

From Static to Reacting Systems on Transition-Metal Surfaces

“…[75][76][77][78][79] This issue is partially addressed in the study of Andersin et al 80 where ethylene conversion to ethylidyne was considered on flat and stepped Pd surfaces. [75][76][77][78][79] This issue is partially addressed in the study of Andersin et al 80 where ethylene conversion to ethylidyne was considered on flat and stepped Pd surfaces.…”