A hydrodehalogenation (HDC) reaction of trichloroethene (TCE) has gained a lot of interest due to its possible application in water purification, but the reaction mechanism has been subject to much controversy. In this work, HDC of TCE on Pd(111) was examined by carrying out kinetic Monte Carlo simulations based on DFT-calculated thermodynamic and kinetic parameters. Obtained kMC results show that the HDC follows a so-called direct pathway, which means that, after adsorption on a catalyst, TCE quickly dechlorinates, producing CH–C and then, more slowly, hydrogenates to form hydrocarbon products. This is reflected in the surface coverage snapshots, where intermediates corresponding to the direct pathway are mostly seen. We also investigated the effect of lateral Cl–Cl repulsions on the distribution and coverage of intermediates, and on the reaction mechanism. In general, the adsorbed Cl atoms retard further dechlorinations, leading to less effective HDC, which is in line with experimental observations.

We employ density-functional-theory calculations to examine carbon adsorption and diffusion in Pd bulk, and on Pd(111) and Pd(211) surfaces. Different possible subsurface and on-surface structures are explored and the most stable structures are analyzed. We calculate various diffusion paths: lateral diffusion on a surface, migration to a subsurface region, and within the first interlayer. Our calculations show in accordance with the earlier theoretical results that on Pd(111) carbon prefers to adsorb on octahedral interstitial sites. On Pd(211) the fourfold hollow site under the step is energetically the most favorable one and the second best sites are the octahedral sites. The calculations indicate that migration into the first interlayer is more favorable than diffusion on the Pd(111) surface and migration into the second interlayer is already highly activated with barrier height close to those obtained in bulk. Nearly nonactivated diffusion paths into the first interlayer are found at the step edge of bare Pd(211) but carbon is found to diffuse easily from the first interlayer to the fourfold hollow site on Pd(211) thus leading to the decoration of step edges with carbon. Preadsorbed carbon increases the surface-subsurface diffusion barrier but it remains smaller than the corresponding value on bare Pd(111). At higher carbon concentration the mixed surface-subsurface structures are the most stable ones and carbon atoms tend to sit as far away from each other as possible.

We applied density functional theory (DFT) calculations to study ethylidyne (CCH3) adsorption and decomposition to C and H over flat and stepped Pd surfaces. Our calculations show that ethylidyne is the most stable molecule among all the possible dehydrogenation or decomposition residues of ethylene. We discuss various possible reaction pathways for ethylidyne decomposition and point out that the most probable one is via ethynyl (CCH) species suggested also by experimental observations. Our calculations indicate that the presence of steps modify the potential energy surface by increasing the binding of most of the species, and also lowering the activation barrier for several reactions. Furthermore we show that the energetics related to dehydrogenation of ethylene and its derivatives manifest a Brønsted–Evans–Polanyi type of behavior.

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.

We present a computational screening study of ternary metal borohydrides for reversible hydrogen storage based on density functional theory. We investigate the stability and decomposition of alloys containing 1 alkali metal atom, Li, Na, or K (M(1)); and 1 alkali, alkaline earth or 3d/4d transition metal atom (M(2)) plus two to five (BH(4))(-) groups, i.e., M(1)M(2)(BH(4))(2-5), using a number of model structures with trigonal, tetrahedral, octahedral, and free coordination of the metal borohydride complexes. Of the over 700 investigated structures, about 20 were predicted to form potentially stable alloys with promising decomposition energies. The M(1)(Al/Mn/Fe)(BH(4))(4), (Li/Na)Zn(BH(4))(3), and (Na/K)(Ni/Co)(BH(4))(3) alloys are found to be the most promising, followed by selected M(1)(Nb/Rh)(BH(4))(4) alloys.