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Dissociative adsorption of impinging gas-phase molecular hydrogen (H2) on a palladium cluster (Pd4) supported on defective graphene (C47) was studied by periodic density functional theory molecular dynamics simulations. The H2 on Pd4/C47 collision dynamics were investigated without any particular constraint, except for the Born–Oppenheimer approximation. The study, which had mostly method-testing aims, provided, anyway, valuable information about the collision kinetics of gas-phase molecular hydrogen. This was treated as an impacting projectile having different kinetic energy values. At lower kinetic energies, sticking was ruled by steering effects imputable to the Pd cluster that easily reoriented the incoming hydrogen molecule to the metallic surface sites, favoring fragmentation hence adsorption. Sticking decreased at higher kinetic energies for which the very fast corresponding projectile acquired a kind of elusiveness toward the metallic surface that for this was not able to steer and adsorb the gas-phase hydrogen molecule. Interestingly, altered steering effects, in this case, ruled by already adsorbed surface hydrogen, seemed to play a decisive role in refocusing both H2 hitting and sticking on the supported palladium surface, irrespective of the energy characterizing the impinging gas-phase molecules. [ABSTRACT FROM AUTHOR]

The proton dynamics in Y-doped BaZrO3 derivatives, in particular the different dopant environments within a Pm ${\bar 3}$ m cubic framework, were studied by using classical molecular dynamics (MD) calculations. Single- and double substitution of zirconium by yttrium atoms was considered. The presence of yttrium induced variations in the surrounding oxygen sites, according to their local geometrical arrangements. The differences among such distinct oxygen sites became evident when protons interacted with them and upon changes in the temperature. So, different proton transfer pathways, which had different energy barriers, characterized the topologically different oxygen sites. The experimental proton-hopping activation energy was only reproduced in those structures in which two yttrium atoms formed a Y-O-Y arrangement, which also acted as multilevel protonic traps. Protonic conduction in these materials could be improved by avoiding such yttrium clustering, hence preventing the formation of the protonic traps. [ABSTRACT FROM AUTHOR]

[Display omitted] • The CO and H 2 oxidation pattern of MnCeO x catalyst was assessed. • The CO and H 2 oxidation functionality relies on large availability of Mn(IV) sites. • MnCeO x catalyst has high CO oxidation activity while a large energy gap hinders H 2 oxidation. • The CO and H 2 oxidations proceed via redox mechanisms limited by the abstraction of lattice O-atoms. • Computational clues are synthesized into macro-kinetic models predicting the CO and H 2 oxidation activity under any condition. The CO and H 2 oxidation functionality of a composite MnCeO x catalyst with large exposure of Mn(IV) sites has been investigated in a wide range of experimental conditions (T, 293–533 K; p CO /p0 or p H2 /p0 , 0.00625–0.025; p O2 /p0 , 0.00625–0.20) to ascertain the mechanistic clues of a peculiar preferential CO oxidation pattern. The MnCeO x shows high CO oxidation activity in the range of 293–533 K, while a large activation energy hinders the H 2 oxidation at T < 373 K. Computational analysis of adsorption and activation energies on a model Mn 4 O 8 cluster, and unchanging energy barriers of CO 2 and H 2 O formation, in absence and in the presence of O 2 , indicate that the abstraction of lattice O-atoms is the rate limiting step (r.l.s.) of the CO and H 2 oxidation. This reactivity pattern relies on strong chemical affinity of Mn(IV) sites toward CO enabling the easy abstraction of lattice O-atoms, while H 2 oxidation occurs via an extrafacial reaction path driven by diatomic oxygen species produced by spillover and adsorption processes at T > 373 K. Mechanistic clues were synthesized into macrokinetic models predicting the CO and H 2 oxidation activity of the MnCeO x catalyst under any conditions. [ABSTRACT FROM AUTHOR]