Dario Duca

Hydrogenation of acetylene–ethylene mixtures on Pd catalysts: computational study on the surface mechanism and on the influence of the carbonaceous deposits

A time-dependent Monte Carlo algorithm was employed to study the effects of carbonaceous surface species on the hydrogenation mechanism of acetylene–ethylene mixtures on a Pd catalyst. Simulations of tail-end and front-end mixture hydrogenation were performed employing the same set of predetermined event probabilities. The involvement of the steric hindrance of the surface species was essential to simulate the experimental data. The catalyst activity and selectivity were promoted or inhibited by different concentrations of surface polymeric species formed along with the hydrocarbon hydrogenation. Tools to get a new interpretation of the catalytic reaction mechanism and an innovative basis to perform catalyst design were suggested by the approach illustrated.

Hydrogenation of light hydrocarbons on palladium: theoretical study of the local surface arrangements

Abstract Quantum mechanical calculations at HF, MP2 and DFT levels were used to rationalise the surface effects of the hydrocarbon lateral interactions occurring on single planar metal surfaces or on different adjacent surfaces during the hydrogenation on palladium catalyst. The different values of electronic charge, found in the different atoms of palladium clusters, were suggested as a possible explanation of the non-homogeneous behaviour already inferred for catalyst surface sites having non-isotropic local arrangement.

Theoretical evaluation of structures and energetics involved in the hydrogenation of hydrocarbons on palladium surfaces

Abstract Quantum mechanical calculations were employed to deepen information about the basic properties of the mechanism occurring in the palladium catalytic hydrogenation involving surface hydrogen species of unsaturated hydrocarbons. Activation energy values of elementary events implicated in the whole reaction were computed by potential energy surface analyses, to determine the corresponding occurrence probabilities of the same events. Different surface hydrogen species were pointed out and their relevance in the overall surface process was discussed together with their geometrical and chemical characteristics.

Ab initio study of structure and energetics of species involved in the 2,4-dinitro-toluene hydrogenation on Pd catalysts

Abstract Quantum-mechanical calculations, at HF level, were performed to gain chemical–physical basis information on the 2,4-dinitro-toluene hydrogenation occurring over palladium catalysts. To investigate the surface characteristics of the species involved in the reaction system, simplified molecular models including small metal clusters were considered. Remarkable findings, useful to elucidate the reaction mechanism and important parameters, working in time dependent Monte-Carlo simulations of the title reaction, were obtained; inter alia: the molar standard free energies of the molecules involved in the reaction, the volume occupied by the species in solution phase and the qualitative order of the desorption activation energy values, of the nitro, amino and hydroxylamino groups of the toluene fragments interacting with the Pd surface. The molecular level interaction modes of the different toluene derivatives on Pd clusters, mimicking the catalyst surface, were visualized. The results have been discussed in terms of microscopic (energetic, structural and steric hindering) factors driving the observed macroscopic reaction.

New time-dependent Monte Carlo algorithm designed to model three-phase batch reactor processes: applications on 2,4-dinitro-toluene hydrogenation on Pd/C catalysts

Abstract The hydrogenation of 2,4-dinitro-toluene on a Pd/C catalyst was employed as a test reaction to simulate, by the time-dependent Monte Carlo method, processes occurring in a three-phase batch reactor working at isobar and isotherm conditions. A new time-dependent Monte Carlo algorithm, including an original subroutine useful to reduce the time of the simulations, was developed and implemented in Fortran language. The paper describes the flowchart of the code together with the main technical details and the involved physical and chemical models. Computational characteristics, such as the simulated time to reach surface steady state conditions and the effects of the catalyst morphology are presented. Correlations between simulated and experimental data are summarized and current mechanistic hypotheses criticized.

N-Diphenylmethyl-2-propenamide: theoretical study of the structure and interaction with a DNA model system

Abstract N -diphenylmethyl-2-propenamide (NDP) was synthesised and characterised. Pharmacological in vitro tests pointed out that NDP had a cytotoxic activity on a human ovarian carcinoma comparable to that of doxorubicin. Hypothesising that this in vitro cytotoxic activity could be mainly due to intercalating interactions, between the drug and DNA fragments, ab initio calculations, at the Hartree–Fock (HF) level, were performed on the structure, and on the conformational properties of NDP, whereas its interaction with an (AC)(TG) dinucleotide triphosphate duplex (DD) was studied by the ONIOM method, at HF and PM3 level for NDP and DD, respectively. The supposed intercalation process with the DNA fragment was discussed in terms of the co-planarity of the aromatic rings present in the NDP molecule.

DFT studies on catalytic properties of isolated and carbon nanotube supported Pd9 cluster Part II. Hydro-isomerization of butene isomers

The processes involved in the butene hydro-isomerization, occurring on a small palladium cluster in the presence of dissociated hydrogen, have been investigated by means of DFT and DFT/MM approaches. This study has been performed both on an isolated (unsupported) Pd(9) cluster and on the same cluster when it is supported on a portion of a single-walled armchair(6,6) carbon nanotube. The study follows another investigation which has already been published concerning the adsorption, fragmentation and diffusion of hydrogen on the same metal cluster. The main aspects involved in the parallel reaction steps of the whole hydro-isomerization mechanisms are not strongly affected by the presence of the support, which does, however, modify the energetics involved, likely due to the presence of strong metal surface interaction (SMSI) effects. Noticeably, a common step corresponding to the diffusion of one hydrogen atom is present. This diffusion step creates a characteristic semihydrogenated surface species along the occurrence of all the reaction pathways. Hence, the semihydrogenated species is a kind of molecular node able to connect the transformation pathways of the different surface species involved in the hydro-isomerization processes. Considering the energetics involved in the processes of both supported and unsupported systems and being aware of the simplification introduced in studying the same systems, it is still possible (i) to emphasize the basis importance of taking account of the support in modeling catalytic properties and (ii) to state that the models proposed here are able to capture the main characteristics of the title reaction.