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Decomposition pathways of 1,2-propanediol (1,2-PDO) on platinum were investigated by means of experiments and quantum-mechanical calculations. Different reaction paths on a Pt(111) model surface were computationally screened. Gas and liquid phase products distribution for aqueous phase reforming of 1,2-PDO solutions was experimentally analyzed. A mechanistic approach was used to trace the preferred paths according to calculated activation barriers of the elementary steps; in this way, the presence or absence of some hypothesized intermediates in the experiments was computationally rationalized. Hydroxyacetone was demonstrated to be among the most favored decomposition products. The competition between C-H, O-H, and C-C bond cleavages was investigated, revealing that shortening of the carbon chain occurs most likely via decarbonylation steps. (Figure Presented).

Boron nitride nanotube (BNNT) as an innovative support for carbohydrate transformation processes was evaluated, using density functional theory. The α-d-glucopyranose adsorption on a Pd30 cluster, supported on BNNT, was used to check both the local activity of topologically different metallic sites and the effects of the proximity of the BNNT surface to the same metallic sites. Detailed geometrical and electronic analyses performed on Pd30/BNNT and α-d-glucopyranose/Pd30/BNNT systems were discussed. It was observed that the deposition of the Pd30 cluster onto the BNNT support gives rise to an electronic rearrangement, determining a charge transfer from the support to the adsorbed metal cluster. The charge transfer, as shown by the analysis of molecular electrostatic potential, seems to generate electron-rich and electron-poor zones in the Pd30 cluster. The α-d-glucopyranose species, regardless the interaction geometry experienced, acts as an electron donor and preferentially adsorbs close to the electron-poor metal/support interface.

The ethylene glycol, CH2OH-CH2OH, decomposition mechanism, occurring on a subnanometric palladium cluster shaped by 12 atoms, was investigated by means of density functional theory. Different reaction routes were identified leading to H2 and CO. The whole reaction network was analyzed, framing the results within the graph theory. The possible decomposition pathways were discussed and compared, allowing one to draw a whole picture of all the parallel, possibly competitive, routes that starting from CH2OH-CH2OH originate H2 and CO.

Nucleation of homo- (Ni, Pd, Re, Pt) and heterometallic (Ni–Pd, Re–Pt) clusters on monovacancy sites of a graphene sheet has been investigated by means of periodic density functional theory calculations. It is shown that a vacant site in graphene is an effective nucleation center for both the monometallic and bimetallic clusters, whose characteristics are described in terms of structural distortions, nucleation energetics, affinities between different metal atoms, metal–carbon interactions, and ease of diffusion of metal atoms on graphene.

A QM/MM investigation is reported dealing with the nucleation and growth of small palladium clusters, up to Pd8, on the outer surface of a suitable model of boron nitride nanotubes (BNNTs). It is shown that BNNTs could have a template effect on the cluster growth, which is due to the interplay between Pd–N and Pd–Pd interactions as well as due to the matching of the B3N3 ring and the Pd(111) face arrangement. The values for the cluster adsorption energies reveal a relatively strong physisorption, which suggests that under particular conditions the BNNTs could be used as supports for the preparation of shape-controlled metal clusters.

The future development and assesment of an industry more environmental friendly will include the use of metal-free catalysts. Most of the reported metal-free catalysts are homogeneous and often their recycle is difficult; therefore, develop and investigate them is of interest both theoretical and experimental. Recently, N-doped nanotubes and graphene sheets, were synthesized [1,2], and it was demonstrated that the incorporation, within these carbon structures, of nitrogen atoms causes a greater electron mobility and introduces more active sites for catalytic reactions. This investigation is aimed at elucidating the main features of the hydrogen fragmentation over these carbon frameworks. Several models and different theoretical approaches were employed in this investigation to characterize the structure and properties of nitrogen pyridinic moieties framed within a carbon network, commonly classified as pyridinic defects. Two different kinds of pyridinic defects configurations within a carbonaceous environment were studied. The influence of the size of the π-system and of the curvature on the ergonicity associated to the H2 bond cleavage were analyzed. It was found that increasing the number of the benzene rings surrounding the defect the ergonicity of the reaction increases whereas the curvature of the carbon network scarcely affects this quantity.

Biomass conversion technologies have recently gained high industrial interest for the production of sustainable fuels and fine chemicals; starting feedstocks for these processes are generally complex mixtures of oxygenated compounds, ranging from lignans, carbohydrates and polyalcohols to carboxylic acids [1]. Framed within this scientific context the entire reforming mechanism of two well-known polyols, namely ethylen glycol (C2) and glycerol (C3), on a small Pd cluster was investigated by means of density functional theory. Among the large amount of reaction pathways that can be followed in the reforming of oxygenates, we discuss here only the route that brings to carbon monoxide and hydrogen as final products, since it is the most relevant in the biomass treatment. It was found that the C-H bond cleavage, where the H atom transfers to the cluster, has an activation energy which is typical of such processes [2] and common to all the mechanism we will deal with. On the other hand, the rate determining step (rds) is the C-C bond breaking, with an activation barrier which exceeds the 160 kJ/mol. The same investigation applied to C3 suggests that the mechanisms of the two studied polyols cross after the C-C reforming step, through a facile 1,2 hydrogen shift in a shared intermediate. In order to obtain information on the reforming of heavier polyols, the rds was calculated for all the stereoisomers of C4 (erythritol), C5 (xilytol, arabitol and ribytol), C6 (mannitol, sorbitol, galactitol and iditol), by including the influence of the position of the breaking C-C bond. Part of the reaction mechanism is in this case affected also by secondary interaction between hydroxiles and the palladium cluster.

The construction of a heterogeneous catalytic systems by a bottom-up approach is a fascinating strategy well assisted by molecular level characterizations. In this sense, DFT investigations can be used with predictive and descriptive purposes both for the treatment of the catalyst/support and for the substrate/catalyst characterization. This should be particularly useful for highly perspective but scarcely treated systems such as boron nitride based supports. Among these, boron nitride nanotubes (BNNT) have been demonstrated to have high chemical and thermal stability as well as great mechanical strength and high thermal conductivity.[1] Moreover, a high affinity toward hydrogen [2] as well as a moderate one to carbon dioxide, suggest their possible use as support for biomass conversion catalysts. In this work we studied through computational methods, how small Pd2 up to Pd9 clusters can nucleate and grow on a BNNT support; the study of the interaction occurring between palladium clusters and the support can be highly revealing for the possible production of shape and size-controlled nanoparticles. We demonstrated that the migration process of a single palladium atom on the BNNT is not highly energy demanding and can be represented as a hopping mechanism between boron and nitrogen. A model was found for the interpretation of the growth energetics, showing that the process is generally favoured increasing the cluster size. Results from the adsorption of oxygenates compounds, as model for biomass feedstocks,[3] are discussed.

Aqueous Phase Reforming (APR) process is one of the most efficient solution for producing hydrogen from biomass renewable feedstocks, such as polyalcohols. [1] Generally the reaction is catalyzed by supported platinoid metals and among these platinum has been recognized as the most active and selective toward the production of hydrogen. However, due to its really high complexity, the reaction mechanism is today poorly understood. DFT methods can be useful for understanding the APR catalytic mechanism at atomistic level. A detailed mechanistic study was carried out using a Pt30 cluster for the modelization of the catalyst and 1,2 propanediol (1,2PDO) as a model feedstock for the APR. Even for this simple molecule five chemically different hydrogen atoms can be recognized which lead to five different reaction paths. The activation energy required for the methylic C-H bond cleavage is approximately 40 kJ mol-1 higher than the HOCH-H and HOC-H bond breakings. This effect arises directly from the presence of the OH group that reasonably enhances the possibility of the C-H bond to break. The key step of the reaction seems to be the formation of the unsaturated 1,2 propenediole species that, if coordinated to the catalyst surface, can be reformed through a C-C bond cleavage or can be easily converted to ketonic species, which are experimentally found as byproducts. [2] The C-C bond cleavage is the rate determing step requiring 95.7 kJ mol-1.

We demonstrated that the migration process of a single palladium atom on the BNNT is not highly energy demanding and can be represented as a hopping mechanism between boron and nitrogen. A model was finally found for the interpretation of the growth energetics, showing that the process is generally favoured increasing the cluster size.

We investigated the interactions of a star-like copolymer with cyclodextrins (CD) with different cavity size. Direct measurements of thermodynamic properties were done, and the application of proper molecular models was useful for the interpretation of the involved phenomena. The CD–copolymer inclusion complexes were characterized by isothermal titration calorimetry. The copolymer aggregation induced by temperature was investigated by differential scanning calorimetry, volume and compressibility measurements. The behavior of the ternary T1107/CD/water mixture was interpreted considering competing equilibria. The investigated systems showed an interesting temperature responsive behavior so that copolymer-CD necklace-like supramolecular structures are formed, being that temperature raise favors CD dethreading that precedes the copolymer self-aggregation.

A QM/MM investigation is reported dealing with the nucleation and growth of small palladium clusters, up to Pd8 , on the outer surface of a suitable model of boron nitride nanotube (BNNT). It is shown that the BNNT could have a template effect on the cluster growth, which is due to the interplay between Pd-N and Pd-Pd interactions as well as to the matching of the B3N3 ring and the Pd(111) face arrangement. The values for the clusters adsorption energies reveal a relatively strong physisorption, which suggests that in particular conditions the BNNTs could be used as supports for the preparation of shape-controlled metal cluster

Biomass-based feedstocks are often oxygenated compounds characterized by large amounts of hydroxyls. As an example, polyols and sugar alcohols are largely employed as reactants for different chemical catalytic transformations such as oxidation, dehydration, and hydrodeoxigenation, which usually occur in aqueous medium. With the goal of gaining new insights into processes that could be industrially relevant, the adsorption of the OH groups on metal surfaces and in the presence of water has to be correctly reproduced and described, within a chosen theoretical framework. Toward this goal, several tests were performed on the catalytically relevant metal Ru, Pd, and Re, benchmarking their bulk and surfaces properties in the frame of the DFT paradigm and employing numerical atomic orbitals, joined with different exchange-correlation vdW-DF functionals. In particular, methanol, ethylene glycol, glycerol, and erythritol adsorption processes on Ru (0001), Pd (111), and Re (0001) surfaces were investigated, as well as their coadsorption with water.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.