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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.

Carbon dots are an emerging family of zero-dimensional nanocarbons behaving as tunable light harvesters and photoactivated charge donors. Coupling them to carbon nanotubes, which are well-known electron acceptors with excellent charge transport capabilities, is very promising for several applications. Here, we first devised a route to achieve the stable electrostatic binding of carbon dots to multi- or single-walled carbon nanotubes, as confirmed by several experimental observations. The photoluminescence of carbon dots is strongly quenched when they contact either semiconductive or conductive nanotubes, indicating a strong electronic coupling to both. Theoretical simulations predict a favorable energy level alignment within these complexes, suggesting a photoinduced electron transfer from dots to nanotubes, which is a process of high functional interest. Femtosecond transient absorption confirms indeed an ultrafast (, A.S. was supported by the “L’Oréal Italia Per le Donne e la Scienza” Program (17th edition). A.S. and F.M. thank the Italian Ministry of University and Research (MUR) for project PRIN2017 “CANDL2”, grant number 2017W75RAE. G.G. thanks the Portuguese Science Foundation (FCT) for Programme Stimulus of Scientific EmploymentIndividual Support (CEECIND/01913/2017). We acknowledge funding received by the Karlsruhe Nano Micro Facility (KNMF)− proposal ID 2019-021025715., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

The models and theories of quantum chemistry are applied in order to study two kinds of materials of interest in the field of energy technology, to understand their behavior and to verify their suitability for possible application. In particular, the effect of single Ru/Fe atom deposition on the CO2 methanation reaction occurring on the Ni(111) surface, and the effect on the band gap produced by carbon atom deposition and carbon cluster accretion on the silicic surface of halloysite, have been investigated by means of the periodic and molecular flavours of density functional theory. In order to accomplish the investigations above two entirely new computer codes were written and are actually maintained: Emphates, implementing a general interface for transition states identification through climbing-image nudged elastic band calculations, and Pathgen, which by using graph theory finds all possible paths between reactant and product for microkinetic analysys.

Metal clusters have been used in catalysis for a long time, even in industrial production protocols, and a large number of theoretical and experimental studies aimed at characterizing their structure and reactivity, either when supported or not, are already present in the literature. Nevertheless, in the last years the advances made in the control of the synthesis and stabilization of subnanometric clusters promoted a renewed interest in the field. The shape and size of sub-nanometer clusters are crucial in determining their catalytic activity and selectivity. Moreover, if supported, subnanometric clusters could be highly influenced by the interactions with the support that could affect geometric and electronic properties of the catalyst. These effects also present in the case of metal nanoparticles assume an even more prominent role in the “subnano world.” DFT-based simulations are nowadays essential in elucidating and unraveling reaction mechanisms. The outstanding position of this corner of science will be highlighted through a selected number of examples present in the literature, concerning the growth and reactivity of subnanometric supported metal catalysts.

A periodic, self-consistent planewave DFT study was carried out to explore the potential use of Pd6 clusters supported on a boron nitride sheet as a catalyst for the selective decomposi- tion of formic acid (HCOOH) to CO2 and H2. The competition between formate (HCOO) and carboxyl (COOH) paths on cata- lytic sites, with different proximities to the support, was stud- ied. Based on energetics alone, the reaction may mainly follow the HCOO route. Slightly lower activation energies were found at the lateral sites of the cluster as compared to top face sites. This is particularly true for the bidentate to monodentate HCOO conversion. Through comparison of results with similar studies on HCOOH decomposition on extended Pd surfaces, it was demonstrated that the existence of undercoordinated sites in the sub-nanometer cluster could play a key role in pref- erentially stabilizing HCOO over COOH, which is a common CO precursor in this reaction. A hydrogen spillover mechanism was also investigated; migration toward the boron nitride sup- port is not favorable, at least in the early stages of the reac- tion. However, hydrogen diffusion on the cluster has low barri- ers compared to those involved in formic acid decomposition.