α-d-Glucopyranose Adsorption on a Pd30 Cluster Supported on Boron Nitride Nanotube

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 clus…

Growth of sub-nanometric palladium clusters on boron nitride nanotubes: a DFT study.

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.

Computational study of metal-free N-doped carbon networks as hydrogenation catalysts

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. Se…

Density Functional Theory Investigation on the Nucleation of Homo- and Heteronuclear Metal Clusters on Defective Graphene

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.

Investigation of Polyol Adsorption on Ru, Pd, and Re Using vdW Density Functionals

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 a…

NAOs and vdW‐DF for simulating co‐adsorption of water and polyols on metal surfaces

The computational approach employed in this study is based on the combined use of numerical atomic orbitals (NAOs), which are recognized as highly efficient basis sets, and different parameterization of vdW-DF exchange-correlation functionals, namely DRSLL and KBM as implemented in the SIESTA code.

Growth of Palladium Clusters on a Boron Nitride Nanotube Support

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.

Graph-based analysis of ethylene glycol decomposition on a palladium cluster

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.

DFT calculations on subnanometric metal catalysts: a short review on new supported materials

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 geo…

Computational Investigation of Palladium Supported Boron Nitride Nanotube Catalysts

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

Inside Back Cover: Boron Nitride‐supported Sub‐nanometer Pd 6 Clusters for Formic Acid Decomposition: A DFT Study (ChemCatChem 9/2017)

Thermodynamics of cyclodextrin-star copolymer threading-dethreading process

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 t…

DFT investigation of polyalcohols reforming on palladium cluster

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 hydr…

Theoretical Investigation of Aqueous Phase Reforming of 1,2 Propanediol over a Pt catalyst

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 fo…

Palladium clusters on BNNT as catalysts for biomass conversion

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…

A Combined Theoretical and Experimental Approach for Platinum Catalyzed 1,2-Propanediol Aqueous Phase Reforming

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 competit…

Boron Nitride‐supported Sub‐nanometer Pd6 Clusters for Formic Acid Decomposition: A DFT Study

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 d…