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The reaction steps involved in the 5‐hydroxymethylfurfural to 2,5‐furandicarboxylic acid conversion by means of H2O2 were investigated employing a dedicated computational protocol based on density functional theory. The catalytic environment of choice was a molecular model representing a portion of the halloysite nanotube outer surface, functionalized by an organosilane, the 3‐aminopropyltriethoxysilane, whose amino group bonds one gold atom. At this stage of the investigation, the process was fully detailed in terms of the interactions between the reaction intermediates and the catalyst, and the reaction standard free energies. In addition, the energy barriers of the elementary steps involving the hydrogen migration from the adsorbed organic species to the gold atom were analyzed. On the basis of the interaction geometries, a certain distinction among the preferred reaction path can be inferred as a function of the net negative charge characterizing the catalyst outer surface. Since the inner surface of halloysite can represent the acid environment needed to obtain 5‐hydroxymethylfurfural through dehydration of fructose, the present study is framed in a wider research field where the possibility to consider functionalized halloysite as one‐pot reactor for the valorization of biomass is explored. [ABSTRACT FROM AUTHOR]

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]

Abstract: The density functional theory was employed to mimic the homogeneous hydro-dimerization of the Zeise-similar dichloro-bis(ethene)-platinum(II), . Three energy minima and four transition-states were involved in the reaction mechanism, which was even characterized by a catalytic cycle. The minima were fully optimized at B3LYP level whereas the transition-states were first individuated at the same level, by the synchronous transit-guided quasi-Newton method, then fully optimized. The mechanistic hypotheses on the dimerization implied the displacement of two ethene or two ethane molecules, respectively, occurring in absence or in presence of molecular hydrogen. In the second case, the dimer platinum product performed as a catalytic center. The study of the reaction paths as well as that of the structural and energetic transformations of the calculated species allowed us to deepen basis aspects of the title reaction. Whereas, a comparative analysis between some species involved in the same reaction and heterogeneous catalytic models, namely ethene on platinum-cluster models, fixed some analogies between the energetics involved in homogeneous and heterogeneous catalytic processes. [Copyright &y& Elsevier]

Molecular dynamics simulations based on density functional theory were employed to investigate the fate of a hydrogen molecule shot with different kinetic energy toward a hydrogenated palladium cluster anchored on the vacant site of a defective graphene sheet. Hits resulting in H2 adsorption occur until the cluster is fully saturated. The influence of H content over Pd with respect to atomic hydrogen spillover onto graphene was investigated. Calculated energy barriers of ca. 1.6 eV for H-spillover suggest that the investigated Pd/graphene system is a good candidate for hydrogen storage. [ABSTRACT FROM AUTHOR]

Since Brønsted acidity is a crucial aspect for the applications of zeolitic materials in heterogeneous catalysis, great effort was devolved to characterize the number, strength and location of the potentially active acidic sites. Quantum chemical calculations can turn out essential in estimating the intrinsic acidity by computing deprotonation energy (DPE) values, although each method comes with its own difficulties. In this context, three approaches within density functional theory were employed to study the intrinsic acidity of 30 topologically distinct Brønsted sites in the β -zeolite framework. Advantages and disadvantages of the three methods were outlined and the acidity order between the sites was assessed, being the DPE range 59 kJ mol−1 wide, with the proposed best approach. By dividing the range into three portions, the sites were classified as having high, medium and low acidity. Hydrogen bonds formation was found to be a contributing factor in determining a low Brønsted acidity. [Display omitted] • A new cluster approach is described for the calculation of β -zeolite sites Brønsted acidity. • Drawbacks associated to the application of ONIOM and periodic methods are examined. • The proposed procedure can be considered as a non-empirical correction to periodic results. • The cluster approach can be easily extended to all zeolite architectures. [ABSTRACT FROM AUTHOR]

In this work, the effect of halloysite nanotubes alkali activation on its grafting efficiency with organosilanes was studied by Density Functional Theory and experimental investigations. In particular, computational analysis allowed to enlight the structural properties of the organic molecules attached to the silanol groups on halloysite outer surface. The energetics of the reactions showed that the pretreatment with a base is crucial for the modification of the surface due to the appearance of a high number of active sites which lead to thermodynamically favored exothermic processes. Experimental evidences are in good agreement with calculation hypothesis. For instance, the coating efficiency is higher after the alkali activation of the inorganic counterpart for both the investigated organosilanes. The findings here reported are important in order to improve any functionalization protocols for aluminosilicates without variations or loss of the hollow nanotubular morphological features and it paves the ground to halloysite based technological applications in many fields, from nanotechnology to catalysis. • The outer surface of halloysite nanotube was functionalized by grafting with organosilanes • The products of halloysite functionalization were characterized by DFT and experimental techniques • Functionalization is more efficient on alkali-treated halloysite • DFT calculations confirm the exothermicity of grafting reactions when silanol groups are on the surface [ABSTRACT FROM AUTHOR]

In situ Attenuated Total Reflection Infrared (ATR-IR) spectroscopy was used to study Aqueous Phase Reforming of hydroxyacetone on Pt/AlO(OH) and Pt/ZrO 2 catalysts at 230 °C/ 30 bar. Formation of strongly adsorbed aldol condensation products was observed on the surface of Pt/ZrO 2 and ZrO 2 in contrast to Pt/AlO(OH) and AlO(OH). Peak assignments were supported by DFT calculations of the IR spectra of the condensation products in vacuum and in the presence of water. Aldol condensation of hydroxyacetone leading to compounds with high molecular weight with unsaturated bonds was suggested as a first step in coke formation. Carbonaceous deposits on the surface of the ZrO 2 support are oxygen-rich and highly reactive, according elemental analysis and TPO. Surprisingly, no adsorbed CO on Pt was observed in the spectra obtained under reaction conditions, suggesting that adsorbed CO is not involved in the rate-determining step in APR of hydroxyacetone. [ABSTRACT FROM AUTHOR]

• The structure of silanols groups on halloysite outer surface are investigated by DFT • Silanol content increases after alkaline treatment • Silanol groups at the outer surface are crucial for halloysite functionalization Density functional theory calculations were performed in order to investigate the formation of silanol groups on the outer surface of halloysite nanotubes, as possible products of the reactions with water in alkaline environments. The results, discussed in terms of energy release and structural properties of the modified surface, suggest that the formation of various kinds of silanol group constellations, and even the extraction of orthosilicic acid, are highly exothermic reaction in the presence of hydroxide ions. Thermogravimetric analysis, FT-IR, XRD and X-ray fluorescence spectrometry performed on halloysite treated at high pH conditions indicate that the adsorption of water on the outer surface occurs with higher percentage after the treatment, confirming the increased number of silanols groups. [ABSTRACT FROM AUTHOR]

The oxidation functionality of Mn(IV) sites has been assessed by density functional theory (DFT) analysis of adsorption and activation energies of CO, H 2 and O 2 on a model Mn 4 O 8 cluster. DFT calculations indicate that Mn(IV) atoms prompt an easy CO conversion to CO 2 via a reaction path involving both catalyst and gas-phase oxygen species, while much greater energy barriers hinder H 2 oxidation. Accordingly, a MnCeO x catalyst (Mn at /Ce at , 5) with large exposure of Mn(IV) sites shows a remarkable CO oxidation performance at T ≥ 293 K and no H 2 oxidation activity below 393 K. Empiric kinetics disclose that the catalyst-oxygen abstraction step determines both CO and H 2 oxidation rate, although different activation energies favor the preferential oxidation (PROX) pattern of the studied catalyst (353–423 K). Conversion-selectivity of 100%, high stability during 72 h reaction time and moderate inhibiting effects of water and CO 2 feeding reveal the potential of MnO 2 materials as efficient, low-cost and robust PROX catalysts. Mn(IV) sites shape the PROX pattern of the MnCeO x catalys [Display omitted] • A DFT study of the CO and H 2 oxidation functionality of Mn(IV) sites is outlined. • DFT analysis predicts a typical preferential CO oxidation behavior of Mn(IV) sites. • A MnCeO x catalyst with large availability of Mn(IV) has been investigated. • Very different energy barriers determine the PROX pattern of the MnCeO x catalyst. • MnO 2 materials are effective, low cost and robust catalysts for the PROX reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metal-free processes are desirable for economic and environmental reasons. • Low cost alkanes conversion to relevant alkenes is an important industrial challenge. • Quasi -molecular BN nanoflakes were proposed as potential dehydrogenating species. • DFT was employed for exploring the use of BN nanoflakes as dehydrogenation catalysts. • BN nanoflakes seem useful to obtain industrially relevant hydrocarbon derivatives. Lower alkanes are feedstocks readily available but relatively inert. The conversion of low cost alkanes to industrially relevant alkenes is usually carried out on metal-based heterogeneous catalysts. Considering both the cost and the potential harmfulness of the metal involved in the dehydrogenation catalysts (typically, platinum or chromium), the study of metal-free processes represents an important challenge for the industrial chemistry in order to address more sustainable protocols and different routes either to activate or transform alkanes. Framed in this context, it was investigated, using a density functional theory approach, the potential dehydrogenation activity of defective and partially hydrogenated boron nitride quasi- molecular nanoflakes, on ethane, chloroethane and phenylethane. Concerted and not concerted reactions were considered, resulting the former always favored with respect to the latter and being the mechanisms and the corresponding energy characterizing the different substrates, in any case, quite similar. Along the dehydrogenation, given a certain hydrocarbon adsorption constellation, the defective nitrogen sites were generally more active than the boron ones, being the energy barriers, in any case, smaller or at least comparable with those already observed for the metal catalyzed dehydrogenation processes. After the dehydrogenation processes, the hydrogenated boron nitride quasi- molecular nanoflakes resulted highly stabilized, suggesting that specific strategies are needed to employ these materials as catalysts. [ABSTRACT FROM AUTHOR]