The structural and catalytic properties of gold nanoparticles are known to be highly sensitive to cluster size, dimensionality, and interactions with the support. In this work, a combined theoretical and experimental approach was employed to investigate systems in which gold nanoclusters are anchored on functionalized halloysite nanotubes. Density functional theory calculations were performed to explore the geometric and electronic characteristics of the anchored Au n (n = 1 - 20) clusters and their interactions with the amino-functionalized support. Multiple anchoring configurations were assessed, with optimized geometries and Au-N interaction distances analyzed in detail. Results indicate a transition from a two-dimensional to a three-dimensional cluster structure occurring at a lower number of atoms if compared with the case of isolated Au n clusters, mainly due to the overall interaction with the halloysite silanolic groups. Complementarily, gold nanoparticles were synthesized and deposited onto functionalized HNTs, and the resulting materials were characterized using experimental techniques. The study demonstrates that halloysite-based hybrid materials offer a promising platform for stabilizing small gold clusters, with potential application as heterogeneous catalysts.

The use of biomass as renewable feedstock for commodity chemicals may largely benefit from the successful development and application of heterogeneous catalysts for decomposition processes. The present investigation combines density functional theory and Christiansen-like microkinetic analysis to describe, at the atomistic level, the mechanisms related to the conversion of oxygenated biomass compounds to deoxygenated and semi-saturated hydrocarbons on a subnanometric Pt10 cluster. The DFT calculations and the kinetic analysis based on the evaluated free energy variations, associated with both elementary step barriers and rearrangement/desorption processes occurring on the cluster, suggest that benzene is the preferred product, together with a compound still bearing oxygen, cyclopentadienone, which would form as a minor product only at high temperature. Other than highlighting the role of the peculiar interaction between carbon and platinum, the reported investigation underlines the importance of cluster fluxionality and reorganization ability in promoting catalyzed reactions.

The acidic activation of halloysite nanotubes (HNTs) surface was investigated by a synergistic approach based on density functional theory (DFT) calculations and experimental methods. In particular, the protonation of halloysite inner lumen was enlightened at the atomic level by considering both the reactions energy and the geometrical properties. The mono-, bi-and tri-protonations are indeed exothermic processes. Similarly, the aluminum leaching was investigated and the energy required for the dealumination (Delta ETOT = +882.9 kJ.mol-1) can be supplied by the refilling of the active vacancy (Delta ETOT =-883.5 kJ.mol-1). Hence, a detailed experimental study of acidic-treated HNTs was carried out by considering their chemical and morphological properties. Most importantly, the nanotubular shape was maintained and the acidic treatment leads to an increase in the total concentration of acid sites and to the formation of new Br & oslash;nsted sites. The catalytic properties were tested through the isomerization of o-xylene and a clear acidity-activity relationship was demonstrated. The synergy between in silico and in lab studies are of utmost importance for the development of efficient acid catalysts, thus paving the way for the development of multifunctional systems for the one-pot conversion of biomass into valueadded molecules.

A comprehensive analysis of selected DFT exchange–correlation functionals is presented, focusing on their performance in treating gold nanoclusters and on their known reliability for the description of organic species, energy barriers and dispersion interactions. To distinguish this study from the existing literature, the investigation specifically considers the practical relevance of the chosen functionals in catalytic contexts, with a particular emphasis on their potential applications in nanocatalysis for biomass valorization. Gold clusters containing 4 to 20 atoms were examined, with special attention given to the number of atoms at which the planar-to-three-dimensional-structure switch occurs. The investigation reported in this work would suggest M06 as the best exchange–correlation functional in terms of applicability and overall accuracy for computational studies of catalyzed processes involving gold nanoclusters and organic components.

This study presents a graph-based approach to investigate the steady-state kinetics of the preferential CO oxidation process in H2 (PROX) occurring on a MnO2 model fragment with manganese centers at varying oxidation states, simulating the surface Mn(IV) active sites of a composite MnO2-CeO2 catalyst previously used in experimental applications. A novel modeling approach, termed DFT graph-based kinetic analysis (DFT-GKA), is introduced. It utilizes free activation energy (ΔG⧧) values to characterize linear elementary events, supposed at pseudosteady-state, in this complex reaction system, as determined through density functional theory (DFT) integrated by thermochemical calculations. The implementation of this model is achieved using a homemade Common Lisp code, specifically designed for efficient manipulation of long lists essential for the analysis. Finally, the comprehensive ab initio DFT kinetic descriptors related to the CO/H2 PROX catalytic process on the manganese oxide fragments are discussed, highlighting their significance for future research and applications.

The CO and H-2 oxidation functionality of a composite MnCeOx catalyst with large exposure of Mn(IV) sites has been investigated in a wide range of experimental conditions (T, 293-533 K; p(CO)/p(0) or p(H2)/p(0), 0.00625-0.025; p(O2)/p(0), 0.00625-0.20) to ascertain the mechanistic clues of a peculiar preferential CO oxidation pattern. The MnCeOx shows high CO oxidation activity in the range of 293-533 K, while a large activation energy hinders the H-2 oxidation at T < 373 K. Computational analysis of adsorption and activation energies on a model Mn4O8 cluster, and unchanging energy barriers of CO2 and H2O formation, in absence and in the presence of O-2, indicate that the abstraction of lattice O-atoms is the rate limiting step (r.l.s.) of the CO and H-2 oxidation. This reactivity pattern relies on strong chemical affinity of Mn(IV) sites toward CO enabling the easy abstraction of lattice O-atoms, while H-2 oxidation occurs via an extrafacial reaction path driven by diatomic oxygen species produced by spillover and adsorption processes at T > 373 K. Mechanistic clues were synthesized into macrokinetic models predicting the CO and H-2 oxidation activity of the MnCeOx catalyst under any conditions.

Three new coordination complexes of Cu(II) ions made from two hydrazone ligands, 7-chloro-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-2-furoyl-hydrazone (HL1) and 6-chloro-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-2-furoyl-hydrazone (HL2) have been synthesized and fully characterized by spectroscopic techniques. Their crystal and molecular structures revealed distorted square pyramidal mononuclear complexes: [(L1)Cu(H2O)2](NO3)·3H2O, 1(NO3), [(L2)Cu(H2O)2](NO3)·2H2O·CH3OH, 2(NO3), and [(L2)Cu(NO3)(CH3OH)]·2CH3OH, 3, comprising the ligand (L1 and L2) in tridentate fashion (ONO) with two water molecules in 1+ and 2+, and a single methanol molecule and a nitrate ion in 3 in their respective copper coordination spheres. EPR spectra in frozen methanol revealed the occurrence of several species arising from different coordination environments. A detailed DFT investigation on the energetics of solvents exchange (H2O, MeOH, and DMSO) and simulation of the EPR parameters showed that the exchange processes occur easily in solution. The value gz indicated the occurrence of a dimeric aggregate for 2+. The new copper complexes exhibited a noticeable antiproliferative activity with IC50 values in the micromolar range against HCT-15, H157, BxPC3, PNS-1, and A431 cell lines and they were found to be 3-fold more effective than cisplatin against pancreatic PSN-1 cell lines. Cross-resistance tests on A2780 and LoVo cancer cell lines and the corresponding multidrug or oxaliplatin resistant sublines showed that complexes 1(NO3) and 2(NO3) were equally cytotoxic to sensitive and resistant cells, thus overcoming multidrug and oxaliplatin resistance.

Nanotechnology's exponential growth has spurred a demand for high-quality and safe nanomaterials, prompting increased interest in cost-effective and fast colloidal syntheses that must mitigate their irreversible aggregation, an issue particularly pertaining to spherical selenium nanoparticles (SeNPs), promising materials in a wide array of technological and biological fields. This study presents a novel approach to SeNP synthesis in confined environments developed from the highly biocompatible surfactant sodium oleate (NaOl) and the amino acid L-cysteine as a selenite-reducing agent. Lcysteine@NaOl (C@NaOl) confined environments were modulable as a function of the amino acid and surfactant concentrations and yielded high-quality spherical SeNPs with enhanced stability. This approach enables generating SeNPs even under alkaline conditions and improving up to 3-fold the final SeNP yield compared to other processes. Besides, we introduce a groundbreaking method for determining SeNP size by adapting Mie's scattering theory to metalloid NPs. This innovative technique proves effective for SeNPs in the 40-100 nm range, offering a reliable alternative to conventional sizing methods. These findings provide valuable insights regarding the generation of bio- and eco-compatible confined environments and SeNPs, paving the way for developing safe, cost-effective, and environmentally friendly strategies for their synthesis with broad applications in various scientific and technological domains.

The debate on climate change and the future of our Planet has brought to general attention the problem of fossil fuels (coal, oil and natural gas), among the main causes of pollution on Earth. At the same time, the necessity to encourage research and development of alternative and renewable energy resources has become increasingly relevant. In this context, biomass is an attractive option to produce biofuels and chemicals currently derived from petroleum. The hydrodeoxygenation process of bio-oils, produced by the rapid pyrolysis of biomass, is the most effective strategy for obtaining biofuels, hence the reason for the investigation of its mechanism on model biomass compounds. Having investigated the direct deoxygenation (DDO) mechanims in the first paper of this series, the present work aims to illustrate the deoxygenation-through-hydrogenation (HYD) mechanism, by which isoeugenol, a compound chosen as a model of bio-oils, is converted into propylcyclohexane on a ten-atom platinum cluster. DFT calculations highlight, from kinetic and thermodynamic perspectives, how the formation of propylcyclohexane takes place through 4-propyl-2-methoxycyclohexane-1-ol, the removal of - OCH 3 as methanol and then of the - OH group as water. Microkinetic analysis, performed by joining findings on both DDO and HYD routes, reveals that the isoeugenol DDO mechanism is favored at any selected temperatures.

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. A novel catalyst architecture is proposed with potential one-pot activity for the valorization of biomass. It exploits the gold coordination on the organosilane functionalization in the outer surface of the halloysite spiral nanotube, to be coupled with the acid catalytic activity of its inner surface. The work is a preliminar computational exploration of the structural and energetic characteristics of the species involved. image

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.

A microkinetic analysis in terms of DFT-calculated temperature-dependent Gibbs free energies was performed for the oxidation reactions of CO and H2 on a model Mn4O8 cluster. Apparent activation energies data predict a peculiar CO preferential oxidation pattern of Mn(IV) sites in presence of hydrogen (PROX) substantiated by the unprecedented PROX behavior of a nanocomposite MnCeOx catalyst in the range of 353–423K under both ideal and real process conditions. Micro- and macrokinetic data on the “model” cluster and “real” catalyst are discussed.

In a scenario of declining fossil resources and increasing demand for renewable and sustainable alternatives, biomass is the only source able to offer an easy and gradual transition in the use of current energy technologies based on the exploitation of carbon derivatives. Its conversion to liquid fuels has oriented our study towards the computational mechanistic analysis of the guaiacol catalytic hydrodeoxygenation, which is currently considered one of the most challenging routes for upgrading biomass-derived bio-oils. For this purpose, a subnanometric Pt10 platinum cluster was chosen as the catalyst model, with Pt as a computational reference element for catalytic hydrogenation, and guaiacol as a model compound of bio-oils. DFT calculations revealed that the energy barriers related to the cleavage of C(sp2)-O bonds in the direct deoxygenation mechanism are significantly lower (by an average of 60 kJ mol-1) than those in the deoxygenation-through-hydrogenation mechanism in which C(sp3)-O bond breaking from a saturated ring occurs. Even if the ring hydrogenation is easier in the oxygenated compound, the analysis reveals that the direct deoxygenation mechanism is favoured at all temperatures. Furthermore, the results obtained highlight that, from a thermodynamic perspective, the removal of oxygen groups preferentially occurs by the elimination of the -OCH3 fragment as methanol and then of the -OH fragment as a water molecule.

The preferred location and the corresponding energeticsof zeolite-embeddedsingle metal atoms and small metal particles are hot topics withinactive site optimization and catalyst tuning, even as part of bifunctionalmaterials design. In this context, periodic density functional theorywas used to provide insights on the interactions of a platinum atomwith the microporous cages of a purely silicious & beta;-zeolite (BEA)framework. Cluster growth was subsequently addressed, up to Pt-3@BEA systems, following a one-by-one platinum atom addition;platinum migration between cages was taken into account as well. Anunbiased approach was employed, which allowed a wide panorama of structuresbeing considered in addition to a thorough analysis in terms of energetics,cluster geometries, and cavity distortions. Calculations revealedthat the optimal interaction geometry for a single platinum atom isrealized where two strong Pt-O bonds in almost linear arrangementcan form, regardless of the cavity involved. This can cause distortionsor even breaking of the zeolite structure, a factor which howeveris not decisive in determining the energetics of systems with twoand three platinum atoms. Platinum migration is associated with energybarriers ranging from 100 to 200 kJ mol(-1), dependingon the cages. Up to the dimensions considered here, preference forclustering is observed, being the embedded Pt-3 systemsin almost all cases energetically favored with respect to isolatedatoms within the BEA framework.

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.

The most common computational methods used for the investigation of molecular and periodic systems will be briefly described, with particular emphasis on those approaches that could be employed for the study of clay structures at the atomistic level. The first part of the chapter is mainly dedicated to the conceptual basis of density functional theoryDensity Functional Theory (DFT) and its implementation for molecular and periodic systems. The tight binding approximation to density functional theory and its modern variants, particularly suitable for atomistic studies of large systems, is treated as well. Classical molecular mechanics and molecular dynamicsMolecular dynamics methods, as well as the definition of force fieldsForce fields suitable for clay materials, are shortly discussed. In the second part, case studies of application of computational approaches for the characterization of structures and properties of clay materials (in particular, the halloysite nanotubeHalloysite nanotubes) are reported.

A new time-dependent Monte Carlo approach, tdMC, is presented. This allows one to manage the quantum-chemical information relating to surface catalytic processes and rationalize, with atomistic dynamical perspectives, the corresponding reaction mechanism by providing descriptors that can be compared with experimentally obtained data. The approach, which falls into the more general microkinetic paradigm, is strictly self-consistent as it exploits information framed in just one computational method based on the density functional theory. The results simulated by the tdMC algorithm concern the isomerization of but-1-ene to cis- and trans-but-2-ene on Pd surfaces. This reaction was chosen mainly to focus on the development and implementation of the model as well as to point out the characteristics of the code and the soundness of the approach. In order to reach these goals, the simulated findings were compared to related experimental and computational literature data. From the study, it clearly emerges that the tdMC approach, although conceptually very straightforward and simple, is flexible enough to pinpoint the main characteristics of the reaction, which is just seemingly elementary and conversely governed by a complex mechanism involving, besides isomerization, even hydrogenation and dehydrogenation processes. Noticeably, new insights into the title reaction were also provided by the proposed approach.

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.

An easy and flexible interface, Empathes(Extensible Minimum PATH EStimator), that allows to perform Nudged Elastic Band calculation for the determination of transition states is presented. The code is designed to be easily modified, in order to be associated with the user's preferred calculation software, even with those which implement composite approaches. In particular, the interfaces to Gaussian and Siesta programs are discussed in details, being the former only used for testing purpose, while the latter can be productively employed for transition states search with that commonly used density functional theory software for periodic calculations. Program summary Program Title: Empathes CPC Library link to program files: https://doi.org/10.17632/v525mwf3cc.1 Developer's repository link: https://github.com/marberti/empathes Code Ocean capsule: https://codeocean.com/capsule/2394233 Licensing provisions: GPLv3 Programming language: Fortran 08 Nature of problem: The search for the structure of transition states through computational methods, essentially based on Density Functional Theory, is of overwhelming importance for the determination of the elementary steps forming a reaction mechanism. Allowing to develop basic knowledge, these investigations can be used to direct experimentalists towards a more efficient realization of chemical compounds synthetic processes. In cases where it is necessary to describe the reactive system through periodic calculations, which is very common in heterogeneous catalysis, this research must be done through the use of non-analytical methods. Solution method: In case of lacking of analytical procedures, the search for the transition states associated with the elementary stages that make up chemical reactions must take place through numerical methods. The Nudged Elastic Band (NEB) approach is, together with its variants, one of the most used for this purpose. In accordance with the NEB algorithm, a chain of geometric structures, generated by interpolating between the reactant and product geometries and joined by fictitious springs, is relaxed on the minimum energy path, allowing the association of the transition state to the maximum along this path. The NEB method involves the determination of molecular energies and forces acting on the nuclei of the system, which is generally carried out through a program for electronic structure calculation. The present code is a useful general interface. (C) 2021 Elsevier B.V. All rights reserved.