A Simple “Nano-Templating” Method Using Zeolite Y Toward the Formation of Carbon Schwarzites

Schwarzites have a three-dimensional sp2 carbon structure with negative Gaussian curvatures. They can be synthesized through the deposition of carbon by chemical vapor deposition on a zeolite template and may be formed by increasing the amount of carbon. In this research, the amount of carbon deposition was increased by shortening the length of the diffusion pathways of the template through the use of nano-sized zeolite Y (nano-FAU). It was found that significantly larger quantities of carbon could be deposited inside the pores of nano-FAU (40 nm), compared to the micro-sized zeolite Y (300 nm). It is thus confirmed that by shortening the diffusion pathways enables more carbon to infiltrate into the center of the template before the pore channels are blocked, which leads to larger carbon depositions. A low acetylene gas concentration (15% vol in N2) and a prolonged period for chemical vapor deposition (6 h) is preferable for effectively loading carbon into the template. The obtained carbon replica exhibits the ordered structure derived from zeolite Y with an unprecedented 72 carbon atoms per supercage, of which a model with a structure similar to schwarzite was proposed.This work was supported by Grant-in-Aid for Scientific Research (A), 17H01042 (HN); the Nano-Macro Materials, Devices and System Research Alliance; and the Network Joint Research Center for Materials and Devices. The support from Sirindhorn International Institute of Technology under the Excellent Thai Student Program (PB) and from the Research Grant for New Scholar (Grant No. MRG6080153) co-funded by the Thailand Research Fund (TRF); the commission on Higher Education, Thailand; and Thammasat University, are also acknowledged

Exploitation of missing linker in Zr-based metal-organic framework as the catalyst support for selective oxidation of benzyl alcohol

Extensive studies have been done on the modification of the organic linkers with different functional groups for ameliorating the properties of Zr-based metal-organic frameworks (MOFs). In contrast, little effort has been devoted to Zr MOF modification at the –OH group arising from the incomplete coordination of Zr with the organic linkers. We focused on covalently immobilizing redox-active iron to the –OH group in the node of a Zr-based MOF for selective oxidation of benzyl alcohol to benzaldehyde, which is an important reaction in organic synthesis, pharmaceutical, and industrial areas. In this work, iron acetylacetonate was incorporated into Zr6(μ3-O)4(μ3-OH)4(HCOO)6(1, 3, 5-benzenetricarboxylate)2 or MOF-808. The air-stable Fe-anchored MOF-808 (Fe-MOF-808) was subjected to screening for the selective oxidation of benzyl alcohol to benzaldehyde. Fe-MOF-808 showed enhanced conversion and selectivity to benzaldehyde as well as catalytically outperforming the pristine MOF-808 in the reaction. The prepared solid catalyst also displayed the robustness without the leaching of the active site during the reaction, along with at least four-time recyclability of use without significant deactivation

Exploitation of missing linker in Zr-based metal-organic framework as the catalyst support for selective oxidation of benzyl alcohol

Extensive studies have been done on the modification of the organic linkers with different functional groups for ameliorating the properties of Zr-based metal-organic frameworks (MOFs). In contrast, little effort has been devoted to Zr MOF modification at the –OH group arising from the incomplete coordination of Zr with the organic linkers. We focused on covalently immobilizing redox-active iron to the –OH group in the node of a Zr-based MOF for selective oxidation of benzyl alcohol to benzaldehyde, which is an important reaction in organic synthesis, pharmaceutical, and industrial areas. In this work, iron acetylacetonate was incorporated into Zr6(μ3-O)4(μ3-OH)4(HCOO)6(1, 3, 5-benzenetricarboxylate)2 or MOF-808. The air-stable Fe-anchored MOF-808 (Fe-MOF-808) was subjected to screening for the selective oxidation of benzyl alcohol to benzaldehyde. Fe-MOF-808 showed enhanced conversion and selectivity to benzaldehyde as well as catalytically outperforming the pristine MOF-808 in the reaction. The prepared solid catalyst also displayed the robustness without the leaching of the active site during the reaction, along with at least four-time recyclability of use without significant deactivation

The Activation of Methane on Ru, Rh, and Pd Decorated Carbon Nanotube and Boron Nitride Nanotube: A DFT Study

Methane decomposition catalyzed by an Ru, Rh, or Pd atom supported on a carbon or boron nitride nanotubes was analyzed by means of the density functional theory with the M06-L hybrid functional. The results suggested that the dissociative reaction of methane was a single-step mechanism. Based on the calculated activation energy, the Ru-decorated carbon nanotube showed superior catalytic activity with an activation barrier of 14.5 kcal mol−1, followed by the Rh-decorated carbon nanotube (18.1 kcal mol−1) and the Pd-decorated carbon nanotube (25.6 kcal mol−1). The catalytic performances of metals supported on a boron nitride nanotube were better than those on a carbon nanotube. The total activation barrier for the Ru, Rh, and Pd atoms on boron nitride nanotube was 10.2, 14.0, and 20.5 kcal mol−1, respectively. Dissociative adsorption complexes on the Ru–boron nitride nanotube were the most stable. The anionic state of the supported metal atom was responsible for decreasing the activation energy of methane decomposition. Our finding provides a crucial point for further investigation

Production of Formic Acid via Hydrogenation of CO₂ over a Copper-Alkoxide-Functionalized MOF: A Mechanistic Study

Conversion of greenhouse gases to more valuable chemicals is important from both the environmental and industrial points of view. Herein, the reaction mechanisms of the hydrogenation of carbon dioxide (CO₂) to formic acid (HCOOH) over Cu-alkoxide-functionalized metal organic framework (MOF) have been investigated by means of calculations with the M06-L density functional. The reaction can proceed via two different pathways, namely, concerted and stepwise mechanisms. In the concerted mechanism, the hydrogenation of CO₂ to formic acid occurs in a single step. It requires a high activation energy of 67.2 kcal/mol. For the stepwise mechanism, the reaction begins with the hydrogen atom abstraction by CO₂ to form a formate intermediate. The intermediate then takes another hydrogen atom to form formic acid. The activation energies are calculated to be 24.2 and 18.3 kcal/mol for the first and second steps, respectively. Because of the smaller activation barriers associated with this pathway, it therefore seems to be more favored than the concerted one. The catalytic effect of Cu-MOF-5 is also highlighted by comparing it with the gas-phase uncatalyzed reaction in which the reaction takes place in one step with a barrier of 73.0 kcal/mol. This study also demonstrates that the metal-functionalized MOF can be utilized for the greenhouse gas catalysis in addition to using it to capture and activate CO₂

Structure, Interaction, and Dynamics of Au/Pd Bimetallic Nanoalloys Dispersed in Aqueous Ethylpyrrolidone, a Monomeric Moiety of Polyvinylpyrrolidone

Bimetallic nanoparticles (NPs) have been shown to exhibit certain advantages over pure NPs in catalysis due to a synergistic effect. It is common to disperse NPs in a polymer matrix such as polyvinylpyrrolidone (PVP) to prevent flocculation, which imparts considerable electronic effects on the NPs. In the present study, the interactions between aqueous solutions of <i>N</i>-ethylpyrrolidone (EP, system chosen to model the monomeric form of PVP) and Au/Pd bimetallic NPs, which are relevant in catalysis, have been investigated using molecular dynamics simulations and density functional theory (DFT) method. The adequacy of the force fields used was assessed based on their ability to reproduce the structures and adsorption energies obtained using DFT calculations. The interactions of NPs with the environment were studied at various concentrations of aqueous solutions of EP to examine the strength of NP–EP and NP–water interactions. Free energy calculations and local mole fraction enhancement values show that that the EP adsorption on NPs is preferred over the adsorption of water. Extensive analysis of the interactions of the NPs with various concentrations of aqueous EP suggests the existence of isolated water molecules that may take part in reactions. Adsorption of unexpectedly large numbers of EP molecules was found to be possible leading to accumulation of the electron density on the Au/Pd NPs, which have previously been shown to enhance the catalytic activity of NPs. This study emphasizes the importance of including the electronic effects on the NPs due to the adsorption of stabilizing agents in modeling and demonstrates the utility of MD simulations to generate appropriate model chemistries for studying catalysis at higher level quantum chemical and density functional theory calculations

C–Cl Bond Activation on Au/Pd Bimetallic Nanocatalysts Studied by Density Functional Theory and Genetic Algorithm Calculations

The C–Cl bond activation by Au/Pd bimetallic alloy nanocatalysts has been investigated with regard to the oxidative addition of chlorobenzene (PhCl). Fifteen stable structures of the Au₁₀Pd₁₀ nanocluster (NC) obtained by a genetic algorithm were examined by DFT calculations using the M06-L, TPSS, and B3LYP functionals. Triplet states of cage-like C₁ and C_s structures are found to be relevant reflecting the quasi-degenerate nature of the Pd moiety, while several other low-lying structures and spin states may also contribute to the oxidative addition. For all examined cluster structures, the oxidative addition step is exothermic, and internal conversion and/or spin crossing are expected to occur as several states are close in energy and geometry. Based on an energetic analysis of a model system consisting of the Au₁₀Pd₁₀ NC surrounded by four poly­(<i>n</i>-vinylpyrrolidone) (PVP) molecules, the PVP units activate the system as electron donors and stabilize it. While a neutral NC model overestimates the energy barrier slightly, the opposite holds for an anionic NC model. In the oxidative addition, the interaction between the phenyl group and the Pd atom on the NC surface as well as a dissociation taking place at the Pd site are found to be essential. This indicates the importance of direct coordination effects in the Au/Pd bimetallic NC. NBO analysis shows that a π back-donation of the M­(dπ) to σ*­(C–Cl) orbital is relevant for the C–Cl bond activation and the interaction energy explains the favorable dissociation at the Pd site compared to the Au site

Mechanism of Ullmann Coupling Reaction of Chloroarene on Au/Pd Alloy Nanocluster: A DFT Study

Recently, a unique catalytic system of bimetallic Au/Pd alloy nanoclusters (NCs) for Ullmann coupling of chloroarenes (ArCl), which works at low temperature in high yield, has been developed (<i>J. Am. Chem. Soc.</i> <b>2012</b>, <i>134</i>, 20250). In this work, the full catalytic cycle of this reaction has been investigated for ArCl, producing biphenyl on the Au/Pd alloy NCs by DFT calculations with the M06-L functional. Two possible reaction pathways are proposed, namely, (i) ArCl oxidative addition followed by Cl abstraction from the NC surface occurs twice stepwise and (ii) the successive oxidative addition of two ArCl proceeds before the Cl abstraction. Both of these pathways are energetically possible, and in the latter case, the Cl atoms stay on the NC surface. The exothermic reaction pathways were obtained for this multistep reaction scheme. The rate-determining step was shown to be hydrogen transfer from dimethylformamide (DMF), which is consistent with the experimental isotope effect observation. The proton shuttle mediated by water considerably reduces the activation barrier. The side reaction, which produces benzene via hydrogenation, is prohibited by the second ArCl oxidative addition. The present study has revealed the essential mechanism of the coupling reaction on supported Au/Pd NC catalysts, suggesting that the entire reaction is controlled by several factors including the surroundings and solvents. These findings provide useful insights for the further developments of efficient NC catalysts through designing the supports, interface, and reaction conditions

Mechanism of Ullmann Coupling Reaction of Chloroarene on Au/Pd Alloy Nanocluster: A DFT Study

Recently, a unique catalytic system of bimetallic Au/Pd alloy nanoclusters (NCs) for Ullmann coupling of chloroarenes (ArCl), which works at low temperature in high yield, has been developed (<i>J. Am. Chem. Soc.</i> <b>2012</b>, <i>134</i>, 20250). In this work, the full catalytic cycle of this reaction has been investigated for ArCl, producing biphenyl on the Au/Pd alloy NCs by DFT calculations with the M06-L functional. Two possible reaction pathways are proposed, namely, (i) ArCl oxidative addition followed by Cl abstraction from the NC surface occurs twice stepwise and (ii) the successive oxidative addition of two ArCl proceeds before the Cl abstraction. Both of these pathways are energetically possible, and in the latter case, the Cl atoms stay on the NC surface. The exothermic reaction pathways were obtained for this multistep reaction scheme. The rate-determining step was shown to be hydrogen transfer from dimethylformamide (DMF), which is consistent with the experimental isotope effect observation. The proton shuttle mediated by water considerably reduces the activation barrier. The side reaction, which produces benzene via hydrogenation, is prohibited by the second ArCl oxidative addition. The present study has revealed the essential mechanism of the coupling reaction on supported Au/Pd NC catalysts, suggesting that the entire reaction is controlled by several factors including the surroundings and solvents. These findings provide useful insights for the further developments of efficient NC catalysts through designing the supports, interface, and reaction conditions