Unraveling the Electrocatalytic Activity in HMF Oxidation to FDCA by Fine-Tuning the Degree of NiOOH Phase Over Ni Nanoparticles Supported on Graphene Oxide.

The development of an efficient electrocatalyst for HMF oxidation to FDCA has been in the early stages. Herein, the NiNPs/GO-Ni-foam is fabricated as an electrocatalyst for FDCA production. However, the electrocatalytic performance of the untreated NiNPs/GO-Ni-foam is observed with moderate Faradaic efficiency (FE) (73.0%) and FDCA yield (80.2%). By electrochemically treating the NiNPs/GO-Ni-foam in an alkaline solution with positive potential at different treatment durations, the degree of NiOOH on metal surfaces is changed. The distinctive electrocatalytic activity obtained when using the different NiOOH degrees allows to understand the crucial impact of NiOOH species in HMF electrooxidation. Enhancing the portion of the NiOOH phase on the electrocatalyst surface improves electrocatalytic activity in terms of FE and FDCA yield up to 94.8±4.8% and 86.9±4.1%, respectively. Interestingly, as long as the NiOOH portion on the electrocatalyst surface is preserved or regenerated, the electrocatalyst performance can be intact even after several catalytic cycles. The theoretical study via density functional theory (DFT) also agrees with the experimental observations and confirms that the NiOOH phase facilitates the electrochemical transformation of HMF to FDCA through the HMFCA pathway, and the potential limiting step of the overall reaction is the oxidation of FFCA to FDCA.

Accelerated Synthesis of Nanolayered MWW Zeolite by Interzeolite Transformation.

Hierarchical zeolites can offer substantial benefits over bulk zeolites in catalysis. A drawback towards practical implementation is their lengthy synthesis, often requiring complex organic templates. This work describes an accelerated synthesis of nanolayered MWW zeolite based on the combination of interzeolite transformation (IZT) with a dual-templating strategy. FAU zeolite, hexamethyleneimine (HMI), and cetyltrimethylammonium bromide (CTAB) were respectively employed as Al source and primary zeolite, structure directing agent, and exfoliating agent. This approach allowed to reduce the synthesis of nanolayered MWW to 48 h, which is a considerable advance over the state of the art. Tracking structural, textural, morphological, and chemical properties during crystallization showed that 4-membered-ring (4MR) units derived from the FAU precursor are involved in the faster formation of MWW in comparison to a synthesis procedure from amorphous precursor. CTAB restricts the growth of the zeolite in the c-direction, resulting in nanolayered MWW. Moreover, we show that this approach can speed up the synthesis of nanolayered FER. The merits of nanolayered MWW zeolites are demonstrated in terms of improved catalytic performance in the Diels-Alder cycloaddition of 2,5-dimethylfuran and ethylene to p-xylene compared to bulk reference MWW sample.

Highly Enantioselective Synthesis of Pharmaceuticals at Chiral-Encoded Metal Surfaces.

Invited for the cover of this issue are the groups of Chularat Wattanakit and Alexander Kuhn at the Vidyasirimedhi Institute of Science and Technology and the University of Bordeaux. The two tunnels in the image illustrate the entrance into a porous heterogeneous catalyst for the stereoselective transformation of adrenalone into the desired epinephrine stereoisomer. Read the full text of the article at 10.1002/chem.202302054.

Highly Enantioselective Synthesis of Pharmaceuticals at Chiral-Encoded Metal Surfaces.

Enantioselective catalysis is of crucial importance in modern chemistry and pharmaceutical science. Although various concepts have been used for the development of enantioselective catalysts to obtain highly pure chiral compounds, most of them are based on homogeneous catalytic systems. Recently, we successfully developed nanostructured metal layers imprinted with chiral information, which were applied as electrocatalysts for the enantioselective synthesis of chiral model compounds. However, so far such materials have not been employed as heterogeneous catalysts for the enantioselective synthesis of real pharmaceutical products. In this contribution, we report the asymmetric synthesis of chiral pharmaceuticals (CPs) with chiral imprinted Pt-Ir surfaces as a simple hydrogenation catalyst. By fine-tuning the experimental parameters, a very high enantioselectivity (up to 95 % enantiomeric excess) with good catalyst stability can be achieved. The designed materials were also successfully used as catalytically active stationary phases for the continuous asymmetric flow synthesis of pharmaceutical compounds. This illustrates the possibility of producing real chiral pharmaceuticals at such nanostructured metal surfaces for the first time.

Density Functional Investigation of the Conversion of Furfural to Furfuryl Alcohol by Reaction with i-Propanol over UiO-66 Metal-Organic Framework.

Carbonyl C═O bond reduction via catalytic transfer hydrogenation (CTH) is one of the essential processes for biomass conversion to valuable chemicals and fuels. Here, we investigate the CTH of furfural to furfuryl alcohol with i-propanol on UiO-66 metal-organic frameworks using density functional theory calculations and linear scaling relations. Initially, the reaction over two defect sites presented on Zr-UiO-66, namely, dehydrated and hydrated sites, have been compared. The hydrated active site is favored over that on the dehydrated active site since the activation free energy of the rate-determining reaction step occurring on the hydrated active site is lower than that occurring on the dehydrated active site (14.9 vs 17.9 kcal/mol). The catalytic effect of exchanged tetravalent metals (Hf and Ti) on Zr-UiO-66 is also considered. We found that Hf-UiO-66 (13.5 kcal/mol) provides a lower activation energy than Zr-UiO-66 (14.9 kcal/mol) and Ti-UiO-66 (19.4 kcal/mol), which corresponds to it having a higher Lewis acidity. The organic linkers of UiO-66 MOFs play a role in stabilizing all of the species on potential energy surfaces. The linear scaling relationship also reveals the significant role of the UiO-66 active site in activating the carbonyl C═O of furfural, and strong relationships are observed between the activation free energy, the charge of the metal at the MOF active sites, and the complexation energies in reaction coordinates.

Effects of single and double active sites of Cu oxide clusters over the MFI zeolite for direct conversion of methane to methanol: DFT calculations.

In this work, we investigate the effect of various species of Cu oxide clusters including single and double active sites incorporated in the MFI zeolite framework for the direct conversion of methane to methanol. An M06-2X density functional calculation is employed to fine-tune the suitable number and species of active sites and to provide insights into the effect of the active sites on the reaction mechanism of methane to methanol. Two models, single and double active sites of Cu oxide clusters, have been chosen, in which the single active site of Cu oxide clusters, (mono(µ-oxo)dicopper(ii)), is located at the Al1'-Al12' pair ([Cu(µ-O)Cu]2+@Al1'-Al12'/MFI) or at the Al6-Al7 pair ([Cu(µ-O)Cu]2+@Al6-Al7/MFI) in the MFI framework. For the double active sites of Cu oxide clusters, two species of double active sites of Cu oxide are considered. The first one is the double active site of mono(µ-oxo)dicopper(ii) containingtwo Al-Al pairs (Al1'-Al12' and Al6-Al7 pairs) in the MFI framework (2[Cu(µ-O)Cu]2+/MFI) and the other is the double active site of trans-µ-1,2-peroxo dicopper(ii), which occupies two Al-Al pairs (Al1'-Al12' and Al6-Al7 pairs) in the MFI framework (2[Cu(µ-1,2-peroxo)Cu]2+/MFI). Furthermore, the activation energy for C-H bond dissociation in direct methane conversion to methanol is considered. Compared with the single active site of [Cu(µ-O)Cu]2+/MFI, the double active sites, in particular (2[Cu(µ-O)Cu]2+/MFI), exhibited the lowest activation energy, approximately 12.5 kcal mol-1. The high charge transfer between activated methane and Cu oxide active sites and also the high negative partial charge at the bridging oxygen of Cu oxide active sites, which directly interact with the methane molecule and abstracts its H atom, are considered as the important factors which affect the catalytic activity of Cu oxide clusters for direct methane conversion to methanol. These findings strongly support that the number and species of Cu oxide active sites incorporated in the MFI framework can highly affect the reaction mechanism of methane to methanol.

Encoding Chiral Molecular Information in Metal Structures.

The concept of encoding molecular information in bulk metals has been proposed over the past decade. The structure of various types of molecules, including enantiomers, can be imprinted in achiral substrates. Typically, to encode metals with chiral information, several approaches, based on chemical and electrochemical concepts, can be used. In this Minireview, recent achievements with respect to the development of such materials are discussed, including the entrapment of chiral biomolecules in metals, the chiral imprinting of metals, as well as the combination of imprinting with nanostructuring. The features and potential applications of these designer materials, such as chirooptical properties, enantioselective adsorption and separation, as well as their use for asymmetric synthesis will be presented. This will illustrate that the development of molecularly encoded metal structures opens up very interesting perspectives, especially in the frame of chiral technologies.

Synthesis, Characterization, and Electrochemical Applications of Chiral Imprinted Mesoporous Ni Surfaces.

The enantioselective synthesis of chiral compounds is of crucial importance for a wide range of potential applications, especially in cosmetic and pharmaceutical industries. Recently, chiral imprinted mesoporous platinum films, produced by the electrodeposition of the metal, in the simultaneous presence of a lyotropic liquid crystalline phase of nonionic surfactants as mesoporogens and chiral templates, have been applied as electrocatalysts and selective stationary phases for the asymmetric synthesis and separation of chiral compounds, respectively. However, platinum is an expensive metal, and therefore it is mandatory to explore the possibility to apply this concept also to other metals. In this contribution, we propose mesoporous chiral imprinted nickel as an alternative cheap and earth-abundant metal. The designed surface layers not only demonstrate electrochemical discrimination between two enantiomers, but most importantly also allow stereospecific electroreduction of a prochiral compound, with very significant enantioselectivity of up to 80% ee. These results open up very promising perspectives for the development of low-cost non-noble-metal matrices for the synthesis of chiral compounds.

Nanocavity effects of various zeolite frameworks on n-pentane cracking to light olefins: combination studies of DFT calculations and experiments.

Better control of the product selectivity of light olefins (e.g., ethylene and propylene) obtained from the n-pentane catalytic cracking process has attracted considerable attention from both scientific and petrochemical industrial points of view. In this context, we report insights into the effects of the nanocavities of various zeolite frameworks, including H-FER, H-ZSM-5, and H-FAU, representing small, medium, and large cavities, on the reaction mechanism of n-pentane cracking to light olefins by using M06-2X/6-31G(d,p) density functional calculations, eventually leading to fine-tuning the product distribution of light olefins. The reaction mechanism consists of the following two main steps: (i) the protolytic cracking of n-pentane to form a pentonium intermediate; and (ii) the subsequent dissociation of the intermediate to either ethane-propylene or ethylene-propane. The key reaction pathways controlling the product distribution of light olefins relate to the dissociation of the pentonium intermediate, which can produce selectively either propylene (P) or ethylene (E), resulting in a controllable P/E ratio. The differences in the activation energies for ethylene production compared with those of propylene production over H-FER, H-ZSM-5, and H-FAU are 6.7, 5.0, and 0.5 kcal mol-1, respectively. Compared with H-ZSM-5 and H-FAU, the higher difference in the activation energy of these two pathways over H-FER implies that the preferable production of ethane-propylene compared with ethylene-propane is more pronounced. It is therefore reasonable to conclude that a smaller pore zeolite such as H-FER eventually leads to a high ratio of production of propylene to ethylene, in accordance with experimental observations.

Insights into the reaction mechanism of n-hexane dehydroaromatization to benzene over gallium embedded HZSM-5: effect of H2 incorporated on active sites.

The catalytic dehydroaromatization of alkanes to aromatics has attracted considerable attention from the scientific community, because it can be used for the upgrading of low-cost alkanes into high added-value aromatics, such as benzene, toluene, and xylene (BTX). In this context, we report the reaction mechanism of n-hexane dehydroaromatization to benzene over two different reduced gallium species embedded in HZSM-5, including univalent Ga+ embedded in HZSM-5 (Ga/HZSM-5) and dihydrido gallium complex (GaH2+) embedded in HZSM-5 (GaH2/HZSM-5) by using the M06-2X/6-31G(d,p) level of calculation. The reaction proceeds by following two main steps: (i) the dehydrogenation of hexane to haxa-1,3,5-triene; (ii) the dehydroaromatization of haxa-1,3,5-triene to benzene. For the univalent Ga+ embedded in HZSM-5, the first step of the hexane dehydrogenation is considered to be the rate-determining step, which requires a high activation energy of 76.6 kcal mol-1. In strong contrast to this, in the case of the GaH2/HZSM-5 catalyst the rate determining step is found to be the second hydrogen abstraction from n-hexane with a lower activation barrier of 11.1 kcal mol-1. The reaction is therefore preferentially taking place over the GaH2/HZSM-5 catalyst. These observations clearly confirm the existence of a dihydrido gallium complex (GaH2+) as one of the most active species for the dehydroaromatization of alkanes and it is obtained in the presence of hydrogen in the catalytic system. This example opens up perspectives for a better understanding of the effect of active species on the catalytic reaction.

Potential-Induced Fine-Tuning of the Enantioaffinity of Chiral Metal Phases.

Concepts leading to single enantiomers of chiral molecules are of crucial importance for many applications, including pharmacology and biotechnology. Recently, mesoporous metal phases encoded with chiral information have been developed. Fine-tuning of the enantioaffinity of such structures by imposing an electric potential is proposed, which can influence the electrostatic interactions between the chiral metal and the target enantiomer. This allows the binding affinity between the chiral metal and the target enantiomer to be increased, and thus, the discrimination between two enantiomers to be improved. The concept is illustrated by generating chiral encoded metals in a microfluidic channel by reduction of a platinum salt in the presence of a liquid crystal and l-tryptophan as a chiral model template. After removal of the template molecules, the modified microchannel retains a pronounced chiral character. The chiral recognition efficiency of the microchannel can be fine-tuned by applying a suitable potential to the metal phase. This enables the separation of both components of a racemate flowing through the channel. The approach constitutes a promising and complementary strategy in the frame of chiral discrimination technologies.

Furfural to Furfuryl Alcohol: Computational Study of the Hydrogen Transfer on Lewis Acidic BEA Zeolites and Effects of Cation Exchange and Tetravalent Metal Substitution.

The hydrogen transfer of furfural to furfuryl alcohol with i-propanol as the hydrogen source over cation-exchanged Lewis acidic BEA zeolite has been investigated by means of density functional calculations. The reaction proceeds in three steps. First the O-H bond of i-propanol is broken to form a propoxide intermediate. After that, the furylmethoxy intermediate is formed via hydrogen transfer process, and finally furylmethoxy abstracts the proton to form the furfuryl alcohol product. The second step is rate-determining by requiring the highest activation energy (23.8 kcal/mol) if the reaction takes place on Li-Sn-BEA zeolite. We find that the catalytic activity of various cation-exchanged Sn-BEA zeolites is in the order Li-Sn-BEA > Na-Sn-BEA > K-Sn-BEA. The lower activation energy for Li-Sn-BEA compared to Na-Sn-BEA and K-Sn-BEA can be explained by the larger charge transfer from the carbonyl bond to the catalyst, leading to its activation and to the attraction of the hydrogen being transferred. The larger charge transfer in turn is due to the smaller gap between the energies of furfural HOMO and the zeolite LUMO in Li-Sn-BEA, compared to both Na-Sn-BEA and K-Sn-BEA. In a similar way, we also compare the catalytic activity of tetravalent metal centers (Sn, Zr, and Hf) substituted into BEA and find in the order Zr ≥ Hf > Sn, based on activation energies. Finally we investigate statistically which property of the reactants is a suitable descriptor for an approximative prediction of the reaction rate in order to be able to quickly screen promising catalytic materials for this reaction.

Enantioselective recognition, synthesis, and separation of pharmaceutical compounds at chiral metallic surfaces.

The development of new pharmaceutical compounds is challenging because most of them are based on enantiopure chiral molecules, which exhibit unique properties for therapy. However, the synthesis of pharmaceutical compounds in the absence of a chiral environment naturally leads to a racemic mixture. Thus, to control their synthesis, an asymmetric environment is required, and chiral homogeneous catalysts are typically used to synthesize enantiopure pharmaceutical compounds (EPC). Nevertheless, homogeneous catalysts are difficult to recover after the reaction, generating additional problems and costs in practical processes. Thus, the development of chiral heterogeneous catalysts is a timely topic. In a more general context, such chiral materials cannot only be used for synthesis, but also to recognize and separate enantiomers. In the frame of these different challenges, we give in this review a short introduction to strategies to extrinsically and intrinsically modify heterogeneous metal matrixes for the enantioselective synthesis, recognition, and separation of chiral pharmaceutical compounds.

Transformation of CO2 to Carbon Nanotubes by Catalytic Chemical Vapor Deposition using a Metal-Supported Hierarchical Zeolite Template.

The conversion of CO2 into valuable substances is a topic of great interest in current research. Carbon nanotubes (CNT) have emerged as highly promising materials for CO2 conversion. In this study, we successfully developed a catalyst by loading active transition metals (Fe or Ni) onto hierarchical zeolite for CNT synthesis. Our catalyst demonstrated excellent performance under synthetic conditions. The most favorable CNT was obtained using the 25 wt.% FeHieFAU catalyst, which exhibited a diameter size of 23.1 nm, a CNT yield of 15.4 %, and an ID /IG ratio of 0.56, indicating high quality. Additionally, we investigated the beneficial effects of the synthesized CNT by testing their current response. Notably, the current response of the synthesized CNT surpassed that of commercial CNT when using a 0.5 M H2 SO4 supporting electrolyte and cyclic voltammetry (V vs. Ag/AgCl). These findings highlight the significant contributions of the small diameter and superior quality of our synthesized pure CNT, which offer potential improvements in current response compared to commercial CNT. This research opens new avenues for utilizing CNT in CO2 conversion and electrochemical applications.

Rational Design of Fe Single Sites Supported on Hierarchical Zeolites via Atomic Layer Deposition for Few-Walled Carbon Nanotube Production.

Metal single-site catalysts have recently played an essential role in catalysis due to their enhanced activity, selectivity, and precise reaction control compared to those of conventional metal cluster catalysts. However, the rational design and catalytic application of metal single-site catalysts are still in the early stages of development. In this contribution, we report the rational design of Fe single sites incorporated in a hierarchical ZSM-5 via atomic layer deposition (ALD). The designer catalysts demonstrated highly dispersed Fe species, predominantly stabilized by oxygen atoms in the zeolite framework at terminal, isolated, and vicinal silanol groups within the micropores and external surfaces of the zeolite. The successful incorporation of highly thermally stable and uniform Fe single sites into hierarchical zeolite through ALD represents a significant advancement in few-walled carbon nanotube production. The inner and outer diameters of produced CNTs are approximately 4.4 ± 2.4 and 8.6 ± 1.8 nm, respectively, notably smaller than those produced via traditional impregnated catalysts. This example emphasizes the concept of rational design of a single Fe site dispersed on a hierarchical ZSM-5 surface, which is anticipated to be a promising catalyst for advancing catalytic applications.

Nanocrystalline BEA-CNT Composites with High Metal Dispersion Obtained via Inter-Zeolite Transformation for Antibacterial Application.

The rational design of interface materials containing carbon nanotubes (CNTs) and zeolites (zeolite-CNTs) is a promising perspective in chemical and biochemical communities because they exhibit several outstanding properties such as tunable hydrophobicity-hydrophilicity at interfaces. In this contribution, we report the fabrication of Ag-incorporated nanocrystalline BEA-carbon nanotube (CNT) composites via the one-pot inter-zeolite transformation of the micron-sized FAU-CNT composite in the presence of a Ag precursor. By varying the crystallization time, the inter-zeolite transformation mechanism was explored. Indeed, this process involves an amorphous intermediate of aluminosilicate species with a significant change of the crystal morphology in the presence of CNTs in the synthesis gel. Interestingly, the redispersion of metal particles was observed after the inter-zeolite transformation process, resulting in the high dispersion of metal nanoparticles over BEA nanocrystals. Notably, it was revealed that the Ag sites were also stabilized in the presence of CNT interfaces, leading to the availability of highly active Ag+ ions. To illustrate the beneficial aspect of designer materials, the synthesized Ag-incorporated BEA-CNT composites exhibited high antibacterial activity againstEscherichia coli due to the synergistic effect of the active Ag+ species and appropriate hydrophobic and hydrophilic properties of the hybrid material interfaces. This first example opens up perspectives of the rational design of zeolite-CNT interfaces with high metal dispersion via the inter-zeolite transformation approach for biomedical applications.

Mild Hydrogenation of 2-Furoic Acid by Pt Nanoparticles Dispersed in a Hierarchical ZSM-5 Zeolite.

Hydrogenation of biobased compounds can add value to platform molecules obtained from biomass refining. Herein, we explore the hydrogenation of 2-furoic acid (2-furancarboxylic acid, FCA), a derivative of furfural, with H2 generated in situ by NaBH4 hydrolysis at ambient conditions. Nearly complete conversion of FCA was obtained with tetrahydrofuroic acid (THFA) and 5-hydroxyvaleric acid (5-HVA) as the only two reaction products over Pt nanoparticles supported on hierarchical ZSM-5. Small Pt nanoparticles (2 to 3 nm) were stabilized by ZSM-5 nanosheets. At an optimized Pt loading, the Pt nanoparticles can catalyze the hydrolysis of NaBH4 and the subsequent hydrogenation of FCA with the assistance of Brønsted acid sites. Nanostructuring ZSM-5 into nanosheets and its acidity contributes to the stability of the dispersed Pt nanoparticles. Deactivation due to NaBO2 deposition on the Pt particles can be countered by a simple washing treatment. Overall, this approach shows the promise of mild hydrogenation of biobased feedstock coupled with NaBH4 hydrolysis.

Enantioselective resolution of two model amino acids using inherently chiral oligomer films with uncorrelated molecular structures.

Preferential crystallization induced by chiral surfaces is an interesting alternative to isolate enantiopure antipodes. Herein, we take advantage of the outstanding enantiorecognition capabilities of inherently chiral oligomers to induce an enantioselective crystallization process. We exemplify this strategy with two amino acid model molecules, asparagine and glutamic acid, having a completely uncorrelated structure with respect to the template. This illustrates the versatility of the approach with potential applications in the resolution of pharmaceutical compounds.

Self-assembled monolayer protection of chiral-imprinted mesoporous platinum electrodes for highly enantioselective synthesis.

In modern chemistry, chiral (electro)catalysis is a powerful strategy to produce enantiomerically pure compounds (EPC). However, it still struggles with uncontrollable stereochemistry due to side reactions, eventually producing a racemic mixture. To overcome this important challenge, a well-controlled design of chiral catalyst materials is mandatory to produce enantiomers with acceptable purity. In this context, we propose the synergetic combination of two strategies, namely the elaboration of mesoporous Pt films, imprinted with chiral recognition sites, together with the spatially controlled formation of a self-assembled monolayer. Chiral imprinted metals have been previously suggested as electrode materials for enantioselective recognition, separation and synthesis. However, the outermost surface of such electrodes is lacking chiral information and thus leads to unspecific reactions. Functionalising selectively this part of the electrode with a monolayer of organosulfur ligands allows an almost total suppression of undesired side reactions and thus leads to a boost of enantiomeric excess to values of over 90% when using these surfaces in the frame of enantioselective electrosynthesis. In addition, this strategy also decreases the total reaction time by one order of magnitude. The study therefore opens up promising perspectives for the development of heterogeneous enantioselective electrocatalysis strategies.

Bifunctional Pt/Au Janus electrocatalysts for simultaneous oxidation/reduction of furfural with bipolar electrochemistry.

The sustainable conversion of biomass-derived compounds into high added-value products is a very important contemporary scientific challenge. In this context, we report here the simultaneous electro-oxidation/-reduction of a biomass-derived compound in a one-pot approach using bipolar electrochemistry. Bifunctional Pt/Au Janus electrocatalysts are employed for a selective conversion of furfural into both, furfuryl alcohol and furoic acid, which can't be achieved when using non-Janus particles. The results emphasize the benefits of bipolar electrochemistry in the frame of electrosynthesis processes.