Stabilization of the Active Ruthenium Oxycarbonate Phase for Low-Temperature CO2 Methanation

Interstitial carbon-doped RuO2 catalyst with the newly reported ruthenium oxycarbonate phase is a key component for low-temperature CO2 methanation. However, a crucial factor is the stability of interstitial carbon atoms, which can cause catalyst deactivation when removed during the reaction. In this work, the stabilization mechanism of the ruthenium oxycarbonate active phase under reaction conditions is studied by combining advanced operando spectroscopic tools with catalytic studies. Three sequential processes: carbon diffusion, metal oxide reduction, and decomposition of the oxycarbonate phase and their influence by the reaction conditions, are discussed. We present how the reaction variables and catalyst composition can promote carbon diffusion, stabilizing the oxycarbonate catalytically active phase under steady-state reaction conditions and maintaining catalyst activity and stability over long operation times. In addition, insights into the reaction mechanism and a detailed analysis of the catalyst composition that identifies an adequate balance between the two phases, i.e., ruthenium oxycarbonate and ruthenium metal, are provided to ensure an optimum catalytic behavior.

One-Pot Synthesis of CHA/ERI-Type Zeolite Intergrowth from a Single Multiselective Organic Structure-Directing Agent

We report the one-pot synthesis of a chabazite (CHA)/erionite (ERI)-type zeolite intergrowth structure characterized by adjustable extents of intergrowth enrichment and Si/Al molar ratios. This method utilizes readily synthesizable 6-azaspiro[5.6]dodecan-6-ium as the exclusive organic structure-directing agent (OSDA) within a potassium-dominant environment. High-throughput simulations were used to accurately determine the templating energy and molecular shape, facilitating the selection of an optimally biselective OSDA from among thousands of prospective candidates. The coexistence of the crystal phases, forming a distinct structure comprising disk-like CHA regions bridged by ERI-rich pillars, was corroborated via rigorous powder X-ray diffraction and integrated differential-phase contrast scanning transmission electron microscopy (iDPC S/TEM) analyses. iDPC S/TEM imaging further revealed the presence of single offretite layers dispersed within the ERI phase. The ratio of crystal phases between CHA and ERI in this type of intergrowth could be varied systematically by changing both the OSDA/Si and K/Si ratios. Two intergrown zeolite samples with different Si/Al molar ratios were tested for the selective catalytic reduction (SCR) of NOx with NH3, showing competitive catalytic performance and hydrothermal stability compared to that of the industry-standard commercial NH3-SCR catalyst, Cu-SSZ-13, prevalent in automotive applications. Collectively, this work underscores the potential of our approach for the synthesis and optimization of adjustable intergrown zeolite structures, offering competitive alternatives for key industrial processes.

An alternative catalytic cycle for selective methane oxidation to methanol with Cu clusters in zeolites

The partial oxidation of methane to methanol catalyzed by Cu-exchanged zeolites involves at present a three-step procedure that requires changing reaction conditions along the catalytic cycle. In this work we present an alternative catalytic cycle for selective methane conversion to methanol using as active species small Cu5 clusters supported on CHA zeolite. Periodic DFT calculations show that molecular O2 is easily activated on Cu5 clusters producing bi-coordinated O atoms able to dissociate homolytically a CH bond from CH4 and to react with the radical-like non-adsorbed methyl intermediate formed producing methanol, while competitive overoxidation to CO2 is energetically disfavored. The present mechanistic study opens a new avenue to design catalytic materials based on their ability to stabilize radical species.

Noble-Metal-Free Carbon Encapsulated CoNi Alloy Catalyst for the Hydrogenation of 5-(Hydroxymethyl) Furfural to Tetrahydrofurandiol in Aqueous Media

The selective hydrogenation of 5-(hydroxymethyl)furfural (HMF) into 2,5-bis-(hydroxymethyl)tetrahydrofuran (BHMTHF) in flow reactor using water as a green solvent, has been achieved on a non-noble metal catalyst based on monodispersed CoNi alloy nanoparticles covered by a thin carbon layer. The alloyed catalyst containing CoNi (molar ratio 1 : 1) was prepared in a one-step synthesis following a hydrothermal method. Total conversion of HMF with 91 % selectivity to BHMTHF was achieved. The reaction network has been stablished, in which the carbonyl group of HMF is first reduced to alcohol giving the 2,5-bis-(hydroxymethyl)furan (BHMF) with an apparent activation energy of 25 KJ/mol, and then the double bonds of the furan ring are hydrogenated (apparent Ea=31 KJ/mol). Formation of byproducts, mainly proceed from furan ring opening and ring rearrangement processes of BHMF, promoted by water. BHMTHF resulted a compound highly stable under reaction conditions. The fixed bed flow reactor was maintained operational for 65 h without observing any loss of catalytic activity and selectivity.

Encapsulation of Palladium Carbide Subnanometric Species in Zeolite Boosts Highly Selective Semihydrogenation of Alkynes

The selective hydrogenation of alkynes to alkenes is a crucial step in the synthesis of fine chemicals. However, the widely utilized palladium (Pd)-based catalysts often suffer from poor selectivity. In this work, we demonstrate a carbonization-reduction method to create palladium carbide subnanometric species within pure silicate MFI zeolite. The carbon species can modify the electronic and steric characteristics of Pd species by forming the predominant Pd-C4 structure and, meanwhile, facilitate the desorption of alkenes by forming the Si-O-C structure with zeolite framework, as validated by the state-of-the-art characterizations and theoretical calculations. The developed catalyst shows superior performance in the selective hydrogenation of alkynes over mild conditions (298 K, 2 bar H2 ), with 99 % selectivity to styrene at a complete conversion of phenylacetylene. In contrast, the zeolite-encapsulated carbon-free Pd catalyst and the commercial Lindlar catalyst show only 15 % and 14 % selectivity to styrene, respectively, under identical reaction conditions. The zeolite-confined Pd-carbide subnanoclusters promise their superior properties in semihydrogenation of alkynes.

Low-temperature hydroformylation of ethylene by phosphorous stabilized Rh sites in a one-pot synthesized Rh-(O)-P-MFI zeolite

Zeolites containing Rh single sites stabilized by phosphorous were prepared through a one-pot synthesis method and are shown to have superior activity and selectivity for ethylene hydroformylation at low temperature (50 °C). Catalytic activity is ascribed to confined Rh2O3 clusters in the zeolite which evolve under reaction conditions into single Rh3+ sites. These Rh3+ sites are effectively stabilized in a Rh-(O)-P structure by using tetraethylphosphonium hydroxide as a template, which generates in situ phosphate species after H2 activation. In contrast to Rh2O3, confined Rh0 clusters appear less active in propanal production and ultimately transform into Rh(I)(CO)2 under similar reaction conditions. As a result, we show that it is possible to reduce the temperature of ethylene hydroformylation with a solid catalyst down to 50 °C, with good activity and high selectivity, by controlling the electronic and morphological properties of Rh species and the reaction conditions.

Synergic Effect of Isolated Ce3+ and Ptδ+ Species in UiO-66(Ce) for Heterogeneous Catalysis

In this work, we have synthesized through an efficient electrostatic deposition a Pt single-atom catalyst (SAC) supported on a Ce-MOF. The basic solution employed in the impregnation process favors the deprotonation of the hydroxyl groups allocated on the clusters that can easily interact with the cationic Pt species. The resulting material, denoted as Pt/UiO-66(Ce), shows an increment of Ce³⁺ content, as demonstrated by UV-vis and Ce L₃-edge XANES spectroscopy. These Ce³⁺ species and their corresponding oxygen vacancies are able to accommodate very disperse Pt single sites. Moreover, Pt L₃-edge XANES and CO-FTIR spectroscopy confirm the cationic nature of the supported Pt^δ+ (2+ < δ < 4+). For comparison purpose, we have synthesized and characterized a well-known Pt single-site catalyst supported on nanocrystalline ceria, denoted as Pt/nCeO₂. Since the simultaneous presence of Ce³⁺ and Pt^δ+ on the MOF clusters were able to activate the oxygen molecules and the CO molecule, respectively, we tested Pt/UiO-66(Ce) for the CO oxidation reaction. Interestingly, this catalyst showed ∼six-fold increment in activity in comparison with the traditional Pt/nCeO₂ material. Finally, the characterization after catalysis reveals that the Pt nature is preserved and that the activity is maintained during 14 h at 100 °C without any evidence of deactivation.

Approaching enzymatic catalysis with zeolites or how to select one reaction mechanism competing with others

Approaching the level of molecular recognition of enzymes with solid catalysts is a challenging goal, achieved in this work for the competing transalkylation and disproportionation of diethylbenzene catalyzed by acid zeolites. The key diaryl intermediates for the two competing reactions only differ in the number of ethyl substituents in the aromatic rings, and therefore finding a selective zeolite able to recognize this subtle difference requires an accurate balance of the stabilization of reaction intermediates and transition states inside the zeolite microporous voids. In this work we present a computational methodology that, by combining a fast high-throughput screeening of all zeolite structures able to stabilize the key intermediates with a more computationally demanding mechanistic study only on the most promising candidates, guides the selection of the zeolite structures to be synthesized. The methodology presented is validated experimentally and allows to go beyond the conventional criteria of zeolite shape-selectivity.

Low-oxidation-state Ru sites stabilized in carbon-doped RuO2 with low-temperature CO2 activation to yield methane

The generation of methane fuel using surplus renewable energy with CO₂ as the carbon source enables both the decarbonization and substitution of fossil fuel feedstocks. However, high temperatures are usually required for the efficient activation of CO₂. Here we present a solid catalyst synthesized using a mild, green hydrothermal synthesis that involves interstitial carbon doped into ruthenium oxide, which enables the stabilization of Ru cations in a low oxidation state and a ruthenium oxycarbonate phase to form. The catalyst shows an activity and selectivity for the conversion of CO₂ into methane at lower temperatures than those of conventional catalysts, with an excellent long-term stability. Furthermore, this catalyst is able to operate under intermittent power supply conditions, which couples very well with electricity production systems based on renewable energies. The structure of the catalyst and the nature of the ruthenium species were acutely characterized by combining advanced imaging and spectroscopic tools at the macro and atomic scales, which highlighted the low-oxidation-state Ru sites (Ruⁿ⁺, 0 < n < 4) as responsible for the high catalytic activity. This catalyst suggests alternative perspectives for materials design using interstitial dopants.

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

Heterogeneous bimetallic catalysts have broad applications in industrial processes, but achieving a fundamental understanding on the nature of the active sites in bimetallic catalysts at the atomic and molecular level is very challenging due to the structural complexity of the bimetallic catalysts. Comparing the structural features and the catalytic performances of different bimetallic entities will favor the formation of a unified understanding of the structure-reactivity relationships in heterogeneous bimetallic catalysts and thereby facilitate the upgrading of the current bimetallic catalysts. In this review, we will discuss the geometric and electronic structures of three representative types of bimetallic catalysts (bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles) and then summarize the synthesis methodologies and characterization techniques for different bimetallic entities, with emphasis on the recent progress made in the past decade. The catalytic applications of supported bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles for a series of important reactions are discussed. Finally, we will discuss the future research directions of catalysis based on supported bimetallic catalysts and, more generally, the prospective developments of heterogeneous catalysis in both fundamental research and practical applications.

Advanced zeolite and ordered mesoporous silica-based catalysts for the conversion of CO2 to chemicals and fuels

For many years, capturing, storing or sequestering CO₂ from concentrated emission sources or from air has been a powerful technique for reducing atmospheric CO₂. Moreover, the use of CO₂ as a C1 building block to mitigate CO₂ emissions and, at the same time, produce sustainable chemicals or fuels is a challenging and promising alternative to meet global demand for chemicals and energy. Hence, the chemical incorporation and conversion of CO₂ into valuable chemicals has received much attention in the last decade, since CO₂ is an abundant, inexpensive, nontoxic, nonflammable, and renewable one-carbon building block. Nevertheless, CO₂ is the most oxidized form of carbon, thermodynamically the most stable form and kinetically inert. Consequently, the chemical conversion of CO₂ requires highly reactive, rich-energy substrates, highly stable products to be formed or harder reaction conditions. The use of catalysts constitutes an important tool in the development of sustainable chemistry, since catalysts increase the rate of the reaction without modifying the overall standard Gibbs energy in the reaction. Therefore, special attention has been paid to catalysis, and in particular to heterogeneous catalysis because of its environmentally friendly and recyclable nature attributed to simple separation and recovery, as well as its applicability to continuous reactor operations. Focusing on heterogeneous catalysts, we decided to center on zeolite and ordered mesoporous materials due to their high thermal and chemical stability and versatility, which make them good candidates for the design and development of catalysts for CO₂ conversion. In the present review, we analyze the state of the art in the last 25 years and the potential opportunities for using zeolite and OMS (ordered mesoporous silica) based materials to convert CO₂ into valuable chemicals essential for our daily lives and fuels, and to pave the way towards reducing carbon footprint. In this review, we have compiled, to the best of our knowledge, the different reactions involving catalysts based on zeolites and OMS to convert CO₂ into cyclic and dialkyl carbonates, acyclic carbamates, 2-oxazolidones, carboxylic acids, methanol, dimethylether, methane, higher alcohols (C₂₊OH), C₂₊ (gasoline, olefins and aromatics), syngas (RWGS, dry reforming of methane and alcohols), olefins (oxidative dehydrogenation of alkanes) and simple fuels by photoreduction. The use of advanced zeolite and OMS-based materials, and the development of new processes and technologies should provide a new impulse to boost the conversion of CO₂ into chemicals and fuels.

Influence of the zeolite support on the catalytic properties of confined metal clusters: a periodic DFT study of O2 dissociation on Cun clusters in CHA

The catalytic properties of sub-nanometer Cu_n clusters are modified by interactions with inorganic supports used for their stabilization. In this work, the reactivity towards O₂ dissociation of Cu₅ and Cu₇ clusters confined within the cavities of the CHA zeolite is theoretically investigated by means of periodic DFT calculations. Increasing the Al content in the zeolite framework not only modifies the cluster morphology, but also leads to a decrease in the electronic density available on the supported Cu_n clusters, which in turn leads to higher activation energies for O₂ dissociation. Together with the cluster size and shape, the Si/Al ratio in the zeolite support appears as a potential parameter to finely tune the stability and oxidation properties of Cu-based catalysts.

Enzymatic and chemo-enzymatic strategies to produce highly valuable chiral amines from biomass with ω-transaminases on 2D zeolites

Amino transaminases (ATAs) have been supported on a 2D ITQ-2 zeolite through electrostatic interactions, resulting in a highly stable active biocatalyst to obtain a variety of valuable chiral amines starting from prochiral ketones derived from biomass. We have extended the biocatalyst applications by designing a chemo-enzymatic process that allows, as the first step, prochiral ketones to be obtained from biomass-derived compounds through an aldol condensation–reduction step using a bifunctional metal/base catalyst. The prochiral ketone is subsequently converted into the chiral amine using the immobilized ATA. We show that it is feasible to couple both steps in a semi-continuous process to produce industrially relevant chiral amines with yields of >95% and ∼100% enantiomer excess.

Sub-nanometer Copper Clusters as Alternative Catalysts for the Selective Oxidation of Methane to Methanol with Molecular O2

The partial oxidation of methane to methanol with molecular O₂ at mild reaction conditions is a challenging process, which is efficiently catalyzed in nature by enzymes. As an alternative to the extensively studied Cu-exchanged zeolites, small copper clusters composed by just a few atoms appear as potential specific catalysts for this transformation. Following previous work in our group that established that the reactivity of oxygen atoms adsorbed on copper clusters is closely linked to cluster size and morphology, we explore by means of DFT calculations the ability of bidimensional (2D) and three-dimensional (3D) Cu₅ and Cu₇ clusters to oxidize partially methane to methanol. A highly selective Eley-Rideal pathway involving homolytic C-H bond dissociation and a non-adsorbed radical-like methyl intermediate is favored when bicoordinated oxygen atoms, preferentially stabilized at the edges of 2D clusters, are available. Cluster morphology arises as a key parameter determining the nature and reactivity of adsorbed oxygen atoms, opening the possibility to design efficient catalysts for partial methane oxidation based on copper clusters.

Tunable CHA/AEI Zeolite Intergrowths with A Priori Biselective Organic Structure-Directing Agents: Controlling Enrichment and Implications for Selective Catalytic Reduction of NOx

A novel ab initio methodology based on high‐throughput simulations has permitted designing unique biselective organic structure‐directing agents (OSDAs) that allow the efficient synthesis of CHA/AEI zeolite intergrowth materials with controlled phase compositions. Distinctive local crystallographic ordering of the CHA/AEI intergrowths was revealed at the nanoscale level using integrated differential phase contrast scanning transmission electron microscopy (iDPC STEM). These novel CHA/AEI materials have been tested for the selective catalytic reduction (SCR) of NOx, presenting an outstanding catalytic performance and hydrothermal stability, even surpassing the performance of the well‐established commercial CHA‐type catalyst. This methodology opens the possibility for synthetizing new zeolite intergrowths with more complex structures and unique catalytic properties.

Synthetic Routes for Designing Furanic and Non Furanic Biobased Surfactants from 5-Hydroxymethylfurfural

5-hydroxymethylfurfural (HMF) is one of the most valuable biomass platform molecules, enabling the construction of a plethora of high value-added furanic compounds. In particular, in the last decade, HMF has been considered as a starting material for designing biobased surfactants, not only because of its renewability and carbon footprint, but also because of its enhanced biodegradability. This Review presents recent examples of the different approaches to link the hydrophilic and lipophilic moieties into the hydrophobic furan (and tetrahydrofuran) ring, giving a variety of biobased surfactants that have been classified here according to the charge of the head polar group. Moreover, strategies for the synthesis of different non-furanic structures surfactant molecules (such as levulinic acid, cyclopentanols, and aromatics) derived from HMF are described. The new HMF-based amphiphilic molecules presented here cover a wide range of hydrophilic-lipophilic balance values and have suitable surfactant properties such as surface tension activity and critical micelle concentration, to be an important alternative for the replacement of non-sustainable surfactants.

Selective Conversion of HMF into 3-Hydroxymethylcyclopentylamine through a One-Pot Cascade Process in Aqueous Phase over Bimetallic NiCo Nanoparticles as Catalyst

5-hydroxymethylfurfural (HMF) has been successfully valorized into 3-hydroxymethylcyclopentylamine through a one-pot cascade process in aqueous phase by coupling the hydrogenative ring-rearrangement of HMF into 3-hydroxymethylcyclopentanone (HCPN) with a subsequent reductive amination with ammonia. Mono- (Ni@C, Co@C) and bimetallic (NiCo@C) nanoparticles with different Ni/Co ratios partially covered by a thin carbon layer were prepared and characterized. Results showed that a NiCo catalyst, (molar ratio Ni/Co=1, Ni_0.5 Co_0.5 @C), displayed excellent performance in the hydrogenative ring-rearrangement of HMF into HCPN (>90 % yield). The high selectivity of the catalyst was attributed to the formation of NiCo alloy structures as hydrogenating sites that limited competitive reactions such as the hydrogenation of furan ring and the over-reduction of the formed HPCN. The subsequent reductive amination of HPCN with aqueous ammonia was performed giving the target cyclopentylaminoalcohol in 97 % yield. Moreover, the catalyst exhibited high stability maintaining its activity and selectivity for repeated reaction cycles.

Magnetically Induced Catalytic Reduction of Biomass-Derived Oxygenated Compounds in Water

The development of energetically efficient processes for the aqueous reduction of biomass-derived compounds into chemicals is key for the optimal transformation of biomass. Herein we report an early example of the reduction of biomass-derived oxygenated compounds in water by magnetically induced catalysis. Non-coated and carbon-coated core-shell FeCo@Ni magnetic nanoparticles were used as the heating agent and the catalyst simultaneously. In this way it was possible to control the product distribution by adjusting the field amplitude applied during the magnetic catalysis, opening a precedent for this type of catalysis. Finally, the encapsulation of the magnetic nanoparticles in carbon (FeCo@Ni@C) strongly improved the stability of the magnetic catalyst in solution, making its reuse possible up to at least eight times in dioxane and four times in water.

Molecularly Engineering Defective Basal Planes in Molybdenum Sulfide for the Direct Synthesis of Benzimidazoles by Reductive Coupling of Dinitroarenes with Aldehydes

Developing more sustainable catalytic processes for preparing N-heterocyclic compounds in a less costly, compact, and greener manner from cheap and readily available reagents is highly desirable in modern synthetic chemistry. Herein, we report a straightforward synthesis of benzimidazoles by reductive coupling of o-dinitroarenes with aldehydes in the presence of molecular hydrogen. An innovative molecular cluster-based synthetic strategy that employs Mo₃S₄ complexes as precursors have been used to engineer a sulfur-deficient molybdenum disulfide (MoS₂)-type material displaying structural defects on both the naturally occurring edge positions and along the typically inactive basal planes. By applying this catalyst, a broad range of functionalized 2-substituted benzimidazoles, including bioactive compounds, can be selectively synthesized by such a direct hydrogenative coupling protocol even in the presence of hydrogenation-sensitive functional groups, such as double and triple carbon-carbon bonds, nitrile and ester groups, and halogens as well as diverse types of heteroarenes.

The 2D or 3D morphology of sub-nanometer Cu5 and Cu8 clusters changes the mechanism of CO oxidation

The mechanism of the CO oxidation reaction catalysed by planar Cu₅, three dimensional (3D) Cu₅, and 3D Cu₈ clusters is theoretically investigated at the B3PW91/Def2TZVP level. All three clusters are able to catalyse the reaction with similar activation energies for the rate determining step, about 16-18 kcal mol^-1, but with remarkable differences in the reaction mechanism depending on cluster morphology. Thus, for 3D Cu₅ and Cu₈ clusters, O₂ dissociation is the first step of the mechanism, followed by two consecutive CO + O reaction steps, the second one being rate determining. In contrast, on planar Cu₅ the reaction starts with the formation of an OOCO intermediate in what constitutes the rate determining step. The O-O bond is broken in a second step, releasing the first CO₂ and leaving one bi-coordinately adsorbed O atom which reacts with CO following an Eley-Rideal mechanism with a low activation energy, in contrast to the higher barriers obtained for this step on 3D clusters.

Silica-Based Stimuli-Responsive Systems for Antitumor Drug Delivery and Controlled Release

The administration of cytotoxic drugs in classical chemotherapy is frequently limited by water solubility, low plasmatic stability, and a myriad of secondary effects associated with their diffusion to healthy tissue. In this sense, novel pharmaceutical forms able to deliver selectively these drugs to the malign cells, and imposing a space-time precise control of their discharge, are needed. In the last two decades, silica nanoparticles have been proposed as safe vehicles for antitumor molecules due to their stability in physiological medium, high surface area and easy functionalization, and good biocompatibility. In this review, we focus on silica-based nanomedicines provided with specific mechanisms for intracellular drug release. According to silica nature (amorphous, mesostructured, and hybrids) nanocarriers responding to a variety of stimuli endogenously (e.g., pH, redox potential, and enzyme activity) or exogenously (e.g., magnetic field, light, temperature, and ultrasound) are proposed. Furthermore, the incorporation of targeting molecules (e.g., monoclonal antibodies) that interact with specific cell membrane receptors allows a selective delivery to cancer cells to be carried out. Eventually, we present some remarks on the most important formulations in the pipeline for clinical approval, and we discuss the most difficult tasks to tackle in the near future, in order to extend the use of these nanomedicines to real patients.

Tailoring graphene-supported Ru nanoparticles by functionalization with pyrene-tagged N-heterocyclic carbenes

Controlling the reactivity and stability of graphene-supported Ru NPs by modifying their surface with pyrene-tagged N-heterocyclic carbene ligands.

Switching between Classical/Nonclassical Crystallization Pathways of TS-1 Zeolite: Implication on Titanium Distribution and Catalysis

In the MFI zeolite crystallization process, the classical crystallization mechanism based upon the addition of silica species is often concomitant with the nonclassical route that is characteristic of the attachment of silica nanoparticle precursors. However, the factors that govern the preferences for each mechanism remain unclear. In this work, we present the impact of switching between these two crystallization pathways on the active sites and the resulting catalytic performance of the titanosilicate TS-1 zeolite. By controlling the self-assembled precursor structures in the early crystallization stage which are mediated by the Ti and H₂O in the reaction system, we could achieve the preferred modes of crystal growth of the TS-1 zeolite. We indicate that by directing the predominant crystallization path from the classical to the nonclassical route, it is possible to generate more stable bridging peroxo species upon reaction with hydrogen peroxide, as confirmed by ¹⁷O solid-state nuclear magnetic resonance spectroscopy, thus substantially increasing the catalytic performance of the resulting TS-1 for olefin epoxidation.

This work demonstrates that the dominant crystallization mode of TS-1 zeolite can be switched between the nonclassical route and classical pathway by regulating the kinetic process of crystal nucleation.

Interrogating the Behaviour of a Styryl Dye Interacting with a Mesoscopic 2D-MOF and Its Luminescent Vapochromic Sensing

In this contribution, we report on the solid-state-photodynamical properties and further applications of a low dimensional composite material composed by the luminescent trans-4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) dye interacting with a two-dimensional-metal organic framework (2D-MOF), Al-ITQ-HB. Three different samples with increasing concentration of DCM are synthesized and characterized. The broad UV-visible absorption spectra of the DCM/Al-ITQ-HB composites reflect the presence of different species of DCM molecules (monomers and aggregates). In contrast, the emission spectra are narrower and exhibit a bathochromic shift upon increasing the DCM concentration, in agreeance with the formation of adsorbed aggregates. Time-resolved picosecond (ps)-experiments reveal multi-exponential behaviors of the excited composites, further confirming the heterogeneous nature of the samples. Remarkably, DCM/Al-ITQ-HB fluorescence is sensitive to vapors of electron donor aromatic amine compounds like aniline, methylaniline, and benzylamine due to a H-bonding-induced electron transfer (ET) process from the analyte to the surface-adsorbed DCM. These findings bring new insights on the photobehavior of a well-known dye when interacting with a 2D-MOF and its possible application in sensing aniline derivatives.

Coordinatively Unsaturated Hf-MOF-808 Prepared via Hydrothermal Synthesis as a Bifunctional Catalyst for the Tandem N-Alkylation of Amines with Benzyl Alcohol

The modulated hydrothermal (MHT) synthesis of an active and selective Hf-MOF-808 material for the N-alkylation reaction of aniline with benzyl alcohol under base-free mild reaction conditions is reported. Through kinetic experiments and isotopically labeled NMR spectroscopy studies, we have demonstrated that the reaction mechanism occurs via borrowing hydrogen (BH) pathway, in which the alcohol dehydrogenation is the limiting step. The high concentration of defective -OH groups generated on the metallic nodes through MHT synthesis enhances the alcohol activation, while the unsaturated Hf⁴⁺, which acts as a Lewis acid site, is able to borrow the hydrogen from the methylene position of benzyl alcohol. This fact makes this material at least 14 times more active for the N-alkylation reaction than the material obtained via solvothermal synthesis. The methodology described in this work could be applied to a wide range of aniline and benzyl alcohol derivates, showing in all cases high selectivity toward the corresponding N-benzylaniline product. Finally, Hf-MOF-808, which acts as a true heterogeneous catalyst, can be reused in at least four consecutive runs without any activity loss.

Data-Driven Design of Biselective Templates for Intergrowth Zeolites

Zeolites are inorganic materials with wide industrial applications due to their topological diversity. Tailoring confinement effects in zeolite pores, for instance by crystallizing intergrown frameworks, can improve their catalytic and transport properties, but controlling zeolite crystallization often relies on heuristics. In this work, we use computational simulations and data mining to design organic structure-directing agents (OSDAs) to favor the synthesis of intergrown zeolites. First, we propose design principles to identify OSDAs which are selective toward both end members of the disordered structure. Then, we mine a database of hundreds of thousands of zeolite-OSDA pairs and downselect OSDA candidates to synthesize known intergrowth zeolites such as CHA/AFX, MTT/TON, and BEC/ISV. The computationally designed OSDAs balance phase competition metrics and shape selectivity toward the frameworks, thus bypassing expensive dual-OSDA approaches typically used in the synthesis of intergrowths. Finally, we propose potential OSDAs to obtain hypothesized disordered frameworks such as AEI/SAV. This work may accelerate zeolite discovery through data-driven synthesis optimization and design.

A priori control of zeolite phase competition and intergrowth with high-throughput simulations

[Figure: see text].

Activation and conversion of alkanes in the confined space of zeolite-type materials

Microporous zeolite-type materials, with crystalline porous structures formed by well-defined channels and cages of molecular dimensions, have been widely employed as heterogeneous catalysts since the early 1960s, due to their wide variety of framework topologies, compositional flexibility and hydrothermal stability. The possible selection of the microporous structure and of the elements located in framework and extraframework positions enables the design of highly selective catalysts with well-defined active sites of acidic, basic or redox character, opening the path to their application in a wide range of catalytic processes. This versatility and high catalytic efficiency is the key factor enabling their use in the activation and conversion of different alkanes, ranging from methane to long chain n-paraffins. Alkanes are highly stable molecules, but their abundance and low cost have been two main driving forces for the development of processes directed to their upgrading over the last 50 years. However, the availability of advanced characterization tools combined with molecular modelling has enabled a more fundamental approach to the activation and conversion of alkanes, with most of the recent research being focused on the functionalization of methane and light alkanes, where their selective transformation at reasonable conversions remains, even nowadays, an important challenge. In this review, we will cover the use of microporous zeolite-type materials as components of mono- and bifunctional catalysts in the catalytic activation and conversion of C₁⁺ alkanes under non-oxidative or oxidative conditions. In each case, the alkane activation will be approached from a fundamental perspective, with the aim of understanding, at the molecular level, the role of the active sites involved in the activation and transformation of the different molecules and the contribution of shape-selective or confinement effects imposed by the microporous structure.

Tailoring Lewis/Brønsted acid properties of MOF nodes via hydrothermal and solvothermal synthesis: simple approach with exceptional catalytic implications

The Lewis/Brønsted catalytic properties of the Metal-Organic Framework (MOF) nodes can be tuned by simply controlling the solvent employed in the synthetic procedure. In this work, we demonstrate that Hf-MOF-808 can be prepared from a material with a higher amount of Brønsted acid sites, via modulated hydrothermal synthesis, to a material with a higher proportion of unsaturated Hf Lewis acid sites, via modulated solvothermal synthesis. The Lewis/Brønsted acid properties of the resultant metallic clusters have been studied by different characterization techniques, including XAS, FTIR and NMR spectroscopies, combined with a DFT study. The different nature of the Hf-MOF-808 materials allows their application as selective catalysts in different target reactions requiring Lewis, Brønsted or Lewis-Brønsted acid pairs.

Design and Synthesis of the Active Site Environment in Zeolite Catalysts for Selectively Manipulating Mechanistic Pathways

By combining kinetics and theoretical calculations, we show here the benefits of going beyond the concept of static localized and defined active sites on solid catalysts, into a system that globally and dynamically considers the active site located in an environment that involves a scaffold structure particularly suited for a target reaction. We demonstrate that such a system is able to direct the reaction through a preferred mechanism when two of them are competing. This is illustrated here for an industrially relevant reaction, the diethylbenzene–benzene transalkylation. The zeolite catalyst (ITQ-27) optimizes location, density, and environment of acid sites to drive the reaction through the preselected and preferred diaryl-mediated mechanism, instead of the alkyl transfer pathway. This is achieved by minimizing the activation energy of the selected pathway through weak interactions, much in the way that it occurs in enzymatic catalysts. We show that ITQ-27 outperforms previously reported zeolites for the DEB-Bz transalkylation and, more specifically, industrially relevant zeolites such as faujasite, beta, and mordenite.

Single-Site vs. Cluster Catalysis in High Temperature Oxidations

The behavior of single Pt atoms and small Pt clusters was investigated for high-temperature oxidations. The high stability of these molecular sites in CHA is a key to intrinsic structure-performance descriptions of elemental steps such as O₂ dissociation, and subsequent oxidation catalysis. Subtle changes in the atomic structure of Pt are responsible for drastic changes in performance driven by specific gas/metal/support interactions. Whereas single Pt atoms and Pt clusters (> ca. 1 nm) are unable to activate, scramble, and desorb two O₂ molecules at moderate T (200 °C), clusters <1 nm do so catalytically, but undergo oxidative fragmentation. Oxidation of alkanes at high T is attributed to stable single Pt atoms, and the C-H cleavage is inferred to be rate-determining and less sensitive to changes in metal nuclearity compared to its effect on O₂ scrambling. In contrast, when combustion involves CO, catalysis is dominated by metal clusters, not single Pt atoms.

Metalloenzyme-Inspired Ce-MOF Catalyst for Oxidative Halogenation Reactions

The structure of UiO-66(Ce) is formed by CeO_2-x defective nanoclusters connected by terephthalate ligands. The initial presence of accessible Ce³⁺ sites in the as-synthesized UiO-66(Ce) has been determined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR)-CO analyses. Moreover, linear scan voltammetric measurements reveal a reversible Ce⁴⁺/Ce³⁺ interconversion within the UiO-66(Ce) material, while nanocrystalline ceria shows an irreversible voltammetric response. This suggests that terephthalic acid ligands facilitate charge transfer between subnanometric metallic nodes, explaining the higher oxidase-like activity of UiO-66(Ce) compared to nanoceria for the mild oxidation of organic dyes under aerobic conditions. Based on these results, we propose the use of Ce-based metal-organic frameworks (MOFs) as efficient catalysts for the halogenation of activated arenes, as 1,3,5-trimethoxybenzene (TMB), using oxygen as a green oxidant. Kinetic studies demonstrate that UiO-66(Ce) is at least three times more active than nanoceria under the same reaction conditions. In addition, the UiO-66(Ce) catalyst shows an excellent stability and can be reused after proper washing treatments. Finally, a general mechanism for the oxidative halogenation reaction is proposed when using Ce-MOF as a catalyst, which mimics the mechanistic pathway described for metalloenzymes. The superb control in the generation of subnanometric CeO_2-x defective clusters connected by adequate organic ligands in MOFs offers exciting opportunities in the design of Ce-based redox catalysts.

Tuning the Catalytic Performance of Cobalt Nanoparticles by Tungsten Doping for Efficient and Selective Hydrogenation of Quinolines under Mild Conditions

Non-noble bimetallic CoW nanoparticles (NPs) partially embedded in a carbon matrix (CoW@C) have been prepared by a facile hydrothermal carbon-coating methodology followed by pyrolysis under an inert atmosphere. The bimetallic NPs, constituted by a multishell core–shell structure with a metallic Co core, a W-enriched shell involving Co₇W₆ alloyed structures, and small WO₃ patches partially covering the surface of these NPs, have been established as excellent catalysts for the selective hydrogenation of quinolines to their corresponding 1,2,3,4-tetrahydroquinolines under mild conditions of pressure and temperature. It has been found that this bimetallic catalyst displays superior catalytic performance toward the formation of the target products than the monometallic Co@C, which can be attributed to the presence of the CoW alloyed structures.

Synthesis and Structure of a 22 × 12 × 12 Extra-Large Pore Zeolite ITQ-56 Determined by 3D Electron Diffraction

A multidimensional extra-large pore germanosilicate, denoted ITQ-56, has been synthesized by using modified memantine as an organic structure-directing agent. ITQ-56 crystallizes as plate-like nanocrystals. Its structure was determined by 3D electron diffraction/MicroED. The structure of ITQ-56 contains extra-large 22-ring channels intersecting with straight 12-ring channels. ITQ-56 is the first zeolite with 22-ring pores, which is a result of ordered vacancies of double 4-ring (d4r) units in a fully connected zeolite framework. The framework density is as low as 12.4 T atoms/1000 Å3. The discovery of the ITQ-56 structure not only fills the missing member of extra-large pore zeolite with 22-ring channels but also creates a new approach of making extra-large pore zeolites by introducing ordered vacancies in zeolite frameworks.

Discovering Relationships between OSDAs and Zeolites through Data Mining and Generative Neural Networks

Organic structure directing agents (OSDAs) play a crucial role in the synthesis of micro- and mesoporous materials especially in the case of zeolites. Despite the wide use of OSDAs, their interaction with zeolite frameworks is poorly understood, with researchers relying on synthesis heuristics or computationally expensive techniques to predict whether an organic molecule can act as an OSDA for a certain zeolite. In this paper, we undertake a data-driven approach to unearth generalized OSDA-zeolite relationships using a comprehensive database comprising of 5,663 synthesis routes for porous materials. To generate this comprehensive database, we use natural language processing and text mining techniques to extract OSDAs, zeolite phases, and gel chemistry from the scientific literature published between 1966 and 2020. Through structural featurization of the OSDAs using weighted holistic invariant molecular (WHIM) descriptors, we relate OSDAs described in the literature to different types of cage-based, small-pore zeolites. Lastly, we adapt a generative neural network capable of suggesting new molecules as potential OSDAs for a given zeolite structure and gel chemistry. We apply this model to CHA and SFW zeolites generating several alternative OSDA candidates to those currently used in practice. These molecules are further vetted with molecular mechanics simulations to show the model generates physically meaningful predictions. Our model can automatically explore the OSDA space, reducing the amount of simulation or experimentation needed to find new OSDA candidates.

Zr-MOF-808 as Catalyst for Amide Esterification

In this work, zirconium-based metal-organic framework Zr-MOF-808-P has been found to be an efficient and versatile catalyst for amide esterification. Comparing with previously reported homogeneous and heterogeneous catalysts, Zr-MOF-808-P can promote the reaction for a wide range of primary, secondary and tertiary amides with n-butanol as nucleophilic agent. Different alcohols have been employed in amide esterification with quantitative yields. Moreover, the catalyst acts as a heterogeneous catalyst and could be reused for at least five consecutive cycles. The amide esterification mechanism has been studied on the Zr-MOF-808 at molecular level by in situ FTIR spectroscopic technique and kinetic study.

Structural transformations of solid electrocatalysts and photocatalysts

Heterogeneous catalysts often undergo structural transformations when they operate under thermal reaction conditions. These transformations are reflected in their evolving catalytic activity, and a fundamental understanding of the changing nature of active sites is vital for the rational design of solid materials for applications. Beyond thermal catalysis, both photocatalysis and electrocatalysis are topical because they can harness renewable energy to drive uphill reactions that afford commodity chemicals and fuels. Although structural transformations of photocatalysts and electrocatalysts have been observed in operando, the resulting implications for catalytic behaviour are not fully understood. In this Review, we summarize and compare the structural evolution of solid thermal catalysts, electrocatalysts and photocatalysts. We suggest that well-established knowledge of thermal catalysis offers a good basis to understand emerging photocatalysis and electrocatalysis research.

Controlling the selectivity of bimetallic platinum–ruthenium nanoparticles supported on N-doped graphene by adjusting their metal composition

Bimetallic platinum–ruthenium nanoparticles supported on N-doped graphene as chemoselective hydrogenation catalysts.