Encapsulation Of Catalysts Research Articles

Readily scalable and controllable micro-structured catalyst with encapsulated Pd@Silicate-1 towards sustainable catalytic emission control

Hierarchical micro-structured catalyst has been proved to be crucial for modular, compact reactor design towards sustainable catalytic processes, including catalytic emission control. However, turning it to reality is hindered by controllability and scalability in high-efficient, cost-effective preparation, particularly when combined with state-of-the-art encapsulated catalysts. Herein, in-situ hydrothermal coating method is developed to achieve tunable incorporation of Pd@S-1 catalyst into micro-structured confined space, and the trade-off between catalyst loading and confined micro-structures’ availability towards the best performance is revealed, e.g. 10 ∼ 50 °C lower T50 with balanced control. Moreover, systematic experiments and CFD simulations prove that (1) flow-through flow pattern, rather than flow-over, in confined space enables better catalyst utilization and performance (>10 °C lower T50), thus optimal micro-structure design is proposed; (3) a loosely bundled scale-up method is the best. This study provides deep insights into understanding and utilizing hierarchical structured catalysts, particularly with confined micro-structures.

A Water-Stable Boronate Ester Cage.

The reversible condensation of catechols and boronic acids to boronate esters is a paradigm reaction in dynamic covalent chemistry. However, facile backward hydrolysis is detrimental for stability and has so far prevented applications for boronate-based materials. Here, we introduce cubic boronate ester cages 6 derived from hexahydroxy tribenzotriquinacenes and phenylene diboronic acids with ortho-t-butyl substituents. Due to steric shielding, dynamic exchange at the Lewis acidic boron sites is feasible only under acid or base catalysis but fully prevented at neutral conditions. For the first time, boronate ester cages 6 tolerate substantial amounts of water or alcohols both in solution and solid state. The unprecedented applicability of these materials under ambient and aqueous conditions is showcased by efficient encapsulation and on-demand release of β-carotene dyes and heterogeneous water oxidation catalysis after the encapsulation of ruthenium catalysts.

Flexible encapsulation polyoxometalate with electrostatically interaction into metal−organic framework for ultra-deep aerobic oxidation desulfurization of diesel via a biomimetic approach in deep eutectic solvents

Flexible encapsulation of polyoxometalates (POMs) into metal–organic frameworks (MOFs) is a promising and emerging research area. Herein, a novel non-homogeneous IL(CoMo6)-MIL-101-NH2 catalyst was prepared by a stepwise modification method, in which the unprecedentedly flexible encapsulation of POM-MOF catalyst was achieved through ion exchange of introducing (NH4)3H6CoMo6O24 into IL(Br)-MIL-101-NH2. This approach firmly encases the POM within the pores of MIL-101 through electrostatic interactions. It not only preserved the catalytic activity of POM, but also provided sufficient space for the reaction to occur. The IL(CoMo6)-MIL-101-NH2 catalyst retained a high similar activity to homogeneous catalyst, while possessing characteristics of a multiphase catalyst for easy separation and recovery. It tackles POM's solubility issue and enables its encapsulation in MOFs for heterogeneous catalysis. Furthermore, the unparalleled catalyst was utilized in a biomimetic approach for coupling with deep eutectic solvents to achieve ultra-deep aerobic oxidative desulfurization of diesel.

Enhanced stability of Pt@S-1 with the aid of potassium ions for n-hexane and n-heptane aromatization

As a typical high-efficient alkane aromatization catalyst, Pt/KL is prone to deactivation due to the sintering growth of Pt on the outer surface of KL and the channel blockage caused by carbon deposition, which is further exacerbated by the one-dimensional channel structure of KL. Therefore, a series of encapsulated catalysts combining the three-dimensional channel structure advantages of S-1 with the role of potassium are prepared and evaluated. It is shown that the encapsulated catalyst KPt@S-1-02 modified by moderate potassium exhibits extremely superior stability and no significant deactivation is observable after n-heptane aromatization for 180 h under harsh conditions. On the one hand, encapsulation structure enables a strong anti-agglomeration ability of Pt and the topological structure of S-1 endows the encapsulation catalysts less susceptible to channel blockage, which has been demonstrated by HAADF-STEM and N2-adsorption. On the other hand, characterizations involving NH3-TPD, CO-DRIFT and HAADF-STEM verify that the modification by an appropriate amount of K can inhibit acid sites of catalysts and improve Pt dispersion and electron density, thus enhance the stability of catalysts. However, excessive K can serve as weak acid sites, poison of active sites and inhibitor of H2 adsorption on Pt surface, leading to deactivation of the catalyst.

Urea-Functionalized Fe4 L6 Cages for Supramolecular Gold Catalyst Encapsulation to Control Substrate Activation Modes.

The excellent catalytic performances of enzymes in terms of activity and selectivity are an inspiration for synthetic chemists and this has resulted in the development of synthetic containers for supramolecular catalysis. In such containers the local environment and pre-organization of catalysts and substrates leads to control of the activity and selectivity of the catalyst. Herein we report a supramolecular strategy to encapsulate single catalysts in a urea-functionalized Fe4 L6 cage, which can co-encapsulate a functionalized urea substrate through hydrogen bonding. Distinguished selectivity is obtained, imposed by the cage as site isolation only allows catalysis through π activation of the substrate and as a result the selectivity is independent of catalyst concentration. The encapsulated catalyst is more active than the free analogue, an effect that can be ascribed to transitionstate stabilization rather than substrate pre-organization, as revealed by the MM kinetic data. The simple strategy reported here is expected to be of general use in many reactions, for which the catalyst can be functionalized with a sulfonate group required for encapsulation.

Urea‐Functionalized Fe4L6 Cages for Supramolecular Gold Catalyst Encapsulation to Control Substrate Activation Modes

AbstractThe excellent catalytic performances of enzymes in terms of activity and selectivity are an inspiration for synthetic chemists and this has resulted in the development of synthetic containers for supramolecular catalysis. In such containers the local environment and pre‐organization of catalysts and substrates leads to control of the activity and selectivity of the catalyst. Herein we report a supramolecular strategy to encapsulate single catalysts in a urea‐functionalized Fe4L6 cage, which can co‐encapsulate a functionalized urea substrate through hydrogen bonding. Distinguished selectivity is obtained, imposed by the cage as site isolation only allows catalysis through π activation of the substrate and as a result the selectivity is independent of catalyst concentration. The encapsulated catalyst is more active than the free analogue, an effect that can be ascribed to transitionstate stabilization rather than substrate pre‐organization, as revealed by the MM kinetic data. The simple strategy reported here is expected to be of general use in many reactions, for which the catalyst can be functionalized with a sulfonate group required for encapsulation.

Integrating surface corrosion and imprinting strategy into PEDOT/Bi12O17Cl2 heterojunction embedded membrane aims to high permeability and selectivity

Development of photocatalytic membrane with antifouling, permeability, selectivity and reusability is highly desired for water treatment. Herein, an imprinted poly-3,4-ethylenedioxythiophene/oxygen-rich bismuth chloride oxide heterojunction embedded membrane (I-PEDOT/Bi12O17Cl2−M) with good self-cleaning and recyclability was fabricated by integrating surface corrosion and imprinting strategy. The introduction of imprinting technology endowed Z-type heterojunction (composed of Bi12O17Cl2 nanosheets and PEDOT) with imprinted cavities which possessed good selective adsorption ability for target pollutant (tetracycline, TC). Compared with pure nanosheets (Bi12O17Cl2) and non-imprinted nanosheets photocatalyst (NI-PEDOT/Bi12O17Cl2), the selectivity coefficient of I-PEDOT/Bi12O17Cl2−M were 3.35 and 2.01, respectively. Importantly, the corrosive solvent (NMP) changed the surface pore structure of polyvinylidene fluoride (PVDF), which firmly stuck the two-dimensional I-PEDOT/Bi12O17Cl2 in the surface pore of PVDF base membrane, avoiding the catalyst encapsulation issue of conventional methods and fully exposing the active sites. Therefore, I-PEDOT/Bi12O17Cl2−M exhibited good catalytic activity and stability. Particularly, the pure water flux and TC flux reached 4620 L/m2·h and 3580 L/m2·h, respectively. This study provides a new strategy for reasonable design of photocatalytic membrane with high permeability and good selectivity.

Molecular Catalysis of Energy Relevance in Metal–Organic Frameworks: From Higher Coordination Sphere to System Effects

The modularity and synthetic flexibility of metal-organic frameworks (MOFs) have provoked analogies with enzymes, and even the term MOFzymes has been coined. In this review, we focus on molecular catalysis of energy relevance in MOFs, more specifically water oxidation, oxygen and carbon dioxide reduction, as well as hydrogen evolution in context of the MOF-enzyme analogy. Similar to enzymes, catalyst encapsulation in MOFs leads to structural stabilization under turnover conditions, while catalyst motifs that are synthetically out of reach in a homogeneous solution phase may be attainable as secondary building units in MOFs. Exploring the unique synthetic possibilities in MOFs, specific groups in the second and third coordination sphere around the catalytic active site have been incorporated to facilitate catalysis. A key difference between enzymes and MOFs is the fact that active site concentrations in the latter are often considerably higher, leading to charge and mass transport limitations in MOFs that are more severe than those in enzymes. High catalyst concentrations also put a limit on the distance between catalysts, and thus the available space for higher coordination sphere engineering. As transport is important for MOF-borne catalysis, a system perspective is chosen to highlight concepts that address the issue. A detailed section on transport and light-driven reactivity sets the stage for a concise review of the currently available literature on utilizing principles from Nature and system design for the preparation of catalytic MOF-based materials.

Floating Fe Catalyst Formation and Effects of Hydrogen Environment in the Growth of Carbon Nanotubes

Hydrocarbon conversion to advanced carbon nanomaterials with concurrent hydrogen production holds promise for clean energy technologies. This has been largely enabled by the floating catalyst chemical vapor deposition (FCCVD) growth of carbon nanotubes (CNTs), where commonly catalytic iron nanoparticles are formed from ferrocene decomposition. However, the catalyst formation mechanism and the effect of the chemical environment, especially hydrogen, remain elusive. Here, by employing atomistic simulations, we demonstrate how (i) hydrogen accelerates the ferrocene decomposition and (ii) prevents catalyst encapsulation. A subsequent catalytic dehydrogenation of methane on a liquid Fe nanoparticle showed that carbon dimers tend to be the dominant on-surface species. Such atomistic insights help us better understand the catalyst formation and CNT nucleation in the early stages of the FCCVD growth process and optimize it for potential scaleup.

NMP-induced surface self-corrosion-assisted rapid spin-coating method for synthesizing imprinted heterojunction photocatalyst anchored membrane towards high-efficiency selective degradation tetracycline

The membrane immobilization of imprinted photocatalysts is a good cooperative model, which not only gives self-cleaning and selectivity to the membrane but also solves the problem of difficult recycling and reuse of powder catalysts. Nevertheless, the problem of catalyst encapsulation and pore blockage limits its practical application. Herein, 1-methyl-2-pyrrolidone (NMP)-induced surface self-corrosion-assisted rapid spin-coating method was first proposed to prepare imprinted perylene diimide/poly-3,4-ethylenedioxythiophene heterojunction photocatalyst anchored membrane (I-PDI/PEDOT-M) with high stability and permeability. NMP can corrode polyvinylidene fluoride (PVDF) membrane and cause pore wall collapse on PVDF surface. The collapse of the pore wall firmly anchored the imprinted PDI/PEDOT heterojunction photocatalyst (I-PDI/PEDOT) into the surface pore of the PVDF membrane, effectively enhancing the stability. More importantly, this method did not produce a dense layer of traditional spin-coating solution, and I-PDI/PEDOT was fully exposed in the surface pores of the membrane to contact pollutants, thus maintaining high water flux and photodegradation activity. Besides, the construction of heterojunction structure and the introduction of imprinted cavities resulted in the good self-cleaning performance, excellent photocatalytic performance and significant specific degradation ability of I-PDI/PEDOT-M. The degradation activity of tetracycline (TC) with I-PDI/PEDOT-M was 11.05 times that of ciprofloxacin, and the selectivity coefficients of I-PDI/PEDOT-M were 2.51and 1.63 relative to PDI-M and non-imprinted PDI/PEDOT heterojunction photocatalyst, respectively. Additionally, the theoretical calculation and toxicity experiment proved that the toxicity was significantly reduced after degrading TC by I-PDI/PEDOT-M. This work provides an interesting idea for the design of highly stable and permeable photocatalytic membrane and highly selective degradation of specific pollutant.

Hydrogen-Enhanced Catalytic Conversion of Amorphous Carbon to Graphene for Achieving Superlubricity.

The solid-state conversion of amorphous carbon into graphene is extremely difficult, but it can be achieved in the friction experiments that induce macroscale superlubricity. However, the underlying conversion mechanisms remain elusive. Here, the friction experiments with Cu nanoparticles and (non-hydrogen (H) or H) a-C in vacuum, show the H-induced conversion of mechanical to chemical wear, resulting in the a-C's tribosoftening and nanofragmentating that produce hydrocarbon nanoclusters or molecules. It is such exactly hydrocarbon species that yield graphene at hydrogen-rich a-C friction interface, through reaction of them with Cu nanoparticles. In comparison, graphene isn't formed at Cu/non-H a-C friction interface. Atomistic simulations reveal the hydrogen-enhanced tribochemical decomposition of a-C and demonstrate the energetically favorable graphitization transformation of hydrocarbons on Cu substrates. The findings are of importance to achieve solid-state transformation between different carbon allotropes and provide a good strategy to synthesize other graphitic encapsulated catalysts with doped elements.

Templated encapsulation of platinum-based catalysts promotes high-temperature stability to 1,100 °C.

Stable catalysts are essential to address energy and environmental challenges, especially for applications in harsh environments (for example, high temperature, oxidizing atmosphere and steam). In such conditions, supported metal catalysts deactivate due to sintering-a process where initially small nanoparticles grow into larger ones with reduced active surface area-but strategies to stabilize them can lead to decreased performance. Here we report stable catalysts prepared through the encapsulation of platinum nanoparticles inside an alumina framework, which was formed by depositing an alumina precursor within a separately prepared porous organic framework impregnated with platinum nanoparticles. These catalysts do not sinter at 800 °C in the presence of oxygen and steam, conditions in which conventional catalysts sinter to a large extent, while showing similar reaction rates. Extending this approach to Pd-Pt bimetallic catalysts led to the small particle size being maintained at temperatures as high as 1,100 °C in air and 10% steam. This strategy can be broadly applied to other metal and metal oxides for applications where sintering is a major cause of material deactivation.

Selectivity catalytic transfer hydrogenation of biomass-based furfural to cyclopentanone

Because of furfural’s diverse unsaturated groups and the rearrangement of oxygen atoms, the production of cyclopentanone (CPO) from furfural (FF) can be challenging. Herein, a novel nitrogen-doped encapsulated catalyst (Co@NC) was synthesized to catalyze the selective hydrogenation of FF in an aqueous phase to CPO. A CPO yield of 86.5 % was obtained at 200 °C and 3 MPa H2. Meanwhile, furfuryl alcohol (FA) was inferred to be the primary intermediate in the formation of CPO and cyclopentanol (CPL). CPL originated from the further hydrogenation of CPO that was produced via FF selective hydrogenation to FA, followed by FA hydrodeoxgenation to CPO. The main presence of CPO illustrated that it avoided overhydrogenation, which contributed to the tailored hydrogenation ability of Co@NC and facilitated the selective preservation of CO bonds. The N atoms acting as electronegative heteroatoms can not only enhance the adsorption of FF but also provide weak Lewis acid sites for CPO production.

Decarbonizing Natural Gas: A Review of Catalytic Decomposition and Carbon Formation Mechanisms

In the context of energy conservation and the reduction of CO2 emissions, inconsistencies between the inevitable emission of CO2 in traditional hydrogen production methods and eco-friendly targets have become more apparent over time. The catalytic decomposition of methane (CDM) is a novel technology capable of producing hydrogen without releasing CO2. Since hydrogen produced via CDM is neither blue nor green, the term “turquoise” is selected to describe this technology. Notably, the by-products of methane cracking are simply carbon deposits with different structures, which can offset the cost of hydrogen production cost should they be harvested. However, the encapsulation of catalysts by such carbon deposits reduces the contact area between said catalysts and methane throughout the CDM process, thereby rendering the continuous production of hydrogen impossible. This paper mainly covers the CDM reaction mechanisms of the three common metal-based catalysts (Ni, Co, Fe) from experimental and modelling approaches. The by-products of carbon modality and the key parameters that affect the carbon formation mechanisms are also discussed.

Structures of synthetic helical filaments and tubes based on peptide and peptido-mimetic polymers.

AbstractSynthetic peptide and peptido-mimetic filaments and tubes represent a diverse class of nanomaterials with a broad range of potential applications, such as drug delivery, vaccine development, synthetic catalyst design, encapsulation, and energy transduction. The structures of these filaments comprise supramolecular polymers based on helical arrangements of subunits that can be derived from self-assembly of monomers based on diverse structural motifs. In recent years, structural analyses of these materials at near-atomic resolution (NAR) have yielded critical insights into the relationship between sequence, local conformation, and higher-order structure and morphology. This structural information offers the opportunity for development of new tools to facilitate the predictable and reproduciblede novodesign of synthetic helical filaments. However, these studies have also revealed several significant impediments to the latter process – most notably, the common occurrence of structural polymorphism due to the lability of helical symmetry in structural space. This article summarizes the current state of knowledge on the structures of designed peptide and peptido-mimetic filamentous assemblies, with a focus on structures that have been solved to NAR for which reliable atomic models are available.

Hexagonal Boron Nitride Meeting Metal: A New Opportunity and Territory in Heterogeneous Catalysis.

Two dimensional (2D) hexagonal boron nitride (h-BN) has been ignored for a long time in catalysis research because of its chemical inertness. Recently there has been a significant advance highlighting the role of metal/h-BN interfaces in catalytic applications. In this Perspective, we summarize state-of-the-art progress regarding h-BN-involved metal catalysts. Vacancy- and defect-rich h-BN sheets are able to anchor and modify supported metals, in which the interfacial metal-support interaction effect helps to enhance catalytic performance. Oxidative etching of h-BN sheets causes encapsulation of metal catalysts via boron oxide (BOx) species, which work synergistically with neighboring metal sites in catalysis. Covering a metal surface with ultrathin h-BN shells creates a 2D nanoreactor featuring confinement effect, providing a novel way to modulate metal-catalyzed reactions. Given all those fascinating combinations of metal catalyst and h-BN, the emerging opportunity when h-BN meets metal in heterogeneous catalysis is clearly underlined. The outlook, especially the challenges in the field, are discussed as well.

Swollen-induced in-situ encapsulation of chiral silver catalysts in cross-linked polysiloxane elastomers: Homogeneous reaction and heterogeneous separation

The immobilization of molecular catalysts to fabricate heterogeneous catalysts for catalytic asymmetric transformations is extremely important and has attracted great attentions. Herein we developed a simple and new strategy for the heterogenization of homogeneous molecular complexes into the cross-linked polymer. It is demonstrated for the first time that the cross-linked polysiloxane elastomers can be applied for the swollen-induced in-situ encapsulation of homogeneous catalysts with or without chiral ligands. The swollen-induced in-situ encapsulation of silver catalyst system in the cross-linked polysiloxane elastomers led to the formation of silicone rubber-based hierarchically porous that could be used in asymmetric [3+2] cycloaddition, asymmetric tandem conjugate addition−elimination reaction and oxidation of hydrosilanes to silanols. The swollen-induced in-situ encapsulation of chiral silver complex in the cross-linked polysiloxane elastomers was proved to be easily recycled by filtration or pick-up and reused by several times. The simplest heterogeneous catalysis by the strategy of swollen-induced in-situ encapsulation can be extended to the encapsulation of chiral metal catalysts into different polymeric materials for the heterogenization of homogeneous catalysis.

Machine Learning Method Reveals Hidden Strong Metal-Support Interaction in Microscopy Datasets.

Forming an ultra-thin, permeable encapsulation oxide-support layer on a metal catalyst surface is considered an effective strategy for achieving a balance between high stability and high activity in heterogenous catalysts. The success of such a design relies not only on the thickness, ideally one to two atomic layers thick, but also on the morphology and chemistry of the encapsulation layer. Reliably identifying the presence and chemical nature of such a trace layer has been challenging. Electron energy-loss spectroscopy (EELS) performed in a scanning transmission electron microscope (STEM), the primary technique utilized for such studies, is limited by a weak signal on overlayers when using conventional analysis methods, often leading to misinterpreted or missed information. Here, a robust, unsupervised machine learning data analysis method is developed to reveal trace encapsulation layers that are otherwise overlooked in STEM-EELS datasets. This method provides a reliable tool for analyzing encapsulation of catalysts and is generally applicable to any spectroscopic analysis of materials and devices where revealing a trace signal and its spatial distribution is challenging.

Encapsulation of Metal Catalysts for Stable Solid Oxide Fuel Cell Cathodes

Metal catalysts have been employed as cathodes for solid oxide fuel cells to facilitate the surface exchange rate in the intermediate temperature range (600–800 °C). However, incorporated metal catalysts easily agglomerate, resulting in the loss of the reaction sites; thus, the electrochemical performance rapidly deteriorates over time. To hinder the agglomeration of metal catalysts while maintaining the catalytic activity, we encapsulated metal catalysts with nano-particulated perovskite materials using an infiltration technique. The encapsulation of Ag nanoparticles with nano-particulated Sm0.5Sr0.5CoO3-δ (SSC) successfully prevented the agglomeration of Ag nanoparticles, maintaining the initial polarization resistance for 200 h at 650 °C, while the polarization resistance of the SSC electrodes with the Ag nanoparticles increased by ~ 190% after 200 h at 650 °C because of the thermal agglomeration of Ag nanoparticles.

Anisotropic nanomaterials for asymmetric synthesis.

The production of enantiopure chemicals is an essential part of modern chemical industry. Hence, the emergence of asymmetric catalysis led to dramatic changes in the procedures of chemical synthesis, and now it provides the most advantageous and economically executable solution for large-scale production of chiral chemicals. In recent years, nanostructures have emerged as potential materials for asymmetric synthesis. Indeed, on the one hand, nanomaterials offer great opportunities as catalysts in asymmetric catalysis, due to their tunable absorption, chirality, and unique energy transfer properties; on the other hand, the advantages of the larger surface area, increased number of unsaturated coordination centres, and more accessible active sites open prospects for catalyst encapsulation, partial or complete, in a nanoscale cavity, pore, pocket, or channel leading to alteration of the chemical reactivity through spatial confinement. This review focuses on anisotropic nanomaterials and considers the state-of-the-art progress in asymmetric synthesis catalysed by 1D, 2D and 3D nanostructures. The discussion comprises three main sections according to the nanostructure dimensionality. We analyze recent advances in materials and structure development, discuss the functional role of the nanomaterials in asymmetric synthesis, chirality, confinement effects, and reported enantioselectivity. Finally, the new opportunities and challenges of anisotropic 1D, 2D, and 3D nanomaterials in asymmetric synthesis, as well as the future prospects and current trends of the design and applications of these materials are analyzed in the Conclusions and outlook section.