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Heterogenized molecular catalysts have shown interesting activities in different chemical transformations. In our previous studies, a molecular catalyst, Re(bpy)(CO)3Cl where bpy is 2,2′-bipyridine, was covalently attached to silica surfaces via an amide linkage for use in photocatalytic CO2 reduction. Derivatizing the bpy ligand with electron-withdrawing amide groups led to detrimental effects on the catalytic activity of Re(bpy)(CO)3Cl. In this study, an alkyl amine linkage is utilized to attach Re(bpy)(CO)3Cl onto SiO2 in order to eliminate the detrimental effects of the amide linkage by breaking the conjugation between the bpy ligand and the amide group. However, the heterogenized Re(I) catalyst containing the alkyl amine linkage demonstrates even lower activity than the one containing the amide linkage in photocatalytic CO2 reduction. Infrared studies suggest that the presence of the basic amine group led to the formation of a photocatalytically inactive Re(I)-OH species on SiO2. Furthermore, the amine group likely contributes to the stabilization of a surface Re(I)-carboxylato species formed upon light irradiation, resulting in the low activity of the heterogenized Re(I) catalyst containing the alkyl amine linkage. [ABSTRACT FROM AUTHOR]

The selectivity of metal nanocatalysts is critical to chemical transformations and industries. Herein, a highly selective heterogeneous living cell catalytic system (LCCS) with intracellular Pd nanodots (bio-nPd) via in situ biomimetic synthesis is constructed. Research studies show that the LCCS is capable of size-selective catalytic hydrogenation for a series of acrylamides in water under mild conditions, and has self-reproducible, reusable and recyclable performance. Moreover, the LCCS also has high catalytic activity: the turnover frequency (TOF) for the acrylamide is up to 198.3 h−1 and the conversion rate is 100%. The calculation results show that the size-selectivity is closely interrelated with the inherent "gating" effect of the cell membrane, which is beneficial for the entry of small molecules. The highly selective and eco-friendly characteristics of the catalytic systems provide an effective strategy for exploring novel catalytic systems that can meet the requirements of sustainable development. [ABSTRACT FROM AUTHOR]

Biopolymer functionalization is perceived as an innovative approach to revolutionizing bio-catalyzed chemical transformations. Lignin, the chief natural source of polyphenols, has an aromatic structure with plenty of beneficial chemical groups. Accordingly, lignin can be functionalized, copolymerized, or recombined with different types of chemicals to produce highly efficient catalysts. Moreover, the stability and biodegradability of lignin make it an efficient bio-immobilizer for diverse metals (Pt, Pd, Ag, Cu, Co, Fe, etc.), which are known for their excellent catalytic performances. In addition, the solid nature of the lignin-derived catalysts has excellent advantages in terms of simple catalyst recovery and reuse over consecutive cycles with high stability. The present work compiles the newly adopted approaches to valorize lignin in the field of catalysis. Lignin-derived acid and base catalysts, lignin metal-free catalysts, and lignin-supported metal catalysts have demonstrated the full potential of lignin in hydrolysis, esterification, oxidation, condensation, hydration, and multicomponent reactions. The synthesis methods, properties, and catalytic capacity of lignin-based catalysts were assessed and contrasted with conventional catalysts. Attractively, the inclusion of lignin in catalysis appeared as a novel upgrading strategy that offers eco-friendly and profitable materials, leading to simple and green chemical synthesis, as well as a revolutionary shift in the industrialization of biomass-derived materials generally, and functionalized lignin-based catalysts specifically. [ABSTRACT FROM AUTHOR]

Chemical reactions require close physical contact between reactants, catalysts, and intermediates to proceed. In a bulk homogeneous solution, this is often governed by random collisions based on molecular diffusion. A powerful concept is the use of confinement to physically restrict the reacting species within the same physical space, increasing the likelihood of successful collisions. Controlling the identity and geometry of the co-located reactants also provides the opportunity to impart improved regio- and chemoselectivity for these processes. This effect has been explored in a number of contexts, including catalytic performance, yet its potential in providing greener processes has not been fully recognized. This review discusses different modes of confinement that have been explored for catalytic applications grouped as confinement within pores and cavities, confinement by encapsulation within hollow solids, and confinement within self-assembled systems. The theory behind changes in reaction outcomes due to confinement and selected examples of reactions where confinement has played an important role are discussed. We highlight the important implications of confinement effects towards the discovery of more sustainable processes as well as the relevance of these outcomes to the field of green chemistry. Key challenges and future directions within the field are highlighted. [ABSTRACT FROM AUTHOR]

A defining characteristic of nearly all catalytically functional MOFs is uniform, molecular-scale porosity. MOF pores, linkers and nodes that define them, help regulate reactant and product transport, catalyst siting, catalyst accessibility, catalyst stability, catalyst activity, co-catalyst proximity, composition of the chemical environment at and beyond the catalytic active site, chemical intermediate and transition-state conformations, thermodynamic affinity of molecular guests for MOF interior sites, framework charge and density of charge-compensating ions, pore hydrophobicity/hydrophilicity, pore and channel rigidity vs. flexibility, and other features and properties. Collectively and individually, these properties help define overall catalyst functional behaviour. This review focuses on how porous, catalyst-containing MOFs capitalize on molecular-scale confinement, containment, isolation, environment modulation, energy delivery, and mobility to accomplish desired chemical transformations with potentially superior selectivity or other efficacy, especially in comparison to catalysts in homogeneous solution environments. [ABSTRACT FROM AUTHOR]

Considering a complete life cycle of metal catalysts, metals are usually mined from ores as salts (MX′n), industrially processed to the bulk metal (M) and then converted into the salts again (MXn) to be used as catalyst precursors. Under catalytic conditions, metal salts undergo transformations to form catalytically active species (MLn), and the anion (X) is typically converted to waste. Thus, there are extra steps before a catalytic process may start, and the chemical transformation involved therein generates considerable amounts of waste. Here, we study the strategy for merging electrodissolution with catalysis to skip these extra steps and demonstrate efficient waste-minimized transformations to access Cu catalysts from the metal. Bulk metal from an electrode can be transformed directly into a catalytic reaction under the action of electric current. As a representative example, dipolar addition of azides to alkynes was successfully catalyzed by copper metal. The reaction was carried out in an ionic liquid (IL), which acted simultaneously as an electrolyte, a solvent and stabilizer of the formed catalytically active species. The used catalyst can be regenerated (or reactivated, if necessary) by application of reverse polarity of electrodes and directly reused again. For metal and solvent recovery, the ILs used were easily separated from copper species by passing an electric current. The applicability of the copper-catalyzed transformation was additionally tested for cross-coupling of thiols with aryl halides (the Ullmann reaction), click reaction with calcium carbide and three-component azide–halide–alkyne coupling. The mechanism of copper dissolution from an electrode was studied, and the intermediates were identified by means of XRD, X-ray and HRESI-MS. [ABSTRACT FROM AUTHOR]

In the last few decades, worldwide scientists have been motivated by the promising production of chemicals from the widely existing methane (CH4) under mild conditions for both chemical synthesis with low energy consumption and climate remediation. To achieve this goal, a whole library of catalytic chemistries of transforming CH4 to various products under mild conditions is required to be developed. Worldwide scientists have made significant efforts to reach this goal. These significant efforts have demonstrated the feasibility of oxidation of CH4 to value-added intermediate compounds including but not limited to CH3OH, HCHO, HCOOH, and CH3COOH under mild conditions. The fundamental understanding of these chemical and catalytic transformations of CH4 under mild conditions have been achieved to some extent, although currently neither a catalyst nor a catalytic process can be used for chemical production under mild conditions at a large scale. In the academic community, over ten different reactions have been developed for converting CH4 to different types of oxygenates under mild conditions in terms of a relatively low activation or catalysis temperature. However, there is still a lack of a molecular-level understanding of the activation and catalysis processes performed in extremely complex reaction environments under mild conditions. This article reviewed the fundamental understanding of these activation and catalysis achieved so far. Different oxidative activations of CH4 or catalytic transformations toward chemical production under mild conditions were reviewed in parallel, by which the trend of developing catalysts for a specific reaction was identified and insights into the design of these catalysts were gained. As a whole, this review focused on discussing profound insights gained through endeavors of scientists in this field. It aimed to present a relatively complete picture for the activation and catalytic transformations of CH4 to chemicals under mild conditions. Finally, suggestions of potential explorations for the production of chemicals from CH4 under mild conditions were made. The facing challenges to achieve high yield of ideal products were highlighted and possible solutions to tackle them were briefly proposed. [ABSTRACT FROM AUTHOR]

The release of large volumes of anthropogenic CO2 coupled with growing exploitation of fossil fuels has led to very serious issues such as global warming and energy crisis in the world. One of the most promising solutions for addressing these challenges is photocatalytic reduction of CO2 into useful chemical feedstocks. The adsorption/activation and reduction of CO2 on the surface of heterogeneous catalysts, in addition to visible light harvesting and efficient charge separation, remains a scientifically challenging problem, which is severely limiting the total photoconversion and selectivity of CO2 reduction on photocatalysts. Reticular materials such as metal organic frameworks (MOFs) and covalent organic frameworks (COFs) are a class of porous materials, which have lately been investigated as photocatalysts due to their excellent tuneable structural and photochemical properties. Single-atom catalysts offer great potential to enable chemical transformation of CO2 when anchored to an appropriate support material. Naturally abundant porphyrin has been effective for a variety of processes including light-harvesting, oxygen transport and catalytic processes. The rigidity, robustness, and multifunctionality of reticular materials enable them to be used in a spectrum of applications. Modular optimization, rational design and integration of single-atoms and porphyrin onto metal- and covalent-organic frameworks pave a new pathway toward the photoreduction of CO2. In the context of recent advancements in the field of reticular materials, porphyrin and single atom based MOFs and COFs towards photocatalytic CO2 reduction are summarised in this review. This review also includes discussion on the current breakthroughs in fundamental knowledge, reaction mechanisms, and pathways of CO2 photoreduction, as well as gives an overview of the approaches towards improving the CO2 reduction efficiency and selectivity of these reticular photocatalytic materials. Also, the challenges and perspectives of CO2 photoreduction over these heterogeneous catalysts have also been presented in this report. [ABSTRACT FROM AUTHOR]