Metal-organic framework (MOF) nanoparticles, also called porous coordination polymers, are a major part of nanomaterials science, and their role in catalysis is becoming central. The extraordinary variability and richness of their structures afford engineering synergies between the metal nodes, functional linkers, encapsulated substrates, or nanoparticles for multiple and selective heterogeneous interactions and activations in these MOF-based nanocatalysts. Pyrolysis of MOF-nanoparticle composites forms highly porous N- or P-doped graphitized MOF-derived nanomaterials that are increasingly used as efficient catalysts especially in electro- and photocatalysis. This review first briefly summarizes this background of MOF nanoparticle catalysis and then comprehensively reviews the fast-growing literature reported during the last years. The major parts are catalysis of organic and molecular reactions, electrocatalysis, photocatalysis, and views of prospects. Major challenges of our society are addressed using these well-defined heterogeneous catalysts in the fields of synthesis, energy, and environment. In spite of the many achievements, enormous progress is still necessary to improve our understanding of the processes involved beyond the proof-of-concept, particularly for selective methane oxidation, hydrogen production, water splitting, CO2 reduction to methanol, nitrogen fixation, and water depollution.

State of the Art and Prospects in Metal-Organic Framework (MOF)-Based and MOF-Derived Nanocatalysis.

Metal-organic frameworks (MOFs) are a class of distinctive porous crystalline materials constructed by metal ions/clusters and organic linkers. Owing to their structural diversity, functional adjustability, and high surface area, different types of MOF-based single metal sites are well exploited, including coordinately unsaturated metal sites from metal nodes and metallolinkers, as well as active metal species immobilized to MOFs. Furthermore, controllable thermal transformation of MOFs can upgrade them to nanomaterials functionalized with active single-atom catalysts (SACs). These unique features of MOFs and their derivatives enable them to serve as a highly versatile platform for catalysis, which has actually been becoming a rapidly developing interdisciplinary research area. In this review, we overview the recent developments of catalysis at single metal sites in MOF-based materials with emphasis on their structures and applications for thermocatalysis, electrocatalysis, and photocatalysis. We also compare the results and summarize the major insights gained from the works in this review, providing the challenges and prospects in this emerging field.

Metal-Organic Framework-Based Catalysts with Single Metal Sites.

Supported metal nanoparticles, M-NPs, are of great scientific and economic interest as they encompass application in chemical manufacturing, oil refining and environmental catalysis. Oxidation and hydrogenation reactions are among the major reactions catalyzed by supported M-NPs. Although supported M-NPs are preferable due to their easy recovery and reuse, there are still some practical issues regarding their catalytic activity and deactivation. This review highlights the general features of supported M-NPs as catalysts with particular attention to copper, gold, platinum, palladium, ruthenium, silver, cobalt and nickel and their catalytic evaluation in various reactions. The catalytic performance of noble M-NPs has been explored extensively in various selective oxidation and hydrogenation reactions. In general, noble metals are expensive and sensitive to poisons. Despite their significant merits and potential (easily available, comparatively inexpensive and less sensitive to poisons), catalysis by base M-NPs is relatively less explored. Therefore, activity of base M-NPs can be improved, and still, there is potential for such catalysts.

Review of supported metal nanoparticles: synthesis methodologies, advantages and application as catalysts

Reductive aminations constitute an important class of reactions widely applied in research laboratories and industries for the synthesis of amines as well as pharmaceuticals, agrochemicals and biomolecules. In particular, catalytic reductive aminations using molecular hydrogen are highly valued and essential for the cost-effective and sustainable production of different kinds of amines and their functionalization. These reactions couple easily accessible carbonyl compounds (aldehydes or ketones) with ammonia, amines or nitro compounds in the presence of suitable catalysts and hydrogen that enable the preparation of linear and branched primary, secondary and tertiary amines including N-methylamines and molecules used in life science applications. In general, amines represent valuable fine and bulk chemicals, which serve as key precursors and central intermediates for the synthesis of advanced chemicals, life science molecules, dyes and polymers. Noteworthily, amine functionalities are present in a large number of pharmaceuticals, agrochemicals and biomolecules, and play vital roles in the function of these active compounds. In general, reductive aminations are challenging processes, especially for the syntheses of primary amines, which often are non-selective and suffer from over-alkylation and reduction of carbonyl compounds to the corresponding alcohols. Hence, the development of suitable catalysts to perform these reactions in a highly efficient and selective manner is crucial and continues to be important and attracts scientific interest. In this regard, both homogeneous and heterogeneous catalysts have successfully been developed for these reactions to access various amines. There is a need for a comprehensive review on catalytic reductive aminations to discuss the potential catalysts used and applicability of this methodology in the preparation of different kinds of amines, which are of commercial, industrial and medicinal importance. Consequently, in this review we discuss catalytic reductive aminations using molecular hydrogen and their applications in the synthesis of functionalized and structurally diverse benzylic, heterocyclic and aliphatic primary, secondary and tertiary amines as well as N-methylamines and more complex drug targets. In addition, mechanisms of reductive aminations including selective formation of desired amine products as well as possible side reactions are emphasized. This review aims at the scientific communities working in the fields of organic synthesis, catalysis, and medicinal and biological chemistry.

Catalytic reductive aminations using molecular hydrogen for synthesis of different kinds of amines.

The capture of CO2 from concentrated emission sources as well as from air represents a process of paramount importance in view of the increasing CO2 concentration in the atmosphere and its associated negative consequences on the biosphere. Once captured using various technologies, CO2 is desorbed and compressed for either storage (carbon capture and storage (CCS)) or production of value-added products (carbon capture and utilization (CCU)). Among various products that can be synthesized from CO2, methanol and formic acid are of high interest because they can be used directly as fuels or to generate H2 on demand at low temperatures (<100 °C), making them attractive hydrogen carriers (12.6 and 4.4 wt % H2 in methanol and formic acid, respectively). Methanol is already produced in huge quantities worldwide (100 billion liters annually) and is also a raw material for many chemicals and products, including formaldehyde, dimethyl ether, light olefins, and gasoline. The production of methanol through chemical recycling of captured CO2 is at the heart of the so-called "methanol economy" that we have proposed with the late Prof. George Olah at our Institute. Recently, there has been significant progress in the low-temperature synthesis of formic acid (or formate salts) and methanol from CO2 and H2 using homogeneous catalysts. Importantly, several studies have combined CO2 capture and hydrogenation, where captured CO2 (including from air) was directly utilized to produce formate and CH3OH without requiring energy intensive desorption and compression steps. This Account centers on that topic. A key feature in the combined CO2 capture and conversion studies reported to date for the synthesis of formic acid and methanol is the use of an amine or alkali-metal hydroxide base for capturing CO2, which can assist the homogeneous catalysts in the hydrogenation step. We start this Account by examining the combined processes where CO2 is captured in amine solutions and converted to alkylammonium formate salts. The effect of amine basicity on the reaction rate is discussed along with catalyst recycling schemes. Next, methanol synthesis by this combined process, with amines as capturing agents, is explored. We also examine the system developments for effective catalyst and amine recycling in this process. We next go through the effect of catalyst molecular structure on methanol production while elucidating the main deactivating pathway involving carbonylation of the metal center. The recent advances in first-row transition metal catalysts for this process are also mentioned. Subsequently, we discuss the capture of CO2 using hydroxide bases and conversion to formate salts. The regeneration of the hydroxide base (NaOH or KOH) at low temperatures (80 °C) in cation-conducting direct formate fuel cells is presented. Finally, we review the challenges in the yet unreported integrated CO2 capture by hydroxide bases and conversion to methanol process.

Integrated CO2 Capture and Conversion to Formate and Methanol: Connecting Two Threads.

The reduction of nitro compounds to the corresponding amines is one of the most utilized catalytic processes in the fine and bulk chemical industry. The latest development of catalysts with cheap metals like Fe, Co, Ni, and Cu has led to their tremendous achievements over the last years prompting their greater application as “standard” catalysts. In this review, we will comprehensively discuss the use of homogeneous and heterogeneous catalysts based on non-noble 3d-metals for the reduction of nitro compounds using various reductants. The different systems will be revised considering both the catalytic performances and synthetic aspects highlighting also their advantages and disadvantages.

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Reduction of Nitro Compounds Using 3d-Non-Noble Metal Catalysts

An overview of the synthesis and chemistry of acylborane compounds is presented. Acylboranes are a rare class of boron compounds, previously proposed as intermediates in several transformations and considered to be difficult to prepare. Methodologies for the preparation of acylborane compounds are based on both electrophilic and nucleophilic sources of boron. The former methods include addition of electrophilic boron reagents to acyl-anion equivalents, while the latter methods are based on boryl anion reagents which are trapped by electrophiles, such as aldehydes, diethyl carbonate and ethyl acetate. New methods to achieve acylboron-compounds based on oxidation of MIDA α-hydroxyboronates or α-bromomethyl alcohol are discussed. A one-step catalytic C–B coupling reaction for preparing acylboranes from palladium-catalyzed borylation of acyl chlorides using nucleophilic borylzinc reagents is included. Applications of acylboranes in chemoselective amide-bond forming reactions, converting them into functionalised boron derivatives are also discussed.

Acylboranes: synthetic strategies and applications

Homogeneous Catalytic Hydrogenation of CO2 to Methanol – Improvements with Tailored Ligands

Hydrogenation of olefins is achieved using biowaste-derived cobalt chitosan catalysts Characterization of the optimal Co@Chitosan-700 by STEM (scanning transmission electron microscopy), EELS (electron energy loss spectroscopy), PXRD (powder x-ray diffraction), and elemental analysis revealed the formation of a distinctive magnetic composite material with high metallic Co content The general performance of this catalyst is demonstrated in the hydrogenation of 50 olefins including terminal, internal, and functionalized derivatives, as well as renewables Using this nonnoble metal composite, hydrogenation of terminal C==C double bonds occurs under very mild and benign conditions (water or methanol, 40° to 60°C) The utility of Co@Chitosan-700 is showcased for efficient hydrogenation of the industrially relevant examples diisobutene, fatty acids, and their triglycerides Because of the magnetic behavior of this material and water as solvent, product separation and recycling of the catalyst are straightforward

https://advances.sciencemag.org/content/advances/4/9/eaau1248.full.pdf

Hydrogenation of terminal and internal olefins using a biowaste-derived heterogeneous cobalt catalyst

Hydroformylation of olefins has been studied in the presence of specific heterogeneous cobalt nanoparticles. The catalytic materials were prepared by pyrolysis of preformed cobalt complexes deposited onto different inorganic supports. Atomic absorption spectroscopy (AAS) measurements indicated a correlation of catalyst activity and cobalt leaching as well as a strong influence of the heterogeneous support on the productivity. These new, low-cost, easy-to-handle catalysts can substitute more toxic, unstable and volatile cobalt carbonyl complexes for hydroformylations on a laboratory scale.

Florian Korbinian Scharnagl

Papers

Reduction of Nitro Compounds Using 3d-Non-Noble Metal Catalysts

Acylboranes: synthetic strategies and applications

Homogeneous Catalytic Hydrogenation of CO2 to Methanol – Improvements with Tailored Ligands

Hydrogenation of terminal and internal olefins using a biowaste-derived heterogeneous cobalt catalyst

Supported Cobalt Nanoparticles for Hydroformylation Reactions