Advanced Catalysts Based on Metal-organic Frameworks (Part 1)

Metal-Organic Frameworks (MOFs), as one type of famous porous material with many advantages (good crystallinity, design ability, facile modification and flexibility), show a wide range of applications in gas adsorption and separation, ion exchange, fluorescent recognition, nonlinear optics, molecular magnets and ferroelectrics, heterogeneous catalysis, semiconductors, and so on. The research of MOFs span many disciplines, such as inorganic chemistry, organic chemistry, coordination chemistry, supramolecular chemistry, crystal engineering and materials science. The design, synthesis, and applications of MOFs have attracted tremendous attention in broad scientific areas. Therefore, it is worth releasing a professional publication to elucidate so many related issues. In this chapter, we start with the introduction of MOFs, including the definition, classification, concepts, terminologies, and some well-known research. Then we carefully summarize the design and synthesis of MOFs from three aspects of raw materials, synthetic methods, and design strategy, aiming to get the goal of controllable syntheses of MOFs. Following this, we report the developments and applications of MOF materials in adsorption and separation, organic catalysis, luminescence, and drug delivery. Finally, we briefly outline challenges and perspectives of MOF materials, and provide some promising research subjects in this area.

Metal-organic frameworks (MOFs) emerged as adjustable and multipurpose materials, which are now intensively investigated worldwide. They are composed of a wide range of organic and inorganic building units which are a susceptible base for various post-synthetic modifications (PSMs). In the last years, altering MOFs composition has significantly contributed to their broad application in many fields, especially in heterogeneous catalysis. PSMs are employed to improve the physicochemical properties of MOFs such as stability or selectivity, but mostly to generate catalytically active sites. Here, we report diverse methods of metal- (exchange, doping, redox transformations) and ligand-based (functionalization, exchange, installation, removal) PSMs of MOFs, which can be effectively used for catalytic purposes. PSMs can either extend the MOF framework with catalytically active functionalities or contribute to defect engineering for open metal site formation. Moreover, combining different modifying procedures has been introduced as a tandem approach when various reactions prompt several changes in the framework. Epitaxial growth was also presented as PSM, which can govern catalytically beneficial features mostly for thin films, unattainable to achieve by conventional methods. Recent MOFs’ PSM findings were reviewed to show new pathways and a continuously developing field of reticular chemistry which come across with the expectations for novel and more efficient catalysts. 

In recent years, metal-organic frameworks (MOFs) have significantly contributed to broadening the frontiers of science. Due to their distinctive properties including well-developed surface area, high porosity, multifarious composition, tunable and uniform pore structures, and comprehensive functionality, they were applied in different fields such as separation, drug delivery, fuel storage, chemical sensing, and catalysis. The application of pristine MOFs as materials that speed up the reaction rate could be restricted mainly because of the limited number of active sites and their low mechanical and thermal stability. In order to enhance their catalytic properties, metalorganic frameworks can be functionalized or integrated with a variety of materials to obtain composites or hybrids. The review outlines the state of art concerning the application of MOFs and their composites as catalysts in various organic transformation processes. A particular focus was given to the oxidation of alkanes, cycloalkanes, alkylbenzenes, alcohols, thiols, sulfides. Furthermore, the role of metalorganic frameworks in hydrogenation and C–C coupling reactions were also presented.

Biomass valorization is receiving increasing attention over the past years with the consumption of traditional fossil fuels as well as the deterioration of the global environment. The transformation of biomass into highly value-added chemicals and important feedstocks will be of keen interest and great impact. The conversion process of biomass requires efficient and durable catalysts with high selectivity and stable structures. This chapter focuses on the employment of metal-organic frameworks (MOFs), MOF composites (metal, metal oxide, or polyoxometalates combined with MOFs), and MOF-derived materials (carbon, carbon-supported metal or metal oxide by using MOF as precursors) as solid catalysts for the upgrading of biomass into important fine chemicals. First, we will give a short introduction of biomass and MOFs, and then the brief biomass valorization reactions by MOFs and MOF-based catalysts based on the types of substrates. The last segment is summary of the state of the art, challenges, as well as prospects of MOFs and MOFs-derived structures for biomass transformation.

Due to the rapid and continuous increase in CO2 concentrations in the atmosphere by the massive combustion of fossil fuels, the global ecosystem is being affected severely. Therefore, balancing the CO2 content in the atmosphere should be our main agenda nowadays. For minimization of CO2 concentration, carbon capture and its conversion to valuable chemicals are being perused worldwide. Metal-organic framework (MOF)-based materials having a porous structure and tuneable structural features, are best candidates for the purpose. Herein, we provide a detailed discussion on the design, synthesis and catalytic applications of MOF-based materials for various CO2 conversion reactions. 

The rapid rise in photocatalytic technology with efficient removal capabilities has attracted wide attention. Recently, metal-organic frameworks (MOFs), a kind of coordination polymers, have also been applied in the field of photocatalytic water purification due to their characteristics such as high specific surface area and adjustable pore structure. However, the weak water stability, low reutilization rate, and poor photocatalytic ability of the constructed MOFs restrict their application in environmental remediation. To tackle these problems, many researchers have devoted themselves to designing highly efficient MOF-based composites by adding other substances. This chapter mainly focuses on the research status of MOF-based composites in the photocatalytic elimination of various pollutants from water. Additionally, the synthetic strategies for MOFs and their composite materials as well as for photodegradation of pollutants in water are reviewed and exemplified. The possible removal mechanisms of some MOF-based composites have also been briefly analyzed. Finally, the achievements and prospects on future research of MOFs and their composite materials have been described in detail.