Preface

The energy crisis combined with environmental pollution has been recognized as one of the most serious global concerns. Therefore, huge attempts have been devoted in recent decades to resolving these challenges by introducing more advanced materials with higher efficiency. Specially-designed catalysts are among the first candidates proposed to combat environmental contaminations. Metal-organic frameworks (MOFs) are a novel class of crystalline porous substances possessing high surface area, excellent structural properties, chemical adjustability, and stability which can be used in different applications including catalysis. The significant benefits of MOFs in the field of catalysis can be found in their tunable porosity, uniformly-distributed active sites, and excellent porosity offering accessible active sites through their open channels facilitating the mass transport and diffusion, and finally, their robust structure ensuring recyclability. Thus, MOFs can efficiently offer the positive features of both homogeneous and heterogeneous catalysts, at high reaction efficiency and recyclability. Catalytic properties of MOFs can be further enhanced when used as precursors and/or templates. Their combination with other compounds as a hybrid can further improve their catalytic activities due to synergic effects. The huge attempts to reinforce and modify this class of materials raise our hopes in the bright future of MOFs in the field of catalysis.

Due to unique features of inorganic-organic hybrid compositions, MOFs, compared with traditional porous materials, have a variety of advantages: (1) Good crystallinity. MOFs with highly ordered structures, could be precisely and intuitively analyzed by X-ray diffraction technology, which is helpful to determine structure-property relationships; (2) Good designability and facile functionalization. Applying to crystal engineering, MOFs can not only be predesigned with expected structures (topologies) and functions, even the coordination diversity of metal ions and organic ligands, but also easily operated by post synthetic methods; (3) High porosity. MOFs are highly porous materials with a large specific surface area (exceeding to 7000 m2 g-1), and more importantly, the size, shape and composition of pores can be well tuned by a lot of methods, which is beneficial for host-guest studies; (4) Flexibility. Due to the flexibility of coordination bond and organic linkers, most of the MOFs are somewhat flexible, which endows MOFs with peculiar properties like dynamic irritating response to external conditions (temperature, pressure, humidity, etc.), and these features make MOFs more intelligent in applications.

The MOF-based materials offer favorable catalytic performance owing to their unique structural attributes and subsequent modulation. Their range of chemical functionalities and porosities facilitate to adsorb/activate other substrates/CO ₂ leading to facile CO₂ conversion. The rise in the number of MOF based catalytic materials with improved performance has opened a new avenue for CO ₂ capture and conversion. One of the most important attributes an MOF has is its chemical tunability along with its interactions with other substrates. MOFs as photocatalysts are benefited from a large surface area, suitable band-gap, the ideal structure for charge transfer, and high photo-corrosion resistance.