Metal organic frameworks (MOFs) are a class of porous crystalline materials that feature a series of unique properties, such as large surface area and porosity, high content of transition metals, and possibility to be designed and modified after synthesis, that make these solids especially suitable as heterogeneous catalysts. The active sites can be coordinatively unsaturated metal ions, substituents at the organic linkers or guest species located inside the pores. The defects on the structure also create these open sites. The present review summarizes the current state of the art in the use of MOFs as solid catalysts according to the type of site, making special emphasis on the more recent strategies to increase the population of these active sites and tuning their activity, either by adapting the synthesis conditions or by post-synthetic modification. This review highlights those reports illustrating the synergy derived from the presence of more than one of these types of sites, leading to activation of a substrate by more than one site or to the simultaneous activation of different substrates by complementary sites. This synergy is frequently the main reason for the higher catalytic activity of MOFs compared to homogeneous catalysts or other alternative solid materials. Besides dark reactions, this review also summarizes the use of MOFs as photocatalysts emphasizing the uniqueness of these materials regarding adaptation of the linkers as light absorbers and metal exchange at the nodes to enhance photoinduced electron transfer, in comparison with conventional inorganic photocatalysts. This versatility and flexibility that is offered by MOFs to optimize their visible light photocatalytic activity explains the current interest in exploiting these materials for novel photocatalytic reactions, including hydrogen evolution and photocatalytic CO2 reduction.

Metal-organic frameworks (MOFs) are crystalline porous materials formed from bi- or multipodal organic linkers and transition-metal nodes. Some MOFs have high structural stability, combined with large flexibility in design and post-synthetic modification. MOFs can be photoresponsive through light absorption by the organic linker or the metal oxide nodes. Photoexcitation of the light absorbing units in MOFs often generates a ligand-to-metal charge-separation state that can result in photocatalytic activity. In this Review we discuss the advantages and uniqueness that MOFs offer in photocatalysis. We present the best practices to determine photocatalytic activity in MOFs and for the deposition of co-catalysts. In particular we give examples showing the photocatalytic activity of MOFs in H2 evolution, CO2 reduction, photooxygenation, and photoreduction.

The present review describes the use of metal-organic frameworks (MOFs) as porous matrices to embed metal nanoparticles (MNPs) and occasionally metal oxide clusters, which are subsequently used as heterogeneous catalysts. The review is organized according to the embedded metal including Pd, Au, Ru, Cu, Pt, Ni and Ag. Emphasis is also given in the various methodologies reported for the formation of the NPs and the characterization techniques. The reactions described with this type of solid catalysts include condensation, hydrogenations, carbon-carbon coupling, alcohol oxidations and methanol synthesis among others. Remaining issues in this field have also been indicated.

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The shortage of fossil fuels and the need to find alternative renewable and sustainable fuels for transportation are triggering an increasing interest in the photocatalytic reduction of CO 2 . In this review, we have focused on titanium containing photocatalysts that effect the reduction of CO 2 to fuels. The various products that are more generally formed are CH 4 , CH 3 OH, CO as well as HCOOH. This review has been organized primarily depending on the type of titanium material used as the photocatalyst. The list includes pure TiO 2 as well as metal-and non metal-doped titania, noble metals supported on titania and micro-/mesoporous titanosilicates or porous matrices containing titania clusters. In a general introduction we comment on the limitations of the current approaches and the various possibilities and conditions for performing the irradiation. In a final section, we also give our view on future developments and open issues to be addressed in this field.

Mixed‐metal metal–organic frameworks (MM‐MOFs) can be considered to be those MOFs having two different metals anywhere in the structure. Herein we summarize the various strategies for the preparation of MM‐MOFs and some of their applications in adsorption, gas separation, and catalysis. It is shown that compared to homometallic MOFs, MM‐MOFs bring about the opportunity to take advantage of the complexity and the synergism derived from the presence of different metal ions in the structure of MOFs. This is reflected in a superior performance and even stability of MM‐MOFs respect to related single‐metal MOFs. Emphasis is made on the use of MM‐MOFs as catalysts for tandem reactions.

Graphenes and related materials have attracted growing interest as metal-free catalysts. The present review is focused on describing the active sites that have been proposed to be responsible for the catalytic activity observed for such systems. It will be shown that diverse defects and chemical functionalities on the graphene layers can catalyze reactions, including oxygenated functional groups, carbon vacancies and holes, edge effects, and the presence of dopant elements. Besides discrete active sites, the catalytic activity arising from the collective properties of graphenes as materials by adsorbing substrates and reagents and activating them by charge transfer is also commented. The review has an introductory general section summarizing the general methodologies that have been used to support the proposed structure of the active sites, including theoretical calculations, comparison of the catalytic activity of graphene samples with different compositions, the use of organic molecules as models of the active centers, and selective masking of functional groups. The review is concluded with our view on future developments in the field.

Two porous iron trimesates, namely, commercial Basolite F300 (Fe(BTC); BTC = 1,3,5-benzenetricarboxylate) with unknown structure and synthetic MIL-100(Fe) (MIL stands for Material of Institut Lavoisier) of well-defined crystalline structure, have been compared as heterogeneous catalysts for four different reactions. It was found that while for catalytic processes requiring strong Lewis acid sites, Fe(BTC) performs better, MIL-100(Fe) is the preferred catalyst for oxidation reactions. These catalytic results have been rationalized by a combined in situ infrared and 57Fe Mössbauer spectroscopic characterization. It is proposed that the presence of extra Brønsted acid sites on the Fe(BTC) and the easier redox behavior of the MIL-100(Fe) could explain these comparative catalytic performances. The results illustrate the importance of structural defects (presence of weak Brønsted acid sites) and structural stability (MIL-100(Fe) is stable upon annealing at 280 °C despite Fe3+-to-Fe2+ reduction) on the catalytic activity of these two solids, depending on the reaction type.