Supported single-metal atom catalysts (SACs) are constituted of isolated active metal centers, which are heterogenized on inert supports such as graphene, porous carbon, and metal oxides. Their thermal stability, electronic properties, and catalytic activities can be controlled via interactions between the single-metal atom center and neighboring heteroatoms such as nitrogen, oxygen, and sulfur. Due to the atomic dispersion of the active catalytic centers, the amount of metal required for catalysis can be decreased, thus offering new possibilities to control the selectivity of a given transformation as well as to improve catalyst turnover frequencies and turnover numbers. This review aims to comprehensively summarize the synthesis of Fe-SACs with a focus on anchoring single atoms (SA) on carbon/graphene supports. The characterization of these advanced materials using various spectroscopic techniques and their applications in diverse research areas are described. When applicable, mechanistic investigations conducted to understand the specific behavior of Fe-SACs-based catalysts are highlighted, including the use of theoretical models. CONTENTS 1. Introduction 13620 2. Scope of This Review 13623 3. Synthesis of Fe-SACs 13623 3.1. N-Doped Graphene-Based Fe-SACs 13623 3.2. Nitrogen-Doped Porous Carbon-Based Fe-SACs 13626 3.3. C 3 N 4 -Based Fe-SACs 13634 4.

In order to achieve these goals, it is of fundamental importance to design new catalysts that enable new benign routes to produce/ store and convert renewable energies and to obtain chemicals from waste. [3][4][5] We need to design new chemical pathways that replace traditional petrochemicalbased routes, considering new platform molecules, possibly derived by renewable resources such as agriculture/municipal wastes. This transition must fully involve the energy sector, with the entire redefinition of the pool of energy vectors for transportations, building heating systems, and power production. As the burning of fossil fuels and biomass are not anymore compatible with the dramatic increasing air pollution and global warming.To achieve all these targets, we will need to design nontoxic, earth-abundant, and less-expensive, highly efficient, and selective catalysts that can work under mild reaction conditions without producing significant waste. [6,7] Catalytic activity and selectivity are enabled via the many factors such as accessibility of active sites, interaction with the surface, i.e., varying support and coordinating sphere, composition of metals (bimetallic and many-metallic), size and shape; and chemical states of active sites which can to tailored via developing 2D catalyst [8][9][10] or via developing single atomic sites stabilized on hollow A heterogeneous catalyst is a backbone of modern sustainable green industries; and understanding the relationship between its structure and properties is the key for its advancement. Recently, many upscaling synthesis strategies for the development of a variety of respectable control atomically precise heterogeneous catalysts are reported and explored for various important applications in catalysis for energy and environmental remediation. Precise atomic-scale control of catalysts has allowed to significantly increase activity, selectivity, and in some cases stability. This approach has proved to be relevant in various energy and environmental related technologies such as fuel cell, chemical reactors for organic synthesis, and environmental remediation. Therefore, this review aims to critically analyze the recent progress on single-atom catalysts (SACs) application in oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and chemical and/or electrochemical organic transformations. Finally, opportunities that may open up in the future are summarized, along with suggesting new applications for possible exploitation of SACs.

We report a facile protocol for the synthesis of fibrous nano-silica (KCC-1) with controllable size and fiber density. In this work, we have shown that the particle size, fiber density, surface area and pore volume of KCC-1 can be effectively controlled and tuned by changing various reaction parameters, such as the concentrations of urea, CTAB, 1-pentanol, reaction time, temperature, solvent ratio, and even outside stirring time. For the first time, we were able to control the particle size ranging from as small as 170 nm to as large as 1120 nm. We were also able to control the fiber density from low to medium to very dense, which consequently allowed the tuning of the pore volume. We were able to achieve a pore volume of 2.18 cm3/g, which is the highest reported for such a fibrous material. Notably we were even able to increase the surface area up to 1244 m2/g, nearly double the previously reported surface area of KCC-1. Thus, one can now synthesize KCC-1 with various degrees of size, surface area, pore volume, and fiber density.

Fibrous nanosilica (KCC-1) oxynitrides are promising solid-base catalysts. Paradoxically, when their nitrogen content increases, their catalytic activity decreases. This counterintuitive observation is explained here for the first time using 15 N-solid-state NMR spectroscopy enhanced by dynamic nuclear polarization.

Hybrid materials by functionalization of fibrous nanosilica (KCC-1) were synthesized for efficient CO2 capture, using various amine molecules by physisorption (ads.) as well as covalent attachment.