Heterogenized cobalt oxide catalysts for nitroarene reduction by pyrolysis of molecularly defined complexes
TL;DR: The conversion of homogeneous Cobalt complexes into heterogeneous cobalt oxide catalysts via immobilization and pyrolysis on activated carbon and reusable non-noble-metal catalysts are highly selective for the industrially important hydrogenation of structurally diverse and functionalized nitroarenes to anilines.
Abstract: Molecularly well-defined homogeneous catalysts are known for a wide variety of chemical transformations. The effect of small changes in molecular structure can be studied in detail and used to optimize many processes. However, many industrial processes require heterogeneous catalysts because of their stability, ease of separation and recyclability, but these are more difficult to control on a molecular level. Here, we describe the conversion of homogeneous cobalt complexes into heterogeneous cobalt oxide catalysts via immobilization and pyrolysis on activated carbon. The catalysts thus produced are useful for the industrially important reduction of nitroarenes to anilines. The ligand indirectly controls the selectivity and activity of the recyclable catalyst and catalyst optimization can be performed at the level of the solution-phase precursor before conversion into the active heterogeneous catalyst.
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TL;DR: This Review will compare the results obtained from different systems and try to give a picture on how different types of metal species work in different reactions and give perspectives on the future directions toward better understanding of the catalytic behavior of different metal entities in a unifying manner.
Abstract: Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...
2,700 citations
TL;DR: FeOx-supported platinum single-atom and pseudo-single-atom structures are reported as highly active, chemoselective and reusable catalysts for hydrogenation of a variety of substituted nitroarenes.
Abstract: The catalytic hydrogenation of nitroarenes is an environmentally benign technology for the production of anilines, which are key intermediates for manufacturing agrochemicals, pharmaceuticals and dyes. Most of the precious metal catalysts, however, suffer from low chemoselectivity when one or more reducible groups are present in a nitroarene molecule. Herein we report FeOx-supported platinum single-atom and pseudo-single-atom structures as highly active, chemoselective and reusable catalysts for hydrogenation of a variety of substituted nitroarenes. For hydrogenation of 3-nitrostyrene, the catalyst yields a TOF of ~1,500 h(-1), 20-fold higher than the best result reported in literature, and a selectivity to 3-aminostyrene close to 99%, the best ever achieved over platinum group metals. The superior performance can be attributed to the presence of positively charged platinum centres and the absence of Pt-Pt metallic bonding, both of which favour the preferential adsorption of nitro groups.
839 citations
TL;DR: In this paper, the authors report convenient and stable iron oxide (Fe2O3)-based catalysts as a more earth-abundant alternative for the transformation of anilines.
Abstract: Production of anilines--key intermediates for the fine chemical, agrochemical, and pharmaceutical industries--relies on precious metal catalysts that selectively hydrogenate aryl nitro groups in the presence of other easily reducible functionalities. Herein, we report convenient and stable iron oxide (Fe2O3)-based catalysts as a more earth-abundant alternative for this transformation. Pyrolysis of iron-phenanthroline complexes on carbon furnishes a unique structure in which the active Fe2O3 particles are surrounded by a nitrogen-doped carbon layer. Highly selective hydrogenation of numerous structurally diverse nitroarenes (more than 80 examples) proceeded in good to excellent yield under industrially viable conditions.
800 citations
TL;DR: The key factors affecting the catalytic activity/selectivity, in particular, the geometric and electronic structure of the active sites, are discussed with the aim to extract fundamental principles for the development of efficient and selective catalysts in hydrogenation as well as other transformations.
Abstract: Selective catalytic hydrogenation has wide applications in both petrochemical and fine chemical industries, however, it remains challenging when two or multiple functional groups coexist in the substrate. To tackle this challenge, the "active site isolation" strategy has been proved effective, and various approaches to the site isolation have been developed. In this review, we have summarized these approaches, including adsorption/grafting of N/S-containing organic molecules on the metal surface, partial covering of active metal surface by metal oxides either via doping or through strong metal-support interaction, confinement of active metal nanoparticles in micro- or mesopores of the supports, formation of bimetallic alloys or intermetallics or core@shell structures with a relatively inert metal (IB and IIB) or nonmetal element (B, C, S, etc.), and construction of single-atom catalysts on reducible oxides or inert metals. Both advantages and disadvantages of each approach toward the site isolation have been discussed for three types of chemoselective hydrogenation reactions, including alkynes/dienes to monoenes, α,β-unsaturated aldehydes/ketones to the unsaturated alcohols, and substituted nitroarenes to the corresponding anilines. The key factors affecting the catalytic activity/selectivity, in particular, the geometric and electronic structure of the active sites, are discussed with the aim to extract fundamental principles for the development of efficient and selective catalysts in hydrogenation as well as other transformations.
674 citations
TL;DR: This Review systematically introduces and discusses the classic synthesis methods, advanced characterization techniques, and various catalytic applications toward two-dimensional materials confining single-atom catalysts.
Abstract: Two-dimensional materials and single-atom catalysts are two frontier research fields in catalysis. A new category of catalysts with the integration of both aspects has been rapidly developed in recent years, and significant advantages were established to make it an independent research field. In this Review, we will focus on the concept of two-dimensional materials confining single atoms for catalysis. The new electronic states via the integration lead to their mutual benefits in activity, that is, two-dimensional materials with unique geometric and electronic structures can modulate the catalytic performance of the confined single atoms, and in other cases the confined single atoms can in turn affect the intrinsic activity of two-dimensional materials. Three typical two-dimensional materials are mainly involved here, i.e., graphene, g-C3N4, and MoS2, and the confined single atoms include both metal and nonmetal atoms. First, we systematically introduce and discuss the classic synthesis methods, advanced ...
647 citations
References
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4,756 citations
10 Jul 1997
TL;DR: This paper presents a meta-modelling system that automates the very labor-intensive and therefore time-heavy and therefore expensive and expensive process of characterization and activation of Solid Catalysts.
Abstract: Preparation of Solid Catalysts. Characterization of Solid Catalysts. Model Systems. Elementary Steps and Mechanisms. Kinetics and Transport Processes. Deactivation and Regeneration. Special Catalytic Systems. Laboratory Reactors. Reaction Engineering. Environmental Catalysis. Inorganic Reactions. Energy-related Catalysis. Organic Reactions.
4,227 citations
TL;DR: In conclusion, MOFs as Host Matrices or Nanometric Reaction Cavities should not be considered as a source of concern in the determination of MOFs’ properties in relation to other materials.
Abstract: 2.2. MOFs with Metal Active Sites 4614 2.2.1. Early Studies 4614 2.2.2. Hydrogenation Reactions 4618 2.2.3. Oxidation of Organic Substrates 4620 2.2.4. CO Oxidation to CO2 4626 2.2.5. Phototocatalysis by MOFs 4627 2.2.6. Carbonyl Cyanosilylation 4630 2.2.7. Hydrodesulfurization 4631 2.2.8. Other Reactions 4632 2.3. MOFs with Reactive Functional Groups 4634 2.4. MOFs as Host Matrices or Nanometric Reaction Cavities 4636
3,106 citations
TL;DR: In this paper, a microporous carbon-supported iron-based catalysts with active sites believed to contain iron cations coordinated by pyridinic nitrogen functionalities in the interstices of graphitic sheets within the micropores was produced.
Abstract: Iron-based catalysts for the oxygen-reduction reaction in polymer electrolyte membrane fuel cells have been poorly competitive with platinum catalysts, in part because they have a comparatively low number of active sites per unit volume. We produced microporous carbon-supported iron-based catalysts with active sites believed to contain iron cations coordinated by pyridinic nitrogen functionalities in the interstices of graphitic sheets within the micropores. We found that the greatest increase in site density was obtained when a mixture of carbon support, phenanthroline, and ferrous acetate was ball-milled and then pyrolyzed twice, first in argon, then in ammonia. The current density of a cathode made with the best iron-based electrocatalyst reported here can equal that of a platinum-based cathode with a loading of 0.4 milligram of platinum per square centimeter at a cell voltage of >/=0.9 volt.
2,762 citations