Construction of Boron-Promoted Ti Active Centers in Titanosilicates for Selective Oxidation Reactions.

This Review provides a summary of the use and the role of coordination complexes as precursors for the generation of heterogeneous catalysts for oxidation reactions of interest for fine chemical synthesis. Specific attention is paid to the comprehension of phenomena explaining the formation of active sites in heterogeneous catalysts. Different families of coordination precursors are considered. For each example, a brief critical description of the synthesis, characterization, and catalytic performance is reported. Special attention is paid to the chemical environment of the first coordination sphere of the active metal centre. The catalysts obtained by heterogenization, grafting, or anchoring of homogeneous catalysts can therefore exhibit enhanced catalytic performance by merging advantages of both homogeneous and heterogeneous systems. The deposition of coordination complexes over a preformed support is indeed a conceptually versatile strategy to design novel catalysts with tuned and controlled properties.

Chapter 19 Metal ions associated to molecular sieve frameworks as catalytic sites for selective oxidation reactions

Carboxylates are important intermediates in oxidative reactions on gold, as they are precursors to carboxylic acids and CO2; they may also act as site-blockers in oxidative coupling of alcohols, thereby decreasing both catalyst activity and selectivity. We demonstrate that the reaction selectivity and pathways for a prototype carboxylate, acetate, adsorbed on Au(111), are dramatically altered by the presence of coadsorbed atomic O. Finely tuning the initial oxygen coverage affords control of the product selectivity and the reaction pathway. Oxygen-assisted γ-C–H activation occurs with coadsorbed oxygen near 425 K, yielding mainly CO2 and formaldehyde, and a kinetic isotope effect is observed for these products. In the absence of coadsorbed oxygen, acetate reacts at 530 K by C–C bond cleavage to form CO2, methyl, and methyl acetate as well as minor products. These studies have led to the identification of a new synthetic pathway for ester formation, in which methyl (either produced in the reaction or intro...

The conversion of an oleochemical waste i.e. glycerol into lactic acid (LA) using bifunctional catalyst is receiving intensive research attention. The major concern is to achieve a suitable combination of the non-precious active metals with specific roles to achieve a fast and selective reaction. Catalyst with a Ce-to-Zr ratio of 1:2 and supported on SBA-15 at total active metal loadings between 10 and 40 wt% were prepared via a two-sequential-step post-impregnation method. The catalysts were then characterized using nitrogen adsorption–desorption and SEM analyses to elucidate their properties. They were then employed in selective glycerol oxidation reaction carried out at between 240 and 280 °C for up to 3 h to yield LA. The catalytic performance in terms of glycerol conversion and lactic acid yield was successfully correlated with the physicochemical properties of the catalysts. The highest glycerol conversion of 91.2% of glycerol was obtained using 10 wt% of CeZr/SBA-15 at a catalyst loading of 25 wt% with almost 51.4% of corresponding LA yield. It was attributed to the desired shape selectivity effect in the benzylic rearrangement (Cannizzaro reaction) of pyruvaldehyde to suppress by-product formations.

The Control of the Coordination Chemistry for the Genesis of Heterogeneous Catalytically Active Sites in Oxidation Reactions

This chapter deals with the use and development of heterogeneous non-precious metal oxide-based catalysts for aerobic oxidation reactions in gas–solid and liquid–solid phases. The main solid catalysts from transition metal ions (Mn, Cu, Fe, V, Ce, Nd, Mo, W) are described. Many examples are given about the reactions, catalytic performances, catalysts used and major industrial processes, either existing at present using petroleum-based raw materials or future processes using biomass-derived raw materials. It concerns selective oxidation and ammoxidation (NH3 + O2) reactions of alkanes to alkenes; alkanes to carboxylic acids, aldehydes and nitriles; olefins to carboxylic aldehydes and acids and aromatics to the corresponding acids or nitriles. Total oxidation reactions for depollution treatment and combustion are also briefly presented regarding atmospheric pollutants, such as industrial volatile organic compounds (VOCs). Some reaction mechanisms (radical-type or Mars and van Krevelen-type) along with concerns on the structure and size of active sites are discussed. Different reactor types, including packed bed, membrane and moving bed technology, are discussed depending on the intended reaction, as well as considerations on physical aspects of the solid catalysts, related to thermal and electrical conductivities, attrition resistance, deactivation and regeneration of the catalysts.

Atomically precise coinage metal nanoclusters (Au, Ag, Cu) with exposed metal sites have garnered significant interest due to their exceptional catalytic properties and tunable electronic structures. These nanoclusters (NCs) provide a unique platform for optimizing catalytic reactions, including CO 2 reduction, hydrogenation, oxidation, and electrochemical water splitting. This review offers an overview of strategies to create and stabilize exposed metal sites in NCs, focusing on ligand engineering, heteroatom doping, and hybrid surface modifications. It is explored how atomic‐level precision enhances catalytic performance, particularly in electrocatalytic CO 2 reduction, hydrogen evolution reaction (HER), and oxygen evolution reaction (OER). Additionally, the catalytic efficiency of these NCs is highlighted in selective reduction and oxidation reactions, such as hydrogenation and C─O bond formation. The review also discusses the effects of structural design, metal doping, and alloying on catalytic performance, along with the role of NC encapsulation in polyoxometalates (POMs) for improved stability and efficiency. Finally, challenges related to the stability of NCs under harsh conditions are addressed and provide insights into future research aimed at improving scalability, durability, and efficiency for sustainable energy conversion and green catalysis applications.

Synthesis, O2-binding ability and catalytic oxidation performance of cobalt(II) complexes with dihydroxamic acid functionalized N-pivot lariat ethers

Kinetics of the Selective CO Oxidation in H2-Rich Gas on Pt/Al2O3

The development of efficient methods for the enantioselective oxidation of organic molecules continues to be an important goal in organic synthesis; in particular, the use of earth-abundant metal catalysts and environmentally friendly oxidants in catalytic asymmetric oxidation reactions has attracted significant interest over the last several decades. In nature, metalloenzymes catalyze a wide range of oxidation reactions by activating dioxygen under mild conditions. Inspired by selective and efficient oxidation reactions catalyzed by metalloenzymes, researchers have developed a number of synthetic model compounds that mimic the functionality of metalloenzymes. Among the reported biomimetic model compounds, tetradentate aminopyridine (N4) ligands have emerged as appealing frameworks because of their easy synthesis and facile diversification, and their complexes with metals such as Fe and Mn have proven to be versatile and powerful catalysts for a variety of (enantioselective) oxidation reactions. In this Account, we describe our efforts on the design of chiral N4 ligands and the use of their manganese and iron complexes in asymmetric oxidation reactions with H2O2 as the terminal oxidant, aiming to show general strategies for asymmetric oxidation reactions that can guide the rational design of ligands and relevant metal catalysts. In studies of manganese catalysts, the aryl-substituted (R,R)-mcp [mcp = N,N'-dimethyl-N,N'-bis(pyridine-2-ylmethyl)cyclohexane-1,2-diamine] manganese complexes exhibited high enantioselectivity in the asymmetric epoxidation (AE) of various olefins with H2O2 while requiring stoichiometric acetic acid as an additive for the activation of H2O2. To address this issue, we established bulkier N4 ligands for this catalytic system in which a catalytic amount of sulfuric acid enables the manganese-complex-catalyzed AE with improved stereocontrol and efficiency. In addition, this system was found to be active for the oxidative kinetic resolution of secondary alcohols. Further exploration of the structure-reactivity relationships has shown that aminobenzimidazole N4 ligands derived from l-proline, in which the conventional pyridine donors are replaced by benzimidazoles, act as promising ligands. These novel C1-symmetric manganese catalysts showed dramatically improved activities with unprecedented turnover numbers in the AE reactions. Notably, this class of manganese complexes can catalyze the oxidation of the C-H bonds of spirocyclic hydrocarbons and spiroazacyclic compounds in a highly enantioselective manner, providing ready access to chiral spirocyclic β,β'-diketones and spirocyclic alcohols. Remarkably, iron catalysts with these chiral N4 ligands are effective for AE of olefins, enabling rare examples of highly enantioselective syntheses of epoxides by the iron catalysts. Finally, mechanistic studies provide valuable insights into the roles of the carboxylic acid and sulfuric acid in the catalytic oxidation reactions. Thus, the results described in this Account have demonstrated the importance of tunability and compatibility of the ligands for the development of efficient oxidation catalysts with earth-abundant transition metals and environmentally benign oxidants, and we hope that our study will pave the way for the discovery of efficient oxidation catalysis.

Single-atom alloys (SAAs) are a different type of alloy where a guest metal, usually a noble metal (e.g., Pt, Pd, and Ru), is atomically dispersed on a relatively more inert (e.g., Ag and Cu) host metal. As a type of atomic-scale catalyst, single-atom alloy catalysts have broad application prospects in the field of heterogeneous catalysis for hydrogenation, dehydrogenation, oxidation, and other reactions. Numerous experimental and characterization results and theoretical calculations have confirmed that the resultant electronic structure caused by charge transfer between the host metal and guest metal and the special geometric structure of the guest metal are responsible for the high selectivity and catalytic activity of SAA catalysts. In this review, the common methods for the preparation of single-atom alloys in recent years are introduced, including initial wet impregnation, physical vapor deposition, and laser ablation in liquid technique. Afterwards, the applications of single-atom alloy catalysts in selective hydrogenation, dehydrogenation, oxidation reactions, and hydrogenolysis reactions are emphatically reviewed. Finally, several challenges for the future development of SAA catalysts are proposed.

Catalytic oxidation performance and ion-exchange of Ti-MWW zeolite membrane with dual organic template agents and potassium carbonate

A double‐sided nanobrush Co3O4 (Co3O4−B) catalyst was successfully prepared by a hydrothermal method for the first time, and Co3O4 rods (Co3O4−R), Co3O4 hexagonal plates (Co3O4−H) and Co3O4 double‐sided helianthus discs (Co3O4−D) were also synthesized through tuning the water/ethanol ratio. Among all of the as‐prepared catalysts, the Co3O4−B catalyst exhibited the best catalytic activity for benzene oxidation. The excellent catalytic performance could be attributed to the surface abundance Co3+ species, good low‐temperature reducibility and high number of lattice defects with substantial active oxygen species, which resulted from the unique structure of the double‐sided nanobrush. The stability and water tolerance tests demonstrated that the Co3O4−B catalyst displays excellent stability for benzene combustion, and the deactivation caused by water vapor is also reversible. It is concluded that the unique structure of the catalysts plays a crucial role in determining its catalytic oxidation performance.

TS-1 zeolite with homogeneous distribution of Ti atoms in the framework: synthesis, crystallization mechanism and its catalytic performance

Spectroscopic and XRD characterisation of zeolite catalysts active for the oxidative methylation of benzene with methane