Ambient base-free glycerol oxidation over bimetallic PdFe/SiO2 by in situ generated active oxygen species

Recent Progress in Situ Application of H2O2 Produced via Catalytic Synthesis

Industrial production of H2O2 requires lots of energy and causes environmental pollution. Moreover, in subsequent applications, much economic loss could be produced during the transportation process of H2O2 and its dilution process. Therefore, it is highly desirable for in situ application of H2O2. In recent years, catalytic synthesis of H2O2, e. g., direct catalytic synthesis, electrocatalytic synthesis, and photocatalytic synthesis, has attracted more and more attention because the continuous and low-concentration H2O2 produced by catalytic synthesis can be directly used for the oxidation of organic compounds, effectively avoiding the shortcomings of the current industrial route. Here, we briefly reviewed the latest processes for the catalytic production of H2O2 via various routes. On this basis, we summarized and discussed the in situ application of H2O2 in typical organic conversion reactions, including the ammoximation of ketones, the oxidation of alcohols, the oxidation of C-H bonds, and the oxidation of olefins. Some in situ coupling reactions have shown excellent performance with high conversion and selectivity, and the economic cost has been significantly reduced. Finally, the shortcomings of the in situ utilization of H2O2 in coupling reactions were analyzed, and some strategies for promoting the efficiency of the H2O2 application in organic synthesis were proposed.

Selective Oxidation Using In Situ-Generated Hydrogen Peroxide

ConspectusHydrogen peroxide (H2O2) for industrial applications is manufactured through an indirect process that relies on the sequential reduction and reoxidation of quinone carriers. While highly effective, production is typically centralized and entails numerous energy-intensive concentration steps. Furthermore, the overhydrogenation of the quinone necessitates periodic replacement, leading to incomplete atom efficiency. These factors, in addition to the presence of propriety stabilizing agents and concerns associated with their separation from product streams, have driven interest in alternative technologies for chemical upgrading. The decoupling of oxidative transformations from commercially synthesized H2O2 may offer significant economic savings and a reduction in greenhouse gas emissions for several industrially relevant processes. Indeed, the production and utilization of the oxidant in situ, from the elements, would represent a positive step toward a more sustainable chemical synthesis sector, offering the potential for total atom efficiency, while avoiding the drawbacks associated with current industrial routes, which are inherently linked to commercial H2O2 production. Such interest is perhaps now more pertinent than ever given the rapidly improving viability of green hydrogen production.The application of in situ-generated H2O2 has been a long-standing goal in feedstock valorization, with perhaps the most significant interest placed on propylene epoxidation. Until very recently a viable in situ alternative to current industrial oxidative processes has been lacking, with prior approaches typically hindered by low rates of conversion or poor selectivity toward desired products, often resulting from competitive hydrogenation reactions. Based on over 20 years of research, which has led to the development of catalysts for the direct synthesis of H2O2 that offer high synthesis rates and >99% H2 utilization, we have recently turned our attention to a range of oxidative transformations where H2O2 is generated and utilized in situ. Indeed, we have recently demonstrated that it is possible to rival state-of-the-art industrial processes through in situ H2O2 synthesis, establishing the potential for significant process intensification and considerable decarbonization of the chemical synthesis sector.We have further established the potential of an in situ route to both bulk and fine chemical synthesis through a chemo-catalytic/enzymatic one-pot approach, where H2O2 is synthesized over heterogeneous surfaces and subsequently utilized by a class of unspecific peroxygenase enzymes for C-H bond functionalization. Strikingly, through careful control of the chemo-catalyst, it is possible to ensure that competitive, nonenzymatic pathways are inhibited while also avoiding the regiospecific and selectivity concerns associated with current energy-intensive industrial processes, with further cost savings associated with the operation of the chemo-enzymatic approach at near-ambient temperatures and pressures. Beyond traditional applications of chemo-catalysis, the efficacy of in situ-generated H2O2 (and associated oxygen-based radical species) for the remediation of environmental pollutants has also been a major interest of our laboratory, with such technology offering considerable improvements over conventional disinfection processes.We hope that this Account, which highlights the key contributions of our laboratory to the field over recent years, demonstrates the chemistries that may be unlocked and improved upon via in situ H2O2 synthesis and it inspires broader interest from the scientific community.

The Direct Synthesis of Hydrogen Peroxide Over Supported Pd-Based Catalysts: An Investigation into the Role of the Support and Secondary Metal Modifiers

The direct synthesis of H2O2 from molecular H2 and O2 over Pd-based catalysts, prepared via an industrially relevant, excess chloride co-impregnation procedure is investigated. Initial studies into the well-established PdAu system demonstrated the key role of Pd: Au ratio on catalytic activity, under conditions that have previously been found to be optimal for H2O2 formation. Further investigations using the optimal Pd: Au ratio identified the role of the catalyst support in controlling particle size and Pd oxidation state and thus catalytic performance. Subsequently, with an aim to replace Au with cheaper alternatives, the alloying of Pd with more abundant secondary metals is explored.

Graphical Abstract

The oxidative degradation of phenol via in situ H2O2 synthesis using Pd supported Fe-modified ZSM-5 catalysts

Bifunctional Pd/Fe-ZSM-5 catalysts promote pollutant degradation through in situ H2O2 synthesis.

A Perspective on Heterogeneous Catalysts for the Selective Oxidation of Alcohols

Selective oxidation of higher alcohols using heterogeneous catalysts is an important reaction in the synthesis of fine chemicals with added value. Though the process for primary alcohol oxidation is industrially established, there is still a lack of fundamental understanding considering the complexity of the catalysts and their dynamics under reaction conditions, especially when higher alcohols and liquid-phase reaction media are involved. Additionally, new materials should be developed offering higher activity, selectivity, and stability. This can be achieved by unraveling the structure-performance correlations of these catalysts under reaction conditions. In this regard, researchers are encouraged to develop more advanced characterization techniques to address the complex interplay between the solid surface, the dissolved reactants, and the solvent. In this mini-review, we report some of the most important approaches taken in the field and give a perspective on how to tackle the complex challenges for different approaches in alcohol oxidation while providing insight into the remaining challenges.

The degradation of phenol via in situ H2O2 production over supported Pd-based catalysts

The oxidative degradation of phenol via in situ H2O2 production offers an attractive route to the destruction of organic contaminants in water streams, overcoming the significant concerns associated with traditional water remediation technologies.