Direct Synthesis Of H2O2 Research Articles

Core-shell structured composite high-efficiency catalyst Co@Pd/TiO2 with a compressed-strain Pd shell for the direct synthesis of H2O2

Direct synthesis of H2O2 from H2 and O2 still faces the dilemma of low selectivity and productivity due to the O-O bond dissociation. To expedite the resolution of this issue, we introduce a core–shell structured catalyst Co@Pd/TiO2 with a compressed-strain Pd shell. The Co@Pd/TiO2 catalyst demonstrates a superior H2O2 productivity of 6.95 × 103 mmol·gPd-1·h−1 and H2O2 selectivity of 98.1 %, with enhancements of over 192 % and 139 %, respectively, when compared to Pd/TiO2. The construction of the compressed-strain Pd shell on the Co@Pd/TiO2 catalyst induces a winder width (wd) and a lower center (εd) of the Pd d-band, allowing the Co@Pd/TiO2 catalyst to achieve the following benefits for improving H2O2 selectivity and productivity: (1) Reducing the degree of electron back-donation to O2* (* denotes adsorbed state, the same below), thus inhibiting the cleavage of the O-O bond in O2*; (2) Showing a weaker Pd-O bond strength, which stabilizes the OOH* species and suppresses the breakage of the O-O bond therein; (3) Weakening the interaction between the catalyst and chemical substances, thereby restraining H2O2 degradation.

Constructing alkaline microenvironment on catalyst surface for enhanced electrocatalytic synthesis of hydrogen peroxide in a neutral electrolyte

The direct electrochemical synthesis of H2O2 via a two-electron oxygen reduction reaction (2e− ORR) offers a feasible alternative to the energy-intensive anthraquinone oxidation process. Compared to alkaline electrolytes, challenges remain in achieving high 2e− ORR selectivity and activity for electrosynthesis of H2O2 in neutral electrolytes due to the low concentration of OH−, which hinders the effective binding of key intermediate OOH*. Here, we introduced Lewis acid TiO2 to modify carbon black catalyst for adsorbing in-situ generated OH− and created a local alkaline microenvironment for enhancing the 2e− ORR activity and selectivity in neutral electrolytes. H2O2 productivity of TiO2 modified carbon black catalyst (52.5 mmol L−1 h−1) in a neutral electrolyte (0.5 M Na2SO4) at 0.2 V vs. RHE was 1.6 times as much as that of pristine carbon black (33 mmol L−1 h−1), which was similar with that of pristine carbon black (58.4 mmol L−1 h−1) in an alkaline electrolyte (0.1 M KOH). The finite-element method simulations and experiments indicated that TiO2 could enhance local alkalinity to increase the current density for facilitating 2e− ORR. The density functional theory calculations indicated that the introducing of TiO2 into the CB structure could promote the adsorption of O2, facilitate the adsorption of *OOH and reduce the overpotential, resulting in high activity towards 2e− ORR to H2O2. This work proposes a new strategy for optimizing electrode–electrolyte interface to enhance 2e− ORR performance in neutral electrolytes.

Exploring the key role of electronic effects in Pd catalysts supported on Ni-modified N-doped porous carbon for direct synthesis of H2O2 under atmospheric pressure

Developing high-performance catalysts for direct synthesis of hydrogen peroxide (H2O2; DSHP) remains challenging. The paper proposes a strategy to optimize Pd catalysts by enriching Ni-modified N-doped porous carbon. The theoretical studies indicate that Ni modulates the electronic structure of Pd through charge transfer and strain effects, effectively reducing the adsorption energy of reaction intermediates. Furthermore, the Crystal Orbital Hamilton Population (COHP) analysis demonstrated that the energy-integrated COHP (ICOHP) of the OO bonds in O2* (* denotes the adsorbed state), OOH*, and HOOH* were positively correlated with dissociation activation energies and negatively correlated with hydrogenation activation energies. The modulation of the electronic structure of Pd by Ni reduces the hydrogenation activation energies of O2* and OOH* and increases the dissociation activation energies of O2*, OOH*, and HOOH*, thereby enhancing the selectivity and productivity of H2O2. The experimental results aligned with the theoretical predictions, showcasing that the optimized Pd-Ni7.5/NPCs catalyst exhibited remarkable H2O2 selectivity and productivity of 70.5 % and 230.31 mol kgcat-1·h-1, respectively, surpassing the performance of Pd/NPCs (47.1 % and 52.3 mol kgcat-1·h-1). This study offers profound insights into the crucial role of electron effects in DSHP using nickel-modified palladium catalysts, providing strong evidence into the design and optimization of Pd catalysts.

Energy band engineering of graphitic carbon nitride for photocatalytic hydrogen peroxide production

AbstractHydrogen peroxide (H2O2) is one of the 100 most important chemicals in the world with high energy density and environmental friendliness. Compared with anthraquinone oxidation, direct synthesis of H2O2 with hydrogen (H2) and oxygen (O2), and electrochemical methods, photocatalysis has the characteristics of low energy consumption, easy operation and less pollution, and broad application prospects in H2O2 generation. Various photocatalysts, such as titanium dioxide (TiO2), graphitic carbon nitride (g‐C3N4), metal‐organic materials, and nonmetallic materials, have been studied for H2O2 production. Among them, g‐C3N4 materials, which are simple to synthesize and functionalize, have attracted wide attention. The electronic band structure of g‐C3N4 shows a bandgap of 2.77 eV, a valence band maximum of 1.44 V, and a conduction band minimum of −1.33 V, which theoretically meets the requirements for hydrogen peroxide production. In comparison to semiconductor materials like TiO2 (3.2 eV), this material has a smaller bandgap, which results in a more efficient response to visible light. However, the photocatalytic activity of g‐C3N4 and the yield of H2O2 were severely inhibited by the electron‐hole pair with high recombination rate, low utilization rate of visible light, and poor selectivity of products. Although previous reviews also presented various strategies to improve photocatalytic H2O2 production, they did not systematically elaborate the inherent relationship between the control strategies and their energy band structure. From this point of view, this article focuses on energy band engineering and reviews the latest research progress of g‐C3N4 photocatalytic H2O2 production. On this basis, a strategy to improve the H2O2 production by g‐C3N4 photocatalysis is proposed through morphology control, crystallinity and defect, and doping, combined with other materials and other strategies. Finally, the challenges and prospects of industrialization of g‐C3N4 photocatalytic H2O2 production are discussed and envisioned.

The direct synthesis of H2O2 and in situ oxidation of methane: An investigation into the role of the support

The selective oxidation of methane to methanol, using H2O2 generated in situ from H2 and O2 has been investigated using bimetallic gold-palladium catalysts, prepared via an industrially relevant wet co-impregnation protocol on a range of zeolite and metal oxide supports. The choice of catalyst support was found to drastically influence catalyst performance, through control of both nanoparticle dispersion and Pd speciation. Notably in the case of those formulations prepared on metal oxides a direct correlation between catalytic performance towards H2O2 synthesis and methane valorisation exists, whereas in the case of the zeolitic-based analogues, no clear correlation could be drawn between activity towards individual reaction pathways.

Reversible hydrogen spillover induced by Brønsted acid for accelerating direct synthesis of hydrogen peroxide

Supported PdAu bimetallic nanoparticles have been developed for the direct synthesis of H2O2 (DSHP). However, to date, the dilute H2 streams necessary to avoid potential risks of explosion limits the attainable product concentrations of H2O2. Here, a series of silicon-modified Al2O3 (SixAl) were synthesized for loading PdAu bimetallic nanoparticles. The H2 consumption turnover frequency (TOF) and H2O2 formation TOF show a volcano trend with the silica content, where PdAu/Si5.6Al exhibits the best H2 consumption TOF and H2O2 formation TOF (11259.3 and 1995.2 h−1). Silica on the surface of Al2O3 is identified as Brønsted (B) acid site. The increase of B acid sites density accelerates the H2 conversion into H atoms, thereby boosting H2O2 formation process. The adsorption and dissociation of H2 into atomic H at B acid sites would spill across the support to PdAu nanoparticles reversely. The reversed hydrogen spillover effect induced by B acid site accounts for enhanced H2 conversion and H2O2 productivity for PdAu/SixAl.

Enhancing Pd Catalytic Activity by Amine Group Modification for Efficient Direct Synthesis of H2O2.

A great deal of research has been carried out on the design of Pd-based catalysts in the direct synthesis of H2O2, mainly for the purpose of improving the H2O2 selectivity by weakening the activation energy on the Pd active site and thus inhibiting the dissociation of the O-O bonds in O2*, OOH*, and HOOH*. However, this often results in insufficient activation energy for the reaction between H2 and O2 on Pd, leading to difficulties in improving both the selectivity and productivity of H2O2 simultaneously. Based on this, this study reports an efficient catalyst composed of amine-functionalized SBA-15-supported Pd. The strong metal-support interaction not only makes the PdNPs highly dispersed with more Pd active sites but also improves the stability of the catalyst. The amine group modification increases the proportion of Pd0, further enhancing Pd activity and promoting the adsorption and conversion of H2 and O2 on Pd, thereby significantly increasing H2O2 productivity. Additionally, the density-functional theory simulation results showed that due to the hydrogen-bonding force between the amine group and H2O2, this particular anchoring effect would make the hydrogenation and decomposition of H2O2 effectively suppressed. Ultimately, both the selectivity and productivity of H2O2 are improved simultaneously.

Deposition of Pd, Pt, and PdPt Nanoparticles on TiO2 Powder Using Supercritical Fluid Reactive Deposition: Application in the Direct Synthesis of H2O2.

In this study, we investigated the catalytic properties of mono- and bimetallic palladium (Pd) and platinum (Pt) nanoparticles deposited via supercritical fluid reactive deposition (SFRD) on titanium dioxide (TiO2) powder. Transmission electron microscopy analyses verified that SFRD experiments performed at 353 K and 15.6 MPa enabled the deposition of uniform mono- and bimetallic nanoparticles smaller than 3 nm on TiO2. Electron-dispersive X-ray spectroscopy demonstrated the formation of alloy-type structures for the bimetallic PdPt nanoparticles. H2O2 is an excellent oxidizing reagent for the production of fine and bulk chemicals. However, until today, the design and preparation of catalysts with high H2O2 selectivity and productivity remain a great challenge. The focus of this study was on answering the questions of (a) whether the catalysts produced are suitable for the direct synthesis of hydrogen peroxide (H2O2) in the liquid phase and (b) how the metal type affects the catalytic properties. It was found that the metal type (Pd or Pt) influenced the catalytic performance strongly; the mean productivity of the mono- and bimetallic catalysts decreased in the following order: Pd > PdPt > Pt. Furthermore, all catalysts prepared by SFRD showed a significantly higher mean productivity compared to the catalyst prepared by incipient wetness impregnation.

Identifying Pd9OX as the optimum catalyst for the direct synthesis of H2O2 through microkinetic modeling with coverage effects

Identifying efficient active sites for the direct synthesis of hydrogen peroxide over Pd-based catalysts has been a subject of considerable debate. In this study, we employ particle swarm optimization method and density functional theory to explore the H2O2 synthesis mechanism on Pd, PdO, and the partially oxidized surface (Pd9OX). A comprehensive mechanism for Pd9OX is elucidated, and subsequent coverage-dependent kinetic analysis allows for a quantitative assessment of catalytic performance at the interphase. Our findings conclusively establish that the interphase between Pd and PdO represents the optimal active site. Phase diagram analysis further aids in determining stable structures under reaction conditions. At 298.15 K and under oxygen balance, the Pd9O6 surface remains stable throughout the reaction, demonstrating high activity and selectivity. This work underscores the significance of the interphase in comprehending catalytic performance and unveils promising avenues for optimizing catalyst performance by controlling reaction conditions and surface composition.

Sustainable solar-and electro-driven production of high concentration H2O2 coupled to electrocatalytic upcycling of polyethylene terephthalate plastic waste

The photoelectro-reforming of poly (ethylene terephthalate) (PET) waste coupled with the synthesis of hydrogen peroxide (H2O2) poses significant implications for environmental and energy engineering, yet it presents substantial with challenges. A strategy offering an energy efficient photo-electrolysis is reported, which couples oxygen reduction reaction (ORR) with oxidation reaction of PET hydrolysate (glycol, EGOR), utilizating a porous hollow double-shell with oxygen vacancies Z-scheme Mo2N-Co3O4@Fe2O3/PVDF/NF cathode and a Co3O4/NF anode within a cell electrolyser. The H2O2 concentration by hydrophobic photocathode (3.4 wt%) significantly surpasses that of hydrophilic electrode (1.9 wt%), attributing to the hydrophobic modified enhances the mass transfer and utilization efficiency of O2. The Mo2N-Co3O4@Fe2O3 has photothermal effect by introducing Mo2N with local surface plasmon resonance (LSPR) for the direct synthesis of high concentration H2O2 (21.4 wt%). The photoelectro-reforming of PET by photoanode yields the value-added products such as terephthalic acid (PTA) and potassium diformate (KDF) with a high Faradic efffciency (89 %). Notably, EGOR assistes the ORR, resulting in a yield of H2O2 by ORR that is significantly improved at least three times in comparison to the water oxidation reaction coordinated with ORR. This research contributes to a feasible methodology for H2O2 production, and the transformation of plastics and other waste materials into value-added chemicals.

Recent advances in tailoring the microenvironment of Pd-based catalysts for enhancing the performance in the direct synthesis of hydrogen peroxide.

Hydrogen peroxide (H2O2) is a valuable clean chemical, which is widely applied in modern industrial production. In the past few decades, H2O2 has been mainly produced industrially by the anthraquinone method, but the process is complicated and energy consuming, which is only economical for large-scale production and is harmful to the environment. The direct synthesis of H2O2 is considered a promising process to replace the anthraquinone method with high atomic economy, no hazardous by-products, and convenient operation, which has attracted much attention. In this review, we systematically present the recent advances in tuning the microenvironment of Pd-based catalysts for enhancing the performance of the direct synthesis of H2O2, including the modulation of active sites and support, from the viewpoint of the reaction mechanism. Finally, a summary and perspective on the most pressing issues and associated untapped research prospects with the direct synthesis of H2O2 are discussed. The purpose of this review is to provide in-depth insights and guidelines to promote the development of novel catalysts for the direct synthesis of H2O2.

Facet-dependent synthesis of H2O2 from H2 and O2 over single Pt atom-modified Pd nanocrystal catalysts

An electron-rich catalyst (Pt1Pd(111)/TiO2) with a prominent facet dependence displays extraordinary catalytic properties in the direct synthesis of H2O2.

Facile synthesis and electronic structure optimization of sub-nanometer palladium clusters for efficient direct synthesis of H2O2

A sub-nanometer Pd/ZDC catalyst for efficient H2O2 direct synthesis has been successfully prepared by regulating the pore size and nitrogen configuration, achieving a remarkable H2O2 selectivity of 81.6% and productivity of 3323 mmol gPd−1 h−1.

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.

Supercritical deposition of mono- and bimetallic Pd and Pt on TiO[formula omitted] coated additively manufactured substrates for the application in the direct synthesis of hydrogen peroxide

In this study we investigated the properties of mono- and bimetallic Pd and Pt deposited via supercritical fluid reactive deposition (SFRD) on TiO2 coated additively manufactured substrates. The focus of this work lies on the suitability of these catalysts for the direct synthesis of H2O2 in the liquid phase. All catalysts produced showed a high activity towards the desired reaction, derived from high productivities towards the desired product. Thereby, the productivity of the different catalysts decreased in the following order: Pd = PdPt > Pt. In agreement with literature, an increase of the Pd loading from 1 to 2 wt.-% led to a decrease in the productivity. Resulting from comparison with productivities from literature, this method indicates a high suitability of the SFRD method for the suggested application. Due to the easy and eco-friendly nature of this deposition method the catalyst production process can be intensified.

The First Application of Palladium–Phosphorus Catalysts in the Direct Synthesis of Hydrogen Peroxide: Reasons for the Promoting Action of Phosphorus

The main reasons for the promoting effect of phosphorus on the properties of Pd–P/ZSM-5 palladium catalysts in the direct synthesis of H2O2 from H2 and O2 under mild conditions are considered based on data from X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and inductively coupled plasma mass spectrometry (ICP MS). It is shown that the introduction of phosphorus into the composition of the catalyst affects the dispersity, the electronic state of palladium in the surface layer, and the surface concentration of phosphate and phosphite ions. An increase in the H2O2 yield is favored by an increase in the dispersion of Pd–P-catalysts, inhibition of the side process of H2O2 decomposition by surface phosphate and phosphite ions, and a decrease in the solubility of hydrogen in solid solutions of phosphorus in palladium.

Facilitating H+ ion heterolysis using lattice strained Pd-tipped Au nanorods for direct H2O2 synthesis in pure water

Direct H2O2 synthesis (DHS) from H2 and O2 over Pd catalyst is a potentially rewarding strategy to replace the industrial anthraquinone method, but the sluggish hydrogenation process seriously impedes production efficiency in pure water. Here, we report a lattice strained Pd catalyst which is formed on Au nanorods (NRs) tips by taking advantage of curvature. The lattice strained Pd tipped Au NRs (PTA) is found to be able to facilitate the H+ ion heterolysis, in particular with light illumination, thereby remarkably enhancing the DHS performance. The lattice strain effect together with light-induced hot electrons enables a production rate of 0.12 mol/g/h for H2O2 generation, which is 3.11 and 3.56 times higher than that of no light assistance or strain effect ones, respectively. Finally, a porous PTA film was assembled, which achieves a H2O2 concentration of ∼2.3% within 24 h that is expected to make for direct medical use (＜3%).

Self-assembled synthesis of Pd/SPEn from polyelectrolyte membranes for efficient direct synthesis of H2O2 via inhibiting the dissociation of O − O bond

Although a high-activity yield of hydrogen peroxide (H2O2) can be achieved by direct synthesis from hydrogen and oxygen, developing an extreme catalyst with high activity and stability is still very challenging, which limits its industrial application. Here, we reported a catalyst Pd/SPE with polyelectrolyte membranes SPE as an electronic acceptor to anchor Pd, which achieves H2O2 selectivity of 90.1% and productivity of 5764.4 mmol∙gPd-1∙h−1. The results of TEM, XRD and ICP-MS, XPS, CO-DRIFT, O2-TPD, synchrotron radiation and density functional theory (DFT) simulations reveal that the electrons of Pd are transferred into polyelectrolyte membranes and Pd clusters are strongly chemisorbed on SPE, which is beneficial for O2 adsorption and inhibits the dissociation of O-O bond, leading to significantly enhanced H2O2 productivity and selectivity.

Effect of a phosphorus modifier on the behavior of palladium catalysts in direct synthesis of hydrogen peroxide

The behavior of palladium-phosphorus catalysts deposited on a Na-ZSM-5 zeolite support, in the direct synthesis of hydrogen peroxide under mild conditions has been studied. It was found that elemental phosphorus exerts a promoting effect on the activity and selectivity of Pd catalysts for synthesizing H2O2. A direct relationship between the P:Pd ratio (in the range P:Pd = 0: 1.0) and the activity of the catalysts is shown. The influence of phosphorus on the properties of palladium catalysts in side reactions: decomposition and hydrogenation of H2O2 is considered. The chemical and phase composition of Pd-P particles was studied by ICP, HRTEM, electron diffraction, and XRD methods. The modifying effect of phosphorus on the properties of Pd catalysts in the direct synthesis of H2O2 is associated with the formation of solid solutions between palladium and phosphorus, an increase in the dispersion, and the surface roughness of Pd-P particles.

Design of yolk-shell structured PdSn@Pd@HCS nanocatalysts for efficient direct synthesis of H2O2

The direct synthesis of hydrogen peroxide (DSHP) from hydrogen and oxygen is a green synthesis method with a high atomic economy. However, H2O2 selectivity and productivity remain a key challenge, the OO bonds are easily broken with supported Pd catalysts to produce water. Herein, we report the synthesis of bimetallic catalyst PdSn@Pd@HCS by adapting reversed-phase micellar and galvanic replacement reaction. The novel bimetallic yolk-shell structure catalysts exhibit excellent catalytic performance, the selectivity and productivity of H2O2 reaching 98% and 4899 mmol/gPd·h − 1, respectively. Theoretical calculations reveal that the presence of Sn inside the bimetallic alloy can enhance the ligand effect and optimize the electronic structure of the surface Pd atoms, weakening the adsorption ability of O2 molecules and inhibiting the dissociation of OO bonded species, resulting in the enhancement of H2O2 selectivity and productivity. This work provides the groundwork for bimetallic yolk-shell structure catalysts to achieve the efficient synthesis of H2O2.