Looking for the “Dream Catalyst” for Hydrogen Peroxide Production from Hydrogen and Oxygen

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.

Heterogeneous H2O2-based selective oxidations over zirconium tungstate α-ZrW2O8

Catalytic properties of a crystalline zirconium tungstate, ZrW2O8, the material known mainly for its isotropic negative coefficient of thermal expansion, have been assessed for the liquid-phase selective oxidation of a range of organic substrates comprising CC, OH, S and other functional groups using aqueous hydrogen peroxide as the green oxidant. Samples of ZrW2O8 were prepared by hydrothermal synthesis and characterised by N2 adsorption, PXRD, SEM, EDX, FTIR and Raman spectroscopic techniques. Studies by IR spectroscopy of adsorbed probe molecules (CO and CDCl3) revealed the presence of Brønsted acidic and basic sites on the surface of ZrW2O8. It was demonstrated that ZrW2O8 is able to activate H2O2 under mild conditions and accomplish the epoxidation of CC bonds in alkenes and unsaturated ketones, oxidation of thioethers to sulfoxides and sulfones, along with the oxidation of alcoholic functions to produce ketones and aldehydes. The oxidation of tetramethylethylene and α-terpinene over ZrW2O8 revealed the formation of peroxidation products, 2,3-dimethyl-3-butene-2-hydroperoxide and endoperoxide ascaridole, respectively, indicating the involvement of singlet oxygen in the oxidation process. The ZrW2O8 catalyst preserves its structure and morphology under the turnover conditions and does not suffer from metal leaching. It can be easily recovered, regenerated by calcination, and reused without the loss of activity and selectivity.

A Direct Catalytic Ethanol Fuel Cell (DCEFC) Modified by LDHs, or by Catalase-LDHs, and Improvement in Its Kinetic Performance: Applications for Human Saliva and Disinfectant Products for COVID-19

In this work, it has been experimentally proven that the kinetic performance of a common Direct Catalytic Ethanol Fuel Cell (DCEFC) can be increased by introducing nanostructured (Zn^II,Al^III(OH)₂)⁺NO₃^-·H₂O Layered Double Hydroxides (LDHs) into the anode compartment. Carrying out the measurements with the open-circuit voltage method and using a kinetic format, it has been shown that the introduction of LDHs in the anodic compartment implies a 1.3-fold increase in the calibration sensitivity of the method. This improvement becomes even greater in the presence of hydrogen peroxide in a solution. Furthermore, we show that the calibration sensitivity increased by 8-times, when the fuel cell is modified by the enzyme catalase, crosslinked on LDHs and in the presence of hydrogen peroxide. The fuel cell, thus modified (with or without enzyme), has been used for analytical applications on real samples, such as biological (human saliva) and hand disinfectant samples, commonly used for the prevention of COVID-19, obtaining very positive results from both analytical and kinetic points of view on ethanol detection. Moreover, if the increase in the calibration sensitivity is of great importance from the point of view of analytical applications, it must be remarked that the increase in the speed of the ethanol oxidation process in the fuel cell can also be extremely useful for the purposes of improving the energy performance of a DCEFC.

The Boundary between Two Modes of Gas Evolution: Oscillatory (H2 and O2) and Conventional Redox (O2 Only), in the Hydrocarbon/H2O2/Cu(II)/CH3CN System

During the oxidation of hydrocarbons using hydrogen peroxide solutions, the evolution of gaseous oxygen is a side and undesirable process, in which the consumption of the oxidizer is not associated with the formation of target products. Therefore, no attention is paid to the systematic study of the chemical composition of the gas and the mechanisms of its formation. Filling this gap, the authors discovered a number of new, previously unidentified, interesting facts concerning both gas evolution and the oxidation of hydrocarbons. In a 33% H2O2/Cu2Cl4·2DMG/CH3CN system, where DMG is dimethylglyoxime (Butane-2,3-dione dioxime), and is at 50 °C, evidence of significant evolution of gaseous hydrogen, along with the evolution of gaseous oxygen was found. In the authors’ opinion, which requires additional verification, the ratio of gaseous hydrogen and oxygen in the discussed catalytic system can reach up to 1:1. The conditions in which only gaseous oxygen is formed are selected. Using a number of oxidizable hydrocarbons with the first adiabatic ionization potentials (AIPs) of a wide range of values, it was found that the first stage of such a process of evolving only gaseous oxygen was the single electron transfer from hydrogen peroxide molecules to trinuclear copper clusters with the formation, respectively, of hydrogen peroxide radical cations H2O2•+ and radical anions Cu3Cl5•− (AIP = 5 eV). When the conditions for the implementation of such a single electron transfer mechanism are exhausted, the channel of decomposition of hydrogen peroxide molecules into gaseous hydrogen and oxygen is switched on, which is accompanied by the transition of the system to an oscillatory mode of gas evolution. In some cases, the formation of additional amounts of gaseous products is provided by the catalytically activated decomposition of water molecules into hydrogen and oxygen after the complete consumption of hydrogen peroxide molecules in the reaction of gaseous oxygen evolution. The adiabatic electron affinity of various forms of copper molecules involved in chemical processes is calculated by the density functional theory method.

High-Efficiency Oxygen Reduction to Hydrogen Peroxide Catalyzed by Oxidized Mo2TiC2 MXene

The two-electron oxygen reduction reaction (2e−ORR) pathway electrochemical synthesis to H2O2 has the advantages of low investment and environmental protection and is considered to be a promising green method. Herein, the oxidized Mo2TiC2 MXene (O-Mo2TiC2) was successfully synthesized by a facile hydrothermal method as an electrocatalyst in electrocatalytic H2O2 production. The O-Mo2TiC2 achieved the 90% of H2O2 selectivity and 0.72 V vs. RHE of the onset potential. Moreover, O-Mo2TiC2 showed high charge transfer ability and long-term stable working ability of 40 h. This significantly enhanced electrocatalytic H2O2 production capacity is assigned the oxidation treatment of Mo2TiC2 MXene to generate more oxygen-containing groups in O-Mo2TiC2. This work provides a promising catalyst candidate for the electrochemical synthesis of H2O2.

Heterogeneous Trimetallic Nanoparticles as Catalysts

The development and application of trimetallic nanoparticles continues to accelerate rapidly as a result of advances in materials design, synthetic control, and reaction characterization. Following the technological successes of multicomponent materials in automotive exhausts and photovoltaics, synergistic effects are now accessible through the careful preparation of multielement particles, presenting exciting opportunities in the field of catalysis. In this review, we explore the methods currently used in the design, synthesis, analysis, and application of trimetallic nanoparticles across both the experimental and computational realms and provide a critical perspective on the emergent field of trimetallic nanocatalysts. Trimetallic nanoparticles are typically supported on high-surface-area metal oxides for catalytic applications, synthesized via preparative conditions that are comparable to those applied for mono- and bimetallic nanoparticles. However, controlled elemental segregation and subsequent characterization remain challenging because of the heterogeneous nature of the systems. The multielement composition exhibits beneficial synergy for important oxidation, dehydrogenation, and hydrogenation reactions; in some cases, this is realized through higher selectivity, while activity improvements are also observed. However, challenges related to identifying and harnessing influential characteristics for maximum productivity remain. Computation provides support for the experimental endeavors, for example in electrocatalysis, and a clear need is identified for the marriage of simulation, with respect to both combinatorial element screening and optimal reaction design, to experiment in order to maximize productivity from this nascent field. Clear challenges remain with respect to identifying, making, and applying trimetallic catalysts efficiently, but the foundations are now visible, and the outlook is strong for this exciting chemical field.

Enhancing the catalytic performance of PdAu catalysts by W-induced strong interaction for the direct synthesis of H2O2

W-Induced strong interaction with PdAu is the key to the enhanced catalytic performance for the direct synthesis of H2O2, with WO3 species partially encapsulating the PdAu particles.

Direct synthesis of H2O2 over Pd–M@HCS (M = Sn, Fe, Co, or Ni): effects of non-noble metal M on the electronic state and particle size of Pd

Direct synthesis of H2O2 in a yolk–shell structure assisted by M (M = Fe,Co,Ni,Sn) metal doping.

Continuous-flow reactor setup for operando x-ray absorption spectroscopy of high pressure heterogeneous liquid-solid catalytic processes

A continuous-flow reactor and a continuous-flow setup compatible with operando x-ray absorption spectroscopy (XAS) were designed for safely studying liquid-phase reactions on solid high atomic number transition metal catalysts (e.g., Au, Pd, and Pt) under pressures up to 100 bars with temperatures up to 100 °C. The reactor has a stainless-steel body, 2 mm thick polyether ether ketone (PEEK) x-ray windows, and a low internal volume of 0.31 ml. The rectangular chamber (6 × 5 × 1 mm³) between the PEEK x-ray windows allows us to perform XAS studies of packed beds or monoliths in the transmission mode at any position in the cell over a length of 60 mm. A 146° wide-angle beam access also allows recording complementary x-ray fluorescence or x-ray diffraction signals. The setup was engineered to continuously feed a single-phase liquid flow saturated with one or more gaseous reactants to the liquid-solid XAS reactor containing no free gas phase for enhanced process safety and sample homogeneity. The proof of concept for the continuous-flow XAS cell and high-pressure setup was provided by operando XAS measurements during the direct synthesis of hydrogen peroxide at room temperature and 40 bars using a 35 ± 5 mg catalyst (1 wt. % Pd/TiO₂) and inline near-infrared spectroscopy. The experiments prove that the system is well suited to follow the reaction in the liquid phase while recording high-quality XAS data, paving the way for detailed studies on the catalyst structure and structure-activity relationships.

High-performance single-atom Ni catalyst loaded graphyne for H2O2 green synthesis in aqueous media

The electrochemical synthesis of hydrogen peroxide (H₂O₂) provides a greener and more efficient method compared with classic catalysts containing toxic metals. Herein, we used first-principles density functional theory (DFT) calculations to investigate 174 different single-atom catalysts with graphyne substrates, and conducted a three-step screening strategy to identify the optimal noble metal-free single atom catalyst. It is found that a single Ni atom loaded on γ-graphyne with carbon vacancies (Ni@V-γ-GY) displayed remarkable thermodynamic stability, excellent selectivity, and high activity with an ultralow overpotential of 0.03 V. Furthermore, based on ab-initio molecular dynamic and DFT calculations under the H₂O solvent, it was revealed that the catalytic performance for H₂O₂ synthesis in aqueous phase was much better than that in gas phase condition, shedding light on the hydrogen bond network being beneficial to accelerate the transfer of protons for H₂O₂ synthesis.

Metal-Organic Frameworks in Oxidation Catalysis with Hydrogen Peroxide

In recent years, metal–organic frameworks (MOFs) have received increasing attention as selective oxidation catalysts and supports for their construction. In this short review paper, we survey recent findings concerning use of MOFs in heterogeneous liquid-phase selective oxidation catalysis with the green oxidant–aqueous hydrogen peroxide. MOFs having outstanding thermal and chemical stability, such as Cr(III)-based MIL-101, Ti(IV)-based MIL-125, Zr(IV)-based UiO-66(67), Zn(II)-based ZIF-8, and some others, will be in the main focus of this work. The effects of the metal nature and MOF structure on catalytic activity and oxidation selectivity are analyzed and the mechanisms of hydrogen peroxide activation are discussed. In some cases, we also make an attempt to analyze relationships between liquid-phase adsorption properties of MOFs and peculiarities of their catalytic performance. Attempts of using MOFs as supports for construction of single-site catalysts through their modification with heterometals will be also addressed in relation to the use of such catalysts for activation of H2O2. Special attention is given to the critical issues of catalyst stability and reusability. The scope and limitations of MOF catalysts in H2O2-based selective oxidation are discussed.

Facile Direct Seed-Mediated Growth of AuPt Bimetallic Shell on the Surface of Pd Nanocubes and Application for Direct H2O2 Synthesis

The selective enhancement of catalytic activity is a challenging task, as catalyst modification is generally accompanied by both desirable and undesirable properties. For example, in the case of the direct synthesis of hydrogen peroxide, Pt on Pd improves hydrogen conversion, but lowers hydrogen peroxide selectivity, whereas Au on Pd enhances hydrogen peroxide selectivity but decreases hydrogen conversion. Toward an ideal catalytic property, the development of a catalyst that is capable of improving H-H dissociation for increasing H2 conversion, whilst suppressing O-O dissociation for high H2O2 selectivity would be highly beneficial. Pd-core AuPt-bimetallic shell nanoparticles with a nano-sized bimetallic layer composed of Au-rich or Pt-rich content with Pd cubes were readily prepared via the direct seed-mediated growth method. In the Pd-core AuPt-bimetallic shell nanoparticles, Au was predominantly located on the {100} facets of the Pd nanocubes, whereas Pt was deposited on the corners of the Pd nanocubes. The evaluation of Pd-core AuPt-bimetallic shell nanoparticles with varying Au and Pt contents revealed that Pd-core AuPt-bimetallic shell that was composed of 2.5 mol% Au and 5 mol% Pt, in relation to Pd, exhibited the highest H2O2 production rate (914 mmol H2O2 gmetal−1 h−1), due to the improvement of both H2O2 selectivity and H2 conversion.

Tailored Palladium-Platinum Nanoconcave Cubes as High Performance Catalysts for the Direct Synthesis of Hydrogen Peroxide

To obtain high catalytic properties, finely modulating the electronic structure and active sites of catalysts is important. Herein, we report the design and economical synthesis of Pd@Pt core-shell nanoparticles for high productivity in the direct synthesis of hydrogen peroxide. Pd@Pt core-shell nanoparticles with a partially covered Pt shell on a Pd cube were synthesized using a simple direct seed-mediated growth method. The synthesized Pd@Pt core-shell nanoparticles were composed of high index faceted Pt on the corners and edges, while the Pd-Pt alloy was located on the terrace area of the Pd cubes. Because of the high-indexed Pt and Pd-Pt alloy sites, the synthesized concave Pd@Pt₇ nanoparticles exhibited both high H₂ conversion and H₂O₂ selectivity compared with Pd cubes.