H2O2 Hydrogen Research Articles

Properties of palladium-phosphorus catalysts supported on HZSM-5 zeolite in the direct synthesis of hydrogen peroxide

The properties of Pd/HZSM-5 and Pd–nP/HZSM-5 catalysts in direct synthesis and side processes of decomposition and hydrogenation of H2O2 under mild conditions in ethanol and aqueous-ethanol medium in the presence of an acid inhibitor were studied. Using HR-TEM, XRD and ICP MS methods, it was shown that as a result of modification with phosphorus, X-ray amorphous highly dispersed systems are formed, which represent structurally disordered solid solutions of phosphorus in palladium. The main reasons for the promoting effect of phosphorus on the yield of H2O2 are considered. It has been established that, along with phosphorus and acid modifiers, the use of a zeolite support in the H-form favors the inhibition of the side process of H2O2 decomposition.

Low-Electronegativity Mn-Contraction of PtMn Nanodendrites Boosts Oxygen Reduction Durability.

Platinum metal (PtM, M=Ni, Fe, Co) alloys catalysts show high oxygen reduction reaction (ORR) activity due to their well-known strain and ligand effects. However, these PtM alloys usually suffer from a deficient ORR durability in acidic environment as the alloyed metal is prone to be dissolved due to its high electronegativity. Herein, we report a new class of PtMn alloy nanodendrite catalyst with low-electronegativity Mn-contraction for boosting the oxygen reduction durability of fuel cells. The moderate strain in PtMn, induced by Mn contraction, yields optimal oxygen reduction activity at 0.53 A mg-1 at 0.9 V versus reversible hydrogen electrode (RHE). Most importantly, we show that relative to well-known high-electronegativity Ni-based Pt alloy counterpart, the PtMn nanodendrite catalyst experiences less transition metals' dissolution in acidic solution and achieves an outstanding mass activity retention of 96 % after 10,000 degradation cycles. Density functional theory calculation reveals that PtMn alloys are thermodynamically more stable than PtNi alloys in terms of formation enthalpy and cohesive energy. The PtMn nanodendrite-based membrane electrode assembly delivers an outstanding peak power density of 1.36 W cm-2 at a low Pt loading and high-performance retention over 50 h operations at 0.6 V in H2 -O2 hydrogen fuel cells.

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.

Inhibition of free heme-catalyzed Fenton-like reaction prevents non-alcoholic fatty liver disease by hepatocyte-targeted hydrogen delivery

The metabolic disorder of hepatocytes in non-alcoholic fatty liver disease (NAFLD) leads to the formation of an iron pool which induces the Fenton reaction-derived ferroptosis and the deterioration of liver disease. The elimination of the iron pool for the removal of Fenton reactions is vitally important to prevent the evolution of NAFLD, but quite challenging. In this work, we discover that free heme in the iron pool of NAFLD can catalyze the hydrogenation of H2O2/‧OH to block the heme-based Fenton reaction for the first time, and therefore develop a novel hepatocyte-targeted hydrogen delivery system (MSN-Glu) by modifying magnesium silicide nanosheets (MSN) with N-(3-triethoxysilylpropyl) gluconamide to block the heme-catalyzed vicious circle of liver disease. The developed MSN-Glu nanomedicine exhibits a high hydrogen delivery capacity as well as sustained hydrogen release and hepatocyte-targeting behaviors, and remarkably improves the metabolic function of the liver in a NAFLD mouse model by the relief of oxidative stress and the prevention of ferroptosis in hepatocytes, accelerating the removal of the iron pool in fundamental support of NAFLD prevention. The proposed prevention strategy based on the mechanisms of NAFLD disease and hydrogen medicine will provide an inspiration for inflammation-related disease prevention.

Boosting Hydrogen Peroxide Electrosynthesis via Modulating the Interfacial Hydrogen-Bond Environment.

Designing highly efficient and stable electrode-electrolyte interface for hydrogen peroxide (H2O2) electrosynthesis remains highly challenging. Inhibition of the side reaction of competitive 4e- oxygen reduction to H2O is essential to obtain highly selective H2O2 electrosynthesis. Instead of catalyst modification to hinder excessive hydrogenation of H2O2, we propose that the addition of a hydrogen-bond acceptor, dimethyl sulfoxide (DMSO) to the KOH electrolyte enables the improvement of the selectivity and activity of H2O2 electrosynthesis simultaneously. Spectral characterization and molecular simulation confirm that the formation of hydrogen bonds between DMSO and water molecules at the electrode-electrolyte interface can reduce the activity of water dissociation into active H* species. The suitable H* supply environment hinders excessive hydrogenation for the oxygen reduction reaction (ORR), thus improving the selectivity of 2e- ORR and achieving over 90% selectivity of H2O2. This work highlights the importance of regulating the interfacial hydrogen-bond environment by organic molecules as a means of boosting electrochemical performance in aqueous electrosynthesis and beyond.

Boosting Hydrogen Peroxide Electrosynthesis via Modulating the Interfacial Hydrogen‐Bond Environment

AbstractDesigning highly efficient and stable electrode‐electrolyte interface for hydrogen peroxide (H2O2) electrosynthesis remains challenging. Inhibiting the competitive side reaction, 4 e− oxygen reduction to H2O, is essential for highly selective H2O2 electrosynthesis. Instead of hindering excessive hydrogenation of H2O2 via catalyst modification, we discover that adding a hydrogen‐bond acceptor, dimethyl sulfoxide (DMSO), to the KOH electrolyte enables simultaneous improvement of the selectivity and activity of H2O2 electrosynthesis. Spectral characterization and molecular simulation confirm that the formation of hydrogen bonds between DMSO and water molecules at the electrode‐electrolyte interface can reduce the activity of water dissociation into active H* species. The suitable H* supply environment hinders excessive hydrogenation of the oxygen reduction reaction (ORR), thus improving the selectivity of 2 e− ORR and achieving over 90 % selectivity of H2O2. This work highlights the importance of regulating the interfacial hydrogen‐bond environment by organic molecules as a means of boosting electrochemical performance in aqueous electrosynthesis and beyond.

Bacteria inactivation using spinel cobalt ferrite catalyst

The E. coli inactivation using hydrogen peroxide (H2O2) and cobalt ferrite granulated catalyst was investigated in a fixed-bed flow reactor. CoFe2O4 catalyst was synthesized by the co-precipitation method, granulated, and annealed at 1150°C. X-ray diffraction analysis was used to identify the crystal structure of the catalyst. CoFe2O4 catalyst demonstrates good catalytic activity for bacteria inactivation in the presence of H2O2. An increase in the hydrogen peroxide concentration increases the inactivation efficiency. The reactor demonstrates the E. coli inactivation of 99.94% at the H2O2 hydrogen peroxide concentration of 15 mM and initial bacterial concentration of 6·103 CFU/L. The water disinfection using a fixed-bed reactor demonstrates the broad prospects for industrial use.

NMR characterization of H2O2 hydrogen exchange

Quantification of H2O2 concentration in aqueous solutions is of interest in many fields. It usually is based on indirect methods that rely on oxidation reactions that turn on/off fluorescent probes. Such methods can suffer from reaction incompleteness and interfering chemical species. We describe optimization of NMR detection that enables direct quantification of H2O2 down to the nanomolar range. Taking advantage of fast hydrogen exchange (HX) between H2O2 and water permits the use of very short interscan delays, greatly increasing sensitivity. The specific acid-, base- and water-catalyzed HX rates at 2 °C were measured to be 2.1 × 107, 6.1 × 109, and 1.4 × 10−1 M−1s−1, respectively, which result in a minimum HX rate at pH 6.2. Furthermore, the exchange is accelerated by general acid/base catalysis. MES and phosphate buffers catalyze HX strongest in their unprotonated forms. For imidazole, only the unprotonated form catalyzes HX, which contrasts with acetic acid where only the protonated state catalyzes exchange. Inorganic salts such as sodium chloride and azide have negligible effect on HX. We present optimal conditions for accurate measurement of H2O2 concentrations as low as 40 nM in aqueous samples in a few hours.

Pd-Ce/AC catalyst with high productivity for direct synthesis of H2O2 at ambient temperature

In this study, a novel catalyst, Pd-Ce/AC catalyst, was synthesized for direct synthesis of H2O2. Compared with Pd/AC catalyst, Pd-Ce/AC catalyst showed higher H2O2 productivity (89 mol H2O2/kgcat·h) and lower H2O2 hydrogenation capacity. The characterization results indicated that the addition of Ce not only reduced the diameter of Pd particles, but also enhanced the content of Pd2+ in the final catalyst. It is expected that the increase of Pd dispersion and Pd2+ content is important for the enhancement of H2O2 productivity.

Direct synthesis of H2O2 in AuPd coated micro channels: An in-situ X-Ray absorption spectroscopic study

For the first time, we perform in-situ X-Ray Absorption Spectroscopy on both Au L3 and Pd K edges during the direct synthesis of hydrogen peroxide in a high-pressure gas-liquid-solid microreactor using SiO2 supported Pd, Au and AuPd catalysts under relevant reaction conditions. The catalysts were coated on the walls of 320 µm ID micro capillaries, used in this work both as microreactors and as spectroscopic cells, ensuring safety of operation, ease of portability and absence of reactor effects during the measurements. XANES analysis revealed that the fresh Pd and AuPd catalysts contained a mix of Pd/PdO phases which was readily reduced in H2 atmosphere. The presence of only metallic Pd under reaction conditions for both catalysts proved that metallic Pd is the active phase for this reaction. Au was present in its metallic form in both Au and AuPd under all conditions tested. Unlike the AuPd, monometallic Pd showed an increase in the Pd-Pd distance under reaction conditions, attributed to the formation of Pd-hydride. We propose that the absence of Pd-hydride in the AuPd catalysts reduces further hydrogenation of H2O2 to water, thereby explaining the increased selectivity to H2O2 observed with AuPd catalysts.

Alternative fuel in the combustion process of combustion engines

Abstract The article analyses the impact of emulsified fuel, containing H2O2 hydrogen peroxide, on the emissions of nitrogen oxides and diesel engine smoke. The process of forming toxic components in exhaust gases of reciprocating engines during the engine operation, and the relationship that specifies the hydrogen peroxide decomposition process were presented. The research was carried out with the use of fuel containing 30%, 20% and 10% of hydrogen peroxide. The concentration courses of the nitric oxide (NO) and nitrogen oxides (NOx), as well as the (CO) carbon monoxide concentration and (S) engine smoke courses were shown separately for the external characteristics of the engine. Finally, the importance of knowledge related to the mechanisms of generation of toxic components in exhaust gases in the reciprocating engines was emphasised.

Direct synthesis of hydrogen peroxide over Pd/C catalyst prepared by selective adsorption deposition method

A new catalyst design based on selective adsorption deposition method was developed to achieve high reaction performance in the direct synthesis of hydrogen peroxide. The activity of the unprecedented Pd/C catalyst was superior to that of the conventionally prepared Pd/C catalysts, and the initial H2O2 productivity and H2 selectivity reached as high as 8606 mmol H2O2/g Pd.h and 95.1%, respectively. This excellent activity may result from the intrinsic structural and electronic features of the active sites, i.e., the extremely small and monodispersed Pd nanoparticles with a high Pd2+/Pd0 ratio, which were realized by combining the selective adsorption of metal precursor cations on a negatively charged activated carbon surface and the subsequent homogeneous surface deposition of palladium hydroxide by the hydroxide ions that are slowly generated upon urea decomposition. The catalytic activity was significantly affected by the oxygen groups of the activated carbon support. The carboxyl groups do not efficiently suppress the unfavorable H-OOH dissociation but rather accelerate the H2O2 hydrolysis by forming hydrogen bonds with H2O2. Moreover, a sharp decrease in the reaction rates of H2O2 hydrogenation and direct synthesis of H2O2 was observed with the increase in the number of carboxyl groups on the activated carbon surface. This loss of activity, as confirmed by acid treatment and olefin hydrogenation experiments, implies that the carboxyl groups in close proximity to the active sites have a detrimental effect by hindering or poisoning the active sites.

Promotional effects of Sb on Pd-based catalysts for the direct synthesis of hydrogen peroxide at ambient pressure

TiO2-supported Pd-Sb bimetallic catalysts were prepared and evaluated for the direct synthesis of H2O2 at ambient pressure. The addition of Sb to Pd significantly enhanced catalytic performance, and a Pd50Sb catalyst showed the greatest selectivity of up to 73%. Sb promoted the dispersion of Pd on TiO2, as evidenced by transmission electron microscopy and X-ray diffraction. X-ray photoelectron spectroscopy indicated that the oxidation of Pd was suppressed by Sb. In addition, Sb2O3 layers were formed and partially wrapped the surfaces of Pd catalysts, thus suppressing the activation of H2 and subsequent hydrogenation of H2O2. In situ diffuse reflection infrared Fourier transform spectroscopy for CO adsorption suggested that Sb homogenously located on the surface of Pd-Sb catalysts and isolated contiguous Pd sites, resulting in the rise of the ratio of Pd monomer sites that are favorable for H2O2 formation. As a result, the Sb modified Pd surfaces significantly enhanced the non-dissociative activation of O2 and H2O2 selectivity.

Effect of Zn addition on the direct synthesis of hydrogen peroxide over supported palladium catalysts

Alumina-supported Pd-Zn bimetallic catalysts were prepared and evaluated for direct synthesis of hydrogen peroxide. The effect of Zn on the catalytic performance was studied via characterizations by transmission electron microscopy (TEM), temperature-programmed reduction (TPR), X-ray photoelectron energy spectroscopy (XPS), temperature-programmed desorption of H2/O2 (H2-/O2-TPD), CO chemisorption and diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption (CO-DRIFTS). H2O2 productivity of up to 25431molkgPd−1h−1 was observed with the optimal bimetallic catalyst 1Pd5Zn, much higher than that over the monometallic catalyst 1Pd (8533molkgPd−1h−1). This increase may be attributed to the geometric change caused by the Zn additive and the electronic interactions between Pd and Zn. The addition of Zn increases the isolated Pd sites (the primary active sites for H2O2 formation), which can promote H2O2 selectivity. PdZn catalysts show a higher Pd dispersion and incremental Pd0 content than monometallic Pd owing to electronic interactions between Pd and Zn, which result in increased H2O2 productivity. However, a high Pd dispersion and incremental Pd0 content can increase the H2O2 hydrogenation rate, negatively affecting the H2O2 selectivity.

Continuous H2O2 direct synthesis process: an analysis of the process conditions that make the difference

Abstract A trickle bed reactor (TBR) was used to study different process parameters upon hydrogen peroxide direct synthesis. The catalysts used were commercial palladium on active carbon. The influence of pressure (1.75–25 barg), temperature (5–60°C), liquid flow rate (2–13.8 ml·min-1), gas flow rate (3.4–58.5 ml·min-1), catalyst amount (90–540 mg), Pd percentage on the support (5% wt., 10% wt. and 30% wt. Pd/C) as well as promoter concentrations (0.0005–0.001 m) were all varied as process parameters to better understand the behaviour of the system. By contrast, the gas phase molar composition of the feed (4:20:76=H2:O2:CO2) was kept constant. The strong influence between liquid flow rate, gas flow rate and catalyst amount were identified as the key parameters to tune the reaction, and related to the activity of the catalyst. In essence, these parameters must be carefully tuned to control the hydrogen consumption. The maximum productivity (289 μmol H2O2·min-1) and yield (83.8%) were obtained when a diluted bed of 30% Pd/C was applied. The H2O2 hydrogenation was studied in order to understand its role in the H2O2 direct synthesis reaction network. The hydrogenation reaction mechanism and the role of NaBr were identified thanks to the experiment proposed in the present work. Consequently, understanding the whole reaction mechanism from the process conditions studied led to a deeper understanding of all of the phenomena involved in the H2O2 direct synthesis.

Insight into active sites of Pd–Au/TiO2 catalysts in hydrogen peroxide synthesis directly from H2 and O2

H2O2 synthesis directly from H2 and O2 and side reactions in this system over a variety of Pd–Au/TiO2 catalysts have been studied systemically. The effects of Pd/Au ratio on H2O2 synthesis and subsequent H2O2 hydrogenation were investigated. The catalysts were characterized using multiple techniques including transmission electron microscopy (TEM), in situ diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption (CO-DRIFTS), X-rays photoelectron spectroscopy (XPS), and temperature-programmed desorption of H2/O2 (H2-/O2-TPD). By detailed analysis of these spectroscopies and the kinetics of this reaction, new insights into various active sites of Pd upon alloying with Au were elaborated. Pd monomer surrounded by Au atoms could be the primary active site for H2O2 formation. In addition, Pd ensembles were assumed to be more active for H2O2 hydrogenation than monomeric Pd sites; the over-oxidation of H2 to H2O likely occurred at the interface between Au and TiO2.

The redox state of young female handball players following acute exercise and a one-month precompetitive training period

Although the relationship between exercise and oxidative stress has been intensively investigated for over 3 decades, there remains a lack of empirical data on exercise-induced oxidative stress in athletes engaged in sporting games, specifically among the population of elite female athletes. Blood samples were taken from female handball players on the Serbian U20 national team at the beginning and end of a one-month preparatory training period, as well as immediately before and after acute treadmill exercise. Levels of superoxide anion radical, hydrogen peroxide, nitric oxide and lipid peroxidation were measured in plasma samples , while levels of reduced glutathione and the activity of superoxide dismutase and catalase were measured in erythrocytes. Both experimental protocols demonstrated significant increases in plasma levels of hydrogen peroxide and decreases in superoxide dismutase activity in erythrocytes. Despite the increase in plasma levels of hydrogen peroxideafter both the treadmill exercise and the one-month training period, the levels of the two antioxidants responsible for eliminating H2O2 hydrogen peroxide were not significantly different, as may be expected. Moreover, the marker of lipid peroxidation, TBARS, was not significantly increased. These findings suggest that the first line of antioxidative defense was effective in the prevention of oxidative stress among young female handball players.

Effect of acid pre-treatment on AuPd/SiO2catalysts for the direct synthesis of hydrogen peroxide

The direct synthesis of hydrogen peroxide is investigated using silica supported Au, Pd and AuPd catalysts. Acid pre-treatment of the silica leads to an increase in the activity of the Pd-containing catalysts and also gives rise to a synergistic enhancement in activity when Au and Pd are combined that is absent in the untreated catalysts. The acid pre-treated mono and bi metallic catalysts show much reduced H2O2 hydrogenation activity compared to their untreated counterparts. The acid pre-treatment increases the concentration of the hydroxyl groups on the support, as demonstrated using inelastic neutron scattering, which helps to disperse the metals on the support. Pd can be dispersed effectively on silica, but Au is very poorly dispersed although this is enhanced marginally by the acid pre-treatment. The origin of the synergistic effect is discussed and is considered to be related to the incorporation of a small amount of Au within the Pd nanoparticles.

Mass transfer and kinetics of H2O2 direct synthesis in a batch slurry reactor

A model of a gas bubbling, batch slurry reactor for H2O2 direct synthesis is presented. Experimental measurements were carried out in the absence of halides and acids at temperatures between 258 and 297K (pressures 14–20bar, depending on temperature) with H2 and O2 diluted in CO2 outside flammability limits (gas phase composition of CO2, O2 and H2 was 77%, 21% and 2%, respectively). Kinetic experiments performed on a commercial 5% Pd/C catalyst (0.15g in 400ml methanolic solution) have been used to identify the intrinsic kinetics and assess the influence of mass transfer. The simplest rate equations compatible with the acknowledged reaction network has been included in a reactor model, which accounts for mass transfer resistances between gas and liquid and bulk of the liquid-catalyst surface.The corresponding Arrhenius parameters were estimated from direct synthesis experiments for all the reactions. Comparable temperature dependence was observed for H2O production, hydrogenation and decomposition (activation energies close to 45kJmol−1), while H2O2 synthesis has a much lower activation energy (close to 24kJmol−1), suggesting that a higher selectivity is achievable at low temperature. Decomposition had a very limited influence on the overall peroxide production rate, being quite slow (its rate is approx. 40% the direct synthesis rate at H2 full conversion). Hydrogenation was the most rapid side reaction, depressing H2O2 production as H2 conversion increased. Independent investigation on the H2O2 hydrogenation in the absence of O2 highlighted significant difference in the kinetics, apparently due to a different oxidation state of the catalyst.A sensitivity analysis on the mass transfer coefficients to allow for uncertainties in the correlations proved that no resistances in the liquid occur, while gas–liquid H2 transfer rate may be limiting, although unlikely, requiring that literature coefficients overestimates the real transfer rate by an order of magnitude.

Selective hydrogenation of hydrogen peroxide in the epoxidation effluent of the HPPO process

Abstract This work describes selective H2O2 hydrogenation in the exit stream of the epoxidation reactor employed in the Hydrogen Peroxide–Propylene Oxide (HPPO) process. Pd/Al2O3 and Pt/Al2O3 catalysts were employed for this purpose. The effect of the reaction temperature, catalyst amount and hydrogen partial pressure on catalyst performance were investigated. It was found that the Pt catalyst is much more active than its Pd counterpart. Under optimized reaction conditions, the hydrogen peroxide present in the exit stream can be completely hydrogenated with the Pt catalyst with a reaction time of no longer than 20 min and an almost negligible amount of byproducts derived from propylene oxide.