The role of activated carbon as a catalyst in GAC/iron oxide/H2O2 oxidation process

The catalytic properties of granular activated carbon (GAC) in GAC/iron oxide/hydrogen peroxide (H₂O₂) system was investigated in this research. Batch experiments were carried out in de-ionized water at the desired concentrations of ethylene glycol and phenol. Rate constants for the degradation of hydrogen peroxide and the formation rate of iron species were determined and correlated with mineralization of ethylene glycol at various GAC concentrations. The observed first order degradation rate of hydrogen peroxide in the absence of iron oxide and organic matter increases linearity with the increasing of the GAC concentration. The decomposition rate of hydrogen peroxide was suppressed significantly as the solution pH became acidic or by reducing the surface area of the GAC. The reduction of the surface area was obtained by loading an organic compound (such as phenol) on the GAC or by using the oxidizing agent (H₂O₂). The addition of both chemicals, phenol and H₂O₂, affects mainly the surface area of the small pores, resulting in reducing the catalytic activity inside the micropores.The catalytic properties of the GAC were used to accelerate the formation rate of the ferrous ions, which is known in the literature to be the limiting rate reaction in the classic Fenton like reagent. It was shown that the ethylene glycol mineralization rate was increased by more than 50%.Finally, optimization of the GAC consumption leading to the fastest mineralization of the ethylene glycol, resulting in decreasing of the decomposition rate of H₂O₂ while enhancing the generation rate of ferrous ions.     

Analysis of products distribution and selectivity in maleic acid epoxidation by hydrogen peroxide in catalytic systems

This paper discusses the results of the analysis of products distribution and selectivity in hydrogen peroxide (H₂O₂) epoxidation of maleic acid (MA) in the presence of sodium tungstate as catalyst in the native form and also immobilized on polymer resin support. A specially designed experimental procedure afforded accurate monitoring of the oxygen released during epoxidation occasioned by H₂O₂ decomposition and also enabled selectivity to be reliably estimated. Irrespective of the catalytic system employed, it was observed that between 10 and 15% of the H₂O₂ initially present in the reaction is lost via decomposition which, presumably, is induced by the action of the metallic catalytic species. Consequently, selectivity was observed to drop gradually in the course of the reaction, but more rapidly in the case of the homogeneous catalysis. ©1997 SCI     

Preparation and Study of Pd Catalysts Supported on Activated Carbon Cloth (ACC) for Direct Synthesis of H2O2 from H2 and O2

Activated carbon cloths (ACCs) were used as supports for Pd catalysts. The catalyst preparation was carried out by the impregnation method using acidic solution of palladium dichloride (PdCl₂) as metal precursor. The effects of the oxidation state of the loaded metal, heat treatment of the catalysts in different atmosphere (H₂, air) at different temperatures and surface chemistry of the support on the catalyst characterizations and the catalytic activities were investigated. Wet oxidation of ACC was done by nitric acid in order to induce oxygen-containing surface functional groups. Surface chemistry of the support and oxidation state of the metallic phase was investigated by means of XPS, TPD, SEM, DTA and TGA tests. Direct synthesis of hydrogen peroxide from H₂ and O₂ was performed batch wise in a stainless steel autoclave. The reactions were conducted under high pressure (38 bar) at 0 °C and methanol was used as reaction medium. The direct synthesis results showed that the oxygen-containing surface functional groups increase the selectivity of the catalysts by reducing the rate of water production. Existence of the oxidized state of Pd (PdO) also makes the catalyst more selective than the corresponding zerovalent state (Pd0). PdO affected on selectivity by increasing the rate of H₂O₂ production and reducing the amount of production of water, simultaneously.     

Platinum catalysed decomposition of hydrogen peroxide in aqueous-phase pulsed corona electrical discharge

Electrical discharges in water produced by a pulsed high voltage power supply generate chemically active species (OH, H₂, O₂, H₂O₂, HO₂ and O) that are capable of degrading various hazardous chemicals. Previous experimental studies showed that platinum high voltage electrodes in a pulsed corona electrical discharge lead to significantly higher pollutant removal in comparison to that with other electrode materials. In the present work it was observed that when nickel–chromium was used as a high voltage electrode, the pulsed corona electrical discharge in water produces hydrogen peroxide at a constant rate regardless of the initial pH of the solution. Replacement of the nickel–chromium electrode with a platinum high voltage electrode leads to the decomposition of hydrogen peroxide where the rate of decomposition increases with increasing pH. An Eley-Rideal mechanism describing heterogeneous catalytic hydrogen peroxide decomposition is proposed. It is assumed that the decomposition occurs on the surface of the platinum particles ejected from the platinum high voltage electrode. Combination of the experimental measurements and a mathematical model describing the platinum catalysed hydrogen decomposition suggests that the pH dependent hydrogen peroxide decomposition is caused by the adsorption of molecular hydrogen produced by the discharge and hydroxyl ions on the platinum surface. The influence of gases bubbled into the reactor (argon, oxygen and hydrogen) on the hydrogen peroxide decomposition was also tested by both experiments and the model. Finally, the model was utilized to predict molecular hydrogen and oxygen concentrations at three pH values when either nickel–chromium or platinum high voltage electrodes are used.     

Direct formation of H2O2 from H2 and O2 and decomposition/hydrogenation of H2O2 in aqueous acidic reaction medium over halide-containing Pd/SiO2 catalytic system

Formation of H₂O₂ from H₂ and O₂ and decomposition/hydrogenation of H₂O₂ have been studied in aqueous acidic medium over Pd/SiO₂ catalyst in presence of different halide ions (viz. F⁻, Cl⁻ and Br⁻). The halide ions were introduced in the catalytic system via incorporating them in the catalyst or by adding into the reaction medium. The nature of the halide ions present in the catalytic system showed profound influence on the H₂O₂ formation selectivity in the H₂ to H₂O₂ oxidation over the catalyst. The H₂O₂ destruction via catalytic decomposition and by hydrogenation (in presence of hydrogen) was also found to be strongly dependent upon the nature of the halide ions present in the catalytic system. Among the different halides, Br⁻ was found to selectivity promote the conversion of H₂ to H₂O₂ by significantly reducing the H₂O₂ decomposition and hydrogenation over the catalyst. The other halides, on the other hand, showed a negative influence on the H₂O₂ formation by promoting the H₂ combustion to water and/or by increasing the rate of decomposition/hydrogenation of H₂O₂ over the catalyst. An optimum concentration of Br⁻ ions in the reaction medium or in the catalyst was found to be crucial for obtaining the higher H₂O₂ yield in the direct synthesis.     

Direct Oxidation of H2 to H2O2 and Decomposition of H2O2 Over Oxidized and Reduced Pd-Containing Zeolite Catalysts in Acidic Medium

Both the conversion and H₂O₂ selectivity (or yield) in direct oxidation of H₂-to-H₂O₂ (using 1.7 mol% H₂ in O₂ as a feed) and also the H₂O₂ decomposition over zeolite (viz. H-ZSM-5, H-GaAlMFI and H- ) supported palladium catalysts (at 22 °C and atmospheric pressure) are strongly influenced by the zeolite support and its fluorination, the reaction medium (viz. pure water, 0.016 M or 1.0 M NaCl solution or 0.016 M H₂SO₄, HCl, HNO₃, H₃PO₄ and HClO₄), and also by the form of palladium (Pd⁰ or PdO). The oxidized (PdO-containing) catalysts are active for the H₂-to-H₂O₂ conversion and show very poor activity for the H₂O₂ decomposition. However, the reduced (Pd⁰-containing) catalysts show higher H₂ conversion activity but with no selectivity for H₂O₂, and also show much higher H₂O₂ decomposition activity. No direct correlation is observed between the H₂-to-H₂O₂ conversion activity (or H₂O₂ selectivity) and the Pd dispersion or surface acidity of the catalysts. Higher H₂O₂ yield and lower H₂O₂ decomposition activity are, however, obtained when the non-acidic reaction medium (water with or without NaCl) is replaced by the acidic one.     

Fe-zeolites as catalysts for chemical oxidation of MTBE in water with H2O2

The heterogeneous catalytic wet oxidation of methyl tert-butyl ether (MTBE) with hydrogen peroxide, catalyzed by the iron-containing zeolites Fe-ZSM5 and Fe-Beta, was studied at ambient conditions and pH 7. The kinetics of MTBE degradation could be well-fitted to a pseudo-first-order model. Using Fe-ZSM5, the dependence of the reaction rate constant on hydrogen peroxide and catalyst concentration was determined. Furthermore, the formation and oxidation of tert-butyl alcohol and tert-butyl formate as intermediates of MTBE oxidation were studied. A comparison of the reaction rates of MTBE, trichloroethylene and diethyl ether in the Fe-ZSM5/H₂O₂ system revealed that adsorption plays a positive role for the degradation reaction.Comparing the two types of Fe-containing zeolites applied in this study, Fe-Beta showed a lower catalytic activity for H₂O₂ decomposition and also MTBE degradation. However, in terms of utilization of H₂O₂ for MTBE degradation Fe-Beta is advantageous over Fe-ZSM5. This could be explained by the stronger adsorptive enrichment of MTBE on the Fe-Beta zeolite. This study shows that Fe-containing zeolites are promising catalysts for oxidative degradation of MTBE by H₂O₂.     

Rapid Hydrogen Peroxide Decomposition Using a Microreactor

The rapid decomposition of hydrogen peroxide (H₂O₂) is often desired in the cleanup of excess H₂O₂ when it is used as an oxidant. Although the decomposition process has been studied in batch reactors, it has never been performed before in a fixed‐bed microreactor with residence time on the scale of seconds. With enhanced mass and heat transfer in microreactors, higher H₂O₂ decomposition efficiency compared to batch reactors was obtained. A variety of parameters including length of microchannels, flow rate, solvent composition, and gas pressure were examined carefully and a first‐order kinetic model was established. Within a few seconds, more than 70 % of the H₂O₂ was decomposed successfully. The challenge of catalyst passivation was discussed as well.     

Direct synthesis of hydrogen peroxide from H2/O2 and oxidation of thiophene over supported gold catalysts

Direct synthesis of hydrogen peroxide from H₂ and O₂ was performed over supported gold catalysts. The catalysts were characterized by means of UV–vis, H₂-TPR, TEM and XPS. Based on the results we conclude that metallic Au is the active species in the direct synthesis of hydrogen peroxide from H₂ and O₂. During preparation process of catalyst by deposition–precipitation with urea, the pH value increased and the gold particle size decreased with increasing the urea concentration. The catalyst prepared with higher urea concentration showed a higher activity and its stability also was efficiently improved. Gold nanoparticles, supported on TiO₂ or Ti contained supports, gave a higher catalytic activity. Thiophene can be efficiently oxidized by hydrogen peroxide synthesized in situ from H₂ and O₂ over Au/TS-1.     

Hydroxylation of phenol with H2O2 over transition metal containing nano-sized hollow core mesoporous shell carbon catalyst

The catalytic performance of transition metal (Fe²⁺ or Cu²⁺) containing nano-sized hol low core mesoporous shell carbon (HCMSC) heterogeneous catalysts for the hydroxylation of phenol with hydrogen peroxide (H₂O₂) in water was investigated in a batch reactor. The metal-containing HCMSC catalyst showed higher activity than the same metal ion-exchanged zeolites. The nature of the metal and its content in the HCMSC had remarkable influence on the reaction results under the typical reaction conditions (PhOH/H₂O₂=3, reaction temperature=60 ‡C). Fe²⁺ containing HCMSC catalyst showed high catalytic activity with phenol conversion of 29%, selectivity to catechol (CAT) and hydroquinone (HQ) about 85%, H₂O₂ effective conversion about 70% and selectivity to benzoquinone (BQ) below 1% in the batch system.     

Decomposition of hydrogen peroxide in the presence of activated carbons with different characteristics

BACKGROUND: Catalytic ozonation promoted by activated carbon is a promising advanced oxidation process used in water treatment. Hydrogen peroxide generated as a by‐product from the reaction of ozone with some surface groups on the activated carbon or from the oxidation of some organic compounds present in the water being treated seems to play a key role in the catalytic ozonation process. Hydrogen peroxide decomposition promoted by two granular activated carbons (GAC) of different characteristics (Hydraffin P110 and Chemviron SSP‐4) has been studied in a batch reactor. The operating variables investigated were the stirring speed, temperature, pH and particle size. Also, the influence of metals on the GAC surface, that can catalyze hydrogen peroxide decomposition, was observed. RESULTS: Chemviron SSP‐4 showed a higher activity to decompose hydrogen peroxide than HydraffinP110 (70 and 50% of hydrogen peroxide removed after 2 h process, respectively). Regardless of the activated carbon used, hydrogen peroxide decomposition was clearly controlled by the mass transfer, although temperature and pH conditions exerted a remarkable influence on the process. Catalytic ozonation in the presence of activated carbon and hydrogen peroxide greatly improved the mineralization of oxalic acid (a very recalcitrant target compound). About 70% TOC (total organic carbon) depletion was observed after 1 h reaction in this combined system, much higher than the mineralization achieved by the single processes used. CONCLUSIONS: Of the two activated carbons studied, Chemviron SSP‐4 with an acidic nature presented a higher activity to decompose hydrogen peroxide. However the influence of the operating variables was quite similar in both cases. Experiments carried out in the presence of tert‐butanol confirmed the appearance of radical species. A kinetic study indicated that the process was controlled by the internal mass transfer and the chemical reaction on the surface of the activated carbon. The catalytic activity of hydrogen peroxide in oxalic acid ozonation promoted by activated carbon (O₃/AC/H₂O₂) was also studied. The results revealed the synergetic activity of the system O₃/AC/H₂O₂ to remove oxalic acid. Copyright © 2010 Society of Chemical Industry     

Catalytic decomposition of N2O on supported Pd catalysts: Support and thermal ageing effects on the catalytic performances

This study is devoted to the catalytic decomposition of N₂O over noble metal-based catalysts under lean conditions in the presence of O₂, NO and water. A particular attention has been paid toward the influence of the support and the thermal ageing-induced effects on the catalytic properties of palladium species. In those operating conditions, the deposition of palladium on reducible supports, such as LaCoO₃, leads to higher activity in comparison with conventional supports such as alumina. Surface reconstructions take place during thermal ageing under reactive conditions on pre-reduced perovskite-based catalysts which lead to a significant rate enhancement in the decomposition of N₂O. On the other hand, it was found that oxygen and water strongly inhibit the surface reconstructions associated with changes in the selectivity towards the production of NO₂.     

Reactions of hydrogen peroxide on a silver electrode in alkaline solution

Reactions with hydrogen peroxide on silver in alkaline solutions with H₂O₂ concentration 5 × 10^?7 mol/ml have been studied with the ring-disk electrode. The amount of oxygen formed on the disk as the result of catalytic decomposition of hydrogen peroxide and its oxidation was established on the ring-electrode made from pyrographite. The rate constants of H₂O₂ electrochemical reduction (k₃), its oxidation (k′₂) and catalytic decomposition (k₄) and their dependence on potential have been evaluated. The constant k₄ scarcely depends on potential; it is ca 10^?2 cm/s.     

Quantitative studies by differential scanning calorimetry of the reaction between hydrogen peroxide and lignocellulose

Heat of reaction and kinetic parameters were determined by differential scanning calorimetry for decomposition of hydrogen peroxide, reaction of hydrogen peroxide with lignocellulosic materials, glucose and pinitol, and for the reaction of the same materials with produced or introduced oxygen. The heat of decomposition of hydrogen peroxide obtained in N₂ (720 cal/g H₂O₂) was in fair agreement with literature data, considering the different temperature and pressure conditions. The heats of reaction of hydrogen peroxide and lignocelluloses were higher when determined in N₂ (1670–2500 cal/g H₂O₂) than in O₂ (1450–2020 cal/g H₂O₂) atmosphere. The activation energy for decomposition of hydrogen peroxide amounted to 20.3 kcal/mol in N₂ and 15.9 kcal/mol in O₂ with frequency factors of 5.7 × 10⁹ and 3.7 × 10⁷ min^?1, respectively. The activation energies for the reaction of hydrogen peroxide and lignocellulosic materials tested were similar and not influenced by the atmospheric composition, ranging overall between 19.7 and 22.4 kcal/mol. The corresponding frequency factors ranged between 2.77 × 10⁹ and 2.23 × 10¹¹.     

Catalytic activities of amino acid modified,starch‐grafted acrylamide for the decomposition of hydrogen peroxide

Acrylamide was grafted onto corn starch with ceric(IV) ions as an initiator. Starch‐graft‐polyacrylamide was modified with amino acids through a reaction with the sodium salts of glycine, β‐alanine, and phenylalanine. The catalytic activities of the iron(III) complexes of the amino acid modified grafted materials were investigated for the decomposition of hydrogen peroxide (H₂O₂). These new polymeric supports were found to be active in the catalytic decomposition of H₂O₂. The extent of decomposition varied with the composition of the support. The iron(III) complex of the glycine‐modified material was the most active of the amino acid supported catalysts. Factors that affected the rate of reaction, such as the concentration of H₂O₂, the amount of the catalyst, the pH, and the temperature, were investigated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 630–636, 2004     

Kinetic study of hydrogen peroxide decomposition at high temperatures and concentrations in two capillary microreactors

On the background of the direct adipic acid synthesis from cyclohexene and H₂O₂, a kinetic model was derived for the H₂O₂ decomposition catalyzed by sodium tungstate at high H₂O₂ concentrations and high temperatures. A perfluoroalkoxy (PFA) and a stainless steel micro‐flow capillary match commonly used microreactor materials. In the PFA capillary, the decomposition of hydrogen peroxide increased with residence time, reaction temperature and catalyst loading. The reaction order with respect to hydrogen peroxide and sodium tungstate was zero and one, respectively. Simulated data fit well with experimental data in the PFA capillary. While showing a similar trend as that in the PFA capillary, the stainless steel capillary exhibited much higher reaction rates. The steel surface participated in the decomposition process as a heterogeneous catalyst. Key influencing factors of the H₂O₂ decomposition provided some clues on the reaction mechanism of the adipic acid synthesis and its process optimization. © 2016 American Institute of Chemical Engineers AIChE J, 63: 689–697, 2017     

H2O2 Generation during Carbon Ozonation – Factors Influencing the Process and Their Implications

Hydrogen peroxide generation during contact of aqueous ozone with activated carbon surface is an established process. However, no systematic research concerning this phenomenon has been conducted. In this paper, factors affecting H₂O₂ generation are presented. Formation of hydrogen peroxide in contact of ozone with carbon is a surface phenomenon, strongly affected by the solution pH. Re-ozonation of the same carbon sample does not lead to H₂O₂ generation. Additionally, the amount of generated H₂O₂ is significant only in strongly acidic environment. It implies that hydrogen peroxide generated by surface of activated carbon cannot be ozone decomposition initiator in catalytic ozonation based on activated carbon as a catalyst.     

Hydrodechlorination of 1,1-Dichlorotetrafluoroethane on Supported Palladium Catalysts. A Static-Circulation Reactor Study

Supported palladium catalysts were studied in CF₃CFCl₂ hydrodechlorination at 100°C using a static-circulation system. In order to minimize catalyst's deactivation a large excess of hydrogen was employed (H₂/CF₃CFCl₂ ratio 54/1). In spite of this precaution significant inhibition of the process occurred, associated with blocking palladium surface by hydrogen chloride species. Differences in the catalytic behavior of alumina-supported and unsupported palladium are discussed. A mild dependence between the catalytic activity and Pd dispersion was found. The Pd/Al₂O₃ catalyst characterized by low metal dispersion was more active than highly dispersed catalysts, showing the overall activity and selectivity to CF₃CFH₂ comparable with those observed by other authors for palladium single crystals. It is speculated that the most active sites for hydrodechlorination are plane atoms, whereas low coordination sites (on edges and corners of metal crystallites) are less suitable.     

Treatment of odorous sulphur compounds by chemical scrubbing with hydrogen peroxide—Application to a laboratory plant

Hydrogen peroxide (H₂O₂) has proved its efficiency when it is used as an oxidant in chemical scrubbing towers. The important H₂O₂ decomposition in basic solutions has been investigated and slowed down by addition of a stabiliser: poly-α-hydroxyacrylic acid. The objective of this work is to implement this alternative in a laboratory scrubbing pilot. H₂S and CH₃SH removals were studied in order to characterise the performances of the process. The consumption of reactants (H₂O₂ and NaOH) was quantified in continuous working with recycling of the scrubbing solution or not. Using hydrogen peroxide in a scrubbing tower gave quite satisfactory results for hydrogen sulphide, and encouraging ones for methylmercaptan. Hydrogen peroxide decomposition observed was economically acceptable, even if compared with the chlorine process. However, sodium hydroxide consumption was found important because of the carbon dioxide competitive absorption.     

Ozone-Based Advanced Oxidation Processes for the Decomposition of N-Methyl-2-Pyrolidone in Aqueous Medium

The present study investigates the decomposition of N-Methyl-2-Pyrolidone (NMP) using conventional ozonation (O₃), ozonation in the presence of UV light (UV/O₃), hydrogen peroxide (O₃/H₂O₂), and UV/H₂O₂ processes under various experimental conditions. The influence of solution pH, ozone gas flow dosage, and H₂O₂ dosage on the degradation of NMP was studied. All ozone-based advanced oxidation processes (AOPs) were efficient in alkaline medium, whereas the UV/H₂O₂ process was efficient in acidic medium. Increasing ozone gas flow dosage would accelerate the degradation of NMP up to certain level beyond which no positive effect was observed in ozonation as well as UV light enhanced ozonation processes. Hydrogen peroxide dosage strongly influenced the degradation of NMP and a hydrogen peroxide dosage of 0.75 g/L and 0.5 g/L was found to be the optimum dosage in UV/H₂O₂ and O₃/H₂O₂ processes, respectively. The UV/O₃ process was most efficient in TOC removal. Overall it can be concluded that ozonation and ozone-based AOPs are promising processes for an efficient removal of NMP in wastewater.