Catalytic Activity For H2O2 Decomposition Research Articles

Surface chemistry and catalytic activity in H2O2 decomposition of pyrolytically fluoralkylated activated carbons.

According to the proposed pyrolytic method, granular activated carbon (AC) Norit 830 W was functionalized by thermal treatment of AC in hydrofluorocarbon (HFC) gases, pentafluoroethane and 1,1,1,2-tetrafluoroethane, at 400-800 °C. This method does not require activation by plasma and photons. Chemical and elemental analysis showed that the pyrolytic treatment provides a loading of 2.95 mmol (5.6 wt%) of fluorine per gram of AC. Nitrogen adsorption measurements indicated that the microporous structure contracted when AC was treated with HFC at temperatures above 400 °C. Thermogravimetry, Fourier transform infrared spectroscopy (FTIR) with attenuated total reflectance (ATR), and X-ray photoelectron spectroscopy (XPS) demonstrated the evolution of oxygen-containing and fluorine-containing groups to more thermostable groups with treatment temperature. The fluorine-containing groups grafted at high temperature, above 600 °C exhibited the highest thermal stability up to 1250 °C in dry argon. From the data of XPS and solid-state 19F nuclear magnetic resonance spectroscopy data, the grafted fluorine exists in several types of grafted F-containing groups, the HFC residues. By changing the thermal regime of fluorination, the composition of fluorine-containing groups on a carbon surface can be regulated. Isolated fluoroalkyl groups can be grafted at temperatures of 400-500 °C, while at 600 °C and above, the semi-ionic fluorine groups increase significantly. The hydrophobized surface demonstrated the ability to effectively decompose H2O2 in methanol solutions.

Spatial geometric effect driven by the different [MnO6] octahedra entity stacking configurations to facilitate the catalytic decomposition of H2O2 in wastewater

Achieving rapid decomposition of H2O2 is crucial for broadening its applications across various fields, as improper disposal or leakage can lead to serious water pollution. In this work, we explore how the octahedral coordination entity [MnO6] stacking configurations in different MnO2 polymorphs (α-, β-, γ- and δ-) affect their catalytic performance towards H2O2 decomposition. Combining experiments and theoretical simulations, we find that the catalytic activity for H2O2 decomposition strongly depends on the [MnO6] stacking configurations, following the order of δ- < α- < γ- < β-MnO2. δ-MnO2 displays edge-sharing octahedral stacking in a layered structure and thus exhibits the highest catalytic activity, efficiently decomposing H2O2 (0.5 M) in just 2 min at 25 °C without excessive energy consumption. Theoretical calculations further show that the superior active sites are located at the edge Mn-site of its 2D layered structure, with the rate-determining step of H2O desorption (0.55 eV). This study provides crucial insights into the impact of coordination entity stacking configurations on the catalytic activity differences.

Preparation of platinum-free manganese oxide (MnOx) catalyst film for H2O2 decomposition in contact-lens cleaning

A platinum (Pt)-free manganese oxide (MnOx) catalyst film for H2O2 decomposition was prepared on an aluminum (Al) substrate (MnOx/Al) by a hydrothermal impregnation method to decrease the cost of a container used in contact lens cleaning and effectively using Pt materials as other several catalysts. Scanning electron microscopy with energy dispersive X-ray spectroscopy images confirmed that the Al substrate was covered with MnOx. The thickness of the MnOx film was about 300 nm. X-ray diffraction spectra showed that the MnOx film consisted of MnO2 and Mn2O3. The catalytic activity for H2O2 decomposition was estimated by measuring the residual H2O2 concentration, and the target value was ≦100 ppm. The MnOx/Al catalyst was immersed in 35,000 ppm H2O2 solution for 360 min, then the H2O2 concentration decreased to 737 ppm. This result indicated that the MnOx catalyst had a high catalytic activity for H2O2 decomposition but it was not enough for practical use. To improve the catalytic activity, an Al substrate was roughened to increase the specific surface area before preparing an MnOx film. A method with the highest effect of increase in surface roughness was a combination of sandblasting and chemical etching. An MnOx catalyst film was prepared on the roughened Al substrate (MnOx/roughened-Al). When the MnOx/roughened-Al catalyst was immersed in 35,000 ppm H2O2 solution for 360 min, the H2O2 concentration decreased to 38 ppm. When the catalyst was used repeatedly for 10 times, the residual H2O2 concentration was 66 ppm, which indicated that the Pt-free catalyst also had high catalytic durability. These results demonstrated that a roughening was extremely effective in improving both the catalyst activity and durability of a MnOx film catalyst, and a conventional catalyst of a Pt plating film can be replaced with the developed catalyst of the MnOx film on the roughened Al substrate.

Novel immobilized polyoxometalate heterogeneous catalyst for the efficient and durable removal of tetracycline in a Fenton-like system

Polyoxometalates (e.g., phosphotungstic acid) provide a new viewpoint for the development of efficient heterogeneous Fenton-like catalysts due to their distinct chemical structure and catalytic properties. In this work, a polymer composite (PWA/PAN) was successfully prepared by doping phosphotungstic acid (PWA) as an active component in the polyaniline (PAN) matrix. The prepared composite was then applied to degrade tetracycline (TC) in a Fenton-like system. Characterization results confirmed that PWA was dispersed in the inorganic carrier with its unique and stable Keggin-type structure, and the inherent chain structure of PAN did not change markedly. Compared with common heterogeneous Fenton-like catalysts, PWA/PAN displayed better catalytic activity for H2O2 decomposition and TC removal. In the pH range of natural water (pH 6–11), PWA/PAN efficiently catalyzed H2O2 decomposition. Under optimal conditions (20 °C, pH0 7, catalyst dose of 0.5 g/L, and H2O2 concentration of 50 mM), the degradation efficiency of TC and the decomposition efficiency of H2O2 reached 100% and 0.1010 min−1 within 30 min, respectively. PWA/PAN exhibited excellent catalytic activity durability and structural stability. TC degradation efficiency by the PWA/PAN/H2O2 system did not distinctly decrease. In addition, the degradation mechanism of TC in the PWA/PAN/H2O2 system was revealed. Results disclosed that •OH was the main contributor to the degradation of TC, and it achieved most of mineralization of TC. This work is expected to tackle the common issues of easy deactivation, poor stability, and low H2O2 decomposition efficiency of Fenton-like catalysts at neutral pH and provide novel materials for the treatment of antibiotic pollution.

Improved Catalytic Durability of Pt-Particle/ABS for H₂O₂ Decomposition in Contact Lens Cleaning.

In a previous study, Pt nanoparticles were supported on a substrate of acrylonitrile–butadiene–styrene copolymer (ABS) to give the ABS surface catalytic activity for H2O2 decomposition during contact lens cleaning. Although the Pt-particle/ABS catalysts exhibited considerably high specific catalytic activity for H2O2 decomposition, the catalytic activity decreased with increasing numbers of repeated usage, which meant the durability of the catalytic activity was low. Therefore, to improve the catalytic durability in this study, we proposed two types of pretreatments, as well as a combination of these treatments before supporting Pt nanoparticles on the ABS substrate. In the first method, the ABS substrate was etched, and in the second method, the surface charge of the ABS substrate was controlled. A combination of etching and surface charge control was also applied as a third method. The effects of these pretreatments on the surface morphology, surface chemical composition, deposition behavior of Pt particles, and Pt loading weight were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cross-sectional SEM, and inductively coupled plasma atomic emission spectroscopy (ICP-AES), respectively. Both etching and controlling the surface charge effectively improved the catalytic durability for H2O2 decomposition. In addition, the combination treatment was the most effective.

INCORPORAÇÃO DE NB EM ZEÓLITAS: USO COMO CATALISADORES NA DECOMPOSIÇÃO DO PERÓXIDO DE OXIGÊNIO

In this work, the comercial zeolites ZSM-5 and Y were submitted to previous ionic change with NH4NO3, followed by the addition of Nb. The incorporation of Nb on its structure aims increasing the acidity and improved the catalyst activity of these zeolites. The materials obtained are characterized by X-Ray diffraction patterns, chemical analysis, SEM and textural analysis by N2 adsorption. Furthermore, the materials were avaliated by decomposition reaction of the H2O2. The Nb presence improved the catalytic activity for H2O2 decomposition. Moreover, high amounts of Nb incorporated into zeolites caused a partial destruction of the structure of the materials as evidenced by X-Ray diffraction patterns.

Radiolytic Synthesis of Pt-Particle/ABS Catalysts for H₂O₂ Decomposition in Contact Lens Cleaning.

A container used in contact lens cleaning requires a Pt plating weight of 1.5 mg for H2O2 decomposition although Pt is an expensive material. Techniques that decrease the amount of Pt are therefore needed. In this study, Pt nanoparticles instead of Pt plating film were supported on a substrate of acrylonitrile–butadiene–styrene copolymer (ABS). This was achieved by the reduction of Pt ions in an aqueous solution containing the ABS substrate using high-energy electron-beam irradiation. Pt nanoparticles supported on the ABS substrate (Pt-particle/ABS) had a size of 4–10 nm. The amount of Pt required for Pt-particle/ABS was 250 times less than that required for an ABS substrate covered with Pt plating film (Pt-film/ABS). The catalytic activity for H2O2 decomposition was estimated by measuring the residual H2O2 concentration after immersing the catalyst for 360 min. The Pt-particle/ABS catalyst had a considerably higher specific catalytic activity for H2O2 decomposition than the Pt-film/ABS catalyst. In addition, sterilization performance was estimated from the initial rate of H2O2 decomposition over 60 min. The Pt-particle/ABS catalyst demonstrated a better sterilization performance than the Pt-film/ABS catalyst. The difference between Pt-particle/ABS and Pt-film/ABS was shown to reflect the size of the O2 bubbles formed during H2O2 decomposition.

Spectroscopic study and catalytic activity for H2O2 decomposition of new zeolite-porphyrin systems

In this paper, some new catalytic systems—a metallic complex of 5,10,15,20-tetra-p-tolyl-porphyrin (TTP) with Fe [ClFe(III)TTP] entrapped into a natural zeolite (clinoptilolite) and into two synthetic zeolites (X-71, HZSM-5) were synthesized and characterized by energy-dispersive X-ray fluorescence (EDXRF), Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy, thermal analyses (TGA/SDTA) and tested subsequently as catalysts in the hydrogen peroxide decomposition reaction. The metalloporphyrin ClFe(III)TTP used was adsorbed in different proportions on the zeolite matrix. It is entrapped into The X-71 zeolite (due to its higher pore size), and adsorbed onto the other zeolites: HZSM-5 and clinoptilolite. The catalytic activities of the synthesized systems were discussed from kinetic and mechanistic aspects points of view. This paper also evidenced the generation of oxo-dimers of porphyrin during the catalytic reaction, this aspect being valuable for ClFe(III)TTP. The study of the catalytic activities of the synthesized systems leads us to the proposal of an adequate mechanism for the degradation of hydrogen peroxide in the presence of the synthesized catalysts. The most efficient catalyst according to our study is the ClFe(III)TTP/X-71 system.

A novel method for the preparation of Co Schiff-base functionalized MgAl layered double hydroxides

In order to immobilize neutral or positive metal complexes on layered double hydroxides (LDHs) and increase the amount of immobilized metal complexes, a novel strategy for the preparation of metal complex functionalized LDHs is proposed. This strategy involves exfoliating glycine-intercalated MgAl LDH in formamide under an ultrasound treatment, and then grafting silylated metal complexes on MgAl LDH nanosheets, as exemplified by immobilization of Co Schiff-base on MgAl LDHs. The prepared hybrids were characterized by XRD, AFM, FT-IR, TG, N2 adsorption–desorption and ICP techniques and their catalytic performances were investigated in H2O2 decomposition and styrene epoxidation with O2. The results showed that the hybrid prepared by this strategy had higher Co Schiff-base loading than the sample prepared by directly grafting silylated Co Schiff-base on glycine-intercalated MgAl LDHs due to the more accessible grafting sites on the exfoliated MgAl LDH nanosheets. Additionally, it was found that the grafted complexes could effectively impede the restack of LDH nanosheets after removal of the solvent. Thus, the prepared hybrid exhibited higher surface area and more accessible active centers, which made the prepared hybrid exhibit high catalytic activity in H2O2 decomposition and styrene epoxidation with O2. This work gives us a new way to prepare LDH hybrids functionalized with various metal complexes.

Assembly of transition metal ion on cellulose surface anchored with azo-Schiff base and its catalytic activity for H2O2 decomposition

To form polymer-supported catalysts, to eliminate excess H2O2 during wastewater treatment, the assembly of metal ion on cellulose was investigated. Cellulose was covalently grafted with reactive azo-Schiff base containing azo-conjugated system, 3,5-bis {2-hydroxyphenyl-5-[(2-sulfate-4-sulfatoethylsulphonyl-azobenzol) methylene amino]} benzoic acid. Metal ions, Co2+, Mn2+, and Cu2+, were anchored to the modified cellulose by controlling assembly. The cellulose-supported complexes were characterized and the catalytic activity for H2O2 was investigated. Elemental analyses of the cellulose supported complexes, MC–Co, MC–Mn, were well agreed with the proposed composition. Three cellulose-supported complexes had strong catalytic activities for H2O2. H2O2 decomposition rates in 10 min were 84.54% for MC–Co, 94.87%, for MC–Mn, and 77.21% for MC–Cu, respectively. The manganese complex had the strongest catalytic activity among them. The cellulose-supported complexes have potential application in wastewater treatment and biotechnology.

Magnetically Modulated Pot‐Like MnFe2O4 Micromotors: Nanoparticle Assembly Fabrication and their Capability for Direct Oil Removal

This work demonstrates a simple‐structured, low‐cost magnetically modulated micromotor of MnFe2O4 pot‐like hollow microparticles as well as its facile, versatile, and large‐scale growing‐bubble‐templated nanoparticle (NP) assembly fabrication approach. In this approach, the hydrophobic MnFe2O4@oleic acid NPs in an oil droplet of chloroform and hexane assembled into a dense NP shell layer due to the hydrophobic interactions between the NP surfaces. With the encapsulated oil continuously vaporizing into high‐pressured gas bubbles, the dense MnFe2O4 NP shell layer then bursts, forming an asymmetric pot‐like MnFe2O4 micromotor by creating a single hole in it. For the as‐developed simple pot‐like MnFe2O4 micromotor, the catalytically generated O2 molecules nucleate and grow into bubbles preferentially on the inner concave surface rather than on the outer convex surface, resulting in continuous ejection of O2 bubbles from the open hole to propel it. Dexterously integrating the high catalytic activity for H2O2 decomposition to produce O2 bubbles, excellent magnetic property with the instinctive surface hydrophobicity, the MnFe2O4 pot‐like micromotor not only can autonomously move in water media with both velocity and direction modulated by external magnetic field but also can directly serve for environmental oil removal without any further surface modification. The results here may inspire novel practical micromotors.

Electrochemiluminescence immunosensor based on multifunctional luminol-capped AuNPs@Fe3O4 nanocomposite for the detection of mucin-1.

In this work, a novel and multifunctional nanocomposite of luminol capped gold modified Fe3O4 (Lu-AuNPs@Fe3O4) was utilized as the carrier of secondary antibody (Ab2) to fabricate a sandwiched electrochemiluminescence (ECL) immunosensor for ultrasensitive detection of mucin-1 (MUC1). Herein, the luminol capped gold nanoparticles (Lu-AuNPs) were synthesized with HAuCl4 and luminol by the help of NaBH4 at room temperature, and then Lu-AuNPs were adsorbed on the Fe3O4 magnetic nanoparticles (MNPs) to form the nanocomposite of Lu-AuNPs@Fe3O4 via electrostatic interaction. Fe3O4 MNPs in Lu-AuNPs@Fe3O4 exhibited excellent conductivity and admirable catalytic activity in H2O2 decomposition, which could enhance the ECL efficiency of luminol-H2O2 system. In addition, the substrates of gold coated ZnO nanoparticles (AuNPs@ZnO), providing large specific surface areas for primary antibody (Ab1) capturing, were modified on the electrode. As a result, a wide linear range of 7 orders of magnitude from 10 fg/mL to 10 ng/mL was obtained with an ultralow detection limit of 4.5 fg/mL for MUC1.

Synthesis of novel Schiff base metal complexes with reactive groups and their catalytic property for hydrogen peroxide decomposition

A novel water soluble azo Schiff base ligand containing crosslinking reactive groups (A), 3,5-bis [(2-hydroxy-4′-sodiumsulphatoethylsulphonyl) azobenzene- methyneimino]-benzoic acid (BHSABA), and its complexes with Mn2+, Cu2+, Co2+, were synthesized and characterized by elemental analysis, Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (1HNMR) spectroscopy. The Schiff base ligand and its complexes had excellent water solubility. Two reactive groups, p-[(2′-sulphatoethyl) sulphonyl groups, were able to form covalent bonds with biomass, such as cellulose, chitosan and so on, to obtain functional material. Ultraviolet–visible (UV-vis) electronic absorbance and fluorescence spectra of the ligand having azo conjugated system and of the metal complexes were measured. The catalytic activity of the ligand and the complexes for H2O2 decomposition were also investigated. The results show that the fluorescence spectra of the complexes, Co2A and Mn2A, had increased fluorescence phenomena. They had strong catalytic activity for H2O2 decomposition. When the concentration of manganese complex, Mn2A, was 5 mg/l, H2O2 decomposition nearly finished in 40 min at 40℃. The order of catalytic activity of three complexes for H2O2 decomposition was Mn2A &gt; Co2A &gt; Cu2A. The ligand itself had no noticeable catalytic activity for H2O2 decomposition. These novel water soluble Schiff base metal complexes with reactive groups have potential application in the H2O2 decomposition of water treatment fields.

New highly ordered hydrophobic siloxane-based coordination polymers

Two H-bond polymers from carboxypropyl disubstituted disiloxane and bipyridyl compounds, as well as the starting components in different ratios were reacted with zinc acetate. Two new siloxane-containing coordination polymers were thus obtained and characterized. They exhibited highly ordered structures, which were investigated by single crystal XRD. One of the H-bond polymers, as well as a third coordination polymer, without the siloxane component (obtained as secondary product) were also structurally characterized. The siloxane coordination polymer obtained with 4,4′-bipyridyl has a 2D MOF structure. The homologous polymer derived from 1,2-(4-bipyridyl)ethylene forms undulated 2D-layers which are packed in the crystal leading to partial interpenetration with formation of two types of channels along crystallographic axis c. The new siloxane-containing coordination polymers were investigated by FT-IR, DSC–TG–TGA, DVS and static contact angle measurements. They are hydrophobic (by contact angle) and even superhydrophobic effect was observed on bulk powder for one of them. The solvent sorption capacity was measured by tensiometry. They were tested for catalytic activity in H2O2 decomposition and preliminary experiments for oxidation of glucose and viscose were done.

Vapour phase H2O2 decomposition on Mn based monolithic catalysts synthesized by innovative procedures

Manganese oxide catalysts supported on monolithic yttria stabilized zirconia honeycombs were studied for H2O2 decomposition in view of space propulsion applications. The materials were prepared by impregnation (IM), precipitation (PR) and sol–gel (SG) methods and characterized by N2 adsorption, SEM and H2 temperature programmed reduction (TPR). The catalytic activity for H2O2 decomposition was studied under vapour phase conditions. The tests were carried out in a flow apparatus at T=200°C, gas hourly space velocity (GHSV)=2.00 and 2.67s−1, H2O2 concentrations of 11.3mol%. The redox properties of the catalysts were markedly influenced by the preparation method. In the SG catalyst, a large fraction of Mn was not reducible in the TPR tests differently from the PR and IM materials. Despite this effect, the SG catalyst showed an activity comparable or higher than that of PR and IM, due to a more effective dispersion of Mn species. A too strong effect of space velocity on H2O2 conversion was attributed to an autocatalytic effect. A radical mechanism was hypothesized: it was assumed that a reaction between O2 and Mn species produced radicals that promoted the overall reaction.

High-yield synthesis of ultrathin silica-based nanosheets and their superior catalytic activity in H2O2 decomposition

Ultrathin silica-based nanosheets with a thickness of ∼1 nm are fabricated in a low-cost and high-yield system excluding alkali metal ions. Unlike the Na-zeolites with a long capillary and microporous structure, the ultrathin nanosheets exhibit highly effective surface and active sites. As a result, the 0.4 wt% Pt-loaded nanosheets exhibit superior catalytic activity in H(2)O(2) decomposition with an O(2) evolution rate of 342.5 mL g(-1) min(-1) in a clean aqueous system.

A sinusoidal chain constructed from decorated Keggin clusters and {Cu(enMe)2}2+ bridging groups in [Cu(enMe)2(H2O)] [{Cu(enMe)2}{Cu(enMe)2(H2O)W12O40(H2)}] · nH2O

A novel organic–inorganic hybrid material, [Cu(enMe)2(H2O)][{Cu(enMe)2}{Cu(enMe)2(H2O)W12O40(H2)}]·nH2O (n=0.33, enMe=1,2-diaminopropane), has been prepared under mild hydrothermal conditions and characterized by single-crystal X-ray diffraction, IR and magnetic susceptibility measurements. It is revealed that the one-dimensional [{Cu(enMe)2}{Cu(enMe)2(H2O)W12O40(H2)}]2− chain in the structure shows a unique sinusoidal ruffling, which is constructed from decorated Keggin clusters and {Cu(enMe)2}2+ bridging groups through sharing one terminal and one doubly-bridging oxygen atoms of a cluster. The magnetic measurements show that the compound possesses well-separated Cu2+ centers. It was indicated that the hybrid exhibits a good catalytic activity in H2O2 decomposition.

ZrIV-Monosubstituted Keggin-Type Dimeric Polyoxometalates: Synthesis, Characterization, Catalysis of H2O2-Based Oxidations, and Theoretical Study

The previously unknown Zr(IV)-monosubstituted Keggin-type polyoxometalates (Zr-POMs), (n-Bu4N)7H[{PW11O39Zr(mu-OH)}2] (1), (n-Bu4N)8[{PW11O39Zr(mu-OH)}2] (2), and (n-Bu4N)9[{PW11O39Zr}2(mu-OH)(mu-O)] (3) differing in their protonation state, have been prepared starting from heteropolyacid H5PW11ZrO40.14H2O. The compounds were characterized by elemental analysis, potentiometric titration, X-ray single-crystal structure, and IR, Raman, and 31P and 183W NMR spectroscopy. The single-crystal X-ray analysis of 2 reveals that two Keggin structural units [PW11O39Zr]3- are linked through two hydroxo bridges Zr-(OH)-Zr with Zr(IV) in 7-fold coordination. The IR spectra of 1 and 2 show a characteristic band at 772 cm(-1), which moves to 767 cm(-1) for 3, reflecting deprotonation of the Zr-(OH)-Zr bond. Potentiometric titration with methanolic Bu4NOH indicates that 1-3 contain 2, 1, and 0 acid protons, respectively. (83W NMR reveals Cs symmetry of 2 and 3 in dry MeCN, while for 1, it discovers nonequivalence of its two subunits and their distortion resulting from localization of the acidic proton on one of the Zr-O-W bridging O atoms. The (31)P NMR spectra of 2 and 3 differ insignificantly in dry MeCN, showing only signals at delta -12.46 and -12.44 ppm, respectively, while the spectrum of 1 displays two resonances at delta -12.3 (narrow) and -13.2 (broad) ppm, indicating slow proton exchange on the (31)P NMR time scale. The theoretical calculations carried out at the density functional theory level on the dimeric species 1-3 propose that protonation at the Zr-O-Zr bridging site is more favorable than protonation at Zr-O-W sites. Calculations also revealed that the doubly bridged hydroxo structure is thermodynamically more stable than the singly bridged oxo structure, in marked contrast with analogous Ti- and Nb-monosubstituted polyoxometalates. The interaction of 1-3 with H(2)O and H(2)O(2) in MeCN has been studied by both (31)P and (183)W NMR. The stability of the [PW(11)O(39)ZrOH](4-) structural unit toward at least 100-fold excess of H2O2 in MeCN was confirmed by both NMR and Raman spectroscopy. The interaction of 1 and 2 with H2O in MeCN produces most likely monomeric species (n-Bu4N)3+n[PW11O39Zr(OH)(n(H2O)(3-n)] (n = 0 and 1) showing a broad 31P NMR signal at delta -13.2 ppm, while interaction with H2O2 leads to the formation of an unstable peroxo species (delta -12.3 ppm), which reacts rapidly with cyclohexene, producing 2-cyclohexen-1-one and trans-cyclohexane-1,2-diol. Both 1 and 2 show a pronounced catalytic activity in H2O2 decomposition and H2O2-based oxidation of organic substrates, including cyclohexene, alpha-pinene, and 2,3,6-trimethylphenol. The oxidation products are consistent with those of a homolytic oxidation mechanism. On the contrary, 3 containing no acid protons reacts with neither H2O nor H2O2 and shows negligible catalytic activity. The Zr-monosubstituted polyoxometalates can be used as tractable homogeneous probes of Zr single-site heterogeneous catalysts in studying mechanisms of H2O2-based oxidations.

The Effect of Calcium Doping on the Surface and Catalytic Properties of Cobaltic Oxide Catalysts

The effects of calcium oxide doping (0.75, 1.5 and 3 mol% CaO) and calcination temperature (400, 500, 600 and 700°C) on different surface properties of Co3O4 were investigated. The structural properties of pure and doped oxide samples were determined by XRD methods, the textural properties were investigated via the adsorption of nitrogen at −196°C while the hydrogen peroxide decomposition activity of the investigated solids was determined by oxygen gasometric measurement of the reaction kinetics at 20–40°C. The dissolution of calcium ions in the Co3O4 lattice at temperatures in the range 400–600°C was accompanied by a marked decrease in the mean hydraulic radii (rh) and an increase in the surface area (SBET) and total pore volume (Vp) of the prepared oxide samples. In contrast, doping at 700°C brought about a decrease in the SBET and Vp values of the investigated solids. The catalytic activity for H2O2 decomposition on cobaltic oxide calcined at 400–700°C was found to decrease considerably on doping with CaO. The activation energy for sintering (ΔEs) of the pure and doped solids was determined from the variation in their SBET values as a function of the calcination temperature of these solids. Calcium oxide treatment resulted in a 50% increase in the activation energy of sintering of cobaltic oxide solid calcined at 400–600°C. This increase reflects the role of CaO doping in hindering the sintering of cobaltic oxide.

Effect of gamma-irradiation on surface and catalytic properties of Co3O4 doped with NiO

NiO-doped Co3O4 samples precalcined at 500 °C were subjected to various doses of γ-rays within the range 0.2-1.6 MGy. The particle size and BET-surface areas of different samples were determined using XRD and nitrogen adsorption at -196 °C. The catalytic reactions studied were conversion of ethanol and isopropanol at 250-400 °C using a micropulse technique and H2O2 decomposition in aqueous solution at 30-50 °C. The results revealed that the γ-irradiation brought a significant decrease in the particle size of Co3O4 phase with subsequent increase in the SBET surface areas. The treatment brought also a progressive decrease in the total conversion of both alcohol (dehydration and dehydrogenation) falling to a minimum value (about 20% of its initial activity) at a dose of 0.8 MGy. The catalysts retain their initial activity upon exposure to a dose of 1.6 MGy. On the other hand, the catalytic activity in H2O2 decomposition of the investigated system decreased progressively by increasing the dose of γ-rays and the catalysts lost more than 90% of their initial activity upon exposure to a dose of 1.6 MGy.