Activity For Benzene Oxidation Research Articles

Bi-component redox systems obtained from iridium or rhodium chlorides and molybdophosphoric heteropoly acid

An XP, IR and UV–VIS spectroscopy study was carried out to characterize the compositions of molybdophosphate heteropoly anions with Ir(III) or Rh(III) hydroxo–chloro complexes, such as Ir1.1Cl2.4OxHy·(PMo12O40)·16.0 H2O, where x is the number of oxygen atoms in the coordination sphere of iridium, and also mixed-valent species containing partially reduced and dehydrated heteropoly acid of suggested composition (Ir0, IrIII)nClmOxHy(PMo12−pVIMopVO40−p/2) (on the average, n ≈ 1, m < 1, p ≥ 4). The mixed-valent Ir containing species showed stable activity in the gas-phase oxidation of benzene by O2–H2 mixture.

Determination of Oxygen Sources for Oxidation of Benzene on TiO2 Photocatalysts in Aqueous Solutions Containing Molecular Oxygen

Photocatalytic oxidation of benzene to CO(2) was studied in aqueous solutions using different kinds of TiO(2) powders, and isotopic oxygen tracers (H(2)(18)O and (18)O(2)) were used to investigate the oxidation process. Phenol was produced as a main intermediate in solution. When anatase powders, which showed high activity for oxidation of benzene, were used, 70-90% of oxygen introduced into phenol was from water. On the other hand, when rutile powders were used, only 20-40% of the oxygen was from water. The rest was from molecular oxygen in both cases. The rate of phenol production by using molecular oxygen was nearly the same between anatase and rutile powders. Hence, the high activity of anatase powders for oxidation of benzene to CO(2) is attributed to their high activity for oxidation of benzene to phenol, which is considered to be the rate-determining step, using water as the oxygen source. The processes using water and molecular oxygen as the oxygen sources are ascribed, respectively, to oxygen transfer and hole transfer processes in the initial step of benzene oxidation.

Synthesis and characterization of Pd/ZSM-5/MCM-48 biporous catalysts with superior activity for benzene oxidation

ZSM-5/MCM-48 composite materials with different acidities and enhanced thermal stability have been synthesized via a simple and reliable in situ overgrowth method. The as-prepared biporous materials and the Pd-impregnated catalysts were systematically investigated by various techniques, including XRD, ICP-OES, N 2 adsorption/desorption, H 2 chemisorption, SEM, TEM/HRTEM, FT-IR, 27Al MAS NMR, NH 3-TPD, H 2-TPR and XPS. The characterization results reveal that all composite catalysts exhibit high surface area, large pore volume and long pore diameter. The quantity of acid sites increases as the ZSM-5 additive amount increases, and Al atoms are in the tetrahedral coordination positions in composite materials. The activity tests demonstrate that all the Pd-loaded catalysts are active in the total elimination of benzene, while the catalytic activity values of Pd-loaded ZSM-5/MCM-48 composite catalysts are much higher than those of Pd/ZSM-5 or Pd/MCM-48 alone. Both Pd 0 and Pd 2+ are responsible for the oxidation reaction, and the catalytic activities are primarily related to the support acidity and the Pd dispersion. In addition, the stability of the composite catalysts also improves with an appropriate amount of ZSM-5 additives in MCM-48. This research shows that the novel Pd-loaded composite catalysts are promising materials in the elimination of VOCs.

Complete Benzene Oxidation over Colloidal Gold Catalysts Supported on Nanostructure Zinc Oxide

The catalytic activities of various nanometer metal oxides (ZnO, CeO2, ZrO2, Al2O3, Co3O4, MgO) supported colloidal gold catalysts with self-designed equipment were evaluated and compared for benzene catalytic oxidation. The results showed that ZnO was the most activive support of the colloidal gold among these nanometer metal oxides. The effects of Au/ZnO on the activity for benzene oxidation were investigated at 50- 300°C. The optimal gold loading was 2 wt%. The Au/ZnO was characterized using BET, XRD, and TEM methods. The XRD patterns and TEM image showed that gold nanoparticles were well dispersed on the surface of ZnO, and the mean diameter was 3.1±0.81 nm. The gaseous products of benzene oxidation and the adsorbed species on Au/ZnO catalyst surface were characterized with FTIR and GC-MS. It was proved that benzene was completely oxidized into CO2 and H2O over the Au/ZnO catalyst at low temperature.

CuO–CeO 2 binary oxide nanoplates: Synthesis, characterization, and catalytic performance for benzene oxidation

This work reports the first synthesis of CuO–CeO 2 binary oxides with a plate-like morphology by a solvothermal method. The as-prepared CuO–CeO 2 nanoplates calcined at 400 °C were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectrum, and tested for catalytic oxidation of dilute benzene in air. Various structural characterizations showed that large amounts of copper species were exposed on the CuO–CeO 2 nanoplate surface. The effect of the synthesis conditions on the structure of the product, as well as the growth process of the nanoplates, has been studied and discussed. The CuO–CeO 2 nanoplates exhibited an excellent catalytic activity for benzene oxidation despite its relatively low surface area and could catalyze the complete oxidation of benzene at a temperature as low as 240 °C.

Nanosized CuO–Zr xCe 1 − xO y aerogel catalysts prepared by ethanol supercritical drying for catalytic deep oxidation of benzene

Nanosized CuO–Zr x Ce 1 − x O y (0 ≤ x ≤ 0.5) solid solution oxide catalysts were prepared using a co-precipitation method followed with ethanol supercritical drying and calcination at 800 °C. The structural characteristics and redox behaviors were investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, and temperature programmed reduction (H 2-TPR). The results revealed that the as-prepared samples not only possessed large specific surface areas, small crystal sizes and high homogeneity of constituents, but also exhibited high catalytic activity for the complete oxidation of benzene. The structural properties and the catalytic performances of the aerogel catalysts strongly depended on the Ce/Zr molar ratio. The most highly active catalyst, CuO–Ce 0.5Zr 0.5O y , could oxidize benzene at 300 °C and kept robust in a 50 h long-term duration test, implying it would be a good and cost-effective alternative to noble metal catalysts for the complete oxidation of VOCs at lower temperatures.

Deep Oxidation of Benzene on Pt/V2O5–TiO2 Catalysts

The combustion of benzene was studied on Pt supported on V2O5–TiO2 samples containing different amounts of V2O5. Vanadium was highly dispersed as V4+ for low V2O5 loadings, forming a vanadia monolayer on titanium dioxide for a V2O5 concentration of about 5%wt. V2O5–TiO2 samples were more active than V2O5 and TiO2 single oxides, and the activity increased with the vanadia content. The platinum dispersion in Pt/V2O5–TiO2 catalysts increased with the V2O5 loading but the activity for the deep oxidation of benzene exhibited an opposite trend. Benzene combustion was a structure sensitivity reaction promoted on larger metallic Pt crystallites which were preferentially formed when the V2O5 content in the sample was decreased.

Liquid-phase oxidation of benzene and phenol on MCM-41 mesoporous molecular sieves modified with iron and cobalt compounds

Nanostructured (I) Fe2O3 and Co3O4 stabilized in the mesopores of an MCM-41 sieve and immobilized (II) FeCl2, Fe(acac)3, and FePc on the surface of an MCM-41 sieve functionalized with 3-aminopropyltriethoxysilane (3-APTES) were synthesized and examined. The materials were characterized by elemental analysis, H2 -TPR, X-ray diffraction analysis, IR and electronic absorption spectroscopy, as well as by low-temperature N2 adsorption. The catalytic activity was evaluated in the reaction of liquid-phase oxidation of benzene and phenol with hydrogen peroxide. Catalysts I showed a low activity in benzene oxidation, whereas catalysts II were active in the oxidation of phenol.

Catalytic combustion of benzene over metal oxides supported on SBA-15

The catalytic combustion of benzene over metal oxides supported on SBA-15 was investigated. The catalysts were prepared by the incipient wetness method and characterized by XRD, BET, TEM, ESR and TPR. The calcined siliceous SBA-15 and CuO/SBA-15 samples displayed well-resolved patterns with a sharp peak at about 1.0°. It is clear that the loading of CuO on the silica matrix drastically decreases the surface area and pore volume of the catalysts, as would be expected for the incorporation of CuO. Among the supported metal oxides, CuO supported on SBA-15 was found to have the highest activity for benzene oxidation. In addition, copper oxide supported on SBA-15 gives higher catalytic activity than copper oxide supported on MCM-41. From the ESR results, the CuO dispersed on the SBA-15 acts as the active site of the CuO/SBA-15 catalysts in the oxidative decomposition of benzene. The catalytic activity gradually increases with increasing CuO loading on SBA-15.

Biofiltration of BTEX by the fungus Paecilomyces variotii

Benzene, toluene, ethyl benzene and xylenes, known collectively as BTEX, are widespread contaminants, commonly found in soil, aquifers, and the atmosphere. BTEX degradation was evaluated as separate substrates and in mixtures, in liquid culture, and in packed biofilters with the filamentous fungus Paecilomyces variotii CBS115145. BTEX were differentially utilized by P. variotii: toluene was completely degraded, followed by ethyl benzene; benzene was partially assimilated (45%), similarly to m- and p-xylenes, while o-xylene was only 30% metabolized in liquid culture. Carbon recoveries as CO 2 were 48, 40, and 53% for toluene, benzene, and ethyl benzene, respectively. Initial toluene addition allowed complete elimination of m-xylene in 12 days. In mixtures of toluene–benzene and ethyl benzene–benzene, the toluene degradation rate (0.27 mg l −3 h −1) was lower than the rate obtained with only toluene (0.37 mg l −3 h −1), while for ethyl benzene the rate was 0.15 mg l −3 h −1 as single substrate and 0.10 mg l −3 h −1 in the ethyl benzene–benzene mixture. Benzene degradation was also negatively affected by both toluene and ethyl benzene. Enzymatic analyses showed benzene oxidation activity. In biofiltration experiments average total carbon elimination capacities (TCECs) of 70 gC m −3 h −1 and a maximum of around 110 gC m −3 h −1 for the BTEX mixture were attained. Toluene, ethyl benzene, and benzene ECs were around 70 gC m −3 h −1, 40 gC m −3 h −1, and 10 gC m −3 h −1, respectively.

Preparation and formation mechanism of mesoporous CuO–CeO 2 mixed oxides with excellent catalytic performance for removal of VOCs

A simple route has been developed to synthesize mesoporous CuO–CeO 2 mixed oxides. X-ray diffraction, N 2 adsorption and desorption isotherms, and high-resolution transmission electron microscopy have been used to characterize the obtained mesoporous CuO–CeO 2 mixed oxides. The results revealed that the as-prepared CuO–CeO 2 mixed oxides possessed a high BET surface area and pores in the range of 1–10 nm after calcination at 600 °C for 4 h. In order to understand the formation mechanism of the mesoporous structure, the precursor before calcination was characterized by FTIR and TG-DSC. The results showed that the formation of the mesoporous structure with the high BET surface area was ascribed to the decomposition of ammonia nitrate. Further experimental investigations revealed that the amount of ammonia nitrate in the precursor greatly influenced the BET surface area and the pore size of the final product. Furthermore, the method could be extended to the synthesis of other mixed oxides with the mesoporous structures, such as ZrO 2–CeO 2 and ZrO 2–Y 2O 3. The as-prepared mesoporous CuO–CeO 2 sample with the high surface area exhibited highly reducible features as compared to the sample with a low surface area. The mesoporous CuO–CeO 2 powder showed excellent catalytic activity for the complete oxidation of benzene.

Mesoporous silica supported cobalt oxide catalysts for catalytic removal of benzene

Two types of mesoporous silica SBA-15 with different pore diameter were synthesized with an ageing temperature of 373 K and an ageing temperature of 308 K, respectively; in addition, mesoporous silica with amorphous structure was synthesized by adding organosiloxane as part of the silica source during the synthesis procedure. Mesoporous silica and conventional alumina supported cobalt oxide catalysts were prepared by incipient wetness impregnation method. These materials were characterized by FT-IR, nitrogen adsorption-desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and Temperature programmed reduction (TPR) techniques, and the activity of the supported cobalt oxide catalysts for deep oxidation of benzene were evaluated in a fixed-bed reactor. It seems that the pore diameter of the silica increase with the elevation of the ageing temperature. Mesoporous silica supported cobalt oxide catalysts are more active than conventional alumina supported ones. Cobalt oxide can be relatively better dispersed on the surface of mesoporous silica which has larger pore diameter and surface areas. Meanwhile, more silanol groups exist on the surface of amorphous silica, which could induce a strong interaction with the supported cobalt oxide species, leading to poor activity for benzene oxidation.

Synthesis and photocatalytic properties of nano bi-crystalline titania of anatase and brookite by hydrolyzing TiOCl2 aqueous solution at low temperatures

Well-dispersed nano-anatase or bi-crystalline (anatase + brookite) titania powders with a average crystal size below 10 nm have been prepared from aqueous TiOCl2 solution by adjusting pH values of starting solution and adding different additives at low temperatures. Amorphous–anatase transformation of titania could proceed in a liquid–solid reaction at low temperatures, even around room temperature, by catalytic support of H+ ion. The presence of a small amount of SO2−4ion is also unfavorable to the formation of both rutile and brookite. By carefully adjusting preparation conditions, nano pure anatase with higher surface area, good crystallinity and a very good photocatalytic activity for gas-phase oxidation of benzene was obtained.

Asymmetrically modified titanium(IV) oxide particles having both hydrophobic and hydrophilic parts of their surfaces for liquid–liquid dual-phase photocatalytic reactions

Titanium(IV) oxide (TiO 2)-based photocatalyst particles assembled at the phase boundary of a liquid–liquid dual-phase mixture were prepared by partial modification of the external surface of each particle with alkylsilyl groups. The average surface coverage of alkylsilyl groups was estimated by elemental analyses of carbon and ash components of the samples and floatability on aqueous ethanol solutions. Results revealed that the hydrophobicity–hydrophilicity of asymmetrically modified samples was comparable to that of samples fully covered with alkylsilyl groups. TiO 2 particles asymmetrically or fully modified with alkylsilyl groups showed photocatalytic activity for benzene oxidation to produce phenol from an aerated benzene–water dual-phase mixture even without agitation, while bare TiO 2 required mechanical agitation to induce the photocatalytic reaction. However, prolonged irradiation precipitated some of the surface-modified particles in the aqueous layer due to photocatalytic decomposition of surface alkylsilyl groups. The photostability was improved by employment of TiO 2 particles coated with porous silica (SiO 2) as a starting material. Compared with the SiO 2-coated TiO 2 particles fully modified with alkylsilyl groups (o-Si/Ti), the asymmetrically modified SiO 2–TiO 2 particles (w/o-Si/Ti) showed slightly higher photocatalytic activity for benzene oxidation. On the other hand, a notable difference between the two types of particles was observed in photocatalytic hydrogen evolution in the presence of sacrificial donors from a benzene–water mixture and from an aqueous solution under deaerated conditions; w/o-Si/Ti showed the activity more than two-fold greater than that of o-Ti/Si, presumably because of efficient contact of w/o-Si/Ti with both aqueous and organic phases compared with o-Si/Ti, which was rather difficult to contact with the aqueous phase.

Mesoporous SBA-15 material functionalized with ferrocene group and its use as heterogeneous catalyst for benzene hydroxylation

An organic–inorganic hybrid heterogeneous catalyst system was synthesized by covalently anchoring ferrocene onto the mesoporous silica SBA-15 materials. FT-IR, TG-DSC-MS, and EDS analyses demonstrate that the ferrocene has been grafted successfully into the mesoporous SBA-15 materials. Powder X-ray diffraction, HRTEM, and nitrogen adsorption–desorption analysis proved that the textural characteristics of the support were preserved during the drafting experiments and the channels remained accessible, despite the sequential reductions in surface area, pore volume and pore size. The hybrid materials exhibit high catalytic activity for benzene oxidation, with hydrogen peroxide as the oxygen source, and are recyclable and reusable without apparently reduced activity.

Isomorphously substituted Fe-ZSM-5 zeolites as catalysts: Causes of catalyst ageing as revealed by X-band EPR, Mössbauer and 29Si MAS NMR spectra

An unconstrained curve fitting/parameter estimation program adapted to PC was applied for the deconvolution of X-band EPR spectra of Fe(III) in ZSM-5 (MFI) zeolites. The sub-spectra of framework (FW) and extra-framework (EFW) Fe(III) ions sited in environments of different (ligand) symmetry could be identified. The EPR transition probability, r, of Fe(III) in the little oxide clusters (diads, triads) was 13.75 times larger than that incorporated into the lattice. Increase of the cluster size and ordering of the random structure led to reduction of r. When the co-ordination of Fe(III) ions in the oxide clusters approached the cubic symmetry of Fe(III) in the lattice, r converged to 1.0. The state: r=1.0 is equivalent to the development of a crystalline phase. The experimental determination of r revealed important details of catalyst action. The initial activity in the direct oxidation of benzene to phenol (oxidant: N 2O) is due to oxide clusters of random structure (known as “ferrihydrite”). Partial and eventually (almost) complete loss of activity occurs when the clusters get ordered to hematite (or in reducing atmosphere to magnetite, as well). Contrary to fully inactive hematite, magnetite retains about 50% of the original activity because it exposes [Fe(III)] Th–O–[FeIII)] Oh linkages supposed to be responsible for oxidation activity.

Catalytic combustion of benzene over supported metal oxides catalysts

Catalytic combustion of benzene over supported metal oxides has been investigated. The catalysts have been prepared by incipient wetness method and characterized by XRD, FT-Raman, ESR and TPR. Among supported metal oxides, CuOx, supported on TiO2 is found to have the highest activity for benzene oxidation. In addition, among the catalysts of copper oxide supported on TiO2, A12O3 and SiO2, titania-supported catalyst (CuOx/TiO2) gives the highest catalytic activity. CuOx/TiO2 (Cu loading 5.5 wt%) shows the total oxidation of benzene at about 250 °C. From the ESR and FT-Raman results, the CuO dispersed on the TiO2 surface acts as an active site of CuOx/TiO2 catalysts on the oxidative decomposition of benzene. The catalytic activity gradually increases with an increase of Cu loading on TiO2. When Cu loading reaches 5.5 wt%, the total conversion temperature is lowered to 300 °C. However, the catalytic activity considerably decreases at 7 wt% Cu loading. The catalytic activity increased with an increase of oxygen concentration but the concentration of benzene showed no difference in the benzene conversion. This result suggests that the rate determining step is the adsorption of oxygen.

Redox catalysis over metallo-zeolites: Contribution to environmental catalysis

The paper reviews development in analysis and understanding of the structure of active sites in metallo-zeolites and their function in SCR–NOx, NO–NO2 equilibration reaction, and benzene oxidation with N2O to phenol. The opportunities and limitations of various spectral techniques (FTIR, UV-Vis, ESR, EXAFS, Moessbauer, Raman spectroscopy) in connection with these studies are discussed. The attention is centered on Co and Fe species planted in pentasil ring zeolites of various topologies, specifically on Co-beta and Fe-oxo species in zeolites, exhibiting stable SCR–NOx activity under presence of high excess of water vapor existing in real exhaust gases from combustion processes. Also participation of the protonic, Al-Lewis sites and specific Fe-oxo sites is analyzed with respect to these redox reactions. It is shown that the zeolite matrix has a dramatic effect on the SCR–NOx activity of the hosted metal ion species. Main parameters controlling metallo-zeolite activity are the type and structure of metallo-species, distances between the cationic sites and concentration and distribution of Al in the framework. Specific Fe-oxo structures coordinated to zeolite framework exhibit extremely high activity in benzene oxidation with N2O to phenol in contrast to protonic and Al-Lewis sites which contribute to these reactions only by activation of hydrocarbons. Analogous (but probably not identical) Fe-oxo structures bear a potential to be applied in SCR–NOx with C3+ paraffins under high excess of water vapor. Stable SCR–NOx activity of Co-beta zeolite indicates either presence of Co-oxo species of extremely high activity or positive effect of high density of aluminium in specific local framework structure of Co-beta zeolite.

Vanadium incorporated mesoporous silicates as catalysts for oxidation of alcohols and aromatics

Abstract The present paper explores different synthesis conditions (direct hydrothermal synthesis or impregnation) for preparation of vanadium incorporated mesoporous silicate catalysts. Both hexagonal and cubic mesostructures have been obtained by varying the gel composition. All the prepared V-MCM-41 molecular sieves were tested in the oxidation of alcohols (hexanol, cyclohexanol and 1,3-hexanediol) and aromatic hydrocarbons (styrene and benzene) under mild conditions with hydrogen peroxide. The fresh (as-synthesized) and used samples after oxidation reactions were intensively characterized by X-ray diffraction (XRD), N2 adsorption–desorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques. The effect of the preparation conditions on the structure, texture, morphology and acidity of samples has been studied. The results show very low activity of all the V-MCM-41 catalysts in the oxidation of alcohols and high activity and selectivity in oxidation of styrene and benzene. It is interesting to note that the catalysts which are active in the oxidation of styrene to benzaldehyde will be less active in the oxidation of benzene to phenol and vice versa, suggesting that active centers for oxidation of styrene might probably be different to those for oxidation of benzene.

Contribution of Fe and Protonic Sites in Calcined and Steamed ZSM-5 Zeolites to Oxidation of Benzene with N2O to Phenol and Selective Catalytic Reduction of NO with Propane to Nitrogen

NH4-(Fe)ZSM-5 zeolites with concentrations of Fe ranging from 30 to 2000 ppm, introduced into zeolites during their synthesis, either calcined in dry oxygen at 720 K or steamed at 870 K in oxygen stream with 30% water vapor, were investigated in benzene oxidation with N2O to phenol and selective catalytic reduction of NOx to nitrogen. The concentration of Brönsted and Lewis sites was determined by quantitative analysis of IR spectra of adsorbed d3-acetonitrile. The changes in Fe ion coordination were monitored by ESR spectra of Fe(III) ions. The Fe ions have been shown to control the activity of zeolites in the above reactions, while the Al-related acid sites play only a minor role. The steamed zeolites compared to calcined ones exhibited substantially higher activity in oxidation of benzene with N2O to phenol, while the reduction of NOx to nitrogen was considerably suppressed. The steaming resulted in a dramatic decrease in concentration of Brönsted sites, low concentration of Lewis sites and relocalization of Fe ions into cationic sites exhibiting distorted tetrahedral coordination (ESR signals at g = 6.0 and 5.6). It has been concluded that specific Fe sites are required for benzene oxidation to phenol without participation of Brönsted sites, while with the complex SCR-NOx reaction both Fe cationic sites and protonic sites are involved in the catalytic process. Fe sites contribute to oxidation of NO to NO2 and protonic sites control reduction of NO2 to molecular nitrogen.