Oxidation Of O-xylene Research Articles

Shape dependence of nanoceria on complete catalytic oxidation of o-xylene

CeO2 nanorods exhibit the highest concentration of oxygen vacancy clusters for O2 activation, guaranteeing the highest activity for o-xylene oxidation.

Controlling Size, Morphology, and Surface Composition of AgAu Nanodendrites in 15 s for Improved Environmental Catalysis under Low Metal Loadings.

In this work, a simple but powerful method for controlling the size and surface morphology of AgAu nanodendrites is presented. Control of the number of Ag nanoparticle seeds is found to provide a fast and effective route by which to manipulate the size and morphology of nanoparticles produced via a combined galvanic replacement and reduction reaction. A lower number of Ag nanoparticle seeds leads to larger nanodendrites with the particles' outer diameter being tunable in the range of 45-148 nm. The size and surface morphology of the nanodendrites was found to directly affect their catalytic activity. Specifically, we report on the activity of these AgAu nanodendrites in catalyzing the gas-phase oxidation of benzene, toluene and o-xylene, which is an important reaction for the removal of these toxic compounds from fuels and for environmental remediation. All produced nanodendrite particles were found to be catalytically active, even at low temperatures and low metal loadings. Surprisingly, the largest nanodendrites provided the greatest percent conversion efficiencies.

Efficient ceria–silica catalysts for BTX oxidation: Probing the catalytic performance and oxygen storage

This paper describes a systematic investigation on the synthesis of CeO2 supported on SiO2 by two different methods: (i) the in situ incorporation of CeO2 onto MCM-41 and (ii) wet impregnation. We were interested in investigating how the CeO2 preparation could influence their physicochemical properties and catalytic performances towards the benzene, toluene, and o-xylene (BTX) oxidation reactions. Our results showed that the catalytic performances were strongly dependent on the synthetic approach, in which the CeO2–MCM-41 material prepared by the in situ incorporation showed better BTX oxidation activities than the CeO2-based catalysts prepared by conventional wet impregnation. This result could be assigned to the higher specific surface area, better interaction between CeO2 and the support, improved Ce4+/Ce3+ redox process, and higher concentration of oxygen vacancies as enabled by the in situ approach. The influence of CeO2 content in the ordering of the SiO2 mesoporous structure was also demonstrated.

Pd-based nanoflowers catalysts: controlling size, composition, and structures for the 4-nitrophenol reduction and BTX oxidation reactions

We describe herein the synthesis of solid Au@Pd and hollow AgPd nanoflowers displaying controlled sizes and compositions in order to investigate how their size, composition, and the presence of Au in the core of the nanoparticles influence their catalytic performance toward both liquid and gas-phase transformations. While the size and composition of Au@Pd and AgPd the nanoflowers could be controlled as function of growth time, their structure (solid or hollow) was dependent on the nature of the seeds employed for the synthesis, i.e., Au or Ag nanoparticles. Moreover, Au@Pd and AgPd nanoflowers were successfully supported onto commercial silica displaying truly uniform dispersion. The catalytic activities of Au@Pd and AgPd nanoflowers were investigated toward the 4-nitrophenol reduction and the benzene, toluene, and o-xylene (BTX) oxidation. The catalytic activities for the reduction of 4-nitrophenol decreased as follows: Au58@Pd42 > Au27@Pd73 > Ag20Pd80 and Ag8Pd92 > Au12@Pd88 > Ag38Pd62, suggesting that the Au core enhanced the catalytic activity relative to the hollow material when for Pd at.% was up to 80. Regarding the BTX oxidation, supported Au@Pd displayed higher catalytic activities than AgPd nanoflowers, also illustrating the role of the Au cores in the nanoflowers for improving catalytic performance. We believe these results may serve as a platform for the synthesis of Pd-based bimetallic nanomaterials that enable the correlation between these physical/chemical parameters and properties and thus optimized catalytic activities.

Enhanced performances in catalytic oxidation of o-xylene over hierarchical macro-/mesoporous silica-supported palladium catalysts

A series of hierarchical macro-/mesoporous silica supports (MMSs) were successfully synthesized using dual-templating technique employing polystyrene (PS) spheres and the Pluronic P123 surfactant. Pd was next loaded on the hierarchical silica supports via colloids precipitation method. Physicochemical properties of the synthesized samples were characterized by various techniques and all catalysts were tested for the total oxidation of o-xylene. Among them, the Pd/MMS-b catalyst with tetraethoxysilane/polystyrene weight ratio of 1.0 exhibited superior catalytic activity, and under a higher gas hourly space velocity (GHSV) of 70000 h–1, the 90% conversion of o-xylene has been obtained at around 200°C. The BET and SEM results indicated that Pd/MMSb catalyst possesses high surface area and large pore volume, and well-ordered, interconnected macropores and 2D hexagonally mesopores hybrid network. This novel ordered hierarchical porous structure was highly beneficial to the dispersion of active sites Pd nanoparticles with less aggregation, and facilitates diffusion of reactants and products. Furthermore, the Pd/MMS-b catalyst possessed good stability and durability.

OXYGEN AS OXIDANT AND ANTIOXIDANT

New reaction scheme is suggested for the initiated nonbranched-chain addition of free radicals to the multiple bond of the molecular oxygen. The scheme includes the addition reaction of the peroxyl free radical to the oxygen molecule to form the tetraoxyl free radical. This reaction competes with chain propagation reactions through a reactive free radical. The chain evolution stage in this scheme involves a few of free radicals, one of which (tetraoxyl) is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. Based on the proposed scheme rate equations (containing one to three parameters to be determined directly) are deduced using quasi-steady-state treatment. The kinetic description with use the obtained rate equations is applied to the γ-induced nonbranched-chain processes of the freeradical oxidation of liquid o-xylene at 373 K and hydrogen dissolved in water containing different amounts of oxygen at 296 K. The ratios of rate constants of competing reactions and rate constants of addition reactions to the molecular oxygen are defined. In these processes the oxygen with the increase of its concentration begins to act as an oxidation autoingibitor (or an antioxidant), and the rate of peroxide formation as a function of the dissolved oxygen concentration has a maximum. From the energetic standpoint possible nonchain pathways of the free-radical oxidation of hydrogen and the routes of ozone decay via the reaction with the hydroxyl free radical in the upper atmosphere (including the addition yielding the hydrotetraoxyl free radical, which can be an intermediate in the sequence of conversions of biologically hazardous UV radiation energy) were examined. The energetics of the key radical-molecule gas-phase reactions is considered.

The effect of cesium and antimony promoters on the performance of Ti-phosphate-supported vanadium(V) oxide catalysts in selective oxidation of o-xylene to phthalic anhydride

In this work, the effect of vanadium loading as an active phase, cesium and antimony as promoters for the performance of Ti-phosphate-supported vanadium(v) oxide catalysts by experiment design method has been investigated. To find out the effects of parameters on the selectivity to phtalic anhydride, Taguchi approach with L16 array and ANOVA analysis was utilized. The catalyst samples were characterized by BET ‘XRD’ ‘TGA’ ‘SEM’ NH3-TPD. In addition, the catalytic measurements were carried out under continuous flow conditions in fixed-bed reactor. The results show that cesium improves not only activity but also selectivity to phtalic anhydride, while antimony just improves the activity. Meanwhile, the antimony itself has a negative effect on the selectivity to phthalic anhydride. By taking into account main factor effect plot, the sample with composition of 15 wt% vanadium, 0.35 wt% cesium and 1 wt% antimony was chosen as the optimum sample. Finally, this catalyst demonstrated 70.9% selectivity to phthalic anhydride and 100% conversion of o-xylene at 410°C.

Photocatalytic oxidation of nitrogen monoxide and o-xylene by TiO2/ZnO/Bi2O3 nanofibers: Optimization, kinetic modeling and mechanisms

Semiconductor heterojunction structures can effectively enhance the separation efficiency of photogenerated electron/hole pairs and the subsequent photocatalytic performance. With enhanced heterojunctions, novel TiO2/ZnO/Bi2O3 composite nanofibers, synthesized by a simple sol–gel assisted electrospinning method, exhibited much higher photocatalytic activity for the oxidation of nitrogen monoxide (NO) under simulated solar irradiation than commercial TiO2 nanoparticles. The composite nanofibers increased absorption in both UV and visible range when compared with TiO2 nanoparticles. The enhanced photocatalytic activity of TiO2/ZnO/Bi2O3 was attributed to the difference in the energy band positions of anatase, rutile, zincite and bismuth oxide, resulting in both lower band-gap energy and reduced recombination rate of photogenerated electron/hole pairs. Moreover, the photocatalytic performances were more stable for TZB nanofibers than that of TiO2 nanoparticles, which were easily deactivated. In addition, a new kinetic model, taken into account of flow retention time and physical–chemical kinetics, was used to shed light on the behavior of the photocatalytic reaction. Faster kinetics (resulting in higher reactor throughput) and higher conversion efficiency of NO could be realized by optimizing the bismuth concentration in the composite nanofibers. The degradation pathway of o-xylene by TZB had also been investigated.

Versatile and efficient catalysts for energy and environmental processes: Mesoporous silica containing Au, Pd and Au-Pd

We described a versatile approach for the synthesis of Au/MCM-41, Pd/MCM-41 and Au-Pd/MCM-41 by the direct incorporation of the noble metals into the MCM-41 framework. The structural, textural and chemical properties were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), N2-adsorption (BET and BJH methods), H2-chemisorption, small angle X-ray scattering (SAXS), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The nanomaterials, being comprised of Au, Pd and Au-Pd nanoparticles and possessing high surface areas were applied as versatile and efficient catalysts in benzene, toluene and o-xylene (BTX) oxidation and in the steam reforming of ethanol for hydrogen production. The results revealed that the catalytic behavior in both processes was influenced by the experimental conditions and the nature of the catalyst employed. The Au-Pd/MCM-41 catalyst was the most active in the BTX total oxidation. On the basis of characterization data, it was proposed that the close contact between Pd and Au and the higher dispersion of Pd may be responsible for the enhanced activity of the bimetallic catalyst. However, the strong interaction between the noble metals did not improve the performance of the bimetallic catalyst in ethanol steam reforming, the Pd/MCM-41 catalyst being the most active and selective for hydrogen production.

Nonbranched-Chain Oxidation: Low-Reactive RO•4 and HO•4 1:2 Adduct Radicals Shortening Kinetic Chains

New reaction scheme is suggested for the initiated nonbranched-chain addition of free radicals to the multiple bond of the molecular oxygen. The scheme includes the reaction competing with chain propagation reactions through a reactive free radical. The chain evolution stage in this scheme involves a few of free radicals, one of which (tetraoxyl) is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. Based on the proposed scheme rate equations (containing one to three parameters to be determined directly) are deduced using quasi-steady-state treatment. The kinetic description with use the obtained rate equations is applied to the ϒ-induced nonbranched-chain processes of the free-radical oxidation of liquid o-xylene at 373 K and hydrogen dissolved in water containing different amounts of oxygen at 296 K. In these processes the oxygen with the increase of its concentration begins to act as an oxidation autoingibitor (or an antioxidant), and the rate of peroxide formation as a function of the dissolved oxygen concentration has a maximum. The heat effects are compared for the overall reactions of dissociation of simple alkylperoxyl (exothermic) and alkoxyl (endothermic) free radicals in the gas phase. Possible nonchain pathways of the free-radical oxidation of hydrogen and the routes of ozone decay from the energetic standpoint via the reaction with the hydroxyl free radical in the upper atmosphere (including the addition yielding the hydrotetraoxyl free radical, which can be an intermediate in the sequence of conversions of biologically hazardous UV radiation energy) were examined. The energetics of the key radical-molecule reactions is considered.

Interface synthesis of MnO2 materials with various structures and morphologies and their application in catalytic oxidation of o-xylene

MnO2 materials with various structures and morphologies were prepared using KMnO4, and n-, i-, and t-butylamine (the 3 isomers of butylamine, that is, respectively, normal butylamine, isobutylamine and tert-butylamine) as precursors at the dichloromethane/water interface without any template. The relationship between the structure and morphology of the products and the polarity and steric hindrance of butylamine precursor was investigated by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the products synthesized by KMnO4/n-, i-,t-butylamine (the corresponding products were denoted as MnO2-n, MnO2-i and MnO2-t, respectively) were quasi-quadrangular α-MnO2, a mixture of α-MnO2 and δ-MnO2 with irregular structure and nano-spheres δ-MnO2, respectively. Nitrogen adsorption analysis showed that MnO2-n and MnO2-i had a mesoporous structure, while MnO2-t exhibited a macroporous structure. Their surface areas were calculated to be about 185, 65, and 15m2g−1 correspondingly. In addition the obtained materials showed different catalytic abilities for the complete catalytic oxidation of a typical volatile organic compound (VOC), o-xylene.

FACILE SYNTHESIS OF VARIOUS MANGANESE OXIDES NANO/MICRO-CRYSTALS BY A LIGNOSULFANATE-MEDIATED HYDROTHERMAL PROCESS: EFFECT OF THE REACTANT CONCENTRATION AND SOLUTION MEDIA

Various manganese oxides nano/micro-crystals, including Mn 3 O 4 octahedrons, hierarchical flower-like K -δ- MnO 2 microspheres, multi-branch and strip-shaped γ- MnOOH , have been prepared by a lignosulfanate (LSN)-mediated hydrothermal process. The effect of LSN on the structure and morphology has been thoroughly investigated by X-ray powder diffraction and scanning electron microscopy (SEM). The results indicated that stepwise reduction and Ostwald's ripening occurred simultaneously in this hydrothermal process, and LSN could serve as both reducing agent and growth modifier. The appropriate reducing capacity and selective absorption ability of LSN played an important role for the formation of various manganese oxides nano/micro-crystals. The catalytic performance of the products for the oxidation of o-xylene has been also investigated. The result showed that the MnO 2 crystals prepared with LSN exhibited the highest catalytic activity.

Ordered mesoporous and bulk Co3O4 supported Pd catalysts for catalytic oxidation of o-xylene

Ordered mesoporous Co3O4 (3D) and the bulk counterpart Co3O4 (B) were prepared by a nanocasting route and precipitation method, respectively. Pd was next loaded on both of them by an impregnation method. All catalysts were tested for the total oxidation of o-xylene in the temperature range of 150–300°C. Mesoporous Co3O4 (3D) exhibited better activity than Co3O4 (B), and Pd addition further improved the catalytic activity of both the mesoporous and bulk Co3O4. The BET and TEM results indicated that the mesoporous catalysts had uniform channel dimensions and the mesostructure was little affected by Pd addition. The TPR and XPS data indicated that Pd was much more exposed on the surface of Co3O4 (3D) than that of Co3O4 (B). TPD results showed that Pd/Co3O4 (3DL) could activate the oxygen species more easily than Pd/Co3O4 (BL). Therefore, Pd/Co3O4 (3DL) presented the best activity among the four catalysts and achieved 90% conversion of 150ppm o-xylene at 249°C at a space velocity of 60,000mLg−1h−1.

Kinetics of Nonbranched-Chain Oxidation Involving 1:2 Adduct Radicals <img src=image/tit1.png></img> and <img src=image/tit2.png></img>

New reaction scheme is suggested for the initiated nonbranched-chain addition of free radicals to the multiple bond of the molecular oxygen. The scheme includes the reaction competing with chain propagation reactions through a reactive free radical. The chain evolution stage in this scheme involves a few of free radicals, one of which (tetraoxyl) is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. Based on the proposed scheme rate equations (containing one to three parameters to be determined directly) are deduced using quasi-steady-state treatment. The kinetic description with use the obtained rate equations is applied to the γ-induced nonbranched-chain processes of the free-radical oxidation of liquid o-xylene at 373 K and hydrogen dissolved in water containing different amounts of oxygen at 296 K. In these processes the oxygen with the increase of its concentration begins to act as an oxidation autoingibitor (or an antioxidant), and the rate of peroxide formation as a function of the dissolved oxygen concentration has a maximum. The heat effects are compared for the overall reactions of dissociation of simple alkylperoxyl (exothermic) and alkoxyl (endothermic) free radicals in the gas phase. Possible nonchain pathways of the free-radical oxidation of hydrogen and the routes of ozone decay from the energetic standpoint via the reaction with the hydroxyl free radical in the upper atmosphere (including the addition yielding the hydrotetraoxyl free radical, which can be an intermediate in the sequence of conversions of biologically hazardous UV radiation energy) were examined. The energetics of the key radical-molecule reactions is considered.

Mesoporous Co3O4-supported gold nanocatalysts: Highly active for the oxidation of carbon monoxide, benzene, toluene, and o-xylene

Three-dimensionally ordered mesoporous Co3O4 (meso-Co3O4) and its supported gold (xAu/meso-Co3O4, x=3.7–9.0wt%) nanocatalysts were prepared using the KIT-6-templating and polyvinyl alcohol-protected colloidal deposition methods, respectively. The meso-Co3O4 and xAu/meso-Co3O4 samples exhibited a high surface area of 91–94m2/g. The Au nanoparticles with a size of 1–5nm were uniformly deposited inside the mesoporous channels of meso-Co3O4. There were good correlations of oxygen adspecies concentration and low-temperature reducibility with catalytic activity of the sample for CO or BTX (benzene, toluene, and o-xylene) oxidation. Among meso-Co3O4 and xAu/meso-Co3O4, the 6.5Au/meso-Co3O4 sample performed the best, giving the T90% (the temperature required for achieving a CO or BTX conversion of 90%) of −45, 189, 138, and 162°C for the oxidation of CO, benzene, toluene, and o-xylene, respectively. The apparent activation energies (23 and 45–55kJ/mol) over 6.5Au/meso-Co3O4 were much lower than those (48 and 72–92kJ/mol) over bulk Co3O4 for CO and BTX oxidation, respectively. The effects of water vapor, carbon dioxide, and sulfur dioxide on the catalytic activity of the 6.5Au/meso-Co3O4 sample were also examined. It is concluded that the higher surface area and oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and meso-Co3O4 were responsible for the excellent catalytic performance of 6.5Au/meso-Co3O4.

Oxide catalysts for oxidation of xylene

Polioxide granulated catalysts based on transition and rare earth metals for oxidative conversion of xylene by oxygen have been investigated. It was defined the effect of the composition and concentration of the active phase of oxide catalysts: Cu-Mn-Ln; Cu-Mn-Ce and Cu-Mn-Nd on the o-xylene oxidation. It was found that the Cu-Mn-Ce catalyst has the highest activity at the concentrations of metals: copper – 3.0%; manganese – 3.0%; cerium – 1.0%.

Oxygen as an Autoinhibitor of Oxidation

New reaction scheme is suggested for the initiated nonbranched-chain addition of free radicals to the multiple bond of the molecular oxygen. The scheme includes the reaction competing with chain propagation reactions through a reactive free radical. The chain evolution stage in this scheme involves a few of free radicals, one of which (tetraoxyl) is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. Based on the proposed scheme rate equations (containing one to three parameters to be determined directly) are deduced using quasi-steady-state treatment. The kinetic description with use the obtained rate equations is applied to the γ-induced nonbranched-chain processes of the free-radical oxidation of liquid o-xylene at 373 K and hydrogen dissolved in water containing different amounts of oxygen at 296 K. In these processes the oxygen with the increase of its concentration begins to act as an oxidation autoingibitor (or an antioxidant), and the rate of peroxide formation as a function of the dissolved oxygen concentration has a maximum. The heat effects are compared for the overall reactions of dissociation of simple alkylperoxyl (exothermic) and alkoxyl (endothermic) free radicals in the gas phase. Possible nonchain pathways of the free-radical oxidation of hydrogen and the routes of ozone decay from the energetic standpoint via the reaction with the hydroxyl free radical in the upper atmosphere (including the addition yielding the hydrotetraoxyl free radical, which can be an intermediate in the sequence of conversions of biologically hazardous UV radiation energy) were examined. The energetics of the key radical-molecule reactions is considered.

Effect of pretreatment on Pd/Al2O3 catalyst for catalytic oxidation of o-xylene at low temperature

The effect of pretreatment on Pd/Al2O3 catalysts for the catalytic oxidation of o-xylene at low temperature was studied by changing the pretreatment and testing conditions. The fresh and pretreated Pd/Al2O3 catalysts were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The results showed that the pretreatment dramatically changed the Pd/PdO ratio and then significantly affected the Pd/Al2O3 activity; while the pretreatment had not much influence on Pd particle size. The Pd/Al2O3 pre-reduced at 300°C/400°C, which has fully reduced Pd species, showed the highest activity; while the fresh Pd/Al2O3, which has fully oxidized Pd species, presented the worst performance, indicating the Pd chemical state plays an important role in the catalytic activity for the o-xylene oxidation. It is concluded that metallic Pd is the active species on the Pd/Al2O3 catalyst for the catalytic oxidation of o-xylene at low temperature.

Non-Adiabatic Multitubular Fixed-Bed Catalytic Reactor Model Coupled with Shell-Side Coolant CFD Model

An overall fixed-bed reactor model that combines a one-dimensional plug flow reactor model with a computational fluid dynamics (CFD) model of the shell-side coolant fluid over a series of individual reactor tubes is presented. The model chemistry is the partial oxidation of o-xylene to phthalic anhydride, a well-studied system for reactor performance. The model is used to investigate the effect of variation in cooling temperature on overall reactor performance: temperature profiles at the wall and centerline and o-xylene conversion. Non-isothermal shell-side cooling temperature profiles are calculated using computational fluid dynamics and heat flux profiles along the reactor tube length. This analysis demonstrates that, with faster coolant flow rates, the coupled fixed-bed reactor and CFD model process outputs approach the nominal case. Alternative shell-side baffle configurations are examined. The calculated coolant velocity profiles, though different between evaluated configurations, result in similar ...

Well-dispersed palladium supported on ordered mesoporous Co3O4 for catalytic oxidation of o-xylene

Ordered mesoporous Co3O4(3D) and Pd/Co3O4(3D) were prepared by a nanocasting route using mesoporous silica (KIT-6) as a hard template. In addition, Pd/Co3O4(3DL) was prepared as a reference by post-impregnation of Pd in Co3O4(3D). All catalysts were tested for the total oxidation of o-xylene in the temperature range of 150–300°C. The mesoporous Co3O4(3D) showed better activity than bulk Co3O4 (B) for o-xylene oxidation. As for Pd-loaded samples, Pd/Co3O4(3D) had much higher activity than Pd/Co3O4(3DL). These catalysts were characterized by BET, XRD, TEM, XPS, H2-TPR and XAFS methods. The characterization results show that the Pd/Co3O4(3D) synthesized by in situ nanocasting presented a more ordered mesostructure and more well-dispersed PdO species than the Pd/Co3O4(3DL) prepared with the post-impregnation method, which account for its excellent activity for o-xylene oxidation. In addition, it was demonstrated that Pd in the oxidized state is the active site for o-xylene oxidation.