Photocatalytic Oxidation Of Benzene Research Articles

Recent trends in phenol synthesis by photocatalytic oxidation of benzene.

Phenol is an important intermediate for manufacturing chemical products in industry. In recent decades, phenol synthesis by one-pot oxidation of benzene has aroused tremendous interest in phenol synthesis due to the enormous energy consumption of the three-step cumene method in the industry. Photocatalysis is promising for the selective conversion of benzene to phenol because it can proceed under mild reaction conditions. However, overoxidation of phenol by photocatalysts with high oxidation ability decreases the yield and selectivity, which is the major limiting factor. Thus, increasing the phenol formation efficiency plays a crucial role in photocatalytic systems for benzene oxidation. In this context, selective photocatalytic benzene oxidation over several types of photocatalytic systems has been developed rapidly in the past few years. In this perspective, current homogeneous and heterogeneous photocatalytic systems for this reaction have been reviewed systematically first. Then, an overview of some strategies from the last decade for increasing phenol selectivity has been provided. In the end, a summary and outlook on the challenges and future directions in the research field are included in this perspective, which would be of great interest for further improving the selectivity of the photocatalytic benzene oxidation reaction.

Impact of intermediate products on benzene photocatalytic oxidation in pulp mills: Experimental and adsorption simulation study

The refractory benzene is revealed in the gaseous pollutants of pulp mills. Although it can be decomposed by photooxidation, the intermediates impact during benzene photooxidation needs to be studied comprehensively. Herein, the benzene photocatalysis was investigated in a reactor with nano-TiO2 colloid under different reaction conditions. The adsorption behavior of mixed benzene and intermediates on TiO2 (101) surface was simulated based on density functional theory, and the influencing mechanism of intermediates was also investigated. Experimental results showed that benzene degradation rate firstly stabilized and then decreased at high initial concentration, accompanying the photocatalyst deactivation and conversion of intermediates into aliphatic carboxylates. Adsorption simulations showed that benzene adsorption was promoted firstly and weakened finally due to the formations of several intermediates. Combined experimental results, adsorption simulation and influencing mechanisms showed that, the enhanced benzene adsorption and weakened photocatalysis contributed to a high and stable rate in the initial stage of benzene degradation. Then, the formed intermediate products weakened the adsorption and photocatalytic reaction of benzene, causing the decrease of degradation rate. The formed aliphatic carboxylates occupied almost all adsorption and catalytic sites, leading to the deactivation of nano-TiO2 photocatalyst. This study provides a comprehensive understanding of intermediates impact on benzene photooxidation.

Photocatalytic oxidation of benzene by ZnO coated on glass plates under simulated sunlight

The photocatalytic oxidation of benzene by ZnO nanoparticles coated on glass plates was studied under simulated sunlight. ZnO nanoparticles were coated on three glass plates by heat attachment method. To evaluate the photocatalytic removal of benzene, coated plates were irradiated by metal halide lamp in a rectangular reactor in batch mode. The effect of initial pollutant concentration, temperature, relative humidity, irradiation time, concentration of zinc oxide suspension, were assessed. The surface morphology and structure of ZnO nanoparticles and ZnO coated on glass plates were characterized by scanning electron microscopy, X-ray diffraction and field emission scanning electron microscopy. Sampling and analysis of benzene were performed according to NIOSH method. To analyze the concentration of benzene, gas chromatography with flame ionization detector (GC-FID) was used. Results indicated that photocatalytic process by ZnO under irradiation of metal halide lamp could remove benzene at optimum experimental conditions. Coating of glass plates by ZnO suspension, resulted in 57% removal of benzene as concentration of 50 ppm at 45 °C, and relative humidity of 40% after 240 min irradiation of metal halide lamp. Results indicated that photocatalytic oxidation process by ZnO nanoparticles can be used as a proper and environmentally friendly method for removing low concentrations of benzene from polluted air under simulated sunlight.

Assessment of Commercial Active Ceramic Tiles on Benzene Degradation for the Pollution Control of Indoor Atmospheric Buildings

Volatile Organic Compounds (VOCs) constitutes an important class of air pollutants, and benzene is one of the main contaminants of indoor air pollution. Among the methods for the treatment of environments with a high VOCs concentration is the photocatalytic oxidation by TiO2 (anatase) ceramic coated surfaces. The effectiveness of VOCs photodegradation studies using active ceramic tiles made in laboratory is well reported in the literature. However, this has not been reported using commercial tiles, although active ceramics are sold for such a function. In this context, this study proposed the assessment of commercial active ceramic tiles capacity in the photocatalytic degradation of benzene in indoor air. The development of this work arose from two questions: a) if the commercial active ceramic tiles are efficient in the VOCs degradation as the manufacturers claim; b) if they are able to degrade VOCs in indoor building environments. Experiments were conducted in laboratory’s scale, using an adapted simulation chamber. The volatilized benzene entered in contact with the commercial ceramic tile under fluorescent light and ultraviolet (UV) light of 365 nm. Samples of the chamber internal air were collected by adsorption on polydimethylsiloxane fibres in headspace technique (SPME-HS). The evaluation of the benzene degradation occurred by gas chromatography analysis with mass spectrometry (GC-MS). The characterization of commercial active ceramic samples occurred by techniques of X-Ray Diffraction Powder (XRD), and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectrometry (EDS). Results showed that, under the experimental conditions, the commercial active ceramic tile was not capable of the benzene photocatalytic oxidation. The ceramic characterization detected very low quantity of TiO2 on ceramic samples, being this fact attributed as the main responsible for the ceramic photocatalytic inactiveness.

Photocatalytic oxidation of benzene in a microreactor with immobilized TiO2 thin films deposited by sputtering

A microreactor with immobilized anatase TiO2 thin films, whose thickness and crystallinity were precisely controlled by sputtering technique, has been developed. Photocatalytic oxidation of benzene in the microreactor resulted in the direct production of hydroquinone with quite high yield by a four-hole reaction mechanism in contrast to a free phenol mechanism. The results indicate capabilities of microreactor with immobilized photocatalyst to be applied for organic synthesis involving multi-hole and/or multi-electron, which may provide new reaction selectivity not obtainable in the conventional batch reactors.

One‐Step Selective Hydroxylation of Benzene to Phenol

AbstractRecent developments in the one‐step thermal and photochemical catalytic hydroxylation of benzene to phenol using various oxidants are described, focusing on the catalytic mechanisms. Hydroxylation of benzene with hydrogen peroxide is catalyzed by homogeneous metal complexes and heterogeneous metal oxides to produce phenol when high‐valent metal‐oxo complexes are reactive species The selective hydroxylation of benzene to phenol is achieved by using mesoporous silica‐alumina as the catalyst support, which prohibits further oxidation of phenol due to the strongly acidic sites. Photocatalytic oxidation of benzene with dioxygen and water is made possible by using organic photocatalysts via photoinduced electron transfer from benzene to the excited states of the photocatalysts, followed by the hydroxylation of the benzene radical cation with water to yield phenol selectively. The further oxidation of phenol is prohibited because of the fast back electron transfer from the one‐electron reduced species of the photocatalyst to the phenol radical cation, whereas back electron transfer from the one‐electron reduced species to the benzene radical cation is slowed down because of the large driving force of the back electron transfer, which is in the Marcus inverted region.

Ambient Oxidation of Benzene to Phenol by Photocatalysis on Au/Ti0.98V0.02O2: Role of Holes

A potential photocatalyst with 2 atom % vanadium incorporated into the lattice of disordered mesoporous titania, Ti0.98V0.02O2, (TV2) was synthesized. Au was deposited on TV2 (Au/TV2) through a photodeposition method. Structural, microscopy, and spectroscopy techniques support the incorporation of vanadium into the TiO2 lattice, and Au was deposited on the surfaces of TV2. Photocatalytic oxidation of benzene was conducted at ambient temperature under UV and/or visible light to demonstrate the catalytic activity of the Au/TV2 catalyst. The TV2 lattice exhibits a quantum jump in benzene to phenol oxidation compared to that of TiO2, highlighting the importance of V for oxidation. Introduction of Au onto TV2 further increases the benzene to phenol oxidation and phenol yield by a factor of 2 under UV light compared to those of bare TV2. No significant phenol production was observed in visible light with or without gold, indicating the role of gold is indirect toward charge separation and electron storage. Nano...

A convenient N2–CCl4 mixture plasma treatment to improve TiO2 photocatalytic oxidation of aromatic air contaminants under both UV and visible light

A convenient N2–CCl4 mixture plasma treatment to improve TiO2 photocatalytic oxidation of aromatic air contaminants under both UV and visible light was reported. X-ray diffraction (XRD), N2 adsorption, UV–vis spectroscopy, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared TiO2 catalysts. The microstructures of the TiO2 catalysts were preserved after plasma treatments. Chlorine ions did not doped into TiO2 lattice but located on TiO2 surface via the coordination with Ti4+ sites. The doping N content of prepared TiO2 catalyst increased obviously by using this N2–CCl4 mixture plasma method. The activities were tested in the photocatalytic oxidation of benzene and toluene under both UV and visible light. Chlorine radicals which formed under illumination are effective in oxidizing aromatic side groups, but ineffective in reactions with the aromatic ring.

Photocatalytic oxidation of benzene, toluene, ethylbenzene and m-xylene in the gas-phase over TiO2-based catalysts

Abstract In the present work, the photocatalytic oxidation of benzene, toluene, ethylbenzene and m-xylene (BTEX) in the gas phase over various UV-irradiated TiO 2 -based catalysts was studied. Specifically, five catalysts were tested: four based on P25 from Degussa adding 0.25% (w/w) Pt, Fe or Ce (P25, P25/Pt, P25/Fe, P25/Ce) and one prepared according to the isopropoxide method. Inlet BTEX concentrations ranged in 0.5–21 ppmv, whereas oxygen concentration was fixed (21%, v/v) at all experiments and the residence time was adjusted to 11.5 s. Ce addition to P25 catalyst led to the highest photocatalytic oxidation rates for benzene and ethylbenzene, whereas P25 proved to be the most active catalyst on toluene photo-oxidation. Regarding m-xylene, the choice of the most effective catalyst depended on m-xylene reactor concentration. Taking all experimental results into account, P25/Ce was the most effective catalyst due to its superiority in the case of benzene and ethylbenzene and its comparable performance to the base catalyst for toluene and m-xylene photocatalytic oxidation. In general, all P25 based catalysts were more active than the isopropoxide catalyst. All conversions showed great dependence on the inlet concentration of the target compound. Water addition to the reactor during ethylbenzene photo-oxidation enhanced the rates achieved for all catalysts tested. It has to be noted that the differences in the reaction rates achieved from catalyst to catalyst decreased with water vapours addition to the reactor. Finally, a Langmuir–Hinshelwood kinetic model has been applied to the experimental data obtained. The kinetic data obtained confirmed the strong beneficial effect of Ce addition to P25 catalyst on benzene and ethylbenzene photocatalytic oxidation.

Gas-Phase Photocatalytic Oxidation of Benzene over TiO2 Supported on Ce0.5-xZr0.5-xBa2xO2

Abstract Photooxidation of gaseous benzene was investigated using anatase TiO2 as the catalyst in a closed steel reactor. The photocatalytic activity can be greatly improved by supporting TiO2 on Ce0.5-xZr0.5-xBa2xO2. The optimal Ba content in the photocatalyst was investigated. The prepared photocatalysts were characterized by X-ray diffraction, UV-Vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The results revealed that the deposited titania is well dispersed as in the Ce0.5-xZr0.5-xBa2xO2 matrix. TiO2/Ce0.5-xZr0.5-xBa2xO2 absorbs much more ultraviolet light in the range of 210–400 nm than TiO2. There are Ti and O elements on the surface of TiO2/Ce0.5-xZr0.5-xBa2xO2, and the binding energy of Ti 2p of TiO2/Ce0.5-xZr0.5-xBa2xO2 shifts to a lower value. Based upon these observations, it is concluded that the role of Ce0.5-xZr0.5-xBa2xO2 is to transfer electrons and enhance the light absorption of the catalyst in the region of 210–400 nm.

Gaseous by-products from the TiO2Photocatalytic Oxidation of Benzene

Photocatalytic oxidations of benzene gas using the closed system (batch reactor) were induced to determine its by-products and investigate the effect of humidity and oxygen concentration on their generation. The study was able to identify 11 gaseous by-products: 2-methylpropene, acetaldehyde, acetone, pentane, methylcyclobutane, methylcyclopentane, cyclohexane, 2,3-dimethylbutane, 2-methylpentane, 3-methylpentane, and hexane. All the by-products were saturated hydrocarbons, which are less toxic than benzene and were probably formed through hydrogenation reaction on the photocatalytic surface. The photocatalytic oxidation of benzene under higher humidity produced less by-products. However, the amount of acetone released increased with higher humidity and oxygen concentration.

Photocatalytic degradation of gaseous benzene over TiO 2/Sr 2CeO 4: Kinetic model and degradation mechanisms

Photocatalytic oxidation of benzene in air was carried out over TiO 2/Sr 2CeO 4 catalysts. The prepared photocatalyst was characterized by S BET, UV–vis diffuse reflectance and XPS. TiO 2/Sr 2CeO 4 absorbs much more visible light than TiO 2 in the visible light region. The XPS spectrum shows that the binding energy value of Ti 2p 3/2 transfers to a lower value. The main purpose was to investigate the kinetic model and degradation mechanisms. The kinetic data matched well with the Langmuir–Hinshelwood (L–H) kinetic model with the limiting rate constant and the adsorption constant in this case were 0.0064 mg l −1 min −1 and 9.2078 l mg −1, respectively. No gas-phase intermediates were detected by direct GC/FID analysis under the conditions despite the high benzene concentration. Ethyl acetate and (3-methyl-oxiran-2-yl)-methanol were two major identified intermediates which were accompanied by butylated hydroxytoluene, 2,6-bis(1,1-dimethylethyl)-4,4-dimethylycyclohe, 2,5-cyclohexadiene-1,4,dione,2,6-bis(1,1-dim). It is plausible that at least one of these less-reactive intermediates caused the deactivation of the photocatalyst. Finally, the photocatalytic oxidation mechanisms were speculated.

Effect of Magnetic Field on the Photocatalytic Oxidation of Benzene and Ethylene over Pt/TiO<sub>2</sub>

Effect of Magnetic Field on the Photocatalytic Oxidation of Benzene and Ethylene over Pt/TiO<sub>2</sub>

Photocatalytic Oxidation of Benzene in Air

Photocatalytic oxidation of benzene in air at room temperature was studied in order to obtain the information on its reactivity on the photoirradiated TiO2 catalyst. The objective of this paper is to describe in detail the dependence of the rate for benzene photooxidation on humidity, initial benzene concentration, and incident light intensity, since they are important factors for construction of VOC control system utilizing solar energy. The reaction mechanism is also discussed to understand the decomposition behavior of benzene.

Extension of a Two-Site transient kinetic model of TiO2 deactivation during photocatalytic oxidation of aromatics: concentration variations and catalyst regeneration studies

In our previous studies, three variations of a kinetic model for the transient gas–solid photocatalytic oxidation of aromatic contaminants on titanium dioxide (TiO2) were developed and compared with experimental data. Two of the models, based upon a single type of catalyst site, were not capable of replicating transient experimental data from the photocatalytic oxidation of benzene, toluene, or m-xylene in air at a single feed concentration (50mg/m3). The remaining kinetic model, the Two-Site model, presumed the presence of a more hydrophilic type of site and was capable of replicating the time-varying behavior seen with all three aromatic contaminants considered. In the present study, this Two-Site kinetic model is extended to separately consider the photocatalytic oxidation of gas-phase toluene at various feed concentrations (20–100mg/m3) and the regeneration of used catalysts via flowing, humidified air and UV illumination. Our Two-Site model provides reasonable fits for experimental data collected during the photocatalytic oxidation of toluene at several concentration levels with no significant changes to the prior model. It is also capable of representing catalyst regeneration, although some significant differences between the model predictions and experimental results are noted.

Complete Oxidation of Benzene in Gas Phase by Platinized Titania Photocatalysts

Photocatalytic oxidation of benzene in gas phase was carried out with a flow reactor at room temperature. In a humidified airstream ([H2O] = 2.2%), benzene was quantitatively decomposed to CO2 over UV-irradiated 1.0 wt %-Pt/TiO2 catalyst. When the benzene conversion was decreased, the selectivity to CO2 was decreased, while that to CO was increased. As the amount of Pt loaded on the TiO2 catalyst was increased, the rate of the CO photooxidation was increased, while that of benzene photooxidation was almost unchanged. These findings showed that the photooxidation of benzene to CO2 over Pt/TiO2 catalyst proceeded by the two sequential steps: (i) benzene was decomposed to CO2 and CO with the selectivities of 94% and 6%, respectively, and (ii) CO was subsequently oxidized to CO2. The rate of CO photooxidation over Pt/TiO2 catalyst was greatly decreased by the presence of benzene in the reaction gas stream. The complete oxidation of benzene to CO2 could be also achieved by using the hybrid catalysts comprising pure TiO2 and platinized TiO2.

Complete Oxidation of Benzene in Air over Pt/TiO2 Photocatalysts.

Photocatalytic oxidation of benzene in air over Pt/TiO2 catalysts was studied at room temperature (relative humidity: 65%). The complete oxidation of benzene to CO2 was achieved when 1.0wt% Pt/TiO2 was used as the catalyst. With the increase in the amount of Pt loaded on TiO2, the selectivity of CO2 was increased and that of CO was decreased without any change in the catalytic activity for the COx formation.