Complete Oxidation Of Benzene Research Articles

Benzene abatement catalyzed by Ceria-Supported platinum nanoparticles and single atoms

Heterogeneous catalysis is one promising technology to abate benzene at relatively low temperatures, but it remains challenging to develop efficient catalysts owing to the difficulties in activating inert benzene molecules and cleaving the strong double bonds of O2. We present the importance of frontier band orbitals in catalyst design for benzene oxidation by correlating electronic structures with catalytic activities over ceria-supported platinum nanoparticles (Ptn/CeO2) or single atoms (Pt1/CeO2). Catalytic tests demonstrate that Ptn/CeO2 shows much higher catalytic activity and lower activation energy than Pt1/CeO2 under identical conditions. By combining the experimental results and theoretical calculations, we reveal that the high activity of Ptn/CeO2 mainly originates from the energy level of the frontier band orbitals, where the lowest unoccupied and the highest occupied band orbitals are energetically favorable for activating benzene and O2, respectively, thus rendering the temperatures required for complete oxidation of benzene significantly lower. Similar trends in activity are found in high-temperature combustion of CH4 and low-temperature oxidation of CO, implicating the universal importance of the energy levels of frontier band orbitals in catalytic oxidation. This work provides a strategy to rationally design high-performance catalysts that can efficiently abate pollutants for environmental protection.

Tuning the Cu/Ce Ratio for Improved Benzene Oxidation over Gold-Promoted Alumina-Supported CuO-CeO2

Increased levels and detrimental effects of volatile organic compounds (VOCs) stimulate research efforts to develop catalysts with high efficiency in complete hydrocarbon oxidation. This work is focused on the complete oxidation of benzene as a probe reaction for VOCs elimination over alumina-supported CuO-CeO2 mixed oxide promoted by gold. The benzene molecule is the most stable among the aromatic hydrocarbons with toxic and often carcinogenic effects known as BTEX (benzene, toluene, ethylbenzene, and xylenes) owing to the symmetry and stability of the benzene ring. Use of low-cost materials as support is an appropriate strategy aimed at improving catalyst economic profitability. The effect of the Cu-Ce ratio, namely 2:1 and 1:5, and the role of supported gold in the catalyst performance were evaluated. Analysis of the impact of support composition in benzene oxidation was based on sample characterization by textural measurements, PXRD, EPR spectroscopy, and the TPR technique. Special attention was paid to the disturbed symmetry of the ceria crystallographic structure by defects formation and its implication for the catalytic activity. Gold on alumina-supported binary oxide catalysts exhibited a significantly higher activity than promoted supported monometallic oxides. The best performance of the Au/Cu-Ce 1:5 sample was related to the highest concentration of paramagnetic Cu2+ ions and the best copper species dispersion evidenced by PXRD, EPR, and TPR results. The catalyst achieved stable total oxidation to CO2 and water by 94% benzene conversion at 250 °C, thus implying the potential of this composition in developing efficient catalytic materials for atmospheric pollutant abatement.

Hydrothermal treatment: an effective method to improve the catalytic activity of the Pt/ZSM-5 catalyst for complete benzene oxidation

Hydrothermal treatment surprisingly enhanced the catalytic activity of Pt/ZSM-5 in benzene oxidation and the treated catalyst exhibited outstanding stability.

Influence of Pt dispersibility and chemical states on catalytic performance of Pt/CeO2-TiO2 catalysts for VOCs low-temperature removal

Catalytic oxidation at low temperature has been considered as an effective technology for the volatile organic compounds (VOCs) elimination. Among many catalysts, the supported noble metal catalysts are the most widely used in practical application, but the correlation between the dispersibility and chemical states of noble metals and the catalytic activity is still unclear. In this paper, four Pt/CeO2-TiO2 catalysts with high catalytic activity of VOCs low-temperature removal were prepared by various methods and systematically evaluated. It is found that the activities of the Pt/CeO2-TiO2 catalysts for the complete oxidation of benzene depend on Pt dispersion, Pt chemical states and Oads./Olatt proportion in the catalysts. The high Pt dispersion (especially Pt single atom dispersion) obviously enhances the interaction between Pt and CeO2-TiO2, resulting in the formation of more Pt2+ and absorbed oxygen species, which promotes the catalytic activity for benzene oxidation. The Pt/CeTi-EFD catalyst prepared by electron free deposition (EFD) method exhibits excellent oxidation activity with T90 % as low as 150 °C for benzene, and possesses satisfying adaptability for various VOCs oxidation and good stability. The large amount of the Pt4+ species has an adverse effect for catalytic oxidation of benzene, leading to the poor oxidation activity. This comprehensive consideration should be very helpful when designing and preparing novel catalysts for the low-temperature removal of VOCs.

Gold-Based Catalysts for Complete Formaldehyde Oxidation: Insights into the Role of Support Composition

Formaldehyde (HCHO) is recognized as one of the most emitted indoor air pollutants with high detrimental effect on human health. Significant research efforts are focused on HCHO removal to meet emission regulations in an effective and economically profitable way. For over three decades, the unique electronic properties and catalytic abilities of nano-gold catalysts continue to be an attractive research area for the catalytic community. Recently, we reported that mechanochemical mixing is a relevant approach to the preparation of Co-Ce mixed oxides with high activity in complete benzene oxidation. A trend of higher surface defectiveness, in particular, oxygen vacancies, caused by close interaction between cobalt oxide and cerium oxide phases, was observed for a mixed oxide composition of 70 wt.% Co3O4 and 30 wt.% CeO2. These results directed further improvement by promotion with gold and optimization of mixed oxide composition, aiming for the development of an efficient catalyst for room temperature HCHO abatement. Support modification with potassium was studied; however, the K addition caused less enhancement of HCHO oxidation activity than expected. This motivated the preparation of new carrier material. In addition to Co3O4-CeO2 mixed metal oxides with preset ratio, γ-Al2O3 intentionally containing 33% boehmite and shortly named Al2O3-b was used for synthesis. Analysis of the role of support composition in HCHO oxidation was based on the characterization of nano-gold catalysts by textural measurements, XRD, HRTEM, XPS, and TPR techniques. Gold supported on mechanochemically treated Co3O4-CeO2-Al2O3-b (50 wt.% Al2O3-b) exhibited superior activity owing to high Ce3+ and Co3+ surface amounts and the most abundant oxygen containing species with enhanced mobility. This catalyst achieved oxidation to CO2 and H2O by 95% HCHO conversion at room temperature and 100% at 40 °C, thus implying the potential of this composition in developing efficient catalytic materials for indoor air purification.

Mechanochemically Prepared Co3O4-CeO2 Catalysts for Complete Benzene Oxidation

Considerable efforts to reduce the harmful emissions of volatile organic compounds (VOCs) have been directed towards the development of highly active and economically viable catalytic materials for complete hydrocarbon oxidation. The present study is focused on the complete benzene oxidation as a probe reaction for VOCs abatement over Co3O4-CeO2 mixed oxides (20, 30, and 40 wt.% of ceria) synthesized by the more sustainable, in terms of less waste, less energy and less hazard, mechanochemical mixing of cerium hydroxide and cobalt hydroxycarbonate precursors. The catalysts were characterized by BET, powder XRD, H2-TPR, UV resonance Raman spectroscopy, and XPS techniques. The mixed oxides exhibited superior catalytic activity in comparison with Co3O4, thus, confirming the promotional role of ceria. The close interaction between Co3O4 and CeO2 phases, induced by mechanochemical treatment, led to strained Co3O4 and CeO2 surface structures. The most significant surface defectiveness was attained for 70 wt.% Co3O4-30 wt.% CeO2. A trend of the highest surface amount of Co3+, Ce3+ and adsorbed oxygen species was evidenced for the sample with this optimal composition. The catalyst exhibited the best performance and 100% benzene conversion was reached at 200 °C (relatively low temperature for noble metal-free oxide catalysts). The catalytic activity at 200 °C was stable without any products of incomplete benzene oxidation. The results showed promising catalytic properties for effective VOCs elimination over low-cost Co3O4-CeO2 mixed oxides synthesized by simple and eco-friendly mechanochemical mixing.

CeCoOx-MNS catalyst derived from three-dimensional mesh nanosheet Co-based metal–organic frameworks for highly efficient catalytic combustion of VOCs

Various three-dimensional (3D) Co-based metal organic frameworks (Co-MOFs) are successfully synthesized through modulation and reconstruction of secondary building units (SBU) with Co ions, including three-dimensional nanocube Co-MOFs (Co-MOFs-NC), three-dimensional mesh nanosheets Co-MOFs (Co-MOFs-MNS) and three-dimensional prismatic nanotube Co-MOFs (Co-MOFs-PNT). Specifically, mesh nanosheets Co-MOFs-MNS and prismatic nanotube Co-MOFs-PNT are synthesized for the first time through a post-processing strategy of nanocubic Co-MOFs-NC. It is discovered that the CeCoOx-MNS catalyst derived from Co-MOFs-MNS precursor following wet impregnation of cerium ions exhibits a superior activity for the complete oxidation of benzene, toluene and δ-xylene. Through a series of characterizations, it is verified that the CeCoOx-MNS catalyst owns more Co3+ and Ce3+ species, excellent redox performance (Ce4++Co2+→Ce3++Co3+), and abundant surface weak acid sites, which promote jointly the conversion of VOCs at a lower temperature. More importantly, in situ DRIFTS results over CeCoOx catalyst verify that the alkoxide, benzoate and anhydride species are the main intermediates, indicating that reaction pathway is likely to be as follows: adsorbed toluene → benzyl alcohol → benzoate → anhydride → acetate→ …→ CO2 and H2O.

Photocatalytic oxidation process for treatment of gas phase benzene using Ti3+ self-doped TiO2 microsphere with sea urchin-like structure

Photocatalytic oxidation processes (PCO processes) are a promising technology for controlling the pollution of working environments, namely, the low concentrations of volatile organic compounds (VOCs) generated in industrial processes, and improving the efficiency of this process is an important issue. In this study, the photocatalytic oxidation of gas-phase benzene was carried out with TiO2 microspheres with a sea-urchin-like structure, and the effect of Ti3+ self-doping on the catalytic performance of TiO2 was investigated in detail. The structures and properties were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV–visible diffuse reflectance spectroscopy, electron spin resonance, scanning electron microscopy, and high-resolution transmission electron microscopy. Ti3+ ions were formed in TiO2 microspheres by heating under vacuum, which improved the catalytic performance of TiO2 for the complete oxidation of benzene to CO2 and CO. The photoelectrochemical measurements showed that the incorporation of Ti3+ into TiO2 microspheres reduced electron-hole recombination and increased the light absorption capacity, which contributed to improving the photocatalytic activity. In situ FTIR spectroscopic studies revealed that in the benzene oxidation process, Ti3+ self-doped TiO2 microspheres suppressed the formation of strongly bound byproduct compounds on the TiO2 surface, which affected the rate of benzene oxidation. Thus, the Ti3+ self-doped TiO2 microspheres are effective catalysts for efficient use of UV light and suppression of catalyst deactivation during benzene oxidation.

Complete Benzene Oxidation over Mono and Bimetallic Pd—Au Catalysts on Alumina-Supported Y-Doped Ceria

The protection of environment and human health stimulates intensive research for abatement of volatile organic compounds (VOCs) in the atmosphere. Complete catalytic oxidation is an efficient, environmentally friendly and economically feasible method for elimination of VOCs. This study aims to design high performing and cost-effective catalytic formulations by exploration of appropriate and economically viable supports. Alumina-supported ceria (30 wt.%) and Y2O3 (1 wt.%)-doped ceria were prepared by mechanical mixing and were used as support of mono Au (2 wt.%) and Pd (1 wt.%) and bimetallic Pd-Au catalysts. The characterization by textural measurements, X-ray powder diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), EPR (electron paramagnetic resonance) and temperature-programmed reduction (TPR) was carried out in order to clarify the relationship between catalyst composition, textural, structural and surface properties, reducibility and catalytic performance for complete benzene oxidation. Among all studied catalysts, Pd-based catalysts exhibited the best combustion activity. In particular, monometallic Pd on alumina supported Y-doped ceria attained 100% of complete benzene conversion at 180 °C. These catalytic materials have potential to meet stringent emission regulations in an economical and effective way.

Low temperature benzene oxidation over copper–silver catalyst: roles of copper oxide and silver on cerium–zirconium mixed oxide

The synergetic effects of the non-PGM catalytic components enabled complete benzene oxidation at low temperature, below 200 °C.

Electric Field Promoted Complete Oxidation of Benzene over PdCexCoy Catalysts at Low Temperature

The application of electric field promotes benzene oxidation significantly over Pd/CoxCey catalysts. For 1% Pd loading catalysts, the complete oxidation of benzene can be realized at 175 °C with an electric field under an input current of 3 mA, 79 °C lower than the temperature demanded for complete benzene conversion without electric field. The introduction of electric field can save Pd loading in the catalysts while maintaining high benzene conversion. The characterization experiments showed that CeO2 reduction was accelerated with electric field and created more active oxygen, promoting the formation of active sites on the catalyst surface. The OH removal ability of PdO was enhanced by forming CoO(OH) species, which can easily dehydroxylate since the reduction of Co3+ was promoted by the electric field. The optimized Ce/Co ratio is a balance between oxygen availability and OH removal ability.

Decomposition of high concentration benzene (produced in paper and painting industries) and its byproducts, methane and carbon dioxide, using plate gliding arc.

High concentration benzene production in paper and painting industries is a restrictive problem in production line of companies. In this study, removal of high concentrated benzene produced in painting companies was investigated using a Plate Gliding Arc (PGA) reactor. Decomposition of methane and carbon dioxide as the most predominate byproducts of benzene decomposition was also studied using (PGA) reactor. The effect of several parameters such as input power, feed gas flow rate, type of carrier gas, and [CH4/CO2] flow ratio was studied by two series of experiments. The results show significant conversion (>70%) of high concentration benzene (74000ppm) without using any catalyst. Selectivity of CO2 and CO was 88% and 10% respectively showing complete oxidation of benzene. The maximum conversion of CH4 and CO2 reached 52% and 69%, respectively by using optimum ratio of 3:4. The main results of this study proved removal of high concentration benzene using a low-energy-density reactor. Furthermore, an optimum value for efficient conversion of methane and carbon dioxide was achieved and the energy density of the PGA reactor was evaluated, which shows a good promise for industrial applications.

Preparation of size-controlled Pt supported on Al2O3 nanocatalysts for deep catalytic oxidation of benzene at lower temperature

A series of Pt/Al2O3 catalysts possessing controlled Pt particle sizes (1.2–2.2 nm) could be single-step synthesized by means of modified ethylene glycol (EG) reduction approach. Their catalytic activities were evaluated for the catalytic complete oxidation of benzene, as typical volatile organic compounds (VOCs). The results showed that Pt/Al2O3 catalyst with 1.2 nm Pt size exhibited optimum catalytic oxidation activity of benzene at 145 °C. It has been confirmed that the content of Pt0 species, which is regarded as active center for complete oxidation of benzene, is not the decisive factor in the process of benzene oxidation. The structure sensitivity was explained by the surface adsorbed oxygen. The electron transportation from Pt to O is in favour of the activation of adsorbed oxygen, which is beneficial to enhance catalytic activity. Moreover, the catalysts showed excellent adaptability for different VOCs and durability for benzene oxidation during the long-term continuous test, whether in dry air or in the coexistence of CO2, cyclohexane or H2O.

Ce-modified mesoporous γ-Al2O3 supported Pd-Pt nanoparticle catalysts and their structure-function relationship in complete benzene oxidation

In this investigation, a mesoporous γ-Al2O3 with large surface area and good thermal stability was synthesized and employed as the support for preparing a series of Pd-Pt nanocrystalline catalysts by using a high-temperature solution-phase reduction method. The PdOx (x = 0, 1) and PtOx (x = 0, 2) nanoparticles were found to have a small diameter (about 2 nm) and were highly dispersed on the surface of the mesoporous γ-Al2O3. The results show that catalysts with the appropriate ceria greatly improved the physical adsorption/chemisorption of benzene to Pd-Pt nanocrystals, which greatly enhanced the activity to achieve the complete oxidation of benzene. The high activity of the catalyst was mainly due to the nano-effects of Pd-Pt nanocrystals and the interactions among the active components. 0.2%Pd-Pt(1:1)/10%Ce/γ-Al2O3 demonstrated the best activity for the complete oxidation of benzene at 200 °C. Furthermore, this catalyst maintained 95% benzene conversion for 1000 h at 190 °C and displayed good resistance to water and Cl-poisoning, which indicated that the Pd-Pt nanocrystalline catalysts have promise for adoption by the industry.

Effect of Y Modified Ceria Support in Mono and Bimetallic Pd–Au Catalysts for Complete Benzene Oxidation

Mono metallic and bimetallic Pd (1 wt. %)–Au (3 wt. %) catalysts were prepared using two ceria supports doped with 1 wt. % Y2O3. Yttrium was added by impregnation or co-precipitation. The catalyst synthesis was carried out by deposition–precipitation method, with sequential deposition–precipitation of palladium over previously loaded gold in the case of the bimetallic samples. The obtained materials, characterized by X-ray powder diffraction (XRD), High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR) techniques, were tested in the complete benzene oxidation (CBO). The results of the characterization analyses and the catalytic performance pointed to a close relationship between structural, redox, and catalytic properties of mono and bimetallic catalysts. Among the monometallic systems, Pd catalysts were more active as compared to the corresponding Au catalysts. The bimetallic systems exhibited the best combustion activity. In particular, over Pd–Au supported on Y-impregnated ceria, 100% of benzene conversion towards total oxidation at the temperature of 150 °C was obtained. Comparison of surface sensitive XPS results of fresh and spent catalysts ascertained the redox character of the reaction.

Monolithic Mn/Ce-based catalyst of fibrous ceramic membrane for complete oxidation of benzene

Herein, a series of monolithic Mn/Ce-based catalyst of ceramic membranes (CMs) were prepared through impregnation method for volatile organic compounds (VOCs) removal. The porous fibrous CMs with a sinter-locked network structure were fabricated by molding method in a feasible sintering process. Then, the catalytic CMs were systematically analyzed by using specific analytical techniques. The results showed that the fibrous CMs possessed a unique interconnected and uniform pore structure, and MnOx-CeO2 active phases were homogenously dispersed into the porous CMs support. The catalytic activity of samples was measured by using benzene as target VOCs. The results revealed that all catalytic CMs were active for oxidation of benzene. Significantly, the catalytic performance was promoted by introducing Ce species into MnOx. Among all, MnOx-CeO2-3:1 catalyst exhibited the lowest 90% benzene conversion temperature (T90) at 244 °C and high stability with continuous benzene stream in the presence of 90 vol.% (20 °C) water vapor under a gaseous hourly space velocity (GHSV) of 5000 h−1, owing to the lower-temperature reducibility and the abundant active oxygen (OAds.) with synergetic effect of MnOx and CeO2. The results indicated a promising way to design a high efficiency dual functional CMs for the industrial application of removal VOCs while controlling particulate matters (PMs) from hot gases.

A Comparative Study of Mn/Co Binary Metal Catalysts Supported on Two Commercial Diatomaceous Earths for Oxidation of Benzene

Two commercial diatomaceous earths were used as supports for the preparation of Mn/Co binary metal catalysts at different metal loads (5 to 10 wt % Mn and 5 to 15 wt % Co) by incipient wetness deposition. The activity of the prepared catalysts towards the complete oxidation of benzene to CO2 and water was investigated between 100 and 400 °C. Raw supports and synthesized catalysts were characterized by XRD, N2 physisorption, SEM-EDS, H2-TPR, and TPD. The purification treatment of food-grade diatomite significantly affected the crystallinity of this support while reducing its specific surface area (SSA). A loss of SSA, associated with the increase in the metal load, was observed on samples prepared on natural diatomite, while the opposite trend occurred with food-grade diatomite-supported catalysts. Metal nanoparticles of around 50 nm diameter were observed on the catalysts’ surface by SEM analysis. EDS analysis confirmed the uniform deposition of the active phases on the support’s surface. A larger H2 consumption was found by TPR analysis of natural diatomite-based samples in comparison to those prepared at the same metal load on food-grade diatomite. During the catalytic oxidation experiment, over 90% conversion of benzene were achieved at a reaction temperature of 225 °C by all of the prepared samples. In addition, the formation of coke during the oxidation tests was demonstrated by TGA analysis and the soluble fraction of the produced coke was characterized by GC-MS.

Recycling of red mud as a catalyst for complete oxidation of benzene

In this work, we investigated waste red mud (WRM) generated from industrial processes as a potential catalyst support for the complete oxidation of toxic organic compounds. Two different types of red mud based catalysts were prepared using calcination (CRM) and hydrochloric acid aqueous solution (HRM) pretreatments. In addition, HRMs loaded with different amounts of palladium were prepared and examined for their catalytic behaviors. For comparison, aluminas (γ-Al2O3) loaded with different amounts of palladium were also used. The catalyst samples prepared were characterized by using nitrogen adsorption, ICP-AES, TPR, XRD, FT-IR, and FE-TEM to examine their textural and chemical characteristics. The catalytic activity of the samples used depended on the pretreatment techniques applied, lattice oxygen mobility, the type of supports, and the loading amount of palladium. It was also interesting to note that water vapor in the feed stream inhibits catalytic activity for the complete oxidation of benzene.

MnO2-nanowire@NiO-nanosheet core-shell hybrid nanostructure derived interfacial Effect for promoting catalytic oxidation activity

Nanostructure-derived interfacial effect plays a great role in enhancing catalytic activities. Herein, a MnO2 nanowires@NiO nanosheets core-shell hybrid nanostructure was successfully prepared by uniformly decorating NiO nanosheets on the one-dimensional MnO2 nanowires. The physi-chemical properties of the MnO2 and MnO2@NiO were characterized by using XRD, BET, SEM, H2-TPR and XPS techniques. Compared to the single MnO2 nanowires, the MnO2@NiO nanocomposite with better low-temperature reducibility and more active surface oxygen species exhibited much better performance in complete oxidation of benzene, giving the temperatures for 100% benzene conversion of 320°C under the conditions of 1000ppm benzene in air and space velocity of 120,000mLg−1h−1 while the value over pure MnO2 was 380°C. The novel hetero-interface constructed between MnO2 and NiO core-shell nanostructures might make a great contribution on this significantly promoting effect.

Promoting effect of acid treatment on Pd-Ni/SBA-15 catalyst for complete oxidation of gaseous benzene

A novel Pd-Ni/SBA-15 catalyst synthesized by co-impregnation of Pd and Ni precursors onto porous SBA-15 silica support was used for catalytic removal of gaseous benzene. Compared to original Pd/SBA-15 catalyst, the addition of Ni significantly promoted the catalytic performance. Moreover, with introducing acid treatment, the new Pd-Ni/SBA-15 catalyst showed much better catalytic activity than both Pd/SBA-15 catalyst and original Pd-Ni/SBA-15 catalyst, and the benzene could be completely oxidized into CO2 and H2O at 260°C over the new catalyst at a high space velocity of 12,0000mL/(gh).