Catalytic oxidation of toluene, ethyl acetate and chlorobenzene over Ag/MnO2-cordierite molded catalyst

Cooperative and Bifunctional Adsorbent-Catalyst Materials for In-situ VOCs Capture-Conversion

Volatile organic compounds (VOCs) are gases that are emitted into the air from products or processes and are major components of air pollution that significantly deteriorate air quality and seriously affect human health. Different types of metals, metal oxides, mixed-metal oxides, polymers, activated carbons, zeolites, metal-organic frameworks (MOFs) and mixed-matrixed materials have been developed and used as adsorbent or catalyst for diversified VOCs detection, removal, and destruction. In this comprehensive review, we first discuss the general classification of VOCs removal materials and processes and outline the historical development of bifunctional and cooperative adsorbent-catalyst materials for the removal of VOCs from air. Subsequently, particular attention is devoted to design of strategies for cooperative adsorbent-catalyst materials, along with detailed discussions on the latest advances on these bifunctional materials, reaction mechanisms, long-term stability, and regeneration for VOCs removal processes. Finally, challenges and future opportunities for the environmental implementation of these bifunctional materials are identified and outlined with the intent of providing insightful guidance on the design and fabrication of more efficient materials and systems for VOCs removal in the future.

Synergistic oxidation of toluene through bimetal/cordierite monolithic catalysts with ozone

Toluene treatment has received extensive attention, and ozone synergistic catalytic oxidation was thought to be a potential method to degrade VOCs (violate organic compounds) due to its low reaction temperature and high catalytic efficiency. A series of bimetal/Cord monolithic catalysts were prepared by impregnation with cordierite, including MnxCu5-x/Cord, MnxCo5-x/Cord and CuxCo5-x/Cord (x = 1, 2, 3, 4). Analysis of textural properties, structures and morphology characteristics on the prepared catalysts were conducted to evaluate their performance on toluene conversion. Effects of active component ratio, ozone addition and space velocity on the catalytic oxidation of toluene were investigated. Results showed that MnxCo5-x/Cord was the best among the three bimetal catalysts, and toluene conversion and mineralization rates reached 100 and 96% under the condition of Mn2Co3/Cord with 3.0 g/m3 O3 at the space velocity of 12,000 h-1. Ozone addition in the catalytic oxidation of toluene by MnxCo5-x/Cord could efficiently avoid the 40% reduction of the specific surface area of catalysts, because it could lower the optimal temperature from 300 to 100 °C. (Co/Mn)(Co/Mn)2O4 diffraction peaks in XRD spectra indicated all the four MnxCo1-x/Cord catalysts had a spinel structure, and diffraction peak intensity of spinel reached the largest at the ratio of Mn:Co = 2:3. Toluene conversion rate increased with rising ozone concentration because intermediate products generated by toluene degradation might react with excess ozone to generate free radicals like ·OH, which would improve the toluene mineralization rate of Mn2Co3/Cord catalyst. This study would provide a theoretical support for its industrial application.

Evaluation of the adsorption performance and thermal treatment-associated regeneration of adsorbents for formaldehyde removal

Indoor air pollution remains a major concern, with formaldehyde (HCHO) a primary contributor due to its long emission period and associated health risks, including skin allergies, coughing, and bronchitis. This study evaluated the adsorption performance and economic efficiency of various adsorbents (biochar, activated carbon, zeolites A, X, and Y) selected for HCHO removal. The impact of thermal treatment on adsorbent regeneration was also assessed. The experimental apparatus featured an adsorption column and HCHO concentration meter with an electrochemical sensor designed for adsorption analysis. Zeolite X exhibited the highest adsorption performance, followed by zeolite A, zeolite Y, activated carbon, and biochar. All adsorbents displayed increased HCHO removal rates with an extended length/diameter (L/D) ratio of the adsorption column. Zeolite A demonstrated the highest economic efficiency, followed by zeolite X, activated carbon, zeolite Y, and biochar. Higher L/D ratios improved economic efficiency and prolonged the replacement cycle (the optimal timing for adsorbent replacement to maintain high adsorption performance). Sensitivity analysis of adsorbent regeneration under varying thermal treatment conditions (150, 120, and 80°C) and durations (60, 45, and 30 min) revealed minimal changes in adsorption efficiency (±3%). The results indicated the potential of adsorbent regeneration under energy-efficient thermal treatment conditions (80°C, 30 min). In conclusion, this study underscores the importance of a comprehensive assessment, considering factors such as adsorption performance, replacement cycle, economic efficiency, and regeneration performance for the selection of optimal adsorbents for HCHO adsorption and removal.Implications: This study underscores the importance of adsorption technology for the removal of formaldehyde and similar volatile organic compounds (VOCs), highlighting the potential of alternative adsorbents, such as environmentally friendly biochar, in addition to traditional strategies, such as activated carbon and zeolites. Our findings demonstrate the feasibility of adsorbent regeneration under energy-efficient thermal treatment conditions. These results hold promise for improving indoor air quality, reducing environmental pollutants, and enhancing responses to air contaminants like fine dust and VOCs.

Ru-based monolithic catalysts for the catalytic oxidation of chlorinated volatile organic compounds

A series of cordierite monolithic catalysts with Ru species supported on different available low-cost carriers were prepared and investigated for the elimination of CVOCs. The results suggest that the monolithic catalyst with Ru species supported on anatase TiO₂ carrier with abundant acidic sites exhibited the desired catalytic activity for DCM oxidation with the T _90% value of 368 °C. In addition, a pseudo-boehmite sol used as binder was introduced into the preparation of the monolithic catalysts to further improve the adhesion between the powder catalysts and cordierite honeycomb carrier. The results suggest that although the T _50% and T _90% of the Ru/TiO₂/PB/Cor shifted to higher temperature of 376 and 428 °C, the weight loss of the coating for the Ru/TiO₂/PB/Cor catalyst was improved and decreased to 6.5 wt%. Also, the as-obtained Ru/TiO₂/PB/Cor catalyst exhibited ideal catalytic properties for the abatement of ethyl acetate and ethanol, indicating that the catalyst can meet the demand for the treatment of actual multi-component industrial gas.

Non-thermal plasma synthesis of supported Cu-Mn-Ce mixed oxide catalyst towards highly improved catalytic performance for volatile organic compound oxidation

Compared with that of the transition metal mixed oxide pellet catalyst, the catalytic activity of the supported mixed oxide catalyst was significantly reduced, which was limited in practical industrial applications. In this work, supported Cu-Mn-Ce mixed oxide catalysts were prepared by non-thermal plasma. Catalyst characterization result demonstrated that plasma treatment could promote the proportion of oxygen vacancy and enhance the adsorptive strength of VOCs on the surface of catalyst. Meanwhile, plasma treatment process exerted a slight influence on the pore structure and morphological property of the catalyst. Consequently, CMC/SiO₂-P exhibited much higher catalytic activity than CMC/SiO₂ prepared by the incipient wetness impregnation method for the catalytic oxidation of toluene and n-hexane. Among the catalysts prepared, the 15%CMC/SiO₂-P catalyst even exhibited a high catalytic activity comparable to that of the supported noble metal catalyst for the oxidation of the inert hexane. The T₉₈ of toluene and n-hexane over 15%CMC/SiO₂-P was 260 and 280°C under the conditions of VOC concentration at 1000 ppm and WHSV at 20,000 mL·g^-1·h^-1, respectively. This work provided a novel method for the preparation of the supported transition metal mixed oxide catalyst.

Highly Resistant LaCo1−xFexO3 Perovskites Used in Chlorobenzene Catalytic Combustion

The stability of LaCo1−xFexO3 perovskite structures (x = 0; 0.25; 0.5; 0.75; 1) was studied in the combustion of chlorobenzene. This family of catalysts was synthesized by the citrate method obtaining pure structures. The Fe doping in the original structure induces electronic environments capable of generating the Co2+/Co3+ redox couple. The characteristics observed in bulk are perfectly reflected on the surface, favoring a high resistance of the solids to chlorine poisoning. Superior stability under reaction conditions was observed in the phase with the lowest Fe content (x = 0.25), remaining stable at 100% combustion of chlorobenzene during 100 h, not observing intermediate reaction products. These results open up a new avenue for designing and fabricating high-performance catalysts in the environmental field

Reduced graphene oxide as an effective promoter to the layered manganese oxide-supported Ag catalysts for the oxidation of ethyl acetate and carbon monoxide

The layered manganese oxide (δ-MnO₂)-supported reduced graphene oxide (rGO)-promoted silver catalysts (xAg- yrGO/δ-MnO₂; x and y are the Ag and rGO contents (wt%), respectively) were prepared via a polyvinyl alcohol-protected reduction route. Physicochemical properties of these materials were determined using the numerous techniques, and their catalytic activities were evaluated for the oxidation of CO and ethyl acetate. It is found that the loading of rGO as an electron transfer promoter could significantly strengthen the metal-support interaction (SMSI) between Ag and δ-MnO₂ and increase specific surface area of the sample, hence improving catalytic performance of the sample. Activity evaluation reveals that 1Ag- 1.0rGO/δ-MnO₂ showed the best catalytic activity and the lowest apparent activation energy (E_a), giving a T_90% of 140 °C and an E_a of 42.7 kJ/mol for CO oxidation, and a T_90% of 160 °C and an E_a of 39.8 kJ/mol for ethyl acetate oxidation at space velocity (SV) = 60,000 mL/(g h). The good performance of 1Ag- 1.0rGO/δ-MnO₂ was associated with its high Mn³⁺/Mn⁴⁺ or O_ads/O_latt molar ratio, good low-temperature reducibility, and strong SMSI between Ag and δ-MnO₂. The in situ DRIFTS characterization demonstrates that the carbonate and acetate species were the main intermediate products in CO and ethyl acetate oxidation over 1Ag- 1.0rGO/δ-MnO₂, respectively. The 1Ag- 1.0rGO/δ-MnO₂ sample was not significantly altered in physicochemical property after 55 h of stability test, but its activity decreased in the presence of water vapor, especially such an effect on ethyl acetate oxidation was more obvious, which was possibly due to the competitive adsorption of water and reactants on the catalyst surface.

Rational Design and Construction of Monolithic Ordered Mesoporous Co3O4@SiO2 Catalyst by a Novel 3D Printed Technology for Catalytic Oxidation of Toluene

Here, we report a novel 3D printed layered ordered mesoporous template that can encapsulate active Co-MOFs species in a confined way to achieve the goal of monolithic catalyst. The monolithic OM-Co₃O₄@SiO₂-S catalyst can maintain a macroscopic porous layered structure and a microscopic ordered mesoporous structure. This monolithic OM-Co₃O₄@SiO₂-S catalyst has excellent catalytic performance (T₉₀ = 236 °C), water resistance, and thermal stability in the catalytic combustion of toluene. The catalytic performance of the monolithic OM-Co₃O₄@SiO₂-S catalyst is much better than that of many monolithic catalysts reported in the former. Among them, the introduction of binder aluminum phosphate (AP) can effectively enhance the rheological properties of the printing ink, achieve the purpose of ink writing monolithic layered porous material, enrich the acidic point of the monolithic catalyst, and increase the number of reactive oxygen species. This work reveals a novel monolithic catalyst forming strategy that can combine the advantages of ordered mesoporous materials with active species to form macro-layered porous materials and provide ideas and an experimental basis for the elimination of VOCs in industrial applications.

Adsorptive removal of some Cl-VOC's as dangerous environmental pollutants using feather-like γ-Al2O3 derived from aluminium waste with life cycle analysis

Herein, we designed a cost-effective preparation method of nanocomposite γ-Al₂O₃ derived from Al-waste. The produced material has a feather-like morphology, and its adsorption of some chlorinated volatile organic compounds (Cl-VOC's) such as benzyl chloride, chloroform and carbon tetrachloride (C₇H₇Cl, CHCl₃ and CCl₄) was investigated due to their potential carcinogenic effect on humans. It showed a characteristic efficiency towards the adsorptive removal of these compounds over a long period, i.e., eight continuous weeks, at ambient temperature and atmospheric pressure. After 8-weeks, the adsorbed amounts of these compounds were determined as: 325.3 mg C₇H₇Cl, 247.6 mg CHCl₃ and 253.3 mg CCl₄ per g of γ-Al₂O_3, respectively. CCl₄ was also found to be dissociatively adsorbed on the surface of γ-Al₂O₃, whereas CHCl₃ and C₇H₇Cl were found to be associatively adsorbed. The prepared γ-Al₂O₃ has a relatively high surface area (i.e., 192.2 m². g^-1) and mesoporosity with different pore diameters in the range of 25-47 Å. Furthermore, environmental impacts of the nanocomposite γ-Al₂O₃ preparation were evaluated using life cycle assessment. For prepartion of adsorbent utilising 1 kg of scrap aluminium wire, it was observed that potential energy demand was 288 MJ, climate change potential was 19 kg CO₂ equivalent, acidification potential was 0.115 kg SO₂ equivalent and eutrophication potential was 0.018 kg PO₄^3- equivalent.

Current progress on catalytic oxidation of toluene: a review

Toluene is one of the pollutants that are dangerous to the environment and human health and has been sorted into priority pollutants; hence, the control of its emission is necessary. Due to severe problems caused by toluene, different techniques for the abatement of toluene have been developed. Catalytic oxidation is one of the promising methods and effective technologies for toluene degradation as it oxidizes it to CO₂ and does not deliver other pollutants to the environment. This paper highlights the recent progressive advancement of the catalysts for toluene oxidation. Five categories of catalysts, including noble metal catalysts, transition metal catalysts, perovskite catalysts, metal-organic frameworks (MOFs)-based catalysts, and spinel catalysts reported in the past half a decade (2015-2020), are reviewed. Various factors that influence their catalytic activities, such as morphology and structure, preparation methods, specific surface area, relative humidity, and coke formation, are discussed. Furthermore, the reaction mechanisms and kinetics for catalytic oxidation of toluene are also discussed.

Facile synthesis of Pt-Ce0.63Zr0·37O2-Y catalysts and the application in catalytic oxidation of toluene

In this work, a series of Pt-Ce_0.63Zr_0·37O₂-Y catalysts were prepared by unique simple mechanical mixing method. The catalytic activity of these catalysts for toluene oxidation was investigated. The physicochemical properties of the catalysts were characterized by XRD, ICP-MS, SEM, TEM, XPS and N₂ sorption. Pore size distribution was analyzed according nitrogen adsorption and desorption isotherms. The catalytic results showed that using NaY as support for Pt-Ce_0.63Zr_0·37O₂-Y could enhance the conversion of toluene during the oxidation process in comparison with HY. Further mixing cerium zirconium solid solution with Pt-NaY can improve the oxidation catalytic property of these catalysts. The conversion of toluene over Pt-Ce_0.63Zr_0·37O₂-NaY reached more than 90% at 200 °C. High catalytic stability was obtained for toluene oxidation over Pt-Ce_0.63Zr_0·37O₂-NaY. Platinum, cerium and zirconium can be uniformly dispersed on Y zeolite with small particle size by simple mechanical synthesis. The effect of drying methods on catalytic activity and hydrothermal stability of catalysts were also investigated in this research.

Enhancement of propane combustion activity over CoOx catalysts by introducing C2–C5 diols

C₂–C₅ diols effectively promote the degradation of propane by weakening the Co–O bond strength of CoO_x.

Manganese-cerium composite oxide pyrolyzed from metal organic framework supporting palladium nanoparticles for efficient toluene oxidation

Manganese-cerium metal oxide with flocculent structure prepared via the pyrolysis of Mn/Ce-MOF and supported Pd were applied for the catalytic oxidation of toluene. The Pd/Mn3Ce2-300 catalyst could completely oxidize toluene at 190 °C, which presented excellent catalytic performance. Moreover, Pd/Mn3Ce2-300 possessed great reusability, stability and water resistance even under 10 vol% water vapors. A series of characterizations including X-ray diffraction (XRD), N₂ adsorption-desorption, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and H₂ temperature programmed reduction (H₂-TPR) were used to investigate the physicochemical properties of the samples. It was found that Pd/Mn3Ce2-300 possessed a better reduction ability at low temperature, more surface absorbed oxygen and surface Pd species, and a strong interaction between Pd and Mn3Ce2-300, resulting in great catalytic performance for toluene degradation.

Effect of Pd/Ce loading on the performance of Pd-Ce/γ-Al2O3 catalysts for toluene abatement

A single metal Pd/γ-Al₂O₃ catalyst and a bimetallic Pd-Ce/γ-Al₂O₃ catalyst were prepared by the equal-volume impregnation method to investigate the effect of CeO₂ loading on the catalytic oxidation of toluene. The specific surface area, surface morphology, and redox performance of the catalyst were characterized by N₂ desorption, scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), H₂-TPR, O₂-TPD, and electron paramagnetic resonance (EPR). The results showed that bimetal catalysts loaded CeO₂ had smaller nano-PdO particles than those of the Pd/γ-Al₂O₃ catalyst. Compared with the catalyst of 0.2Pd/γ-Al₂O₃ (percentage of mass, the same as below), the catalyst doped with 0.3CeO₂ had a stronger reduction peak, which was shifted to the low-temperature zone by more than 80 °C. The results of XPS and O₂-TPD showed that the introduction of CeO₂ provided more surface oxygen vacancy for the catalyst and enhanced its catalytic oxidation ability, and the amount of desorbed O₂ increased from 3.55 μmol/g to 8.54 μmol/g. The results of EPR were that the addition of CeO₂ increased the content of active oxygen species and oxygen vacancies on the surface of the catalysts, which might be due to the supply of electrons to the O₂ and PdO during the Ce³⁺toCe⁴⁺ conversion process. That could have accelerated the catalytic reaction process. Compared with the single precious metal catalyst, the T₁₀ and T₉₀ of the Pd-Ce/γ-Al₂O₃ catalyst were decreased by 22 °C and 40 °C, respectively.