Elimination Of Volatile Organic Compounds Research Articles

Engineering light propagation for synergetic photo- and thermocatalysis toward volatile organic compounds elimination

Photo-thermal catalysis emerged as a new fast-growing research area for volatile organic compounds (VOCs) elimination. However, despite some significant achievements, the research on engineering the light propagation to promote the photo-thermal catalytic efficiency has been largely overlooked so far. Herein, we reported Pt nanoparticle decorated three-dimensionally ordered macroporous (3DOM) LaMn1.2O3 with multiple light scattering and the slow photon effect for improving the light-harvesting, thus achieving synergetic photo- and thermal catalysis toward complete toluene mineralization. As a result, a 100% conversion of toluene (200 ppm with a flow rate of 12.8 mL∙min−1) is achieved with high selectivity to CO2 (88%) and good stability (100 h) under solar light irradiation. Combining characterizations and activity experiments, the multiple scattering and slow photon effect over Pt/3DOM LaMn1.2O3 are confirmed to enhance the reducibility and migration of lattice oxygen and facilitate the migration of the charge carrier, thus contributing to the improved photo-thermal catalytic performance. This work demonstrates that a well-considered design of catalysts with optimized structural and electronic properties effectively maximizes solar energy utilization.

Emission Control of Toluene in Iron Ore Sintering Using Catalytic Oxidation Technology: A Critical Review

Iron ore sintering flue gas containing large amounts of volatile organic compounds (VOCs) can form secondary photochemical smog and organic aerosols, thus posing a serious threat to human health and the ecological environment. Catalytic combustion technology has been considered as one of the most prospective strategies for VOC elimination. This paper focuses on a review of studies on catalytic removal of typical VOCs (toluene) on transition metal oxide catalysts in recent years, with advances in single metal oxides, multi-oxide composites, and supported metal oxide catalysts. Firstly, the catalytic activities of a series of catalysts for toluene degradation are evaluated and compared, leading to an analysis of the key catalytic indicators that significantly affect the efficiency of toluene degradation. Secondly, the reaction pathway and mechanism of toluene degradation are systematically introduced. Considering the site space and investment cost, the conversion of VOC pollutants to harmless substances using existing selective catalytic reduction (SCR) systems has been studied with considerable effort. Based on the current development of simultaneous multi-pollutant elimination technology, the interaction mechanism between the NH3-SCR reaction and toluene catalytic oxidation on the surface is discussed in detail. Finally, views on the key scientific issues and the challenges faced, as well as an outlook for the future, are presented. This overview is expected to provide a guide for the design and industrial application of NO/VOC simultaneous removal catalysts.

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.

Electron Transfer Trade-offs in MOF-Derived Cobalt-Embedded Nitrogen-Doped Carbon Nanotubes Boost Catalytic Ozonation for Gaseous Sulfur-Containing VOC Elimination

High-performance and robust catalysts act as core drivers for catalytic ozonation to eliminate gaseous sulfur-containing volatile organic compounds (VOCs). Herein, nitrogen-doped carbon nanotubes embedded with Co species (Co@NCNT) are synthesized by thermolysis of a ZIF-67/melamine mixture. The carbon-confinement effects in Co@NCNT not only improve the stability of Co species but also regulate the electronic structure of Co─C bonds, consequently synergistically improving the catalytic ozonation performance. The experimental results indicate that the Co@NCNT catalyst could still remove ∼86% of odorous methyl mercaptan (CH3SH) after running for 60 h at 25 °C under an initial concentration of 50 ppm CH3SH and 40 ppm ozone, relative humidity of 60%, and space velocity of 600,000 mL h–1 g–1, outdistancing reported values under comparable reaction conditions. Detailed characterization and theoretical simulations reveal that the electronic metal–support interaction of Co─C bonds in Co@NCNT significantly adjusts the electronic structure of Co species, thereby promoting ozone-specific adsorption/activation to convert the surface atomic oxygen (*Oad) and ·OH/1O2/·O2–. Also, the electrons obtained from CH3SH in the electron-poor center transferred through the C─Co bond bridge to maintain the redox cycle of ≡Co0/2+ → ≡Co3+ → ≡Co0/2+ and realize the efficient and stable removal of CH3SH into CO2/SO42–/H2O. This work demonstrates that MOF-derived materials with tunable electronic structures achieve the stable removal efficiency for gaseous sulfur-containing VOCs via electron transfer trade-offs and provide potential candidate catalysts for the application of air purification.

In Situ Fabrication of Highly Dispersed Co-Fe-Doped-δ-MnO2 Catalyst by a Facile Redox-Driving MOFs-Derived Method for Low-Temperature Oxidation of Toluene.

Cost-efficient and durable manganese-based catalysts are in great demand for the catalytic elimination of volatile organic compounds (VOCs), which are dominated not only by the nanostructures but also by the oxygen vacancies and Mn-O bond in the catalysts. Herein, a series of nanostructured Co-Fe-doped-δ-MnO2 catalysts (Co-Fe-δ-MnO2) with high dispersion were in situ fabricated by employing metal-organic-frameworks (MOFs) as reducing agents, dopants, and templates all at the same time. The as-obtained Co-Fe-δ-MnO2-20% catalyst exhibited robust durability and high catalytic activity (225 °C) for toluene combustion even in the presence of 5 vol % water vapor, which is 50 °C lower than that of pristine δ-MnO2. Various characterizations revealed that the homogeneously dispersed codoping of Co and Fe ions into δ-MnO2 promotes the generation of oxygen vacancies and weakens the strength of the Mn-O bond, thus increasing the amount of adsorbed oxygen (Oads) and improving the mobility of lattice oxygen (Olatt). Meanwhile, due to successfully inheriting the framework structures of MOFs, the obtained catalyst exhibited a high surface area and three-dimensional mesoporous structure, which contributes to diffusion and increases the number of active sites. Moreover, in situ DRIFTS results confirmed that the toluene degradation mechanism on the Co-Fe-δ-MnO2-20% follows the MVK mechanism and revealed that more Oads and high-mobility Olatt induced by this novel method contribute to accumulating and mineralizing key intermediates (benzoate) and thus promote toluene oxidation. In conclusion, this work stimulates the opportunities to develop Co-Fe-δ-MnO2 as a class of nonprecious-metal-based catalysts for controlling VOC emissions.

Understanding the mechanisms of catalytic enhancement of La-Sr-Co-Fe-O perovskite-type oxides for efficient toluene combustion

The merits of ABO3-type perovskite oxides as catalysts for volatile organic compounds (VOCs) combustion are that the redox capability of transition metal elements in their lattice structure can be well tailored through a facile doping strategy. In particular, La-Sr-Co-Fe-O perovskite-type oxides possess excellent tunable physicochemical properties, making them an ideal platform for promising prospects in VOCs combustion. This work synthesized a series of La1-xSrxCo1-yFeyO3 (x = 0, 0.3, 0.5, 0.8; y = 0, 0.2, 0.5) perovskites and analyzed their reaction kinetics on toluene combustion. Among all the catalysts, La0.5Sr0.5Co0.8Fe0.2O3-δ (LSCF) showed a remarkable catalytic activity towards the toluene oxidation with T90 of 270 °C at a weight hourly space velocity (WSHV) of 30000 mL·g−1·h−1 and apparent activation energy (Ea) of 44.76 kJ·mol−1 and obtained the superior stability. Based on the characterizations and analysis of in-situ DRIFTS, the outstanding catalytic activity of LSCF perovskite is mainly induced by the improvement of the redox ability, the enriched generation of oxygen vacancies, and the activation of the lattice oxygen species. The catalytic mechanism of toluene conversion over the LSCF perovskite was revealed to be consistent with Mars-van Krevelen (MVK) models. The knowledge obtained in this study provides helpful guidance for designing efficient heterogeneous catalysts of La-Sr-Co-Fe-O perovskite-type oxides toward efficient catalytic combustion for VOCs elimination.

Photocatalytic Oxidation for Volatile Organic Compounds Elimination: From Fundamental Research to Practical Applications.

Photocatalysis is regarded as one of the most promising technologies for indoor volatile organic compounds (VOCs) elimination due to its low cost, safe operation, energy efficiency, and high mineralization efficiency under ambient conditions. However, the practical applications of this technology are limited, despite considerable research efforts in recent decades. Until now, most of the works were carried out in the laboratory and focused on exploring new catalytic materials. Only a few works involved the immobilization of catalysts and the design of reactors for practical applications. Therefore, this review systematically summarizes the research and development on photocatalytic oxidation (PCO) of VOCs, with emphasis on recent catalyst's immobilization and reactor designs in detail. First, different types of photocatalytic materials and the mechanisms for PCO of VOCs are briefly discussed. Then, both the catalyst's immobilization techniques and reactor designs are reviewed in detail. Finally, the existing challenges and future perspectives for PCO of VOCs are proposed. This work aims to provide updated information and research inspirations for the commercialization of this technology in the future.

Chlorine-Coordinated Pd Single Atom Enhanced the Chlorine Resistance for Volatile Organic Compound Degradation: Mechanism Study.

The development of catalysts with high chlorine resistance for volatile organic compound (VOC) degradation is of great significance to achieve air purification. Herein, Pd@ZrO2 catalysts with monodispersed Pd atoms coordinated with Cl were prepared using an in situ grown Zr-based metal-organic framework (MOF) as the sacrifice templates to enhance the chlorine resistance for VOC elimination. The residual Cl species from the Zr-MOF coordinated with Pd, forming Pd1-Cl species during the pyrolysis. Meanwhile, abundant oxygen vacancies (VO) were generated, which enhanced the adsorption and activation of gaseous oxygen molecules, accelerating the degradation of VOCs. In addition, the Pd@ZrO2 catalysts exhibited satisfactory water resistance, long-term stability, and great resistance to CO and dichloromethane (DCM) for VOC elimination. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results elucidated that the generation of Pd1-Cl species in Pd@ZrO2 suppressed the absorption of DCM, releasing more active sites for toluene and its intermediate adsorption. Simultaneously, the monodispersed Pd atoms and VO improved the reactivity of gaseous oxygen molecule adsorption and dissociation, boosting the deep decomposition of toluene and its intermediates. This work may provide a new strategy for rationally designing high-chlorine resistance catalysts for VOC elimination to improve the atmospheric environment.

Metal organic frameworks derived metal oxides prepared by oxygen vacancy engineering with the enhanced catalytic activity for toluene oxidation

Herein, MnOx catalysts were prepared by in situ pyrolysis of Mn metal organic frameworks (Mn-MOF). The Mn-5TA with proper doping of tartaric acid (Mn-MOF/ tartaric acid mass ratio of 5), exhibited superior catalytic activity and stability towards catalytic removal of toluene under simulated real-exhaust conditions. Mn3+ and oxygen vacancies were beneficial for toluene degradation, whereas Mn3+ can generate oxygen vacancies to maintain charge conservation and then responsible for toluene adsorption and generation of intermediates. In addition, the oxygen vacancies were explored by EPR, Raman and O2-TPD. Compared with other catalysts, Mn-5TA has higher oxygen vacancy contents. Meanwhile, in-situ DRIFTS also indicated that oxygen vacancies could play a key role in the adsorption-oxidation process of toluene. Therefore, the present study provides a simple method to introduce and control the content of oxygen vacancies, and the obtained results provide a new strategy for the rational design of efficient catalytic materials for the elimination of volatile organic compounds.

Surfactant-assisted synthesis of MOF-derived CeO2 for low-temperature catalytic o-xylene combustion

CeO2 applied for catalytic elimination of volatile organic compounds have received great attention for their superior oxygen storage capacity and reducibility. In this work, CeO2-C catalyst is prepared through pyrolysis of Ce-MOF precursor with assistance of cetyltrimethylammonium bromide (CTAB). The T50 and T90 of the strip-like CeO2-C are 155 and 193 °C (WHSV= 48000 mL·g−1·h−1, o-xylene concentration= 500 ppm), which take significant advantages over literature results. Compared with the catalyst prepared without CTAB (CeO2-B), the CeO2-C possesses a 1.5 times reaction rate and an apparent activation energy (Ea) as low as 39.82 kJ·mol−1. Meanwhile, CeO2-C also demonstrates good thermal stability in long-term test and water resistance. The characterization results reveal that the assistance of CTAB increases oxygen vacancy density and generates more active oxygen species, resulting in the improvement of catalytic performance. Furthermore, the reaction route, o-xylene → 2-methyl benzaldehyde (benzaldehyde) → benzoic acid → maleic anhydride → ethanol and acetone → H2O and CO2, is also probed.

Optimization of photothermal conversion and catalytic sites for photo-assisted-catalytic degradation of volatile organic compounds

Solar energy conversion is a promising strategy to enhance the elimination of volatile organic compounds (VOCs) and minimize power consumption. Herein, non-noble metal WC@WO3 as cocatalyst was composited with CeO2 to optimize photochemical and photothermal conversion for the catalytic ozonation of toluene and acetone. The photothermal conversion efficiencies of visible and infrared lights on 20%WC@WO3–CeO2 were 2.2 and 10.4 times higher than those on CeO2, respectively, which indicates that the equilibrium temperature of the catalyst remarkably increased under full-spectrum light irradiation. Moreover, WC@WO3 transferred electrons to CeO2 in 20%WC@WO3–CeO2 and thus remarkably improved the activity of catalytic sites. The synergy factor of light and O3 on 20%WC@WO3–CeO2 was 5.8, and the reaction rate of toluene and acetone reached 9274.5 and 35779.0 mg/(m3∙min), respectively. This work provides a low-cost and high-efficient catalyst for the utilization of solar energy for VOC control.

An efficient process for aromatic VOCs degradation: Combination of VUV photolysis and photocatalytic oxidation in a wet scrubber

The elimination of volatile organic compounds (VOCs) via vacuum ultraviolet (VUV) photolysis is greatly limited by low removal efficiency and gaseous byproducts generation, while photocatalytic oxidation of VOCs suffers from catalytic deactivation. Herein, a coupled process of gaseous VUV photolysis with aqueous photocatalytic oxidation with P25 as the catalyst was firstly proposed for efficient aromatic VOCs removal (VUV/P25). The removal efficiency of toluene reached 86.2% in VUV/P25 process, but was only 33.6% and 58.1% in alone gaseous VUV photolysis and aqueous ultraviolet photocatalytic oxidation (UV/P25) process, respectively. Correspondingly, the outlet CO2 concentration in VUV/P25 process reached 132 ppmv. Toluene was firstly destructed by high-energy photons generated from gaseous VUV photolysis, resulting in its incomplete oxidation to form soluble intermediates including acids, aldehydes, esters. These soluble intermediates would be further degraded and mineralized into CO2 in subsequent aqueous UV/P25 process. Notably, the concentrations of intermediates in VUV/P25 were much lower than those in VUV photolysis, indicating the synergy effect of VUV photolysis and UV/P25 process. The stability tests proved that VUV/P25 process maintained an excellent toluene degradation performance and P25 did not suffer from catalytic deactivation. In addition to toluene, the VUV/P25 system also achieved the efficient and sustainable degradation of styrene and chlorobenzene, suggesting its good application prospect in industrial VOCs treatment. This study proposes an efficient and promising strategy for deep oxidation of multiple aromatic VOCs in industries.

Oxygen-vacancy-induced O2 activation and electron-hole migration enhance photothermal catalytic toluene oxidation

The rapid elimination of volatile organic compounds and the intermediate analysis with efficient photothermal catalysis are of great significance to the environment. Oxygen vacancies (Vo) play a crucial role in structural modification and performance improvement of heterogeneous catalysts. Accordingly, here, abundant Vo sites are introduced into Co 3 O 4 /TiO 2 composite via treatment under H 2 and Ar flow at 200°C, and the photothermal catalytic performance of toluene is significantly improved. The molecular oxygen (O 2 ) adsorbed by Vo is activated to form reactive oxygen species for deep oxidation of toluene. Vo generated on the unilateral side in Co 3 O 4 /TiO 2 heterojunctions serves to capture electrons and break the dynamic balance of electron-hole pairs. The excited electrons are trapped by Vo, and the direct recombination of electron-hole pairs is inhibited, thus promoting the photochemical process. Moreover, the photothermal synergy effect and the relationship between Vo evolution and intermediates transformation mechanism are systematically studied. • The oxygen-vacancy-induced O 2 adsorption and activation mechanism in photothermal catalysis is studied • Oxygen-vacancy-trapped electrons inhibit electron-hole pair recombination • Oxygen vacancies promote rapid photothermal oxidation of toluene and intermediates Oxygen vacancies are known to influence the performance of heterogeneous catalysts. Herein, Yang et al. show that oxygen vacancies in Co 3 O 4 /TiO 2 induce the activation of O 2 and migration of electron holes, with light-generated carriers promoting the generation of active radicals to catalyze the oxidation of toluene.

Boosting catalytic stability for VOCs removal by constructing PtCu alloy structure with superior oxygen activation behavior

The elimination of volatile organic compounds (VOCs) emitted from the process of industry production is of great significance to improve the atmospheric environment. Herein the catalytic oxidation of the toluene and iso-hexane mixture, as the typical components from furniture paint industry, and the enhancement in the catalytic stability for toluene oxidation were investigated in detail. The formation rate of active oxygen species was very important for the development of the catalyst with high catalytic stability. Compared with the Pt/M catalyst, the Pt-Cu/M catalyst owned stronger ability of VOCs adsorption and gaseous oxygen activation by introducing additional sites for activating O2. The Langmuir–Hinshelwood (adsorbed oxygen) and Mars–van Krevelen (lattice oxygen) mechanism existed in toluene oxidation over the present Pt/M and Pt-Cu/M catalysts, respectively. The change in the involved active oxygen species during toluene oxidation was resulted from the Pt-Cu alloy structure. In addition to the adsorption of O2, a part of active lattice oxygen species can also be replenished by the migration of bulk lattice oxygen over Pt-Cu/M. With a rise in the reaction temperature, weakly adsorbed iso-hexane could be timely reacted with the more active lattice oxygen species to keep the catalytic stability over the Pt/M and Pt-Cu/M catalysts. Generally, we not only prepared a promising material for the catalytic removal of VOCs from the furniture paint industry, but also provided a new strategy for the generation of active oxygen species, making the catalyst exhibit high catalytic oxidation stability.

Reduction of non-methane hydrocarbons in cooking oil fumes via adsorption on MFI: Effect of zeolitic framework composition

The growth of public awareness of hazard from gaseous pollutants emitted by cooking activities spawned the implement of new laws & regulations as well as new technologies for cooking oil fumes emission control. Considering the emission characteristics of large air volume and intermittence of cooking fumes, in this work, TS-1 was firstly applied as an efficient adsorbent for enriching the low-concentrated complex humid volatile organic compounds (VOCs) from cooking oil fumes. In order to illustrate the superiority of Ti-O-Si framework as a cooking VOCs adsorbent, zeolites with the same MFI topology to TS-1 but different framework compositions of Si-O-Al (ZSM-5) and Si-O-Si (silicalite-1, hereinafter referred as S-1) were also investigated for comparison. Related characterizations were performed to reveal the difference among three zeolites. It was found that textural properties, surface silanol density and defect content significantly affect the adsorption site accessibility, water resistance as well as organophilicity of zeolites adsorbents, all of which play a decisive role in the adsorption process of cooking oil fumes. Both TS-1 and S-1 present much stronger water resistance than commercial ZSM-5 due to lacking hydrophilic Si-OH-Al groups (S-1 > TS-1 > ZSM-5), while TS-1 shows better organophilic property than both S-1 and ZSM-5 (in an order of TS-1 > ZSM-5 > S-1) due to the physical and electrical interaction between Ti-contained framework and organic molecular. These characteristics jointly make the zeolite with Ti-O-Si framework be a good adsorbent candidate for VOCs elimination from cooking fumes.

Efficient Photothermal Elimination of Formaldehyde under Visible Light at Room Temperature by a MnOx-Modified Multi-Porous Carbon Sphere.

Volatile organic compounds (VOCs) exert a serious impact on the environment and human health. The development of new technologies for the elimination of VOCs, especially those from non-industrial emission sources, such as indoor air pollution and other low-concentration VOCs exhaust gases, is essential for improving environmental quality and human health. In this study, a monolithic photothermocatalyst was prepared by stabilizing manganese oxide on multi-porous carbon spheres to facilitate the elimination of formaldehyde (HCHO). This catalyst exhibited excellent photothermal synergistic performance. Therefore, by harvesting only visible light, the catalyst could spontaneously heat up its surface to achieve a thermal catalytic oxidation state suitable for eliminating HCHO. We found that the surface temperature of the catalyst could reach to up 93.8 °C under visible light, achieving an 87.5% HCHO removal efficiency when the initial concentration of HCHO was 160 ppm. The microporous structure on the surface of the carbon spheres not only increased the specific surface area and loading capacity of manganese oxide but also increased their photothermal efficiency, allowing them to reach a temperature high enough for MnOx to overcome the activation energy required for HCHO oxidation. The relevant catalyst characteristics were analyzed using XRD, measurement of BET surface area, scanning electron microscopy, HR-TEM, XPS, and DRS. Results obtained from a cyclic performance test indicated high stability and potential application of the MnOx-modified multi-porous carbon sphere.

Accelerated oxidation of VOCs via vacuum ultraviolet photolysis coupled with wet scrubbing process

Vacuum ultraviolet (VUV) photolysis is a facile method for volatile organic compounds (VOCs) elimination, but is greatly limited by the relatively low removal efficiency and the possible secondary pollution. To overcome above drawbacks, we developed an efficient method for VOCs elimination via VUV photolysis coupled with wet scrubbing process. In this coupled process, volatile toluene, a representative of VOCs, was oxidized by the gas-phase VUV photolysis, and then scrubbed into water for further oxidation by the liquid-phase VUV photolysis. More than 96% of toluene was efficiently removed by this coupled process, which was 2 times higher than that in the gas-phase VUV photolysis. This improvement was attributed to the synergistic effect between gas-phase and liquid-phase VUV photolysis. O3 and HO• are the predomination reactive species for the toluene degradation in this coupled process, and the generation of O3 in gas-phase VUV photolysis can efficiently enhance the HO• production in liquid-phase VUV photolysis. The result from in-situ proton transfer reaction ionization with mass analyzer (PTR-MS) further suggested that most intermediates were trapped by the wet scrubbing process and efficiently oxidized by the liquid-phase VUV photolysis, showing a high performance for controlling the secondary pollution. Furthermore, the result of stability test and the reuse of solution demonstrated that this coupled process has a highly stable and sustainable performance for toluene degradation. This study presents an environmentally benign and highly efficient VUV photolysis for gaseous VOCs removal in the wet scrubbing process.

Bifunctional zeolites-silver catalyst enabled tandem oxidation of formaldehyde at low temperatures

Bifunctional catalysts with tandem processes have achieved great success in a wide range of important catalytic processes, however, this concept has hardly been applied in the elimination of volatile organic compounds. Herein, we designed a tandem bifunctional Zeolites-Silver catalyst that enormously boosted formaldehyde oxidation at low temperatures, and formaldehyde conversion increased by 50 times (100% versus 2%) at 70 °C compared to that of monofunctional supported silver catalyst. This is enabled by designing a bifunctional catalyst composed of acidic ZSM-5 zeolite and silver component, which provides two types of active sites with complementary functions. Detached acidic ZSM-5 activates formaldehyde to generate gaseous intermediates of methyl formate, which is more easily oxidized by subsequent silver component. We anticipate that the findings here will open up a new avenue for the development of formaldehyde oxidation technologies, and also provide guidance for designing efficient catalysts in a series of oxidation reactions.

Perovskite Oxides in Catalytic Combustion of Volatile Organic Compounds: Recent Advances and Future Prospects

Volatile organic compounds are a kind of important indoor and outdoor air pollutants. In recent years, more and more attention has been paid to the ways of volatile organic compound elimination because of its potential long‐term effects on human health. Among the various available methods for volatile organic compound elimination, the catalytic combustion is the most attractive method due to its high efficiency, low cost, simple operation, and easy scale‐up. Perovskite oxides, as a large family of metal oxides with their A‐site mainly of lanthanide element and/or alkaline earth metal element and B‐site of transition metal element, have been extensively investigated as active and stable catalysts for volatile organic compound removal reactions due to their abundant compositional elements, high thermal/chemical stability, and compositional/structural flexibility. The catalytic performance of perovskite oxides is strongly depended on its material composition, morphology, and surface/bulk properties, while the doping, tailored synthesis route, and composite construction may have a significant effect on the bulk (oxygen vacancy concentration, lattice structure), surface (oxygen species, defect) properties, and particulate morphology, consequently the catalytic activity and stability for volatile organic compound removal. Herein, a comprehensive review about the recent advances in perovskite oxides for volatile organic compound elimination reactions based on catalytic combustion is presented from different aspects with a special emphasis on the material design strategies, such as compositional tuning, morphology control, nanostructure building, hybrid construction, and surface modification. At last, some perspectives are presented on the development and design of perovskite oxide‐based catalysts for volatile organic compound removal applications by highlighgting the critical issues and challenges.

Energy-balanced and effective adsorption-catalytic multilayer bed system for removal of volatile organic compounds

• Dual-functional adsorption-catalytic system enables very effective VOCs elimination. • Adsorption-oxidation cycles can be repeated at maintained efficiency. • Inert separator is crucial to protect an adsorbent and to control diffusion. • The combined system produces a substantial amount of heat for most cases. • Diffusion model reveals that amounts of adsorbent and separator influence conversion. A dual-functional adsorption-catalytic system for elimination of volatile organic compounds (VOCs) in a cyclic mode, consisting of various configurations of three components, i.e. carbon adsorbent, inert silica separator and Pt/ZrO 2 catalyst, was developed. Both adsorbent and ZrO 2 support were synthesized by the nanoreplication method using spherical silica as a template, whereas the Pt active phase was deposited by the polyol approach. Properties of the functional materials were studied by several techniques, including N 2 adsorption, SEM-EDS, TGA, XRD, XRF and XPS. It was shown that the inert silica separator played an essential role protecting the carbon adsorbent from undesirable partial oxidation. The highest possible effectiveness of the toluene removal (conversion of 94.5%) was obtained for the configuration with 150 mg of Pt/ZrO 2 per 40 mg of the adsorbent. A fair stability of the optimal dual-functional system was proved by performing five consecutive adsorption–desorption-oxidation cycles. The experimental study was complemented by energy demand calculations, which confirmed the superiority of the hybrid system over a classic catalytic flow reactor in terms of energy requirements for the desorption-oxidation step. It was demonstrated that the system might operate autothermally due to a substantial amount of generated heat. Additionally, a simplified dynamic mathematical model of the system was developed, which enabled the identification of key aspects, including directions towards more complex mathematical description, to be taken into account in further research aimed at optimization of the hybrid system. The proposed hybrid dual-functional system can therefore be a step forward in developing cost-effective elimination technologies of VOCs from lean waste gases.