Catalytic Oxidation Of Volatile Organic Compounds Research Articles

Modification of Fe on hydrophobic ZSM-5 zeolite: Optimization of adsorption and catalytic performance for decomposition of VOCs at low-temperature

The conjugation of high adsorption and excellent catalytic characteristics is desirable for the removal of volatile-organic-compounds (VOCs) at low-temperatures. In this study, ZSM-5 zeolites with varying Si/Al ratios (15, 30, 100, and 200) were synthesized using the hydrothermal-method to assess their adsorption capability for VOCs. Among them, the ZSM-5(30) sample exhibited a well-defined zeolite structure, exceptional hydrophobicity, a high surface area (SBET), and micropores, resulting in a higher toluene adsorption capacity of 135 mg/g compared to other adsorbents. Additionally, the ZSM-5(30) sample demonstrated excellent regenerative stability in both dry and humid environments. Consequently, ZSM-5(30), identified as the most effective adsorbent, was subjected to loading with various amounts of Fe metal for the catalytic-oxidation of toluene at low-temperatures. Due to its abundant oxygen-vacancies, adequate acid-sites, and various active oxygen-species, the Fe0.2/ZSM-5(30) catalyst (Fe/(Si + Al) = 0.2) not only exhibited a high adsorption capacity for toluene with good stability over five successive cycles but also demonstrated excellent performance in the catalytic oxidation of toluene. The complete conversion of toluene was attained at temperatures approximately 200 °C, with a gas hourly space velocity (GHSV) of 20,000 mL/(g∙h), and maintained stability for 40 h. Furthermore, in-situ diffuse-reflectance infrared-Fourier-transform-spectroscopy (DRIFTS) and gas chromatography-mass spectrometry (GC–MS) results, along with the Mars-Van-Krevelen model, were utilized to elucidate the adsorption and oxidation mechanism of toluene. The unique adsorption and oxidation capabilities of Fe0.2/ZSM-5(30) for toluene indicate its promising potential for the removal of VOCs in real industrial-environments. This study provides valuable insights for the design of high-performance bifunctional materials for the adsorption and catalytic-oxidation of VOCs.

Ultrathin MnO2 with strong lattice disorder for catalytic oxidation of volatile organic compounds

Catalytic oxidation proves the most promising technology for volatile organic compounds (VOCs) abatement. Lattice disorder plays a crucial role in the catalytic activity of catalysts due to the exposure of more active sites. Inspired by this, we successfully prepared a series of ε-MnO2 with different lattice disorder defects via several simple methods and applied them to the catalytic oxidation of two typical VOCs (toluene and acetone). Various characterizations and performance tests confirm that the ultrathin (1.4–1.8 nm) structure and strong lattice disorder can enhance the low temperature reduction and reactive oxygen species, so that MnO2-R exhibits excellent toluene and acetone oxidation activities. In-situ DRIFTS tests were carried out to detect reaction intermediates in the toluene and acetone oxidation process on the catalyst surface. Moreover, we propose a possible synergistic mechanism for toluene and acetone mixtures catalytic oxidation. This work reveals the important role of lattice disorder defects in the catalytic oxidation of VOCs on Mn-based catalysts, and deepens the insights of the reaction path in toluene and acetone catalytic oxidation.

Regulating the surface local environment of MnO2 materials via metal-support interaction in Pt/MnO2 hetero-catalysts for boosting methanol oxidation

Rational use of the strong metal-support interaction (SMSI) is an important way to achieve the complete destruction of volatile organic compounds (VOCs). In order to investigate the influence of SMSI on the catalytic oxidation of VOCs, three Pt/MnO2 hetero-catalysts, i.e., Pt/α-MnO2, Pt/γ-MnO2 and Pt/δ-MnO2, were synthesized and then applied to the catalytic oxidation of methanol. The results showed that, compared with their corresponding pure MnO2, the temperatures (T90) at which 90% of methanol is converted to CO2 for the above three synthesized catalysts were reduced by 54 °C, 67 °C and 32 °C, respectively. The Pt/α-MnO2 catalyst has the best reducibility at lower temperature (T90 = 91 °C). Multiple characterization analyses confirm that the interaction between Pt and MnO2 support can increase the amount of Mn4+ and surface lattice oxygen on the catalyst surface. Thanks to the optimization of local reaction environment on the catalyst surface, Pt/MnO2 hetero-catalysts have better low temperature reduction capacity and stronger VOC deep oxidation capacity than corresponding pure MnO2 catalysts.

Weak Metal-Support Interaction over CuO/TiO2 Catalyst Governed Low-Temperature Toluene Oxidation.

Regulating the metal-support interaction is essential for obtaining highly efficient catalysts for the catalytic oxidation of volatile organic compounds (VOCs). In this work, CuO-TiO2(coll) and CuO/TiO2(imp) with different metal-support interactions were prepared via colloidal and impregnation methods, respectively. The results demonstrated that CuO/TiO2(imp) has higher low-temperature catalytic activity, with a 50% removal of toluene at 170 °C compared to CuO-TiO2(coll). Additionally, the normalized reaction rate (6.4 × 10-6 mol·g-1·s-1) at 160 °C over CuO/TiO2(imp) was almost four-fold higher than that over CuO-TiO2(coll) (1.5 × 10-6 mol·g-1·s-1), and the apparent activation energy value (27.9 ± 2.9 kJ·mol-1) was lower. Systematic structure and surface analysis results disclosed that abundant Cu2+ active species and numerous small CuO particles were presented over CuO/TiO2(imp). Owing to the weak interaction of CuO and TiO2 in this optimized catalyst, the concentration of reducible oxygen species associated with the superior redox property could be enhanced, thus significantly contributing to its low-temperature catalytic activity for toluene oxidation. This work is helpful in exploring the influence of metal-support interaction on the catalytic oxidation of VOCs and developing low-temperature catalysts for VOCs catalytic oxidation.

Heterointerface engineering regulating the energy-level configuration of α-MnO2/δ-MnO2 for enhancing toluene catalytic combustion performance

This work offers a novel approach to prepare manganese oxides with heterointerface structure as a superior catalyst for the catalytic combustion of Volatile Organic Compounds (VOCs). The α-MnO2/δ-MnO2 with heterointerfaces were prepared via annealing δ-MnO2 precursors which were obtained from the redox precipitation between HCl and KMnO4. The characterization results indicate that the heterointerface structure of α-MnO2/δ-MnO2 optimizes energy level structure and provides abundant surface defects, showing superior low-temperature reducibility and preferable mobility of oxygen species. Such features significantly enhance the catalytic activity of the α-MnO2/δ-MnO2 with heterointerfaces catalysts for the complete oxidation of toluene (the toluene conversion rates of 10 % and 90 % are 191 °C and 213 °C, respectively). Moreover, the catalysts show high stability for 50 h. The presented catalysts disclose an avenue to address current obstacles in the catalytic oxidation of VOCs.

Review on Catalytic Oxidation of VOCs at Ambient Temperature.

As an important air pollutant, volatile organic compounds (VOCs) pose a serious threat to the ecological environment and human health. To achieve energy saving, carbon reduction, and safe and efficient degradation of VOCs, ambient temperature catalytic oxidation has become a hot topic for researchers. Firstly, this review systematically summarizes recent progress on the catalytic oxidation of VOCs with different types. Secondly, based on nanoparticle catalysts, cluster catalysts, and single-atom catalysts, we discuss the influence of structural regulation, such as adjustment of size and configuration, metal doping, defect engineering, and acid/base modification, on the structure-activity relationship in the process of catalytic oxidation at ambient temperature. Then, the effects of process conditions, such as initial concentration, space velocity, oxidation atmosphere, and humidity adjustment on catalytic activity, are summarized. It is further found that nanoparticle catalysts are most commonly used in ambient temperature catalytic oxidation. Additionally, ambient temperature catalytic oxidation is mainly applied in the removal of easily degradable pollutants, and focuses on ambient temperature catalytic ozonation. The activity, selectivity, and stability of catalysts need to be improved. Finally, according to the existing problems and limitations in the application of ambient temperature catalytic oxidation technology, new prospects and challenges are proposed.

Low-Temperature Catalytic Ozonation of Multitype VOCs over Zeolite-Supported Catalysts.

Volatile organic compounds (VOCs) are an important source of air pollution, harmful to human health and the environment, and important precursors of secondary organic aerosols, O3 and photochemical smog. This study focused on the low-temperature catalytic oxidation and degradation of benzene, dichloroethane, methanethiol, methanol and methylamine by ozone. Benzene was used as a model compound, and a molecular sieve was selected as a catalyst carrier to prepare a series of supported active metal catalysts by impregnation. The effects of ozone on the catalytic oxidation of VOCs and catalysts' activity were studied. Taking benzene as a model compound, low-temperature ozone catalytic oxidation was conducted to explore the influence of the catalyst carrier, the active metal and the precious metal Pt on the catalytic degradation of benzene. The optimal catalyst appeared to be 0.75%Pt-10%Fe/HZSM(200). The catalytic activity and formation of the by-products methylamine, methanethiol, methanol, dichloroethane and benzene over 0.75%Pt-10%Fe/HZSM(200) were investigated. The structure, oxygen vacancy, surface properties and surface acidity of the catalysts were investigated. XRD, TEM, XPS, H2-TPR, EPR, CO2-TPD, BET, C6H6-TPD and Py-IR were combined to establish the correlation between the surface properties of the catalysts and the degradation activity.

Influences of different surface oxygen species on oxidation of toluene and/or benzene and their reaction pathways over Cu-Mn metal oxides

Catalytic oxidation is considered as the most effective and economical method to remove low concentration volatile organic compounds (VOCs). Activation of oxygen to form active oxygen species on metal oxides catalyst plays a key role in the process. Three copper-manganese oxide catalysts with cubic Cu1.5Mn1.5O4 phases were prepared by microwave heating (CM-MW), sol–gel (CM-SG) and co-precipitation (CM-CP) methods, and applied for the elimination of toluene and benzene as representative aromatic VOCs. These catalysts exhibit different catalytic oxidation performance due to their different physicochemical properties. Various characterizations were used to clarify the role of different oxygen species in the oxidation of VOCs, and the reaction pathway. In situ DRIFTS were carried out to explore the function of surface adsorbed oxygen, oxygen vacancy, and surface lattice oxygen in the catalytic oxidation of VOCs over three catalysts. Various types of intermediate species and detailed reaction pathways are also explored by combining in situ DRIFTS and mass spectrometry. Among these catalysts, CM-MW with nanosheet morphology shows the best catalytic oxidation performance of toluene and/or benzene with/without H2O due to the most abundant active oxygen species, and the highest oxygen vacancy concentration which is beneficial to activate oxygen. Meanwhile, toluene and benzene do not interfere with each other during the mixture oxidation. This study can provide new inspiration for rational design of metal oxide catalysts to remove VOCs.

Thermal catalytic device for toluene decomposition via direct heating

A thermal catalytic device that reduces the energy required for the catalytic oxidation of volatile organic compounds (VOCs) was developed. The catalytic oxidation of VOCs is typically performed under indirect heating conditions resulting in high energy consumption. The proposed device drastically decreases the energy consumed and increases the amount of toluene decomposed during catalytic oxidation because the catalysts are heated directly via a carbon nanotube (CNT) element. The proposed device consists of a glass-fiber textile coated in CNTs, α-MnO<sub>2</sub> nanostructures, and Pt nanostructures. The effect of different α-MnO<sub>2</sub> nanostructures (granular and urchin-like) on device performance was investigated. Moreover, the effect of each device component on the toluene decomposition efficiency and energy consumption of the device was explored by determining the toluene concentration of gaseous toluene after the catalytic oxidation process and the associated energy consumption. The device featuring urchin-like α-MnO<sub>2</sub> nanostructures coated in a thin layer of Pt achieves higher toluene decomposition efficiency than the device featuring granular α-MnO<sub>2</sub> nanostructures coated in Pt nanoparticles. Moreover, the device featuring urchin-like α-MnO<sub>2</sub> nanostructures coated in a thin Pt layer achieves higher toluene decomposition efficiency and lower energy consumption under direct heating conditions than under conventional indirect heating conditions.

Catalytic oxidation of volatile organic compounds by non-noble metal catalyst: Current advancement and future prospectives

Since the inception of urbanization and industrialization, emissions of volatile organic compounds (VOCs) have become serious concern due to harmful effects on terrestrial biota, serious measures must be taken to minimize the emissions of VOCs. Catalytic oxidation is considered one of the most promising technologies for removing VOCs for its low ignition temperature, high efficiency, and no secondary pollution in the process of treatment. This review summarizes progress made in the catalytic oxidation of VOCs over last ten years. We have discussed the mechanism and current advancement of non-noble metal catalysts to remove VOCs. Besides, the characteristics and the factors affecting catalytic performance of non-noble metal catalysts are comprehensively explained. The critical factors that affect the catalytic performance of catalysts mainly include preparation methods, modification technologies, and carrier materials. Therefore, future research should focus on developing efficient catalysts and performance improvement. We believe that current review will provide a great foundation and reference point for future design and development in this field.

Removal of VOCs by Ozone: n-Alkane Oxidation under Mild Conditions

Volatile organic compounds (VOCs) have a negative effect on both humans and the environment; therefore, it is crucial to minimize their emission. The conventional solution is the catalytic oxidation of VOCs by air; however, in some cases this method requires relatively high temperatures. Thus, the oxidation of short-chain alkanes, which demonstrate the lowest reactivity among VOCs, starts at 250–350 °C. This research deals with the ozone catalytic oxidation (OZCO) of alkanes at temperatures as low as 25–200 °C using an alumina-supported manganese oxide catalyst. Our data demonstrate that oxidation can be significantly accelerated in the presence of a small amount of O3. In particular, it was found that n-C4H10 can be readily oxidized by an air/O3 mixture over the Mn/Al2O3 catalyst at temperatures as low as 25 °C. According to the characterization data (SEM-EDX, XRD, H2-TPR, and XPS) the superior catalytic performance of the Mn/Al2O3 catalyst in OZCO stems from a high concentration of Mn2O3 species and oxygen vacancies.

Promotional role of Mn doping on catalytic oxidation of VOCs over mesoporous TiO2 under vacuum ultraviolet (VUV) irradiation

Volatile organic compounds (VOCs) are the crucial precursors to the formation of fine particulate matter and photochemical smog. Photocatalytic oxidation (PCO) under vacuum ultraviolet (VUV) irradiation has attracted increasing interest for VOCs degradation owing to its strong oxidation capability and excellent stability. However, the generation of O3 from VUV irradiation causes secondary pollution and needs to be addressed. In this study, the Mn doped mesoporous TiO2 (Mn/meso-TiO2) was developed and first combined with VUV irradiation to remove O3 as well as enhance benzene degradation via O3-assited catalytic oxidation. Results indicate that the Mn doped TiO2 exhibited a much higher benzene removal efficiency (82%) than undoped one (70%) and commercial TiO2 P25 (48%). The O3 by-product can be completely eliminated by Mn/meso-TiO2 and contributed to benzene removal efficiency of about 34%. The excellent performance was attributed to the formation of highly reactive oxidizing species such as O(1D), O(3P), hydroxyl radicals (OH) via catalytic decomposition of O3 over oxygen vacancy sites of Mn oxides. Mn/meso-TiO2 cooperated well with VUV and such a VUV-PCO process is very promising for VOCs degradation.

VOC oxidation in excess of oxygen using flow-through catalytic membrane reactor

Platinum gamma-alumina (Pt/γ-Al2O3) impregnated membrane was prepared through the evaporative-crystallization deposition method for volatile organic compounds (VOCs) conversion to carbon dioxide (CO2) and water (H2O). The catalytic oxidation of VOCs (propane, n-butane and propylene), fed alone with oxygen were obtained after characterization (SEM-EDXA observation, BET measurement, permeability assessment). VOC conversion of 95%, 52% and 82% for propane, n-butane and propylene was achieved at 378 °C, 245 °C and 420 °C respectively, by varying the reaction temperature using the contactor flow-through catalytic membrane reactor operating in the Knudsen flow regime. The BET surface area and the pore diameter of the 3.52 wt% Pt membrane are 0.426 m2/g and 3.70 nm respectively. The results are comparable with the literature.

Catalytic oxidation of VOCs on MnMgAlOx mixed oxides obtained by auto-combustion

MnMgAlOx mixed oxides were prepared by means of the auto-combustion methodology using glycine/nitrate ratios of 1.0, 0.56 and 0.2; and M2+/M3+=3.0 and Mn2+/Mg2+=1.0 ratios. Additionally, MnMgAlOx oxide was obtained from the hydrotalcite-type precursor by the traditional co-precipitation method. The catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction (H2-TPR), temperature programmed desorption (O2-TPD), textural analysis, scanning electron microscopy (SEM) and their catalytic performances were evaluated in the total oxidation of two volatile organic compounds (VOCs) representative of aromatic compounds (toluene) and of esters (ethyl acetate). The manganese mixed oxides resulting from the auto-combustion exhibited a chemical composition similar to that of the oxide obtained by thermal decomposition of the hydrotalcite with ∼36% of manganese loading. The mixed oxides obtained by both methodologies were active in the VOC oxidation. However, the mixed oxides synthesized by the auto-combustion methodology with stoichiometric and rich fuel conditions, showed better performance in the oxidation of toluene and ethyl acetate. The fuel/oxidizer ratio determined the redox properties, specific area and the catalytic performance of the materials in the oxidation of VOCs.Using the auto-combustion method was possible to obtain mixed oxides with a high manganese load which showed lower size particle (4–7nm) and better structural stability than the mixed oxide obtained by the co-precipitation method (34nm). The auto-combustion allowed for the obtaining of mixed oxides in very short synthesis times (∼5h) with equal or superior catalytic properties as the oxide obtained by the co-precipitation method probably due to the maximization of the properties of the materials, where the decrease of the particle sizes and the improvement of the active phase distribution and oxidation-reduction properties are favorable for the improvement of catalytic performances.

Catalytic oxidation of VOCs over Al- and Fe-pillared montmorillonite

Al- and Fe-pillared montmorillonite (Al- and Fe-PILCs) were prepared and examined as catalysts in the deep oxidation of toluene and chlorobenzene. The catalysts before and after reaction were characterized by X-ray powder diffraction, N2 adsorption, scanning electron microscopy, and energy dispersive X-ray spectrometer. Results show that Al- and Fe-PILCs with layer structures increase the surface area. For the catalytic oxidation of volatile organic compounds (VOCs), Fe-PILCs exhibit higher performance than fresh montmorillonite and Al-PILCs. Higher concentration of Fe also resulted in higher catalytic activity. Fe-PILCs also exhibited higher stability than Al-PILCs. Even at a low temperature (100°C), Fe-PILCs still exhibited certain activity. Lifetime evaluation results show that the activity of Fe-PILC (3) did not vary after a 96-hour reaction. BET and XRD results indicate that these pillared catalysts have very stable structures even after prolonged reaction. Hence, Fe-PILCs are potential materials for VOC decontamination.

Catalytic oxidation of VOCs and CO by ozone over alumina supported cobalt oxide

An alumina-supported cobalt oxide system with overstoichiometric oxygen (CoO x /Al 2O 3) was investigated with respect to heterogeneous catalytic decomposition of ozone, complete oxidation of volatile organic compounds (VOCs) and oxidation of CO. The experiments were performed in the temperature range of −45 to 250 °C in an isothermal plug-flow reactor. The characterization of the CoO x /Al 2O 3 catalyst was performed by chemical analysis, XPS, XRD, IR techniques, magnetic and adsorption measurements. A very high activity of the catalyst towards ozone decomposition was observed even at temperatures below −40 °C, the catalyst remaining active for a long time. The activity of the catalyst with respect to complete oxidation of VOCs and oxidation of carbon monoxide was studied in presence of different oxidizing agents (ozone or oxygen). A significant increase in the catalytic activity and decrease in the reaction temperature was observed using ozone as an oxidant. Two main reasons for this behaviour were found: (i) the high content of active and mobile oxygen obtained during the synthesis on the catalyst surface; (ii) the catalytically active complex of O −[Co 4+], formed during the reaction of ozone decomposition and able to oxidize VOCs at room temperature.

The effect of K and Al over NiCo2O4catalyst on its character and catalytic oxidation of VOCs

Abstract NiCo 2 O 4 , K-NiCo 2 O 4 , and Al-NiCo 2 O 4 spinel oxides were prepared by co-precipitated method. The properties of these three samples were investigated by X-ray powder diffraction (XRD), temperature-programmed reduction (TPR), Brunauer–Emmett–Teller (BET) measurement, and X-ray photoelectron spectroscopy (XPS) technologies. The catalytic activity of volatile organic compounds (VOCs) oxidation was found to be decreased after adding aluminum and increased after adding potassium in NiCo 2 O 4 sample. The small particle size of NiCo 2 O 4 was responsible for VOCs oxidation. The potassium was the most effective in promoting NiCo 2 O 4 sample in reducibility and surface area. XPS analysis indicated that the electrophonic oxygen species on the catalyst surface is the main active oxygen and plays an important role in total oxidation of VOCs.