Removal of ethylene from air stream by adsorption and plasma-catalytic oxidation using silver-based bimetallic catalysts supported on zeolite

Enhanced Removal Performance and Economical Efficiency of Volatile Organic Sulfur Compounds by Silver-Modified ZSM-5 Zeolites under a High-Humidity Environment: A Mechanistic Study of the Adsorption-Plasma Catalytic Process

Dimethyl sulfide (DMS) is a harmful volatile organic sulfur compound (VOSC), which must be effectively controlled. The adsorption-plasma catalytic (APC) process is an efficient and economical route for the elimination of low-concentration VOSCs; however, there are still many challenges in humid environment. In this study, a series of zeolites with different Si/Al ratios and Ag loadings were designed, and were performed for DMS removal by APC process. At 80% relative humidity, the DMS adsorption capacity of Ag5-ZSM25 reached 33.9 mg/g, which was 7.9 times that of ZSM25 and nearly 2 times that of Ag5-ZSM200. Analyses via UV-vis, X-ray photoelectron spectroscopy (XPS), and CO-FTIR confirmed that Ag+ was the predominant species for DMS adsorption and degradation in Ag5-ZSM25. DMS-temperature-programmed desorption (TPD) and density functional theory (DFT) calculations indicated that Ag+ significantly enhanced the binding energy with DMS and weakened the competitive adsorption impact of H2O. In the plasma regeneration stage, Ag5-ZSM25 demonstrated an 89% mineralization, with Ag+ being crucial for DMS mineralization. Based on the in situ plasma DRIFT spectra, a possible degradation pathway for DMS was proposed. The APC process achieved an energy efficiency of 1.66 g/kWh, tripling that of the continuous plasma catalytic process and providing guidance for low-concentration DMS elimination.

Metal-anchored oxidized starch-pullulan nanofiber films enhance ethylene adsorption and banana preservation

The development of novel strategies to control ethylene accumulation of fruit is crucial for improving food preservation and reducing spoilage-related losses. In this study, an oxidized starch-pullulan (OS-PUL) nanofiber films were prepared with silver, copper, and iron to control ethylene accumulation. The starch nanofiber film exhibited an average diameter of 96 nm at an OS-PUL concentration of 25 % (wt/wt). Adsorption test showed the maximum ethylene adsorption capacity (21.86 mg·m-2) of metal-nanofiber film with typical hierarchical microporous and mesoporous structure. Oxidized starch-pullulan-metal-nanofiber film extended the shelf life of bananas from 8 to 15 days by efficiently absorbing ethylene. This work will contribute to the development of innovative packaging materials with ethylene adsorption properties, which can help reduce food waste.

Efficient Catalytic Oxidation of Ethylene at 0 °C on an in Situ Carbon Modified Pt Catalyst Supported on SBA-15

The design of efficient catalysts for catalytic ethylene (C2H4) oxidation is of crucial importance for extending the shelf life of fruits and vegetables. Herein, a carbon modified SBA-15 supported Pt catalyst (Pt/CSBA-15) was prepared in situ by a facile solid phase grinding-infiltration-inert atmosphere calcination method. Characterization results reveal that in the Pt/CSBA-15 catalysts thin carbon layers are successfully formed in the hexagonal pores of SBA-15. Additionally, Pt particles are well dispersed in the channels of SBA-15, and Pt/CSBA-15 has a smaller Pt particle size than the catalyst without carbon modification (i.e., Pt/SBA-15). O2 is more feasibly adsorbed and activated on small-sized Pt particles, and in situ formed carbon species enhance the hydrophobicity of catalysts. As a result, both 3Pt/CSBA-15 and 5Pt/CSBA-15 are able to maintain 100% conversion of 50 ppm of C2H4 for more than 7 h at 0 °C. 3Pt/CSBA-15 even achieves 81.5% C2H4 conversion and 71.6% CO2 yield after 20 h, exhibiting much more prominent catalytic performances than 3Pt/SBA-15. DFT calculations and in situ FTIR measurements confirm that small-sized Pt particles possess strong O2 affinity to promote O2 adsorption, and in situ formed hydrophobic carbon layers efficiently suppress competitive H2O adsorption. Such a unique one-step catalyst preparation method for regulating the size of metal particles and the hydrophobicity of catalysts can be perfectly utilized to develop simple and efficient hydrophobic catalysts applied in low-temperature oxidation of C2H4.

Research status of volatile organic compound (VOC) removal technology and prospect of new strategies: a review

As an important component of air pollution, the efficient removal of volatile organic compounds (VOCs) is one of the most important challenges in the world. VOCs are harmful to the environment and human health. This review systematically introduced the main VOC control technologies and research hotspots in recent years, and expanded the description of electrocatalytic oxidation technology and bimetallic catalytic removal technology. Based on a three-dimensional electrode reactor, the theoretical design of a VOC removal control technology using bimetallic three-dimensional particle electrode electrocatalytic oxidation was proposed for the first time. The future research focus of this method was analyzed, and the importance of in-depth exploration of the catalytic performance of particle electrodes and the system reaction mechanism was emphasized. This review provides a new idea for using clean and efficient methods to remove VOCs.

Catalysts for gaseous organic sulfur removal

Organic sulfur gases (COS, CS₂ and CH₃SH) are widely present in reducing industrial off-gases, and these substances pose difficulties for the recovery of carbon monoxide and other gases. The reaction pathways and reaction mechanisms of organic sulfur on different catalyst surfaces have yet to be fully summarized. The literature shows that many factors, such as catalyst synthesis method, loaded metal composition, number of surface hydroxyl groups, number of acid-base sites and methods of surface modification, have important effects on the catalytic performance of metal catalysts. Therefore, this paper presents a comprehensive review of the research on the application of catalysts such as zeolites, metal oxides, carbon-based materials, and hydrotalcite-like derivatives in the field of organic sulfur removal. Future research prospects are summarized, more in situ characterization experiments and theoretical calculations are needed for the catalytic decomposition of methanethiol to analyze the coke generation pathways at the microscopic level, while the simultaneous removal of multiple organic sulfur gases needs to be focused on. Based on previous catalyst research, we propose possible innovations in catalyst design, desulfurization technology and organic sulfur resource utilization technology.

Oxidation of Toluene by Ozone over Surface-Modified γ-Al2O3: Effect of Ag Addition

In this study, the ability of ozone to oxidise toluene present in low levels into CO and CO2 was studied. The catalytic ozonation of toluene was carried out in a micro-fixed bed reactor. The oxidation was done in two steps: toluene adsorption on the catalyst followed by sequential ozone desorption. Toluene breakdown by ozone at low temperature and atmospheric pressure was achieved using γ-Al2O3 supported transition metal oxides impregnated with a reduced noble metal. The catalyst Ag–CoOx/γ-Al2O3 efficiently oxidised and transformed toluene into products (52.4% COx yield). This catalyst has a high surface area, more acidic sites, and lattice oxygens for better toluene oxidation. The addition of Ag to the CoOx/γ-Al2O3 catalyst surface improved toluene adsorption on the catalyst surface, resulting in improved product yield, selectivity, and carbon balance.

Activation and characterization of environmental catalysts in plasma-catalysis: Status and challenges

Plasma-catalysis has attracted great attentions in environmental/energy-related fields, but the synergetic mechanism still suffers intractable defects. Key issues are that what kind of catalysts are applicable for plasma system, how are they activated in plasma, and how to characterize them in plasma. This review systematically gives a comprehensive summarization of the selection of catalysts and its activation mechanism in plasma, based on the character of plasma, including physical effects containing the enhancement of discharge intensity and adsorption of reactants, and the utilization of plasma-generated active species such as·O, heat, O₃, ultraviolet light and e* . Focus is given to the illumination of the activation mechanisms of catalysts when placed in plasma zone. Subsequently, the novel characterization techniques for catalysts, which may associate properties to performance, are critically overviewed. The challenges and opportunities for the activation and characterizations of catalysts are proposed, and future perspectives are suggested about where the efforts should be made. It is expected that a bridge between catalysts design and character of plasma can be built to shed light on the synergetic mechanism for plasma-catalysis and design of new plasma-catalysis systems.

Elimination or Removal of Ethylene for Fruit and Vegetable Storage via Low-Temperature Catalytic Oxidation

Ethylene acts as an important hormone to trigger the ripening and senescence of fruits and vegetables (F&V). Thus, it is essential to eliminate trace ethylene and prevent F&V losses effectively. There are several technologies currently applying to control the ethylene concentration in the storage and transportation environment, including adsorption, gene modification, oxidation, etc. These protocols will be compared, and special attention will be paid to the low-temperature catalytic oxidation that has already been applied to practical production in this review. The active sites, supports, and reaction and deactivation mechanism of the catalysts for the low-temperature ethylene oxidation will be discussed and evaluated systematically to provide new insights for the development of effective catalysts, along with the suggestion of some perspectives for future research on this important catalytic system for F&V preservation.

Modified Camellia oleifera Shell Carbon with Enhanced Performance for the Adsorption of Cooking Fumes

Using Camellia oleifera shell (COS) as a raw material and phosphoric acid as the activator, activated Camellia oleifera shell carbon (COSC-0) was prepared and then modified by Fenton’s reagent (named as COSC-1). SEM, GC-MS, FTIR, and specific surface area and pore analyzers were used to study the adsorption performance of COS, COSC-0, and COSC-1 on cooking fumes. Results showed that COSC-1 was the best adsorbent compared with COS and COSC-0. The adsorption quantity and penetrating time of COSC-1 were 44.04 mg/g and 4.1 h, respectively. Most aldehydes could be adsorbed by COSC-1, which was due to the large number of carbonyl and carboxyl groups generated on the surface of COSC-1 from the action of Fenton’s reagent. The adsorption effect of COSC-1 on different types of pollutants in cooking fumes was analyzed based on the similar compatibility principle. COSC-1 showed a much higher adsorption effect on the strong polarity functional groups than on weak polar groups. The results provide a theoretical basis for the application of Camellia oleifera shell carbon adsorption technology in the treatment of cooking fumes.

Catalytic conversion of ethene to butadiene or hydrogenation to ethane on HY zeolite-supported rhodium complexes: Cooperative support/Rh-center route

Rh(C₂H₄)₂ species grafted on the HY zeolite framework significantly enhance the activation of H₂ that reacts with C₂H₄ ligands to form C₂H₆. While in this case, the simultaneous activation of C₂H₄ and H₂ and the reaction between these species on zeolite-loaded Rh cations is a legitimate hydrogenation pathway yielding C₂H₆, the results obtained for Rh(CO)(C₂H₄)/HY materials exposed to H₂ convincingly show that the support-assisted C₂H₄ hydrogenation pathway also exists. This additional and previously unrecognized hydrogenation pathway couples with the conversion of C₂H₄ ligands on Rh sites and contributes significantly to the overall hydrogenation activity. This pathway does not require simultaneous activation of reactants on the same metal center and, therefore, is mechanistically different from hydrogenation chemistry exhibited by molecular organometallic complexes. We also demonstrate that the conversion of zeolite-supported Rh(CO)₂ complexes into Rh(CO)(C₂H₄) species under ambient conditions is not a simple CO/C₂H₄ ligand exchange reaction on Rh sites, as this process also involves the conversion of C₂H₄ into C₄ hydrocarbons, among which 1,3-butadiene is the main product formed with the initial selectivity exceeding 98% and the turnover frequency of 8.9 × 10^-3 s^-1. Thus, the primary role of zeolite-supported Rh species is not limited to the activation of H₂, as these species significantly accelerate the formation of the C₄ hydrocarbons from C₂H₄ even without the presence of H₂ in the feed. Using periodic density functional theory calculations, we examined several catalytic pathways that can lead to the conversion of C₂H₄ into 1,3-butadiene over these materials and identified the reaction route via intermediate formation of rhodacyclopentane.

Promotion of TiO2 Nanotube-Confined Pt Nanoparticles via Surface Modification with Fe2O3 for Ethylene Oxidation at Low Temperature

A modified confined catalyst with Pt nanoparticles on the interior and Fe₂O₃ on the exterior surface of TiO₂ nanotubes (Pt-in/Fe₂O₃-TNTs) was prepared and investigated for catalyzing the oxidation of ethylene. Compared with the Pt-in/TNTs without Fe₂O₃ modification, the Pt-in/Fe₂O₃-TNTs exhibited a significantly enhanced activity, and the complete conversion temperature of ethylene decreased from 170 to 95 °C. X-ray photoelectron spectroscopy analysis indicated that the Pt nanoparticles were stabilized at higher oxidation states in the Pt-in/Fe₂O₃-TNT catalyst. It was proposed that the modification of Fe₂O₃ on the outer surface can tune the electronic state of the encapsulated Pt particles and accelerate the electrons transferred from Pt to Fe species via TiO₂ nanotubes, thus improving the catalytic oxidation performance of the confined catalyst.

Improvement of Ethylene Removal Performance by Adsorption/Oxidation in a Pin-Type Corona Discharge Coupled with Pd/ZSM-5 Catalyst

The adsorption and plasma-catalytic oxidation of dilute ethylene were performed in a pin-type corona discharge-coupled Pd/ZSM-5 catalyst. The catalyst has an adsorption capacity of 320.6 μ mol   g cat − 1 . The catalyst was found to have two different active sites activated at around 340 and 470 °C for ethylene oxidation. The removal of ethylene in the plasma catalyst was carried out by cyclic operation consisting of repetitive steps: (1) adsorption (60 min) followed by (2) plasma-catalytic oxidation (30 min). For the purpose of comparison, the removal of ethylene in the continuous plasma-catalytic oxidation mode was also examined. The ethylene adsorption performance of the catalyst was improved by the cyclic plasma-catalytic oxidation. With at least 80% of C2H4 in the feed being adsorbed, the cyclic plasma-catalytic oxidation was carried out for the total adsorption time of 8 h, whereas it occurred within 2 h of early adsorption in the case of catalyst alone. There was a slight decrease in catalyst adsorption capability with an increased number of adsorption cycles due to the incomplete release of CO2 during the plasma-catalytic oxidation step. However, the decreased rate of adsorption capacity was negligible, which is less than one percent per cycle. Since the activation temperature of all active sites of Pd/ZSM-5 for ethylene oxidation is 470 °C, the specific input energy requirement by heating the feed gas in order to activate the catalyst is estimated to be 544 J/L. This value is higher than that of the continuous plasma-catalytic oxidation (450 J/L) for at least 86% ethylene conversion. Interestingly, the cyclic adsorption and plasma-catalytic oxidation of ethylene is not only a low-temperature oxidation process but also reduces energy consumption. Specifically, the input energy requirement was 225 J/L, which is half that of the continuous plasma-catalytic oxidation; however, the adsorption efficiency and conversion rate were maintained. To summarize, cyclic plasma treatment is an effective ethylene removal technique in terms of low-temperature oxidation and energy consumption.

Niobium doping enhanced catalytic performance of Mn/MCM-41 for toluene degradation in the NTP-catalysis system

The destruction of toluene in a dielectric barrier discharge (DBD) reactor with Nb-Mn/MCM-41 had been investigated and compared with X (X = Cu, Ce, Co)-Mn/MCM-41 catalysts. The XRD and TEM result confirms that the metal species were highly dispersed on the MCM-41. The results of XPS, O₂-TPD and H₂-TPR clearly demonstrate that Nb doping facilitated formation of lattice oxygen (O_latt) and the acid sites, which are all beneficial to catalytic degradation of toluene. Compared to X (Cu, Ce, Co)-Mn/MCM-41, Nb-Mn/MCM-41 had the most contents of O_latt, the most amounts of acid sites and the strongest acidity. Consequently, the catalytic performance tests identify that Nb-Mn/MCM-41 had the best catalytic performance, the highest removal efficiency and CO₂ selectivity as well as carbon balance especially at low SIE. These results indicate that Nb was an important promoter improving the activity and CO₂ selectivity of Mn/MCM-41 for the decomposition of toluene in NTP-catalysis system.

Kinetics study on non-thermal plasma mineralization of adsorbed toluene over γ-Al2O3 hybrid with zeolite

Non-thermal plasma mineralization of the adsorbed toluene over γ-Al₂O₃ hybrid with 13X, ZSM-5, and HY was investigated in a sequential adsorption and plasma oxidation system. The γ-Al₂O₃-13X was shown to have a better plasma oxidation performance with fewer by-products as compared to γ-Al₂O₃-ZSM-5 and γ-Al₂O₃-HY, which was due to its better discharge performance and O₃ decomposition ability. For all of the tested materials, the plasma mineralization of the adsorbed toluene process had a good match with the pseudo-second-order kinetic model: kt = 1/n - 1/n_o, where n₀ and n are the amount of adsorbed toluene (mmol) at discharge time = 0 and t, respectively. The overall reaction constant (k) was shown to be affected by the packing materials. The reason for the kinetic model following the pseudo-second-order in the sequential process was analyzed based on the chemical reaction and mineralization mechanism.

Application of palladium-modified zeolite for prolonging post-harvest shelf life of banana

BACKGROUND

The marketability of banana is limited by the rapid rate of ripening. However, the traditional post-harvest technologies may not be desirable. The aim of this study was to investigate the potential of a reusable material for the food preservation industry.

RESULTS

The nanocomposite-based palladium (Pd)-modified zeolite (Pd/zeolite) was prepared by impregnating Pd into zeolite. Pd/zeolite had a Brunauer-Emmett-Teller dinitrogen specific surface area of 475 m² g^-1 with crystal structure similar to Y-zeolite. Transmission electron microscopy images showed the dispersion of Pd particles over the multi-pore zeolite support. Pd/zeolite uniquely acted as an adsorbent and a catalyst and was able to remove ethylene even after reaching breakthrough point. To prove Pd/zeolite is reusable, a 99 ± 0.8% ethylene removal efficiency still remained even after five consecutive cycles with repeated use of Pd/zeolite. The presence of Pd/zeolite significantly decreased the ethylene concentration during 18 days of storage at 20 ± 2 °C.

CONCLUSIONS

Pd/zeolite could delay the ripening of banana and improve its firmness and the peel color significantly. Findings indicated that the as-prepared Pd/zeolite is an effective adsorbent/catalyst with high potential for practical application in ethylene removal, especially for the post-harvest period. © 2019 Society of Chemical Industry.

Acid-Alkali-Treated Natural Mordenite-Supported Platinum Nanoparticles (Pt/MORn-H-OH) for Efficient Catalytic Oxidation of Formaldehyde at Room Temperature

In this work, a series of natural mordenite-supported platinum (Pt) catalysts were prepared by a facile two-step method, namely, treatment of natural mordenite and then the loading of Pt nanoparticles. The acid-alkali-treated natural mordenite-supported Pt samples (1% Pt/MORn-H-OH) exhibited the highly enhanced catalytic oxidation activity of formaldehyde (HCHO) at room temperature. XRD results showed that the crystalline phase of the mordenite did not change significantly in 1% Pt/MORn-H-OH catalyst. However, the acid-alkali treatment endowed the Pt particles excellent dispersion with the smallest diameter of 2.8 nm in a high loading content, which contributed to the optimal catalytic activity of 1% Pt/MORn-H-OH.

A Cooperative Effect in a Novel Bimetallic Mo-V Nanocomplex Catalyzed Selective Aerobic C-H Oxidation

In this study, a new heterobimetallic Mo(VI)-V(V) organosilicon Schiff base complex has been prepared and characterized by different techniques, such as FTIR, Raman, MS, ICP-AES, TGA, and XPS. The bimetallic nanocomplex, revealed by TEM images, showed high oxidation stability and desired activity in the aerobic oxidation of a structurally diverse set of benzylic alcohols in ethanol as a safe solvent. Further, oxidation of benzylic hydrocarbons successfully occurred, producing the target compounds in high yields and excellent selectivities. Our results demonstrated a cooperative effect between Mo(VI) and V(V) as redox active sites in an organosilicon Schiff base framework. A facile and practical reusability of the solid catalyst at the end of the reaction was observed.

The Use of Zeolites for VOCs Abatement by Combining Non-Thermal Plasma, Adsorption, and/or Catalysis: A Review

Non-thermal plasma technique can be easily integrated with catalysis and adsorption for environmental applications such as volatile organic compound (VOC) abatement to overcome the shortcomings of individual techniques. This review attempts to give an overview of the literature about the application of zeolite as adsorbent and catalyst in combination with non-thermal plasma for VOC abatement in flue gas. The superior surface properties of zeolites in combination with its excellent catalytic properties obtained by metal loading make it an ideal packing material for adsorption plasma catalytic removal of VOCs. This work highlights the use of zeolites for cyclic adsorption plasma catalysis in order to reduce the energy cost to decompose per VOC molecule and to regenerate zeolites via plasma.

Plasma-catalytic removal of toluene over the supported manganese oxides in DBD reactor: Effect of the structure of zeolites support

The degradation of toluene in dielectric barrier discharge (DBD) reactor packed with zeolites or MnO_x/zeolites was investigated. The supported catalysts were prepared by loading 3 wt% of manganese on different zeolites (MCM-41, ZSM-5 and 13X) and were characterized in detail using N₂ adsorption, XRD, TEM, H₂-TPR and XPS analysis technology. Compared to the non-thermal plasma (NTP) alone system, the toluene degradation was improved significantly in NTP-MnO_x/zeolites system. The highest toluene conversion of 99.4%, the CO₂ selectivity of 73%, the carbon balance of 99.5% can be achieved in DBD reactor packed with MnO_x/MCM-41. Both XRD and TEM results confirm that the manganese oxides were dispersed more uniformly on MnO_x/MCM-41 than on MnO_x/ZSM-5 or MnO_x/13X. H₂-TPR and XPS results suggest that manganese oxides on MnO_x/MCM-41 are MnO₂ and Mn₂O₃, while those on MnO_x/ZSM-5 or MnO_x/13X are MnO₂ and MnO. These results indicate that the structures of zeolites play a significant role in the dispersion and oxidation state of manganese oxides, then affecting the activity of catalyst for toluene removal in plasma-catalysis system.

Synergistic effects and mechanism of a non-thermal plasma catalysis system in volatile organic compound removal: a review

Non-thermal plasma catalysis with high efficiency, high by-product selectivity and superior carbon balance is one of the most promising technologies in the control of volatile organic compounds (VOCs).

Desorption of isopropyl alcohol from adsorbent with non-thermal plasma

Effective desorption of isopropyl alcohol (IPA) from adsorbents with non-thermal plasma is developed. In this system, IPA is effectively adsorbed with activated carbon while dielectric barrier discharge is applied to replace the conventional thermal desorption process to achieve good desorption efficiency, making the treatment equipment smaller in size. Various adsorbents including molecular sieves and activated carbon are evaluated for IPA adsorption capacity. The results indicate that BAC has the highest IPA adsorption capacity (280.31 mg IPA/g) under the operating conditions of room temperature, IPA of 400 ppm, and residence time of 0.283 s among 5 adsorbents tested. For the plasma desorption process, the IPA selectivity of 89% is achieved with BAC as N₂ is used as desorbing gas. In addition, as air or O₂ is used as desorbing gas, the IPA desorption concentration is reduced, because air and O₂ plasmas generate active species to oxidize IPA to form acetone, CO₂, and even CO. Furthermore, the results of the durability test indicate that the amount of IPA desorbed increases with increasing desorption times and plasma desorption process has a higher energy efficiency if compared with thermal desorption. Overall, this study indicates that non-thermal plasma is a viable process for removing VOCs to regenerate adsorbent.

Removal of toluene by sequential adsorption-plasma oxidation: Mixed support and catalyst deactivation

A sequential adsorption-plasma oxidation system was used to remove toluene from simulated dry air using γ-Al₂O₃, HZSM-5, a mixture of the two materials or their supported Mn-Ag catalyst as adsorbents under atmospheric pressure and room temperature. After 120min of plasma oxidation, γ-Al₂O₃ had a better carbon balance (∼75%) than HZSM-5, but the CO₂ yield of γ-Al₂O₃ was only ∼50%; and there was some desorption of toluene when γ-Al₂O₃ was used. When a mixture of HZSM-5 and γ-Al₂O₃ with a mass ratio of 1/2 was used, the carbon balance was up to 90% and 82% of this was CO₂. The adsorption performance and electric discharge characteristics of the mixed supports were tested in order to rationalize this high CO_x yield. After seven cycles of sequential adsorption-plasma oxidation, support and Mn-Ag catalyst deactivation occurred. The support and catalyst were characterized before and after deactivation by SEM, a BET method, XRD, XPS and GC-MS in order to probe the mechanism of their deactivation. 97.6% of the deactivated supports and 76% of the deactivated catalysts could be recovered by O₂ temperature-programmed oxidation.

Toluene removal by sequential adsorption-plasma catalytic process: Effects of Ag and Mn impregnation sequence on Ag-Mn/γ-Al2O3

A series of Ag-Mn/γ-Al2O3 were prepared under different Ag/Mn impregnation sequence and tested in the sequential adsorption-plasma catalytic removal of toluene. When Mn was impregnated first, the resulting catalyst, Ag-Mn(F)/γ-Al2O3, had longer breakthrough time, gave less emission of toluene, had higher CO2 selectivity, and had better carbon balance and COx yield compared to catalysts prepared via other impregnation sequences. After 120 min of NTP treatment, the carbon balance of Ag-Mn(F)/γ-Al2O3 was 91%, with 87% as COx contributions. A Brunauer-Emmett-Teller (BET) analysis and X-ray photoelectron spectroscopy (XPS) results show that, the impregnation sequence impacts the BET surface area and the ratio and existing state of Ag on the surface of the catalysts. The longer breakthrough time when using Ag-Mn(F)/γ-Al2O3 as catalyst is attributed to the large amount of Ag(+) on the surface. Ag(+) is a new active site for toluene adsorption. When Ag was impregnated first (Ag(F)-Mn/γ-Al2O3) or Ag and Mn co-impregnated (Ag-Mn-C/γ-Al2O3), the predominant specie was Ag(+). Both Ag(0) and Ag(+) species were detected on Ag-Mn(F)/γ-Al2O3. Ag(0) cooperation with MnOx may promote the migration of surface active oxygen. This would facilitate the oxidation of adsorbed toluene with CC bond already weakened by Ag(+) and would result in higher CO2 selectivity and better carbon balance as seen in the Ag-Mn(F)/γ-Al2O3 system.

Removal of toluene in adsorption–discharge plasma systems over a nickel modified SBA-15 catalyst

In situ FT-IR spectra show the toluene adsorption process of SBA and Ni–SBA catalysts.