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NO x and toluene have been identified as the dominant air pollutants in solid wasted combustion, and it is of great importance to remove these two pollutants simultaneously. Here, we found that Mn/CeO 2 and Mn/TiO 2 exhibited a bifunctional property in both NO reduction and toluene oxidation, and both of which could achieve 80% of conversion rate in NO reduction and toluene oxidation processes. However, the activity of both Mn/CeO 2 and Mn/TiO 2 decreased in simultaneous removal of NO x and toluene compared with separate NO x reduction and toluene oxidation. This indicates that there is a mutual inhibition between NO x reduction and toluene oxidation in simultaneous removal process over Mn-based catalysts, attributing to the competitive adsorption and utilization of active oxygen. In detail, the adsorption of toluene occupied the Lewis acid sites and restrained the NH 3 adsorption. Meanwhile, the competitive utilization of active oxygen by NH 3 /NO x inhibited toluene oxidation to CO 2 by active oxygen species as the reaction between NH 3 /NO x and active oxygen species would occur more easily., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

In this study, mesoporous SBA-15 supported Pd catalysts were synthesized through impregnation and grafting approaches. Moreover, the influences of different solvents (ethanol, H(2)O, tetrahydrofuran, dimethyl sulphoxide and N,N-dimethylformamide) on the dispersion of supported Pd nanoparticles were also systematically investigated. The prepared materials were comprehensively explored by various techniques, including XRD, EDS, ICP-OES, H(2) chemisorption, N(2) adsorption/desorption, TG-DSC, FT-IR, TEM and STEM. It is found that the traditional impregnation method has some disadvantages in obtaining highly dispersed Pd active phase. Whereas, the grafting method could highly disperse Pd nanoparticles within the mesoporous channels of support material, and the grafting procedure should be promising in designing highly dispersed Pd particles on the silica-based mesoporous materials. The catalyst prepared via the grafting procedure possesses much higher activity and selectivity than that prepared by impregnation method for deep catalytic oxidation of toluene., (Copyright 2010 Elsevier B.V. All rights reserved.)

Highlights: [•] A facile and universal self-precipitation route for mesoporous metal oxides preparation. [•] CuCeO x catalysts with high surface area and homogeneous mesostructure. [•] Catalysts combined promoted reducibility and surface oxygen concentration. [•] Mesostructured metal oxides with superior low-temperature catalytic efficiency. [•] Catalysts possess remarkable enhanced reaction rate and selectivity. [Copyright &y& Elsevier]

Abstract: A series of micro/mesoporous hybridized materials with coke-resistant ZSM-5 and three-dimensional large pore KIT-6 as their micro- and mesoporous components were synthesized and investigated for toluene deep oxidation. The characterization results show that most of Al atoms are tetrahedrally coordinated in the framework of the samples, and the ratio of ZSM-5 to KIT-6 can be systematically controlled by varying the Si/Al molar ratio in the synthesis mixture. The acid sites over the supports are favorable for Pd nanoparticle dispersion and metallic Pd oxidation due to their electrophilic characters. All Pd supported composite materials are found to be powerful catalysts for the total oxidation of toluene. Particularly, Pd/ZK-50 possesses the highest catalytic activity with 90% toluene decomposition at 197°C, this temperature is much lower than that of Pd/KIT-6 (T 90 =234°C). CO2 desorption capability has positive effects on catalytic activity, while the influence of toluene adsorption property is negligible. The superior activity of the composite catalysts can be ascribed to the cumulative of specific surface area, support acidity, Pd particles dispersion and CO2 desorption capability. [Copyright &y& Elsevier]

Abstract: Short column SBA-15 supported Pd mesoporous catalysts with controllable acidity and expanded microporosity were firstly prepared through a simple “two-solvents” approach. The catalytic performances of the synthesized catalysts were evaluated for toluene oxidation. The characterization results reveal that Al atoms prefer to be tetrahedrally coordinated in the framework of the synthesized materials, and the acid sites can significantly promote Pd particle dispersion and metallic Pd oxidation due to their electrophilic characters. The Pd-confined catalysts possess high toluene turnover frequencies and toluene can be totally converted to CO2 and H2O below 210°C. The oxidation reaction can be suppressed by water vapor due to the formation of inactive Pd-hydroxides, and the synthesized catalyst has a good hydrothermal stability and high tolerance to moisture. Both the specific surface area and the toluene adsorption/desorption property are not the main factors determining the catalytic activity. Overall, the toluene oxidation performance is closely related to the support microporosity and acidity, the Pd dispersion and the CO2 desorption capability. [Copyright &y& Elsevier]

Abstract: A series of novel Pd/Co3AlO catalysts derived from hydrotalcite-like compounds (HTlcs) have been prepared and investigated for total oxidation of toluene. The HTlcs phase Co–Al precursors were prepared by coprecipitation method and Pd active species were introduced by different approaches, i.e., impregnation (IMP), wet ion exchange (WIE) or directly at coprecipitation stage (COP). It is found that all hydrotalcite-derived Pd/Co3AlO catalysts are much more active than the Pd/Co3AlO catalyst prepared via traditional thermal combustion method (TCB) in toluene elimination. The activities of all synthesized catalysts obey the following sequence: Pd/Co3AlO (COP)>Pd/Co3AlO (WIE)≥Pd/Co3AlO (IMP)>Pd/Co3AlO (TCB). Excellent catalytic activities of the novel hydrotalicite-derived Pd/Co3AlO catalysts could be contributed to their high surface area, small mean crystallized size of support and highly dispersed PdO particles. Besides, they are well positively associated with catalyst reducibilities and the amounts of oxygen vacancies. According to the XPS, TEM and TPR results, it was found that the strong synergistic effect between Co3O4 and PdO, but not the amount of the surface palladium species which are generally believed to be the active sites, is the main factors determining the catalytic activity in this work. The stability tests indicate that all Pd/Co3AlO catalysts have no obvious deactivation, and some catalysts even show improved activities during the reaction process due to the emergence of metal Pd. [ABSTRACT FROM AUTHOR]

The feasibility and mechanism of five molecular sieves-supported palladium catalysts in elimination of benzene, toluene, and ethyl acetate were investigated. The experimental results indicate that Pd particles are well dispersed on these porous supports with size of 2−10 nm, while mesoporous supports with a larger specific surface area and pore diameter lead to a better dispersion. The activity of freshly made catalysts obeys the following order: Pd/Beta > Pd/ZSM-5 > Pd/SBA-15 > Pd/MCM-48 > Pd/MCM-41. Although Pd/Beta has the highest activity for removal of these VOCs in the beginning, its activity quickly decreases. However, Pd/ZSM-5 and Pd/SBA-15 show a good stability, without activity loss in a 72 h test. Our research reveals that higher acidity can facilitate catalytic reaction and gives rise to higher activity, but it also enhances coke formation and decreases the catalyst stability. In addition, the porosity of supports has a certain impact on catalytic oxidation of VOCs. [ABSTRACT FROM AUTHOR]

Aliovalent substitution reduces the oxygen vacancy formation energy and generates more oxygen vacancies to facilitate the catalytic reaction. [Display omitted] Developing cost-effective monolith catalyst with superior low-temperature activity is critical for oxidative efficacious removal of industrial volatile organic compounds (VOCs). However, the complexity of the industrial flue gas conditions demands the need for high moisture tolerance, which is challenging. Herein, CoMn–Metal Organic Framework (CoMn–MOF) was in situ grown on Ni foam (NiF) at room temperature to synthesize the cost-effective monolith catalyst. The optimized catalyst, Co1Mn1/NiF, exhibited excellent performance in toluene oxidation (T 90 = 239 °C) due to the substitution of manganese into the cobalt lattice. This substitution weakened the Co–O bond strength, creating more oxygen vacancies and increasing the active oxygen species content. Additionally, experimentally and computationally evidence revealed that the mutual inhibiting effect of three typical aromatic hydrocarbons (benzene, toluene and m–xylene) over the Co1Mn1/NiF catalyst was attributed to the competitive adsorption occurring on the active site. Furthermore, the Co1Mn1/NiF catalyst also presents outstanding water resistance, particularly at a concentration of 3 vol%, where the activity is even enhanced. This was attributed to the lower water adsorption and dissociation energy derived from the interaction between the bimetals. Results demonstrate that the dissociation of water vapor enables more reactive oxygen species to participate in the reaction which reduces the formation of intermediates and facilitates the reaction. This investigation provides new insights into the preparation of oxygen vacancy–rich monolith catalysts with high water resistance for practical applications. [ABSTRACT FROM AUTHOR]

A series of carbon-supported Cu Co oxide catalysts (Cu-Co/C) were prepared via the combination methods of impregnation and pyrolysis using Co-doped Cu-based metal organic framework (Cu 3 (BTC) 2 ·3H 2 O, Cu-BTC) precursor. Physicochemical properties of prepared catalysts were characterized by using various technologies and toluene was chosen as the probe molecule to evaluate their catalytic performance. Results revealed that the successive calcination in Ar and air was conducive to the formation of 3D porous carbon matrix and homogeneous elemental dispersion. The Cu-Co/C catalysts with spinel structure exhibited higher catalytic activity than that of Cu-500/C material. Moreover, CuCo 0.5 /C material exhibited superior catalytic durability and water resistance in catalytic oxidation of toluene. The excellent catalytic performance of CuCo 0.5 /C was mainly related to large specific surface area, high amounts of surface chemisorbed active oxygen and high ratio of Co2+/Co3+. Unlabelled Image • Cu-Co/Carbon catalysts were prepared using Co-doped Cu-MOF precursor. • Porous carbon matrix with homogeneous element dispersion was formed. • Surface area, chemisorbed active oxygen and Co2+/Co3+ ratio determined activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • K/MnO 2 prepared by hydrothermal impregnation method shows superior performance. • MnO 6 -K-MnO 6 bridging bond leads to the uniform energy of Mn-O bonds. • High electron density of K promotes the activation of oxygen molecules. • Excellent reducibility and abundant Brønsted acid sites promote toluene mineralization. • Effect of K doping position on oxygen vacancy and adsorption energy was proposed. Alkali metal potassium is conducive to structure promotion and electronic modulation in metal oxides. Here, K species was successfully introduced into α-MnO 2 via in situ synthesis (Pre-K/MnO 2) and hydrothermal impregnation method (Post-K/MnO 2) with target to boost the low-temperature reactivity and deep destruction efficiency for toluene oxidation. Results reveal that Post-K/MnO 2 possesses the highest catalytic activity with toluene (1000 ppm) totally mineralized at just 258 °C, achieving over 70 °C of temperature reduction than that of Pre-K/MnO 2. K specie shows obvious charge transfer balance ability in MnO 2 , forming MnO 6 -K-MnO 6 bridging bond and leading to more uniform energy of Mn-O bonds. High electron density of K+ can promote the activation of oxygen molecules, resulting in a better catalytic performance of toluene. Abundant Brønsted acid sites are beneficial for toluene adsorption and regeneration of hydroxyl on the surface, which promote the degradation of intermediates during toluene oxidation. Moreover, Post-K/MnO 2 shows satisfied catalytic performance under different space velocities and initial concentrations and humid condition. Density functional theory (DFT) calculation revealed the situation of oxygen vacancy and toluene/oxygen adsorption energy in catalysts with different K doping locations. Results showed that the adsorption energy is stronger when K located in large tunnel (0.46 × 0.46 nm), and it is easier to form oxygen vacancy while K entered the small tunnel (0.33 × 0.33 nm). The present work paves new insights into the designing of efficient transition metal oxide catalyst for VOC deep purification. [ABSTRACT FROM AUTHOR]

[Display omitted] • K-doped ɑ-MnO 2 were synthesized by a reproducible post processing process. • Oxygen vacancies can be modulated by varying K+ incorporation amount. • 4-K/MnO 2 has the highest activity due to abundant surface absorbed oxygen (O ads). • O ads plays an important role in toluene dehydrogenation and benzoate formation. Oxygen vacancy plays an important role in adsorption and activation of oxygen species and therefore promotes the catalytic performance of materials in heterogeneous oxidation reactions. Here, a series of K-doped ɑ-MnO 2 materials with different K loadings were synthesized by a reproducible post processing process. Results show that the presence of K+ enhances the reducibility and oxygen vacancy concentration of ɑ-MnO 2 due to the break of charge balance and the formation of low valence Mn species. 4-K/MnO 2 material exhibits the highest toluene oxidation activity and satisfied long-term stability and water resistance owing to its superior reducibility and abundant surface absorbed oxygen (O ads). In situ DRIFTS demonstrate that O ads greatly accelerates toluene dehydrogenation rate and promotes benzoate formation, enhancing the activation and decomposition of toluene molecules. Moreover, the C C cleavage of benzene ring (forming maleic anhydride) is the rate-determining step of toluene oxidation, which can be easily occurred over 4-K/MnO 2. [ABSTRACT FROM AUTHOR]

[Display omitted] Fabricating of economical transitional metal oxide-based materials with satisfied low-temperature catalytic performance and application perspective is still a challenge in deep degradation of VOCs. Here, Mn-Cu bimetallic oxides were facilely prepared by one-step hydrothermal-redox method, which displayed much higher catalytic activity in toluene oxidation than those synthesized by hydrolysis-driven redox-precipitation or co-precipitation approach. It is shown that the lattice defect and oxygen vacancy concentration over prepared materials can be tuned by controlling Cu/Mn molar ratio. Amongst, spinel structured MnCu 0.5 exhibited the highest catalytic activity, superior durability and water resistance in toluene total oxidation owing to abundant surface adsorbed oxygen species, excellent low-temperature reducibility, and high amounts of Cu+ and Mn3+. In detail, the reaction rate of MnCu 0.5 was over 9.0 times higher than that of MnCu 0.75 , MnCu 0.75 -P and MnCu 0.75 -H 2 O 2 at relative low temperature of 210 °C. The cyclic redox process with easier oxygen species mobility played a key role in the catalytic oxidation of toluene. Typical reaction intermediates as benzyl alcohol, benzaldehyde, benzene, phenol, and benzoquinone could be detected by PTR-MS, which further decomposed to acetone, ethanol, ketone, acetic acid, methanol, formaldehyde and acetaldehyde species by ring opening before total mineralization. [ABSTRACT FROM AUTHOR]

• Porous MnCoNiO x trimetallic spinel-type oxide (MCNO) catalyst was prepared. • MCNO material possesses large specific surface area and superior reducibility. • Non-thermal plasma-MCNO system has excellent toluene decomposition efficiency. • Catalyst combined with plasma enhances CO 2 selectivity and O 3 decomposition rate. A novel strategy for removal of toluene by non-thermal plasma (NTP) coupled with metal-organic frameworks (MOFs) derived catalyst was proposed in this work. The MOF-derived porous trimetallic oxide catalyst (MnCoNiO x , MCNO) was prepared by simple pyrolysis of a MOF-74(Mn-Co-Ni) precursor. We found that the MCNO material can well synergy with NTP in total decomposition of toluene owing to its high specific surface area, regular porous structure and excellent reducibility, which endow superior catalytic activity and CO 2 selectivity of NTP-MCNO system compared to that of NTP-MnO x , NTP-CoO x and NTP-NiO x. For instance, the toluene degradation efficiency can reach up to 75.7% in NTP-MCNO system with a low specific input energy of 101 J/L, much higher than that of NTP-MnO x (59.3%), NTP-CoO x (70.9%), NTP-NiO x (65.0%) and NTP alone (42.9%). Moreover, the formed ozone (O 3) can be well-controlled by the NTP-MCNO system due to the spinel-type oxides (MCNO) derived from MOF could generate more open-formwork structure and improve the mobility of oxygen. The results of this work would shed light on rational design and preparation of spinel-type oxides for oxidation applications, which provides guidance for further improvement of plasma-catalysis system. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of Mn-Ce@Na-Al 2 O 3 @Al mesh monolithic catalysts were facilely prepared. • Appropriate Ce doping can obviously enhance the toluene oxidation efficiency. • Ce species promotes the adsorption of oxygen and toluene molecules. • Oxygen vacancies can form easier on Ce modified monolithic catalysts. • Benzoate species oxidation was the rate determining step in toluene destruction. Here, a series of Mn-Ce binary oxides loaded monolith catalysts, with the support consisting of Na-Al 2 O 3 grown on Al mesh obtained by steam vapor treating, were prepared to attain efficient toluene destruction. On increasing CeO 2 loading, the toluene conversion over prepared catalysts shows an exponential rise, with Mn-4Ce@Na-Al 2 O 3 @Al monolithic catalyst exhibiting the optimal performance, over which 90% of toluene can be decomposed at 239 °C with oxidation rate over 5.57 × 10−7 mol·g−1·s−1, obviously higher than those over 4Ce/Na-Al 2 O 3 @Al (239 °C; 0.99 × 10−7 mol·g−1·s−1) and Mn/Na-Al 2 O 3 @Al (291 °C; 4.12 × 10−7 mol·g−1·s−1). H 2 -TPR and XPS results reveal that the superior redox ability and the formation of MnCeO x solid solution are favorable for toluene abatement. Oxygen vacancies form easily on the surface of Ce modified samples, resulting in superior oxygen and toluene adsorption ability, as demonstrated by DFT theoretical calculation. Besides, the pathways of toluene oxidation over Mn-4Ce@Na-Al 2 O 3 @Al catalyst were identified by using the in situ DRIFTS, and the key intermediates of toluene oxidation reaction are determined to be benzoyl, benzaldehyde, and benzoate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mn-Cu bimetallic catalysts were facilely prepared by one-step hydrothermal-redox method. • Hydrothermal-redox was superior to other preparation methods for Mn-Cu catalysts. • MnCu spinel type catalyst exhibited excellent low-temperature catalytic performance. • PTR-MS results revealed the reaction routes of toluene oxidation over MnCu catalyst. Developing facile preparation method to obtain the satisfied low-temperature catalytic performance of transitional metal oxide-based materials is still a challenge in deep degradation of VOCs. Here, a series of Mn-Cu bimetallic oxide catalysts were prepared by one-step hydrothermal-redox method for catalytic total oxidation of toluene. The CH 3 COOH concentration, Cu/Mn molar ratio and calcination temperature greatly affected the crystal structure, micromorphology and catalytic performance. Amongst, MnCu spinel structured catalyst exhibited excellent low-temperature catalytic activity, superior durability and water resistance in toluene total oxidation owing to its abundant surface adsorbed oxygen species, higher amount of Cu+ and Mn3+ and excellent low-temperature reducibility. The reaction rate of MnCu was 7.0 times higher than that of MnCu 0.5 at 210 °C. The cyclic redox process with enough oxygen vacancy played a vital role in toluene oxidation. The deep oxidation of benzene was the key step in the toluene oxidation. Proton transfer reaction-mass spectrometry (PTR-MS) results revealed the reaction intermediates including benzaldehyde, benzene and phenol, which further decomposed to acetone, ethanol, acetic acid, ketone and acetaldehyde by ring opening before total mineralization. Therefore, PTR-MS provided a facile method to investigate the reaction mechanism of toluene oxidation. [ABSTRACT FROM AUTHOR]

• Mn-MIL-100 materials with different morphologies and porous structures were prepared. • Lauric acid has remarkable tailoring property for the Mn-MIL-100 catalysts (LA). • Non-thermal plasma-LA system has high toluene removal efficiency and energy yield. • The presence of LA samples effectively inhibits the formation of O 3 and NO x. • A two-step toluene decomposition process was proposed by on-line FTIR and GC-MS. Here, lauric acid (LA) with a remarkable tailoring property of pore structure and porosity was adopted as modulator for the synthesis of Mn-MIL-100. Results reveal that LA amount has a significant effect on the morphology, crystal size and porous structure of prepared materials. The synthesized catalysts were coupled with a dielectric barrier discharge reactor to improve toluene decomposition performance. We found that the introduction of catalysts can remarkably enhance toluene removal efficiency (TRE), CO 2 /CO x selectivity and energy yield (EY), and simultaneously inhibit the generation of O 3 and NO x compared with the non-thermal plasma (NTP) system as the presence of catalysts with developed hierarchical porous structure and well-dispersed crystal particle provides abundant adsorbed centers and active sites for surface reactions. Amongst, LA-8 sample shows the best catalytic performance with TRE, CO 2 and CO x selectivity of 94.7%, 44.9% and 92.4%, respectively (specific energy density (SED) of 473 J L−1), much higher than the NTP system (respectively; 63.3%, 34.2% and 73.6%). Moreover, the EY of NTP-Catalysis system (5.19 g kWh−1) is also obviously higher than that of single NTP (1.94 g kWh−1) at SED of 262 J L−1. This work paves a way for application of MOFs in NTP-Catalysis system for VOC decomposition. [ABSTRACT FROM AUTHOR]