Catalytic combustion of chlorobenzene on modified LaMnO3 catalysts

Catalytic Combustion of Propane over Ce-Doped Lanthanum Borate Loaded with Various 3d Transition Metals

Ce-doped LaBO3 (Ce0.05La0.95BO3) and a corresponding incorporation with 3d transition metals (TMs) were prepared and evaluated for eliminating propane. Our results showed the catalytic activity toward propane combustion has a close relationship with the loaded TMs, which promoted oxygen vacancies density and further enhanced the reduction and acidity of this material. This eventually led to 90% propane conversion at 718 K for a Cu-loaded Ce0.05La0.95BO3 catalyst. During 10 h of catalytic propane oxidation, the propane-elimination rate was maintained very well, with no degradation of the catalyst.

Boosting the surface oxygen activity for high performance Iron-based perovskite oxide

Surface oxygen activities always play an important role in various heterogeneous reaction processes. In this study, the surface oxygen activity of studied perovskite oxides is greatly enhanced after the composition and morphology are tuned. It is worth noting that the surface oxygen activity is enhanced correspondingly, accompanied by higher surface area, better reducibility, and superior low-temperature reactivity of studied catalysts. The sample introduced with nickel atom and nanorods structure possesses higher surface oxygen activity and vacancies with superior performance including T₁₀ at 221 °C and T₉₀ at 243 °C, nearly 90 °C elevations. Double perovskite oxides, especially with nanorods structure are verified to be composed of more surface active oxygen, which could be related to low-temperature redox ability and superior oxygen vacancies. Based on the DFT calculation, introducing nickel element is confirmed to be able to efficiently boost the generation of oxygen vacancies and adsorption of oxygen molecular, in accord with the analysis of characterization. To sum up, the strategy of introducing the nickel atom and nanorods structure could effectively tune the surface oxygen activity and generate more oxygen vacancies, which would be beneficial to the catalytic performance of toluene catalytic oxidation correspondingly.

Comparative Investigation on Chlorobenzene Oxidation by Oxygen and Ozone over a MnOx/Al2O3 Catalyst in the Presence of SO2

Catalytic oxidation of volatile organic compounds (VOCs) usually encounters complicated components in flue gas causing severe deactivation that restrict its application in specific conditions. The Cl substitution in chlorobenzene further increases poisoning risks. Ozone assistance has unique superiority that can overcome these bottleneck problems. Herein, this study performs a comparative investigation of CB oxidation by oxygen and ozone over a simple Mn/Al₂O₃ catalyst. CB conversion suffered from slight deactivation in oxygen atmosphere (from 90 to 70%) and more severe deactivation in the presence of SO₂ (from 90 to 45%) at 480 °C. Introduction of ozone successfully attained high CB conversion at low temperature (120 °C) with excellent stability and less byproducts. Especially, CB oxidation by ozone maintained its original conversion in the presence of SO₂. The deactivation process was simulated by synthesizing several sulfated catalysts. Direct sulfation on Mn/Al₂O₃ attained more severe deactivation in CB conversion and CO₂ formation than sulfation on the Al₂O₃ support. Ozone with a strong oxidation property promoted the CB oxidation cycle, facilitated desorption of carbonaceous intermediates, and protected MnO_x species from severe erosion, thus exhibiting high and stable performance in CB oxidation.

Catalytic performance of the Ce-doped LaCoO3 perovskite nanoparticles

A series of La1-xCexCoO3 perovskite nanoparticles with rhombohedral phases was synthesized via sol-gel chemical process. X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Electron Diffraction Spectroscopy (EDS), Thermogravimetric Analysis (TGA), UV-Vis spectroscopy, Fourier Transform Infrared spectra (FTIR), Nitrogen Adsorption/desorption Isotherm, Temperature Program Reduction/Oxidation (TPR/TPO), X-ray Photoelectron Spectroscopy (XPS) techniques were utilized to examine the phase purity and chemical composition of the materials. An appropriate doping quantity of Ce ion in the LaCoO3 matrix have reduced the bond angle, thus distorting the geometrical structure and creating oxygen vacancies, which thus provides fast electron transportation. The reducibility character and surface adsorbed oxygen vacancies of the perovskites were further improved, as revealed by H2-TPR, O2-TPD and XPS studies. Furthermore, the oxidation of benzyl alcohol was investigated using the prepared perovskites to examine the effect of ceria doping on the catalytic performance of the material. The reaction was carried out with ultra-pure molecular oxygen as oxidant at atmospheric pressure in liquid medium and the kinetics of the reaction was investigated, with a focus on the conversion and selectivity towards benzaldehyde. Under optimum reaction conditions, the 5% Ce doped LaCoO3 catalyst exhibited enhanced catalytic activity (i.e., > 35%) and selectivity of > 99%, as compared to the other prepared catalysts. Remarkably, the activity of catalyst has been found to be stable after four recycles.

Catalytic Oxidation of Chlorobenzene over Pd-TiO2 /Pd-Ce/TiO2 Catalysts

A series of Pd-TiO2/Pd-Ce/TiO2 catalysts were prepared by an equal volume impregnation method. The effects of different Pd loadings on the catalytic activity of chlorobenzene (CB) were investigated, and the results showed that the activity of the 0.2%-0.3% Pd/TiO2 catalyst was optimal. The effect of Ce doping enhanced the catalytic activity of the 0.2% Pd-0.5% Ce/TiO2 catalyst. The characterization of the catalysts using BET, TEM, H2-TPR, and O2-TPD showed that the oxidation capacity was enhanced, and the catalytic oxidation efficiency was improved due to the addition of Ce. Ion chromatography and Gas Chromatography-Mass Spectrometer results showed that small amounts of dichlorobenzene (DCB) and trichlorobenzene (TCB) were formed during the decomposition of CB. The results also indicated that the calcination temperature greatly influenced the catalyst activity and a calcination temperature of 550 °C was the best. The concentration of CB affected its decomposition, but gas hourly space velocity had little effect. H2-TPR indicated strong metal–support interactions and increased dispersion of PdO in the presence of Ce. HRTEM data showed PdO with a characteristic spacing of 0.26 nm in both 0.2% Pd /TiO2 and 0.2% Pd-0.5% Ce/TiO2 catalysts. The average sizes of PdO nanoparticles in the 0.2% Pd/TiO2 and 0.2% Pd-0.5% Ce/TiO2 samples were 5.8 and 4.7 nm, respectively. The PdO particles were also deposited on the support and they were separated from each other in both catalysts.

High-yield synthesis of Ce modified Fe-Mn composite oxides benefitting from catalytic destruction of chlorobenzene

Ce–Fe–Mn catalysts were prepared by an oxalic acid assisted co-precipitation method. The influence of Ce doping and calcination temperature on the catalytic oxidation of chlorobenzene (as a model VOC molecule) was investigated in a fixed bed reactor. The Mn₃O₄ phase was formed in Ce–Fe–Mn catalysts at low calcination temperatures (<400 °C), which introduced more chemisorbed oxygen, and enhanced the mobility of O atoms, resulting in an improvement of the reduction active of Mn₃O₄ and Fe₂O₃. Additionally, CeO₂ has strong redox properties, and Ce⁴⁺ would oxidize Mn^x+ and Fe^x+. Therefore, the interaction of Ce, Fe and Mn can improve the content of surface chemisorbed oxygen. As compared with Fe–Mn catalysts, the catalytic conversion of chlorobenzene over Ce(5%)–Fe–Mn-400 was about 99% at 250 °C, owing to high specific surface area, Mn₃O₄ phase, and Ce doping. However, with the increase in roasting temperature, the performance of the catalysts for the catalytic combustion of chlorobenzene was decreased, which probably accounts for the formation of the Mn₂O₃ phase in Ce–Fe–Mn-500 catalysts, leading to a decrease in the specific surface area and concentration of chemically adsorbed oxygen. As a result, it can be expected that the Ce–Fe–Mn catalysts are effective and promising catalysts for chlorobenzene destruction.

Ce–Fe–Mn catalysts were prepared by an oxalic acid assisted co-precipitation method.

Direct Z-scheme La1-xCexMnO3 catalyst for photothermal degradation of toluene

A series of Ce-doped LaMnO₃ (La_1-xCe_xMnO₃) were prepared and were tested for gaseous toluene oxidation in order to investigate the effect of cerium doping in LaMnO₃ on activity under photothermal conditions. It was found that the activity and CO₂ yield of the catalyst can be effectively increased when x = 0.25. A group of characterization is used to characterize the morphology, composition, and physical properties of the as-prepared catalysts. Results show that the Ce-doped LaMnO₃ can form coexistence of La_1-xCe_xMnO₃ and CeO₂, the reaction of CeO₂/La_1-xCe_xMnO₃ under photothermal conditions follows the Mars-van Krevelen redox cycle mechanism, and the prepared CeO₂/La_1-xCe_xMnO₃ can form a highly efficient Z-scheme heterojunction, which can enhance the electrons transfer speed of the catalyst. Moreover, in the photothermal catalytic degradation, lattice oxygen is the most important active substance, a small amount of cerium doping can increase the lattice oxygen content of perovskite and increase the activity of the reaction.

Physico-chemical properties and catalytic activity of the sol-gel prepared Ce-ion doped LaMnO3 perovskites

Ce-doped LaMnO₃ perovskite ceramics (La_1−xCe_xMnO₃) were synthesized by sol-gel based co-precipitation method and tested for the oxidation of benzyl alcohol using molecular oxygen. Benzyl alcohol conversion of ca. 25–42% was achieved with benzaldehyde as the main product. X-ray diffraction (XRD), thermogravimetric analysis (TGA), BET surface area, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (H₂-TPR), temperature-programmed oxidation (O₂-TPO), FT-IR and UV-vis spectroscopic techniques were used to examine the physiochemical properties. XRD analysis demonstrates the single phase crystalline high purity of the perovskite. The Ce-doped LaMnO₃ perovskite demonstrated reducibility at low-temperature and higher mobility of surface O₂-ion than their respective un-doped perovskite. The substitution of Ce³⁺ ion into the perovskite matrix improve the surface redox properties, which strongly influenced the catalytic activity of the material. The LaMnO₃ perovskite exhibited considerable activity to benzyl alcohol oxidation but suffered a slow deactivation with time-on-stream. Nevertheless, the insertion of the A site metal cation with a trivalent Ce³⁺ metal cation led to an enhanced in catalytic performance because of atomic-scale interactions between the A and B active site. La_0.95Ce_0.05MnO₃ catalyst demonstrated the excellent catalytic activity with a selectivity of 99% at 120 °C.

High Catalytic Performance of Mn-Doped Ce-Zr Catalysts for Chlorobenzene Elimination

Mn-Ce-Zr-O catalysts doped with varying Mn content were prepared and assessed for the catalytic combustion of chlorobenzene (CB). Nanosized MCZ-0.67 catalyst with amorphous phase exhibited a high and stable catalytic activity among the studied catalysts, achieving 90% CB conversion at 226 °C and withstanding stability tests, including time-based stability and the successive influence of various operating conditions. Meanwhile, the MCZ-0.67 catalyst used showed good recyclability by calcination in air. Characterization results suggested that Mn doping played a dominant role in improving the catalytic performance, resulting in larger surface area, better redox properties and greater amounts of surface active oxygen. In addition, the introduction of Zr was also indispensable for maintaining the good catalytic performance of catalysts. Finally, trace amounts of polychlorinated by-products during CB oxidation were monitored and the oxidation process was discussed.

Catalytic Oxidation of Chlorinated Organics over Lanthanide Perovskites: Effects of Phosphoric Acid Etching and Water Vapor on Chlorine Desorption Behavior

In this article, the underlying effect of phosphoric acid etching and additional water vapor on chlorine desorption behavior over a model catalyst La₃Mn₂O₇ was explored. Acid treatment led to the formation of LaPO₄ and enhanced the mobility of lattice oxygen of La₃Mn₂O₇ evidenced by a range of characterization (i.e., X-ray diffraction, temperature-programmed analyses, NH₃-IR, etc.). The former introduced thermally stable Brönsted acidic sites that enhanced dichloromethane (DCM) hydrolysis while the latter facilitated desorption of accumulated chlorine at elevated temperatures. The acid-modified catalyst displayed a superior catalytic activity in DCM oxidation compared to the untreated sample, which was ascribed to the abundance of proton donors and Mn(IV) species. The addition of water vapor to the reaction favored the formation and desorption of HCl and avoided surface chlorination at low temperatures. This resulted in a further reduction in reaction temperature under humid conditions ( T₉₀ of 380 °C for the modified catalyst). These results provide an in-depth interpretation of chlorine desorption behavior for DCM oxidation, which should aid the future design of industrial catalysts for the durable catalytic combustion of chlorinated organics.

A citric acid-assisted deposition strategy to synthesize mesoporous SiO2-confined highly dispersed LaMnO3 perovskite nanoparticles for n-butylamine catalytic oxidation

A citric acid-assisted deposition strategy was applied to synthesize mesoporous SiO₂-confined highly dispersed LaMnO₃ perovskite nanoparticles with optimum catalytic performance and N₂ selectivity.

Catalytic oxidation of trichloroethylene from gas streams by perovskite-type catalysts

Three perovskite-type catalysts including LaMnO₃, La_0.8Ce_0.2MnO₃, and La_0.8Ce_0.2 Mn_0.8Ni_0.2O₃ are prepared using citric acid sol-gel method and evaluated as catalyst for the oxidation of trichloroethylene (TCE) in air with temperature ranging from 100 to 600 °C. The physicochemical properties of three perovskite-type catalysts were characterized by SEM, EDS, XRD, BET, and XPS to investigate the relationship with catalytic activities. The results show that the removal efficiency of TCE achieved with La_0.8Ce_0.2Mn_0.8Ni_0.2O₃ (the best one) reaches 100% at 400 °C and the mineralization efficiency reaches 100% at 600 °C. The enhanced activity can be attributed to the addition of Ce and Ni which increases the surface areas, active oxygen species, and the redox ability of the Mn⁴⁺/Mn³⁺ ratio on the catalyst surface. As La_0.8Ce_0.2Mn_0.8Ni_0.2O₃ is applied for TCE oxidation, the main intermediate chlorinated byproduct detected is tetrachloroethylene (C₂Cl₄) which is generated by the reaction of TCE and chlorine (Cl₂). The activation energy for the TCE oxidation with La_0.8Ce_0.2Mn_0.8Ni_0.2O₃ catalyst is 51 kJ/mol using kinetic models of power-law type.

Three-dimensionally ordered macroporous LaMnO3 with tunable oxygen vacancies via nitric acid-aided modulating and their catalytic combustion properties

Three-dimensionally ordered macroporous (3DOM) LaMnO₃ oxides with tunable oxygen vacancies have been successfully fabricated via a facile nitric acid-aided modulating sol–gel method.

Enhancement of resistance to chlorine poisoning of Sn-modified MnCeLa catalysts for chlorobenzene oxidation at low temperature

The Sn-modified MnCeLa catalysts show significantly higher resistance to chlorine poisoning than MnCeLa catalysts at different temperatures.