Catalytic conversion and DFT analysis of post DDBD-catalysis system for degradation of toluene,ethyl acetate and acetone with different metal-oxides catalysts

A series of multiphase metal-oxide catalysts(MnO_x/γ-Al₂O₃,CuO_x/γ-Al₂O₃,FeO_x/γ-Al₂O₃,CeO_x/γ-Al₂O₃and LaO_x/γ-Al₂O₃) were prepared for plasma-catalyst degradation of multicomponent volatile organic compounds(VOCs,such as toluene,acetone and ethyl acetate).The results reveal that the degradation efficiency(DE) of acetone,toluene and ethy...     

Effect of different supports on activity of Mn–Ce binary oxides catalysts for toluene combustion

The effects of support materials on catalytic performance were investigated in catalytic removal of toluene. And the Mn–Ce binary oxides as active components were supported on ZrO₂, SiO₂, γ-Al₂O₃ and TiO₂ support materials. Many techniques, including X-ray diffraction (XRD), Brunauer–Emmett–Teller method (BET), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and NH₃-temperature-programmed desorption (NH₃-TPD), were used to characterize physicochemical properties. Among the different catalysts, the MnCe/ZrO₂ catalyst with the lowest specific surface area (39.7 m²/g) shows the best catalytic activity. In terms of toluene conversion, the activity order is as follows: MnCe/ZrO₂ > MnCe/TiO₂ ≈ MnCe/SiO₂ > MnCe/Al₂O₃. The better performance of MnCe/ZrO₂ should be attributed to the low-temperature reducibility, and abundant surface species (Mn⁴⁺ and lattice oxygen). And XPS and TPR results reveal that more surface abundant Mn and Ce elements generate good interaction in MnCe/ZrO₂. The weak interaction between metal oxide and support also boosts the dispersion and complete reduction of MnCe oxides at low temperature. In addition, the in-situ DRIFTS results clarify that the carbonate species are main intermediates in MnCe/ZrO₂ sample during surface reaction process.     

Catalytic combustion of toluene over Pd-based monolithic catalysts with a novel washcoat Ce0.8Zr0.15La0.05Oδ

Two novel washcoats Ce_0.8Zr_0.15La_0.05O_δ and Ce_0.8Zr_0.2O₂ was prepared by an impregnation method, which acted as a host for the active Pd component to prepare Pd/Ce_0.8Zr_0.15La_0.05O_δ/substrate and Pd/Ce_0.8Zr_0.2O₂/substrate monolithic catalysts for toluene combustion. The washcoats was characterized by X-ray diffraction (XRD), Raman spectroscopy, Brunauner-Emmett-Teller (BET), and H₂-temperature-programmed reduction (H₂-TPR). The result indicated that both the washcoats had strong vibration-shock resistance according to ultrasonic test. Doping La³⁺ into CeO₂-ZrO₂ solid solution could generate more oxygen vacancies, and could inhibit the sinter of CeO₂-ZrO₂ solid solution when calcined at high temperatures (800, 900 and 1000 °C). The washcoat Ce_0.8Zr_0.15La_0.05O_δ had much better redox properties. The reductive temperature of Ce⁴⁺ species shifted to low temperature by 60 °C when the washcoats calcined at high temperatures (800, 900 and 1000 °C). The Pd/Ce_0.8Zr_0.15La_0.05O_δ/substrate monolithic catalyst calcination at 500 °C had the best catalytic activity and the 95% toluene conversion at a temperature as low as 190 °C. When calcined at low temperature (500 and 700 °C), the catalytic activity has little improvement, however, when calcined at high temperature, the catalytic activity of Pd/Ce_0.8Zr_0.15La_0.05O_δ/substrate monolithic catalysts had significant improvement. As catalyst washcoat, the Ce_0.8Zr_0.15La_0.05O_δ had better thermal stability than the washcoat Ce_0.8Zr_0.2O₂, the developed Pd/Ce_0.8Zr_0.15La_0.05O_δ/substrate monolithic catalyst in this work was promising for eliminating Volatile organic compounds.     

Preparation of MnCe（y）O_x/TiO_2 catalysts and their catalytic activity for catalytic combustion of toluene

以TiO2为载体,采用浸渍法制备了不同配比的MnCe复合型催化剂,并采用X射线衍射（XRD）、氧气的程序升温脱附（O2-TPD）和氢气的程序升温还原（H2-TPR）对制备的催化剂进行表征,比较了催化剂催化氧化（燃烧）甲苯的活性。研究结果表明,所制备的催化剂MnCe（y）Ox/TiO2对甲苯有明显的催化活性。当Ce/（Mn＋Ce）的摩尔比为0.1时,催化剂MnCe（0.1）Ox/TiO2的催化活性最高,甲苯的转化率达到90%时的温度为254℃。在催化剂MnOx/TiO2中掺杂少量的Ce元素,有利于活性组分Mn物种在载体表面上以更小颗粒而且更高的分散度存在,从而提高催化剂的催化活性。     

Effect of active oxygen on the performance of Pt/CeO2 catalysts for CO oxidation

This study was focused on the influence of active oxygen on the performance of Pt/CeO_2 catalysts for CO oxidation. A series of CeO_2 supports with different contents of active oxygen were obtained by adding surfactant at different synthesis steps. 0.25 wt% Pt was loaded on these CeO_2 supports by incipientwetness impregnation methods. The catalysts were characterized by N2 adsorption, X-ray diffraction(XRD), high-resolution transmission electron microscopy(HRTEM), H_2 temperature-programmed reduction(H_2-TPR), dynamic oxygen storage capacity(DOSC) and in-situ DRIFTS technologies. For S-f supports, the surfactant was added into the solution before spray-drying in the synthesis process, which facilitates more active oxygen formation on the surface of CeO_2. After loading Pt, the more active oxygen on CeO_2 contributes to dispersing Pt species and enhancing the CO oxidation activity. As for the aged samples,Pt-R-h shows the highest activity above 190 ℃ because of the presence of more partly oxidized Pt~(δ+) species. Thus the activity is also influenced by the states of Pt and the Pt~(δ+) species may contribute to the high activity at elevated temperature.     

Active manganese oxide on MnOx–CeO2 catalysts for low-temperature NO oxidation: Characterization and kinetics study

MnO_x–CeO₂ catalysts were synthesized to investigate the active sites for NO oxidation by varying the calcination temperature. XRD and TEM results showed that cubic CeO₂ and amorphous MnO_x existed in MnO_x–CeO₂ catalysts. High temperature calcination caused the sintering of amorphous MnO_x and transforming to bulk crystalline Mn₂O₃. H₂-TPR and XPS results suggested the valence of Mn in MnO_x–CeO₂ was higher than pure MnO_x, and decreased with the increasing calcination temperature. The turnover frequency (TOF) was calculated based on the initial reducibility according to H₂-TPR quantitation and kinetic study. The TOF results indicated that the initial reducibility of amorphous MnO_x with high valence manganese ions was equivalent to the active sites for NO oxidation. It can be inferred that the amorphous MnO_x plays a key role in low-temperature NO oxidation.     

Comparative study of La_(1-x)Ce_xMnO_(3+δ) perovskites and Mn-Ce mixed oxides for NO catalytic oxidation

A series of La_(1-x)Ce_xMnO_(3+δ)(x=D,0.05,0.1,0.2,and 0.3) perovskites and Mn-Ce mixed oxides were prepared.Their physico-chemical properties were systematically characterized and the NO oxidation activities of the catalysts were investigated.The La_(0.9)Ce_(0.1)MnO_(3+δ) has the best activity among all of the catalysts,with a maximum NO conversion of 85% at 300℃.The characterization results indicate that the doping of Ce improves the properties of the perovsidtes in terms of the specific surface area,the average valence state of Mn ions,the number of reactive oxygen species and the NO_x desorption behaviors.The Mn-Ce mixed oxide calcined at 500℃ shows a similar NO oxidation activity with La_(0.9)Ce_(0.1)MnO_(3+δ).However,the activity of the mixed oxide obtained at 750℃ decreases a lot,which results from the loss of active sites and active oxygen species.     

Surface reactive species on MnOx（0.4）-CeO2 catalysts towards soot oxidation assisted with pulse dielectric barrier discharge

MnOx(0.4)-CeO2 was investigated for soot oxidation assisted with a pulse dielectric barrier discharge(DBD).The catalysts were evaluated and characterized with TPO(temperature programmed oxidation),X-ray diffraction(XRD),Raman and X-ray photoelectron spectroscopy(XPS).The ignition temperature Ti for soot oxidation decreased from 240.8 to 216.4 oC with the increase of the pulse DBD frequencies from 50 to 400 Hz,lower than that of the case without pulse DBD present(253.4 oC).The results of XRD,Raman and XPS agreed well with the TPO activities of MnOx(0.4)-CeO2 towards soot oxidation.More solid solution of ceria and manganese,and surface reactive species including O2–,O– and Mn4+ were responsible for the enhancement of soot oxidation due to pulse DBD injection in the present study.For solid solution favors to the activation and transformation of those species,which are believed to be involved in the soot oxidation in a hybrid catalysis-plasma.     

Effects of sol-gel method and lanthanum addition on catalytic performances of nickel-based catalysts for methane reforming with carbon dioxide

The nickel-based catalysts were prepared by the sol-gel method and used for the CH4 reforming with CO2. The effects of the sol-gel method on the specific surface area, catalytic activity, desorption, and reduction performances of catalysts were investigated with BET, TPR, and TPD. Compared with the catalyst prepared by the impregnation method, the results indicated that the catalysts prepared by the sol-gel method had larger specific surface area, showing higher catalytic activities and exhibiting perfect desorption and reduction per-formances. In addition, the modification effects of adding La were studied, and it was found that the 0.75NLBT catalyst constituted of 5wt.%Ni-0.75wt.%La was optimal.     

Design and synthesis of Fe-Ce-O@C with efficient photocatalytic activity

Fe-Ce-OH@AR14 was obtained via the adsorption of acid red 14(AR14) on Fe-Ce-OH prepared by the codeposition of cerium nitrate hexahydrate,ferric nitrate nonahydrate,and ammonia,and then Fe-Ce-O@C with high photocatalyic efficiency was synthesized by the calcination of Fe-Ce-OH@AR14 in N₂.For comparison,Fe-Ce-O was also prepared by the calcination of Fe-Ce-OH in N₂.The obtained materials were characte rized by X-ray diffraction(XRD),Raman,X-ray photoelectron spectroscopy(XPS...     

Effect of different doping elements on performance of Ce-Mn/TiO2 catalyst for low temperature denitration

Sm and Ho were doped in Ce-Mn/TiO₂ catalyst respectively to enhance its denitration performance at low temperature.X-ray diffraction(XRD),N₂ adsorption-desorption,X-ray photoelectron spectroscopy(XPS),NH₃-temperature programmed desorption(NH₃-TPD),H₂-temperature programmed reduction(H₂-TPR) and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS) techniques were used to analyze the structure and performance ...     

Lanthanum-doped Cu-Mn composite oxide catalysts for catalytic oxidation of toluene

CuMn mixed oxides catalysts doped with La were prepared following a co-precipitation method and used for the catalytic oxidation of toluene. Catalysts properties of the catalysts were investigated by X-ray diffraction, N_2 adsorption/desorption,scanning electron microscopy, H_2-temperature-programmed reduction(H_2-TPR), O_2-temperature-programmed desorption(O_2-TPD) and X-ray photoelectron spectroscopy techniques. Characterization data reveal that the phase change and decrease in crystallinity of the La-doped catalysts increase the number of oxygen vacancies. Improvements in reducibility and an increase in the amount of chemisorbed oxygen of the La-doped catalysts were also verified by H_2-TPR and O_2-TPD. The activity of the CuMn mixed oxides catalysts is significantly improved by the addition of a nominal amount of La. The CuMn/La-4 mol% catalyst exhibits the best catalytic activity, with a 90%conversion temperature of 255 ℃,attributed to a high Mn~(3+)ratio, superficial chemisorbed oxygen,and high surface area. This study indicates La to be a promising dopant for Cu-Mn catalysts toward toluene oxidation.     

Effect of Na~+ on catalytic performance of CoCe/ZSM-5 catalysts for oxidation of toluene

A CoCe/ZSM-5 catalyst was prepared by ultrasonic-assisted impregnation for the catalytic combustion of toluene.To study the effect of Na+on catalytic performance of CoCe/ZSM-5 catalysts,a series of different Si/Al ZSM-5 zeolites and catalysts doped with Na were synthesized.The experimental results show that 0.71 wt%Na+can inhibit active growth,generate more active small crystal grains,and promote improvement of the catalytic activity by the grain boundary segregation block mechanism,and the catalyst with 0.71 wt%of Na shows toluene conversion of 90 vol%at 250℃.Over 0.71 wt%of Na+content will neutralize the acid centre of the catalyst,lowering the specific surface area of the catalyst and resulting in a gradual decrease in the catalytic activity.     

Construction of mesoporous ceria-supported gold catalysts with rich oxygen vacancies for efficient CO oxidation

Bearing unique redox nature and high oxygen storage capacity, ceria (CeO₂) has always been a promising CO oxidation catalyst support for gold (Au) catalysts and the like. Herein, a series of Au–CeO₂–P (P stands for pH value) samples was prepared by a co-precipitation method with the assistance of an alkaline environment and amino groups functionalized ordered mesoporous polymer (OMP-NH₂). Afterward, all samples described above were characterized that the Au–CeO₂–P catalysts are made of Au–Ce–O solid solution and Au nanoparticles (NPs) supported on CeO₂. It turns out that OMP-NH₂ is not just a simple sacrificial template for mesoporous structure, but also plays an important role as an amino source, explaining the presence of rich oxygen vacancies. Due to the concentration of oxygen vacancies in Au–Ce–O solid solution is the key factor for the oxygen mobility of CO oxidation, the catalytic results also demonstrate that the catalytic activity of Au–CeO₂–P catalysts is related to the concentration of their oxygen vacancies. Moreover, Au–CeO₂-9.6 with a highest concentration of oxygen vacancies (as high as 13.98%) in Au–CeO₂–P catalysts exhibits the best catalytic activity (complete conversion at 10 °C).     

Effect of interaction between different CeO2 plane and platinum nanoparticles on catalytic activity of Pt/CeO2 in toluene oxidation

The plane exposure of support vitally affects the catalytic performance of the catalyst. In this work, CeO₂ nanorods ((110) plane exposure), nano-octahedrons ((111) plane exposure) and nano-cubes ((100) plane exposure) were prepared as the supports of Pt/CeO₂ samples to investigate the effect of CeO₂ plane exposure on total toluene oxidation. Characterizations reveal that the (110) plane of CeO₂ is more helpful to the dispersion of Pt species, followed by (111) face. The improved dispersion of Pt species can enhance the metal-supports interaction, which promotes the electron transfer of CeO₂ carrier to Pt nanoparticles and the adsorption-activation of O₂, thereby facilitating the total oxidation of toluene via the Langmuir–Hinshelwood (L-H) mechanism. Therefore, Pt/CeO₂-r (nanorods) sample expresses excellent catalytic performance of toluene oxidation. Finally, the procedure of toluene total oxidation was studied by in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. We expect that this work can contribute to the development of an effective sample for the decomposition of volatile organic compounds (VOCs).     

Fabricating PdCe/OMS-2 catalysts with boosted low-temperature activity for toluene deep degradation

Porous cryptomelane-type octahedral molecular sieve(OMS-2) with mixed Mn valence and abundant lattice oxygen species has attracted much attention in volatile organic compounds(VOC) catalytic elimination.However,complete conversion of arene over OMS-2 catalysts at relatively low temperature is still a challenge due to its limited crystal structure and inferior stability.Here,a series of PdCe/OMS-2 catalysts with different Pd/Ce molar ratios was fabricated by a facile impregnation method and the p...     

Core-shell MnCeOx catalysts for NO oxidation and mild temperature diesel soot combustion

Environmental contamination such as soot particles and NO_x has aroused extensive attraction recently.However,the main challenge lies in the oxidation of soot at mild temperature with the assistance of NO_x.Here,a series of core-shell MnCeO_x catalysts were successfully synthesized by hydrothermal method and employed for low-temperature catalytic oxidation of soot in the presence of NO_x.X-ray diffraction(XRD),inductively coupled plasma-optical emission sp...     

Effects of cerium precursors on surface properties of mesoporous CeMnO_x catalysts for toluene combustion

Mesoporous CeMnOx composite oxides catalysts were prepared by surfactant-assisted co-precipitation method and used for the catalytic oxidation of toluene.The effect of different cerium precursors[Ce(NO_3)_3 and(NH_4)_2 Ce(NO_3)_6] on catalyst structure,surface properties and toluene combustion activities of mesoporous CeMnO_x catalysts were investigated.The Ce(Ⅲ)MnO_x catalyst prepared from Ce(NO_3)_3 precursor shows higher catalytic activity,with a 90% conversion temperature of 240℃,which is better than the Ce(Ⅳ)MnO_x catalyst derived from(NH_4)_2 Ce(NO_3)_6] precursor.On the basis of characterizations,it reveals that abundant surface content of Mn~(4+),better redox behavior and larger concentration of surface active oxygen species are responsible for the excellent catalytic performance.     

Enhancement of potassium resistance of Ce-Ti oxide catalyst for NH3-SCR reaction by modification with holmium

Alkali metal K in exhaust gas has a deactivation effect on NH₃-SCR catalysts.In this work,it is discovered that the addition of Ho on CeTi catalyst can remarkably strengthen its K tolerance.The conclusions of Brunauer-Emmett-Teller(BET),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),NH₃ temperature programmed desorption(NH₃-TPD)and H₂temperature programmed reduction(H₂-TPR)analyses demonstrate that the enhancement of K resistance mainly originates from its stronger surface acidity and redox capability,the higher concentration of Ce³⁺species and surface chemisorbed oxygen.In situ DRIFT analysis reveals that the introduction of Ho on CeTi can remarkably improve the adsorption of NH₃ and NO_x species on catalyst surface,accompanied by the intensified reactivity of ad-NH₃ species,which should also administer to improve the K resistance.