Oxygen Temperature-programmed Desorption Research Articles

Constructing a Pt/YMn2O5 Interface to Form Multiple Active Centers to Improve the Hydrothermal Stability of NO Oxidation.

The hydrothermal stability of NO oxidation is the key to the practical application of diesel oxidation catalysts in diesel engines, which in the laboratory requires that NO activity does not decrease after aging for 10 h with 10% H2O/air at 800 °C. On the one hand, the construction of a metal/oxide interface can lead to abundant oxygen vacancies (Ov), which compensate for the loss of activity caused by the aggregation of Pt particles after aging. On the other hand, YMn2O5 (YMO) has excellent thermal stability and NO oxidation capacity. Therefore, a Pt/YMn2O5-La-Al2O3 (Pt/YMO-LA) catalyst was prepared by the impregnation method. The support of the catalyst, YMn2O5-La-Al2O3 (YMO-LA), was obtained by mixing high specific surface LA and YMO ball-milling. Under laboratory-simulated diesel exhaust flow, the NO oxidation performance of Pt/YMO-LA did not decrease after hydrothermal aging. Combining high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and oxygen temperature-programmed desorption (O2-TPD), the Pt/YMn2O5 interface was formed after hydrothermal aging, and the increased Ov can provide reactive oxygen to Pt and YMO. The cooperative catalysis of multiple active centers composed of Pt, YMO, and Ov is the crucial factor to maintain the NO oxidation performance. In addition, in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) show that an increase in Ov is beneficial to the adsorption and desorption of more nitrate and nitrite intermediates, thus achieving the hydrothermal stability of NO oxidation.

Component regulation in novel La-Co-O-C composite catalyst for boosted redox reactions and enhanced thermal stability in methane combustion

A novel La-Co-O-C (LC-C) composites were prepared via a facile co-hydrothermal route with oxides and glycerol and further optimized for methane catalytic activity and thermal stability via component regulation. It was demonstrated that Co3O4 phase was the main component in regulation. The combined results of X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of oxygen (O2-TPD), temperature-programmed reduction of hydrogen (H2-TPR), temperature-programmed desorption of ammonia/carbon dioxide (NH3/CO2-TPD) revealed that component regulation led to more oxygen vacancies and exposure of surface Co2+, lower surface basicity and optimized acidity, which were beneficial for adsorption of active oxygen species and activation of methane molecules, resulting in the excellent catalytic oxidation performance. Especially, the (3.5)LC-C (3.5 is Co-to-La molar ratio) showed the optimum activity and the T50 and T90 (the temperature at which the CH4 conversion rate was 50% and 90%, respectively) were 318 and 367°C, respectively. Using theoretical calculations and in situ diffuse reflection infrared Fourier transform spectroscopy characterization, it was also found that the catalytic mechanism changes from the “Rideal-Eley” mechanism to the “Two-term” mechanism depending on the temperature windows in which the reaction takes place. Besides, the use of the “Flynn-Wall-Ozawa” model in thermoanalytical kinetics revealed that component regulation simultaneously optimized the decomposition activation energy, further expanding the application scope of carbon-containing composites.

Surface mechanism and optimization of catalytic ozonation with CoxFe oxides as catalyst for degradation of sodium p-toluenesulfonate in water.

In this study, the removals of sodium p-toluenesulfonate (NaTSA) by catalytic ozonation with two different cobalt-iron compounds, CoxFe oxides prepared by co-precipitation/calcination (CPO) and CoxFe oxides prepared by direct calcination (DCO), as the catalysts, had a difference of about 12%. It was found that the CPO surface contained active type c water, which was generally adsorbed on the oxygen vacancy. The test of oxygen temperature-programmed desorption (O2-TPD) showed that the surface of CPO was rich in oxygen vacancy. Through the electrochemical oxygen evolution reaction (OER) detection, a pair of Co valence redox peaks were detected from the CV curves, and the results of XPS test showed the replacement of octahedral Co3+ with Fe3 + in the Co3O4 during preparation of CPO. The enriched oxygen vacancy could be used as active sites for ozone adsorption and improve the charge transfer capacity. The number of hydroxyl radicals was detected by electron spin resonance (EPR) and it indicated that CPO contained more hydroxyl radicals, so it had higher effect in catalytic ozonation for organic pollutant degradation. In this paper, the relationship between oxygen vacancy and reactive center in the microstructure of the catalysts was established to discuss their working mechanism. The influence of the initial pH value, catalyst dosage, and ozone concentration on the removal of NaTSA was investigated by response surface design, and the optimal experimental conditions were predicted and verified.

The Effect of Transition Metal Substitution in the Perovskite-Type Oxides on the Physicochemical Properties and the Catalytic Performance in Diesel Soot Oxidation

The paper is focused on the Fe for Co substitution effect on the redox and catalytic properties in the perovskite structure of GdFeO3. The solid oxides with the composition GdFe1−xCoxO3 (x = 0; 0.2; 0.5; 0.8; 1) were obtained by the sol-gel method and characterized by various methods: X-ray diffraction (XRD), temperature-programmed reduction (H2-TPR), N2 sorption, temperature-programmed desorption of oxygen (TPD-O2), simultaneous thermal analysis (STA), and X-ray photoelectron spectroscopy (XPS). The H2-TPR results showed that an increase in the cobalt content in the GdFe1−xCoxO3 (x = 0; 0.2; 0.5; 0.8; 1) leads to a decrease in the reduction temperature. Using the TPD-O2 and STA methods, the lattice oxygen mobility is increasing in the course of the substitution of Fe for Co. Thus, the Fe substitution in the perovskite leads to an improvement in the oxygen reaction ability. Experiments on the soot oxidation reveal that catalytic oxidation ability increases in the series: GdFe0.5Co0.5O3 ˂ GdFe0.2Co0.8O3 ˂ GdCoO3, which is in good correlation with the increasing oxygen mobility according to H2-TPR, TPD-O2, and STA results. The soot oxidation over GdFeO3 and GdFe0.8Co0.2O3 is not in this range due to the impurities of iron oxides and higher specific surface area.

Chromium-doped cryptomelane: Mn-O debilitation and reactive enhancement in formaldehyde abatement

Nano-rod chromium-doped cryptomelane was prepared by co-precipitation and characterized by XRD, EDX elemental maps, SEM, ICP-MS and N2 adsorption. Temperature-programmed desorption of oxygen (O2-TPD) revealed a significant down-shift of oxygen desorption temperature regarding atomic oxygen bounded Mn3+ sites from ~40 to ~488 °C corresponded to 0–4.9 wt% of chromium loading. This result was consistent with the elevation of Mn-average-oxidation-state (Mn-AOS) from 3.6 to 3.8 for non-doped and Cr-doped cryptomelane samples. The catalytic performance of Cr-doped cryptomelane on formaldehyde oxidation was correlated with the chromium loading because of the change in Mn-AOS values and debilitation of Mn-O in Mn-O-Cr bridges.

Influence of Structure on Catalytic Properties of La0.7Sr0.3BO3 (B = Mn, Fe, Ni) Perovskite Catalysts in Total Oxidation Reaction of M-Xylene

In this study, the influence of structure on catalytic properties of La0.7Sr0.3BO3 (B = Mn, Fe, Ni) perovskite catalysts in total oxidation reaction of m-xylene was studied. Perovskite oxides of La0.7Sr0.3BO3 (B = Mn, Fe, Ni) were prepared by sol-gel citrate method. Structural properties of these materials were determined by various physico-chemical methods such as X-ray diffraction method (XRD) with Rietveld analytical method using Fullprof program, infra - red spectroscopy method (IR), temperature - programmed desorption of oxygen (TPDO) method and nitrogen adsorption and desorption isotherms method (BET). Obtained results show that there is a close relationship between the structural properties and catalytic activity of these materials: the catalyst that has the more of structural distortion, the larger of specific surface area, the greater of the amount of chemically adsorbed oxygen on the catalyst and the less durable of B-O link that has the higher of catalytic activity in total oxidation recation of m-xylene. Perovskite of La0.7Sr0.3MnO3 has structural features the best, so it has the highest of catalytic activity in total oxidation recation of m-xylene.

Reducing carbon deposition and enhancing reaction stability by ceria for methane dry reforming over Ni@SiO2@CeO2 catalyst

Low temperature methane dry reforming by Ni-based catalysts is an economic way to convert greenhouse gases of CH4 and CO2, but carbon deposition is a great challenge. Taking the advantage of mobile oxygen on CeO2, we synthesized a Ni@SiO2@CeO2 catalyst by coating ceria on surface of Ni@SiO2 to reduce carbon deposition. H2 temperature-programmed reduction, X-ray photoelectron spectra and oxygen temperature-programmed desorption demonstrated the high oxygen mobility from ceria in Ni@SiO2@CeO2 catalyst, which significantly reduced carbon deposition and enhanced stability of methane dry reforming reaction. Experimental results revealed that methane dry reforming performance was one and a half times higher, but carbon deposition was one half lower, over the Ni@SiO2@CeO2 catalyst than over the Ni@SiO2 catalyst. The strategy of ceria coating in reducing carbon deposition and enhancing reaction stability could also be applied to other heterogeneous reactions suffering carbon deposition.

Enhanced Catalytic Oxidation of Chlorobenzene over MnO2 Grafted In Situ by Rare Earth Oxide: Surface Doping Induces Lattice Oxygen Activation

A series of highly active MnO2@REOx (RE = Gd, Sm, Ce, and La) catalysts were successfully synthesized via in situ growth on the surface of MnO2, wherein the rare earth oxides were planted on the defect sites left by hydrogen peroxide etching of the surface of MnO2. Their physicochemical performance was investigated by scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), N2 adsorption-desorption, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction with hydrogen (H2-TPR), and temperature-programmed desorption of oxygen (O2-TPD). The catalytic properties are compared through the catalytic oxidation of chlorobenzene. Among all catalysts, MnO2@GdOx showed better mobility of surface lattice oxygen and higher molar ratios of Mn4+/Mn3+ (1.10) and Oads/Olatt (0.45), which promoted the superior low-temperature catalytic activity for chlorobenzene oxidation. The long-term chlorobenzene oxidation test (18 h) at different temperatures and the experiments with a mixture of VOCs showed that the as-prepared catalyst not only possessed a high stability but also was suitable for the efficient and simultaneous removal of multicomponent VOCs (toluene, benzene, acetone, and chlorobenzene). This work also provided an idea for the further development of high-efficiency catalysts for the purification of VOCs from complex atmosphere environment.

Highly Uniform Alkali Doped Cobalt Oxide Derived from Anionic Metal-Organic Framework: Improving Activity and Water Tolerance for CO Oxidation

A sequence of alkali metal cation-exchanged Co metal-organic frameworks(Co-MOFs), therein after denoted as M@Co-MOF, M=Na+, K+, Rb+, and Cs+, was prepared and used as the precursors to obtain the corresponding alkali doped cobalt oxide(defined as M/Co3O4, M=Na+, K+, Rb+, and Cs+) through calcination under air atmosphere. The cobalt oxide modified by uniform alkali metals exhibited a significant promotion of catalytic activity for CO oxidation. The activity of M/Co3O4 decreased in the order of Cs+>Na+>K+>Rb+. Experimental and theoretical results revealed that the anionic skeleton of Co-MOF could facilely adsorb alkali metal cations and play a crucial role in the formation of highly uniform alkali doped cobalt oxide. The further characterizations, such as temperature-programmed reduction of H2(H2-TPR), oxygen temperature-programmed desorption(O2-TPD), X-ray photoelectron spectroscopy (XPS), and in situ diffuse reflectance infrared Fourier transform(DRIFT) spectra demonstrated that the enhanced catalytic activity is originated from the interfacial electron transfer as well as weakened the Co— O bond strength, which promoted oxygen desorption from Co3O4 and formation of cobalt species with the lower valence state. The Cs/Co3O4 catalyst was maintained for 60 h without deactivation and still showed a high activity in the presence of water.

Effect of Fe, Ni and Zn dopants in La0·9Sr0·1CoO3 on the electrochemical performance of single-component solid oxide fuel cell

Fe-, Ni- and Zn- doped La0·9Sr0·1CoO3 are prepared and a single-component solid oxide fuel cell composed of 30 wt% perovskite oxide and 70 wt% samarium-doped ceria (SDC)-(Li0·67Na0.33)2CO3 is fabricated and characterized. When doping with either Fe, Ni or Zn, most cations occupy the Co3+ sites. X-ray photoelectron spectroscopy and oxygen temperature-programmed desorption characterizations show that Zn-doped La0·9Sr0·1CoO3 exhibits notably high surface oxygen, causing higher catalytic activity for oxygen reduction reaction (ORR) than that of nondoped La0·9Sr0·1CoO3. Fe or Ni doping into La0·9Sr0·1CoO3 decreases surface oxygen, resulting in a lower catalytic activity toward ORR than La0·9Sr0·1CoO3. Furthermore, X-ray diffraction, temperature-programmed reduction and transmission electron microscopy characterizations prove that after reduction, Fe-doped La0·9Sr0·1CoO3 is reduced to Co0·72Fe0.28 alloy-oxide core-shell nanoparticles, resulting in a high catalytic activity for hydrogen oxygen reaction (HOR). However, NiCo2O4 are formed during the reduction of Ni-doped La0·9Sr0·1CoO3, exhibiting a low catalytic activity for the HOR. Similarly, the low catalytic activity of reduced Zn-doped La0·9Sr0·1CoO3 for the HOR is caused by the formation of ZnCo2O4. A single component fuel cell composed with Fe-doped La0·9Sr0·1CoO3-SDC-(Li0·67Na0.33)2CO3 exhibits the highest Pmax of 239.1 mW cm−2 at 700 °C with H2 as fuel, indicating that HOR processes are rate-determining steps.

Cu-Mn-Ce mixed oxides catalysts for soot oxidation and their mechanistic chemistry

A series of flower-like CuxMnyCez mixed oxides catalysts for soot removal were prepared via a facile co-precipitation approach followed by calcination. The structural and surface properties of these catalysts were investigated by powder X-ray diffraction, N2 physisorption, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, oxygen temperature-programmed desorption and NO temperature-programmed oxidation. Superior soot oxidation performance was obtained over these ternary mixed oxides catalysts and the corresponding mechanism was explored. In particular, the Cu1Mn1Ce1 catalyst showed a remarkable improvement in soot oxidation activity in both NO + O2 and O2 atmospheres. The reusability and durability of these catalysts were assessed, and these materials showed high soot oxidation activity after the hydrothermal stability test.

Enhanced selective catalytic reduction of NO with CO over Cu/C nanoparticles synthetized from a Cu-benzene-1,3,5-tricarboxylate metal organic framework by a continuous spray drying process

Cu-benzene-1,3,5-tricarboxylate (BTC), Cu-BTC (FNP), and Cu-BTC (SD) precursors were prepared by direct mixing (DM), flash nanoprecipitation (FNP) and spray drying (SD), respectively. The precursors were pyrolyzed under nitrogen to obtain the corresponding Cu/C-DM, Cu/C-FNP, and Cu/C-SD catalysts. The physicochemical and catalytic properties of these samples were characterized by scanning electron microscopy (SEM), N2 adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, electronic paramagnetic resonance (EPR), temperature-programmed reduction with hydrogen (H2-TPR), temperature-programmed desorption of oxygen (O2-TPD), and CO + NO model reactions. Regarding the CO + NO model reactions, the Cu/C-SD catalyst exhibited the best denitrification performance, reaching complete NO conversion and N2 selectivity of 98.8% at 300 °C. The Cu/C-SD catalyst removed 88.1% of the initial NO at temperatures as low as 200 °C, being this value was significantly higher than those obtained by Cu/C-DM (2.6%) and Cu/C-FNP (10.2%) catalysts. The Cu/C-SD catalyst also showed excellent stability in the independent presence of O2 (5 vol%), H2O (5 vol%) or SO2 (100 ppm). The Cu1+/Cu0 ratio played a key role in the selective NO catalytic reduction process. The larger specific surface area of the Cu/C-SD catalyst and its ability for the reduction and desorption of oxygen chemically adsorbed has a positive impact on the catalytic performance of this material. These results were theoretically supported by a DFT analysis.

Supported Gold Nanoparticles as Catalysts in Peroxidative and Aerobic Oxidation of 1-Phenylethanol under Mild Conditions.

The efficiency of Au/TiO2 based catalysts in 1-phenylethanol oxidation was investigated. The role of support modifiers (La2O3 or CeO2), influence of gold loading (0.5% or 4%) and redox pretreatment atmosphere, catalyst recyclability, effect of oxidant: tert-butyl hydroperoxide (TBHP) or O2, as well as the optimization of experimental parameters of the reaction conditions in the oxidation of this alcohol were studied and compared with previous studies on 1-octanol oxidation. Samples were characterized by temperature-programmed oxygen desorption (O2-TPD) method. X-ray photoelectron spectroscopy (XPS) measurements were carried out for used catalysts to find out the reason for deactivation in 1-phenylethanol oxidation. The best catalytic characteristics were shown by catalysts modified with La2O3, regardless of the alcohol and the type of oxidant. When O2 was used, the catalysts with 0.5% Au, after oxidative pretreatment, showed the highest activity in both reactions. The most active catalysts in 1-phenylethanol oxidation with TBHP were those with 4% Au and the H2 treatment, while under the same reaction conditions, 0.5% Au and O2 treatment were beneficial in 1-octanol oxidation. Despite the different chemical nature of the substrates, it seems likely that Au+(Auδ+) act as the active sites in both oxidative reactions. Density functional theory (DFT) simulations confirmed that the gold cationic sites play an essential role in 1-phenylethanol adsorption.

Effect of Nd-incorporation and K-modification on catalytic performance of Co3O4 for N2O decomposition

Nd-Co3O4 catalysts were prepared by hydrothermal and co-precipitation methods to catalyze the decomposition of N2O. The catalysts prepared by hydrothermal method showed higher activity. Among the hydrothermal Nd-Co3O4 catalysts, the catalyst with Nd/Co molar ratio of 0.01 had higher activity. 0.01Nd-Co3O4 catalyst was then impregnated by K2CO3 solution to prepare K-modified catalyst. The catalysts were characterized by means of X-ray diffraction (XRD), nitrogen physisorption, scanning electrons microscopy (SEM), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), and oxygen temperature-programmed desorption (O2-TPD). The results show that Nd-Co3O4 and K-modified catalysts exhibit spinel structure. In contrast to bare Nd-Co3O4, the K-modified catalyst with higher activity is due to its weaker strength of Co–O bond and easier desorption of surface oxygen species. In addition, over 90% conversion of N2O can be reached over 0.02K/0.01Nd-Co3O4 at 350°C for 40 h under the co-presence of oxygen and steam in feed gases.

Highly dispersed Pd/modified-Al2O3 catalyst on complete oxidation of toluene: Role of basic sites and mechanism insight

Noble metal catalysts face high cost and limited resources challenge. Developing a high efficiency catalyst with low noble metal loading is an important way to meet this challenge. In this study, Mg-, Ba- and Zr-doped Pd/Al2O3 catalysts with Pd loading of 0.5 wt% were prepared by stepwise wet impregnation method and used for complete oxidation of toluene. These catalysts were characterized by powder X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), CO chemisorption, hydrogen temperature-programmed reduction (H2-TPR), temperature-programmed desorption of CO2 (CO2-TPD) and temperature-programmed desorption of oxygen (O2-TPD). Catalytic reaction of toluene and isopropyl alcohol were carried out in a fixed bed micro-reactor under the condition of GHSV = 24,000 ml h−1gcat−1 with 500 ppm toluene or isopropyl alcohol. The results of XRD, Raman and XPS revealed that PdO is the major species in all of the catalysts. The size of PdO remarkably decreased on MgO-doped Al2O3 surface. The results of H2 temperature-programmed reduction and O2 temperature-programmed desorption indicated that the reducibility of PdO and the active oxygen species were enhanced by doping basic element. In situ diffusion reflectance-infrared Fourier transform spectroscopy proved that benzaldehyde and carboxylates were the intermediate products of toluene oxidation. The results of X-ray photoelectron spectroscopy on used catalysts demonstrated that many more Pd2+ species were detected in Pd/MgO-Al2O3 sample, suggesting that a Pd2+/Pd0 pairs was formed which is favored to the combustion of toluene. The results show that the catalytic performance of Pd/Al2O3 was promoted by modifying basic oxides in the order of Pd/MgO-Al2O3 > Pd/BaO-Al2O3 > Pd/ZrO2-Al2O3 > Pd/Al2O3. The catalytic activity of 0.5 wt% Pd/MgO (2.0 wt%)-Al2O3 was similar with that of 1.0 wt% Pd/Al2O3.

Facile synthesis of ceria–zirconia solid solutions with cubic–tetragonal interfaces and their enhanced catalytic performance in diesel soot oxidation

The rational design of a catalyst interface is crucial for the improvement of catalytic performance. Here, a CeO2–ZrO2 solid solution catalyst with cubic–tetragonal interfaces, CeO2–ZrO2(C-T), was synthesized using a solvothermal method. The catalytic performance of the prepared CeO2–ZrO2(C-T) catalyst in soot oxidation was compared with that of the current commercial CeZrLaPrOx and CeO2–ZrO2 soot oxidation catalysts; meanwhile, the catalysts were characterized systematically. X-ray diffraction and Raman spectroscopy results imply that cubic and tetragonal structures coexist, and the amounts of these phases are approximately equal (C/T = 41/59) in the synthesized CeO2–ZrO2(C-T) catalyst. Transmission electron microscopy images clearly demonstrate the presence of many cubic–tetragonal interfaces in the CeO2–ZrO2(C-T) catalyst. The prepared CeO2–ZrO2(C-T) catalyst has markedly better catalytic activity for soot oxidation than the commercial CeO2–ZrO2-based catalysts. This result is influenced by the existence of cubic-tetragonal interfaces in CeO2-ZrO2(C-T). X-ray photoelectron spectroscopy and oxygen temperature-programmed desorption results further indicate that the cubic–tetragonal interfaces in the synthesized CeO2–ZrO2(C-T) catalyst promote the production of structural defects (oxygen vacancies) and the release of surface lattice oxygen in the CeO2–ZrO2 solid solutions. The oxygen vacancies play a key role in the activation of gaseous oxygen to form active oxygen species (Ox- species) for soot oxidation, and the lattice oxygen atoms also play a favorable role in the creation of highly active Ox- species. The surface-active Ox- species created by the surface lattice oxygen can immediately contact the soot and then rapidly promote the oxidation reaction. Hence, this work suggests that the cubic–tetragonal interfaces present in CeO2–ZrO2 solid solutions are also a relevant factor contributing to their excellent catalytic performance in diesel soot oxidation.

Temperature Programmed Oxygen Desorption and Sorption Processes on Pr2-XLaxNiO4+ δ Nickelates

The present work is devoted to the investigation of temperature programmed oxygen desorption - sorption (TPD) processes performed on SOFC innovative cathode materials with Pr2-xLaxNiO4+δ composition. The experiments were performed using the coulometric titration technique involving an OXYLYT™ device, over the temperature cycle 20 – 900 – 20 °C. The considered parameters were the time and temperature dependences of both the titration current and the oxygen over-stoichiometry. TPD spectra of Pr2-xLaxNiO4+δ (x ≠ 0) exhibited two sharp peaks (maxima) of titration current with excellent resolution at p(O2) = 50 Pa, induced by removal of oxygen from different sites of the crystal lattice. TPD spectrum of Pr2NiO4+δ recorded under the same conditions drastically differs from the spectra of Pr2-xLaxNiO4+δ as four sharp maxima of titration current are detected. The TPD spectra of Pr2-xLaxNiO4+δ then strongly depend on the nature of the rare-earth (La or Pr) in link with the oxygen over-stoichiometry amount.

Effect of praseodymium substitution on La1-xPrxMnO3 (x=0–0.4) perovskites and catalytic activity for NO oxidation

La1-xPrxMnO3(x = 0, 0.05, 0.1, …, 0.4) perovskites were prepared readily via citric acid sol–gel method in the present study. Several characterization techniques have been employed, such as X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), Brunauer-Emmett-Teller (BET), N2 adsorption–desorption analyses, Oxygen temperature-programmed desorption (O2-TPD), Hydrogen temperature-programmed reduction (H2-TPR) and NO temperature-programmed desorption (NO-TPD), with the aim of exploring the effects of Pr substitution. Then the samples were submitted to activity test in catalytic NO oxidation. NO conversion was improved with the increase of Pr substitution when x ≤ 0.2, and then decreased with further addition of Pr. The most excellent catalytic activity with NO conversion of 91% at 260 °C was observed on La0.8Pr0.2MnO3. It was revealed that the appropriate Pr addition (x ≤ 0.2) at A-site led to the modified reducibility of LaMnO3, as well as the increased molar ratio of Mn4+/Mn3+ and Oads/Ototal, which was benificial for NO oxidation. Moreover, the increase of NO adsorption amount and the shift of the decomposition temperature of nitrates to lower temperautre with the aid of appropriate Pr component accounted for the enhanced activity.

New Insights into Excellent Catalytic Performance of the Ce-Modified Catalyst for NO Oxidation

Diesel exhaust has recently become a severe problem, and diesel oxidation catalyst (DOC) installed in the diesel exhaust treatment system is used to reduce automobile pollution containing CO, hydrocarbons (HC), and NO. In this work, for the purpose of elucidating the effect of ceria addition on the catalytic performance of Pt-based DOC in CO, HC, and NO oxidation reactions, a range of catalysts were prepared by impregnation method. Among them, the Pt/15CeSA catalyst showed excellent catalytic activity, and its NO maximum conversion could reach 62%. The experimental results of X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) confirmed that the interface Pt–O–Ce–O–Al existed in the Pt/15CeSA catalyst. Besides, more oxygen vacancies were created at this interface, which were confirmed by oxygen temperature-programmed desorption (O2-TPD) and Raman spectroscopic experiments, resulting in an outstanding catalytic performance of Pt/15CeSA. It is expected our res...

Catalytic decomposition of N2O over Y-Co3O4 composite oxides prepared by one-step hydrothermal method

Abstract Y-Co3O4 catalysts with Y/Co molar ratio of 0.03 were prepared by several methods, such as one-step hydrothermal, two-step hydrothermal, and impregnation methods, to catalyze the decomposition of N2O. Among these catalysts, the one prepared by one-step hydrothermal method exhibited the highest activity, and then the Y-Co3O4 catalysts with various molar ratios of Y/Co were synthesized by one-step hydrothermal method. Subsequently, the optimized 0.03Y-Co3O4 was impregnated by K2CO3 solution to prepare K-modified catalyst and named as 0.02K/0.03Y-Co3O4. These catalysts were characterized by X-ray diffraction (XRD), nitrogen physisorption, hydrogen temperature-programmed reduction (H2-TPR), oxygen temperature-programmed desorption (O2-TPD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques. The results show that both Co3O4 and Y-Co3O4 exhibit spinel structure, however Y-doped Co3O4 catalysts are more active than bare Co3O4. After further modified by potassium, the 0.02K/0.03Y-Co3O4 reveals higher activity due to the more active sites (Co2+) and easier desorption of surface oxygen species than un-modified 0.03Y-Co3O4. In detail, the temperatures of N2O full conversion over 0.02K/0.03Y-Co3O4 catalyst are 325, 350, 375°C, under the reaction atmospheres of 1%N2O+Ar, 1%N2O+2%O2+Ar, 1%N2O+2%O2+8.2%H2O+Ar, respectively. In addition, over 90% conversion of N2O can be maintained at 350°C after continuous reaction for 50 h in the co-presence of oxygen and steam on K-modified Y-Co3O4 catalyst. There is a dynamic compensation effect between apparent activation energy (Ea) and pre-exponential factor (A) in N2O decomposition over Y-Co3O4 and K-modified catalysts.