Jiaxiu Guo

CeO2-ZrO2-La2O3-Al2O3 composite oxide and its supported palladium catalyst for the treatment of exhaust of natural gas engined vehicles

Abstract Composite supports CeO2-ZrO2-Al2O3 (CZA) and CeO2-ZrO2-Al2O3-La2O3 (CZALa) were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and NOx in the mixture gas simulated the exhaust from natural gas vehicles (NGVs) operated under stoichiometric condition was investigated. The effect of La2O3 on the physicochemical properties of supports and catalysts was characterized by various techniques. The characterizations with X-ray diffraction (XRD) and Raman spectroscopy revealed that the doping of La2O3 restrained effectively the sintering of crystallite particles, maintained the crystallite particles in nanoscale and stabilized the crystal phase after calcination at 1000 °C. The results of N2-adsorption, H2-temperature-programmed reduction (H2-TPR) and oxygen storage capacity (OSC) measurements indicated that La2O3 improved the textural properties, reducibility and OSC of composite supports. Activity testing results showed that the catalysts exhibit excellent activities for the simultaneous removal of methane, CO and NOx in the simulated exhaust gas. The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the three pollutants, especially for NOx. The prepared palladium catalysts have high ability to remove NOx, CH4 and CO, and they can be used as excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition. The catalysts reported in this work also have significant potential in industrial application because of their high performance and low cost.

Effect of BaO on Catalytic Activity of Pt-Rh TWC

Abstract The effects of BaO doping on the three-way catalytic activity of Pt-Rh catalyst and on water-gas shift were investigated. The results show that the light-off temperatures of hydrocarbon and carbon monoxide and nitrogen oxides of the fresh catalysts slightly differ from those of the aged catalysts, and the catalysts containing CeO 2 -ZrO 2 BaO have lower light-off temperature and better catalytic activity than these containing BaO and CeO 2 -ZrO 2 after hydrothermal aging for 5 h at 1000 °C. The catalysts were characterized by means of the temperature-programmed reduction (TPR) in hydrogen and the temperature-programmed desorption (TPD) in oxygen. It is confirmed that the suggested route of CeO 2 -ZrO 2 -BaO by coprecipitation can improve the catalytic activity of catalysts.

Influence of Ce0.35Zr0.55Y0.10 Solid Solution on Peroformance of Pt-Rh Three-Way Catalysts

Abstract Ce 0.35 Zr 0.55 Y 0.10 solid solution was prepared by co-precipitation technique and characterized by specific surface area measurements (BET) and X-ray diffraction (XRD). Ce 0.35 Zr 0.55 Y 0.10 was used to prepare low Pt-Rh three-way catalyst (TWC), and its influence on the performance of TWC was investigated. The results revealed that Ce 0.35 Zr 0.55 Y 0.10 had a cubic structure similar to Ce 0.50 Zr 0.50 O 2 and its specific surface area can maintain higher than Ce 0.50 Zr 0.50 O 2 after 1000 °C calcination for 5 h. Being hydrothermal aged at 1000 °C for 5 h, the catalyst containing Ce 0.35 Zr 0.50 Y 0.10 still exhibited higher conversion of C 3 H 3 , CO and NO and lower light-off temperature in comparison with Ce 0.50 Zr 0.50 O 2 TWC.

Influence of Ce0.35Zr0.55La0.10O1.95 Solid Solution on the Performance of Low Pt-Rh Three-way Catalysts

Abstract Ce 0.35 Zr 0.55 La 0.10 O 1.95 solid solution was prepared by coprecipitation technique and characterized by specific surface area measurements (BET), X-ray diffraction (XRD), and temperature-programmed (TP) technique. Ce 0.35 Zr 0.55 La 0.10 O 1.95 was used to prepare low Pt-Rh three-way catalyst (TWC) and its influence on the performance of TWC was investigated. The results showed that Ce 0.35 Zr 0.55 La 0.10 O 1.95 had a cubic structure similar to Ce 0.50 Zr 0.50 O 2 and a large specific area after calcined at 600 °C for 5 h. Furthermore, after being aged at 1000 °C for 5 h, Ce 0.35 Zr 0.55 La 0.10 O 1.95 still maintained a stable cubic structure and a specific surface area of 47.25 m 2 ·g −1 . The results of H 2 -TPR and O 2 -TPO indicated that Ce 0.35 Zr 0.55 La 0.10 O 1.95 had good redox properties. The catalyst containing Ce 0.35 Zr 0.55 La 0.10 O 1.95 possessed a fairly wide range of three-way working-windows, good low-temperature light-off properties, and better ability of water-gas shift. Being hydrothermally aged at 1000 °C, the catalyst containing Ce 0.35 Zr 0.55 La 0.10 O 1.95 still showed good catalytic activity in comparison with Ce 0.50 Zr 0.50 O 2 TWC, which indicated that Ce 0.35 Zr 0.55 La 0.10 O 1.95 improved the anti-aging properties of the catalyst.采用共沉淀技术制备了Ce0．35Zr0．55La0．10O1．95固溶体，其织构和结构性能以及氧化还原性能分别采用BET、XRD和程序升温（TP）技术进行了表征．制备了低贵金属Pt-Rh型三效催化剂，考察了Ce0．35Zr0．55La0．10O1．95对催化剂性能的影响．XRD和BET的结果表明，经600℃焙烧5h后，Ce0．35Zr0．55La0．10O1．95具有与Ce0.50Zr0.50O2相似的立方结构和高的比表面积；经1000℃焙烧5h后，仍能保持稳定的立方结构和47．25m^2·g^-1的比表面积，表现出优越的织构性能和高的热稳定性．H2-TPR和O2-TPO的结果表明，Ce0．35Zr0．55La0．10O1．95具有比Ce0.50Zr0.50O2更好的氧化还原性能．和含Ce0.50Zr0.50O2的催化剂相比，含Ce0.35Zr0.55La0.10O1.95的催化剂具有较宽的工作窗口，优越的低温起燃性能，较强的水气变换能力；催化剂经1000℃高温水热老化5h后，仍具有良好的催化活性，表现出了优异的抗老化性能．

Effects of preparation conditions on Mn-based activated carbon catalysts for desulfurization

A series of Mn-based activated carbon catalysts were prepared by excessive impregnation with or without ultrasonic assistance, and manganese (Mn) species and surface chemical properties of catalysts before and after SO2 removal were studied. The results showed that different preparation conditions significantly influence the desulfurization activity of Mn-based activated carbon catalysts. The breakthrough sulfur capacity of 5FMn/ACA36 prepared by ultrasonic assisted excessive impregnation is 73.0 mg g−1, while that of 5FMn/ACN36 increases to 126.1 mg g−1. The catalysts exhibit different desulfurization activities when carbon carriers are pretreated with nitric acid at different concentrations, and with the increase of concentrations, the breakthrough sulfur capacity of catalysts increases from 118.1 to 141.6 mg g−1. Catalysts calcined at different temperatures show different desulfurization activities. Both 5FMn/ACW and 5Mn/ACW calcined at 800 °C have the best desulfurization activity, but 5FMn/ACN36 and 5Mn/ACN36 calcined at 650 and 800 °C are similar. The optimal loading of catalysts prepared by excessive impregnation is 7%, but that of catalysts prepared by ultrasonic assisted excessive impregnation is 0.5%. Nitric acid pretreatment can change surface chemical properties and reduce the formation temperature as well as the crystalline size of Mn oxide species such as MnO and Mn3O4. The introduction of ultrasonic oscillation cannot change active species and oxygen-containing functional groups (such as C–O, CO and OC–OH) but reduce the active component content to enhance the activity. Mn loading influences the content of active components and oxygen-containing functional groups on carbon supports, leading to a different desulfurization activity. After SO2 removal, MnO, Mn2O3 and Mn3O4 are still observed, but some of them transform into MnO2 with low crystallinity, and some react with generated H2SO4 to form MnSO4, resulting in catalyst deactivation. Types of oxygen-containing functional groups after SO2 removal remain the same but the relative contents decrease, showing that they participate in the reaction of SO2 removal.

Low temperature selective catalytic reduction of NO by C3H6 over CeOx loaded on AC treated by HNO3

Abstract The activated carbons from coal were treated by HNO 3 (named as NAC) and used as carriers to load 7% Ce (named as Ce(0.07)/NAC) by impregnation method. The physical and chemical properties were investigated by thermogravimetric-differential thermal analysis (TG-DTA), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM) and NH 3 -temperature programmed desorption (NH 3 -TPD) and NO-temperature programmed desorption techniques. The catalytic activities of Ce(0.07)/NAC were evaluated for the low temperature selective catalytic reduction (SCR) of NO with C 3 H 6 using temperature-programmed reaction (TP-reaction) in NO, C 3 H 6 , O 2 and N 2 as a balance. The results showed that the specific surface area of Ce(0.07)/NAC was 850.8 m 2 /g and less than NAC, but Ce oxides could be dispersed highly on the activated carbons. Ce oxides could change acid sites and NO adsorption as well as oxygen-containing functional groups of activated carbons, and Ce 4+ and Ce 3+ coexisted in catalysts. The conversion of NO with C 3 H 6 achieved 70% at 280 °C over Ce(0.07)/NAC, but with the increase of O 2 concentration, heat accumulation and nonselective combustion were exacerbated, which could cause surface ashing and roughness, resulting in a sharp decrease of catalytic activities. The optimum O 2 concentration used in the reaction system was 3% and achieved the high conversion of NO and the widest temperature window. The conversion of NO was closely related to the NO concentrations and [NO]/[C 3 H 6 ] ratios, and the stoichiometric number was just close to 2:1, but the presence of H 2 O could affect the denitration efficiency of catalyst.

Influence of Fe loadings on desulfurization performance of activated carbon treated by nitric acid

ABSTRACT A series of Fe supported on activated carbon treated by nitric acid are prepared by incipient wetness impregnation with ultrasonic assistance and characterized by N2 adsorption–desorption, X-ray diffraction, Fourier transform infrared spectrum and X-ray photoelectron spectroscopy. It has shown that Fe loadings significantly influence the desulfurization activity. Fe/NAC5 exhibits an excellent removal ability of SO2, corresponding to breakthrough sulfur capacity of 323 mg/g. With the increasing Fe loadings, the generated Fe3O4 and Fe2SiO4 increase, but Fe2(SO4)3 is observed after desulfurization. Fe/NAC1 has a Brunauer–Emmett–Teller (BET) surface area of 925 m2/g with micropore surface area of 843 m2/g and total pore volume of 0.562 cm3/g including a micropore volume of 0.300 cm3/g. With the increasing Fe loadings, BET surface area and micropore volume decrease, and those of Fe/NAC10 decrease to 706 m2/g and 0.249 cm3/g. The Fe loadings influence the pore-size distribution, and SO2 adsorption mainly reacts in micropores at about 0.70 nm. C=O and C–O are observed for all samples before SO2 removal. After desulfurization, the C–O stretching is still detected, but the C=O stretching vibration of carbonyl groups disappears. The stretching of S–O or S=O in sulfate is observed at 592 cm−1 for the used sample, proving that the existence of .

Microstructure of epitaxial VO[sub 2] thin films deposited on (11[bar 2]0) sapphire by MOCVD

Epitaxial VO[sub 2] thin films grown on (11[bar 2]0) sapphire ([alpha]--Al[sub 2]O[sub 3]) substrates by MOCVD at 600 [degree]C have been characterized by conventional electron microscopy and high resolution electron microscopy (HREM). Three different epitaxial relationships between the monoclinic VO[sub 2] films and sapphire substrates have been found at the room temperature: (I) (200)[010] monoclinic VO[sub 2]//(11[bar 2]0)[0001] sapphire; (II) (002)[010] monoclinic VO[sub 2]//(11[bar 2]0)[0001] sapphire; and (III) (020)[102] monoclinic VO[sub 2]//(11[bar 2]0)[0001] sapphire. Epitaxial relationships II and III are equivalent to each other when the film possesses tetragonal structure at the deposition temperature: i.e., they can be described as (010)[100] tetragonal VO[sub 2]//(11[bar 2]0)[0001] sapphire and (100)[010] tetragonal VO[sub 2]//(11[bar 2]0)[0001] sapphire. HREM image shows that the initial nucleation of the film was dominated by the first orientation relationship, but the film then grew into the grains of the second and the third (equivalent to each other at the deposition temperature) epitaxial relationships. Successive 90[degree] transformation rotational twins around the [ital a]-axis are commonly observed in the monoclinic films.

Structure Evolution Process of Ce0.65Zr0.25Y0.1O1.95 Prepared by Oxidation-Coprecipitation Method

以氨水和碳酸铵为沉淀剂，采用氧化-共沉淀法制备了Ce0.65Zr0.25Y0.1O1．95 复合氧化物，并对不同处理温度下制备的样品用热重-差示扫描分析（TG—DSC）、傅里叶变换红外（FT-IR）光谱、X射线衍射（XRD）和表面分析仪（BET）等进行了表征。结果表明，共沉淀法得到的沉淀物同时含有羟基和羧基，随着焙烧温度的升高，分别在100—170℃、250-300℃和420—500℃温度范围内先后发生脱水、脱羟基和脱羧基反应，在此过程中固溶体逐渐形成。提出了由沉淀物转变为Ce0.65Zr0.25Y0.1O1．95复合氧化物的结构转变模型。Abstract Ce0.65Zr0.25Y0.1O1.95 oxides were prepared by oxidation-coprecipitation method using ammonia and salvolatile as precipitators. The as-prepared samples were thermally treated at different temperatures and characterized by thermogravimetry-differential scanning calorimetry (TG-DSC), Fourier transform-infrared (FT-IR) spectrometry, X-ray diffraction (XRD), and specific surface area measurements (BET). The results showed that the hydroxyl and carboxyl groups coexisted in the precipitate and a perfect solid solution was gradually formed with an increase in calcination temperature. The physisorbed water was lost from 100 to 170 °C, hydroxyl groups were removed from 250 to 300 °C, and the carboxyl groups were eliminated from 420 to 500 °C. A structure model was further proposed to understand the Ce0.65Zr0.25Y0.1O1.95 structure evolution process in depth.