In-situ UV-Raman study on soot combustion over TiO_2 or ZrO_2-supported vanadium oxide catalysts

UV-Raman spectroscopy was used to study the molecular structures of TiO2 or ZrO2-supported vana-dium oxide catalysts.The real time reaction status of soot combustion over these catalysts was de-tected by in-situ UV-Raman spectroscopy.The results indicate that TiO2 undergoes a crystalline phase transformation from anatase to rutile phase with the increasing of reaction temperature.However,no obvious phase transformation process is observed for ZrO2 support.The structures of supported va-nadium oxides also depend on the V loading.The vanadium oxide species supported on TiO2 or ZrO2 attain monolayer saturation when V loading is equal to 4(4 is the number of V atoms per 100 support metal ions).Interestingly,this loading ratio(V4/TiO2 and V4/ZrO2) gave the best catalytic activities for soot combustion reaction on both supports(TiO2 and ZrO2).The formation of surface oxygen com-plexes(SOC) is verified by in-situ UV Raman spectroscopy and the SOC mainly exist as carboxyl groups during soot combustion.The presence of NO in the reaction gas stream can promote the pro-duction of SOC.     

In-situ UV-Raman study on soot combustion over TiO2 or ZrO2-supported vanadium oxide catalysts

UV-Raman spectroscopy was used to study the molecular structures of TiO₂ or ZrO₂-supported vanadium oxide catalysts. The real time reaction status of soot combustion over these catalysts was detected by in-situ UV-Raman spectroscopy. The results indicate that TiO₂ undergoes a crystalline phase transformation from anatase to rutile phase with the increasing of reaction temperature. However, no obvious phase transformation process is observed for ZrO₂ support. The structures of supported vanadium oxides also depend on the V loading. The vanadium oxide species supported on TiO₂ or ZrO₂ attain monolayer saturation when V loading is equal to 4 (4 is the number of V atoms per 100 support metal ions). Interestingly, this loading ratio (V₄/TiO₂ and V₄/ZrO₂) gave the best catalytic activities for soot combustion reaction on both supports (TiO₂ and ZrO₂). The formation of surface oxygen complexes (SOC) is verified by in-situ UV Raman spectroscopy and the SOC mainly exist as carboxyl groups during soot combustion. The presence of NO in the reaction gas stream can promote the production of SOC.     

铈铁锆三元复合氧化物上碳烟的催化燃烧

采用水热法制备了纯CeO₂、Fe₂O₃和系列Ce₀.5Fe₀.5-xZr_{xO2复合氧化物催化剂,采用XRD、Raman、H2-TPR和BET等方法对其进行了表征,并利用程序升温氧化反应(TPO)技术研究了其碳烟燃烧催化性能。结果表明,Zr⁴+完全进入CeO2晶格中形成了固溶体,而Fe³+较难进入CeO2晶格中,部分Fe2O3分散在固溶体表面。固溶体形成产生的氧空位和表面高度分散的氧化铁协同作用是铈铁锆三元复合氧化物具有较高碳烟燃烧催化性能的关键。同时,与单纯的铈铁二元复合氧化物相比,Zr⁴+的掺杂明显提高了催化剂的抗老化能力,使Ce0.5Fe0.5-xZrxO2复合氧化物显示出更好的应用前景。在系列样品中,Ce0.5Fe0.30Zr0.20O2样品由于形成了最多的固溶体并具有良好分散性的表面Fe2O3,显示出最好的催化活性和稳定性。其催化碳烟的起燃温度(ti)和峰顶温度(tp)分别为251℃和310℃,长时间高温老化后其ti和tp仍较低,分别为273℃和361℃。}     

Catalytic combustion of chlorobenzene over V2O5/TiO2 catalysts prepared by the precipitation-deposition method

Catalytic combustion of chlorobenzene over supported vanadium oxides has been investigated. TiO₂ was prepared by the sol-gel method from titanium isopropoxide. The supported vanadium oxide catalysts have been prepared by precipitation-deposition and impregnation method and characterized by XRD, FT-Raman and TPR. In the VO_x/TiO₂catalysts prepared using the impregnation method, when vanadium loading reaches 3 wt.%, the activity shows a maximum. However, in the VO_x/TiO₂catalysts prepared by precipitation-deposition, when vanadium loading reaches 7 wt.%, the activity shows a maximum. This result suggests that the precipitation-deposition can yield a higher metal loading on the support and a high dispersion compared to the impregnation method. This revised version was published online in August 2006 with corrections to the Cover Date.     

Vapor-phase Beckmann rearrangement of cyclohexanone oxime over B2O3 catalysts supported on TiO2-ZrO2 mixed oxide

A novel catalyst, boria supported on titania-zirconia mixed oxide, exhibits very high catalytic activity and selectivity in vapor-phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam. It gives 99.7% oxime conversion and 97.0% lactam selectivity at 300°C.     

Low temperature complete combustion of dilute propane over Mn-doped ZrO2 (cubic) catalysts

Combustion of dilute propane (0.9 mol%) over Mn-doped ZrO₂ catalysts prepared using different precipitating agents (viz. TMAOH, TEAOH, TPAOH, TBAOH and NH₄OH), having different Mn/Zr ratios (0.05—0.67) and calcined at different temperatures (500—800°C), has been thoroughly investigated at different temperatures (300—500°C) and space velocities (25,000–100,000 cm³ g⁻¹ h⁻¹) for controlling propane emissions from LPG-fuelled vehicles. Mn-doped ZrO₂ catalyst shows high propane combustion activity, particularly when its ZrO₂ is in the cubic form, when its Mn/Zr ratio is close to 0.2 and when it is prepared using TMAOH as a precipitating agent and calcined at 500—600°C. Pulse reaction of propane in the absence of free-O₂ over Mn-doped ZrO₂ (cubic) and Mn-impregnated ZrO₂ (monoclinic) catalysts has also been investigated for studying the relative reactivity and mobility of the lattice oxygen of the two catalysts. Both reactivity and mobility of the lattice oxygen of Mn-doped ZrO₂ are found to be much higher than that of Mnimpregnated ZrO₂. Propane combustion over Mn-doped ZrO₂ catalyst involves a redox mechanism     

Kinetics of methane combustion on Fe2O3/TiO2 catalysts

The objective of this work was to study the kinetics of methane combustion for a series of Fe₂O₃/TiO₂ catalysts. An increase in activity is observed as iron loading increases, and can be attributed to an increase of surface coverage by Fe₂O₃ species. Kinetic studies revealed that the reaction orders with respect to methane, oxygen, carbon dioxide and water are 1, 0, 0 and -1 respectively. This revised version was published online in June 2006 with corrections to the Cover Date.     

High surface area MoO3/TiO2 hydrodesulfurization catalysts

The catalytic combustion of benzene over SBA-15-supported copper oxide has been investigated. The SBA-15-supported copper oxide catalysts have been prepared by the precipitation-deposition method, and characterized by XRD, BET and TPR. In the CuO/SBA-15 catalysts, the catalytic activity increases with increasing copper oxide loading ratio. Metallic Cu is much more active than copper oxides. When the reduction temperature increases to 500°C the benzene conversion increases until the maximum vlaue is obtained. Further increase in the reduction temperature to 600°C results in a decrease of benzene conversion.     

Structural characterization and photocatalytic activity of hollow binary ZrO2/TiO2 oxide fibers

The formation of hollow binary ZrO₂/TiO₂ oxide fibers using mixed precursor solutions was achieved by activated carbon fibers templating technique combined with solvothermal process. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N₂ adsorption, X-ray photoelectron spectroscopy (XPS), UV-vis, and infrared (IR) spectroscopy. The binary oxide system shows the anatase-type TiO₂ and tetragonal phase of ZrO₂, and the introduction of ZrO₂ notably inhibits the growth of TiO₂ nanocrystallites. Although calcined at 575 °C, all hollow ZrO₂/TiO₂ fibers exhibit higher surface areas (>113 m²/g) than pure TiO₂ hollow fibers. The Pyridine adsorption on ZrO₂/TiO₂ sample indicates the presence of stronger surface acid sites. Such properties bring about that the binary oxide system possesses higher efficiency and durable activity stability for photodegradation of gaseous ethylene and trichloromethane than P25 TiO₂. In addition, the macroscopic felt form for the resulting materials is more beneficial for practical applications than traditional catalysts forms.     

Bi2Ti2O7/TiO2复合纤维：原位水热合成及光催化性能

采用静电纺丝技术制备的TiO2纤维作为模板和反应物,通过原位水热合成了具有异质结构的Bi2Ti2O7/TiO2复合纤维。利用X射线衍射(XRD)、扫描电镜(SEM)、能量散射光谱(EDS)、高分辨透射电镜(HRTEM)和紫外可见吸收光谱(UV-Vis)等分析测试手段对样品的结构和形貌进行表征。以罗丹明B为模拟有机污染物进行光催化降解实验。结果表明:花状Bi2Ti2O7纳米结构均匀地生长在TiO2纤维上,制备了Bi2Ti2O7与TiO2相复合的光催化材料,其光谱响应范围拓宽至可见光区,与纯TiO2纤维相比可见光催化活性显著提高,且易于分离、回收和循环使用。初步探讨了Bi2Ti2O7/TiO2异质结的生长机制和光催化活性提高机理。     

Oxidative dehydrogenation of propane over chromium and nickel oxide modified V2O5/ZrO2 catalysts

The effect of addition of chromium and nickel oxides on the physicochemical properties and performance of V₂O₅/ZrO₂ catalysts was studied for the oxidative dehydrogenation of propane. Addition of chromium oxide increased, whereas addition of nickel oxide lowered the activity. Selectivity for propene was lower for the doped catalysts. The selectivity was lowered by higher total acidity as well as the higher concentration of stronger acid sites in doped catalysts.     

A new kinetic model of photocatalytic degradation of formic acid in UV/TiO2 suspension system with in-situ monitoring

The results show that a newly developed kinetic model can successfully explain the photocatalytic kinetics of formic acid in UV/TiO₂ suspension system with in-situ monitoring and the apparent rate constant (k) is affected by the initial concentrations of formic acid, amounts of TiO₂, UV intensity and pH.     

SnO_2改性TiO_2对V_2O_5-WO_3/TiO_2催化剂结构和SCR性能影响

采用共沉淀法将SnO_2组分掺入到V_2O_5-WO_3/TiO_2催化剂载体TiO_2中,并通过多种物理化学手段,考察了不同SnO_2掺入量时对催化剂结构,表面分散物种和SCR性能影响.结果表明,SnO_2掺入到TiO_2中,元素Sn与Ti以Sn—O—Ti键形式相互作用,促进锐钛矿型TiO_2向金红石型TiO_2转变.在特定条件下,VO_x与WO_x物种和SnTi氧化物之间以V—O—Ti(Sn)和W—O—Ti(Sn)键形式相互作用,提高了VO_x物种可还原能力、促进了具有更多B酸酸量四面体WOx物种和V~(5+)物种生成.VW/SnTi催化剂表面VO_x物种与WO_x物种之间的相互作用更强.因此,VW/SnTi催化剂具有更好的SCR活性.     

Catalytic Performance of Re/Ga2O3/WO3/ZrO2 Catalyst for n-Hexane Isomerization

A series of Re/Ga₂O₃/WO₃/ZrO₂ catalysts were prepared by the impregnation method. The crystalline structure, redox, and acid site distribution of the catalysts were characterized by X-ray powder diffraction, temperature-programmed reduction of H₂, and temperature-programmed desorption of NH₃. Their catalytic performance for n-hexane isomerization was studied. The results showed that the addition of Re greatly affected the redox properties and the acid site distribution of the catalysts. Owing to the presence of Re, n-hexane isomerization was catalyzed by metal and acid sites, and thus the conversion of n-hexane and the selectivity for 2,2-dimethylbutane were significantly increased. Under the conditions of 195 °C, 1.0 MPa, LHSV = 1.0 h⁻¹, and n(H₂)/n(C₆) = 2.0, the conversion of n-hexane over 1.0%Re/1.0%Ga₂O₃/WO₃/ZrO₂ is 84.8%, and the selectivities for 2,2-dimethylbutane, i-hexane, and cracking products (C_5-) are 20%, 97.7%, and 2.1%, respectively. The catalyst is stable during 150 h operation.     

Diesel soot combustion. KNO3 and KOH catalysts supported on zirconia

KNO₃/ZrO₂ and KOH/ZrO₂ catalysts were studied and found active in the catalytic soot combustion. Two equipments were used to carry out the combustion experiments: a thermogravimetric reactor with an O₂/He feed and a fixed bed microreactor with NO/O₂/He feed.     

Influence of Nox on soot combustion with supported molten salt catalysts

Diesel soot is combusted simultaneously by two reactions: combustion with NO₂ and combustion with O₂ with the aid of a molten salt catalyst. Both reaction pathways should always be considered to avoid misinterpretation of experimental data.     

Usy supported Pt-bearing SO42?/ZrO2 catalysts promoted by Cr for hydroisomerization of n -heptane

The Pt-bearing SO₄ ²⁻/ZrO₂ catalysts doped with Cr and supported on USY zeolite were prepared by impregnation, and characterized by XRD and IR spectroscopy of pyridine adsorption. Their catalytic activities were evaluated in the hydroisomerization of n-heptane with a fixed-bed atmospheric reactor. The Cr-promoted catalysts exhibited much higher catalytic activity and selectivity for isomerization products than the catalysts without the Cr dopant. Both the conversion and selectivity were discussed in relation with the physicochemical properties of catalysts.     

碳纳米管上原位沉积钯-钴-镍纳米颗粒及其对乙醇氧化的电活性

以水合肼为还原剂,在水和乙醇的混合溶液中制备多壁碳纳米管(MWCNT)负载的纳米镍(Ni/MWCNT)和纳米镍钴(Ni-Co/MWCNT)颗粒,然后将它们分别与氯化钯溶液反应,形成的钯纳米颗粒原位沉积在MWCNT表面,从而得到MWCNT负载的Pd-Ni/MWCNT和Pd-Ni-Co/MWCNT催化剂。SEM和TEM图像显示,MWCNT上的催化剂颗粒是由5~10 nm的小颗粒团聚而成的30~100 nm的大颗粒,三金属催化剂的粒径比双金属的粒径小,在MWCNT上的分散度更高。ICP和EDS分析显示,Pd直接还原并包覆在纳米镍和纳米镍钴表面;采用循环伏安和计时电流技术,研究了催化剂在碱性溶液中对乙醇氧化的电催化活性,结果表明,Pd-Ni-Co/MWCNT催化剂对乙醇氧化具有强的电催化活性,乙醇氧化对应的峰电流密度达101.8 mA·cm^-2,并且催化剂催化活性稳定。     

Acidic properties of V2O5-WO3/ZrO2 catalysts

The adsorption of pyridine on V₂O₅−WO₃/ZrO₂ has been studied by FTIR. In V₂O₅/ZrO₂ (2 wt.%), the number of both Br?nsted and Lewis acidic sites increased with the addition of WO₃, while in V₂O₅/ZrO₂ (5 wt.%), Br?nsted sites increased and Lewis sites did not change.     

硫中毒对Co3O4/CeO2复合氧化物上炭黑催化燃烧的影响

采用共沉淀法制备了CeO₂,Co₃O₄和一系列Co₃O₄/CeO₂复合氧化物催化剂,在400 ℃下含SO₂的氧化气氛中对催化剂进行了硫中毒处理,通过原位红外光谱、X射线衍射、程序升温脱附和X射线光电子能谱对新鲜和硫中毒的样品进行了表征. 结果表明,所有测试的硫中毒样品上均形成了硫酸盐,CeO₂上累积的硫酸盐明显比Co₃O₄上的多,Co₃O₄/CeO₂复合氧化物在硫中毒过程中形成了硫酸钴和硫酸铈. 对新鲜和硫化样品在NO/O₂气氛下进行了催化炭黑燃烧实验,发现Co₃O₄/CeO₂复合氧化物的活性和抗硫性能优于CeO₂,但抗硫性能低于Co₃O₄.