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.     

CeO2改性Ag-V2O5/TiO2催化剂的甲基吡啶氧化脱甲基性能

以锐钛矿TiO_2为载体,考察了CeO_2改性对Ag-CeO_2-V_2O_5/TiO_2催化3-甲基吡啶氧化脱甲基性能的影响,并优化了催化剂组成与制备条件.结果表明:Ce掺杂改性不仅能够与V物种作用形成Ce VO_4,而且促进V_2O_5分散,改善活性组分的氧化还原性能,从而提高3-甲基吡啶脱甲基转化率与选择性,改善Ag-V_2O_5/TiO_2催化性能.适宜的催化剂组成为V_2O_5负载量15%,Ce/V的摩尔比0.33,Ag质量分数1.0%.过高的焙烧温度将导致TiO_2载体向金红石型转变,Ag-CeO_2-V_2O_5/TiO_2适宜制备条件为450℃焙烧4 h.     

邻二甲苯氧化制苯酐催化剂的研究I.V2O5-TiO2的组成、物性和反应性能

用XPS,IR,TG和脉冲色谱法考察了V_2O_5-TiO_2复合氧化物催化剂中V_2O_5与TiO_2的相互作用,V_2O_5的分散状态和释氧活性,以及催化剂对邻二甲苯氧化的活性和生成苯酐的选择性。阐明了该催化剂组成对活性和选择性的影响。XPS和TG结果表明,V_2O_5含量<10wt%时,它与TiO_2可形成有V_2O_5与TiO_2相互作用和释氧活性的表面层;在V_2O_5含量～10wt%时,该表面层形成得最充分。IR研究证实表面层的释氧活性是由V_2O_5的V=O键松弛引起。V_2O_5>10wt%时,样品中除有释氧活性的V_2O_5外,还有不具有释氧活性的V_2O_5,前者对催化活性和选择性有主要贡献,后者则有不利影响。     

V_2O_5/Ti-Ce-PILC在H_2S选择性催化氧化过程中的催化性能

合成了TiO_2-CeO_2柱撑黏土负载V_2O_5催化剂,通过XRD、氮气吸附脱附、TG、FT-IR、H_2-TPR、NH_3-TPD、XPS等方法对其物理化学性质进行了表征,研究了该催化剂在H2S选择性催化氧化反应中的活性。结果表明,负载5%V_2O_5的TiO_2-CeO_2柱撑黏土在180℃下催化效果最好,且尾气中不含SO_2。V_2O_5、TiO_2和CeO_2之间的相互作用提高了催化剂的活性,CeO_2提高了催化剂的热稳定性,同时提供大量晶格氧,加强了V_2O_5的氧化还原作用,降低了反应温度;TiO_2加强了VO_x和CeO_x的再氧化,降低了硫酸盐的覆盖率,从而降低了催化剂的失活速率。     

共沉淀法掺杂SiO_2对V_2O_5-WO_3/TiO_2催化剂SCR性能的影响

通过共沉淀法将SiO_2组分掺入到V2O5-WO3/SiO_2-TiO_2催化剂TiO_2载体中,并通过多种物理化学手段,考察了不同SiO_2掺杂量对催化剂结构、表面性质与SCR性能的影响.结果表明,SiO_2掺入到TiO_2中,Si与Ti形成Si—O—Ti键,使催化剂比表面积增加.Si—O—Ti键的生成以及Si Ox物种上的-OH基团使催化剂表面Br?nsted酸增加,但新增的Br?nsted酸对SCR反应不利,并且SiO_2的掺杂也使得V~(5+)含量降低,Si—O—V键合作用使分散的VOx物种更难还原.Si组分以共沉淀法掺入到V_2O_5-WO_3/TiO_2催化剂会造成脱硝活性的显著下降.     

氨法选择性还原氮氧化物V_2O_5/TiO_2-PILC催化剂的抗硫性能（英文）

选择性催化还原(SCR)是目前去除氮氧化物最有效的方法之一.V_2O_5/TiO_2催化剂被广泛应用于氨法选择性还原氮氧化物(NH_3-SCR)反应,但该催化剂存在工作温度高(300–400℃)及SO_2氧化率高引起设备腐蚀和管路堵塞等问题,开发低温SCR催化剂具有重要意义.过渡金属氧化物(如Fe_2O_3,MnO_x和CuO等)催化剂用于低温SCR先后见诸文献报道,但这些催化剂在SO_2和H_2O存在下易失活.近年来柱撑黏土(PILC)引起科学家广泛关注,Yang等首次将V_2O_5/TiO_2-PILC催化剂应用于NH_3-SCR反应,发现其催化活性高于传统V_2O_5/TiO_2催化剂.柱撑黏土基催化剂在NH_3-SCR反应中也显示出良好抗硫性能,但V_2O_5/TiO_2-PILC催化剂的抗硫机理至今尚未见深入研究.因此我们制备了一系列V_2O_5/TiO_2-PILC催化剂,采用原位漫反射红外等方法详细研究了其抗硫性能较好的原因.首先采用离子交换法制备出TiO_2-PILC载体,之后采用浸渍法制备了不同钒含量(质量分数x/%=0,3,4,5)的xV_2O_5/TiO_2-PILC催化剂.同时,制备了传统V_2O_5/TiO_2和V2O5-MoO_3/TiO_2催化剂作为对比.活性评价结果显示,4V/TiO_2-PILC催化剂具有最高的催化活性,其催化性能与传统钒钛催化剂相当.在160℃时,NO转化率可达80%以上.同时,4V/TiO_2-PILC催化剂还具有较宽的反应温度窗口,在260–500℃范围内,NO转化率保持在90%以上.向反应体系中加入0.05%SO_2和10%H_2O后,在低温(160℃以下)时所有催化剂的反应活性都有一定提高,可能是由于SO_2的加入提高了催化剂的表面酸性.继续升高温度,4V/TiO_2和4V6Mo/TiO_2催化剂活性均明显下降,而4V/TiO_2-PILC催化剂的活性则未出现明显下降.原位漫反射红外光谱结果显示,SO_2在三种催化剂表面的吸附以表面硫酸盐或亚硫酸盐物种以及离子态SO_4~(2–)物种形式存在,而在4V/TiO_2-PILC催化剂表面离子态SO_4~(2–)物种的量最少.X射线光电子能谱及O_2程序升温脱附结果显示,在4V/TiO_2-PILC催化剂上,表面吸附氧(Oads)的量最少.综合上述分析可以得出,在SO_2气氛下,离子态SO_4~(2–)物种在SCR催化剂表面的累积可能是导致其失活的主要原因,而离子态SO_4~(2–)物种的形成可能与催化剂表面吸附氧的量有关.     

MoO3/TiO2-Al2O3催化剂表面结构的LRS研究

负载型Mo和Co-Mo催化剂由于工业上的广泛应用,多年来一直是催化工作者的重要研究课题.工业上应用的Mo和Co-Mo催化剂多以活性Al_2O_3和SiO_2-Al_2O_3为载体,近年来也有用TiO_2,ZrO_2和活性碳作为催化剂载体的研究报导.有关催化剂活性组分与载体之间相互作用对催化剂表面相结构和催化性能的影响方面研究已引起人们的重视。我们多年来在金属-载体相互作用研究基础上,以石油加氢精制催化剂为应用背景,开     

氧化物担载铑原子簇催化剂的金属载体相互作用的考察——Ⅰ.Rh/V_2O_5和RH/TiO_2催化剂的金属载体强相互作用的比较

本文用XPS和XRD考察了由Rh_4(CO)_(12)出发制得的Rh/V_2O_5和Rh/TiO_2两种催化剂的金属载体强相互作用的差别。实验结果表明,1)高温H_2还原的Rh/TiO_2催化剂,经氧处理后即能恢复吸H_2能力。Rh/V_2O_5催化剂在较低温度(473K)H_2还原时Rh就进入SMSI状态,吸H_2能力被完全抑制,373K氧处理并不能使之恢复,吸H_2性质表现出不可逆性。2)与Rh/TiO_2催化剂的TiO_2相比,Rt/V_2O_5催化剂的V_2O_5更易还原,Rh对V_2O_5的还原有明显的促进作用。3)担载在TiO_2上的Rh比在V_2O_5上更易还原。4)还原后,催化剂表层的Rh/V、RH/Ti均有较大幅度的降低。用氧空位模型能较好地说明Rh/TiO_2催化剂的实验结果,而Rh/V_2O_5催化剂的实验结果适于用钒氧化物覆盖模型解释。     

TiO_2晶面依赖的Ir-TiO_x相互作用对Ir/TiO_2催化剂巴豆醛选择性加氢性能的影响（英文）

不饱和醇是一类重要的精细化学品,主要通过α,β-不饱和醛选择性加氢获得.由于α,β-不饱和醛分子中含有共轭的C=C键和C=O键,且后者键能更大,在热力学和动力学上均不利于C=O键的选择性加氢生成α,β-不饱和醇.因此,提高α,β-不饱和醛中C=O的加氢选择性是催化领域中一项挑战性的课题.巴豆醛属于典型的α,β-不饱和醛,研究其选择性加氢生成巴豆醇具有广泛的代表意义;Ir负载在具有还原性载体(如TiO_2)上时,表现出很好的C=O加氢选择性,因此,成为近年来的研究热点.由于暴露不同晶面的TiO_2具有不同的形貌和电子结构,因此研究Ir-TiO_2相互作用的晶面依赖性及其对巴豆醛选择性加氢反应的影响具有重要意义.本文以分别暴露{101}、{100}和{001}晶面的锐钛矿TiO_2纳米晶为载体,制备了负载型Ir/TiO_2催化剂,系统研究了催化剂经过不同的预处理过程(在不同温度下H_2还原和O_2再氧化)后对巴豆醛的气相选择性加氢的性能.利用高分辨透射电镜、原位X射线光电子能谱和原位漫反射红外光谱及氨程序升温脱附等技术研究发现,预处理条件显著改变了Ir-TiO_x的相互作用,包括Ir金属的几何、电子性质及催化剂表面酸性.这种相互作用与TiO_2的暴露晶面密切相关,从而改变了不同Ir/TiO_2催化剂上不同加氢反应行为.研究结果表明,经300°C预还原的Ir/TiO_2-{101}催化剂催化性能最好,在80°C下初始反应速率为166.1μmol g-Ir~(-1) s~(-1),巴豆醇的生成转化频率为0.022 s~(-1).与其他催化剂相比,Ir/TiO_2-{101}催化剂表面Ir~0浓度最高,表面酸度适中,因此表现出最佳的催化性能.同时Ir-TiO_x界面在反应中的协同作用,对H_2和巴豆醛分子中C=O键的吸附和活化起到了关键作用.然而当催化剂经过400°C的H_2预还原后,由于产生了强的金属-载体相互作用使得TiO_x对Ir粒子进行了包裹从而导致Ir-TiO_x界面缺失,因而催化剂催化巴豆醛加氢性能降低.本文为理解金属-载体相互作用对巴豆醛选择性加氢反应的影响提供了新的见解,并为设计高性能α,β-不饱和醛选择性加氢催化剂提供了理论依据.     

载体La_2O_3—TiO_2的热稳定性

本文采用BET、XRD、SEM、XPS技术,研究了TiO_2和La_2O_3-TiO_2载体的烧结过程。结果表明,TiO_2的烧结由体积扩散控制。La_2O_3阻止了TiO_2的烧结,并且通过混晶与TiO_2之间的强表面相互作用,抑制了TiO_2从锐钛型向金红石型的相变。     

Factors determining the selective exposure of (010) plane of V2O5 Catalysts supported on various TiO2

V₂O₅ supported on various TiO₂ including anatase, rutile and mixtures of both have been investigated with various physicochemical measurements such as BET, NH₃-TPD, NARP, XRD and so on, and the effect of the crystal phase of the TiO₂ support on the structure of the supported V₂O₅ was discussed. It has been found that the V=O species on the (010) plane of V₂O₅ on the TiO₂ supports with large BET surface area are selectively exposed to the surface, though different crystal phases of TiO₂ result in different characteristics of exposure of the (010) plane. Anatase gives the maximum exposure of the surface V=O species at significantly lower surface concentration of V₂O₅ than that for rutile. For the mixture of both, two maxima are obtained at the surface concentration of V₂O₅ corresponding to those for anatase and rutile respectively. The chemical activity of the TiO₂ surface also seems to have an effect on the exposure of the (010) plane. That is, the higher surface area and the stronger acidic property resulted in the higher exposure of the (010) plane. On leave from: Department of Applied Chemical Engineering, South-China University of Science and Technology, Guangzhou 510641, P.R. China     

钒掺杂TiO2/AC负载催化剂的制备及光催化活性

以TiO2为主要成分的光催化剂的研究已日益受到人们的广泛关注[1-6]。但TiO2粉末的回收和流失问题难以解决,固定化TiO2负载催化剂的研制是解决这一问题的有效手段[2-6]。从实际应用的观点看,TiO2的光催化剂活性还有待进一步提高。研究发现,大多数过渡金属离子和少数非金属离子的     

V2O5/TiO2催化剂表面结构FT-IR发射光谱研究(II)

用傅里哀变换红外发射光谱原位考察了V_2O_5/TiO_2催化剂在制备焙烧过程中担载偏钒酸铵的热分解步骤及其形成的表面活性相结构。偏钒酸铵在200 ℃左右分解, 在300 ℃之前完全转化为晶相V_2O_5。担载于TiO_2上的偏钒酸铵在100 ℃左右与TiO_2已产生强的化学作用, 在200 ℃之前已完全分解。对于10%(质量分数)V_2O_5/TiO_2催化剂其担载偏钒酸分解后在1020 cm~(-1)附近出现晶相V_2O_5的特征峰。但在500 ℃进一步焙烧后晶相V_5O_5的峰减弱并在1025—900 cm~(-1)区出现宽峰, 表明部分晶相V_2O_5可能转化为二维高分散的VO_x物种。2%(质量分数)V_2O_5/TiO_2催化剂在焙烧过程中也显示晶相V_2O_5的弱峰, 但同时也观察到属于VO_x物种的宽峰。进一步降低钒担载量, V_2O_5晶相特征峰逐渐消失, 而在1025—900 cm~(-1)区出现二维VO_x物种的宽峰。结果还表明傅里哀变换红外发射光谱是表征氧化物催化剂表面相结构的一种有力的方法。     

Cu/V2O5-TiO2/SiO2上光催化CO2和丙烷合成异丁烯醛反应性能的研究

采用表面改性法和等体积浸渍法制备了金属修饰的负载型复合半导体材料Cu/V2O5-TiO2/SiO2，用X射线衍射、比表面测定、红外光谱、拉曼光谱、紫外可见漫反射等技术对固体材料的结构、吸光性能和化学吸附性能进行了表征；研究了该材料对CO2和丙烷合成异丁烯醛的光促表面催化规律。结果表明，半导体活性组分V2O5和TiO2在所制备的催化剂Cu/V2O5-TiO2/SiO2表面形成化学键联，并存在多种活性吸附位；金属Cu的修饰拓展了固体材料对光源的响应范围，提高了反应体系的吸光能力；固体材料对CO2和丙烷的有效吸附使得其在较低温度下能促进异丁烯醛的紫外光化学合成。根据实验结果，对光促CO2和丙烷表面催化合成异丁烯醛的机理进行了讨论。     

V2O5在硅胶表面的分散及助剂K2SO4作用的研究

用原位XRD方法证明V_2O_5能在硅胶表面自发分散, 但所需温度较高. 水汽对V_2O_5的分散有一定的阻碍作用. K_2SO_4可显著加快V_2O_5在SiO_2表面的分散速度, 并能降低V_2O_5/SiO_2的表面酸性. 被中和的主要是强酸位. 这可能是K_2SO_4能够改善V_2O_5/SiO_2催化剂在选择氧化反应中选择性的重要原因之一.     

La2O3掺杂TiO2光催化剂的制备和性能

采用溶胶-凝胶法制备了La2O3掺杂TiO2纳米光催化剂，并通过XRD、TEM、BET和XPS等手段进行了表征．掺入La2O3后，阻止了TiO2从锐钛矿晶型向金红石晶型的转变，使TiO2的粒径减小，比表面积增大．以甲基橙为光催化降解反应模型化合物，考察了光催化剂的活性．测定了甲基橙在纯TiO2和La2O3掺杂TiO2光催化剂上的吸附常数．考察了pH、H2O2对降解性能的影响．讨论了光催化活性与催化剂性质的关系．     

应用X射线无标样相定量法研究V2O5-TiO2体系的表面分散

The standardless simultaneous equation method with regression analysis of multi specimens in quantitative phase determination of XRD was applied for sur- face dispersion studies on V_2O_5-TiO_2 system. The dispersive characteristics of vana- dium oxide in V_2O_5-TiO_2 mixtures and in V_2O_5/TiO_2 catalysts prepared from oxyvanadium oxalate after roasting were compared in this paper.     

MoO3 / Al2O3、MoO3 / TiO2与NiO-MoO3 / TiO2催化剂上活性相还原行为的XPS考察

The H_2 reduction behaviours of MoO_3/Al_2O_3, MoO_3/TiO_2 and NiO-MoO_3/TiO_2 samples prepared by impregnation method were studied at various temperatures for different times by XPS technique. The recored XPS spectra of Mo3d from those samples were treated by computer curve fittingprogram to measure the distribution of various molybdenum oxide species with different valence states. The results of computer fitting shows that there areMo(Ⅵ), Mo(Ⅴ)and Mo(Ⅳ) on the all of reduced samples. However, after H_2 reductonin same way, the percentage of low valence species Mo(V) and Mo(IV) on the MoO_3/TiO_2 is much higher than on the MoO_3/Al_2O3 (Fig.2). For example, after H_2 treatment at 500 ℃ for 2 hrs., Mo(IV) species on the surface of MoO_3/TiO_2 sample is about 60% and it is three times higher than what is found on the MoO_3/Al_2O_3 sample. In addition, the reduction of molybdena on TiO_2 support is much easier and faster than on Al_2O_3 support (Fig.3). Addition of NiO further promotes the reduction of molybdena to cause the strting reduction temperature producing Mo(IV) and Mo(V) to be decreased about 100 ℃. and 80% of molyb dena on NiO-MoO_3/TiO_2 support could be reduced to Mo(IV) (Fig.2). A detail discussion about the interaction between molybdena and carries was presented. It was suggested that TiO_2 is certainly involved in the reduction and oxidation process of molybdenum oxide species on the surface of it.     

Insights into the H_2O/V_2O_5 Interface Structure for Optimizing Water-splitting

The interaction of water(H2O) with metal oxide surfaces is of fundamental importance to various fields of science, ranging from batteries to catalysis. In particular, vanadium pentoxide(V2O5) has been widely used as electrode materials for aqueous-battery and catalysts. Herein, theoretical(density functional theory) study gives atomic-scale insights into water monolayers in V2O5 and single-molecule adsorption and dissociation at three low-index surfaces and oxygen-vacancy V2O5(001) surface. The H2O/V2O5 interface structure was identified. The results show that H2O is adsorbed on the stoichiometric V2O5(001) surface with physisorption mechanism, and the dissociation hardly occurs. Water adsorbs as an intact monomer with a computed binding energy of 0.75 eV. The formation of ordered water overlayers has been observed on V2O5(001) surface, suggesting a locally ordered superstructure of molecular water. The molecular H2O adsorption on oxygen-vacancy V2O5(001) surface is stronger than that on the stoichiometric V2O5(001) surface, and H2O can undergo dissociative chemisorption to form a surface hydroxyl group and a H adatom. V2O5 can take the oxygen from H2O, which is consistent with the experimental results.     

Dispersion state and catalytic properties of vanadia species on the surface of V_2O_5/TiO_2 catalysts

The dispersion state and catalytic properties of anatase-supported vanadia species are studied by means of X-ray diffraction (XRD), laser Raman spectroscopy (LRS), H2 temperature-programmed reduction (TPR) and the selective oxidation of o-xylene to phthalic anhydride. The almost identical values of the experimental dispersion capacity of V2O5 on anatase and the surface vacant sites available on the preferentially exposed (001) plane of anatase suggest that the highly dispersed vanadium cations are bonded to the vacant sites on the surface of anatase as derived by the incorporation model. When the loading amount of V2O5 is far below its dispersion capacity, the dispersed vanadia species might mainly consist of isolated VOx species bridging to the surface through V-O-Ti bonds. With the increase of V2O5 loading the isolated vanadia species interact with their nearest neighbors (either isolated or polymerized vanadia) through bridging V-O-V at the expenses of V-O-Ti bonds, resulting in the increase of the ra