V2O5-WO3/TiO2-SiO2制备及其选择性催化还原脱硝活性

以硫酸氧钛和硅溶胶为原料,通过共沉淀法制备得到高比表面积的TiO2-SiO2复合氧化物(Ti/Si=1:1atom),并以此复合氧化物为载体用浸渍法制备了V2O5-WO3/TiO2-SiO2脱硝催化剂,考察了催化剂脱硝性能。结果表明,TiO2-SiO2复合氧化物载体出现较多的隧道孔,提高了载体的比表面积,同时Ti元素更易分布在复合氧化物的表面。相比较于纯TiO2,以复合氧化物为载体的V2O5-WO3催化剂表现出更好的活性温度窗口,催化剂表面酸性更强,催化剂对NH3的吸附性能更好,在低的NH3/NO摩尔比情况下(0.8～1.0mol?mol?1),仍然具有较好的脱硝活性,反应温度280～350℃时,脱硝率可达到98%。     

烟气脱硝催化剂中载体TiO2对催化性能的影响

选用纳米级TiO2和工业级TiO2作为烟气脱硝催化剂的载体,采用分步浸渍法在载体TiO2上负载WO3和V2O5,得到商业催化剂的活性成分1%V2O5-10%WO3/TiO2,用以去除烟道气中的氮氧化合物(NOx)。纳米级催化剂所允许的空速范围远比工业级催化剂高,氨氮比(≥1.0)对纳米级催化剂脱硝效率基本没有影响,且当氨氮比为1.2时,在300～350℃脱硝效率可以达到100%。而工业级催化剂的脱硝效率随着空速的增加和氨氮比的降低而显著减小。在相同的空速(7500h-1)和氨氮比(1.0)条件下,纳米级催化剂的脱硝效率几乎为100%,而工业级催化剂只有在400℃时达到最大脱硝效率,且仅为85%。此外,以纳米级TiO2为载体的催化剂具有更宽的脱硝温度窗。利用扫描电镜(SEM)、N2物理吸附脱附、X射线衍射(XRD),程序升温脱附(NH3-TPD)和粒径分析等方法进行载体和催化剂表征。结果表明,纳米级催化剂的比表面积,孔容和表面酸性都远大于工业级催化剂。     

柠檬酸引入方式对CoMo/TiO2-Al2O3催化剂加氢脱硫性能的影响

采用改进溶胶-凝胶法制备的TiO_2-Al_2O_3作复合载体,制备不同柠檬酸引入方式改性的CoMo/TiO_2-Al_2O_3加氢脱硫催化剂。利用低温N_2吸附-脱附、XRD、SEM和H_2-TPR等对催化剂进行表征,并采用固定床反应器对催化剂加氢脱硫性能进行评价。结果表明,后处理法制备的催化剂比表面积相对较大,孔道结构较好,活性金属组分以无定形形态均匀分散在载体表面,一定程度上减弱了其与载体间的相互作用;该催化剂可以延缓Co硫化,并且络合生成较多易于硫化还原的Mo物种,利于MoS_2在催化剂表面的堆叠,生成更多的Co-Mo-S(Ⅱ)活性相,因而相应的CoMo催化剂对噻吩加氢脱硫转化率显著提高。     

Co负载量对Co/TiO2催化CO2甲烷化性能影响

采用沉淀-沉积法制备出w(Co)=10%、15%、20%和25%的Co/TiO_2催化剂,并用于催化CO_2甲烷化反应。通过XRD、TEM、N_2吸附-脱附、H_2程序升温还原(H_2-TPR)和CO_2程序升温脱附(CO_2-TPD)对催化剂进行了表征与测试。结果表明,Co的负载影响了催化剂中Co3O4晶粒尺寸、比表面积、孔径以及催化剂的还原性能,且Co物种与TiO_2载体发生了强相互作用。其中,w(Co)=20%的Co/TiO_2催化剂中Co颗粒平均尺寸约为8nm,比表面积及孔径分别为40.9 m2/g和6.96 nm,且Co分散度达10.1%,从而更有利于CO_2甲烷化反应。此外,w(Co)=20%的Co/TiO_2催化剂表面具有最大的中强碱位量(28μmol/g),从而可活化更多的CO_2。活性测试结果表明,当反应温度为400℃、压力0.5 MPa、原料气空速3 600 m L/(g·h)、V(H_2)/V(CO_2)=4时,w(Co)=20%的Co/TiO_2催化剂的活性最好,其CO_2转化率和CH_4选择性可分别达到69.9%和98.3%,且在20 h内保持稳定。     

TiO_2-SiO_2复合氧化物载体的pH值和焙烧温度对催化剂的辛烷异构化性能的影响

采用溶胶-凝胶法制备TiO_2-SiO_2复合氧化物载体,通过超声浸渍法制备Ni O和WO3改性负载的Ni O-WO3/TiO_2-SiO_2催化剂,考察不同p H值和焙烧温度条件下制备的载体对催化剂辛烷异构化性能的影响。结果表明,制备的Ni O-WO3/TiO_2-SiO_2催化剂呈多孔结构,平均孔径约5 nm,平均晶粒尺寸(10~20)nm。以焙烧温度500℃和p H=2条件下制备的TiO_2-SiO_2为载体,制得的催化剂比表面积达322.51 m2·g-1,在辛烷异构化反应中,正辛烷转化率为28.3%,选择性85.1%。     

Sm~(3+)掺入对MnO_2/TiO_2催化剂低温脱硝性能的影响

采用挤出成型法制备Sm3+掺杂MnO2/TiO_2催化剂(Sm-Mn/Ti),研究Sm3+掺入对MnO2/TiO_2催化剂低温脱硝性能的影响,采用X射线衍射、氮气吸附脱附、可见光拉曼光谱以及扫描电子显微镜等对催化剂进行表征。结果表明,Sm3+的掺入抑制了TiO_2的颗粒长大,不仅增大了催化剂的比表面积,同时提高MnO2/TiO_2催化剂的缺陷浓度,有利于催化剂表面反应气体的吸附以及催化反应的进行。因此,适量Sm3+掺入会明显提升MnO2/TiO_2催化剂的低温脱硝活性、抗硫中毒、抗碱金属中毒能力,拓宽其活性温度窗口。5 000 h-1条件下,4%Sm-Mn/Ti催化剂在195℃达到最高脱硝率99%,并且在115℃脱硝率达到86%。     

Sm~(3+)掺入对MnO_2/TiO_2催化剂低温脱硝性能的影响

采用挤出成型法制备Sm3+掺杂MnO2/TiO_2催化剂(Sm-Mn/Ti),研究Sm3+掺入对MnO2/TiO_2催化剂低温脱硝性能的影响,采用X射线衍射、氮气吸附脱附、可见光拉曼光谱以及扫描电子显微镜等对催化剂进行表征。结果表明,Sm3+的掺入抑制了TiO_2的颗粒长大,不仅增大了催化剂的比表面积,同时提高MnO2/TiO_2催化剂的缺陷浓度,有利于催化剂表面反应气体的吸附以及催化反应的进行。因此,适量Sm3+掺入会明显提升MnO2/TiO_2催化剂的低温脱硝活性、抗硫中毒、抗碱金属中毒能力,拓宽其活性温度窗口。5 000 h-1条件下,4%Sm-Mn/Ti催化剂在195℃达到最高脱硝率99%,并且在115℃脱硝率达到86%。     

Cu(x)/TiO2催化剂NH3-SCR低温脱硝性能

以硝酸铜和二氧化钛为原料,采用浸渍法制备Cu(x)/TiO_2(x为以TiO_2载体质量为基准的铜负载量,下同)催化剂。运用XRD、XPS、NO-TPD、H_2-TPR等对催化剂进行了表征,在微型固定床反应器中评价了Cu(x)/TiO_2催化剂在以NH_3为还原剂的选择性催化还原NO反应(NH_3-SCR)中的脱硝活性。结果表明,铜物种以Cu_2O和Cu O的形式共存于TiO_2载体上;铜负载量影响催化剂的脱硝性能;Cu(6)/TiO_2催化剂(6代表铜的负载量为6%)表现出较好的氧化还原性和对反应物NO的吸附-脱附能力,低温脱硝活性较好,NO转化率达到85%和95%时对应反应温度T85和T95分别为195和218℃,NO转化率大于95%的活性窗口温度为218～270℃,宽度为52℃。     

混合载体锰基宽温SCR脱硝催化剂的研究

为制备宽温脱硝催化剂，采用机械研磨方法获得了TiO₂和ZSM-5混合载体，并采用浸渍法制备了负载型MnO_x/TiO₂-ZSM-5脱硝催化剂。对制得的催化剂进行了X射线衍射(XRD)、N₂等温吸附-脱附、H₂程序升温还原(H₂-TPR)、NH₃程序升温脱附(NH₃-TPD)和NO程序升温脱附(NO-TPD)等表征，并考察了其催化脱硝活性。结果表明：MnO_x/TiO₂-ZSM-5催化剂具有较大的比表面积、更多的表面活泼锰物种、较多的酸位点，其对低温NH₃和NO吸附量及高温NH₃吸附量均有所增加，从而表现出更好的脱硝催化活性，在200～350℃时NO转化率达99%以上。     

Ni/Al_2O_3催化剂的CO_2-TPD表征

Ni/Al_2O_3催化剂是甲烷二氧化碳重整反应制取合成气研究最多、最具应用潜力的一种催化剂。通过对催化剂进行CO_2-TPD研究,考察还原态Ni/Al_2O_3催化剂的CO_2脱附特性。结果表明,浸渍法制备的Ni/Al_2O_3催化剂CO_2脱附曲线呈现双峰,分别在(60~65)℃和(350~380)℃出现高低温两个活性位;高温CO_2吸附量为3.0 cm~3·g~(-1),低温CO_2吸附量为24.0 cm~3·g~(-1)。催化剂的CO_2吸附量与其Ni含量无关。考察选用不同载体的CO_2脱附行为,发现以Al_2O_3为载体的催化剂CO_2吸附量是MgO和SiO_2为载体催化剂的2~4倍,以TiO_2为载体的催化剂几乎不吸附CO_2。     

TiO2-SiO2 and V2O5/TiO2-SiO2 catalyst: Physico-chemical characteristics and catalytic behavior in selective catalytic reduction of NO by NH3

TiO₂-SiO₂ with various compositions prepared by the coprecipitation method and vanadia loaded on TiO₂-SiO₂ were investigated with respect to their physico-chemical characteristics and catalytic behavior in SCR of NO by NH₃ and in the undesired oxidation of SO₂ to SO₃, using BET, XRD, XPS, NH₃-TPD, acidity measurement by the titration method and activity test. TiO₂-SiO₂, compared with pure TiO₂, exhibits a remarkably stronger acidity, a higher BET surface area, a lower crystallinity of anatase titania and results in allowing a good thermal stability and a higher vanadia dispersion on the support up to high loadings of 15 wt% V₂O₅. The SCR activity and N₂ selectivity are found to be more excellent over vanadia loaded on TiO₂-SiO₂ with 10–20 mol% of SiO₂ than over that on pure TiO₂, and this is considered to be associated with highly dispersed vanadia on the supports and large amounts of NH₃ adsorbed on the catalysts. With increasing SiO₂ content, the remarkable activity decrease in the oxidation of SO₂ to SO₃, favorable for industrial SCR catalysts, was also observed, strongly depending on the existence of vanadium species of the oxidation state close to V⁴⁺ on TiO₂-SiO₂, while V⁵⁺ exists on TiO₂, according to XPS. It is concluded that vanadia loaded on Ti-rich TiO₂-SiO₂ with low SiO₂ content is suitable as SCR catalysts for sulfur-containing exhaust gases due to showing not only the excellent de-NO_x activity but also the low SO₂ oxidation performance.     

水基纳米TiO_2路径制备有序介孔TiO_2-SiO_2及其可见光催化性能

在多巴胺修饰的水基TiO_2纳米微粒(TiO_2NPs)悬浮液中,以正硅酸乙酯为硅源,十六烷基三甲基溴化铵为模板剂,分别采用碱性水热方法或酸性溶胶-凝胶方法,制备了有序介孔TiO_2-SiO_2(TiO_2NPs/MCM-41或TiO_2NPs/SBA-3)。采用XRD、TEM、ICP和N2吸附-脱附实验对样品进行表征。结果表明,制备的介孔TiO_2-SiO_2在TiO_2高负载质量分数(23.98%TiO_2NPs/MCM-41、17.27%TiO_2NPs/SBA-3)时,仍能保持长程有序的介孔氧化硅结构。TiO_2NPs随机地嵌入在有序介孔氧化硅孔道所组成的网络结构中。在可见光下催化甲基橙降解反应中,反应时间120 min时,在P25上甲基橙相对浓度降为57%,在TiO_2NPs/MCM-41上降为33%,而在TiO_2NPs/SBA-3上降为5.7%。     

负载型CuMnO_x/TiO_2催化剂催化燃烧甲苯

采用沉积-沉淀法制备CuMnO_x/TiO_2新型甲苯燃烧催化剂,考察焙烧温度、Cu与Mn物质的量比、Cu和Mn总负载量、空速及水蒸汽含量对催化甲苯燃烧性能的影响。研究表明,焙烧温度500℃和Cu与Mn物质的量比为1∶1时,催化剂活性最好,反应温度250℃时,甲苯去除率为100%;水蒸汽的出现明显降低了甲苯转化率。XRD和H2-TPR表征结果表明,CuMnO_x/TiO_2催化剂的主要活性相为铜锰尖晶石(Cu1.5Mn1.5O4),它的存在降低了CuMnO_x/TiO_2催化剂的还原温度,是催化活性优良的主要原因。     

Effects of microwaves on selective oxidation of toluene to benzoic acid over a V2O5/TiO2 system

Two series of catalysts, V₂O₅/TiO₂ and modified V₂O₅/TiO₂, were prepared with a conventional impregnation method. They were tested in the selective oxidation of toluene to benzoic acid under microwave irradiation. The reaction conditions were optimized over V₂O₅/TiO₂. It was found that in the microwave catalytic process the optimum reactor bed temperature of the titled reaction decreases to 500 K (600 K in the conventional process). The modification of V₂O₅/TiO₂ with MoO₃, WO₃, Nb₂O₅ or Ta₂O₅, which has no negative influence on the reaction in the conventional catalytic process, can greatly promote the catalytic activities in the microwave process, leading to a high yield of benzoic acid (41%). The effects of microwave electromagnetic field on the catalysts are discussed.     

Photocatalytic activity of TiO2/ZSM-5 composites in the presence of SO4 ion

TiO₂/ZSM-5 composites were prepared from SiO₂ of rice husk ash and TiO₂ sol from hydrolyzed TiOSO₄ salt. The combined effect of these two materials greatly enhanced the photocatalytic decolorization of methylene blue dye solution. The instant decolorization of the dye solution in the dark by the composite, TiO₂/ZSM-5 (wt ratio 1:1), resulted from the combination of the adsorption by ZSM-5 zeolite and TiO₂ nano-particles, and of Na₂SO₄ salt adhering to the composite surface. As a strong flocculating agent, the SO₄²⁻ ion caused the precipitation of the dye onto the composite surface which consequently enhanced the photocatalytic decolorization of the dye under UV irradiation. The composite, TiO₂/ZSM-5 (wt ratio 1:5), completely decolorized the methylene blue dye in 2.5 h, giving an equivalent performance to that of TiO₂, P-25 powder.     

The preparation of coupled WO3/TiO2 photocatalyst by ball milling

The coupled photocatalyst WO₃/TiO₂ is prepared by ball milling by doping WO₃ into TiO₂ and using H₂O solution as disperser. The coupled photocatalyst WO₃/TiO₂ is characterized by UV–VIS diffuse reflection spectrum, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and Transmission electron microscopy (TEM). The results show that the optimum percentage of WO₃ doped is 3% and that the photocatalytic activity of the coupled WO₃/TiO₂ photocatalyst is much higher than that of TiO₂ and WO₃–TiO₂ with no ball milling. Compared with TiO₂, the photoexcited wavelength range of the WO₃/TiO₂ photocatalyst red-shifts about 50 nm, and the light absorption intensity is also improved. The crystal phase of TiO₂ is not changed and new crystal phases are not found during the process of ball milling. WO₃ and TiO₂ coupled highly, forming the WO₃/TiO₂ photocatalyst. The increased photocatalytic activity of the coupled photocatalyst may be attributed to the enhance charge separation efficiency and the extend wavelength range of photoexcitation.     

TiO2-SiO2复合材料应用研究进展

无机材料TiO₂和SiO₂因稳定性好、无毒害等性能得到广泛关注和应用,TiO₂-SiO₂复合材料因TiO₂和SiO₂组分的协同作用,表现出更加优异的性能。综述TiO₂-SiO₂复合材料在药物缓释、光催化、吸附、抗菌等相关应用领域中的研究进展,以期为其后续研究提供参考。     

Role of the support on the activity of silica-supported TiO2 photocatalysts: Structure of the TiO2/SBA-15 photocatalysts

Immobilization of TiO₂ on silica materials has been commonly proposed in order to make easier the separation of the catalyst after the photocatalytic reactions in aqueous systems. The main drawback of the supported photocatalysts is that they usually show lower activities in comparison with powdered TiO₂ materials. The aim of this work is to elucidate the structure of some silica-supported TiO₂ photocatalysts recently developed as well as to evaluate the role that the porous structure of the support can play in the observed photocatalytic activities. In comparison with the use of an amorphous silica support, the use of the mesostructured silica SBA-15 produces an ordered structure in which TiO₂ crystals of similar sizes, independently of titania loading, are located inside the mesoporous channels of the support. The photocatalytic treatment of several cyanide-containing compounds is analyzed and the results are explained in terms of the structure of every catalyst. Depending on the model compound, the characteristic structure of the TiO₂/SBA-15 materials allows increasing up to eight times the activity achieved by the Degussa P25 TiO₂. The main conclusion of this work is the strong influence of the textural properties of the support on the catalytic activity of immobilized TiO₂ photocatalysts.     

Ag-Fe_2O_3-V_2O_5/TiO_2催化剂制备及其甲基吡啶催化氧化脱甲基性能

针对甲基吡啶氧化脱甲基反应,以TiO_2为载体经浸渍法制备Ag-Fe_2O_3-V_2O_5/TiO_2催化剂,结合结构表征和催化剂性能评价,考察制备条件对其催化甲基吡啶氧化脱甲基性能的影响。结果表明,通过Fe_2O_3改性可以提高Ag-V_2O_5/TiO_2催化剂对3-甲基吡啶氧化脱甲基化反应的催化性能,其作用主要是抑制V_2O_5团聚,促进V物种的分散。同时,锐钛矿相TiO_2载体表面B酸中心有利于催化3-甲基吡啶脱甲基,提高产物吡啶选择性。经实验优化,Ag-Fe_2O_3-V_2O_5/TiO_2催化剂适宜制备条件为:焙烧温度450℃、焙烧时间4 h、V_2O_5和Ag的负载质量分数分别为15%和1.5%、Fe与V物质的量比1∶2。在优化条件下,吡啶收率与选择性最高可达到62.97%和78.75%。     

SO2 resistant antimony promoted V2O5/TiO2 catalyst for NH3-SCR of NOx at low temperatures

To get the low temperature sulfur resistant V₂O₅/TiO₂ catalysts quantum chemical calculation study was carried out. After selecting suitable promoters (Se, Sb, Cu, S, B, Bi, Pb and P), respective metal promoted V₂O₅/TiO₂ catalysts were prepared by impregnation method and characterized by X-ray diffraction (XRD) and Brunner Emmett Teller surface area (BET-SA). Se, Sb, Cu, S promoted V₂O₅/TiO₂ catalysts showed high catalytic activity for NH₃ selective catalytic reduction (NH₃-SCR) of NO_x carried at temperatures between 150 and 400 °C. The conversion efficiency followed in the order of Se > Sb > S > V₂O₅/TiO₂ > Cu but Se was excluded because of its high vapor pressure. An optimal 2 wt% ‘Sb’ loading was found over V₂O₅/TiO₂ for maximum NO_x conversion, which also showed high resistance to SO₂ in presence of water when compared to other metal promoters. In situ electrical conductivity measurement was carried out for Sb(2%)/V₂O₅/TiO₂ and compared with commercial W(10%)V₂O₅/TiO₂ catalyst. High electrical conductivity difference (ΔG) for Sb(2%)/V₂O₅/TiO₂ catalyst with temperature was observed. SO₂ deactivation experiments were carried out for Sb(2%)/V₂O₅/TiO₂ and W(10%)/V₂O₅/TiO₂ at a temperature of 230 °C for 90 h, resulted Sb(2%)/V₂O₅/TiO₂ was efficient catalyst. BET-SA, X-ray photoelectron spectroscopy (XPS) and carbon, hydrogen, nitrogen and sulfur (CHNS) elemental analysis of spent catalysts well proved the presence of high ammonium sulfate salts over W(10%)/V₂O₅/TiO₂ than Sb(2%)/V₂O₅/TiO₂ catalyst.