改性Al_2O_3对单钯催化剂净化甲醇性能的影响

以稀土助剂Ce,Zr,La改性的Al_2O_3为载体,采用等体积浸渍法制备了一系列单Pd催化剂,运用低温N2吸附-脱附,X射线衍射(XRD),H2程序升温还原(H2-TPR),CO2-程序升温脱附(CO2-TPD),X射线光电子能谱(XPS)对催化剂进行表征,并考察其对甲醇的催化氧化性能以及对氧的利用性能。结果表明:Ce与Al_2O_3可形成均一的固溶体结构,改善催化剂的还原性能,增加金属与载体界面上晶格氧的浓度,进而提高催化剂对氧的利用性能,使氧完全利用窗口宽至0%~1.88%;La通过电子效应改善了Pd与载体间相互作用,重新分配催化剂表面碱性位,生成有利于甲醇活化的Lewis强碱性位,并使Pd向高氧化态过渡,两者协同作用改善了催化剂对甲醇的催化活性,T50,T90以及ΔT分别降低28,52和24℃;Zr引起催化活性下降可能与碱性位数量减少以及较低氧化态的Pd物种的存在有关。3种助剂助催化效果递变规律为:La2O3Ce O2Zr O2。     

Pd/MnOx+Pd/γ-Al2O3整体式催化剂降解地表臭氧

用高锰酸钾与硝酸锰氧化还原反应制备了高活性的氧化锰(MnO x)催化组分,用胶溶法制备了高比表面积的γ-Al2O3载体,分别用等体积浸渍法制备了Pd/MnO x和Pd/γ-Al2O3催化剂,然后将两者机械混合涂覆于堇青石上制得Pd/MnO x+Pd/γ-Al2O3整体式催化剂。采用X射线衍射(XRD)、X射线光电子能谱(XPS)、程序升温还原(H2-TPR)和低温N2吸附-脱附对催化剂进行了表征。考察了在300至700℃焙烧MnO x对催化剂降解地表O3活性的影响。结果表明,Pd和MnO x之间存在协同作用;MnO x焙烧温度对催化剂活性有一定的影响,其中以600℃焙烧时催化剂的活性最高,O3的起始(12℃)转化率达到88%,完全转化温度为18℃。MnOx的物相和催化剂表面的吸附氧物种对催化活性影响较大,适当比例的MnO2和Mn2O3共存有利于O3分解,表面吸附氧为O3分解的活性氧物种。     

铌改性的Pd/Al2O3催化剂催化苯燃烧反应简

采用浸渍法制备了Nb改性的Pd/Al2O3催化剂,考察了该催化剂催化苯燃烧反应性能,并研究了催化剂的稳定性. 结果表明,Nb的添加明显提高了Pd/Al2O3催化剂性能,在195 ℃时苯转化率达到90%,苯的完全燃烧温度降低了40 ℃. 采用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、H2 程序升温还原(H2-TPR)、NH3程序升温脱附(NH3-TPD)和氮气吸附等手段对催化剂进行了表征,结果表明,Nb的加入不仅提高了Pd物种的分散度,同时改变了部分Pd的价态,形成适宜反应的PdO-Pd物种,并促进了催化剂表面氧浓度的增加,使氧物种氧化能力增强,从而提高了催化性能. 1%Pd-5%Nb/Al2O3催化剂的催化活性高于2.0%Pd/Al2O3催化剂.     

浸渍/共沉淀法对BaO改性单Pd催化剂净化甲醇汽油车尾气性能的影响(英文)

采用浸渍和共沉淀两种方法分别制备了Ba O改性的Pd/CeO2-ZrO2-La2O3-Al2O3催化剂。运用N2吸附-脱附,X射线衍射(XRD),H2程序升温还原(H2-TPR),NH3程序升温脱附(NH3-TPD),透射电子显微镜(TEM)和X射线光电子能谱(XPS)对催化剂进行表征,并考察其对甲醇,CO,C3H8和NO的催化性能。活性测试结果表明,Ba O的引入可明显改善Pd催化剂对甲醇,CO,C3H8和NO的催化活性,且浸渍法最佳,起燃温度(T50)分别降低了43,31,45和35℃。XRD,H2-TPR及XPS结果表明,浸渍法引入Ba O主要通过表面改性方式,强化Pd-Ce界面间的相互作用,改善催化剂的还原性能,进而提高催化剂的低温活性;而共沉淀法则是通过结构改性方式增加CeO2晶格缺陷,加速活性氧物种的流动,Ce3+浓度的增加是促使CO氧化活性显著提高的主要原因。     

铌改性的Pd/Al_2O_3催化剂催化苯燃烧反应

采用浸渍法制备了Nb改性的Pd/Al2O3催化剂,考察了该催化剂催化苯燃烧反应性能,并研究了催化剂的稳定性.结果表明,Nb的添加明显提高了Pd/Al2O3催化剂性能,在195℃时苯转化率达到90%,苯的完全燃烧温度降低了40℃.采用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、H2程序升温还原(H2-TPR)、NH3程序升温脱附(NH3-TPD)和氮气吸附等手段对催化剂进行了表征,结果表明,Nb的加入不仅提高了Pd物种的分散度,同时改变了部分Pd的价态,形成适宜反应的PdO-Pd物种,并促进了催化剂表面氧浓度的增加,使氧物种氧化能力增强,从而提高了催化性能.1%Pd-5%Nb/Al2O3催化剂的催化活性高于2.0%Pd/Al2O3催化剂.     

碱土金属改性V/K-γ-Al2O3催化剂环己烷氧化脱氢性能的研究

以γ-Al2O3为载体,采用浸渍法制备了以V和K为主活性组分、碱土元素为助剂的催化剂M-3%V-6%K/γ-Al2O3(M=Mg、Ca、Sr、Ba),考察了该催化剂在环己烷氧化脱氢制环己烯反应中的催化活性,并采用X射线衍射(XRD)、N2吸附(BET)、氢-程序升温还原(H2-TPR)、氨-程序升温脱附(NH3-TPD)和X射线光电子能谱(XPS)方法对催化剂进行了理化表征.H2-TPR和NH3-TPD的表征结果显示碱土助剂的添加会影响催化剂的氧化还原能力和酸性;XPS表征结果表明碱土金属的添加影响了催化剂上钒物种和氧物种的组成,其中添加助剂Ca和Ba后,催化剂上钒钾物种的相对浓度升高,且催化剂表面晶格氧物种的含量增加.活性评价结果表明经碱土助剂Ca和Ba修饰后的3%V-6%K/γ-Al2O3催化剂均具有较好的催化性能,在425℃反应时环己烯的选择性均达56%以上;催化剂也表现出较好的催化稳定性和再生性能.     

Cl–改性对Ag/Al2O3催化剂结构及其催化C3H6-SCR和H2/C3H6-SCR反应性能的影响

以烯烃为还原剂的NOx选择性催化还原(HC-SCR)是重要的环境催化反应之一.Ag/Al2O3催化剂(SA)因在HC-SCR反应中表现高活性、高N2选择性及中等H2O和SO2耐受性等优点,而被广泛研究.SA催化剂中存在不同的Ag物种,包括孤立Ag+离子,带部分正电荷Agnδ+团簇和金属态Agn0团簇.文献研究结果表明,SA催化剂中Agnδ+团簇是催化HC-SCR反应的活性Ag物种,而Ag物种类型与Ag的负载量密切相关.因此文献中研究SA催化HC-SCR反应的结构-性能关系主要是通过改变Ag负载量来开展的,最优Ag负载量约为1％～2％.本文以Cl–改性的γ-Al2O3作为载体,采用传统的浸渍法制备了Ag/Al2O3-Cl催化剂(SA-Cl),通过XRD、TEM、H2-TPR、UV-Vis DRS以及XPS对催化剂进行了结构表征,并结合C3H6-SCR和H2/C3H6-SCR活性测试,建立催化剂结构-催化性能关系;同时利用原位傅里叶变换红外光谱(DRIFTS)和在线同步辐射单光子电离质谱(SVUV-PIMS)研究了SA催化HC-SCR的反应机理.结构表征结果表明,在SA催化剂中,Ag负载量的提高主要是增加了Agn0物种,而在SA-Cl催化剂中,Ag负载量的提高主要是增加了Agnδ+物种,因此Cl?改性能促进SA催化剂中Agnδ+物种的形成.活性测试结果表明,在相同Ag负载量下,SA-Cl催化剂表现出比SA催化剂更好的HC-SCR催化性能.Cl?改性对SA催化剂中Ag物种的调控作用和HC-SCR催化性能的促进作用随Ag负载量的增加变得更为明显.原位DRIFTS结果表明,γ-Al2O3载体(Al位点)是NO氧化形成硝酸盐物种的主要活性位点;Agnδ+物种催化丙烯适度氧化主要生成乙酸盐类物种,可以还原表面硝酸盐物种;而Agn0催化丙烯过度氧化主要生成羧酸盐类物种,进而生成CO2,不能还原表面硝酸盐物种.由此可见,Agnδ+是催化HC-SCR反应的活性Ag物种,而Agn0是催化烃类完全氧化反应的活性Ag物种;Cl–改性能有效促进Agnδ+的形成,进而提高HC-SCR催化反应活性.在线SVUV-PIMS结果检测到H2/C3H6-SCR反应中存在气态中间物种丙烯腈(CH2=CHCN).–CN和–NCO物种被认为是HC-SCR反应的关键中间物种,能够直接与气相NO+O2反应生成N2.因此,CH2=CHCN的存在说明HC-SCR反应涉及到气相反应机理.基于SA和SA-Cl催化剂,进一步研究了H2对C3H6-SCR低温活性的促进作用.结果表明,H2的促进作用是通过作用于Agnδ+物种,而不是通过Agn0物种来实现的;H2的引入有利于低温下强吸附硝酸盐物种的脱附或分解以及中间体向–NCO和–CN物种的转化,从而提高HC-SCR低温催化活性.综上,基于Cl–改性的Ag/Al2O3-Cl催化剂,本文成功证实了Agnδ+物种是催化HC-SCR反应的活性Ag物种,并结合原位DRIFTS在线SVUV-PIMS谱分别鉴定了催化反应表面中间物种和气相中间物种.这些结果加深了对SA催化HC-SCR反应构-效关系和反应机理的基础理解.     

不同金属负载对Cr/Al2O3-TiO2催化剂结构及氧化NO性能的影响

采用溶胶-凝胶法和浸渍法制备Cr/Al_2O_3-TiO_2催化剂,在考察不同Cr负载量的基础上,研究不同金属负载与焙烧温度对Cr/Al_2O_3-TiO_2催化剂结构与性能影响。程序升温氧化(TPO)结果表明,当Cr负载量为10%(w/w)时具有较好的催化活性;不同金属负载Cr/Al_2O_3-TiO_2时,负载Co及在焙烧温度为550℃时催化剂具有较好的活性。通过程序升温还原(H_2-TPR)表征发现,Co的负载使催化剂的低温氧化还原能力逐渐提高,表明Co-Cr具有较好的协同催化作用。X射线光电子能谱(XPS)表征表明,Co增加了Cr~(6+)和表面吸附氧(O_β)含量,随着焙烧温度的升高(450～550℃),晶格氧不断向催化剂表面流动,表面化学吸附氧O_β比例逐渐增加,导致催化活性不断升高,说明Cr~(6+)和O_β是催化氧化NO的重要活性物种。     

CexZr1-xO2/Co/C-N催化CO2加氢性能研究

将不同比例的铈锆前驱体负载到ZIF-67,氮气气氛焙烧制备CexZr1-xO2/Co/C-N催化剂,对催化剂进行了XRD,H2-TPR、XPS表征,并在固定床反应器评价其CO2加氢制甲醇性能。XRD结果表明,在铈中加入适量锆形成铈锆固溶体,铈锆固溶体与钴物种较强的相互作用力可以阻止表明金属Co的氧化。但过量加入的锆又会削弱这一作用力,部分金属Co被氧化为Co3O4。H2-TPR结果表明适量的锆的加入改善催化剂的还原性能,催化剂还原温度降低。XPS证实了25%Ce0.67Zr0.33O2/Co/C-N催化剂中含有更多的氧空穴及氮含量,氧空穴和碱性氮都有利于CO2的解离吸附。优化后的25%Ce0.67Zr0.33O2/Co/C-N 催化剂在225 oC,2 MPa,GHSV = 6 L/gcat/h反应条件下取得最高甲醇时空收率,为3.0 mmol/gcat/h。     

浸渍法制备的Pd-MnO_x/γ-Al_2O_3催化剂及不同载体对地表O_3降解的影响(英文)

在γ-Al2O3载体上用等体积浸渍法浸渍Pd、MnOx活性组分,然后涂覆于堇青石基体上制备Pd-MnOx/γ-Al2O3整体式催化剂.分别用X射线衍射(XRD)、H2-程序升温还原(H2-TPR)、低温N2吸附-脱附及X射线光电子能谱(XPS)对制备的催化剂进行表征.研究了Pd、MnOx浸渍顺序对催化剂活性、氧化还原性能及织构性质的影响.实验结果表明,Pd、MnOx共浸渍较分别浸渍制备的催化剂活性好,Pd和MnOx之间存在一定的协同作用.考察了不同载体如La-Al2O3、SiO2、γ-Al2O3和Zr-Al2O3对催化剂活性、氧化还原性能、织构性质及表面电子性能的影响.研究表明,以La-Al2O3或SiO2为载体的催化剂活性最好,即,14°C时O3转化率为82%,完全转化温度为36°C.γ-Al2O3载体次之,Zr-Al2O3载体较差.不同载体制备的催化剂中MnOx的氧化还原性能顺序为:PdMnOx/SiO2Pd-MnOx/La-Al2O3Pd-MnOx/γ-Al2O3Pd-MnOx/Zr-Al2O3.     

Sm2O3Ga2O3 and Gd2O3Ga2O3 phase diagrams

Four definite compounds exist in the Sm₂O₃Ga₂O₃ binary phase diagram, namely: Sm₃GaO₆, Sm₄Ga₂O₉, SmGaO₃, and Sm₃Ga₅O₁₂. The $\text{3}\text{1}$ compound is orthorhombic (space group Pnna - Z.4) with the cell parameters: a = 11.40₀Å, b = 5.51₅Å, c = 9.07Å and belongs to the oxysel family. Sm₃GaO₆ and SmGaO₃ melt incongruently at 1715 and 1565°C; Sm₄Ga₂O₉ and Sm₃Ga₅O₁₂ have a congruent melting point at 1710 and 1655°C. With regard to the Gd₂O₃Ga₂O₃ system three definite compounds have been identified: Gd₃GaO₆, Gd₄Ga₂O₉, and Gd₃Ga₅O₁₂. Only the garnet melts congruently at 1740°C with the following composition: Gd_3.12Ga_4.88O₁₂. Gd₃GaO₆, and Gd₄Ga₂O₉ melt incongruently at 1760 and 1700°C. GdGaO₃ is only obtained by melt overheating which may yield an equilibrium or a metastable phase diagram.     

Garnet-perovskite transformations in the Sm2O3Ga2O3 and Gd2O3Ga2O3 systems

The effect of heating garnet melts to various temperatures has been investigated. The previously reported decomposition of the garnet phase due to loss of Ga₂O₃ was corroborated. However, it was also observed that when gallium oxide loss is prevented and the maximum temperature of the melt exceeds a critical value, phase separation of garnet to perovskite and β-gallium oxide occurs:

$\text{RE}{}_3\text{Ga}{}_5\text{O}{}_{12}\text{?3RE}\text{GaO}{}_3\text{+}\text{Ga}{}_2\text{O}{}_3$

.The reverse reaction will occur by reheating the two-phase mixture to the garnet melting point.     

Structural changes resulting from doping Ti2O3 with Sc2O3 or Al2O3

The crystal structures of (Ti_1?xSc_x)₂O₃, x = 0.0038, 0.0109, and 0.0413, and of (Ti_0.99Al_0.01)₂O₃, have been determined from X-ray diffraction data collected from single crystals using an automated diffractometer, and have been refined to weighted residuals of 25–34. Cell constants have also been determined for x = 0.0005, 0.0019, and 0.0232. The compounds are rhombohedral, space group $\text{R}\text{3}\text{c}$, and are isomorphous with α-Al₂O₃. The hexagonal cell dimensions range from a = 5.1573(2)Å, c = 13.613(1)Å for (Ti_0.9995Sc_0.0005)₂O₃ to a = 5.1659(4)Å, c = 13.644(1)Å for (Ti_0.9587Sc_0.0413)₂O₃, and a = 5.1526(2)Å, c = 13.609(1)Å for (Ti_0.99Al_0.01)₂O₃. Sc and Al substitution cause similar increases in the short near-neighbor metal-metal distance across the shared octahedral face; for Sc doping the increase is from 2.578(1) Å in pure Ti₂O₃ to 2.597(1) Å in (Ti_0.9587Sc_0.0413)₂O₃. By contrast, changes in the metal-metal distance across the shared octahedral edge appear to be governed by ionic size effects. The distance increases from 2.994(1) Å in Ti₂O₃ to 3.000(1) Å in (Ti_0.9587Sc_0.0413)₂O₃ and decreases to 2.991(1) Å in (Ti_0.99Al_0.01)₂O₃.     

Ion-beam irradiation of lanthanum compounds in the systems La2O3-Al2O3 and La2O3-TiO2

Thin crystals of La₂O₃, LaAlO₃, La_2/3TiO₃, La₂TiO₅, and La₂Ti₂O₇ have been irradiated in situ using 1 MeV Kr²⁺ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La₂O₃ remained crystalline to a fluence greater than 3.1×10¹⁶ ions cm⁻² at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (T_c) of 647 K for LaAlO₃, 840 K for La₂Ti₂O₇, 865 K for La_2/3TiO₃, and 1027 K for La₂TiO₅. The T_c values observed in this study, together with previous data for Al₂O₃ and TiO₂, are discussed with reference to the melting points for the La₂O₃-Al₂O₃ and La₂O₃-TiO₂ systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between T_c and melting temperature (T_m) in the two systems. More complex relationships exist between T_c and crystal structure, with the stoichiometric perovskite LaAlO₃ being the most resistant to amorphisation.     

BaO-Al2O3-B2O3系密封玻璃的结构与性质

The BaO-Al₂O₃-B₂O₃ glasses manufactured for solid oxide fuel cell(SOFC) sealing were studied. The effect of different n_BaO/n_B2O3 on crystal, thermal properties, density and infrared spectra of this system has been discussed. The results show that the trends of crystallization, glass transformation temperature, dilatometric softening temperature and density increase with n_BaO/n_B2O3 values. But a typical property deviation occurs when n_BaO/n_B2O3 is 0.875, and its coefficient of thermal expansion has the maximum at this point. The changes of properties can attribute to the conversion of boron from tetrahedral coordination to trigonal, breakage of the local glass network and interaction between the network modifiers. These can be proved by infrared spectra of glasses. Thermal properties of some studied samples are suitable for the sealing of SOFC using Sm doped ceria electrolyte and operating at 400～600 ℃.     

Partial oxidation of methane on Cr2O3/Al2O3

The oxidation of methane on supported chromia was studied at temperatures varying between 423 and 743 K and CH₄/O₂ ratios between 1 and 9 in a differential reactor. The main reaction products observed were carbon monoxide and formaldehyde. The rates of reaction obey a power law expression.

---

, 423 743 CH₄/O₂ 1 9, . . .

     

Chemical twinning of the pyrochlore structure in the system Bi2O3-Fe2O3-Nb2O5

New ternary bismuth iron niobates having structures based on chemical twinning of pyrochlore are described. Bi_5.67Nb₁₀FeO₃₅ has hexagonal symmetry, P6₃/mmc, , , Z=2 and Bi_9.3Nb_16.9Fe_1.1O_57.8 has rhombohedral symmetry, R-3m, , , Z=3. The structures of both phases were determined and refined to R₁=0.04 using single-crystal X-ray data. They can be described as being derived from the pyrochlore structure by chemical twinning on (111)_py oxygen planes. The chemical twin operation produces pairs of corner-connected hexagonal tungsten bronze (HTB) layers as in the HTB structure, so the structures may alternatively be described as pyrochlore:HTB unit-cell intergrowth structures. In the hexagonal phase the pyrochlore blocks have a width of 12 Å, whereas the rhombohedral phase has pyrochlore blocks of two widths, 6 and 12 Å, alternating with HTB blocks. It is proposed that the previously reported binary 4Bi₂O₃:9Nb₂O₅ phase has a related structure containing pyrochlore blocks all of width 6 Å. A feature of the structures is partial occupancy (∼65%) of the Bi sites and displacement of the Bi atoms from the ideal pyrochlore A sites towards the surrounding oxygen atoms, as observed in Bi-containing pyrochlores.     

Surface acidity of the La2O3/Al2O3 system

Surface acidity of aluminium oxide containing 5 wt. % lanthanum oxide has been determined by IR spectroscopy. Strength of Lewis sites of the La₂O₃/Al₂O₃ system was lower than that of pure aluminium oxide. However, the presence of La₂O₃ in aluminium oxide increased the thermostability of these sites in the mixed system.