Ni对Cu/ZnO基甲醇裂解催化剂的促进机制

通过XRD,BET,In-situ XPS等表征技术对Cu/ZnO基甲醇裂解制氢催化剂进行 了详细的研究。XRD结果表明,Cu-Zn合金的生成是Cu/ZnO基催化剂在反应初期快速 失活的主要原因;XRD,BET和N_2O滴定实验结果表明,Ni助剂可能是通过提高 Cu~0活性物种的分散度并维持Cu~0活性物种在催化反应过程中的稳定性而使 Cu/Zn/Ni催化剂的活性及稳定性大幅度提高。In-situ XPS结果表明,Ni助剂的加 入可以诱导Cu/Zn/Ni催化剂表面在甲醇裂解反应过程中出现Cu~+,从而由 Cu~0/Cu~+共同构成催化剂的活性中心,并最终导致Cu/Zn/Ni催化剂的高活性。     

负载型Cu/Al_2O_3和Cu/ZnO催化剂上CO_2加氢的原位FTIR及准原位XPS/HS-LEIS研究（英文）

铜基催化剂是工业合成甲醇中常用的催化剂,其主要包含Cu, ZnO, Al_2O_3三种组分,研究各组分在催化合成甲醇过程中的本质作用及其相互间的协同作用不仅是一个催化基础科学问题,同时对于设计和合成新型高性能的铜基催化剂也有重要指导作用.以往的研究主要针对Cu和ZnO二元组分,关于Al_2O_3的作用很少有报道,主要观点认为Al_2O_3起结构助剂的作用.在Cu/Al_2O_3/ZnO(0001)-Zn模型催化体系的研究中,我们发现Al_2O_3具有稳定Cu~+的能力.为了更接近于实际催化体系,并进一步探索铜基催化剂中载体Al_2O_3及ZnO的作用,我们制备了负载型的5 wt%Cu/Al_2O_3及5 wt%Cu/ZnO催化剂,并通过原位傅里叶变换红外光谱(in situ FTIR)、准原位X射线光电子能谱(ex situ XPS)及高灵敏度低能离子散射谱(HS-LEIS),着重考察H2还原及CO_2加氢过程中表面吸附物种的转变及催化剂表面结构变化,更深一步理解Cu, ZnO, Al_2O_3三组分在催化CO_2加氢过程中所起的作用及相互间的协同作用.通过XRD, BET和TEM表征,发现采用浸渍负载法制备的、经过焙烧后的5 wt%Cu/Al_2O_3及5 wt%Cu/ZnO催化剂的结构和形貌有明显差别, Al_2O_3载体具有较大的比表面积, CuO在其表面分散性较好,而ZnO的比表面积很小、CuO颗粒也相对较大.ExsituXPS及HS-LEIS显示,经过H2还原后, Cu在Al_2O_3表面的颗粒粒径略有增大,表面仍有较大比例的Cu~+物种.以CO为探针分子的FTIR光谱也表明, H2还原后5 wt%Cu/Al_2O_3存在一定量的Cu~+,而5 wt%Cu/ZnO催化剂还原后形成Cu纳米粒子表面被ZnOx包覆, exsituXPS及HS-LEIS的深度剖析也证实了上述结果.CO_2加氢过程中, 5wt%Cu/Al_2O_3表面能够形成大量碳酸氢盐及碳酸盐物种并在升温过程中逐渐转变为甲酸盐,表面仍有一定量的Cu~+;5wt%Cu/ZnO表面形成的碳酸盐及碳酸氢盐物种含量相对较少,但Cu-ZnOx的协同作用形成活化H2的高活性表面,在室温下就可以生成甲酸盐物种,在随后的升温过程中甲酸盐逐渐转变为甲氧基.通过对比负载型Cu/Al_2O_3及Cu/ZnO催化剂的研究,得以更加深入地理解铜基催化剂中载体在CO_2加氢制甲醇过程中所起的作用:Al_2O_3能较好分散Cu,且能够稳定Cu~+;相对于ZnO, Al_2O_3具有较强的吸附CO_2能力,能够在表面形成大量的碳酸氢盐物种及碳酸氢盐物种,与表面Cu作用在升温过程中能够生成大量的甲酸盐物种;对于5wt%Cu/ZnO在H2还原和CO_2加氢过程中Cu表面被ZnOx包覆,其高度缺陷的表面结构能在室温下解离H2.这些结果表明,实际Cu Zn AlO催化剂上CO_2加氢制备甲醇的活性位点可能包含Cu~+, Cu~0及相邻的具有高度缺陷结构的ZnOx包覆层.     

CO2加氢低压合成甲醇催化剂CuO／ZnO／ZrO2的光电子能谱研究

本文应用XPS和XAES(X光激发俄歇电子能谱)考察了CO_2加氢低压合成甲醇用CuO/ZnO/ZrO_2催化剂在反应条件下的表面状态。结果表明,在还原及反应状态下,催化剂表面没有稳定的Cu~(2+)、Cu~+离子存在,仅有Cu~0能被检测到;ZnO部分被还原,产生低价锌Zn~[(2-δ)](0<δ<2)物类。结合活性测试结果,认为高活性、高选择性的CO_2加氢合成甲醇催化剂要以Cu、Zn共同存在为前提,即Cu~0与部分还原的ZnO共同组成甲醇合成的活性中心。     

柠檬酸盐凝胶法制备纳米CuO-ZnO-ZrO_2的工艺分析及CO_2加氢制甲醇的性能

采用柠檬酸盐凝胶法制备出纳米CuO-ZnO-ZrO_2(CZZ)催化剂,应用XPS、BET、XRD、H_2-TPR、H_2-TPD、CO_2-TPD和TG-DTA等检测手段对催化剂及前驱体的结构进行表征。研究了湿凝胶干燥时间和柠檬酸用量对催化剂结构的影响,并与燃烧法制得的催化剂进行对比,考察了不同催化剂CO_2加氢制甲醇的性能。研究表明,延长湿凝胶干燥时间可有效防止催化剂焙烧时发生喷溅,有利于催化剂中各组分的分散,提高催化剂对H_2和CO_2的吸附能力;112℃干燥48h制得的催化剂(CZZ-48h)BET比表面积为43.5m~2/g,高于燃烧法;柠檬酸用量等于化学计量比时催化剂的性能最佳,在240℃、2.6MPa、空速为3600h-1、H_2/CO_2(体积比)为3的条件下甲醇时空收率达109.4g/(kg·h);柠檬酸过量会影响催化剂组分的分散度,并造成分解残留覆盖催化剂表面活性位而不利于CO_2加氢反应。     

机械研磨时间对铜基甲醇合成催化剂性能的影响

采用机械研磨燃烧法在不同研磨时间下制备了系列Cu/ZnO/Al2O3催化剂,并评价了其在一氧化碳加氢制备甲醇反应中的活性。催化剂前驱体的焙烧过程通过热重-差热分析仪(TG-DSC)监测。采用X射线衍射(XRD)、扫描电镜(SEM)、N2吸附、程序升温还原(TPR)和N2O氧化后氢气滴定等方法对催化剂进行了表征。结果表明,催化剂的结构性质与研磨时间密切相关,催化剂的比表面积和铜原子的分散度随研磨时间延长先增大后减小,研磨2 h制得的催化剂显示了最高的催化活性。     

焙烧温度对Ni/CaO-Al_2O_3结构及其催化重整性能的影响

采用共沉淀法制备了一系列具有类水滑石结构前驱体的Ni/CaO-Al_2O_3复合催化剂,考察了制备过程中焙烧温度对复合催化剂结构及性能的影响。结果表明,焙烧温度可调控活性组分Ni与载体之间的相互作用力,进而调变复合催化剂的比表面积、活性组分Ni的颗粒粒径。当焙烧温度为700℃时,Ni与载体之间相互作用力适宜,复合催化剂具有最大的比表面积(21.42 m~2/g)和最小的Ni颗粒粒径(19.51 nm);该复合催化剂在CO_2吸附强化CH_4/H_2O重整制氢过程中可得到98.31%的H_2浓度和94.87%的CH_4转化率,循环10次后,H_2浓度仍能保持在97.35%以上。这是因为大的比表面积为反应提供了更多的活性位点,利于CO_2吸附过程的强化,而小的Ni颗粒粒径提高了复合催化剂的抗烧结能力。     

液相还原法制备Cu/Zn/Al/Zr催化剂用于CO_2加氢合成甲醇（英文）

近年来,由于大气CO_2浓度增加引起的温室效应正日益威胁着人类的生存与发展,CO_2的捕获与利用是有望解决温室效应和能源危机的有效途径.CO_2催化转化为甲醇成为众多研究者关注的焦点,这是因为甲醇不仅是一种重要的基本化工原料,也是一种洁净的绿色燃料和能源载体.Cu基催化剂广泛应用于CO_2加氢合成甲醇反应,并表现出良好的催化性能.通常,金属催化剂的制备是采用H_2对金属氧化物进行还原.然而,传统的气相还原过程伴随着强烈的热效应,且需要在高温(473-573 K)下进行,会引起表面铜颗粒长大并加速其聚集烧结,使得活性组分利用率下降.近年来,以NaBH_4为还原剂的液相还原法逐渐受到人们的重视,该方法操作简单、快捷且条件可控,反应在低温下进行,放出的热量可在液相环境中迅速得到转移,大大抑制了铜颗粒的聚集.因此,液相还原法可制备出高铜分散度、高活性的催化剂.焙烧温度对铜基催化剂结构和催化性能的影响已得到广泛探究,但这仅限于含二价铜物种催化剂,焙烧温度对含多种铜价态催化剂的影响未见报道.由于液相还原法制备的催化剂含有还原态的铜物种(Cu~0和Cu~+),它们比Cu~(2+)具有更强的流动性,因此在后续的焙烧过程中催化剂更容易发生烧结和聚集.本文采用液相还原法合成了Cu/Zn/Al/Zr催化剂,分别于423,573,723和873 K焙烧后用于CO_2加氢合成甲醇反应,考察了焙烧温度对制备的铜基催化剂结构性质和催化性能的影响,并与传统共沉淀法制备的催化剂进行了对比.结果显示,随着焙烧温度升高,铜物种聚集作用增强,金属铜颗粒尺寸增大,873 K时烧结出现显著增强.由于比表面积随焙烧温度升高而减小,高温度焙烧的催化剂具有小的表面碱性位数目.焙烧温度会影响催化剂中铜物种与其它组分的相互作用,进而影响催化剂的还原.随着焙烧温度的升高,催化剂的还原温度逐渐降低,表面Cu~+/Cu~0的比例先增后减.CO_2加氢活性评价显示,液相还原法制备的催化剂具有更高的催化活性,尤其是甲醇选择性;随着焙烧温度升高,催化剂的CO_2转化率和甲醇选择性先增后减,CZAZ-573催化剂具有最高活性,且在1000 h长周期活性测试中表现稳定.CO_2转化率与催化剂暴露金属铜的比表面积密切相关.相比Cu~0,产物甲醇更容易在Cu~+表面催化生成,催化剂表面的Cu~+/Cu~0比与甲醇选择性的变化规律一致.通过调控焙烧温度可得到高Cu比表面积以及高Cu~+/Cu~0比的催化剂,有利于CO_2加氢生成甲醇.     

不同助剂对CuO-ZnO/SBA-15催化CO_2加氢制甲醇性能影响的研究

以硅质骨架结构介孔分子筛SBA-15为载体,采用浸渍法合成CuO-ZnO/SBA-15(CZ/SBA-15)、CuO-ZnO-MnO_2/SBA-15(CZM/SBA-15)、CuO-ZnO-ZrO_2/SBA-15(CZZ/SBA-15)三组多孔催化剂,在固定床反应器上评价了各组催化剂催化CO_2加氢合成甲醇的性能,同时结合N_2吸附-脱附(BET)、X射线衍射(XRD)、H_2程序升温还原(H_2-TPR)、程序升温脱附(H_2-TPD、CO_2-TPD)、N_2O滴定、X射线光电子能谱(XPS)、透射电子显微镜(TEM)等表征研究了不同助剂对CO_2催化加氢制甲醇的影响。结果表明,催化剂中的金属氧化物改变了SBA-15分子筛载体的孔径大小和比表面积;催化剂CuO-ZnO-MnO_2/SBA-15、CuO-Zn O-ZrO_2/SBA-15中铜的分散度(D_(Cu))和比表面积(A_(Cu))更大,表面CuO粒径更小,更易被还原;相比Mn-O簇,Zr-O簇为增强了碱性位点,提高了甲醇选择性。此外,CuO-ZnO-ZrO_2/SBA-15具有更高的氧空位浓度,催化活性更好,其甲醇选择性为25.02%,与CuO-ZnO/SBA-15、CuO-ZnO-Mn O_2/SBA-15相比分别提高了28%和136.9%,催化效果最好。     

CO2辅助老化制备的Cu/ZnO/Al2O3催化剂上CO2加氢制甲醇

对传统共沉淀法进行改进,在老化阶段通入CO2促进母液中前驱体物相的转变,制备了Cu/ZnO/Al2O3催化剂.N2吸附、X 射线衍射、场发射扫描电子显微镜、程序升温还原、程序升温分解结果表明,改进共沉淀法制备的催化剂前驱体中碱式硝酸铜更易转变为碱式碳酸铜,从而提高了前驱体的稳定性,并使得焙烧后的催化剂具有较大的比表面积...     

CaO对Cu-ZnO-ZrO_2催化CO_2加H_2合成甲醇性能影响

用CaO作为改性助剂,采用并流共沉淀法制备了CuO∶ZnO∶ZrO_2为5∶4∶1(物质的量比),CaO添加量为0、1%、2%、4%、8%、16%(摩尔分数)的六组催化剂。用X射线衍射(XRD)、微商热重(TG-DTG)、傅里叶红外(FT-IR)、N2吸附脱附(BET)、X射线光电子能谱(XPS)、氢气程序升温还原(H_2-TPR)、CO_2程序升温脱附(CO_2-TPD)、NH_3程序升温脱附(NH_3-TPD)对催化剂进行了表征。用自制固定床评价了催化剂活性。结果表明,添加CaO后,催化剂路易斯酸性和表面碱性增强;催化剂母体中高温碳酸盐含量增加,热稳定性增强,CuO颗粒粒径变小,Cu-Zn协同作用增强,Cu比表面积增大,分散性变好。催化剂活性受到表面酸碱性、铜比表面积、Cu-Zn协同作用和铜分散性共同影响。当CaO为2%时,铜比表面积为79.3 m2/g、铜分散度为34.8%、CO_2转化率为24.55%、甲醇选择性为19.01%、甲醇收率为0.044 g/(gcat·h),催化剂活性最好。过量CaO占据催化剂孔道和覆盖表面活性位,使催化剂路易斯酸性和表面碱性过强,CuO与H_2有效接触减少,CO_2难以脱附,催化活性下降。因此,适量CaO(2%)添加可促进CO_2加氢反应合成甲醇。     

溶剂极性对微波辐射老化制备前驱体及CuO/ZnO/Al2O3催化剂结构的影响

在制备CuO/ZnO/Al2O3催化剂的老化过程中,采用微波辐射老化技术,着重研究了溶剂极性对前躯体物相组成,烧后CuO/ZnO/Al2O3催化剂结构及其在浆态床合成甲醇工艺中催化性能的影响。通过XRD、DTG、H2-TPR,FTIR、HR-TEM和XPS对前驱体及催化剂表征表明,沉淀母液在微波辐射条件下进行老化,溶剂的极性对前躯体物相组成及催化剂结构影响显著。随着溶剂极性的增大,Zn2+/Cu2+取代Cu2(CO3)(OH)2/Zn5(CO3)2(OH)6中Cu2+/Zn2+的取代反应增强,使得前躯体中(Cu,Zn)5(CO3)2(OH)6和(Cu,Zn)2(CO3)(OH)2物相的含量增多,结晶度提高,导致烧后CuO/ZnO/Al2O3催化剂中CuO-ZnO协同作用增强,且CuO晶粒减小,表面Cu含量增加,催化剂活性和稳定性提高。水溶剂的极性最大,制备的催化剂活性和稳定性最好,甲醇的时空收率(STY)和平均失活率分别为320 mg.g-1.h-1和0.11%.d-1。     

微波辐射对浆态床合成甲醇CuO/ZnO/Al2O3催化剂前驱体晶相转变的影响

在微波辐射条件下,对CuO/ZnO/Al2O3催化剂的沉淀母液进行老化,通过XRD、TG、H2-TPR,FTIR、HR-TEM和XPS对前驱体及催化剂微观结构的进行表征,探讨了CuO/ZnO/Al2O3催化剂前驱体晶相转变过程中微波辐射的作用。结果表明,微波辐射有利于Cu2+取代Zn5(CO3)2(OH)6中Zn2+的同晶取代反应。微波辐射的老化过程中,首先发生Cu2+取代Zn5(CO3)2(OH)6中Zn2+生成(Cu,Zn)5(CO3)2(OH)6的同晶取代反应,并于1.0 h内基本完成;随着老化时间继续延长,主要进行Zn2+取代Cu2(CO3)(OH)2中Cu2+生成(Cu,Zn)2(CO3)(OH)2的同晶取代反应,同时(Cu,Zn)5(CO3)2(OH)6进一步结晶。与常规老化1 h制备的前驱体相比,微波辐射老化1.0 h制备的前驱体含有较多的(Cu,Zn)5(CO3)2(OH)6物相,有助于增强焙烧后CuO/ZnO/Al2O3催化剂中CuO-ZnO协同作用,提高表面铜含量,进而提高CuO/ZnO/Al2O3催化剂在浆态床合成甲醇的催化活性和稳定性,在400 h浆态床合成甲醇评价期间,甲醇时空收率最大达318.9 g.kg-1.h-1,失活率仅为0.11%.d-1。     

Production of hydrogen by oxidative steam reforming of methanol over Cu/SiO2 catalysts

Selective production of hydrogen by oxidative steam reforming of methanol (OSRM) was studied over Cu/SiO₂ catalyst using fixed bed flow reactor. Textural and structural properties of the catalyst were analyzed by various instrumental methods. TPR analysis illustrates that the reduction temperature peak was observed between 510?K and 532?K at various copper loadings and calcination temperatures and the peaks shifted to higher temperature with increasing copper loading and calcination temperature. The XRD and XPS analysis demonstrates that the copper existed in different oxidation states at different conditions: Cu₂O, Cu⁰, CuO and Cu(OH)₂ in uncalcined sample; CuO in calcined sample: Cu₂O and metallic Cu after reduction at 600?K and Cu⁰ and CuO after catalytic test. TEM analysis reveals that at various copper loadings, the copper particle size is in the range between 3.0?nm and 3.8?nm. The Cu particle size after catalytic test increased from 3.6 to 4.8?nm, which is due to the formation of oxides of copper as evidenced from XRD and XPS analysis. The catalytic performance at various Cu loadings shows that with increasing Cu loading from 4.7 to 17.3?wt%, the activity increases and thereafter it decreases. Effect of calcination shows that the sample calcined at 673?K exhibited high activity. The O₂/CH₃OH and H₂O/CH₃OH molar ratios play important role in reaction rate and product distribution. The optimum molar ratios of O₂/CH₃OH and H₂O/CH₃OH are 0.25 and 0.1, respectively. When the reaction temperature varied from 473 to 548?K, the methanol conversion and H₂ production rate are in the range of 21.9–97.5% and 1.2–300.9?mmol?kg^?1?s^?1, respectively. The CO selectivity is negligible at these temperatures. Under the optimum conditions (17.3?wt%, Cu/SiO₂; calcination temperature 673?K; 0.25 O₂/CH₃OH molar ratio, 0.5 H₂O/CH₃OH molar ratio and reaction temperature 548?K), the maximum hydrogen yield obtained was 2.45?mol of hydrogen per mole of methanol. The time on stream stability test showed that the Cu/SiO₂ catalyst is quite stable for 48?h.     

Hydrotalcite-derived Co-containing mixed metal oxide catalysts for methanol incineration

The Co–Mg–Al mixed metal oxides were prepared by calcination of co-precipitated hydrotalcite-like precursors at various temperatures (600–800 °C), characterised with respect to chemical (AAS) and phase (XRD) composition, textural parameters (BET), form and aggregation of cobalt species (UV–vis-DRS) and their redox properties (H₂-TPR, cyclic voltammetry). Moreover, the process of thermal decomposition of hydrotalcite-like materials to mixed metal oxide systems was studied by thermogravimetric method combined with the analysis of gaseous decomposition products by mass spectrometry. Calcined hydrotalcite-like materials were tested as catalysts for methanol incineration. Catalytic performance of the oxides depended on cobalt content, Mg/Al ratio and calcination temperature. The catalysts with lower cobalt content, higher Mg/Al ratio and calcined at lower temperatures (600 or 700 °C) were less effective in the process of methanol incineration. In a series of the studied catalysts, the best results, with respect to high catalytic activity and selectivity to CO₂, were obtained for the mixed oxide with Co:Mg:Al molar ratio of 10:57:33 calcined at 800 °C. High activity of this catalyst was likely connected with the presence of a Co–Mg–Al spinel-type phases, containing easy reducible Co³⁺ cations, formed during high-temperature treatment of the hydrotalcite-like precursor.     

Synthesis of biodiesel over ZnO/Ca(OH)2/KF catalyst prepared by the grinding method

A novel ZnO/Ca(OH)₂/KF solid base catalyst was prepared by the grinding method and applied to biodiesel synthesis by the transesterification of soybean oil. The effect of various parameters such as KF molar amount, calcination temperature, the amount of catalyst, molar ratio of methanol to oil, reaction temperature, and time on the activity of the catalyst were investigated. The catalysts were characterized by several techniques of thermogravimetry/derivative thermogravimetry, X–ray diffraction, Hammett indicator method, and scanning electron microscopy. The analysis results indicated that the KF interacted with Ca(OH)₂ and formed KCaF₃ phase before calcination of the catalyst. The formed KCaF₃ crystal phase was the main catalytic active component for the catalyst activity. In addition, the basicity of ZnO/Ca(OH)₂/KF was greatly influenced by the different calcination temperates, and the catalyst activity was correlated closely with the basicity. A desired biodiesel yield of 97.6 % was obtained at catalyst amount of 3 %, methanol/oil of 12:1, and reaction time of 1.5 h at 65 °C.     

Cu‐Based Catalyst Resulting from a Cu,Zn,Al Hydrotalcite‐Like Compound: A Microstructural,Thermoanalytical, and In Situ XAS Study

A Cu‐based methanol synthesis catalyst was obtained from a phase pure Cu,Zn,Al hydrotalcite‐like precursor, which was prepared by co‐precipitation. This sample was intrinsically more active than a conventionally prepared Cu/ZnO/Al₂O₃ catalyst. Upon thermal decomposition in air, the [(Cu_0.5Zn_0.17Al_0.33)(OH)₂(CO₃)_0.17] ? mH₂O precursor is transferred into a carbonate‐modified, amorphous mixed oxide. The calcined catalyst can be described as well‐dispersed “CuO” within ZnAl₂O₄ still containing stabilizing carbonate with a strong interaction of Cu²⁺ ions with the Zn–Al matrix. The reduction of this material was carefully analyzed by complementary temperature‐programmed reduction (TPR) and near‐edge X‐ray absorption fine structure (NEXAFS) measurements. The results fully describe the reduction mechanism with a kinetic model that can be used to predict the oxidation state of Cu at given reduction conditions. The reaction proceeds in two steps through a kinetically stabilized Cu^I intermediate. With reduction, a nanostructured catalyst evolves with metallic Cu particles dispersed in a ZnAl₂O₄ spinel‐like matrix. Due to the strong interaction of Cu and the oxide matrix, the small Cu particles (7 nm) of this catalyst are partially embedded leading to lower absolute activity in comparison with a catalyst comprised of less‐embedded particles. Interestingly, the exposed Cu surface area exhibits a superior intrinsic activity, which is related to a positive effect of the interface contact of Cu and its surroundings.     

Pt/TiO2催化剂上CO氧化反应动力学研究

利用沉积沉淀法制备了Pt/TiO₂催化剂, 将其在不同温度下焙烧, 以得到不同颗粒尺寸的Pt. 并将这些样品用于CO催化氧化反应以及反应动力学研究. 结果表明: 焙烧温度对催化剂有明显影响, Pt 颗粒尺寸随着焙烧温度的升高而增加; 与此同时, CO催化活性随焙烧温度的升高呈先增加后降低的趋势, 其中, 400℃焙烧的样品表现出最高的催化活性. 反应动力学结果表明, 催化剂上CO氧化反应表观速率方程为r=5.4×10^-7p_CO^0.17p_O2^0.36,说明在该催化剂上CO氧化遵循Langmuir-Hinshelwood机理. 同时, 对催化剂进行了CO化学吸附红外光谱和O₂化学吸附表征. 结果表明, 随着焙烧温度的升高, 催化剂上CO和O₂吸附量均呈现先升高后降低的趋势, 这与反应结果和反应动力学方程一致, 说明反应受到催化剂表面上CO和O₂吸附浓度的影响. 而在400℃焙烧的催化剂上, CO和O₂吸附量均最高, 因此其反应活性也最好. 这可能是焙烧过程影响了Pt 和TiO₂之间的相互作用引起的.     

焙烧温度对MnOx-CeO2-WO3-ZrO2催化剂上NH3选择性还原NO的影响

采用共沉淀法制备了MnO_x-CeO₂-WO₃-ZrO₂催化剂,考察了催化剂焙烧温度对O₂和H₂O存在下NH₃选择性催化还原（NH₃-SCR） NO的影响,并利用低温N₂吸附、X射线衍射（XRD）、透射电镜（TEM）、X射线光电子能谱（XPS）、NH₃程序升温脱附（NH₃-TPD）和CO脉冲反应对催化剂进行了表征. 结果表明在NH₃-SCR反应中,催化剂的低温活性随焙烧温度的提高而降低,这是由于催化剂表面化学吸附氧和酸性位减少引起的;催化剂的高温活性随焙烧温度的提高先增加后减小,这与催化剂表面最易释放氧数量的变化趋势相反. 700 ℃焙烧的催化剂具有良好的低温活性和最宽的反应温度窗口,在空速为90000 h^-1的条件下,该催化剂的起燃温度（50% NO转化率）为189 ℃,且反应温度在218-431 ℃范围内,NO转化率可达到80%-100%.     

Preparation and characterization of nanocrystalline ZnO by direct precipitation method

Nanocrystalline ZnO was prepared with ZnCl₂·2H₂O and (NH₄)₂CO₃ as raw materials by direct precipitation method. The precursor was proved to be [Zn₅(OH)₆(CO₃)₂] by TG-DTG-DTA and IR analysis. This precursor was calcined at 300°C for 1, 2 and 3 hours respectively, and then the nanocrystalline ZnO of different grain size were obtained. The nanocrystalline ZnO was characterized using X-ray diffraction (XRD), TEM and Brunner-Emmett-Teller method (BET). Experimental results for nanocrystalline ZnO showed that the minimum size was about 8nm, the maximum was about 15 nm and the mean grain size was 12 nm, the surface area was 80.56 m²/g and the purity was 99.9% when the precursor was calcined at 300°C for 2 h. __________ Translated from Journal of Inner Mongolia Normal University (Natural Science Edition), 2006, 35(1) (in Chinese)     

表面助剂改性对Cu/ZnO/Al2O3甲醇合成催化剂性能的影响

采用共沉淀-后浸渍方法制备了表面助剂改性的Cu/ZnO/Al₂O₃ (CZA)甲醇合成催化剂, 在固定床反应器上以合成气为原料分别考察了三种助剂(Zr、Ba和Mn)对CZA催化剂性能的影响; 以Zr为助剂时反应温度的影响; 并进行了催化稳定性试验. 利用粉末X射线衍射(XRD)、低温氮气吸脱附(N₂-sorption)、氧化亚氮(N₂O)反应吸附技术、X射线光电子能谱(XPS)、氢气程序升温吸脱附(H₂-TPD)、扫描电子显微镜(SEM)和高分辨透射电子显微镜(HR-TEM)技术对催化剂进行了表征.结果显示: 以Zr或Ba作为助剂能够明显提高CZA催化剂耐热前后的甲醇时空收率(STY); Mn的引入降低了CZA催化剂的耐热前活性; Zr的引入降低了CZA催化剂最高活性温度点, 增强了CZA催化剂的催化稳定性; 还原态CZA催化剂表面Cu⁰和ZnO都能吸附活化氢气, Cu⁰与ZnO的强相互作用有利于提高催化剂的性能, 耐热后催化剂性能的降低归因于Cu晶粒的长大. 在实验和表征结果基础上,提出了CZA催化剂上合成气制甲醇的“双向同步催化反应历程”.