镍基气凝胶催化CH4—CO2重整制取合成气反应的研究——Ⅰ.制备方法对NiO—CeO2—Al2O3催化剂物化性质的影响

采用浸渍法、溶胶-凝胶过程与普通干燥、超临界干燥过程相结合的方法制备了具有不同结构特点的NiO-CeO2-Al2O3催化剂,分别为浸渍型催化剂（iNCA)、干凝胶催化剂（xNCA)和气凝胶催化剂（aNCA),利用BET、TEM、XRD、TPR、NH3-TPD、H2-TPD等方法对各催化剂样品的物化化质进行了考察。研究结果表明,经823K焙烧后,镍含量为9%的各催化剂样品中镍物种分散良好;与iNCA相比,以溶胶-凝胶法为基础制备的xNCA和aNCA中镍物种与载体的相互作用用强并且存在状态均一;三种催化剂中,气凝胶样品具有比表面积高、堆密度低、表面酸中心数多及表面镍分散度高的特点。     

镍基气凝胶催化CH4-CO2重整制取合成气反应的研究Ⅱ.制备方法对Ni/CeO2-Al2O3催化剂反应性能的影响

采用浸渍法、溶胶 凝胶过程与普通干燥、超临界干燥过程相结合的方法制备了三种 82 3K焙烧的NiO CeO2 Al2 O3 体系催化剂 ,分别为浸渍型催化剂 (iNCA5 5 0 )、干凝胶催化剂 (xNCA5 5 0 )和气凝胶催化剂 (aNCA5 5 0 ) ,考察了它们在CH4 CO2 重整反应中的催化性能及反应的稳定性 ,采用TG、TEM、XPS等手段研究了反应前后催化剂的结构性质。研究结果表明 ,在 10 73K、CH4 CO2 =1∶1、180 0 0mL h·g的反应条件下 ,三种催化剂中aNCA5 5 0在CH4 CO2 重整反应过程中的积碳量较大 ,但却具有最好的反应稳定性 ;aNCA5 5 0具有较大积碳量与其表面酸量较大、酸性较强及较大镍分散度有关 ,然而由于它具有较大的积碳容量和很强的金属抗烧结能力 ,因此保持了较好的反应稳定性。催化剂积碳和金属镍烧结导致催化剂表面活性中心数目减少是催化剂失活的主要原因。     

超细镍基催化剂的CH4—CO2重整反应性能——Ⅲ制备方法对催化剂吸附CO2性能的影响

采用溶胶－凝胶法和超临界干燥技术,制备了气凝胶超细氧化铝载体、超细二元（NiO-Al2O3）和三元（NiO-La2O3-Al2O3）催化剂,同时以超细氧化铝载体浸渍镍盐的二元催化剂和普通氧化铝浸渍的镍镧铝的三元催化剂作为对比。通过CO2－TPD实验及XRD、XPS和IR技术表征,考察了制备方法和氧化镧改性对催化剂吸附二氧化碳能力的影响。结果表明,超细样品的吸附能力明显高于浸渍型催化剂,具有明显的纳米粒子效应,La2O3的加入,提高了强碱中心数,使催化剂的吸附能力显著增强,且不受制备方法的影响,还原后的镍物种吸附CO2后,与载体之间的相互作用被消弱,容易被重新氧化成粒度较大的氧化镍晶粒。     

镍基气凝胶催化CH4-CO2重整制取合成气反应的研究 Ⅲ.影响催化剂积碳性能因素的探讨

考察了823K焙烧的干凝胶xNCA550、气凝胶aNCA550及浸渍型催化剂iNCA550在923K、1073K、1173K反应温度下的积碳行为，对催化剂表面碳的活性及类型进行了分析，并探讨了影响催化剂积碳的因素。实验结果表明，随反应温度的提高，催化剂的积碳能力减弱，尤以气凝胶催化剂aNCA550明显。催化剂的积碳主要发生在反应的初期，反应温度越高，到达积碳量相对稳定期所需要的时间越短；随着反应时间的延续，催化剂积碳量缓慢增长，并且表面碳的活性降低。催化剂的酸性和镍晶粒大小是影响其积碳性能的主要内在因素，而它们对积碳的影响程度受反应温度的影响，反应温度越高，催化剂表达酸性中心利于积碳的作用越小，小晶粒镍抑制催化剂积碳的能力越强。     

流化床反应器中不同Ni/Al2O3催化剂上CH4-CO2重整反应性能的比较研究

采用浸渍法、溶胶 凝胶过程与普通干燥、超临界干燥过程相结合的方法制备了三种20%的NiO-Al2O3体系催化剂，利用BET、XRD、H2 TPR、H2-TPD等方法对各催化剂样品物化性质进行了表征，并考察了催化剂在流化床反应器中CH4-CO2重整反应的催化性能。研究结果表明，经923K焙烧后气凝胶催化剂中镍与载体间作用力最强，主要为固定NiO和尖晶石NiAl2O4结构，而浸渍型催化剂和干凝胶催化剂中镍与载体间作用力较弱。三种催化剂中，气凝胶催化剂具有比表面积较大、堆密度较低、Ni还原度及分散度较高的特点。它在流化床反应器中所形成的聚团流态化状态具有较高的床层膨胀率，大量多孔疏松状的纳米颗粒聚团在床内的循环运动有效地提高了传质效率，能使得生成的沉积炭快速得到气化，从而抑制了催化剂失活；对于浸渍型催化剂和干凝胶催化剂，流化床反应器中床层膨胀率较低、颗粒循环量较少、传质效率较低，易于造成催化剂表面积炭失活。经用TG和XRD等方法对反应后催化剂分析表征，证明催化剂表面石墨碳的沉积是导致浸渍型催化剂和干凝胶催化剂失活的主要原因。     

溶胶-凝胶和浸渍-水热制备方法对TiO_2/AC光催化剂结构和性能的影响

分别采用溶胶-凝胶法和浸渍-水热法制得负载于活性炭(AC)的TiO2催化剂,并用扫描电镜(SEM)、X射线衍射(XRD)、拉曼光谱和氮气吸附等方法对催化剂进行了表征.结果表明:溶胶-凝胶法制得的TiO2以不规则碎片形式涂附在载体表面,而浸渍-水热法制得的球形TiO2颗粒呈柱形生长均匀覆盖在载体表面;不同温度处理的浸渍-水热法制得的TiO2/AC光催化剂的中孔和微孔比表面积均大于溶胶-凝胶法制得的样品,负载的TiO2粒径则小于溶胶-凝胶法制得的样品.对甲基橙(MO)溶液的光催化降解测试结果表明,600℃煅烧为两种方法的最佳热处理温度,浸渍-水热法制得的催化剂光催化效果明显强于溶胶-凝胶法的.     

MoO3/SiO2催化剂的异丁烷选择氧化反应性能

分别采用浸渍法和溶胶－凝胶法制备了MoO3/SiO2催化剂，用XRD，TPR，IR，TPD和活性评价等手段对催化剂的影响，晶格氧活泼性，化学吸附性能和异丁烷选择氧化反应性能进行了研究。结果表明，催化剂表面由Lewis碱位Mo=M,Mo-O-Mo中的晶格氧和Lewis酸位Mo^6 构成，在MoO3/SiO2催化剂上，异丁烷主要通过甲基的H双位吸附在表面的Lewis碱位Mo=O上；在常压条件下，异丁烷选择氧化产物主要为异丁烷，甲基丙烯醛和甲基丙烯酸，其中深度氧化产物CO2主要由吸附的异丁烯继续反应生成；采用溶胶－凝胶法制备的MoO3/SiO2催化剂，可得到较高的异丁烷转化率和含氧有机物选择性。     

介孔纳米 MoPO-AlPO4 的制备及其对异丁烯选择氧化的催化性能

 分别采用溶胶-凝胶法和等体积浸渍法制备了 MoPO-AlPO4 催化剂, 考察了钼物种存在状态对催化剂晶格氧活性以及异丁烯选择氧化反应性能的影响. N2 吸附-脱附、X 射线衍射、高分辨透射电镜、X 射线光电子能谱、傅里叶变换红外光谱、程序升温还原和微反实验结果表明, 与浸渍法制备的催化剂相比, 溶胶-凝胶法制备的 MoPO-AlPO4 催化剂为介孔纳米材料, 其比表面积和孔数量均有较大程度的提高. 在浸渍法制备的催化剂中, 钼物种以四面体 MoO42− 和八表面体 MoO66− 形式存在; 而在溶胶-凝胶法制备的催化剂中钼物种主要以四面体 MoO42− 的形式存在, 并有部分钼物种嵌入到了 AlPO4 骨架中. 钼物种的种类对异丁烯选择氧化反应的活性和选择性有较大影响, 溶胶-凝胶法制备的催化剂由于嵌入 AlPO4 骨架中钼物种的存在, 异丁烯选择氧化反应性能得到较大提高.     

固相浸渍法制备NiO/CeO2催化剂及其在CO氧化反应中的应用

采用固相浸渍法制备了一系列NiO/CeO2催化剂,并通过与常规湿浸渍法比较,考察了制备方法对催化剂和CO氧化反应性能的影响.同时结合X射线衍射(XRD),N2吸附-脱附(BET),透射电镜(TEM),氢气-程序升温还原(H2-TPR),拉曼(Raman)光谱,X射线光电子能谱(XPS)等手段对催化剂的结构和表面物种分散状态进行了表征.CO氧化活性测试结果表明,当镍负载量相同时,固相浸渍法制备的催化剂相比于湿浸渍法表现出更好的催化性能.TEM、XPS、H2-TPR结果表明,固相浸渍法更有利于加强镍铈间的相互作用和得到高分散的镍物种,从而促进镍物种的还原.Raman结果表明固相浸渍法相比于湿浸渍法能产生更多氧空位,这有利于氧气在催化剂表面的活化,使得CO氧化反应更容易进行.     

制备方法对Pd催化剂上丙烯选择性还原NO反应性能的影响

 采用三种不同方法制备了氧化铝负载的Pd催化剂．比表面积测定\r\n结果表明,与浸渍法相比,溶胶－凝胶加浸渍法和溶胶－凝胶法制备的\r\nPd／Al2O3样品具有较大的比表面积,但抗烧结性能不佳．其中采用溶\r\n胶－凝胶法制备的样品中,由于Pd分散于体相中,表面的活性位相对较\r\n少,造成催化剂在NO选择性还原反应中的活性较差;而将Pd浸渍于溶胶\r\n－凝胶法制得的Al2O3载体上所获得的催化剂比表面积较大,活性较好\r\n．添加CeO2的样品活性总体上比Pd／Al2O3样品高．其中采用溶胶－凝\r\n胶法制备的样品比表面积不大,并且XRD数据表明Al2O3和CeO2是高度分\r\n散并均匀地搀杂在一起的,不象在浸渍法制备的样品中那样以大晶粒的\r\n形式存在,因而CeO2的助剂作用没有充分体现出来,催化剂的活性比浸\r\n渍法制备的样品差一些．     

Textural,structural and catalytic properties of zirconia doped by heteropolytungstic acid: a comparative study between aerogel and xerogel catalysts

Zirconia doped by heteropolytungstic acid HPW have been synthesized by sol–gel method using two drying techniques of the solvent evacuation. Samples were analyzed with adsorption–desorption of N₂ at 77 K, and the aerogel catalyst was found to exhibit a higher surface area and a higher average pore diameter compared to xerogel. XRD results show that aerogel develops ZrO₂ tetragonal phase, whereas xerogel is amorphous. The thermal analysis studies show that the aerogel’s thermal stability is better than the xerogel one. The catalytic behavior of the aerogel and xerogel toward the nature of the isomerization products probably depends on the acidity and the presence of carbide species. This has been explained by XPS and isopropanol dehydration reaction. In fact, the deconvolution aerogel’s Cls bands reveals the presence of four carbon species assigned to C–C, C=O, C–O and carbide species.     

超细镍基催化剂上CH4-CO2重整反应的性能Ⅰ.制备方法对催化剂结构和还原性能的影响

通过BET ,XRD ,XPS ,IR和TPR等表征手段 ,考察了制备方法对CH4 CO2 重整用镍基催化剂物性结构和还原性能的影响 .与浸渍的超细载体二元NiO Al2 O3 及浸渍的普通载体三元NiO La2 O3 Al2 O3 催化剂相比 ,采用溶胶 凝胶法和超临界干燥技术制备的超细二元和三元气凝胶超细催化剂具有高表面积、高孔隙率及孔结构可控等特点 ,且组分之间的相互作用强 ,分布均匀 ,较低温度下即可形成NiAl2 O4 尖晶石结构 ,吸附能力强 ,还具有更丰富的表面缺陷和暴露原子数等纳米材料特性 .同时 ,该方法适宜于制备负载多组分金属催化剂 ,有利于发挥助剂的改善调节作用 ,满足CH4 CO2 重整反应对催化剂的要求 .     

Hydrogen Production by Steam Reforming of Ethanol Over Mesoporous Ni–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> Catalysts

This review paper reports the recent progress concerning the application of nickel–alumina–zirconia based catalysts to the ethanol steam reforming for hydrogen production. Several series of mesoporous nickel–alumina–zirconia based catalysts were prepared by an epoxide-initiated sol–gel method. The first series comprised Ni–Al₂O₃–ZrO₂ xerogel catalysts with diverse Zr/Al molar ratios. Chemical species maintained a well-dispersed state, while catalyst acidity decreased with increasing Zr/Al molar ratio. An optimal amount of Zr (Zr/Al molar ratio of 0.2) was required to achieve the highest hydrogen yield. In the second series, Ni–Al₂O₃–ZrO₂ xerogel catalysts with different Ni content were examined. Reducibility and nickel surface area of the catalysts could be modulated by changing nickel content. Ni–Al₂O₃–ZrO₂ catalyst with 15 wt% of nickel content showed the highest nickel surface area and the best catalytic performance. In the catalysts where copper was introduced as an additive (Cu–Ni–Al₂O₃–ZrO₂), it was found that nickel dispersion, nickel surface area, and ethanol adsorption capacity were enhanced at an appropriate amount of copper introduction, leading to a promising catalytic activity. Ni–Sr–Al₂O₃–ZrO₂ catalysts prepared by changing drying method were tested as well. Textural properties of Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst produced from supercritical drying were enhanced when compared to those of xerogel catalyst produced from conventional drying. Nickel dispersion and nickel surface area were higher on Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst, which led to higher hydrogen yield and catalyst stability over Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst.     

The properties of nickel aluminate nanoparticles prepared by sol–gel and impregnation methods

Nickel aluminates were prepared by sol–gel and impregnation methods and calcined at 1100 °C. The sol–gel made samples were prepared with different amounts of nickel (Ni/Al molar ratio equal to 0, 0.25, 0.5, and 0.75) and aging times (24 and 48 h). The samples were characterized by X-ray diffraction, induced couple plasma, nitrogen physisorption, transmission and scanning electron microscopy, and ammonia temperature programmed desorption (NH₃-TPD). In the sol–gel made samples, only the NiAl₂O₄ structure of nickel aluminate was defined, while for impregnation, NiAl₁₀O₁₆ was formed as well. The sol–gel made samples had low specific surface areas (7.7–12.4 m²/g), but a sample prepared by impregnation method had higher specific surface area (67.2 m²/g). The surface acidity density decreased by increasing the amount of nickel and was the lowest for impregnation method.     

Ni-based xero- and aerogels as catalysts for nitroxidation processes

Porous nanocomposites made out of nickel dispersed on silica or alumina matrices were prepared as prospective catalysts for the nitroxidation of hydrocarbons in the form of aerogel or xerogel by adopting either a supercritical or a conventional gel drying procedure. The structural and textural features of the materials were investigated by X-ray diffraction, transmission electron microscopy and N₂ physisorption and combined to the acid/base and reducibility data as deduced by adsorption microcalorimetry and temperature programmed reduction (TPR) profiles. The alumina-based samples are made out of nanocrystalline nickel aluminate and are mesoporous, although the aerogel has larger pore volumes and surface area than the xerogel. On the other hand, in the silica-based samples nickel oxide nanocrystals are dispersed on amorphous silica, the size of the nanocrystals being around 5 nm in the microporous xerogel and 14 nm in the mainly mesoporous aerogel. TPR data point out that the alumina-based samples have similar reducibility, whereas significant differences were observed in the silica-supported composites, the NiO–SiO₂ aerogel exhibiting improved reducibility at low temperature. The NO-catalyst interaction was monitored by temperature programmed NO reaction coupled to mass spectrometry and preliminary tests on the use of the NiO–SiO₂ xerogel and aerogel nanocomposites for the catalytic nitroxidation of 1-methyl-naphthalene to 1-naphthonitrile were obtained in a fixed-bed continuous-flow reactor. The data indicate that the aerogel exhibits larger selectivity than the corresponding xerogel, pointing out the importance of tuning the sol–gel parameters in the design of porous composite materials for catalytic applications.     

SiO2-AEO凝胶体系的织构特性

采用溶胶 凝胶法 ,以正硅酸乙酯 (TEOS)为前驱体 ,用脂肪醇聚氧乙烯醚 (AEO)为改性剂制备结构可控的多孔SiO2 干凝胶.结果表明 :通过调节添加量和聚合度以及溶胶老化时间可以对SiO2 干凝胶织构性质进行有效的调控 ;采用不同的环境气氛对SiO2 AEO干凝胶进行热处理 ,则AEO表现出不同的热稳定性 ;经热处理后 ,AEO等有机残留物被脱除的同时 ,SiO2 AEO干凝胶柔性骨架得到加强 ,孔分布更趋集中 ,干凝胶结构的热稳定性得到进一步提高.