镍基催化剂上苯酐选择性加氢合成苯酞

分别以SiO2,TiO2,γ-Al2O3,TiO2-SiO2和TiO2-Al2O3为载体,以硝酸镍为镍源,采用等体积浸渍法制备了一系列镍基催化剂,并将其用于苯酐选择性加氢合成苯酞反应.结果表明,以TiO2-SiO2为载体制备的镍催化剂上Ni0活性组分分散度较高,催化剂表现出较高的活性和苯酞选择性.在此基础上,采用溶胶-凝胶法制备出了一系列Ni/TiO2-SiO2催化剂,考察了催化剂制备中各因素(包括溶剂、焙烧温度、还原温度和镍前驱体类型等)对其催化苯酐加氢反应性能的影响.结果表明,将镍前驱体溶于不同溶剂制备的催化剂性能差异很大,其中以水为溶剂制备的催化剂活性较高,且性能优于等体积浸渍法制备的相应催化剂.焙烧温度和还原温度过高会导致活性组分镍晶粒度变大,致使催化剂活性明显降低.镍源对Ni/TiO2-SiO2催化剂的性能影响较大,以硫酸镍为镍源制备的催化剂几乎无活性,而以氯化镍和硝酸镍为镍源制备的催化剂表现出较高的催化活性和选择性,其中以氯化镍制备的催化剂性能略高于硝酸镍,苯酐转化率为100%,苯酞选择性为88.5%.     

NiO/SiO2气凝胶催化剂性能研究 Ⅰ. 镍含量的影响

以硝酸镍和正硅酸乙酯为原料采用溶胶凝胶超临界流体干燥法制备了不同镍含量的气凝胶催化剂.XRD,TPR,TEM,IR等物理技术表征和顺酐液相催化加氢活性评价结果表明NiO/SiO2气凝胶催化剂中NiO与SiO2有较强的相互作用,镍含量对活性组分与载体之间相互作用的影响导致催化剂具有不同的丁二酸酐和γ-丁内酯的选择性.在镍含量为30w%,经673K焙烧的催化剂上γ-丁内酯的选择性最佳.     

溶胶—凝胶法制备NiO／SiO2催化剂研究

分别以正硅酸乙酯、硝酸镍为硅源和镍源,采用溶胶－凝胶法,经超临界流体干燥和普通干燥制备了NiO-A-SiO2、NiO-G-SiO2催化剂;以气凝胶和干凝胶为载体,采用浸渍法制备了NiO/A-SiO2、NiO/G-SiO2催化剂。并用XRD、TEM、BET、TPR等手段,研究了制备方法对催化剂织构、结构和Ni物种存在形态的影响,发现NiO-A-SiO2和NiO-G-SiO2催化剂上高度分散的NiO簇团与SiO2之间有较强的相互作用,其顺酐液相选择加氢转化率低于10％;NiO/G-SiO2催化剂上,以单一物种形态存在的NiO与SiO2相互作用弱,顺酐转化率为42％;NiO/A-SiO2催化剂上,以多种形态存在的微量NiO与SiO2间的相互作用较复杂,其顺酐液相选择加氢的转化率和丁二酸酐的选择性分别可达100％和98％。     

CuO／ZrO_2超细粒子催化剂的制备和物性结构表征Ⅰ．水凝胶pH值的影响

用乙醇超临界流体干燥法制备了ＣｕＯ／ＺｒＯ２超细粒子催化剂，考察了制备过程中水凝胶ｐＨ值对催化剂物性参数如比表面积、孔结构和晶相等的影响，并与干凝胶进行了对比．结果表明，ｐＨ值在６．５～１０．０范围内对晶相影响不大，但对物性结构的影响较大，比表面积和孔体积很快增大，孔形由椭圆形转变为均一的圆柱形，最可几孔径减小，微孔增多；与干凝胶相比，气凝胶表现出高比表面积和多孔结构的特点．ｐＨ＝１０．０时，气凝胶型催化剂的物性参数最佳     

镍基气凝胶催化CH_4-CO_2重整制取合成气反应的研究 Ⅰ.制备方法对NiO-CeO_2-Al_2O_3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 Al2 O3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性质进行了考察。研究结果表明 ,经 82 3K焙烧后 ,镍含量为 9%的各催化剂样品中镍物种均分散良好 ;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——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。     

Ni／MgO／Al2O3催化剂中Ni前体对甲烷—二氧化碳重整反应活性的影响

考察了以硝酸镍、氯化镍、硫酸镍、醋酸镍及硝酸六氨合镍5种Ni盐制备的Ni/MgO/Al2O3催化剂在CO2与CH4重整制合成气反应中的催化活性,发现Ni前体对活性有明显的影响,以硝酸镍、醋酸镍、硝酸六氨合镍为前体制备的Ni催化剂,反应性较高;以硫酸镍为前体制备的Ni催化剂,可能由于硫中毒等原因而显示出很低的活性;以氯化镍为前体制备的 Ni催化剂,其活性与制备方法有关,未经烧而直接还原的催化剂显示出较好的活性,X－射线粉末衍射（XRD）、BET比表面积及反应后的积量测定结果表明,以硝酸镍、醋酸镍、硝酸六氨合镍为前体制备的Ni催化剂,表面分散性好,比表面积大,积炭量少。     

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。     

前驱物对NiO/SiO_2气凝胶催化剂性能的影响

分别用硝酸镍、醋酸镍和氯化镍为活性组分前驱物,正硅酸乙酯为硅源,采用 溶胶凝胶超临界流体干燥法制备了N-SiO_2,Ac-SiO_2和C-SiO_2催化剂,经TEM, TPR,XRD,IR等物性结构表征及催化加氢活性评价结果表明：前驱物对由溶胶凝胶 法制备催化剂中氧化镍的分散性,晶粒大小及与载体的相互作用都有明显的影响, N-SiO_2催化剂有Ni-O-Si键形成,NiO呈簇团结构,粒径最小,分散性最好,但加 氢活性最低;Ac-SiO_2和C-SiO_2催化剂中氧化镍呈微晶态,与载体相互作用较弱 。在三种催化剂中,NiO与载体相互作用强弱顺序为：N-SiO_2 > Ac-SiO_2 > C- SiO_2,但加氢活性大小顺序相反为：C-SiO_2 > Ac-SiO_2 > N-SiO_2;C-SiO_2催 化剂加氢活性和丁二酸酐的选择性均在99%以上。     

SiO2气凝胶的制备及微孔分布

本文以正硅酸乙酯(TEOS)为原料，水和乙醇为溶剂，盐酸和氨水为催化剂，采用溶胶-凝胶，水热合成和低温冷冻干燥等工艺，制备了SiO₂气凝胶，研究了pH值、TEOS浓度及焙烧温度对气凝胶的比表面积、孔径分布的影响。结果表明：在碱性条件下，制得的气凝胶比表面积较大，孔径较窄。气凝胶在较高温度下，比表面积有所下降，孔径略微变粗。     

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.     

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.     

A Novel Catalyst for Liquid Phase Hydrogenation of m-Dinitrobenzene to m-Phenylenediamine

A novel lanthana-promoted nickel catalyst supported on silica for the liquid phase hydrogenation of m-dinitrobenzene to m-phenylenediamine was prepared by an incipient wetness sequential impregnation method. It was found that Ni-La/SiO2 catalyst exhibited high activity and stability for m-dinitrobenzene hydrogenation. Over this catalyst, the conversion of m-dinitrobenzene and the yield of m-phenylenediamine were up to 97.1% and 93.5%, respectively,at 373 K and 2.6 MPa hydrogen pressure after reaction for 1 h.     

Effect of alcohol solvents treated ZrO（OH）2 hydrogel on properties of ZrO2 and its catalytic performance in isosynthesis

A series of ZrO2 catalysts were prepared by treating ZrO(OH)2 hydrogel with different alcohol solvents (C2-C4 alcohols) and calcining under N2 flow at 773 K for 3 h. The obtained ZrO2 catalysts were systematically characterized by the methods of N2 adsorption-desorption, powder X-ray diffraction, NH3 temperature-programmed desorption, and CO2 temperature-programmed desorption. The catalytic performance of each catalyst was evaluated in the selective synthesis of iso-C4 (isobutene and isobutane) and light olefins (C2= ～C4= ) from CO hydrogenation. The specific surface area increased for the ZrO2 catalysts obtained by treating ZrO(OH)2 hydrogel with different alcohol solvents. The amounts of both acidic and basic sites on the catalyst surface increased obviously. The catalytic activity (CO conversion) of ZrO2 catalysts also increased after the treatment with different alcohol solvents. The highest activity was obtained over the catalyst which was pretreated with isopropanol. However, alcohol solvent treatment retarded the transformation of ZrO2 crystal structure from tetragonal phase to monoclinic phase, and subsequently resulted in the decrease of monoclinic phase in ZrO2, which led to the decrease of olefin selectivity in corresponding hydrocarbon products (C2=～C4= /CH).     

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.     

Nanocomposites based on nickel ferrites dispersed in sol–gel silica matrices

In this work, we describe the effects of thermal treatments on the structural, morphological, and textural properties of nanocomposites formed by nickel ferrite dispersed in xerogel and aerogel silica matrices. The catalytic properties for the total oxidation of an organochloro model contaminant, the chlorobenzene, are also evaluated. Wet samples with different amounts of NiFe₂O₄ in matrix were prepared by sol–gel process. Xerogels and aerogels obtained in monolithic form were prepared by controlled and hypercritical drying, respectively, and heated at temperatures between 300 and 1,100°C. The specific surface area and total pore volume of the samples change with heating mainly due to the variation on their texture. The xerogel treated at 500°C and the aerogel treated at 700°C showed the most catalytic activity, converting chlorobenzene at temperatures as low as 150°C, while the other catalysts were active only at temperatures higher than 300°C. No organic by-products were observed in the oxidation of chlorobenzene, suggesting that total oxidation takes place under the reaction conditions. A strong decrease in catalytic activity was observed for nanocomposites treated at 1,100°C, due to matrix densification, which led to the encapsulation of the ferrite particles and hindered the access of the gas to the ferrite surface.     

Application of Alumina Aerogels as Catalysts

Al₂O₃ gels prepared by hydrolysis of Al-alkoxide were applied as catalysts for NO reduction by hydrocarbon. Xerogels were obtained by drying at 90°C, for 24 h, in air. Aerogels were prepared by supercritical drying of the wet gels in ethanol, using an autoclave. The catalyst activity of the gels for NO reduction with C₃H₆ as determined at 200–600°C in a fixed bed flow reactor. NO conversion to N₂ was about 60% at 550°C with both catalysts, and at 600°C it was better with the aerogel than with the xerogel. The specific surface area of the xerogel, which was larger than that of the aerogel as-dried, decreased to 1/3 by annealing at >500°C. However, the surface area of the aerogel hardly changed by annealing at temperatures up to 700°C. The bimodal pore size distribution of the aerogel hardly changed by annealing, too. The microstructure of the aerogels is stable at high temperatures, and they are better catalysts at high temperatures.     

氧化铝载体对Pt-Sn/Al2O3催化剂上苯胺和苯甲醇一步合成N-苯基苄胺催化反应性能的影响

以基于借氢策略的苯甲醇和苯胺一步合成N-苯基苄胺为模型反应,研究了三种不同表面结构的氧化铝对其负载的Pt-Sn催化剂上N-烷基化合成仲胺反应性能的影响.采用N₂吸附-脱附法、压汞法、X射线衍射、透射电镜、扫描电镜、CO脉冲吸附、H₂-程序升温还原及NH₃-程序升温脱附等技术对载体和Pt-Sn/Al₂O₃催化剂进行了表征.结果表明,与Al₂O₃相互作用较弱且高度分散的Pt颗粒具有很高的催化活性,Al₂O₃载体较大的孔体积和大孔分布的孔结构有助于反应物扩散和吸附到催化剂表面并提高反应活性.同时也有利于反应产物从催化剂表面离开,从而提高催化剂的稳定性.然而Al₂O₃较强的酸性及酸性分布降低了产物仲胺的选择性和催化剂稳定性.