Genesis and activity of mo-based hydrotreating catalysts prepared by a sol-gel method

Molybdenum oxide-alumina catalysts used in hydrodesulfurization (HDS) with a wide range of Mo loadings (1–25% Mo) were prepared by the sol-gel process. Two different methods of adding the molybdenum oxide precursor to the support were used.In the first route, alumina is prepared by hydrolysis of aluminium tri sec-butylate in butanol and butanediol, and molybdenum is deposited by a classical dry impregnation with ammonium heptamolybdate (AHM). In the second route, the molybdenum oxospecies are dispersed in butanediol and added to the aluminium alkoxide before hydrolysis. The solids were calcined to obtain the oxide precursors which are then sulfided to give the active phase in hydrodesulfurization.The effect of preparation on the structural properties of alumina as well as on the state and dispersion of molybdenum in the dried, calcined and sulfided form was studied by various characterization techniques (XRD, XPS, Raman spectroscopy). Molybdenum appears to be present as well dispersed oxomolybdenum species in the oxide form even at high loadings. This good dispersion of molybdenum is preserved after sulfidation which induces the formation of MoS₂ crystallites whose morphology has been determined by HREM.The catalyst activities were evaluated in thiophene hydrodesulfurization and compared with that of catalysts prepared by dry impregnation of a commercial alumina. The observed performances are in agreement with the good dispersion of molybdenum at high loadings we were able to obtain owing to the sol-gel process.     

Sol-Gel Preparation of Highly Active Sulfated Zirconia Supported by Alumina Catalysts

A series of sulfated mixed oxides of alumina and zirconia having a relative composition of 5% and 10% of ZrO₂ was prepared by means of sol-gel methods using zirconium propoxide or zirconium acetylacetone as precursor. The characterization of the physicochemical properties was carried out using ²⁷Al NMR, XRD, N₂ adsorption at 77 K, thermogravimetry, FTIR analysis of adsorbed pyridine, ²⁷Al NMR-MAS and XPS. The catalytic properties were studied by means of isomerization of n-hexane at 250°C. Results obtained allowed to propose that the use of Zr(acac)₄ as a zirconium precursor leads to a better retention of sulfate species which seems to form polymeric superficial sites. The symmetry of aluminium undergo an increase from tetrahedral to octahedral coordination and Zirconium atoms seems to be located in the second coordination sphere of Al. XRD analysis indicated an amorphous structure of obtained solids calcined at 650°C. The sulfated solids presented both Lewis and Brönsted acidic sites. Catalytic results showed that both activity and selectivity towards isomerization products were better using Zr (acac)₄ as precursor. Furthermore, the increase of the Zr loading affected considerably the catalytic properties of sulfated zirconia supported by alumina.     

Comparative study of the textural and structural properties of the aerogel and xerogel sulphated zirconia

Aerogel and xerogel sulphated zirconia with defined atomic ratio S/Zr = 0.5 and molar hydrolysis ratio h = nH₂O/nZrO₂ = 3 show different textural and structural properties after calcination at high temperatures. The aerogel obtained just after solvent evacuation develops only the tetragonal phase, whereas the xerogel dried in an oven is amorphous. Heating to a temperature above 833 K, leads to transition of the tetragonal phase to the monoclinic one for the two solids, due to sulphur loss but the tetragonal phase remains stable for the aerogel . Raman, Infrared and XPS spectroscopies show that the loss of the sulphur at high temperatures seems to be easier for the xerogel than for the aerogel.     

Isobutane dehydrogenation over chromia alumina catalysts prepared from MIL-101: Insight into chromium species on activity and selectivity

Various mesoporous chromia alumina catalysts were prepared by five different methods based on a metal-organic framework MIL-101 and their catalytic performances over isobutane dehydrogenation were investigated. The highly dispersed chromium species were produced on catalyst KCr Al-I1 with largest specific surface area of 198 m2 g-1prepared with aluminium isopropoxide(Al(i-OC3H7)3) by ultrasonic impregnation method. However, the catalyst KCr Al-I2 synthesized by stirring impregnation possessed crystalline α-Cr2O3 phase, which was poorly dispersed. Two types of Cr-rich and Al-rich Crx Al2-xO3 solid solutions, designated as Cr Al-I and Cr Al-II phase, were formed over the catalysts KCr Al-I3(prepared by Al(i-OC3H7)3with nitric acid regulation), KCr Al-C4(prepared by aluminium chloride hexahydrate) and KCr Al-N5(prepared by aluminium nitrate nonahydrate). Catalytic evaluation results revealed that KCr Al-I1 exhibited the high isobutane conversion due to its highly dispersed chromium species. However, KCr Al-I3, KCr Al-C4 and KCr Al-N5 showed the higher isobutene selectivity(95.2%-96.4%) on account of the formation of chromia alumina solid solutions in the catalysts. Moreover, the solid solution over the chromia alumina catalysts could greatly suppress the coke formation.     

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。     

负载型氧化锆催化剂上甲醇脱氢制甲醛

甲醇在无氧条件下脱氢,可以制得含水量极低的甲醛。在上述反应中,主要采用以硅胶为载体的负载型氧化物催化剂,其中以周期表ⅠB和ⅡB族金属,如铜、银或锌为主要组分。这些金属的氧化物在高温下易还原、烧结和表面积炭而使催化剂失活。添加P,S,Se或Te等组分作为助催化剂,在一定程度上可以改善催化性能。最近的发展倾向是采用非负载的碱金属盐作为催化剂,如Na_2CO_3,Na_2MoO_4,或Na_xLi_(1-x)AlO_2(0≤x≤1)。这类催化剂要求过高的反应温度,如高于650℃,甚至900℃条件下使用。     

锰铈混和氧化物气凝胶催化剂的研究

采用溶胶-凝胶法和超临界干燥技术制备出CeO2和Ce1-xMnxO2(x分别为0.05, 0.10, 0.15,0.20)气凝胶。以硝酸锰浸渍制得的氧化铈气凝胶Mn/CeO2,用TEM、BET、一氧化碳催化氧化活性评价和H2-TPR对所制备的催化剂进行了研究。TEM、BET的结果表明，随着锰含量的增加，氧化铈气凝胶的粒度减小，表面积增大。一氧化碳催化氧化活性评价显示,氧化铈中添加锰制得的催化剂的一氧化碳低温催化氧化的活性比未添加锰的氧化铈提高。且锰加入量为15 mol%时，气凝胶的催化活性最高。锰的引入方式不同，气凝胶的催化活性不同。浸渍方式负载锰所制备的Mn/CeO2气凝胶的一氧化碳催化氧化活性低于Ce1-xMnxO2(x分别为0，0.05, 0.10, 0.15,0.20)气凝胶。TPR实验发现，与氧化锰相同，氧化铈上负载的锰的还原也分三步进行。     

TiOx(x＜2)表面修饰Ni/TiO2-SiO2催化顺酐液相选择加氢合成γ-丁内酯

以TiO2-SiO2复合氧化物气凝胶为载体,制备了一系列Ni/TiO2-SiO2催化剂,并采用N2物理吸附-脱附、H2程序升温还原/脱附、X射线衍射及原位漫反射傅里叶变换红外光谱等技术对催化剂进行了表征,考察了载体中钛含量对催化剂结构、表面性质及其催化顺酐液相选择加氢合成γ-丁内酯反应性能的影响.结果表明,较小的Ni0...     

介孔氧化铝负载Ni-Co氧化物催化剂上丙烷氧化脱氢制丙烯

以非离子型三嵌段共聚物作为模板剂, 异丙醇铝为氧化铝的前驱物, 采用一锅法合成了一系列介孔氧化铝负载镍氧化物、钴氧化物以及镍-钴双金属氧化物催化剂, 并以介孔氧化铝为载体, 采用浸渍法制备了负载Ni-Co 氧化物催化剂. 采用N₂吸附-脱附、高分辨透射电镜(HRTEM)、X射线粉末衍射(XRD)、H₂程序升温还原(H₂-TPR)以及激光拉曼光谱(LRS)等技术对催化剂的结构与性质进行表征, 并考察了催化剂的丙烷氧化脱氢反应性能. 结果表明: 一锅法制备的各催化剂均有大的比表面积和规整的孔道结构, 且负载的金属氧化物高度分散; 而浸渍法制备的催化剂, 其载体的介孔结构被破坏并有Co₃O₄晶相生成. 在考察的催化剂中, 一锅法合成的介孔氧化铝负载Ni-Co 氧化物催化剂表现出最佳的丙烷氧化脱氢性能. 在450 °C、C₃H₈:O₂:N₂的摩尔比为1:1:4和空速(GHSV)为10000 mL·g^-1·h^-1条件下, 该催化剂上丙烯产率为10.3%, 远高于浸渍法制备的催化剂上所获得的丙烯产率(2.4%). 关联催化剂表征和反应结果, 讨论了催化剂结构与性能之间的关系.     

Physicochemical properties and hydrogenation activity of nickel-alumina aerogels

Nickel-alumina aerogel catalysts were prepared by three methods: (I) hydrolysis of a mixture of aerogel precursors, followed by cogelation of the sols obtained and drying under supercritical conditions; (II) impregnation of thermally treated alumina aerogels with nickel salt solutions followed by drying of the suspensions obtained under supercritical or (III) conventional conditions. Activity of the aerogel catalysts prepared was determined in cyclohexene hydrogenation.     

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。     

Effects of promoters on catalytic performance of Fe-Co/SiO2 catalyst for Fischer-Tropsch synthesis

2%Fe-10%Co/SiO₂ catalysts with different potassium or zirconium loadings were prepared by aqueous incipient wetness impregnation and tested for Fischer-Tropsch synthesis in a flow reactor, using H₂/CO = 1.6 (molar ratio) in the feed, under the condition of an overall pressure of 1 MPa, GHSV of 600 h⁻¹ and temperature of 503 K. The zirconium and potassium promoters remarkably influenced hydrocarbon distribution of the products. CO conversion increased on the catalysts with the increase of zirconium loadings, which indicated that zirconium enhanced the activity of iron-cobalt catalysts. Low potassium loadings also enhanced the activity of the catalysts. However, high potassium loading made CO conversion on the catalysts decrease and weakened the secondary hydrogenations. The catalyst was characterized by BET, XRD and TPR. The catalyst characterization revealed that the Co₃O₄ phase was presented on the fresh catalyst, whereas the spinel phase of Fe-Co alloy and CoO existed on the used catalyst.     

Hierarchical Porous and Three-Dimensional MXene/SiO2 Hybrid Aerogel through a Sol-Gel Approach for Lithium–Sulfur Batteries

A unique porous material, namely, MXene/SiO₂ hybrid aerogel, with a high surface area, was prepared via sol-gel and freeze-drying methods. The hierarchical porous hybrid aerogel possesses a three-dimensional integrated network structure of SiO₂ cross-link with two-dimensional MXene; it is used not only as a scaffold to prepare sulfur-based cathode material, but also as an efficient functional separator to block the polysulfides shuttle. MXene/SiO₂ hybrid aerogel as sulfur carrier exhibits good electrochemical performance, such as high discharge capacities (1007 mAh g^–1 at 0.1 C) and stable cycling performance (823 mA h g^–1 over 200 cycles at 0.5 C). Furthermore, the battery assembled with hybrid aerogel-modified separator remains at 623 mA h g^–1 over 200 cycles at 0.5 C based on the conductive porous framework and abundant functional groups in hybrid aerogel. This work might provide further impetus to explore other applications of MXene-based composite aerogel.     

Synthesis and characterization of multiwall carbon nanotubes/alumina nanohybrid-supported cobalt catalyst in Fischer-Tropsch synthesis

Multiwall carbon nanotubes (MWNTs) and alumina are combined to give a new type of nanohybrid for Fisher-Tropsch synthesis (FTS) catalyst support. Alumina nano-particles (10 wt%) were introduced directly on functionalized MWNTs by a modified sol-gel method. Microstructure observations show that alumina particles were homogeneously dispersed on the inside and outside of modified MWNTs surfaces. 15 wt% cobalt loading catalysts were prepared with this nanohybrid and γ-alumina as a reference, using a sol-gel technique and wet impregnation method respectively. These catalysts were characterized by TEM, XRD, N₂-adsorption, H₂ chemisorption and TPR. The deposition of cobalt nanoparticles synthesized by sol-gel technique on the MWNTs nanohybrid shift the reduction peaks to a low temperature, indicating higher reducibility for uniform cobalt particles. Nanohybrid also aided in high dispersion of metal clusters and high stability and performance of catalyst. The proposed MWNTs nanohybrid-supported cobalt catalysts showed the improved FTS rate (g_HC/(g_cat·min)), CO conversion (%), and water gas shift rate (WGS)(g_CO2/(g_cat·h)) of 0.012, 52, and 30E-3, respectively, as compared to those of 0.007, 25, and 18E-3, respectively, on the γ-alumina-supported cobalt catalysts with the same Co loading.     

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 .     

Preparation of Alumina Supported Palladium Catalysts by Sol-Gel Method

The chemical reactivity of the aluminium-sec-butoxide (ASB) and the palladium acetylacetonate Pd(acac)₂, used as precursors for the preparation of the alumina supported palladium catalysts by sol-gel method was investigated by the spectroscopic study of the precursor mixture during ageing, using FTIR, UV-VIS and ²⁷Al NMR. The obtaind results showed that acetylacetonate ligands were linked to aluminum when the mixture was aged at 40°C. This was proved by the bands observed at 1530 and 1600 cm^–1 in the FTIR spectra, the band obtained at 289 nm in the UV-VIS spectra and the ²⁷Al NMR sharp peak at 3 ppm. Furthermore, in order to avoid the Pd(acac)₂ reduction to metallic palladium by the SB occurring when the mixture is aged for 3 h, an optimum ageing time should be selected. The precursors modification and the preservation of the palladium oxidation state during ageing could be the required conditions to create a bond between palladium and aluminium during the gelation step. This should be the reason of the thermal stability improvement of the alumina supported palladium catalyst prepared by the sol-gel method.     

Promoting effect of sol-gel method and pre-treatment on the activity of SnO2/Al2O3 catalyst for NO reduction by propene

SnO₂/Al₂O₃ catalyst prepared by sol-gel method showed higher activity than those prepared by impregnation method, and their activity was significantly improved by pre-treatment in the reaction gas. The increased activity is closely related to the agglomeration of SnO₂ species and the re-exposure of Al₂O₃, which was previously covered by dispersed SnO₂ species. This revised version was published online in June 2006 with corrections to the Cover Date.     

New process to control hydrolysis step during sol-gel preparation of sulfated zirconia catalysts

Sulfated zirconia catalysts were prepared by sol-gel process using a new method allowing the control of the hydrolysis step of zirconium alkoxides. Prepared samples were characterized by N₂ adsorption (desorption) at 77 K, XRD, chemical analysis of total sulfur and XPS. Catalytic properties have been evaluated in n-butane and n-hexane isomerization reactions. Obtained results show that time necessary for gelation is significant and depends considerably on the nature of the zirconium precursor. Concerning the properties of the solids obtained by this method, it has been noted that the use of the zirconium propoxide led to a better retention of the sulfate species, which improves activity during isomerization reactions. It has been found also that an initial S/Zr molar ratio equal to 0.5 allowed to obtain an optimal sulfur content and a high specific surface area.     

Composite SiO2—Iron Oxide Materials for Magnetically Intensified Adsorption

Composite SiO₂—iron oxide materials were prepared by three experimental procedures. In the first case, the iron oxides were precipitated during a sol-gel process. In the second case, a SiO₂ matrix was initially obtained, and the iron oxides were formed by thermal treatment after impregnation of a soluble Fe²⁺ salt in the previously processed matrix. In the third method, ferrite powders, prepared by wet chemical method, were embedded into a SiO₂ based sol-gel matrix. Materials with convenient porosity and nano-sized iron oxide content could be prepared using the mentioned methods. The prepared composite has been tested for arsenic(V) removal.     

Application of Sol-Gel Method to Preparation of Ultra-Uniform Co-Based Catalysts for Fischer-Tropsch Reaction

Uniformly dispersed Co/SiO₂ catalysts (10–60 wt% on metal basis) were prepared by the sol-gel method, and used for the Fischer-Tropsch (F-T) synthesis in slurry phase at 503 K and 1 MPa in a flow of synthesis gas (H₂/CO = 2/1, W/F = 10 g-catal·h/mol). The catalysts were characterized by temperature-programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and chemisorption. Although CO conversion over the unpromoted catalysts prepared by the sol-gel method was lower than the conventional catalysts prepared by impregnation, the catalytic activity of the former catalysts was more stable than the latter catalysts. The conversion was improved drastically, when 0.01–1 wt% of Ir or Ru (on metal basis) was added to the catalysts prepared by the sol-gel method. The TPR and XPS spectra and the H₂ chemisorption revealed that the noble metal addition was responsible for the reduction of Co particles in the catalysts. It is supposed that the durability of the promoted catalysts prepared by the sol-gel method was ascribed to the high dispersion of Co particles stabilized on the catalyst surface.