Improvement of the Pd/Al2O3 Catalyst by the Control of the Sol-Gel Preparative Parameters

In this work, the metal dispersion of the Pd/Al₂O₃ catalyst prepared by sol-gel method is improved by an adequate optimisation of the preparative variables. First, the gelation temperature and the ageing time are selected, in order to avoid the reduction of the metal precursor (palladium acetylacetonate, Pd(acac)₂) by the solvent (sec-butanol, sB). The metal sintering effect on the catalysts treated in oxygen at 500°C is then minimized when the alumina pore size is controlled by the variation of the alumium alkoxide (AsB) concentration and the acetic acid amount ([AcA]/[AsB]). The appearance of new palladium particles on the alumina surface and the matching between the particle diameters and the pore sizes were also effective for the metallic surface area improvement on the samples treated in oxygen at 800°C. Compared to the reference catalysts, the higher metal dispersion obtained on the sol-gel ones was the determinant factor for their higher catalytic activity in methane combustion.     

Effect of Preparation Conditions on the Stability of Pt/Al2O3 Catalysts in Methane Combustion

Alumina supported platinum catalysts were prepared by sol-gel method using aluminum-sec-butoxide, platinum acetylacetonate and sec-butanol. Various gelation process were performed either by the help of a gelation agent (water or acetic acid) or by a slow condensation without hydrolysis source. The textural and the structural study of the catalysts using the nitrogen physical adsorption and the hydrogen chemisorption showed that the BET surface area and the metal dispersion varied when the hydrolysis and the gelation processes were modified. The catalytic activities for methane combustion performed on the fresh and aged catalysts were correlated to the metal dispersion values. In addition the catalytic activity loss under reaction mixture seemed to be caused by the metal dispersion decrease. When the catalysts were aged under the reaction mixture at 600°C for 72 h, a BET surface area decrease and a metallic surface area loss were observed. The resistance to sintering observed to be dependant on the hydrolysis and the gelation processes was in favor of the catalyst prepared by acetic acid.     

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.     

碳纳米管负载的Fe2O3催化剂制备

Carbon nanotubes were modified by FeSO₄-H₂O₂ system, iron hydroxides were adsorbed on the wall of carbon nanotubes simultaneously. These precursors were treated at 723K for 2 h under hydrogen, nitrogen and air atmosphere to prepare carbon nanotubes supported γ-Fe₂O₃catalyst, γ-Fe₂O₃and α-Fe₂O₃compound catalyst and amorphous Fe₂O₃catalyst, respectively. This is green method to prepare high Fe₂O₃loading (≥50 %) catalyst without adding other cation. The different structures Fe₂O₃catalysts can be synthesized by controlling the condition of thermal treatment to content active phase requirements for different catalytic reactions. The paper presents a new method to prepare carbon nanotubes supported catalysts.     

Ultradeep Hydrodesulfurization of Dibenzothiophene (DBT) Derivatives over Mo-Sulfide Catalysts Supported on TiO2-Coated Alumina Composite

The present paper reviews in detail the different studies now being conducted by our research team concerning the ultradeep hydrodesulfurization (HDS) of dibenzothiophene (DBT) derivatives over Mo/TiO₂ and Mo/TiO₂–Al₂O₃ catalysts. First, a detailed characterization of Mo/TiO₂ (P-25 Degussa, 50 m²/g) catalysts prepared by equilibrium adsorption technique shows that Mo- species are highly and uniformly dispersed on the surface of titania up to 6.6 wt% MoO₃ loading. Above this value, some aggregation of Mo occurs, leading to the formation of bulk MoO₃. Below 6.6 wt% MoO₃ loading, the Raman spectroscopy data of the calcined samples show that the supported Mo-species possess a highly distorted octahedral MoO₆ structure. TiO₂–Al₂O₃ composites were prepared by chemical vapor deposition (CVD) using TiCl₄ as a precursor. Using several characterization techniques, we demonstrated that the support composite presents a high dispersion of TiO₂ over -Al₂O₃ without forming precipitates up to ca. 11 wt% loading. Moreover, the textural properties of the composite support are comparable to those of alumina. Under the present sulfidation conditions (673 K, 5%H₂S/95%H₂), Mo-species supported on TiO₂ are better sulfided than on alumina, as demonstrated using XPS. This can be attributed to the relatively lower interaction between Mo-species and titania. The state of sulfide species supported on the composite support can be considered as a transition state between TiO₂ and Al₂O₃. However, at relatively higher TiO₂ loadings (ca. 11 wt%), Mo/TiO₂–Al₂O₃ catalysts exhibit sulfidability similar to that of Mo/TiO₂. The HDS tests conducted in both the laboratory and in industry show that sulfide catalysts supported on TiO₂–Al₂O₃ (ca. 11 wt% TiO₂) are more active than those supported on TiO₂ or Al₂O₃.     

Thermal Stability of Pt/Al2O3 Catalysts Prepared by Sol-Gel

A series of Pt/Al₂O₃ catalysts were prepared using a sol-gel method. The influence of several parameters used in the synthesis including: metal content, identity of the metal precursor, and the water/alkoxide ratio on the structural properties of the fresh (dried) and calcined samples were studied. It was found that the BET surface area decreased with an increase in the platinum content. A surface area of 500 m²/g was obtained following calcination at 773 K. The structure of fresh samples as determined by FTIR corresponded to that of a pseudoboehmite structure. Samples prepared using a water/alkoxide ratio (H₂O/ATB) of 9 showed a well-defined, uniform pore size distribution following calcination at 773 K. Metal dispersions comparable to those obtained using impregnation methods were obtained. Aging studies (calcination at 873 K for 24 h) performed on these catalysts, exhibited sintering behavior which were similar to Pt/Al₂O₃ catalysts prepared by other methods. The sample prepared using a H₂O/ATB ratio of 9 had the highest surface area and was more thermally resistant towards metal sintering. A bimodal metal particle size distribution was observed: some particles exhibited sintering while others of similar size showed a greater thermal stability to sintering. The sample having the largest surface area and the highest thermal stability following thermal treatment was a consequence of a more condensed structure and a higher pore roughness obtained after drying the gel. This enabled the formation of an alumina structure which was more amorphous and limited aggregation of platinum particles due to surface diffusion within the pore structure.     

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.     

New Gelation Process for Pt/Al2O3 Catalysts Preparation

Gel of platinum and aluminum was prepared by an anhydrous gelation process using a mixture of aluminum sec butoxid, platinum acetylacetonate and Butanol-2. The investigation of this gelation by FTIR, UV-vis and ²⁷Al NMR spectroscopies suggest that a slow polymerization of aluminum precursors occurs according to an etheration mecanism likely catalysed by metallic platinum which could be formed by the reduction of platinum in Pt(acac)₂ by sBuOH in the mixture during aging.     

模板-聚合法Pd/Al2O3催化剂制备及其蒽醌加氢性能研究

以丙烯酸铵为模板剂,由油柱成型法制备了系列球形Al2O3载体,采用XRD、BET等分析测试手段对其晶体结构、比表面积、孔容和孔径分布进行了表征,结果表明,600℃焙烧的球形γ-Al2O3载体具有介孔结构,并且比表面较不使用模板剂的样品有大幅度增加。焙烧温度升至960℃得到δ-Al2O3,介孔结构消失,但由于结构记忆效应,载体的大表面特性得以保持。以δ-Al2O3为载体制备Pd/Al2O3催化剂,采用氢-氧滴定(HOT)方法测定发现,比表面的增加显著提高了Pd金属的分散度,从而大幅度提高了催化剂的蒽醌加氢活性,氢化效率最高可达10.5 g.L-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。     

微乳法合成可控粒径纳米Pt/Al2O3电催化CO氧化的尺寸效应

采用微乳法室温下合成了粒径可控Pt/Al₂O₃催化剂(1～10 nm), 以CO电催化氧化为探针反应考察了Pt微粒尺寸与催化反应性能之间的关系. 利用透射电镜(TEM), 扫描电镜(SEM), 循环伏安法(CV)等手段对催化剂进行表征, 结果表明催化剂性能与Pt粒径之间存在明显的尺寸效应, 催化剂存在最佳活性尺寸.     

Highly Dispersed and Stable Supported Metal Catalysts Prepared by Solid Phase Crystallization Method

Starting from the precursors containing active metal species in the crystal structure, highly dispersed supported metal catalysts have been prepared by the calcination-reduction treatment. This method is named as solid phase crystallization (spc) method and was compared with the conventional impregnation (imp) method. As the precursors, both perovskite-type and hydrotalcite-type oxides have been utilized for preparing various supported metal catalysts, which were successfully applied for the reforming of CH₄ and the decomposition of methanol. Especially spc-Ni/Mg–Al catalyst prepared from the hydrotalcite-type precursors showed high activity as well as high sustainability for the hydrogen production from methane.     

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.     

改性介孔Al_2O_3负载的高分散铜基催化剂的结构与催化性能

采用浸渍法制备了LaCeZr或YCeZr改性的γ-Al2O3负载的系列Cu基催化剂,运用XRD、BET、EXAFS、XPS和H2-TPR等技术对催化剂的结构进行了详细表征,探讨了催化剂中Cu物种的存在形式及其还原性能,并与CO的氧化性能相关联。氮气吸附-脱附测试结果表明,催化剂具有很高的比表面积以及较均一的介孔结构。XRD结果表明,未改性的γ-Al2O3负载的Cu基催化剂经800℃高温焙烧后,Cu物种与载体作用强烈,形成了CuAl2O4尖晶石相,而EXAFS结果显示,助剂改性后的γ-Al2O3负载的Cu基催化剂上Cu物种主要以高分散的CuO形式存在,促进了催化剂对CO的低温氧化性能。H2-TPR结果表明,同一系列样品随焙烧温度提高,CuO的还原温度升高,晶格氧的活动度降低,导致活性的下降。LaCeZr改性的γ-Al2O3负载的铜基催化剂于650℃焙烧后显示出了较强的抗硫和抗水性能。     

Mn修饰Al2O3载体负载Pd催化剂及其蒽醌加氢催化性能

以活性氧化铝(γ-Al2O3)为载体,分别以Mn(NO3)2溶液和酸性氯化钯(PdCl2)溶液为修饰组分和活性组分前体,采用分步浸渍法制备了Mn修饰Al2O3载体负载钯催化剂。将催化剂应用于蒽醌加氢反应,考察了催化剂制备方法、活性组分负载量和催化剂还原温度对反应效果的影响。用XRD、BET、XPS和TPR对催化剂进行了表征。结果表明,催化剂活性受到制备方法的影响,在对Mn修饰Al2O3载体进行焙烧,Pd负载量0.2(wt)%、还原温度300℃的条件下,催化剂蒽醌加氢活性较高,较未修饰的催化剂提高了约16%。催化剂中Mn以MnO的形式存在,影响了γ-Al2O3的组织结构,使载体与活性组分之间的作用力增强,活性组分Pd高度分散在催化剂表面,从而提高了催化剂的活性。     

The Preparation and Characterization of Highly Dispersed PdO over Alumina for Low‐temperature Combustion of Methane

PdO/Al₂O₃ catalysts prepared by glow discharge plasma treatment followed by thermal calcination show a much higher dispersion and a better catalytic activity for methane combustion at relatively low temperatures. The dispersion of palladium active species by such plasma prepared catalysts is 29.7%, 5.4 times higher than that of conventional catalysts. XPS analysis indicates that a surface enrichment of Pd active species (PdO) has been achieved after plasma treatment. The surface atomic composition of PdO of plasma prepared catalysts reaches 10.5%. XRD characterization also confirms a wellcrystallized PdO phase present on the plasma prepared catalyst. The lightoff temperature of the plasma prepared catalyst is 370°C, 50°C lower than that obtained from the conventional catalyst.     

Carbon Dioxide Reforming of Methane over Ni Catalysts Supported on Al2O3 Modified with La2O3, MgO, and CaO

The preparation of synthesis gas from carbon dioxide reforming of methane (CDR) has attracted increasing attention. The present review mainly focuses on CDR to produce synthesis gas over Ni/MO_x/Al₂O₃ (X = La, Mg, Ca) catalysts. From the examination of various supported nickel catalysts, the promotional effects of La₂O₃, MgO, and CaO have been found. The addition of promoters to Al₂O₃-supported nickel catalysts enhances the catalytic activity as well as stability. The catalytic performance is strongly dependent on the loading amount of promoters. For example, the highest CH₄ and CO₂ conversion were obtained when the ratios of metal M to Al were in the range of 0.04–0.06. In the case of Ni/La₂O₃/Al₂O₃ catalyst, the highest CH₄ conversion (96%) and CO₂ conversion (97%) was achieved with the catalyst (La/Al = 0.05 (atom/atom)). For Ni/CaO/Al₂O₃ catalyst, the catalyst with Ca/Al = 0.04 (atom/atom) exhibited the highest CH₄ conversion (91%) and CO₂ conversion (92%) among the catalysts with various CaO content. Also, Ni/MgO/Al₂O₃ catalyst with Mg/Al = 0.06 (atom/atom) showed the highest CH₄ conversion (89%) and CO₂ conversion (90%) among the catalysts with various Mg/Al ratios. Thus it is most likely that the optimal ratios of M to Al for the highest activities of the catalysts are related to the highly dispersed metal species. In addition, the improved catalytic performance of Al₂O₃-supported nickel catalysts promoted with metal oxides is due to the strong interaction between Ni and metal oxide, the stabilization of metal oxide on Al₂O₃ and the basic property of metal oxide to prevent carbon formation.     

Sol-Gel Poly-Component Nano-Sized Oxide Powders

Nano-sized, amorphous and monodispersed poly-component powders in the Al₂O₃–TiO₂–MgO and Al₂O₃–TiO₂–SiO₂ systems have been obtained by the sol-gel method. These powders have been characterized by XRD, IR spectroscopy, DTA/TGA and EDAX spectrometry. This last method confirmed the composition of the ternary powders, which are formed during the gelation process.The powders were tested as precursors for obtaining advanced ceramics, as tialite, Al₂TiO₅. The samples prepared with powders obtained by sol-gel method have shown a high reactivity, and the formation of tialite was improved.     

溶胶-凝胶法制备MoO3/SiO2催化草酸二甲酯和苯酚酯交换反应

采用溶胶-凝胶法在碱性条件下制备了一系列MoO_3/SiO_2催化剂用于草酸二甲酯和苯酚酯交换反应,并利用XRD、IR、XPS、NH3-TPD等表征催化剂结构.结果表明:弱酸中心是草酸二甲酯和苯酚酯交换反应的活性中心.当MoO_3负载量为12%(重量百分比),p H为9.1时的MoO_3/SiO_2催化剂具有更高的催化性能,这可能与该催化剂表面Mo物种分散更好和更高的酸量有关.在1.20 g MoO_3/SiO_2催化剂,0.20 mol苯酚,n(草酸二甲酯)/n(苯酚)=2,180℃反应3 h的条件下,苯酚转化率达70.0%,甲基苯基草酸酯和草酸二苯酯选择性分别为88.4%和11.5%.     

负载Ni催化剂上1,4-丁炔二醇加氢反应的载体效应研究

制备了Ni负载量为15%的3种催化剂Ni/Al_2O_3、Ni/SiO_2、Ni/ZrO_2,考察了其在1,4-丁炔二醇加氢反应中的催化性能,结合XRD、H_2-TPR、H_2-TPD、N_2物理吸附等表征,研究了载体性质对催化剂1,4-丁炔二醇加氢性能的影响.结果表明,Ni/SiO_2催化剂上,由于Ni与SiO_2间弱的相互作用,Ni物种主要以大晶粒形式存在,产生大量弱吸附H_2物种,有利于低温下1,4-丁炔二醇加氢,在温度50℃,氢气压力1 MPa时,反应2 h可实现1,4-丁炔二醇的完全转化,1,4-丁烯二醇和1,4-丁二醇选择性分别达到68.1%与18.2%.Ni/Al_2O_3中Ni与载体间具有强相互作用,主要存在Ni-Al_2O_3界面或溢流到Al_2O_3载体表面的强吸附H_2物种,而Ni表面的弱吸附H_2物种较少,催化加氢活性明显降低.Ni/ZrO_2中由于还原过程中ZrO_2的迁移包裹作用,Ni表面低温吸附H_2物种最少,活性最低,1,4-丁炔二醇转化率仅为8.1%,主产物为1,4-丁烯二醇.