Deposition of CoO onto MoO3/Al2O3 hydrodesulfurization catalysts by solvent assisted spreading

Solvent assisted spreading of CoO over monolayer MoO₃/Al₂O₃ catalysts has been studied. CoCO₃ · Co(OH)₂ and CoCO₃ reacted with MoO₃/Al₂O₃ in water slurries. CoO deposition over MoO₃/Al₂O₃ extrudates was followed by EPMA. In the set of eleven MoO₃/Al₂O₃ catalysts, the amount of CoO adsorbed was roughly proportional to the surface area of MoO₃ monolayer. The adsorbed Co species efficiently enhanced the HDS activity.     

UV Raman spectroscopic studies of V/θ-Al2O3 catalysts in butane dehydrogenation

To explore the coke formation mechanism and catalyst structure under alkane dehydrogenation (DH) conditions, the DH of butane on V/θ-Al₂O₃ was explored by in situ UV Raman spectroscopy and reactivity tests. Studies of butane DH on V/θ-Al₂O₃ catalysts with various distributions of surface VO_x species identify a structure–coke relationship. The deactivation of the catalysts in butane DH is due mainly to the formation of coke species. Both the nature and amount of coke formed are related to the structure of VO_x species. Monovanadates make chain-like polyaromatics, whereas polyvanadates produce mainly sheet-like (two-dimensional) polyaromatics that are detrimental to catalytic activity. The amount of coke formed from butane DH follows this sequence: polymeric VO_x > monomeric VO_x > V₂O₅, Al₂O₃. Raman spectroscopy studies of butane, 1-butene, cis/trans-2-butenes, and 1,3-butadiene reactions on V/θ-Al₂O₃ catalysts enable the formulation of a coke formation pathway for butane DH, in which polystyrene is found to be a key intermediate. Although the surface of V/θ-Al₂O₃ is partially reduced under butane DH conditions, the structure of VO_x species can be fully regenerated by oxidation of the coke species at temperatures up to 873 K.     

High resolution optical microprobe investigation of surface grinding stresses in Al2O3 and Al2O3/SiC nanocomposites

It has previously been suggested that Al₂O₃/SiC nanocomposites develop higher surface residual stresses than Al₂O₃ on grinding and polishing. In this work, high spatial resolution measurements of residual stresses in ground surfaces of alumina and nanocomposites were made by Cr³⁺ fluorescence microspectroscopy. The residual stresses from grinding were highly inhomogeneous in alumina and 2 vol.% SiC nanocomposites, with stresses ranging from ～ ?2 GPa within the plastically deformed surface layers to ～ +0.8 GPa in the material beneath them. Out of plane tensile stresses were also present. The stresses were much more uniform in 5 and 10 vol% SiC nanocomposites; no significant tensile stresses were present and the compressive stresses in the surface were ～ ?2.7 GPa. The depth and extent of plastic deformation were similar in all the materials (depth ～ 0.7–0.85 μm); the greater uniformity and compressive stress in the nanocomposites with 5 and 10 vol% SiC was primarily a consequence of the lack of surface fracture and pullout during grinding. The results help to explain the improved strength and resistance to severe wear of the nanocomposites.     

MoO3／Al2O3催化剂上MoO3的脱附平衡和流失速度

分别测定了在氮，水气氛下ＭｏＯ３自ＭｏＯ３／Ａｌ２Ｏ３催化剂上脱附的平衡数据。发现尽管ＭｏＯ３和Ａｌ２Ｏ３存在着强的化学作用，但气固平衡关系仍然可用Ｆｒｅｕｎｄｌｉｃｈ方程式描述。讨论了钼升华流失速度方程式与Ｆｒｅｕｎｄｌｉｃｈ式的关系。发现在氮水混合气流中，钼的流失总速度可以用它们单独存在时流失速度线性加和来表示。给出了水分压对流失速度影响的级数值。这一综合速度方程式经简化后，可以用于工业过程中钼流失数据的估算。     

Effect of the preparation method on the surface coverage of Mo/Al2O3 catalysts

Two series of Mo/Al₂O₃ catalysts were prepared by equilibrium adsorption and incipient wetness impregnation methods. The effect of preparation method on the surface coverages of the calcined catalysts was investigated by the combined use of CO₂ chemisorption, low temperature CO adsorption and ion scattering spectroscopy (ISS). For a given Mo loading, the CO₂ and CO adsorption results showed little difference between the two preparation methods. As previously noted, the CO₂ chemisorption method overestimated the Mo surface coverage. In contrast to the adsorption methods, the ISS technique gave different Mo surface coverage values for a given Mo content of the two series of catalysts. This apparent discrepancy was attributed to different repartition of the Mo phase between the internal and external surfaces which can only be detected by ISS. This interpretation is supported by the observed agreement between the coverage values measured from ISS and low temperature CO adsorption for presumably uniform catalysts obtained by the equilibrium adsorption method.     

FTIR study of the rearrangement of adsorbed CO species on Al2O3-supported rhodium catalysts

The adsorption of CO at low temperatures (130–293 K) has been investigated on Rh/Al₂O₃ catalysts of low (0.001–1 wt%) Rh loadings by means of Fourier transform infrared spectroscopy. The surface structure of Rh produced at different reduction temperatures (573 and 1173 K) was shock-cooled to 130 K, where the addition of CO caused the appearance of the band due to bridge-bonded CO ((Rh⁰)₂–CO) on all samples. The appearance of the bands due to gem-dicarbonyl (Rh⁺(CO)₂) and linearly bonded CO (Rh_x–CO) depended on the Rh content and the reduction temperature of the catalysts. The positions and the integrated absorbances of the symmetric and asymmetric stretchings of the Rh⁺(CO)₂ changed with temperature. On the basis of the above findings the rearrangement of the adsorbed CO species (indirectly that of surface Rh) is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

氧化铝载体对镍/氧化铝催化剂性能的影响

氧化铝是化工催化行业广泛应用的催化剂载体。油脂加氢催化剂主要是以氧化铝为载体、镍为主要活性组分的催化剂。在制备镍/氧化铝催化剂的过程中,载体氧化铝使用的最佳条件：载体在共沉淀反应前加入,载体氧化铝比表面积为340.6 m2/g,载体氧化铝加入量为m（镍）∶m（氧化铝）=5∶4,反应的老化时间为45 min。在此条件下,制备的镍/氧化铝催化剂活性最高,应用效果最好。     

Synergistic effect of Pd in methane combustion PdMnOx/Al2O3 catalysts

The catalytic methane combustion was investigated over alumina-supported monometallic and bimetallic palladium and manganese oxide catalysts. The catalytic activity of these systems showed that palladium incorporation on MnO_x/Al₂O₃ catalyst leads to an enhancement in methane combustion. The higher catalytic activity of the PdMn/Al₂O₃ catalysts is related to a greater mobility of lattice oxygen in manganese oxide in the presence of palladium. These bimetallic catalysts also showed a significant improvement in catalysts stability with respect the monometallic ones. Surface analysis of the used catalysts revealed less amount of coke and Mn/Al and Pd/Al atomic ratios almost unchanged, which is indication of absence of active phase sintering.     

The effect of La2O3 on dynamic OSC over the Pd/OSC/Al2O3-based catalysts

In this study, fresh and aged Pd/(OSC–Al₂O₃) and Pd/(Al₂O₃–OSC–La₂O₃) metallic monoliths (OSC material Ce_0.75Zr_0.25O₂) were used to find out the effect of La₂O₃ on the catalyst behaviour in dynamic oxygen storage capacity (OSC) measurements. In addition, the interaction of CO, NO and O₂ reaction compounds over the studied catalysts was investigated in order to understand the effect of La₂O₃ in the oxidation and reduction reactions in lean automotive exhaust gas conditions. A FT-IR gas analyser was used to analyse the product gas composition. The presence of La₂O₃ on fresh and aged catalysts had negative effect on both the dynamic OSC and the activity of the catalyst. The reason for this is the different washcoat compositions between the studied catalysts which could explain the differences in BET surface areas.     

EDTA对NiW／Al2O3催化剂表面金属分散性、形貌及HDN性能的影响

为提高负载催化剂中金属的分散性,以含EDTA螫合剂的浸渍液浸渍制备了NiW／Al2O3加氢处理脱氮催化剂,其中络合剂与Ni的摩尔比为1：1,考察了EDTA对活性金属分散性及加氢脱氮性能的影响。通过BET、XRD、XPS和HRTEM表征发现,EDTA的引人,可以提高M和W在氧化铝载体表面的分散性,W／A1原子比从0．096提高到0．127。EDTA的引入,同时减弱了活性金属与氧化铝载体间的相互作用,有利于形成堆积程度较高的WS：相。EDTA的引入,可以大幅提高催化剂对喹啉的加氢脱氮活性,相对于传统方法制备的催化剂,其加氢脱氮活性可提高27％。     

Effect of lithium and residual nitrate species on platinum dispersion in Pt/Al2O3 catalysts

The effect of lithium (ex LiNO₃) on the metallic dispersion of 0.8 wt% Pt/Al₂O₃ catalysts, prepared by different impregnation techniques, was investigated by temperature programmed reduction (TPR) and the frontal method of H₂ chemisorption. The temperature at which platinum precursor is reduced at a maximum rate (543 K) was not modified by 0.1 wt% lithium addition, whatever the preparation technique used. The dispersion values of platinum (70–90%), after reduction at 773 K, were slightly dependent on the preparation procedure. After the addition of 0.8 wt% lithium the TPR profile presented two well defind peaks and the dispersion values (20–50%), measured after reduction at 773 K, presented a significant decrease. The results are linked with the presence of residual nitrate ions, that had not been eliminated during calcination at 773 K in air, but had been decomposed under the reducing atmosphere of the TPR experiment.     

EXAFS study on the dispersion of molybdenum sulfide catalysts on γ-Al2O3

The dispersion of molybdenum sulfide catalysts was characterized based on the lateral dimensions of MoS₂ crystallites estimated by EXAFS. A new index ofN(Mo)/N(S), instead ofN(Mo), was used to estimate the average MoS₂ size to minimize the contribution of the coexisting oxide or oxisulfide phase in the catalysts. EXAFS showed some advantages over other techniques, such as TEM or XPS.     

Metal oxide catalysts for DME steam reforming: Ga2O3 and Ga2O3–Al2O3 catalysts

The steam reforming of dimethyl ether (DME) was performed on Ga₂O₃–Al₂O₃ mixed oxides prepared by sol–gel method. Ga₂O₃ significantly affects the catalytic performance with respect to the DME conversion and H₂ yield. The catalytic activity increases with the Ga concentration in Ga₂O₃–Al₂O₃ mixed oxides. It is very interesting that without the aid of an additional transition metal component, Ga₂O₃ and Ga₂O₃ containing Al₂O₃ mixed oxide system exhibit good activity in the reforming reaction. To the best of our knowledge, this is the first report that reveals the reforming ability of Ga₂O₃ for the production of H₂ from DME and/or methanol.     

Promoting effect of NiAl2O4 for supported Ni particles on sprayed Ni/Al2O3 catalysts

Ni/Al₂O₃ catalysts were prepared by the spray reaction method. The NiO particles supported on NiAl₂O₄ were stabilized against the aggregation and converted into smaller Ni particles by H₂ reduction. The Ni particles stabilized on NiAl₂O₄ marked anomalous high activity for CO hydrogenation, due to the stronger interaction between Ni and NiAl₂O₄. This revised version was published online in July 2006 with corrections to the Cover Date.     

Propylene metathesis over Re2O7/Al2O3-B2O3 catalysts

A series of alumina aluminum borate (AAB) with various Al/B molar ratios were prepared by the coprecipitation method. The supported rhenium oxide catalysts with various contents of Re₂O₇ were also prepared by the impregnation method with perrhenic acid. The catalytic activity and stability of Re₂O₇/AAB catalysts for the reaction of propylene metathesis were tested in a fixed-bed microreactor. It was found that Re₂O₇/AAB is more active, stable and regenerable than Re₂O₇/Al₂O₃ for propylene metathesis. The optimum Al/B molar ratio was found to be in the range of 4–10.     

助剂对PdO/Al2O3催化剂的抗硫中毒性能影响

浸渍法制备了不同助剂掺杂的PdO/Al<,2>O<,3>催化剂,以H<,2>S为硫源考察了催化剂的抗硫中毒性能以及催化剂对甲烷的催化燃烧性能,并用库仑滴定法测定了中毒及再生后催化剂表面的含硫量,以此分析催化剂中毒模式.结果表明,助剂MgO、ZnO<,2>、K<,2>O的添加均不同程度的提高了催化剂的抗硫中毒性能.再生后...     

负载型Pt/Al2O3催化剂中铂的测定

利用Pt（Ⅳ）在盐酸介质中与过量的氯化亚锡形成黄色的氯铂酸锡络合物，采用紫外-可见分光光度计在403 nm处测定该络合物显色液的吸光度，然后通过换算因子计算出负载型Pt/Al₂O₃催化剂中的铂含量。方法简单、快捷、准确，回收率在97％以上，相对标准偏差在2.0％以内 。在选定的试验条件下，负载型Pt/Al₂O₃催化剂中的常见元素对测定铂含量无干扰，但NO^－₃的存在对测定有影响。     

Surface acidity investigation of A12O3 supports and Ni-Mo/Al2O3 catalysts using the temperature-programmed desorption oftert-butylamine

The relative acid site densities of a range of Ni-Mo/Al₂O₃ based catalysts were measured by the temperature-programmed desorption of tert-butylamine. The catalysts investigated possessed different surface areas and active species loadings. The effect of active species impregnation on the acidity of blank aluminas was also determined. Similarly the effect of sulphiding on catalyst acidity was also addressed.