CuO-ZrO_2-CeO_2复合氧化物的催化性能研究

研究了氧化铜的加入对锆铈复合氧化物的结构与性能的影响 ,发现氧化铜的加入可降低氧化铈的还原温度 ,稳定复合氧化物的立方结构 ,提高对CO氧化的催化活性。增加铈含量能提高催化剂的活性 ,而硫酸盐等可使催化剂的活性降低。掺铜锆铈复合氧化物催化剂的活性几乎不受高温灼烧的影响 ,是一种具有较高热稳定性的催化剂。     

Sulfated binary and trinary oxide solid superacids

A series of sulfated binary and trinary oxide solid superacids were prepared, and their catalytic activities for n-butane isomerization at low temperature were measured. The incorporation of different metal oxides into ZrO2 may produce a positive or negative effect on the acid strength and catalytic activity of the solid superacids. Sulfated oxides of Cr-Zr, Fe-Cr-Zr and Fe-V-Zr are 2 - 3 times more active than the reported sulfated Fe-Mn-Zr oxide. The enhancement in the superacidity and catalytic activity of these new solid superacids has been discussed on account of the results of various characteriation techniques.     

铜锆复合氧化物的结构对其催化选 择还原－氧化氮性 能的影响

用浸渍法和共沉淀法分别制得CuO---ZrO~2复合氧化具物有不同的选择还原NO~x的催化性能,采用XRD,BET,EXAFS和H~2---TPR等手段对样品进行了表征,发现浸渍法制备的样品具有的比表面较大,氧化锆被稳定在四方相。EXAFS实验表明,浸渍法制得样品的铜离子填入氧化锆表面空穴中,并以Cu^2+形式存在;500℃焙条件下用共沉淀法引入的铜离子可部分取代锆离子,在氧化锆体相高度分散形成均匀的无定形固溶体,铜离子在氧化锆体相的高度分散是形成表面弧立铜物种的关键。溶入氧化锆体相的铜离子在取代部位由于局部负电荷而使氧化性降低,是共沉淀法制备样品具有较高催化活性的主要原因。     

Fe-K/AC催化氧化脱硫剂制备及反应机理研究

采用正交实验法制备了负载铁、钾的活性炭(Fe-K/AC)热煤气催化氧化脱硫剂,考察了活性组分铁、钾含量、二价铁和三价铁比例、煅烧温度对催化氧化脱硫反应活性的影响。由正交实验极差分析可知,各因素影响程度依次为:钾含量>铁含量>煅烧温度> Fe²⁺/Fe³⁺,最优制备条件为,铁含量0.5%、钾含量5.0%、煅烧温度600 ℃、Fe²⁺/Fe³⁺比0.5。通过对脱硫剂的孔隙结构和表面形貌分析可知,活性炭表面负载的铁金属氧化物具有催化氧化硫化氢生成单质硫的活性,碱金属氧化物具有协同作用,可以改变表面酸碱性,促进硫化氢的催化转化,但过高的金属氧化物负载量会阻塞孔道,减小反应比表面积,从而降低脱硫剂的反应活性。     

Mesoporous Silica Supported Sulfated Zirconia Prepared by a Sol–Gel Process

Mesoporous silica-supported sulfated zirconia aerogels with different Zr/Si and S/Zr molar ratios were prepared using a one-step preparation. The characterization of these solids was conducted using N₂ physisorption at 77 K, X-ray diffraction, mass spectrometry, and sulfur chemical analysis. The isomerization of n-Hexane was used as a catalytic test. Highly improved textural properties were obtained for these solids, and two types of mesopores were observed. Depending on the zirconium content, the size and amount of mesopores are highly affected. The importance of sulfates effectively bonded to Zr(IV) is elucidated, both for achieving high catalytic activity and for a good sulfur thermal stability. The catalytic activity (for a sample prepared with a particular S/Zr ratio) expressed per gram of Zr(IV) is comparable to that of pure sulfated zirconia.     

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.     

Transformation of Nanostructured Schwertmannite and 2‐Line‐Ferrihydrite into Hematite

Nanostructured ferric oxides and sulfated ferric oxides are of high interest in catalysis, e.g. for hydrocarbon isomerization. Sulfated ferric oxides are often prepared by immersion of ferric oxides in sulfate containing solutions which technique is facile to conduct, yet poorly reproducible. This problem is circumvented by sulfate incorporation into ferric oxide particles during precipitation. This way of intrinsic sulfation generated ferric oxides with defined properties. The precipitation reaction is accomplished by using a microjet mixer, in which ferric sulfate is brought to reaction with ammonia, what allows for forming schwertmannite and ferrihydrite qualities with defined sulfate content. As ferric oxide synthesis is conducted at ambient conditions, while catalysis mainly occurs at elevated temperatures, it is important to study structural as well as chemical changes during heating. Thus these materials were analysed in terms of structural and chemical changes during heating. In this course it was found that both materials are transformed into hematite, the crystallization degree as well as specific surface properties of which depend both on annealing temperature and the precursor used. This transformation was accompanied by dehydration and liberation of sulfur trioxide.     

Control Preparation of Sulfated Zirconia by Sol-Gel Process: Impact on Catalytic Performances During n-Hexane Isomerization

Sulfated zirconia catalysts were prepared by sol-gel method using CH₃COOH as in situ water source to control hydrolysis of alkoxide, and following two sulfation procedures. The samples were characterized by N₂ adsorption, XRD, chemical analysis, and the activity for isomerization of n-hexane was assessed. It was found that sulfation procedure and the amount of acetic acid added exert a great influence on the catalysts properties. Mixture of sulfuric acid with zirconium propoxide before addition of acetic acid allows the retention of a larger amount of sulfur after calcination and enhances catalytic performances of sulfated zirconia. The use of CH₃COOH reduces the rate of hydrolysis, and improves considerably acidic and catalytic properties.     

Calorimetric study of the acidic character of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–TiO<Subscript>2</Subscript>/SO<Subscript>4</Subscript><Superscript>2−</Superscript> catalysts used in methanol oxidation to dimethoxymethane

The surface acidic properties of sulfated vanadia–titania catalysts prepared by various methods were investigated by adsorption microcalorimetry, using ammonia as probe molecule. The acidic characteristics of the samples were shown to be strongly affected by the preparation method, calcination temperature, and sulfur content. The samples prepared by sol–gel and mechanical grinding exhibited higher acidity than co-precipitated samples. Moreover, increasing the calcination temperature of co-precipitated samples resulted in a decrease in surface area from 402 to 57 m² g⁻¹ and sulfur content from around 4 to 0.2 mass%, but up to a certain point generated a stronger acidity. The optimal calcination temperature appeared to be around 673 K.     

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.     

Effect of calcination temperature on the physicochemical and catalytic properties of FeSO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> in hydrogen sulfide oxidation

The effect of calcination temperature on the state of the active component of iron-containing catalysts prepared by the impregnation of silica gel with a solution of FeSO₄ and on their catalytic properties in selective H₂S oxidation to sulfur was studied. With the use of thermal analysis, XPS, and Mössbauer spectroscopy, it was found that an X-ray amorphous iron-containing compound of complex composition was formed on the catalyst surface after thermal treatment in the temperature range of 400–500°C. This compound contained Fe³⁺ cations in three nonequivalent positions characteristic of various oxy and hydroxy sulfates and oxide and sulfate groups as anions. Calcination at 600°C led to the almost complete removal of sulfate groups; as a result, the formation of an oxide structure came into play, and it was completed by the production of finely dispersed iron oxide in the ?-Fe₂O₃ modification (the average particle size of 3.2 nm) after treatment at 900°C. As the calcination temperature was increased from 500 to 700°C, an increase in the catalyst activity in hydrogen sulfide selective oxidation was observed because of a change in the state of the active component. A comparative study of the samples by temperature-programmed sulfidation made it possible to establish that an increase in the calcination temperature leads to an increase in the stability of the iron-containing catalysts to the action of a reaction atmosphere.     

Catalytic Properties of the Thermal Decomposition Products of Zr(SO4)2 · 4H2O

The catalytic activity of the thermal decomposition products of Zr(SO₄)₂ · 4H₂O in the reactions of 1-butene isomerization to 2-butenes, isobutanol dehydration, and n-butane skeletal isomerization was studied. Their behaviors in typical acid reactions and in skeletal isomerization were found to be considerably different. In the first two reactions, which occur with the participation of proton sites, the activity of zirconium sulfates was an extremal function of hydrate calcination temperature. Zirconium sulfate calcined at 400–550°C was the most active catalyst. The reasons for such behavior are discussed. In the skeletal isomerization of n-butane, crystalline zirconium sulfate was practically inactive, and it became active only after degradation. The results suggest that the activation of n-butane molecules did not occur at proton sites.     

Influence of sulfation conditions on the acidic and catalytic properties of sulfated alumina in isobutane alkylation with butylenes and <Emphasis Type="Italic">n</Emphasis>-pentane isomerization

The influence of the sulfation parameters (the source and concentration of sulfate ions) and the calcination temperature on the acidic and catalytic properties of sulfated alumina in the alkylation of isobutane with butylenes and n-pentane isomerization was studied. IR spectroscopy of adsorbed probe molecules and temperature-programmed desorption of ammonia were used to characterize the acidic properties of the catalysts. An increase in the content of sulfate groups to the value corresponding to a formal value of the monolayer capacity increases the activity of alkylation and the concentration of strong Brönsted sites. The dependence of the stability of activity in alkylation on the sulfate group concentration is extreme with a maximum at the concentration close to the monolayer capacity. It was concluded from the IR spectroscopic data that the decrease in the stability of activity with the further increase in the content of sulfate groups is due to an increase in the concentration of strong Lewis sites and/or an increase in the surface density of strong Brönsted sites. The absence of the correlation between the catalytic behavior of sulfated alumina samples in n-pentane isomerization and acidity indicates that paraffin activation on these samples occurs via the non-acidic mechanism.     

Influence of the conditions of manufacture of nanomeric zirconium dioxide,stabilized with yttrium oxide,on its catalytic properties in the oxidation of CO

The morphological and catalytic properties of samples of nanomeric zirconium dioxide, stabilized with yttrium oxide, manufactured via the effect of a UHF field during the process of drying precipitated zirconium hydroxide and calcination at temperatures from 300 to 1000 °C, were studied. It was shown that the highest activity in the oxidation of CO occurred with 40 nm particles of zirconium dioxide prepared at 1000 °C. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 96–101, March–April, 2007.     

Catalysis of SO42--ZrO2/TiO2 nanometer solid superacid

Superacid catalyst SO42--ZrO2/TiO2 was applied in esterification of Acetic Acid and Butanol. The particle size of ZrO2 in the catalyst was about 12.5 nm. In catalyst preparation conditions, the effect factor order on catalytic activity is H2SO4 concentration ＞ calcination temperature ＞ ZrO2 supported content. The optimum preparation condition is as follows: ZrO2 content 3.5g/g; calcination temperature 600℃, and H2SO4 concentration 0.5mol/L. The catalytic activity is 96.5 vol%.SO42-/MxOy solid superacid is a kind of green catalyst, whose application perspective is bright. In this paper, SO42--ZrO2/TiO2 solid superacid was prepared with nanometer compound carrying method. The acidic strength of catalysts was measured with the following Hammett indicators, 2,4-dinitrofluorobenzene (H0=-14.52) and p-nitrochlorobenzene (H0=-12.70). Catalytic activity was evaluated with esterification reaction of Acetic Acid and Butanol. Reaction temperature was at 105℃, and reaction time was only 1h. The conversion rate of Acetic Acid was analyzed by a gas chromatograph (GC-14C SHIMADZU in Japan)The experimental results showed that H2SO4 concentration had more influences on catalytic activity than other two factors, calcination temperature and ZrO2 supported content. Since sulfur absorbed on the surface of metal oxides is necessary to the acidity of SO42-/MxOy solid superacid,H2SO4 concentration in impregnation solution is needed enough high. But, it can't be too much high,otherwise, Zirconium sulfate formed on the catalyst surface will be harmful influences on catalytic activity. In researched cover, 0.5mol/L H2SO4 concentration is the most suitable, and the catalyst prepared with this concentration has very strong acidity.The optimum preparation condition is as follows: ZrO2 content 3.5g/g; calcination temperature 600℃, and H2SO4 concentration 0.5mol/L. In the catalyst prepared with above conditions, the acidic strength (H0) of the catalyst is smaller than ＜-14.52, and catalytic activity is 96.5 vol%. When it was re-used in esterification reaction, catalytic activity decreased gradually with re-used times increasing(seen in Table 1). But after catalyst is used repeatedly up to five times, catalytic activity (84.3 vol %)is still higher than that of H2SO4 catalyst.The X-ray diffraction patterns showed that ZrO2 supported in TiO2 belonged tetragonal zirconia phases. Through the calculation of Scherrer formula, the particle size of ZrO2 in the catalyst is about 12.5 nm. After SO42- promoted nanometer ZrO2/TiO2 compound carrier, the diffraction peaks of tetragonal zircoma become broader and the strength weaker. It shows that adding SO4 ions restrains the crystallization of ZrO2, diminishes the size of particles. This might be why SO42--ZrO2/TiO2 has high catalytic activity and stability in acidic catalysis reaction.     

CeO2-Al2O3负载金催化剂用于水煤气变换反应的催化活性

采用浸渍法和沉积 沉淀法制备了CeO₂-Al₂O₃复合氧化物,比较了复合氧化物负载纳米金催化剂对水煤气变换反应的催化活性。通过N2物理吸附、XRD、TEM、H₂-TPR等表征手段对复合氧化物及其负载金催化剂的物相和结构进行分析,发现复合氧化物的制备方法及其焙烧温度对其比表面积、孔结构及水煤气变换反应活性有明显的影响。与沉积 沉淀法相比,浸渍法制备的CeO₂-Al₂O₃复合氧化物具有较大的CeO₂晶粒尺寸,经500℃焙烧后再负载金,所得催化剂具有更高的活性,250℃时CO转化率可达78.1%。     

Structural and adsorption characteristics and catalytic activity of titania and titania-containing nanomaterials

Morphological, structural, adsorption, and catalytic properties of highly disperse titania prepared using sulfate and pyrogenic methods, and fumed titania-containing mixed oxides, were studied using XRD, TG/DTA, nitrogen adsorption, (1)H NMR, FTIR, microcalorimetry on immersion of oxides in water and decane, thermally stimulated depolarization current (TSDC) and catalytic photodecomposition of methylene blue (MB). Phase composition and aggregation characteristics of nanoparticles (pore size distribution) of sulfate and pyrogenically prepared titania are very different; temperature dependent structural properties are thus very different. Catalytic activity for the photodecomposition of MB is greatest (per gram of TiO(2) for the pure oxide materials) for non-treated ultrafine titania PC-500, which has the largest S(BET) value and smallest particle size of the materials studied. However, this activity calculated per m(2) is higher for PC-105, possessing a much smaller S(BET) value than PC-500. The activity per unit surface area of titania is greatest for the fumed silica-titania mixed oxide ST20. Calcination of PC-500 at 650 degrees C leads to enhancement of anatase content and catalytic activity, but heating at 800 and 900 degrees C lowers the anatase content (since rutile appears) and diminishes catalytic activity, as well as the specific surface area because of nanoparticle sintering.     

LaCoO3对H2S选择氧化性能的影响

使用溶胶-凝胶法制备了LaCoO₃催化剂,采用XRD、BET和XPS等方式对催化剂进行了表征,考察了该催化剂制备过程中煅烧温度、表面活性剂PEG-6000和PEG-20000含量对其H₂S选择氧化制硫磺反应催化活性的影响。结果表明,表面活性剂PEG-6000及PEG-20000的添加能明显提高LaCoO₃的催化活性。0.02 mol La（NO₃）₃+0.02mol Co（NO₃）₂溶液中添加0.30 g PEG-20000、煅烧温度为650℃时所制备的LaCoO₃催化活性最好;在最佳反应温度260℃下,H₂S的转化率达到96.10%,硫选择性为93.77%。     

Synthesis of Ni／Mg／Al Layered Double Hydroxides and Their Use as Catalyst Precursors in the Preparation of Carbon Nanotubes

Ni/Mg/Al layered double hydroxides(LDHs) with different n(Ni) : n(Mg) : n(Al) ratio values were prepared via a coprecipitation reaction. Then Ni/Mg/Al mixed oxides were obtained by calcination of these LDHs precursors. Carbon nanotubes were produced in the catalytic decomposition of propane over the Ni/Mg/Al mixed oxide catalysts. The quality of as-made nanotubes was investigated by SEM and TEM. The nanotubes were multiwall with a high length-diameter ratio and appeared to be flexible. The catalytic activities of these mixed oxides increased with increasing the Ni content. The Ni/Mg/Al mixed oxide with the highest Ni content [ n( Ni)/n( Mg)/n(Al) = 1/1/1 ] showed the highest activity and the carbon nanotubes grown on its surface had the best quality.