Surface redox properties of Rh/AlPO4 and Rh/AlPO4?SiO2 catalysts

Electron donor and acceptor properties of AlPO₄ and AlPO₄–SiO₂ (2080 wt. %) supported rhodium catalysts have been studied. It was observed that the effect of metal deposition on both electron acceptor and donor properties depend on the support and precipitation agent. AlPO₄ supported rhodium showed better acoeptor than donor properties, while for Rh/AlPO₄–SiO₂, the acceptor properties were superior. However, the effect of metal on the redox properties is slight.

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AlPO₄ QlPO₄ SiO₂ (2080 .%). ]ye . AlPO₄ , , Rh/AlPO₄–SiO₂ . , - .

     

CO and NO adsorption on photoreduced Mo/SiO2 catalysts

CO and NO adsorption on photoreduced Mo/SiO₂ catalysts has been studied by IR and mass-spectrometric methods. Products of interaction between adsorbed molecules and surface molybdates of various structures have been identified.

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- - CO NO CO Mo/SiO₂ . .

     

Ring opening of methylcyclopentane over Al2O3 and SiO2 supported Rh catalysts

Hydrogenolytic ring opening of methylcyclopentane (MCP) was investigated on Rh/Al₂O₃ and Rh/SiO₂ catalysts, prepared by the incipient wetness method. Strong dependence can be seen in the yield and distribution of ring opening products as a function of temperature and hydrogen pressure. They depended also on the support used. The ring opening reaction required high hydrogen coverage, and was not random (hindered in the vicinity of the methyl group), thus, mainly 2-methylpentane (2MP) and 3-methylpentane (3MP) were formed. The fragments consisted of C₁–C₅ alkanes, with methane andi-pentane as main fragments. This means the possibility of breaking two C−C bonds during one sojourn of the reactant on the catalyst, both taking place far from the substituent. The loose positive correlation between the ratios ofi-pentane/n-pentane and 3MP/n-hexane seems to support this conclusion. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday     

Effect of iron on the properties of supported Rh?Fe catalysts. Rh?Fe/SiO2 catalysts

The state of metals in Rh–Fe/SiO₂ catalysts has been examined. Iron is shown to form clusters with rhodium, whose size and composition depend on the metal ratio in the catalyst. The structure of active sites affects the amount and adsorption heat of hydrogen and carbon monoxide and their interaction mechanism.

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Rh–Fe/SiO₂-. , , . , CO .

     

改性SiO2对铁基催化剂H2、CO吸附及加氢性能的影响

采用溶胶凝胶方法通过掺杂修饰剂M（M=Mn、Zn、Zr、Sr）制备出改性SiO₂载体,再用浸渍法将Fe元素负载于该载体上制成系列催化剂。采用X射线衍射（XRD）、氮气物理吸附-脱附、X射线光电子能谱（XPS）等手段表征了催化剂的织构性质、晶相组成和电子性质。利用程序升温手段研究了催化剂的H₂还原吸附性质和CO加氢性能。借助动力学分析方法研究了催化剂与H之间的相互作用。结果表明,少量掺杂的修饰剂对催化剂的Fe物相组成以及表面Fe物种电子状态基本没有影响,但降低了催化剂的比表面积以及活性相分散度,削弱了对H₂的吸附能力,降低催化剂的H₂脱附活化能。Zn、Zr的掺杂抑制了催化剂的还原,而Mn、Sr的掺杂却促进催化剂的还原。Mn、Zn、Zr的掺杂抑制催化剂表面CO的解离吸附,Sr则促进CO的解离吸附,Mn、Zn、Zr、Sr均促进低温区间C-C耦合和加氢反应,其中,Mn、Zr促进加氢的作用更显著。     

Chemisorption of H2, O2 and CO on bimetallic catalysts Rh?Ag/Al2O3

Comparison of adsorptive properties of Rh–Al₂O₃ catalysts in relation to H₂, O₂ and CO as adsorbates points to different surface interactions between the adsorbates and metallic surface of the catalysts. The differences may result from the changing composition of bimetal surface in relation to the catalyst composition and/or from the changing stoichiometry of surface interactions of the adsorbates.

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H₂, O₂ CO Rh–Ag/Al₂O₃ . , , () .

     

Hydrogen pressure dependence of the reaction of neopentane with hydrogen over Pd/SiO2 and Pt/SiO2 catalysts

H₂ pressure influences in different ways the reaction rates of neopentane conversion over Pd/SiO₂ and Pt/SiO₂ catalysts. It seems that on Pt/SiO₂ both isomerization and hydrogenolysis involve a common surface intermediate (probably an adalkyl), whereas on Pd/SiO₂ the hydrogenolysis goes via more dehydrogenated species than those involved in isomerization.

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H₂ Pt/SiO₂ Pd/SiO₂. , Pt/SiO₂ (, ), Pd/SiO₂ , .

     

Product oriented oxidative bromination of methane over Rh/SiO2 catalysts

Rh/SiO2 was prepared for the oxidative bromination of methane. The catalyst was prepared by calcination at different temperatures and for different times to obtain catalysts with different specific surface areas for the purposes of producing either CH3Br or CH3Br and CO. It was found that the catalyst having a low specific surface area (calcined at relatively high temperature) favors the selective oxidation of methane to prepare CH3Br, while the catalyst having a high specific surface area favors the deeper partial oxidation of methane, which is good for CH3Br and CO preparation. The 650 h on stream life-time test revealed that the catalytic performance of the 0.4Rh/SiO2--900-10 catalyst was excellent. Both methane conversion and CH3Br selectivity kept increasing trends during the life-time test. No matter how serious was the Rh leaching during the reaction, the 0.4Rh/SiO2--900-10 catalyst did not deactivate at all.     

Acidic properties of TiO2?SiO2 catalysts

The acidic properties of a series of TiO₂–SiO₂ catalysts with different Ti/Si mole ratios have been studied. In order to determine the amount of acid centers and the acid strength distribution, the Benesi method of discontinuous titration has been used. Thermogravimetric measurements were also carried out.

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TiO₂–SiO₂ Ti/Si. , - . .

     

La2O3助剂对Rh/SiO2催化CO加氢反应性能的影响

采用溶胶凝胶法制备了SiO_2和La_2O_3-SiO_2载体,再通过浸渍法分别引入Rh-La和Rh组分,研究考察了La引入方式对Rh/SiO_2催化CO加氢反应性能的影响。结果表明,La的添加有利于提高Rh的分散度,促进Rh+中心数的增加,有效地抑制产物中CO2的生成,提高含氧化合物选择性。此外,La的引入方式会影响La与Rh间的相互作用强弱,Rh和La共浸渍制得的2Rh-5La_2O_3/SiO_2催化剂中Rh-La相互作用较强,削弱的Rh-CO键有利于反应过程中CO的插入反应,使得产物以C_(2+)含氧化合物为主。而La以助剂形式掺入SiO_2制得的2Rh/5La_2O_3-SiO_2催化剂具有较弱的La-Rh相互作用,其产物则以甲醇、乙醇等低碳醇为主。     

Hydrogenolysis of n-butane on Ni-Pd/SiO2 catalysts

Supported Ni-Pd/SiO₂ catalysts of different Ni and Pd composition were studied in n-butane hydrogenolysis. The reaction rate, selectivity towards methane, ethane and propane were determined. On the basis of these data the relationship between the size and composition of the active center and the possibility of surface segregation of one of the components is discussed.

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Ni-Pd/SiO₂ Ni Pd -. , . .

     

Influence of fluorine-modified SiO2-surfaces on the properties of V2O5/SiO2 catalysts

The preparation of vanadium catalysts is described using fluorine modified Aerosil as support. It is shown that modification with fluorine changes the concentration and topology of the surface silanol groups and, as a consequence, the catalytic properties.

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, , . , , , .

     

The role of acidity of MoO3?SiO2 and WO3?SiO2 catalysts

The acidity of various MoO₃–SiO₂ and WO₃ catalysts has been measured by means of ammonia adsorption. Whereas the acidity of silica and pure metal oxides is very low, an increase of surface acidity results from a reaction between silica support and metal oxides. A significant correlation between surface acidity and catalytic activity for aromatization of lower olefines could be found.

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MoO₃–SiO₂ WO₃ . SiO₂ . , SiO₂ . .

     

Acidity of SiO2, SiO2?Al2O3 and γ-Al2O3 supports and supported molybdena catalysts

Acidity of SiO₂, -Al₂O₃ and SiO₂–Al₂O₃ supports and supported Mo-catalysts in oxidized and reduced state are characterized by IR-spectroscopic and gravimetric pyridine (py) adsorption measurements. Differences in surface acidities are interpreted as results of differences in chemical compositions, molybdena-support interactions and molybdena dispersities.

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SiO₂, -Al₂O₃ SiO₂–Al₂O₃, Mo -- . , .

     

Aromatization of propylene and butadiene over MoO3?SiO2 and WO3?SiO2 catalysts

The activity of various MoO₃–SiO₂ and WO₃–SiO₂ catalysts for the aromatization of propylene and butadiene has been investigated. The results obtained show a comparatively high aromatization activity of the catalysts for propylene to benzene and toluene. The direct conversion of butadiene to ethylbenzene, using WO₃ on acid treated silica, is considered to be an alternative reaction pathway to the known metathesis step to ethylene and benzene.

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MoO₃–SiO₂ WO₃–SiO₂ . . , WO₃ .

     

Non-conventional preparation of Ru/SiO2 catalysts

A metal-supported catalyst (Ru/SiO₂) has been prepared using the sol-gel technique. The structural properties of the solid obtained are compared to those of a conventionally impregnated catalyst.

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(Ru/SiO₂) -. .

     

XPS and TEM characterization of pure and Th, Pr or Ce oxide containing Rh/SiO2 catalysts

Summary The promotor action of thoria and rare earth oxides in Rh/SiO₂ catalysts for syngas conversion to ethanol has been examined using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The catalysts were investigated after calcination, reduction and synthesis, and in some cases after in situ synthesis experiments by XPS measurements. Changes in surface composition and oxidation state of the metals as a function of treatment conditions and kind of added promotor are discussed. Special care has to be taken with respect to the determination of the active Rh species since the Rh compounds were reduced during the XPS measurements. In no case carbon deposition or loss in surface area was observed during synthesis. With the exception of praseodymium containing catalysts, all catalysts exhibited a homogeneous distribution of metal and promotor over the whole surface. Cerium addition led to Rh-Ce interactions after reduction and synthesis runs. The metal particles of catalysts prepared from nitrate solutions were of spherical shape and a growth in size up to a diameter of about 3.5 nm was observed after the synthesis treatments. Catalyst preparation using chloride solutions drastically altered the surface properties. Chlorine remnants, only observable after calcination, led to partly negatively charged rhodium species after reduction, and no formation of crystallites could be seen by TEM independent of the applied treatment, additionally no CO was chemisorbed on the reduced catalyst.     

Gas-phase hydroformylation of propylene on Ru/SiO2 catalysts

Ru/SiO₂ catalysts prepared by reduction of supported RuCl₃·xH₂O are active in gas-phase hydroformylation of propylene at low pressure (ca. 0.3 MPa) of H₂+CO+C₃H₆ mixtured and show unexpectedly high selectivity towards unbranched oxo-products. Data concerning the effect of electronic state and dispersity of Ru on their catalytic behavior have been obtained.

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Ru/SiO₂, RuCl₃·xH₂O, (0,3 ) - . .

     

Gas-phase phenyl acetate conversion on AlPO4, γ-Al2O3 and SiO2 catalysts

The conversion of phenyl acetate over AlPO₄ (Al/P=1), γ-Al₂O₃ and SiO₂ catalysts generated phenol, by deacetylation, ando-hydroxycetophenone, by Fries rearrangement, as the main reaction products. The activity for Fries rerrangement was in accordance with the acidity data measuredversus cyclohexene skeletal isomerization. Thus, AlPO₄ showed the highest activity. Moreover,o-hydroxy-acetophenone formation increased with the reaction temperature. Besides, in AlPO₄ catalysts 4-methylcoumarin and 2-methylchromone were also found, although in low amounts.     

Infrared spectroscopic study of CO adsorption on supported bimetallic Pt?Pb/SiO2 catalysts

With increasing Pb content, the IR band of linearly adsorbed CO is significantly shifted to lower frequencies. The greatest influence of lead is observed up to 15% Pb. An X-ray diffraction study indicates the formation of Pt_5–7–Pb and Pt–Pb alloys for bimetallic catalysts with a Pt/Pt+Pb ratio equal to 30%.

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Pb CO . 15% Pb. 30% , , Pt–Pb Pt_5–7–Pb.