Propane combustion over supported Pt catalysts

We prepared Pt catalysts supported on various metal oxides, viz., ZrO₂, CeO₂, TiO₂, yttria-stabilized zirconia (YSZ), SiO₂, SiO₂–Al₂O₃, and γ-Al₂O₃, using an incipient wetness method and applied them to propane combustion. In the cases of ZrO₂-, CeO₂-, and TiO₂-supported Pt catalysts, supports with different surface areas were also used. The Pt dispersion in Pt catalysts supported on metal oxides increased with increasing surface area of the support for the same metal oxide. Pt catalysts on supports with lower surface areas (ZrO₂, CeO₂, and TiO₂) showed higher catalytic activities for propane combustion than did Pt catalysts on supports with higher surface areas. The catalytic activity decreased in the following order: Pt/ZrO₂ (2) > Pt/CeO₂ (9) > Pt/TiO₂ (1) = Pt/SiO₂ (350) > Pt/ZrO₂ (18) = Pt/YSZ > Pt/TiO₂ (330) > Pt/SiO₂–Al₂O₃ (350) > Pt/ZrO₂ (73) > Pt/γ-Al₂O₃ (180) > Pt/CeO₂ (160). The catalytic activity is inversely proportional to the amount of O₂ chemisorbed up to the reaction temperature. It can be concluded that metallic Pt is essential for propane combustion and is maintained for the Pt catalysts with large Pt metal particles, which can be prepared by using a support with a low surface area.     

n-Hexane dehydrocyclization over Pt?Ni supported on alumina catalysts

Pt–Ni/-Al₂O₃ catalysts have been prepared and studied in n-hexane dehydrocyclization. The selectivity for benzene and toluene, a chain lengthening product formation was improved by Ni and correlated with its content.

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Pt–Ni/-Al₂O₃ -. Ni . Ni , .

     

Ring opening metathesis polymerization catalysts

Over the past eight years, early transition metal catalysts for the ring opening metathesis polymerization of cyclic olefins have been developed. These catalysts are simple organometallic complexes containing metal carbon multiple bonds that in most cases polymerize olefins by a living process. These catalysts have been used to prepare a family of near monodispersed and structurally homogeneous polymers. A series of group VIII ROMP catalysts that allow a wide range of functionality to be incorporated into the polymer side chains have recently been prepared. This most important members of this family of complexes are the bisphosphinedihaloruthenium carbene complexes. These catalysts show excellent functional group stability and can be used to prepare well defined telechelic polymers, polyolefins with ordered functionality, and highly functionalized block copolymers.     

Hydrogenation of chloronitrobenzenes over Pd and Pt catalysts supported on cationic resins

Liquid phase hydrogenation of chloronitrobenzene isomers (x-CNB x = 2, 3, 4) to the corresponding chloroanilines (x-CAN) at mild reaction conditions (0.6 MPa, 25°C, diethyl ether-methanol as solvents) over palladium and platinum catalysts containing 1 mass % of metal on trimethylammonium functionalized poly{styrene-co-divinylbenzene} (Dowex-D) was studied. The average selectivities to x-CAN over Pd/D-Cl and Pd/D-OH catalysts were 72 % and 42 %, respectively, at the x-CNB conversion of about 80 %. The average selectivities of 81 % and 84 % were achieved using Pt/D-Cl and Pt/D-OH, respectively, at the x-CNB conversion of approximately 90 %, whereas the average starting reaction rates were 1.2 × 10^?3 mol g^?1 s^?1 and 2.6 × 10^?3 mol g^?1 s^?1 (hydrogen consumption rate per mass of platinum), respectively. Under similar reaction conditions, using palladium catalysts supported on a resin with anionic groups anchored to polymeric chains at the average reaction rate equal to 3.8 × 10^?3 mol g^?1 s^?1 (hydrogen consumption rate per mass of palladium), the selectivities from 85 % (2-CAN and 3-CAN) to 95 % (4-CAN) were achieved (Kratky et al., 2002).     

整体式担载型Pt基催化剂上航空煤油的裂解:助剂SrO和BaO的影响

考察了整体式担载型Pt基催化剂上国产3号航空煤油(RP-3)的常压裂解反应,着重探讨了添加BaO和SrO助剂对裂解效果的影响,以及裂解时间对积炭量的影响.采用全自动吸附仪、程序升温还原、X射线光电子能谱以及X射线衍射和扫描电镜等方法对催化剂进行了表征.结果表明,在整体式担载型Pt基催化剂上RP-3裂解的总产气量比热裂解提高了39.7%;BaO或SrO助剂的添加又使其总产气量又分别提高了25.6%和37.0%;同时添加BaO和SrO的催化剂,其催化裂解总产气量则提高了96.5%.BaO和SrO助剂均可有效地抑制积炭的生成,而两者间的协同作用,进一步抑制了RP-3催化裂解过程中积炭的生成.     

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     

Propane combustion over supported Pd catalysts

We prepared Pd catalysts supported on various metal oxides, viz. γ-Al₂O₃, α-Al₂O₃, SiO₂–Al₂O₃, SiO₂, CeO₂ and TiO₂ by an incipient wetness method and applied them to propane combustion. Several techniques: N₂ physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), CO chemisorption, temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPO) were employed to characterize the catalysts. Pd/SiO₂–Al₂O₃ showed the least catalytic activity at high temperatures among Pd catalysts supported on irreducible metal oxides, viz. SiO₂, Al₂O₃ and SiO₂–Al₂O₃. Pd/γ-Al₂O₃ was much superior for this reaction to Pd/α-Al₂O₃. The Pd catalyst supported on reducible metal oxides (CeO₂ and TiO₂) with a less specific surface area showed the higher catalytic activity compared with that supported on reducible metal oxides with a higher specific surface area, even though the former had a less Pd dispersion than the latter. In the case of Pd/SiO₂–Al₂O₃, the initially reduced Pd catalyst was superior to the fully oxidized one. The oxidation of metallic Pd occurred in the presence of O₂ with increasing reaction temperature, which resulted in the change in the catalytic activity.     

Hydrogenation of xylenes over supported Pt catalysts. Influence of different variables on their catalytic activity

In this work we studied and compared the catalytic activity of various supported Pt systems on the gas-phase hydrogenation of o-, m- and p-xylene. We analyzed the influence of different catalyst preparation variables (solvent, precursor, salt, support and catalyst reduction temperature used) on the catalytic activity and selectivity towards the corresponding cis-and trans-dimethylcyclohexanes.

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- o-, m- -. (, , ) - -.

     

Hydrodechlorination of chlorobenzene over supported metal catalysts

The use of supported Pd catalysts, with low and high metal content, for the hydrodechlorination of chlorobenzene is presented in this article. Application of microwave irradiation during preparation of catalysts resulted in the synthesis of large Pd particles at moderate temperatures. The nature of the support played a key role in the formation of cationic Pd species. The extent of interaction of the Pd species with the support, the nature of metal precursor, particularly the residual chlorine on the surface were found to significantly affect the activity of the catalysts. In the case of bimetallic catalysts also microwave heating resulted in creation of bigger particles of Pd compared to those observed in conventionally heated catalysts. Besides, it minimized alloy formation as a result of which the activity of the catalysts in hydrodechlorination was found to be higher compared to that observed on conventionally prepared catalysts. Contrary to the general observation that low dispersed Pd catalysts are preferable for high stability, by means of the deposition-precipitation method adopted for catalyst preparation it was demonstrated that even highly dispersed (low Pd containing) catalysts can exhibit comparable activity and stability. An analysis of the nature of Pd species and its role in the stability of the catalysts is presented.IICT communication No. 051224     

Reduction of benzylideneaniline over supported Pd catalysts

In this work we have carried out a study on the liquid phase hydrogenation of benzylideneaniline, using dihydrogen over various supported Pd catalysts. Benzyl-ideneaniline reduction can be classified as insensitive to the catalyst structure. On the other hand, no compensating effect has been observed in performing the reaction over different supported Pd catalysts.

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Pd , . . Pd , .

     

Decomposition of methomyl over supported iron catalysts

Catalytic wet peroxide oxidation of methomyl over Fe-ZSM-5 and AlFe-pillared montmorillonite was carried out at room temperature, in a glass batch reactor, under constant airflow and halogen lamp light. Both catalysts have shown significant activity in the degradation reaction of methomyl at a concentration of 1.0×10⁻⁴ mol.     

全氢菲在分子筛催化剂上环烷环开环反应的研究

在小型固定流化床(FFB)装置上考察了Y与ZSM-5分子筛催化剂以及Y分子筛催化剂上温度、剂油比对全氢菲裂化环烷环开环反应的影响。结果表明,全氢菲在分子筛催化剂上通过环烷环开环反应生成环己烷、十氢萘等单环或双环环烷烃;单环或双环环烷烃进一步侧链断裂生成2-甲基戊烷、甲基己烷等异构烷烃等,异构化生成二甲基环戊烷、甲乙基环戊烷等烷基环戊烷,氢转移生成苯、甲苯、二甲苯等烷基苯,进行深度氢转移反应生成萘、烷基萘等双环芳烃;另外,全氢菲也会通过脱氢缩合生成菲、芘等三环以上芳烃甚至焦炭等。由于扩散和吸附性能的影响,其裂化开环反应的选择性在Y分子筛催化剂上比在ZSM-5分子筛催化剂上高。因此,全氢菲环烷环开环与脱氢缩合反应的相对比例(s(NRO)/s(DHC))在Y分子筛催化剂上较高;在Y分子筛催化剂上,温度为475~550 ℃、剂油比为3.0~9.0,反应温度升高或者剂油比增加,双分子氢转移以及脱氢缩合反应增强,导致环烷环开环反应产物选择性降低。     

Phosphorus modification of supported Pt catalysts for carbon monoxide hydrogenation

Modifying effect of phosphorus on the catalytic activity of supported Pt and Pt–Fe catalysts for CO hydrogenation has been studied. Phosphorus-containing compounds decrease significantly the methane yield with increasing yield of C₂–C₇ hydrocarbons.

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CO Pt- Pt–Fe-. , C₂–C₇.

     

Stereoselective stilbene epoxidation over supported gold-based catalysts

The gold reference catalyst Au/TiO(2) exhibits high activity in the stereoselective epoxidation of trans-stilbene in methylcyclohexane in the presence of 5 mol% TBHP, by taking part in a chain reaction involving the activation of molecular oxygen by a radical produced from methylcyclohexane.     

镍基催化剂上乙醇水蒸气重整反应的研究

考察了载体对Ni催化剂乙醇水蒸气重整制氢反应性能的影响。结果表明,Ni/CeO2催化剂具有较好的低温活性和氢气选择性。对Ni担载量和焙烧温度考察发现,400℃焙烧的15%NiCeO2催化剂具有较好的催化性能;继续升高焙烧温度引起NiO和CeO2粒子的显著增大,导致对氢气选择性的降低。较小的Ni和CeO2粒子有利于乙醇水汽重整反应的进行,而大的粒子倾向于乙醇的分解反应。 350℃时,在反应过程中分别添加CO、CO2和CH4的结果表明没有发生CO和CO2甲烷化反应,而发生了一定程度的CH4水汽重整反应。     

Wormholelike mesoporous carbon supported Pt Ru catalysts toward methanol electrooxidation

Wormholelike mesoporous carbons(WMCs) with three different pore diameters(D_p),namely WMC-F7(D_p=8.5nm),WMC-F30(D_p=4.4nm),and WMC-FO(D_p = 3.1nm) are prepared via a modified sol-gel process.Then PtRu nanoparticles with the particle size(d_(Pt)) of ~3.2 nm supported on WMCs are synthesized with a modified pulse microwave-assisted polyol method.It is found that the pore diameter of WMCs plays an important role in the electrochemical activity of PtRu toward alcohol electrooxidation reaction.PtRu/WMC-F7 with Dp 2d_(Pt) exhibits the largest electrochemical surface area(ESA) and the highest activity toward methanol electrooxidation.With the decrease in D_p,PtRu/WMC-F30 and PtRu/WMC-FO have much lower ESA and electrochemical activity,especially for the isopropanol electrooxidation with a larger molecular size.When D_p is more than twice d_(Pt),the mass transfer of reactants and electrolyte are easier,and thus more PtRu nanoparticles can be utilized and the catalysts activity can be enhanced.     

Partial hydrogenation of benzene over platinum supported catalysts

Partial hydrogenation of benzene to cyclohexene has been studied on Pt/Nylon 66, Pt/MgO and Pt/TiO₂. An effect of the support on the selectivity to cyclohexene was observed, Pt/Nylon showing the highest selectivity, followed by Pt/MgO and Pt/TiO₂. An interaction of platinum with the more basic supports (Nylon, MgO) and a pretreatment under oxidizing conditions, results in a higher selectivity to cyclohexene.

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Pt/ 66, Pt/MgO PtTiO₂. , Pt/, Pt/MgO Pt/T,O₂. (, MgO) .

     

Hydrogenation of ethyl acetate over supported rhenium catalysts

Re/Sibunite is a more active and selective catalyst for hydrogenation of ethyl acetate to ethanol under elevated temperatures and hydrogen pressures than Re/θ-Al₂O₃ and Re/γ-Al₂O₃. The activity of the catalyst is increased on replacing NH₄ReO₄ with HReO₄ and treatment of the support with a 13% solution of HNO₃. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1006–1008, May, 1999.     

Combustion of methane over supported palladium-copper bimetallic catalysts

Monometallic and bimetallic catalysts based on palladium and copper deposited on a spinel carrier have been investigated in the catalytic combustion of methane. Great differences were found in catalytic activity, according to the sequence Pd/MgAl₂O₄>CuO–Pd/MgAl₂O₄>Pd–CuO/MgAl₂O₄>CuO/MgAl₂O₄. They were explained by changes in surface composition of the catalysts. In the case of bimetallic catalysts the metallic surface is preferentially enriched in copper, which acts as a diluting agent for the Pd atom ensembles. As a consequence, the adsorption of reactants is limited and the catalysts so obtained behave like copper slightly doped with palladium.     

Systems of supported Pt as catalysts in the isomerization of dimethylcyclohexanes

We report on results obtained for the isomeratization of the different dimethylcyclohexanes over diverse systems of supported Pt. As support systems AIPO₄, SiO₂–AlPO₄ and AlPO₄–Al₂O₃ have been used. The reactions have been carried out in a pulse reactor coupled to a gas chromatograph. The process of isomerization, within the temperature interval studied (393–543 K), requires the presence of hydrogen and of the metallic catalyst, and the results obtained highlight the influence on the selectivity by the temperature, the support used for the deposition of the metal, and the relative stability of the reaction products.

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, . AlPO₄, SiO₂–AlPO₄ and AlPO₄–Al₂O₃. , . , (393–543 ), . , , , , .