Investigation of n-hexane dehydrocyclization over supported Pt catalyst modified by adsorbed Pd

A -Al₂O₃ supported Pd–Pt bimetallic catalyst prepared by electrochemical metal adsorption has been tested in n-hexane dehydrocyclization. The Pd–Pt/Al₂O₃ catalyst, after calcination in oxygen followed by hydrogen treatment, showed higher activities and better selectivities for benzene and iso-hexane formation. The Pd–Pt/Al₂O₃ catalyst appeared to be less sensitive to the changes in the temperature of hydrogen treatment than the base Pt/Al₂O₃ catalyst.

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Re–Pt, -Al₂O₃, . -. , Re–Pt/Al₂O₃, , , , . , Pt/Al₂O₃.

     

Investigation of n-hexane dehydrocyclization over supported Pt catalyst modified by adsorbed rhenium

A -Al₂O₃ supported Re–Pt bimetallic catalyst prepared by electrochemical adsorption has been studied in n-hexane dehydrocyclization, using the slug-pulse method. The activity of the Re–Pt/Al₂O₃ catalyst treated only in hydrogen was low, but markedly increased by a calcination step before hydrogen treatment. The modified catalyst showed higher activity and increased selectivities for benzene and iso-hexanes than the base Pt/Al₂O₃ catalyst.

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Pd/Pt, -Al₂O₃, -. Pd–Pt/Al₂O₃, , , . Pd–Pt/Al₂O₃ , Pt/Al₂O₃.

     

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).     

Hydrocarbons from synthesis gas over Pd supported on silica-alumina catalyst

We have studied the operational conditions which allow the synthesis gas to hydrocarbon transformation in only one step using Pd supported over an amorphous silica-alumina catalyst. The increase of temperature, pressure and time factor favors carbon monoxide conversion. Methanol synthesis reaction can be considered as the limiting step of the overall process. The product distribution is governed by the reaction medium (type and distribution of active sites and the presence of hydrogen).     

Steam reforming of methanol over Ni, Co, Pd and Pt supported on ZnO

Pd/ZnO and Pt/ZnO exhibited anomalously high selectivity for the steam reforming of methanol, when PdZn and PtZn alloys phases were developed. The selectivity decreased over the catalysts having metal phases.     

磷钼酸（PMA）修饰炭载Pd催化剂对甲酸氧化的电催化性能

为了提高直接甲酸燃料电池（DFAFC）中炭载Pd（Pd/C）催化剂对甲酸氧化的电催化性能,用回流法制备了磷钼酸（PMA）修饰的炭载Pd（PMA-Pd/C）催化剂.并用谱学技术和电化学技术表征了催化剂的组分和结构,发现PMA通过化学作用而牢固地固定在Pd表面.由于PMA-Pd/C催化剂能抑制甲酸的自分解,因此,PMA-Pd/C催化剂对甲酸氧化的电催化性能优于Pd/C催化剂.     

Partial oxidation of dimethyl ether to H2/syngas over supported Pt catalyst

Dimethyl ether （DME） is a non-toxic fuel with high H/C ratio and high volumetric energy density, and could be served as an ideal source of H2/syngas production for application in solid oxide fuel cells （SOFC）. This study presents results of DME partial oxidation over a 1.5 wt% Pt/Ce0.4Zr0.6O2 catalyst under the condition of gas hourly space velocity （GHSV） of 15000-60000 ml/（g·h）, molar ratio of O2/DME of 0.5 and 500-700 ℃, and this temperature range was also the operation temperature range for intermediate temperature SOFC. The results indicated that the catalyst showed good activity for the selective partial oxidation of DME to H2/syngas. Under the working conditions investigated, DME was completely converted. Increase in reaction temperature enhanced the amount of syngas, but lowered the H2/CO ratio and yield of methane; while increase in reaction GHSV resulted in only slight variation in the distribution of products. The good catalytic activity of Pt supported on Ce0.4Zr0.6O2 for the partial oxidation of DME may be directly associated with the good oxygen storage capacity of the support, which is worth of further investigation to develop materials for application in SOFC.     

Importance of surface morphology in n-pentane reactions over Pt/alumina catalysts

The hydrocracking activity of a Pt/alumina catalyst has been determined and found to depend on surface morphology. Observed differences in thermal stability depend on whether the Pt is initially in a reduced or oxidized form. Various models proposed to account for the loss of hydroracking activity are re-examined in the light of the new data.

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Pt/Al₂O₃ , . , , , Pt . , .

     

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 ), . , , , , .

     

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 , .

     

Unsteady state behavior of CO oxidation over a supported Pt catalyst in the millibar range

The alkylation of naphthalene with isopropanol was investigated over a HY (Si/Al=4) zeolite under the following conditions: flow reactor, liquid phase with decalin as solvent, 623 K, 40 bar. Despite complete filling of the zeolite pores by coke during the first hour of reaction, the rate of formation of isopropylnaphthalene remained very high. This is due to the development of a new reaction process involving transalkylation between the polyisopropyl naphthalenes entrapped in the pores and naphthalene followed by the realkylation of the former compounds with isopropanol.     

Investigation of Co304 nanorods supported Pd anode catalyst for methanol oxidation in alkaline solution

A CO3O4 nanorod supported Pd electro-catalyst for the methanol electro-oxidation （MEO） has been fabricated by the combination of hydrother- mal synthesis and microwave-assisted polyol reduction processes. The crystallographic property and microstructure have been characterized using XRD, SEM and TEM. The results demonstrate that Pd nanoparticles （PdNPs） with a narrow particle size distribution （3-5 nm） are uni- formly deposited onto the surface of Co304 nanorods. Electrochemical measurements show that this catalyst having a larger electrochemically active surface area and a more negative onset-potential exhibits enhanced catalytic activity of 504 mA/mg Pd for MEO comparing with the Pd/C catalyst （448 mA/mg Pd）. The dependency of log/against logv reveals that MEO on Pd-CO304 electrode is under a diffusion control. Electrochemical impedance spectroscopy （EIS） measurement agrees well with the CV results. The minimum charge transfer resistance of MEO on Pd-CO304 is observed at -0.05 V, which coincides with the potential of MEO peak.     

Assessment of environmental contamination risk by Pt, Rh and Pd from automobile catalyst

The main active components of present-day car catalysts are the noble metals Pt, Pd and Rh, belonging to the platinum group elements (PGEs). It is recognized that these elements are being spread into the environment to an as-yet incompletely known extent, mainly due to surface abrasion of the catalyst during car operation. These new pollutants have motivated extensive research on PGE determination. Our work is planned to ascertain the health and ecosystem risks of these PGEs emitted through a series of interrelated objectives that address the pathway of these elements from the catalyst to the different environmental compartments. Combined studies of catalyst surface abrasion and exhaust fumes analysis, the monitoring of Pt, Pd and Rh in airborne particles and road dust sediments and bioaccumulation studies in aquatic organisms, plants and urine enable a realistic assessment of the risk that this release represents for man and environment. In this work some previous results are presented.     

ICP-AES测定废Al2O3基催化剂中Pt、Pd

研究了废Al2O3基催化剂中Pt,Pd的ICP－AES测定新方法。以王水溶解样品，在HCl(5 95)介质中，用工作曲线法对废Al2O3基催化剂中的Pt,Pd直接进行测定，不需进行基体匹配。方法的检出限分别为：Pt 0.1μg/mL，P 0.045μg／mL；样品的加标回收率为Pt 95.2%-105.5%,Pd 95.3%-100.6%;RSD(n=6)均＜9％。     

活性炭担载的铂催化剂在碱性条件下选择性氧化甘油制备乳酸

生物柴油是一种环境友好的燃料,随着其生产及应用的快速增长,其生产过程中重要的副产物甘油将会大量过剩.因此,将甘油转化为高附加值的化学品对于提高生物柴油整体竞争力具有重大意义.乳酸是重要的化工原料,可用于制备生物兼容和可降解的聚乳酸塑料,广泛应用于食品和医药等领域.近年来,由甘油制乳酸的研究受到格外关注,相对于水热反应和氢解反应等,催化选择氧化反应因温和的反应条件而更具竞争力.
　　目前,甘油催化选择氧化制乳酸一般需加入较高比例的NaOH,而碱的类型对反应性能的影响鲜有报道.另外,催化剂常采用TiO2和CeO2等氧化物载体,而炭载体具有比表面积较大、在酸碱溶液中稳定及贵金属易于回收等优点,在催化领域有着广泛应用.因此,本文研究了活性炭(AC)担载的Pt催化剂在甘油催化选择氧化制乳酸反应中的催化性能.
　　首先研究了Pt/AC催化剂和碱在甘油催化选择氧化制乳酸过程中的催化作用.实验发现, Pt/AC和碱协同作用才能得到乳酸. Pt/AC催化剂在甘油脱氢生成中间产物(甘油醛和二羟基丙酮)的过程中起主导作用,碱的存在能够促进甘油羟基脱氢;中间产物实验证实,中间产物生成乳酸过程中碱起主导作用,它促进甘油醛和二羟基丙酮脱水反应和坎尼扎罗重排反应获得乳酸.进一步研究发现,中间产物二羟基丙酮比甘油醛更有利于乳酸生成,而Pt/AC催化剂有利于中间产物氧化为甘油酸.
　　进一步研究了不同类型的碱对反应性能的影响.结果表明,碱金属氢氧化物(LiOH, NaOH, KOH)比碱土金属氢氧化物(Ba(OH)2)更有利于提高甘油转化率和乳酸选择性.在加入碱金属氢氧化物条件下,甘油转化率与其离子半径呈正相关,而乳酸选择性则呈相反趋势.在LiOH存在下,乳酸选择性明显高于NaOH和KOH条件.当LiOH：甘油摩尔比为1.5时,甘油转化率和乳酸选择性均最高.在较低的LiOH与甘油摩尔比时,随着反应的消耗,溶液中的OH–减少,其促进甘油脱氢的作用变弱,并且不利于中间产物进行坎尼扎罗反应,故反应活性和乳酸选择性较差;而当LiOH比例过高时,会导致溶解氧浓度迅速降低,从而使甘油转化率和乳酸选择性下降,同时副产物甘油酸的选择性有所提高.这可能是因为较高比例的碱会促进中间产物甘油醛生成,该中间产物在Pt/AC催化作用下发生进一步氧化反应生成甘油酸.
　　研究了反应时间对催化性能的影响.结果表明,反应6 h后,甘油已经完全转化,乳酸选择性最高,达到69.3%;进一步延长反应时间,乳酸选择性有所下降,而副产物乙酸选择性略有增加,这可能是部分乳酸分解所致. Pt/AC催化剂经5次循环使用后仍保持了较高的甘油转化率和乳酸选择性.     

Ring opening of ehtylcyclopentane over supported Pt catalysts

Ring opening of ethylcyclopentane (ECP) was studied over 6.3% Pt/SiO₂ (EUROPT-1) and 10% Pt/Al₂O₃, as a function of the hydrogen pressure. Both catalysts gave almost nonselective ring opening. Pt/Al₂O₃ produced also olefins, more side dealkylation and less fragmentation products. It is likely, that adlineation sites are operative over both catalysts.

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6,3% Pt/SiO₂ (EUROPT-1) 10% Pt/Al₂O₃, . . Pt/Al₂O₃ . , .

     

Understanding the electrochemical differences of Pt doped and Pt supported over CeO2

Pt supported over CeO₂ (Pt on CeO₂) and Pt doped CeO₂ (Pt in CeO₂) are synthesized using chemical reduction and solution combustion method. In chemical reduction two different reducing agents are used namely; hydrazine hydrate and formaldehyde giving Pt supported over CeO₂. Solution combustion method is used to prepare Pt doped CeO₂. Detailed characterization using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area measurement and transmission electron microscopy (TEM) is carried out to distinguish the Pt supported and doped compounds. XRD and TEM results have clearly shown the differences in the structure and morphology, however, BET results do not show significant differences. Further, electrochemical measurements are performed in neutral medium to differentiate the electrochemical activity. Cyclic voltammetry (CV) indeed shows noticeable differences between Pt supported over CeO₂ and Pt doped CeO₂. CeO₂ alone has also shown different electrochemical behavior compared to the Pt containing CeO₂. Considering oxygen evolution reaction (OER) as a model reaction, Tafel slope measurements are performed for CeO₂, Pt supported over CeO₂ and Pt doped CeO₂ to observe the differences. It was noted that CeO₂ and Pt doped CeO₂ showed similar Tafel slope indicating the same mechanism, while Pt supported over CeO₂ showed different Tafel slopes, hence the different mechanism.     

n-Pentane isomerization in a continuous-flow reactor on Pt/Al2O3 catalysts modified by adsorbed bismuth and palladium

Isomerization of n-pentane has been studied in a continuous-flow reactor at atmospheric pressure on Pt/Al₂O₃ catalysts modified by adsorbed bismuth and palladium. Lower activity and higher selectivity have been obtained on a catalyst modified by bismuth. Both activity and selectivity have decreased on a catalyst modified by palladium. After oxygen treatment the Pd–Pt/Al₂O₃ catalyst showed the most pronounced change in catalytic properties and its stability was lower than that of the unmodified Pt/Al₂O₃ catalyst.

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- , Pt/Al₂O₃, . , . , , . Pd–Pt/Al₂O₃ , Pt/Al₂O₃.

     

A novel asymmetric heterogeneous catalytic reaction: hydrogenation of ethyl 2-acetoxyacrylate on cinchonidine modified Pd and Pt catalyst

Summary The transformations of a-ICN and b-ICN were studied in the presence of hydrogen in AcOH over Pt-alumina catalyst under the conditions of the enantioselective hydrogenation of EtPy (hydrogen pressure 1-30 bar, temperature 298-323 K). It was established that the quinoline skeleton of the alkaloids is hydrogenated even under mild experimental conditions, whereas hydrogenolysis of the oxazacycloalkane structure only takes place at hydrogen pressures exceeding 1 bar. ESI-MS-MS, HPLC-ESI-ion-trap MS and NMR made possible the identification of several hydrogenated cinchona alkaloid derivatives with so far unknown structures. According to these experimental results, the conformation of isocinchona alkaloids remains unchanged under the conditions of the enantioselective hydrogenation of activated ketones, making them suitable for utilization as chiral modifiers of well-defined conformation.     

Adsorption/oxidation of CO on highly dispersed Pt catalyst studied by combined electrochemical and ATR-FTIRAS methods: oxidation of CO adsorbed on carbon-supported Pt catalyst and unsupported Pt black

ATR-FTIRAS measurements combined with linear potential sweep voltammetry were conducted to investigate oxidation of CO adsorbed on a highly dispersed Pt catalyst supported on carbon black, Pt/C, and carbon-unsupported Pt black catalyst, Pt-B. Bands nu(CO) of atop- and bridge-bonded COs were resolved into those of COs adsorbed at terrace and step edge sites by curve-fitting analysis. At the high coverage near the saturation, a band around 1950-1960 cm(-1) assigned to asymmetric bridge-bonded CO, CO(B)(asym), was observed to develop on both Pt/C and Pt-B, which was the predominant type on the latter. Preferential oxidation of atop-CO adsorbed at the step edge site was commonly observed on both Pt/C and Pt-B during the potential sweep from 0.05 to 1.2 V. However, it has been found that CO(B)(asym) is the most reactive species. The high reactivity of the CO(B)(asym) on Pt/C and Pt-B is demonstrated for the first time in the present report. Adsorption of CO on the Pt/C and Pt-B resulted in growth of a sharp nu(OH) band around 3642-3645 cm(-1) which is assigned to non-hydrogen-bonded water molecules coadsorbed with CO. The nu(OH) band frequency exhibits a linear increase with potential with a Stark tuning rate of ca. 20 cm(-1)/V. Analysis of the potential dependence of this band in the CO oxidation potential region led us to conclude that this is the oxygen-containing species to oxidize adsorbed CO. Stark tuning rates of nu(CO) bands for the COs at the terrace and step edge sites on both Pt/C and Pt-B are almost independent of the adsorption sites for both atop- and bridge-bonded COs. However, CO(B)(asym) exhibits tuning rates of 41 cm-1/V and 37 cm-1/ V on Pt/C and Pt-B, respectively, which is in between the rates of atop and symmetric bridge-bonded COs.