Sulfuration of Pt/Al2O3, Pt?Re/Al2O3 and Pt?Ir/Al2O3 catalysts

Three reforming catalysts Pt/Al₂O₃, Pt–Ir/Al₂O₃ and Pt–Re/Al₂O₃ have been sulfurated by H₂S and tested by their activities in benzene hydrogenation. By treatment at 500°C under hydrogen flow only a part of the initial activity of the non-sulfurated catalyst is retained. So only a part of the adsorbed sulfur is easily removed in these conditions. The remaining sulfur for each of the catalysts (Pt/Al₂O₃, Pt–Ir/Al₂O₃ and Pt–Re/Al₂O₃) gives the same atomic ratio of 0.5 sulfur atom per accessible metallic atom.

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Pt/Al₂O₃, Pt–Ir/Al₂O₃ Pt–Pe/Al₂O₃ . 500°C H₂ . . ., . (Pt/Al₂O₃, Pt–Ir/Al₂O₃ Pt–Pe/Al₂O₃) 0,5.

     

Sulfurization of Pt/Al2O3?Cl catalysts. IV. Adsorption sites of H2S on Al2O3, Al2O3?Cl and Pt/Al2O3?Cl

Chemisorption of H₂S on Al₂O₃, Al₂O₃–Cl and Pt/Al₂O₃–Cl has been studied by gravimetry and IR spectroscopy. The influence of the amount of Cl on the H₂S adsorption equilibrium value and the nature of the adsorption sites at low and high coverages are discussed.

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H₂S Al₂O₃, Al₂O₃–Cl Pt/Al₂O₃–Cl . Cl H₂S, .

     

Structure sensitivity and coke formation on Pt/Al2O3 catalysts

The initial rate of carbon formation during cyclopentane reaction has been studied on different Pt/Al₂O₃ catalysts of varying metal dispersity. It has been shown that coke deposition on the metal is a structure sensitive reaction which is preferably produced on large metallic particles. On the other hand, coke deposition on the whole catalyst is relevant to cyclopentadiene formation and is a structure insensitive reaction since the initial rate of coke deposition on the whole catalyst is proportional to the metallic surface area.

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Pt/Al₂O₃ . , , . , , , .. .

     

X-ray study of Re/Al2O3 and Re+Pt/Al2O3 catalysts using synchrotron radiation

Uning synchrotron radiation, L_III rhenium absorption spectra have been studied for Re/Al₂O₃ and Re+Pt/Al₂O₃ catalysts obtained by impregnation. For individual rhenium compounds a linear dependence between the shift of absorption edge and the state of rhenium oxidation has been found. The absorption spectra of reduced catalysts are significantly broadened as compared with those of individual compounds of the same valency. This points to the presence of rhenium compounds in different oxidation states.

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L_III- , Re/Al₂O₃ Re+Pt/Al₂O₃, . . . .

     

Influence of the preparation method on the pore spectrum of Pt?Cr/Al2O3 and Pt?Sn/Al2O3 catalysts

It is shown that, in contrast to classical impregnation methods, in bimetallic catalyst production the texture of the carrier is stabilized by introducing the promoting ion on the surface of Pt/Al₂O₃ with vapors of CrO₂Cl₂ or SnCl₄. This is shown by a relatively slower decrease of the specific area and the volume of the pores upon calcination.

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, Pt/Al₂O₃- CrO₂Cl₂ SnCl₄ . .

     

Non-stoichiometric oxygen in Cr2O3 catalysts of different dispersities

The content of non-stoichiometric oxygen in Cr₂O₃ catalysts of different dispersity has been determined by a direct thermodesorption method. A sharp decrease in the content of non-stoichiometric oxygen after calcination of the samples above 500°C was observed.

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Cr₂O₃ . 500°C.

     

Modification effect of Cu upon Pt In Pt?Cu?Al2O3 catalysts

In Pt–Cu–Al₂O₃ catalysts Cu might display either Electronic Ligand Effect or Ensemble Effect, depending on the preparation method of catalysts. For catalysts with Pt added before Cu, the latter exhibits an Electronic Ligand Effect. However, for catalysts with Cu added before Pt or with co-added Pt and Cu, Cu mainly demonstrates an Ensemble Effect.

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Pt–Cu/Al₂O₃ , . Pt Cu, , .

     

低温下Pt/Al_2O_3和Pd/Al_2O_3光辅助乙二醇水相重整制氢研究

采用浸渍还原法制备了氧化铝负载的Pt和Pd纳米颗粒催化剂,用于光辅助乙二醇水相重整制氢反应。结果表明,光照能够有效降低乙二醇水相重整制氢的活化能,Pt/Al_2O_3比Pd/Al_2O_3具有更高的H_2转换频率(TOF)和更低的CO选择性。采用XRD、TEM、UV-vis等技术对催化剂的结构和形貌进行了表征,原位漫反射红外光谱(DRIFTS)表明,光照能促进乙二醇分子O-H键的断裂。理论计算表明,Pt/Al_2O_3催化乙二醇重整制氢反应产物中较低的CO选择性主要归因于CO在Pt表面较小的反应能垒,能够较快与H_2O解离的O反应生成CO_2。     

Pt/Al2O3 and Pt/Ba?Al2O3 catalysts studied by temperature programmed desorption of oxygen: Evidence for a low temperature desorbing species

For fresh and aged Pt/Al₂O₃ catalysts, TPD of oxygen is fairly well related to the noble metal surface areas and to the catalytic activity in butane combustion, whereas for aged Pt/Ba−Al₂O₃ solids, the catalytic activity is still preserved despite a tremendous sintering of the metallic phase and seems to be connected to a surface barium superoxide.     

Catalytic incineration of n-hexane on Pt/Al2O3

The catalytic incineration of n-hexane over a Pt/Al₂O₃ catalyst has been studied using a fixed bed reaction. The reaction was carried out in dry air between 250 and 350 °C and at 1 atm pressure. The concentration of n-hexane was between 25 and 300 ppm. The reaction was found to be zero order in n-hexane concentration and the activation energy was found to be 21 kcal/mol. The zero order kinetics can be explained by a surface redox cycle known as Mars-van Krevelen mechanism in which the oxidation of surface Pt is the rate-controlling step.

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- Pt/Al₂O₃ . , 250–350°C 1 . - 25–300 .. - –21 /. , — , , , Pt.

     

Effect of pressure on the rate of n-heptane conversion on Pt/Al2O3 catalysts

The effect of pressure on the rates of product formation in n-heptane conversion on Pt/Al₂O₃ has been studied at 490 °C over the pressure range of 10–50 atm. It has been shown that the rate of isomerization is practically independent of pressure, and the dependence of the rates of dehydrocyclization and hydrocracking on pressure is described by simple kinetic equations. The reaction order of dehydrocyclization with respect to hydrogen tends to –2.0 at high pressures.

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- 10–50 490°C. , , . –2,0.

     

Oxidized platinum surface in Pt/Al2O3 reforming catalysts: IR studies

The influence of halide ions on the state of dispersed Pt in oxidized catalysts has been investigated, adsorbed CO being used as a probe. Charged platinum complexes form upon catalyst oxygenation, with CO bands at 2130, 2150, 2165, 2170 and 2180 cm^–1. Composition of the complexes depends on the oxidation temperature and the nature of the halide ion.     

Effect of the activation conditions on the catalytic properties of Pt/Al2O3 catalysts

The effect of the activation conditions of Pt/Al₂O₃ catalysts has been investigated in the hydrogenation of benzene and in the hydrogenolysis of ethane. Whatever the conditions of calcination or reduction, specific activities of all catalysts for benzene hydrogenation remain constant. On the other hand, for identical dispersities, the cacination in a wet argon flow increases the specific activity of platinum for hydrogenolysis of ethane, pointing out the role of wet pretreatment on defect building or on the faceting of supported metallic catalysts.

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Pt/Al₂O₃ . , . , , . .

     

Studies on the active sites for dehydrocyclization reaction over Pt?Al2O3 catalysts

The work represents a search for direct evidence of the existence of low temperature and high temperature active sites over Pt–Al₂O₃ for dehydrocyclization reaction. It is suggested that the former consists of dispersed metallic Pt and the latter of super-dispersed metallic Pt or isolated atomic Pt and ionic Pt.

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- - Pt/Al₂O₃ . , Pt, Pt, Pt.

     

Reduction kinetics of Mo/Al2O3 catalysts

Studies of the reduction kinetics of MoO₃ and Al₂O₃–MoO₃ catalysts in H₂ at 523–823 K indicate that molybdenum is present in Al₂O₃/MoO₃ in three forms: as Mo⁶⁺ in the Al₂O₃ lattice and as MoO₃ and Al₂(MoO₄)₃ phases. Activation energies of reduction E_act determined according to the Avrahmy-Erofeev equation, are reported.

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MoO₃ Al₂O₃–MoO₃ H₂ 523–823 . Al₂O₃–MoO₃ : Mo⁶⁺ Al₂O₃ MoO₃ Al₂(MoO₄)₃, . -.

     

Hydrocarbon conversion on promoted rhodium/Al2O3 catalysts

In (E+Rh)/Al₂O₃ catalysts (E=Sn, Pb, Mo and W) the catalytic properties of rhodium in benzene hydrogenation, propane hydrogenolysis and n-hexane conversion change drastically. For modified rhodium the decrease in the hydrogenolysis rate of C–C bonds in paraffins leads to an increased yield of the products of non-destructive conversion of n-hexane.

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(E+Rh)/Al₂O₃ (E:Sn, Pb, Mo, W) , , -. C–C -.

     

Investigation of the acidity of Ni/Al2O3 and Ni/SiO2?Al2O3 catalysts

Acidity of Ni-modified alumina and silica-alumina catalysts was determined using n-butylamine titration and pyridine adsorption methods. Strong influence of Ni²⁺ ions on the Brönsted acidity of silicaalumina was observed. Improved Brönsted acidity of such system was confirmed by the results of the test reaction.     

Performance of Pt?Sn/Al2O3?Cl catalysts in isopropanol decomposition

Highly dispersed TiO₂-supported copper with strong interactions with the support has been prepared. After reduction at 770 K, H₂ chemisorption is suppressed. Two types of copper sites exist, one easily and reversibly oxidized by O₂ at room temperature, and another interacting with the support.

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, TiO₂, . 770 H₂ . , O₂ , - .