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, .

     

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, . -.

     

Fischer-Tropsch synthesis over Ru/Al2O3 catalysts

Fischer-Tropsch syntheses (FTS) were carried out in a slurry phase over Ru/Al₂O₃ catalysts using hexadecane as a solvent. The outcome of the FTS was dependent on the oxide support, calcination temperature, synthesis gas composition and sulfur content. The addition of Mn/Na to Ru/Al₂O₃ was effective in raising the initial activity and C5+ selectivity, but after 20 hours, the performance of the modified catalyst was similar to that of the unmodified catalyst. An additional investigation involving the use of fresh vs used catalysts demonstrated that an agglomeration of the metallic Ru, at least in part, does occur during the reaction.     

Pyrolytic and catalytic conversion of rape oil into aromatic and aliphatic fractions in a fixed bed reactor on Al2O3 and Al2O3/B2O3 catalysts

In the, at present, unstable fuel market, much attention is devoted to alternative technologies for fuel production and development of alternative products of the petrochemical industry. One of the prospective sources of fuel and alternative petrochemical products is biomass, and the use of oil plants is one of the possibilities. This paper reports on a possible conversion of rapeseed oil produced in Poland into intermediate hydrocarbon fractions by pyrolysis combined with parallel catalytic conversion. The products were analysed by gas chromatography coupled with a mass detector. The process was performed in a fixed-bed reactor and was monitored by FTIR and ¹H NMR. Depending on the catalysts applied, the products contained: water, carbon oxides, hydrogen, aliphatic or aromatic hydrocarbons accompanied by some amount of C2-C5 hydrocarbons formed during the cracking process. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.     

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.

     

Cyclohexane dehydrogenation over Pt-Dy/Al2O3 catalysts

The conversion of cyclohexane dehydrogenation over Pt–Dy/Al₂O₃ has been studied with a pulsed microcatalytic reactor. Two interesting experiments utilizing CS₂ and thiophene poisoning Pt/Al₂O₃ and Pt–Dy/Al₂O₃ for cyclohexane dehydrogenation are shown and the reaction mechanism is described. The kinetic parameters of cyclohexane dehydrogenation have been calculated. Correlation of the catalytic behavior with the properties of active sites is also discussed.     

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.     

Hydrocarbon conversion over Pt?Re/Al2O3-ZSM-5 bifunctional catalysts. II. Sulfur resistance of Pt?Re/Al2O3 modified with ZSM-5

The sulfur resistance of Pt–Re/Al₂O₃-ZSM-5 catalyst has been investigated for normal heptane reforming. It was found that while sulfur acts as a poison for Pt–Re/Al₂O₃, it can play an important role in activity maintenance and aromatics production when ZSM-5 zeolite is present.

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Pt–Re/Al₂O₃-ZSM-5 -. , , Pt–Re/Al₂O₃, ZSM-5.

     

Hydrodechlorination of dichlorodifluoromethane (CFC-12) over Pd/Al2O3 and Pd-Au/Al2O3 catalysts

During an initial stage of the reaction of CCl₂F₂ with hydrogen on alumina-supported Pd and Pd-Au catalysts, an extensive defluorination occurs. However, at steady state, this undesired defluorination is greatly reduced; CH₄ and CH₂F₂ constitute the only major reaction products. A temperature programmed hydrogen treatment study shows retention of fluorine (and carbon) in used catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

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, . . . .

     

TPR studies on steam reforming of 2-propanol on Rh/Al2O3, Ru/Al2O3 and Pd/Al2O3

Reaction pathways for steam reforming of 2-propanol (isopropyl alcohol, IPA) on Rh/Al₂O₃, Ru/Al₂O₃ and Pd/Al₂O₃ have been studied by temperature-programmed reactions (TPRs) of IPA and acetone in the presence of steam. The results of TPRs suggest that that of IPA on Rh/Al₂O₃ and Ru/Al₂O₃ proceeds via acetone, while the steam reforming of IPA on Pd/Al₂O₃ takes place via propene from acetone. This revised version was published online in August 2006 with corrections to the Cover Date.     

Investigation of n-heptane conversion over Pt?Al2O3 catalysts under gradientless reforming conditions

The rates of the total and individual directions of n-heptane conversion in reforming over platinum-on-alumina catalysts were shown to be independent of dilution with hydrogen. They can be described by simple equations following from kinetic concepts in ideal adsorbed layers.

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, - , .

     

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 . , , . , , , .. .

     

Photocatalytic conversion of NOx on AgCl/Al2O3 catalyst

The rate of NO conversion under UV illumination was evaluated over Ag/Al₂O₃ and AgCl/Al₂O₃ catalysts at room temperature. The AgCl/Al₂O₃ catalyst is highly active for the conversion of NO_x. The conversion is enhanced in the presence of O₂ and further enhanced when oxygen coexists with hydrocarbons. Diffuse reflectance spectra of AgCl/Al₂O₃ and Ag/Al₂O₃ show an absorption band at 250 nm, and a weak and broad band at 230 nm, respectively. The high photocatalytic NO_x conversion is achieved over the AgCl/Al₂O₃ catalyst. The conversion level of NO_x is maintained above 60% over 5 h in the presence of O₂ and hydrocarbons under UV-irradiation. The absorption band at 250 nm is ascribed to the band gap energy of crystallized AgCl particles on Al₂O₃. These results suggest that high photocatalytic NO_x conversion proceeds on crystallized AgCl particles formed on Al₂O₃.     

Temperature-programmed reduction of CuO?NiO/Al2O3 catalysts

Reducibility of NiO/Al₂O₃ and CuO–NiO/Al₂O₃ catalysts has been studied by the TPR method within the temperature range 293–873 K. The results suggest that the copper content essentially does not influence the reducibility of NiO/Al₂O₃.

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NiO/Al₂O₃ CuO–NiO/Al₂O₃ TPR 293–873 . , NiO/Al₂O₃.

     

Thermal activation of Al2O3 supported MoO3 and WO3 metathesis catalysts

Alumina-supported MoO₃ and WO₃ catalysts were activated for the metathesis of propene by thermal treatment in Ar. Temperatures up to 1140 K are required for catalysts with low metal contents. These exhibit the highest specific activities though they are known to be highly resistant to reduction. It is proposed that the active sites are formed from Mo(VI) and W(VI) species under the conditions employed.

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MoO₃ WO₃, Al₂O₃, . 1140 . , , . , , Mo W.

     

Synthesis and characterization of SnOx/Al2O3 derived gel catalysts

SnO_x/Al₂O₃ catalysts were prepared by the sol-gel method using as starting reactants aluminium-tri-s-butoxide and (i) tetrabutyltin, (ii) tin tetrachloride and (iii) tin tetra-t-amyloxide. The gel derived catalysts show acidities of 0.72, 1.08 and 1.05 mol NH₃/m² and BET areas of 91, 112 and 189 m²/g. The activity and selectivity pattern for isopropanol decomposition were found to depend strongly on the tin precursor used.