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, .

     

Hydrogen effects on the electric conductivity of a Pt/Al2O3 catalyst

Hydrogen desorption, hydrogen spillover and reduction processes have been evidenced using a new experimental strategy based on AC electric conductivity measurements during TPD and TPR experiments on a 0.5% Pt/Al₂O₃ catalyst.     

Investigation of toluene formation on Pt/Al2O3 catalyst in n-hexane dehydrocyclization

Formation of toluene, a chain lengthening product, has been observed on Pt/Al₂O₃ catalyst in n-hexane dehydrocyclization. Toluene formation is influenced by the catalyst pretreatment processes and the reaction temperature. A correlation has been found between the ageing phenomena and toluene formation.

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- Pt/Al₂O₃ — . . .

     

Interaction of propylene with a V2O5/Al2O3 catalyst

IR-spectroscopic studies indicate that on the oxidized surface of V₂O₅/Al₂O₃ catalysts propylene interacts mainly with Brönsted acid centers to form an alcoholate type complex transforming into acetone. On the reduced surface propylene is stabilized as a -complex of V³⁺ and V⁴⁺ ions.

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- , V₂O₅/Al₂O₃ , . - V³⁺ V⁴⁺.

     

Kinetics of catalytic combustion in air over Pt/Al2O3/Al catalyst

Summary Catalytic combustion of toluene, propylene and CO over Pt/Al₂O₃ /Al catalyst was investigated. Strong inhibition effects are observed when the mixture of toluene, propylene and CO is oxidized. A reaction mechanism of catalytic combustion over Pt/Al₂O/Al is proposed. The results from kinetic models are in good agreement with the experimental data.     

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.     

Dilatometric studies of Y2W3O12 with added Al2O3

Y₂W₃O₁₂ exhibits negative thermal expansion along the three crystallographic directions due to the transverse thermal vibrations perpendicular to the Y-O-W linkage. It is highly hygroscopic and forms a trihydrate structure at room temperature. Dilatometric studies of Y₂W₃O₁₂ show large thermal expansion hysteresis due to large grain size and a large initial positive thermal expansion due to the removal of water molecules. Al₂O₃ has been added to Y₂W₃O₁₂ upto 10 wt% in an attempt to overcome the hygroscopicity and reduce the particle size and thereby the thermal expansion hysteresis. Thermo gravimetric, dilatometric and electron microscopic studies are presented to support these observations. Dedicated to Professor C N R Rao on his 70th birthday     

Kinetic studies of hydrogen and carbon monoxide adsorption on Re2O7/Al2O3 catalysts

Kinetic studies of hydrogen and carbon monoxide adsorption on reduced Re₂O₇/Al₂O₃ catalysts have revealed that its activation energy decreases with increasing reduction degree of rhenium oxide. Adsorption of gases is suggested to take place on metallic rhenium atoms.

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- . , . , .

     

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.

     

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, . . . .

     

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.     

M?ssbauer spectroscopic studies of the state of Pt?Sn/Al2O3 catalyst for hydrocarbon conversion

Mössbauer spectroscopic studies of the state of Pt–Sn catalyst for hydrocarbon conversion supported on prechlorinated -Al₂O₃ indicate that, unlike nonchlorinated Al₂O₃, this system is much more reduced and besides Pt₃Sn–PtSn₂, its surface contains sigfificant amounts of Sn(II) and Sn(IV) chlorides bonded to the surface.

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Pt–Sn , -Al₂O₃. , Al₂O₃, Pt–Sn Pt₃Sn–PtSn₂ Sn(II) (IV), .

     

AC electrical conductivity measurements during H2-TPD experiments on a Pt/Al2O3 catalyst

The kinetics of the reaction of cyclopentanol with PhNCO or OCN(C₆H₁₂)NCO was studied in toluene, di-n-butyl ether and acetonitrile. The results suggest a predominant influence of the aggregation state of alcohol.     

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 . .

     

纳米膜组装介孔Al2O3：合成及Pt/Al2O3的硝基苯催化加氢性能

以"乙酸乙酯(EA)-偏铝酸钠-水"体系在室温下合成了纳米膜组装介孔Al2O3。研究发现:合成反应时间、静置前搅拌时间、NaAlO2用量、EA用量及反应温度等对合成产物的形貌有影响;另外,与用商品γ-Al2O3制备的Pt/γ-Al2O3催化剂相比,纳米膜组装介孔Al2O3制备的Pt/Al2O3催化剂含有部分易被还原的PtOx物种。在硝基苯催化加氢反应中,用合成Al2O3为载体制备的Pt/Al2O3催化剂,比用商品γ-Al2O3制备的Pt/γ-Al2O3催化剂具有更好的催化活性。     

Active site for hydrogenation on reduced V2O5/Al2O3 catalyst

Active sites for C₂H₄ hydrogenation produced by reduction of V₂O₅/Al₂O₃ catalyst pretreated at 450°C were found to be composed of both strong Lewis acid sites associated with V⁴⁺ and basic sites of Al₂O₃. C₂H₄ polymerization concurrent with hydrogenation was assumed to occur on Lewis acid sites with higher acid strengths than those of the hydrogenation sites.

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C₂H₄, V₂O₅/Al₂O₃, 450°C, , Al₂O₃. , , , C₂H₄.

     

制备方法对Al2O3掺杂Pt/WO3-ZrO2催化剂上正庚烷异构化反应的影响

采用恒pH法和非恒pH法制备了Al₂O₃掺杂的Pt/WO₃/ZrO₂催化剂,并用N₂吸附-脱附、X射线衍射、紫外-可见漫反射、CO化学吸附、X射线光电子能谱、²⁷Al魔角旋转核磁共振和吡啶吸附红外等技术对催化剂进行了表征.结果表明,相比于非恒pH法制备的催化剂,恒pH法制备的催化剂具有较高的比表面积和Pt分散度,在H₂气氛中产生更多的B酸位,从而表现出更高的催化正庚烷临氢异构化反应活性; 在200℃和质量空速0.9h^-1的反应条件下,正庚烷转化率达70.0%,明显高于非恒pH法制备的催化剂(43.5%).     

Mechanistic studies of methane partial oxidation to syngas over LiNiLaOx/Al2O3 catalyst

Reduction of vanadium-titanium oxide catalysts with hydrogen in the temperature range of 150–450°C results in the increase of the content of V⁴⁺ ions in substitution positions of TiO₂ with the anatase structure. The temperature increase up to 250°C results in the growth of the spectral intensity of V⁴⁺ associates in substitution positions of anatase. At higher treatment temperatures their intensity decreases due to the formation of VO₂ fragments in anatase. At 400°C and higher temperatures a solid solution of V⁴⁺ ions in rutile is formed.