R. Frety

Platinum-rhenium-alumina catalysts: III. Catalytic properties

Abstract The activity of PtRe catalysts on α- or γ-alumina has been determined for various reactions. In no case is the activity of bimetallic catalysts the sum of the activity of platinum and rhenium of which the catalyst is composed. Curves of activity as a function of the composition of the catalyst exhibit one or two maxima in benzene hydrogenation, benzene-deuterium exchange, cyclopentane, and butane hydrogenolysis, those maxima being more or less pronounced according to the reaction and the support. Conversely, the rate of 1,1,3-trimethyl cyclohexane dehydrogenation decreases when the percentage of rhenium is increased. A pronounced analogy has been established between, on the one hand, the changes of activity with bimetallic composition, and, on the other hand, with the position of the metal in the Periodic Table for the monometallic period Pt, Ir, Os, Re deposited on alumina.

Platinum-rhenium-alumina catalysts: II. Study of the metallic phase after reduction

Abstract Two percent ( Pt + Re ) Al 2 O 3 catalysts prepared by co-impregnation of Al2O3 with H2PtCl6 and Re2O7 and generally reduced by hydrogen at 500 °C were mainly investigated by thermogravimetry (H2O2 cycles at 25 °C), electron microscopy, and infrared spectroscopy (chemisorption of CO at 25 °C). The greater reducibility in the presence of Pt of oxygen chemisorbed by Re, and the vCO frequency shifts of the PtCO and ReCO species against the percentage of Re indicated a strong interaction between both metals. Most probably Pt and Re are alloyed. The H2O2 cycles at 25 °C allowed the determination of the overall dispersion of the (Pt + Re) phase while the optical density of the infrared band of CO adsorbed on platinum gave some information about the surface concentration of Pt in the (Pt + Re) phase.

Platinum-rhenium/alumina catalysts: I. Investigation of reduction by hydrogen

Abstract Pure Re2O7 when heated in a hydrogen atmosphere, sublimes before reduction. However, when Re2O7 is mixed with Pt or Pd or Re powder, instead of volatilization complete reduction to metallic Re occurs below 200 °C. A strong activation by Pt of the reduction of Re2O7 also takes place on Al2O3 samples coimpregnated with H2PtCl6 and Re2O7. With such catalysts, the reduction of Re2O7 to metallic Re under 1 atm pressure of hydrogen seems to be complete at a rather low temperature.

Characterization of palladium-copper bimetallic catalysts supported on silica and niobia

Abstract Silica and niobia Pd-Cu supported bimetallic catalysts were characterized by temperature-programmed reduction (TPR), hydrogen chemisorption and infrared spectroscopy of adsorbed carbon monoxide. On catalysts reduced at 573 K, the metal-metal interaction was confirmed from the analysis of TPR profiles and the decreased capacity of hydrogen chemisorption with increasing copper content. After reduction at 773 K, the palladium/niobia catalyst displays a SMSI effect; however, the increase in copper content in the bimetallic catalyst led to a suppression of the SMSI.

Temperature-programmed reduction: limitation of the technique for determining the extent of reduction of either pure ceria or ceria modified by additiv

Abstract The classical temperature-programmed reduction technique using a thermally controlled detector and a water vapour trap did not permit the quantification of the extent of reduction of unsupported ceria with a high surface area. During temperature-programmed reduction of pure ceria with hydrogen, not only is water formed; carbon monoxide and carbon dioxide desorbing from the sample are also able to reach the thermally controlled detector and contribute to the variations in conductivity of the actual reduction mixture. When ceria is modified by impregnation with alkaline nitrate, followed by calcination at 673 K, NO x , compounds are also formed and contribute both to hydrogen uptake and to variations in gas conductivity. A further complication is caused by the storage of some hydrogen in ceria, below 773 K, followed by the release of hydrogen above this temperature. Temperature-programmed oxidation of the reduced samples is an alternative way to measure the extent of ceria reduction.

Determination of the Accessible Metallic Surface of Supported Platinum Quantitative Infrared Spectroscopic Study of Carbon Monoxide Adsorption

Abstract Catalysts containing platinum on carriers which do not exhibit strong metal support interaction (SMSI) behaviour have been prepared. Metal dispersion was measured by volumetric chemisorption measurements. Adsorption of carbon monoxide on the same samples was followed by infrared spectroscopy. A linear relationship was found between the optical density of the band due to carbon monoxide linearly bonded to platinum and the metallic area accessible to gases measured either by hydrogen and oxygen chemisorptions or by hydrogen-oxygen titration. Platinum supported on carriers liable to exhibit a SMSI character has also been examined. When direct chemisorption of hydrogen is higher than the experimental error, the value of the metallic area so obtained is in good agreement with the corresponding infrared determination. Hydrogen—oxygen titration measurements are not suited to the determination of the metallic surface for catalysts exhibiting a SMSI behaviour. The spectroscopic method seems to be suitable for the measurement of the metallic surface area of automotive post combustion catalysts.

Catalytic decomposition of vegetable oil

Abstract Vapours of crude and prehydrogenated soybean oil were decomposed by passage over solid acid (Al 2 0 3 − n) and base (MgO) in a glass tubular reactor at 300–500°C. The liquid products were analyzed by infrared spectroscopy and gas chromatography. The degree of unsaturation of the oil was found to have a dominant effect on the products. Soybean oil prehydrogenated to a low iodine value of 10 yields essentially pure hydrocarbon products with a mean molecular weight comparable to that of diesel oil, while crude soybean oil yields a mixture of oxygen containing products and hydrocarbons of lower mean molecular weight. These observations were compared to catalytic decomposition of stearic and oleic acids under similar conditions.

Partial oxidation of methane to synthesis gas. Behaviour of different Ni supported catalysts

The behaviour of Ni supported catalysts, obtained using Ni(NO3)2 and Ni-acetylacetonate as precursor compounds, is analyzed. It is observed that initial activities and selectivities are similar for both systems, but the stability differs significantly. The systems show different carbon structures and sintering rates, depending on the precursor compound employed.

Influence of the nature of the platinum precursor on the surface properties and catalytic activity of alumina-supported catalysts

The influence of the nature of the metal precursor — platinum acetylacetonates and chloroplatinic acid — on the surface properties and catalytic activity of Pt/Al2O3 catalysts is reported. The obtained results indicate that the catalysts prepared by the organometallic route present higher metal dispersion and lower acidity compared with those prepared from H2PtCl6. On the other hand, XPS results showed that the state of platinum is essentially Pt0 in the catalysts obtained from Pt(acac)2 while in the solids prepared by impregnation of H2PtCl6 there exists an important contribution of Ptδ+ species which plays a positive role in the hydrogenation of toluene. An additional hydrogen spillover due to the presence of more acidic support is also suggested as an explanation of the observed catalytic results.

Unsupported Cobalt Molybdenum Sulfide Catalysts .2. Characterization and Evolution of Physicochemical Properties During Catalytic Reaction

Abstract Cobalt molybdenum sulfide catalysts were prepared by two different methods, comaceration (CM) and homogeneous sulfide precipitation (HSP). Both types o catalysts were characterized by several techniques, DTA, XPS, AEM, conductivity measurements and temperature programmed reduction. Physicochemical properties were determined for different states of the catalyst:precursor, fully sulfided and catalytically tested. It is confirmed t