Controlled preparation and characterization of plurimetallic Pt–Sn and Pt–Ir–Sn/Al2O3 reforming catalysts

International audienceThe preparation of bimetallic 0.6 wt.% Pt–xwt.% Sn/Al2O3and trimetallic 0.5 wt.% Pt–0.1 wt.% Ir–xwt.% Sn/Al2O3and 0.3 wt.%Pt–0.3 wt.% Ir–xwt.% Sn/Al2O3catalysts (0<x<0.4) by surface redox reaction between hydrogen activated on a parent platinum orplatinum–iridium catalyst and tin chloride (SnCl4) dissolved in hydrochloric medium (‘‘catalytic reduction’’ method) was investigated.Elemental analysis of catalysts indicated that tin can be deposited by surface redox reaction, this reaction competing with the adsorption of thetin precursor on the alumina support. The deposition on the metal by redox reaction being more rapid than the one on the support by exchange,the reaction time was limited to 15 min. Moreover, the addition of citric acid in the acidic medium allowed to decrease both the tin deposit on thesupport and the chloride content of the catalysts. The characterization of tin modified catalysts by temperature programmed reduction and byactivity measurements for cyclohexane dehydrogenation showed that a large amount of tin is deposited on or close to the active metallic phase

Influence of chlorine on the catalytic properties of supported rhodium, iridium and platinum in ring opening of naphthenes

International audienc

Characterization of bimetallic rhodium-germanium catalysts prepared by surface redox reaction

International audienceThe preparation of bimetallic rhodium-germanium/silica and rhodium-germanium/alumina catalysts was investigated by controlled surface reaction. Their catalytic performances were measured for two gas phase reactions (toluene hydrogenation at 323 K and cyclohexane dehydrogenation at 543 K) and for a liquid phase reaction (citral hydrogenation at 343 K). Elemental analysis of bimetallic catalysts showed that germanium can be deposited by redox reaction between hydrogen activated on a parent monometallic rhodium catalyst and germanium tetrachloride dissolved in water (catalytic reduction method). EDX microanalysis of rhodium-germanium/silica catalysts indicated that rhodium and germanium were deposited in close contact on the silica support. However, on alumina-supported catalysts, germanium deposition occurred also separately on the support. For the different test reactions, the catalytic properties of rhodium were strongly altered by the addition of Germanium. On alumina-supported catalysts, interesting catalytic effects were observed in citral hydrogenation when not only close contact exists between both metals but when, in addition, the second metal was deposited on the support in the close vicinity of rhodium

Deactivation by coking of supported palladium catalysts. Effect of time and temperature

International audienceThe coking reaction with cyclopentane was investigated on silica supported palladium catalysts in the temperature range 400-500 degrees C at various times. After reaction, the catalysts were characterized by temperature programmed oxidation by the fouling effect of coke on the reaction of cyclohexane dehydrogenation and by infrared spectroscopy of chemisorbed CO. TPO profiles of coked catalysts show the presence of two oxidation peaks corresponding to coke deposition on the metallic function: the first one near 250 degrees C which would correspond to coke deposited on palladium atoms of high coordination number, depends very little on the temperature or the time of the coking reaction. On the other hand, the second TPO peak near 400 degrees C which would involve palladium atoms of low coordination number, is enhanced by an increasing time or temperature of the reaction. These results clearly indicate that low coordinated palladium atoms are more resistant to the deactivation by coke under reforming condition

Preparation of alumina supported palladium-platinum catalysts by surface redox reactions. Activity for complete hydrocarbon oxidation

International audienceThe complete oxidation of hydrocarbons (methane, propane and propene) and the O-18/O-16 isotopic exchange were investigated on supported palladium-platinum catalysts. The bimetallic catalysts were prepared by controlled surface reactions (the "refilling" RC and the "direct redox reaction" RD) and by coimpregnation CI. The preparation methods lead to different kinds of platinum deposit, which involve different behaviours in hydrocarbon oxidation and in isotopic exchange. Even if the structure of bimetallic catalysts is modified under oxygen, the results show that the bimetallic catalysts keep a memory effect of their preparation method under the reaction conditions used in this wor

Relationship between the structural properties of supported bimetallic Pt–Rh catalysts and their performances for methylcyclopentane ring opening

International audienc

Selective ring-opening of methylcyclopentane on platinum-based bimetallic catalysts

International audienc

Bimetallic Rh-Ge and Pt-Ge catalysts supported on TiO2 for citral hydrogenation I. Preparation and characterization of the catalysts

International audienceBimetallic TiO2-supported Rh-Ge and Pt-Ge catalysts were prepared by surface redox reaction between hydrogen activated on a parent monometallic rhodium or platinum catalyst and a germanium salt dissolved in water (catalytic reduction method). They were characterized by elemental analysis, transmission electronic microscopy (TEM), temperature-programmed reduction (TPR) and by their activity for the gas phase dehydrogenation of cyclohexane. Elemental analysis of the bimetallic catalysts showed that germanium can effectively be deposited by the catalytic reduction method on titania-supported Rh and Pt catalysts. Moreover, the different characterization methods (TEM, TPR and cyclohexane dehydrogenation) proved that germanium is in great interaction with rhodiurn and platinum. Nevertheless, some germanium deposition occurred also separately on the titania support. TEM and cyclohexane dehydrogenation results revealed that both rhodium and platinum particles were stable on titania support under the conditions of bimetallic catalyst preparation contrary to previous results obtained with silica or alumina supports. Effectively, no sintering has been observed when they were immersed in an aqueous solution under hydrogen bubbling (catalytic reduction protocol). Their catalytic performances for the cyclohexane dehydrogenation reaction indicate that all the catalysts reduced at high temperature (500 degrees C versus 300 degrees C developed the. strong metal-support interaction (SMSI) effect, which implied the formation of TiO(2-x) species. Whatever the nature of the parent metal (Rh and Pt), this effect was totally destroyed by air exposure of the samples at ambient temperature whereas one part of the TiO(2-x) moieties remained after immersion of the catalysts in an aqueous medium