Rhenium bimetallic catalysts

Valence State of Rhenium in Reduced Bimetallic Catalysts With and Widiout Alkali Metals... 

Only scare data is available in the literature on the application of rhenium containing mono- or bimetallic catalysts in the hydrogenolysis of esters to alcohols. Decades ago Broadbent and co-workers studied the hydrogenation of organic carbonyl compounds (aldehydes, ketones, esters, anhydrides, acids,... 

Re) for the preparation of solid catalysts refer to bimetallic catalysts containing manganese or rhenium. These systems are covered in the Section 8.2.3.1 (Pt-Re) and Section 8.3.1.1 (Fe-Mn). 

The use of carbonyl complexes has enabled proper study of the role of rhenium in Pt-Re bimetallic catalysts used in the reforming of naphtha [57-60] and tailoring of the preparation of Pt-Ru bimetallic particles. Pt-Ru systems are of interest in developing electrodes for fuel cell applications [61]. 

On such bimetallic catalysts the rhenium loading at saturation of a 0.6% Pt/Al2C>3 catalyst depends on the hydrogen pressure. From a thermodynamic point of view the quantity of additive deposited at saturation is defined by the equilibrium conditions of the system under consideration. By taking into account the reduction of Re04 to Re0 at 303 K (Table 1),... 

Carboxylic acids are one of the most difficult of all functional groups to hydrogenate. They can be hydrogenated to the alcohol, however, over ruthenium 34 or rhenium heptoxide 35,136 t 150°-200°C and 300-400 atmospheres pressure. Activated Cu-Ba-CrO is also effective at 250°-300°C and 300-400 atmospheres (Eqn. 18.31). 3 A Re-Os bimetallic catalyst has been used to hydrogenate carboxylic acids at 100 -120°C and 20-100 atmospheres of hydrogen. High conversions to the alcohol were reported. 38... 

The purpose of our paper is to compare the behaviors of platinum,rhenium, iridium and rhodium under the same coking conditions (Cyclopentane, 400 C)h He and Ir were chosen as they are usually added to Pt in reforming bimetallic catalysts. Rh was studied since it is the most active metal in hydrocarbon steain reforming (Refs. 5-7). 

In the early 1970s, bimetallic catalysts were introduced to meet the increasing severity requirements. Platinum and another metal (often rhenium, tin, or iridium) account for most commercial bimetallic reforming catalysts. The Pt-Re catalyst has proven to be reliable and easily regenerable, making it the primary catalyst in use today in semiregenerative units. " The catalyst is most often presented as 1/16, 1/8, or 1/4 in. AI2O3 cylindrical extrudates or beads into which Pt and other metals have been deposited. 

J. C. Dellamorte, J. Lauterbach, M. A. Barteau, Rhenium promotion of Ag and Cu-Ag bimetallic catalysts for ethylene epoxidation, Catal. Today 120 (2007) 182. 

Augustine and Sachtler, on reduction, rhenium oxides migrate over the support surface and become reduced in contact with a prereduced platinum particle. In this way, each platinum particle can generate a mixed platinum-rhenium cluster that has the beneficial effects of bimetallic catalysts on selectivity and stability. 

Nevertheless only scare data is available in the recent literature on the application of Group VIII noble metal (M) or rhenium-based mono- and Re-M bimetallic catalysts, in the hydrogenolysis of esters or hydrogenation of acids to alcohols. Recently a few publications, - and patents. have been reported on the transformation of different carbonyl compounds (saturated and unsaturated esters, acids and carboxamides) over rhenium-containing catalysts. In the bimetallic catalysts used for the hydrogenation of carbonyl compounds the rhenium was combined with Pd, or Rh. In the case of catalysts used for the hydrogenation of unsaturated carbonyl compounds the rhenium is usually modified with tin. ... 

Figure 43 shows that the higher the temperature of oxidation the higher the amount of the hydrogen consumed in high temperature part of TPR for the reduction of separate rhenium oxide species. The low temperature peak between 200 and 300 C indicates the presence of the oxide precursor of bimetallic nanoclusters that can be formed during the reduction of bimetallic catalysts. All... 

Numerous studies were devoted to the use of bimetallic catalysts, promoted either by an active metal such as rhenium or iridium, or an inactive one such as tin or germanium. These different catalysts were generally prepared by co-impregnation or successive impregnations. Moreover, most of the catalysts prepared by redox reactions were only evaluated in model reactions. For example, Corro et al. [87] prepared Pt-Sn/Al203-Cl catalysts by catalytic reduction or co-impregnation and compared their resistance to coking under cyclopentane feed. Thus, catalysts prepared by the surface redox reaction were less sensitive than the others to deactivation. This result was explained in terms of a more effective interaction between... 

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