Hydrogenation catalysts metals deposition

The catalyst is also employed in the form of the finely-divided metal deposited upon activated carbon (usually containing 5 or 10 per cent. Pd) two methods of preparation are described, in one reduction is effected with alkaline formaldehyde solution and in the other with hydrogen ... 

Electroless reactions must be autocatalytic. Some metals are autocatalytic, such as iron, in electroless nickel. The initial deposition site on other surfaces serves as a catalyst, usually palladium on noncatalytic metals or a palladium—tin mixture on dielectrics, which is a good hydrogenation catalyst (20,21). The catalyst is quickly covered by a monolayer of electroless metal film which as a fresh, continuously renewed clean metal surface continues to function as a dehydrogenation catalyst. Silver is a borderline material, being so weakly catalytic that only very thin films form unless the surface is repeatedly cataly2ed newly developed baths are truly autocatalytic (22). In contrast, electroless copper is relatively easy to maintain in an active state commercial film thicknesses vary from <0.25 to 35 p.m or more. 

The reverse ME technique provides an easy route to obtain monodispersed metal nanoparticles of the defined size. To prepare supported catalyst, metal nanoparticles are first purified from the ME components (liquid phase and excess of surfactant) while retaining their size and monodispersity and then deposited on a structured support. Due to the size control, the synthesized material exhibits high catalytic activity and selectivity in alkyne hydrogenation. Structured support allows suitable catalyst handling and reuse. The method of the catalyst preparation is not difficult and is recommended for the... 

This study presents catalytic properties of Pd and Pt for hydrogen adsorption. Metals were deposited by easy to perform procedure on powder materials. This method does not required use of hydrogen as reactant gas and can be easy scale-up. Presence of metal particles was verified by SEM experiment. Average size of noble metals was approximately 1pm. From experiment conditions amount of catalyst was found and it was revealed that mass of metal (Pt or Pd) do not exceed l %wt. 

In this paper we report the application of bimetallic catalysts which were prepared by consecutive reduction of a submonolayer of bismuth promoter onto the surface of platinum. The technique of modifying metal surfaces at controlled electrode potential with a monolayer or sub-monolayer of foreign metal ("underpotential" deposition) is widely used in electrocatalysis (77,72). Here we apply the theory of underpotential metal deposition without the use of a potentiostat. The catalyst potential during promotion was controlled by proper selection of the reducing agent (hydrogen), pH and metal ion concentration. 

Catalytic hydrogenation of DHL by various catalysts such as bulk metals and metals deposited on the carbon, oxides and salts has been studied since the 70 s of the last century (3). The disadvantages of such catalysts are the low surface area and the high content of the noble metals, which result in their high cost price. 

Modification of the hydrogenolysis (metal deposition)-hydrogenation selectivity in the demetallation of Ni-T3MPP has been achieved by chemically doping a CoMo/A203 catalyst. Ware and Wei (1985b) demonstrated... 

Tamm et al. (1981) have suggested that metals are primarily responsible for the initial deactivation. They report that the length of the initial deactivation period is directly related to the concentration of metals in the feedstock and the total run length or catalyst lifetime. Tamm et al. (1981) also observed that the initial deactivation period responds to process variables that influence the metal deposition pattern in catalysts. Lower hydrogen pressure and smaller catalyst size result in a greater loss of initial... 

Laboratory studies on both model compounds and real residuum feedstocks under commercial conditions have shown that the metal deposit profile on aged catalyst pellets is often M shaped, having a concentration maximum at some internal radial position. The simple first- or second-order kinetics employed by the models discussed cannot predict such a profile. This profile is a consequence of the sequential path for HDM where the hydrogenated intermediate B must first be formed from the original oil compound A prior to forming the deposit C ... 

Homogeneous hydrogenation in the fluorous phase has been so far reported only for a limited set of simple olefins (Richter et al., 1999, Rutherford et al., 1998), as exemplified with the neutral rhodium phosphine complex 18 as catalyst precursor (eq. 5.7). Isomerization of the substrate 1-dodecene (17a) was observed as a competing side reaction under the reaction conditions. The catalyst formed from 18 could be recycled using a typical FBS protocol, but deactivation under formation of metal deposits limited the catalyst lifetime. 

In a study of the deactivation by coking of an atmospheric residue HDM catalyst, we have been able to obtain coked catalysts almost free from metal deposits in batch reactor and coked catalysts containing small amounts of metal sulfide deposits in continuous flow reactor using a Safaniya atmospheric residue under similar experimental conditions (30). We report in this paper a study of the deactivating effects of the deposits using toluene hydrogenation, cyclohexane isomerization and thiophene hydrodesulfurization reactions. 

The Bi-promoted catalysts were prepared by consecutive deposition of Bi onto a commercial 5 wt% Pt/alumina (Engelhard E 7004, Pt dispersion 0.30 determined by TEM) [7]. The reduction of bismuth-nitrate was carried out in a dilute aqueous acidic solution O10"6 M, pH = 3-4) by hydrogen. The metal content of the catalysts was determined by inductive coupled plasma atomic emission spectroscopy (ICP-AES). Preferential deposition of Bi onto Pt particles has been confirmed by TEM, combined with energy dispersive X-ray analysis (EDX) [7]. Pb-, Sn- and Ag-promoted catalysts were prepared similarly. 

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