Metal catalytic features

At IREQ, besides the participation in the field tests run by the engineers of Hydro-Quebec (12), the main effort has been to tackle fundamental problems in the field of electrocatalysis (18-22) and of anodic oxidation of different potential fuels (23-26). A careful and extensive study of the electrochemical properties of the tungsten bronze has been carried out (18-20) the reported activity of these materials in acid media for the oxygen reduction could not be reproduced and this claim by other workers has been traced back to some platinum impurities in the electrodes. Some novel techniques in the area of electrode preparation are also under study (21,22) the metallic deposition of certain metals on oriented graphite show some interesting catalytic features for the oxygen reduction and also for the oxygen evolution reaction. 

Catalytic Features of Carbon-Supported Group VIII Metal Catalysts for Methanol Carbonylation... 

FUJIMOTO ET AL. Catalytic Features of Carbon-Supported Metal Catalysts 209... 

In the present work some of the catalytic features of nickel and other group VIII metals for methanol carbonylation and the role of activated carbon as carrier were studied. 

A number of studies have made use of functionalized cyclophanes for developing supramolecular catalysts and enzyme models [4.31-4.34, 5.37, 5.38]. Their catalytic behaviour is based on the implementation of electrostatic, hydrophobic and metal coordination features for effecting various reactions in aqueous media. 

RHE) and coinciding with the peak (see Fig. 8) associated with the Ru(IV)/ Ru(VI) couple beginning at about 1.25 V (RHE) and the second coinciding with the peak usually associated with the Ru(VI)/Ru(VII) couple [209]. Formate was observed to be the product of HCHO oxidation in the first wave, while 4e oxidation of HCHO to carbonate was observed in the second wave. Despite its interesting catalytic features for the electro-oxidation of formaldehyde, Ru02 is not as active as the noble metal catalysts Pt and Pd for this reaction, however. 

Fig. 2.20 Formal fitness landscape of various biocatalytic and inactive (i.e., the latter being located outside the window of essentiality ) metal ions for the carboxypeptidase A (Vallee and Williams 1968). The enzyme reconstituted by cobalt (treatment with EDTA, then addition of Co +) is considerably more active than the native Zn version , while Cd (and other ions) afford poorly to non-active metalloproteins in this case. (Relative) catalytic turnover rates are from Vallee and Williams 1968, x and c values this work and previous publications by this author. Here, sufficient abundance of the corresponding ions is taken for granted owing to in-vitro addition to apoprotein, so c k is not hmited by c, but merely represents the catalytic features pertinent to k, obtained from either biochemistry (several metal ions being present, e.g. in phosphatases) or experiments with reconstituted apoproteins...

Different characterization methods are used in order to determine whether the element is incorporated at framework or at Cationic exchangeable site position or as tiny metallic oxide particles entrapped in the pores or cavities. Several examples are presented including substitution of B, Ga, Fe, V, Cr, Cu in zeolitic frameworks or Si, Co, Mn etc in AlPO-4 molecular sieves. Effect of such isomorphous substitution on acidic properties is described and discussed. The case of Ti is described in the same book by G. Bellusi and V. Fattore (Milano) while catalytic features are presented by P.A. Jacobs (Leuven). 

Upon introduction of the rare-earth metal onto the Pd surface, the hydrogenation behavior of propene is markedly changed, and the following catalytic features are observed (Imamura et al. 1996b, 1994) ... 

Another type of modification may also be performed by ionic exchange of alkaline cations which compensate framework negative charges due to the tetracoordination of trivalent cations by other cations as alkaline, earth alkaline or transition metal cations which induce new catalytic features either by their different size or by their specific chemical features. 

Preparation and stabilization of highly dispersed particles exerting catalytic activity can be generally attained by procedures starting with incorporation of metal cation species onto exchange sites in the structure of microporous systems (e.g. zeolites) by conventional as well as solid-state ion exchange [1]. The incorporation of transition metal cations is of special interest since valency changes may easily occur and transition metal species are known to exert unique catalytic features. 

The present work was undertaken to examine this possibility by trying a new method of low-temperature catalyst preparation. The method studied involves the adsorption of metal precursors on supports and the reduction by sodium tetrahydroborate solution for the preparation of supported platinum catalysts. The adsorption and reduction of platinum precursors are carried out at room temperature and the highest temperature during the preparation is 390 K for the removal of solvent. The activities of the catalysts prepared were examined for liquid-phase hydrogenation of cinnamaldehyde under mild conditions. Our attention was directed to not only total activity but also selectivity to cinnamyl alcohol, since it is difficult for platinum to hydrogenate the C=0 bond of this a, -unsaturated aldehyde compared to the C=C bond [2]. We examined the dependence of the catalytic activity and selectivity on preparation variables including metal precursor species, support materials and reduction conditions. In addition, the prepared catalysts were characterized by several techniques to clarify their catalytic features. The activity of the alumina-supported platinum catalyst prepared by the present method was briefly reported in a recent communication [3]. 

According to Pumera (2009), there is also a problem connected with the features of CNTs synthesis. CNTs are typically grown from carbon-containing gas with the use of metallic catalytic nanoparticles. It is well documented that such nanoparticles remain in the CNTs even after extensive purification procedures, leading to two very significant problems (Pumera et al. 2007). It has been shown that such residual metallic impurities are electrochemically active even when intercalated within the CNTs and... 

The study of the catalytic activity of mono- and disilanolates and alcoholates and hydroxides of alkali metals in the polymerization of 1,1-dimethyl-MSCB, and of the effect of the nature of solvent and initiator and other features of this reaction, showed that in the KOH catalysis, organopotassium compounds were responsible for the propagation of polymer chains [53]. For all three types of initiators (alcoholates, disilanolates, and hydroxides of alkali metals), catalytic activity showed a qualitative dependence on the nature of alkali metal. The activity decreased on passage from Cs- to K- and Na-containing initiators. The polarity of solvents in this process exerted the activating effect. Thus, the AROP ofMSCBs in the presence of alkali derivatives can be described by the following scheme ... 

Homogeneous catalysts may fulfill the role of the surface metal catalytic sites in the above systems (for example, copper). Homogeneous catalysis is important in electrochemical reductions systems, as well as photochemical systems. Indeed the two approaches share many features, as discussed later. 

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