Metal-support interaction specific catalysts

Vannice (232) measured turnover numbers for methanation on a variety of well-characterized palladium catalysts. The supported catalysts were all more active than unsupported palladium (Pd black) and PdHY was intermediate between Pd/Si02 and Pd/Al203 in specific activity (see Table VII). As is evident from the data there is no obvious correlation betwen particle size and turnover number. It was therefore suggested that the enhanced activity of various supported catalysts was due to a metal-support interaction. Figureas et al. (105) also found good evidence for a support effect during benzene hydrogenation studies. In this case the palladium zeolite... 

One factor that may be important, but not systematically investigated, is the influence of the Pt electrocatalyst-support interactions on the electrocatalytic activity for O2 reduction. In Figure 14, an attempt to incorporate the pHzpc as a qualitative measure of the importance of carbon surface chemistry and metal-support interaction on the electrocatalytic activity of Pt is reported. The trend of the data in Figure 14 suggests that the specific activity for oxygen reduction increases as the pHzpc of the surface becomes more basic this effect may be related to the parallel increase of the particle size with the pHzpc of the catalyst. At this stage, one... 

Palladium-silica catalysts prepared from tetra-ammine palladous nitrate (to avoid chlorine introduction) showed a marked reduction effect , viz, the specific activity for benzene hydrogenation decreased with increased reduction temperature, i.e., 573 or 723Various explanations were considered, including a metal-support interaction. After reduction at 873 K, X-ray diffraction provided clear evidence of chemical reaction and at lower temperatures silicon insertion into palladium might still occur, which could either disrupt the palladium ensembles required for benzene adsorption or modify the properties of single palladium atoms, if these are the active sites. 

But how can we decide whether a reaction catalyzed by a given metal is a demanding one It is unfortunately all too easy to obtain a different specific activity as one goes from one catalyst to the next. How can we decide whether the measured difference is indeed attributable to a different surface structure and not to an impurity or a metal-support interaction or even perhaps a mass-transfer limitation ... 

One of the main aspeets that determine the properties of a given catalyst is the nature of the interaction between the oxide support and the dispersed active metal. The influence of this interaction on the activity, selectivity and stability of the catalyst is determined by factors such as the preparation method, the atmosphere and temperature of the calcination and reduction stages (1,2), and the specific metal-support system studied. The latter is especially important for catalysts based on transition metals supported on partially reducible oxides (3). Such catalysts displaying strong metal-support interaction (SMSI) exhibit suppression of chemisorption of H2 and CO (4-6) when reduced at temperatures up to 773 K. 

Unreducible ions of the transition metal component of supported catalysts, which survive a severe reduction, are clear evidence of a strong interaction between the support and the metallic element. Currently there is a discussion in the literature on this subject, specifically 1) Do some Pt-ions survive a severe reduction 2) Are they accessible 3) Do they play a role in the metal-support interaction and reactions of hydrocarbons ... 

The purpose of the present paper was 10 study the feasibility of using the hydrogenolysis of cyclopentane and the hydrogenation of benzene, typical examples of structure-sensitive and nonstructure-sensitive reactions, to measure the residual activity of specific centers remaining after coke is deposited on supported Ni and Ni-K catalysts. Potassium was chosen as the promoter, for it is often used in the formulation of nickel-based catalyst for steam reforming of naphthas (refs. 2-3). Comparisons between the promoted and unpromoted catalysts were performed at two different extents of metal-support interaction, which were caused by calcination to 400 or 700°C Some attention was paid to changes in selectivity induced by alkali promotion and/or carbon deposition. 

The aim of this work is to test different Pt and Pd catalysts supported on basic MgO in the hydrodechlorination of CCI4. Particular attention was devoted to the choice of the organometallic precursor, in order to maintain the basic properties of activated MgO and consequently to increase metal support interactions. A specific metal-support interaction on Pd(acac)2/MgO °° catalysts was observed by previous studies [13]. 

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