Metal catalyst-support interactions

Considering the importance of these metal-metal and metal-catalyst support interactions, a Cyclic Deactivation procedure will be preferred in order to simulate the actual metal distribution and interactions on the catalyst surface and to mimic the correct metal age distribution (2, 23, 27, 34]. 

Consequently the absolute potential is a material property which can be used to characterize solid electrolyte materials, several of which, as discussed in Chapter 11, are used increasingly in recent years as high surface area catalyst supports. This in turn implies that the Fermi level of dispersed metal catalysts supported on such carriers will be pinned to the Fermi level (or absolute potential) of the carrier (support). As discussed in Chapter 11 this is intimately related to the effect of metal-support interactions, which is of central importance in heterogeneous catalysis. 

Pristine CNTs are chemically inert and metal nanoparticles cannot be attached [111]. Hence, research is focused on the functionalization of CNTs in order to incorporate oxygen groups on their surface that will increase their hydrophilicity and improve the catalyst support interaction (see Chapter 3) [111]. These experimental methods include impregnation [113,114], ultrasound [115], acid treatment (such as H2S04) [116— 119], polyol processing [120,121], ion-exchange [122,123] and electrochemical deposition [120,124,125]. Acid-functionalized CNTs provide better dispersion and distribution of the catalysts nanoparticles [117-120],... 

Another level of surface chemical complexity results from catalytic metal-catalyst support surface interactions. Table 3, taken from Bell [7], shows the surface-specific activity of Rh for CO hydrogenation as a function of... 

When considering metal-support interaction effects, the whole set of Electron Microscopy data presented in the previous section point out some important differences between the behaviour of noble metal catalysts supported on ceria and that of titania-supported catalysts. Much higher reduction temperatures are required in the case of ceria-type supports to observe nanostructural features similar to those described for the so called SMS I efTect. 

The 3d transition metals are widely employed as catalyst and catalyst support materials in industry [3]. To gain insight into how these support materials and the catalyst support interaction influence catalytic activity, GIB-MS experiments were undertaken in our laboratory to determine the structural characteristics of cobalt oxide and nickel oxide clusters as well as their reactivity with CO. CID experiments were conducted employing Xe gas to elucidate the structural building blocks of the larger clusters. These studies provided insight into how additional (i-electrons impact the dissociation pathways and bonding motifs of 3d transition metal oxide clusters. Reactivity studies with CO were carried out, which revealed that oxide clusters composed of different 3d metals have specific stoichiometries which are most active for CO oxidation. 

Promotion of catalyst nanoparticles, electrochemical promotion (NEMCA) of porous and of single-crystal catalyst films, and metal nanoparticle-support interactions are three, at a first glance, independent phenomena that can all dramatically affect catalytic activity and selectivity on metal and metal oxide catalyst surfaces. 

Influence of Metal Oxide-Support Interactions in Supported La-Promoted CaO Catalysts for Oxidative Coupling of Methane... 

Bi- and multicomponent metallic catalysts supported on metal oxides are complex objects for preparation and characterization. It is difficult to achieve a uniform particle composition within the catalyst [1] and exclude strong metal/support interactions [2]. Moreover, the question whether the supported particles of the two or more metals are coexisting as elements (next to each other, separated or as core/shell particles), or forming alloys (randomly distributed elements on the crystallographic sites) or intermetallic compounds... 

A great variety of oxides can be used as supports. These materials are chemically stable, but in some cases, interactions between the metallic particles and the support can occur. Thus, in the particular case of metal catalysts supported on some reducible oxides, the occurrence of so-called metal-support interaction effects has been reported. " " In order to minimize the metal-support interaction, stable oxides (not reducible), such as alumina or silica, are used. Moreover, the size-dependent electronic, structural, and chemical properties of metal nanoparticles on oxide supports are an important aspect of heterogeneous catalysis. " " ... 

Before selecting catalyst materials for use in our study, particular attention was paid to characterization results. Regarding the use of C0/AI2O3 catalysts, from the standpoint of activity, it is often reported that the metal oxide-support interaction is a major problem. Certainly, it is true that after a standard reduction at 350°C, only a fraction of the cobalt is reduced [7,20,21]. However, the number of active sites depends not only on the degree of... 

Thus, the analysis of FITR sp>ectra of alumina provides data on the nature and amount of various surface sites moreover, it allows identification of the sites where active component precursor is anchored during catalyst synthesis, and makes it possible to hypothesize about mechanism and strength of the metal complex-support interaction. 

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