Open edge sites

It is believe that the HDS sites (rim sites and edge sites) are different than the olefin hydrogenation sites (rim sites) opening an opportunity for the development of selective HDS catalysts [45 171. Another concept to exploit in catalyst development is the competitive adsorption, by which the sulfur compounds inhibit olefins hydrogenation [48]. 

In this case, a given lattice site can be occupied at random by particle A with the probability q or by particle B with the probability 1 - q. Each edge is declared to be open if its end vertices are occupied by particles of different types (the idea is that dissimilar particles bind together, whereas similar ones repel each other). Of principal interest is the probability of the lattice origin to be an infinite cluster of open edges. 

The reduced form of titanium is octahedral and contains open coordination sites ( ) and chloride ligands on crystallite edges. Initiation begins by formation of an active center, believed to be a titanium alkyl. Alkylation by TEAL cocatalyst produces an active center ... 

The alkyl migrates (rearranges) such that an open coordination site moves to a crystallite edge position. Coordination of an ethylene monomer occurs to create a Ji-complex as in eq 3.5. Subsequent addition across ethylene results in the propagating species ... 

Joining all pieces together, the proposal involved in this explanation is that the compounds 5, 6, and 7 contain a masked anion, the hypothetical cluster [Rh3(/z-N- -tolyl)2(CO)6] , showing two coordination sites with tuneable donicity the rj -cyclohexadienyl coordination site and that provided by the two rhodium atoms of the open edged trimetallic core. The connection between these two sites should occur through the bond of one para-toXylimido ligand. Its partial double... 

The planar structure of surface terraces puts a geometric constraint on the orientation of the molecular or atomic species that are part of the adsorption overlayer. For instance, two coadsorbed CO molecules on a metal surface will not be able to interact with the same surface metal atom. This remains the case even on more open and step-edge sites. The direct repulsive interaction between the adsorbates inhibits their close approach as the direction of the surface adsorbate chemical bond is constrained. Therefore, one will rarely observe the high coordination of several adsorbates to the same surface metal atom as observed in coordination complexes of small metallic clusters. 

It has also been shown on Co that increased adsorption of C atoms on the (111) surface of a small particle with fee bulk structure leads to transformations of the Co(lOO) surface. This surface becomes stabilized because the C atom prefers the fivefold coordination possible on this surface. The reconstmetion will generate step-edge sites on the surface because of the decreased Co metal density on the more open [87], which are potential sites for low-activation CO bond cleavage as... 

Figure 11.1 illustrates situations of atomic CN imperfection. The CN is two for an atom in the interior of a monatomic chain or an atom at the open edge of a SWCNT or a graphene sheet while in the CNT wall and graphene interior, the CN is three. At the atomic chain ends, it is one. For an atom in the fee unit cell, the CN varies from site to site. The CN of an atom at the edge or comer differs from the CN of an atom in the plane or inside the unit cell. The CN imperfection is not limited to the CN loss but covers situations of bond angle distortion. The effective... 

In contrast to the unsymmetric structure for Zr(2,4-C7H 11)2(00)2, the dmpe complex adopts a more symmetric structure in which the phosphine donor sites each coordinate by an open edge of one of the C5H7 ligands (Fig. 6). 

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