Dual-vacancy site

On sulphided M0/AI2O3 stoicheiometric calculations and kinetic data showed that the catalytic activity for thiophen hds depended on the concentration of dual surface sites, anion vacancies for thiophen adsorption, and surface sulphide and/or oxide ions for hydrogen adsorption. The overall reaction was controlled by a surface reaction between adsorbed species on these sites. 

From the results of this work, it is not possible to choose between these two explanations, PdMn dual sites or bifimctionnal mechanism. Other experiments, namely water gas shift or steam reforming reactions, occurring via a mechanism implying oxygen vacancies, could give informations for a better understanding of the Mn role in the reaction process. 

For each of these combinations, determine the overall nonbonding densities and identify the face-dual or excluded sites as possible vacancies for ligands. 

The square planar geometry also serves as another example other than the I65 square planar complex that 18-electron rule is relaxed. When we put 8 d electrons into a four-coordinate complex, we will soon notice that we can only place the four lone pairs into d a and three four-lobe d orbitals (say dxy, dy, and d z), because if we fill all lone pairs into four-lobe d orbitals, the dual d 2 will only have two vacancies which is inadequate for four coordinations. With dz2, d y, dy, and dxz being filled, exactly four vacancies will remain (which resembles the density peaks of dx2-y2)> when we place four ligands on these four sites, we will naturally get a square planar geometry. 

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