Active Ingredient and the Support Surface

Interaction Between an Active Ingredient and the Support Surface. - For 

We postulate that binding to the surface can be either direct, via metal-metal bond, or indirect through a bridging ligand oxide ion or possibly a bridging chloride or hydrogen atom. In general several of these surface compounds will coexist and, in favourable circumstances, these can now be identified and quantified by TPR.  

In certain cases the surface of the support may be pre-modified to either increase or decrease its absorptive capacity. Techniques for the former have been thoroughly explored in the area of anchoring homogeneous catalyst complexes and metal clusters. Since this subject has been amply reviewed we will not discuss it further. These techniques primarily involve pre-treatment of the support surface with a compound that can serve as a bridging ligand. Techniques for decreasing the absorptive capacity are also of importance and these will be covered later in greater detail when we come to consider metal location on a catalyst support. 

A completely different type of interaction from the above, in all of which the metal ends up attached to the support surface, is that in which the support acts as a reactant to precipitate the active material in a highly dispersed form within its pore structure but not attached to the support. Examples of this latter type of interaction would be the precipitation of a metal hydroxide from an acidic impregnating solution by a strongly basic support, e.g, a sodium X zeolite, and the precipitation by reduction to the 

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