Reactions Exhibiting Strong Structure Sensitivity

Reactions Exhibiting Strong Structure Sensitivity. Reactions for which there is at least an order of magnitude difference in activity as a function either of particle size or of exposed crystal planes include the ammonia synthesis reaction and the hydrogenolysis of hydrocarbons. 

The formation of PO over Au-based catalysts is a structure-sensitive reaction. Only hemispherical Au particles with a suitable size (2-5 nm) will selectively produce PO [167,168,403] and 2.2 to 2.4 nm particle size seemed to be optimum in the early experiments [31]. The most effective type of Au nanoparticles is prepared by the DP technique, which brings them in strong contact with the support. Gold particles smaller than 2 nm show a shift in selectivity from PO to propane [7,169-171,403]. This switch of epoxidation to hydrogenation for particles under 2 nm size indicates that small Au clusters exhibit different behaviour in surface properties from that of metallic Au [171] (see Fig. 6.17). 

Within the topic catalysis, the properties associated with different morphologies, activities, and selectivities which are strongly affected by the shape and particle size, and in the case of crystalline metallic phases, and the orientation of crystal faces exhibiting differentiation, should be highlighted. The reactions that are influenced by the factors mentioned above (morphological) are known as sensitive reactions to the catalyst structure. 

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