(159d) Quantum Mechanical Investigation of Ammonia Adsorption On Mixed Hydroxylated Copper Sulfate-Silica System

In the present study, we perform a quantum mechanical investigation to compare the adsorption of ammonia on (a) silica, (b) copper sulfate pentahydrate and (c) a mixture of both of these adsorbents. We use the hydroxyl group attached to a hydridosilsesquioxane cluster to represent an isolated silanol at the surface of silica. We employ B3LYP/6-311G* level of theory to derive the associated adsorption energies from optimized structures. We start with the simplest system consisting of the dehydrated adsorbents and then systematically add water to the systems to understand its role in adsorption. This also aids in testing our hypothesis that the adsorption may occur by the displacement of water with ammonia, or with the participation of water in the adsorbed complex. Our preliminary results indicate that, in a super-dry environment, a combination of silica and copper sulfate exhibits significantly stronger binding with ammonia when compared to the individual adsorbents, implying that copper sulfate (even if physically bound) is a promising additive for enhanced efficiency of silica adsorbents.