Bg Baekelandt

Comparing homogeneous and heterogeneous acid catalysts by a density-functional based sensitivity analysis of their interaction with carbenium ions

Abstract An attempt has been made to develop a quantitative comparison of the properties of homogeneous and heterogeneous catalyst systems. The bond formation, and its projected covalent character, of a carbenium ion with the surface of zeolites and with water molecules in solution served as a basis to collect quantitative data. These data are the global electronegativity and hardness and the local softness (reactivity parameter of atoms-in-molecules) as these can be calculated for solids and molecules in the EEM formalism. A consistent model could be developed for a quantitative and qualitative comparison. It shows that generally, hydrated carbenium ions remain more ionic than those interacting with the surface of silicates or zeolites.

The electronegativity equalization method (EEM) as a promising tool for the analysis of zeolite catalyzed reactions

The H-exchange of methane in FAU and MFI is analyzed with the Electronegativity Equalization Method (EEM). The polarization channels and their hardnesses are presented as promising criteria for estimating the reactivity of acid zeolite catalyzed reactions. The reaction mode hardness is shown to depend on structural parameters (topology) as well as chemical composition (Si/Al ratio and the Al distribution), the latter being dominant. The results theoretically confirm the Next Nearest Neighbors (NNN) principles, which stresses the importance of the number of Al atoms in the second coordination sphere as a key reactivity parameter.