Theoretical study of vanadium oxides interaction with Y-zeolite

A current problem about oils and feedstock in fluid catalytic cracking (FCC) is the continuous cumulative deposition of metal contaminants on the catalyst, resulting in important modifications of its properties. Vanadium plays a detrimental role on the catalyst components because enhances the destruction of the Y-zeolite structure during regeneration stage when it is exposed by steam and oxygen at high temperatures. Knowledge of the mechanism interaction of vanadium with the catalyst is important to improve FCC performance. Quantum Molecular Dynamics calculations were done introducing the VO, V2O3, VO2 or V2O5 molecules at the center of a Y-zeolite ring simulating regeneration conditions. The results indicate that the principal reaction is carried out among the zeolite and the vanadium atoms of molecules. This happens, when interaction is presented, since the loss of a hydrogen atom of the active place causes high degree of oxygen reactivity.

A density functional study of the reactivity and stability of mixed copper complexes. Is hardness the reason?

Mixed-ligand Cu2+ ternary complexes, formed by an aromatic diimine and a second ligand with O donor atoms, show a higher than expected stability. To understand the factors affecting the stability of these systems, we performed a density functional study of [Cu(H2O)5]2+, [Cu(N-N)(H2O)3]2+, and [Cu(N-N)(O-O)H2O] (N-N is 1,10-phenanthroline, 5-nitro-1,10-phenanthroline, or 3,4,7,8-tetramethyl-1,10-phenanthroline; and O-O is oxalate). In the present study, full geometry optimization (B3LYP/3-21G**) has been performed without symmetry constraints and a comparison with some available experimental results has been made. Bond distances, equilibrium geometries, harmonic frequencies, and net atomic charges from Mulliken populations are presented. Since the principle of hard and soft acids and bases has been widely used to explain the stability of these complexes, we also calculated and analyzed the global hardness and the local softness. The results of the global hardness do not support the commonly held idea that harder acids will preferably bind to harder ligands, while softer acids will bind to softer ligands. Interestingly, local softness and electron affinity correlate well with the formation constants of these compounds and provide an explanation of the reactivity behavior. The present results may help to rationalize the stability and reactivity of these systems.