Nickel Coordination to Lattice Oxygens in Basic LSX, X and Y Sodium Faujasites: A DFT Study

Abstract

The location and coordination of nickel cations inside the hexagonal prism of dehydrated sodium faujasites have been investigated as a function of the framework Al content and distribution by density functional theory (DFT) calculations. Three different Si/Al ratios have been considered in order to represent the Na−LSX (Si/Al = 1), Na−X (Si/Al = 1.4), and Na−Y (Si/Al = 2.0) faujasites that have the same framework topology but different basic properties. For each system, the most representative Al repartitions among the framework tetrahedral sites have been taken into account and their related preferred Ni2+ configurations have been established. Upon decrease of the Al content, the Ni2+ coordination changes from a perfect octahedral environment with Ni2+ located in the center of the hexagonal prisms (Ni/Na−LSX) to five 4-fold and four 3-fold coordinations in Na−X and Na−Y faujasites, respectively. The preferred locations, inside the hexagonal prism, are those where Ni2+ can bind the highest number (highest...