Computer Simulation Study of Aluminum Incorporation in the Microporous Titanosilicate ETS-10

Abstract

The preferred framework site for Si substitution by Al in the ETS-10 structure has been modeled by both lattice energy minimization (LEM) and semiempirical quantum chemical (QC) calculations on model clusters. Both approaches suggest that Al substitution in the ETS-10 structure will follow an Al, Ti avoidance rule, consistent with conclusions drawn from analysis of solid-state 29Si and 27Al NMR spectra of Al-substituted ETS-10 reported elsewhere. The Al-substituted ETS-10 structure (ETAS-10) involving a Al−O−Si−O−Ti (T1) linkage was successfully minimized, showing only minor deviations from the optimized ETS-10 structure. In contrast, constant pressure minimizations of ETAS-10 substituted at T2 sites lead to the cleavage of the Ti−O−Al linkage. Indeed, QC calculations indicate that, compared to Al−O−Si−O−Ti linkages, Al−O−Ti direct linkages result in enhanced electronic repulsion between neighboring negative charges on Al and Ti sites and higher lattice strains. This suggests that both electronic and stra...