Physical Chemistry

The Role of Water Loading and Germanium Content in Germanosilicate Hydrolysis

Lukas Grajciar Department of Physical and Macromolecular Chemistry, Charles University

Abstract

New zeolitic frameworks can be prepared through the Assembly-Disassembly-Organisation-Reassembly (ADOR) process by exploiting the lability of Ge-O bonds in germanosilicate zeolites to control their hydrolysis. In the disassembly step, two key factors are water and germanium content, but their exact roles remain unknown. Nevertheless, we combined experimental water-vapor adsorption with first principles simulations to identify the mechanism of germanosilicate zeolite disassembly. The results showed that water vapor adsorption on UTL germanosilicate proceeds in reversible (at low partial pressures) and irreversible (at higher partial pressures) modes. Based on our ab initio molecular dynamics simulations, we related these two modes to weak physisorption at low water loading and to reactive transformations at high water loading, via collective mechanisms requiring high local water concentrations. This bimodal behavior also depends on the germanium content as high Ge-content further decreases UTL hydrolytic stability by opening up yet another low-energy disassembly pathway at high water loading. Overall, we discovered, verified and explained the mechanisms of UTL disassembly and its factors. These findings will likely be generalized to other ADORable germanosilicate zeolites and help to find the optimal protocol for the synthesis of new zeolites.

Content

Thumbnail image of TheRoleOfWaterLoadingAndGermaniumContentInGermanosilicateHydrolysis_v1.pdf
download asset TheRoleOfWaterLoadingAndGermaniumContentInGermanosilicateHydrolysis_v1.pdf 0.95 MB [opens in a new tab]

Supplementary material

Thumbnail image of TheRoleOfWaterLoadingAndGermaniumContentInGermanosilicateHydrolysis_SI_v1.pdf
download asset TheRoleOfWaterLoadingAndGermaniumContentInGermanosilicateHydrolysis_SI_v1.pdf 9 MB [opens in a new tab]
TheRoleOfWaterLoadingAndGermaniumContentInGermanosilicateHydrolysis SI v1