Thermochemistry of (GexSi1-x)O2 zeolites

Qinghua Li, Alexandra Navrotsky, Fernando Rey, Avelino Corma

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

A series of Ge-zeolites, (GexSi1-x) O2, (ITQ-7, polymorph C and zeolite Beta) with varying Ge content is investigated by high-temperature oxide melt solution calorimetry. The enthalpies of formation relative to a mixture of germania and silica in the quartz structure (ΔHf) are in the range 14.8-21.1 kJ/mol, which implies greater metastability than for pure silica zeolites (6.8-14.4 kJ/mol relative to quartz) and aluminophosphates (5.5-8.5 kJ/mol relative to berlinite on a two-oxygen basis). All the zeolite frameworks examined become energetically less stable with increasing Ge content, but the decrease in stability is considerably different for each framework. The linear regressions of ΔHf vs. Ge content (Ge/(Ge + Si)) for the three structures of Ge-zeolites intersect, though the data are somewhat sparse, implying a possible crossover in framework stability with increasing germanium content. This crossover favors structures with double four member rings (D4MR) at higher Ge/(Ge + Si).

Original languageEnglish (US)
Pages (from-to)127-133
Number of pages7
JournalMicroporous and Mesoporous Materials
Volume64
Issue number1-3
DOIs
StatePublished - Oct 3 2003
Externally publishedYes

Keywords

  • Calorimetry
  • Ge/(Ge + Si)
  • ITQ-7
  • Polymorph C
  • Zeolite Beta

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials

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