Thermochemistry of (GexSi1-x)O2 zeolites

Qinghua Li, Alexandra Navrotsky, Fernando Rey, Avelino Corma

Research output: Contribution to journalArticlepeer-review

22 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 (Δ Hf) 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 Δ Hf 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)177-183
Number of pages7
JournalMicroporous and Mesoporous Materials
Volume59
Issue number2-3
DOIs
StatePublished - May 19 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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