Carbon dioxide uptake in nitrite-sodalite: reaction kinetics and template ordering of the carbonate-nosean formation

Abstract

Abstract We report on the phase transformation and the reaction kinetics of aluminosilicate nitrite-sodalite |Na8(NO2)2|[AlSiO4]6 crystallizing in space group P 4 ¯ 3 n $P\bar 43n$ into carbonate-nosean |Na8(CO3)□|[AlSiO4]6 described in space group P23. Investigations were carried out in carbon dioxide atmosphere by in situ high-temperature X-ray diffraction measurements. The collected diffraction patterns were examined using the autocorrelation method and Rietveld and structure independent refinements. For this reaction an activation energy of E A =7.788(6) kJ/mol was observed. Whereas the framework remains almost unchanged during the phase transformation first a high number of newly formed template-domains are observed indicating only a short range order of CO3 2– occupied and empty cages. This can be deduced from the obtained average crystallite size ratios taken from structure independent Pawley fits of the reflections allowed in P 4 ¯ 3 n $P\bar 43n$ and constrained single-peak refinements of the remaining ones additionally allowed in P23. This initially high number of template domains is reduced with increasing reaction time developing faster at higher temperatures. An average formation of 2.2(1) ordered domains within one crystallite could be evaluated for the longest reaction time.