GAM-5: A microporous cobalt-containing aluminophosphate with ATV topology formed by the interzeolite conversion of CoAPO-5 via AWO-type zeolite

Abstract

The interzeolite conversion of metallo-aluminophosphate zeolite, designated as izcMAP, was demonstrated using CoAPO-5 as the parent and a pyrrolidine as an organic structure-directing agent (OSDA). The izcMAP of CoAPO4-5 with AFI topology successfully yielded a crystal of CoAPO4-21 with AWO topology, designated as GAM-5P, and the followed calcination under airflow conditions caused a further structural change into CoAPO4-25 with ATV topology, named GAM-5. UV–vis measurement revealed that the incorporated Co atom in the framework retained tetrahedral coordination during the synthesis; however, the oxidation reaction of the Co atom (CoII-to-CoIII) occurred during the calcination process. NH3-TPD analysis of the GAM-5 clearly shows a reasonable solid acidity, resulting in two types of distinct acid sites. Consistent structural elucidations of GAM-5P and GAM-5 zeolites based on the high-resolution powder XRD, solid-state NMR measurements, and Rietveld structural refinements were non-doubtfully taken place. By adopting two-phase Rietveld structural refinement analysis for the GAM-5 zeolite, it found that GAM-5 has two-types of quite similar crystal phases with different space groups (and unit-cell volumes), Aem2 (a = 9.3661(12) Å, b = 15.1105(2) Å, c = 8.3470(4) Å) and Iba2 (a = 15.1233(3) Å, b = 18.7517(3) Å, c = 8.4216(2) Å). This is the first report on presenting the crystallographic models in which (Al + Co) and P atoms are alternatively distributed in ATV topology.