Temperature-Induced Transformations in CoAPO-34 Molecular Sieve:  A Combined In Situ X-ray Diffraction and FTIR Study

Abstract

Thermally induced processes of CoAPO-34, an aluminophosphate molecular sieve with chabasite-type structure, synthesized in the presence of morpholine as a structure-directing agent and HF as a mineralizing agent, have been studied by in situ X-ray synchrotron powder diffraction augmented with Fourier transform (FT) IR analysis. A time-resolved experiment was performed using a translating imaging plate system. At room temperature, the structure refinement by full-profile Rietveld analysis showed P-1 symmetry and the presence of one Al site with sixfold coordination. At around 400 degrees C, both fluorine and morpholine are lost, and the four-connected chabazite (CHA)-type topology is restored. Notwithstanding the metrically rhombohedral values of the cell parameters, the symmetry remains triclinic P-1. Inhomogeneous dealumination of the framework begins at 725 degrees C, accompanied by a strong triclinization of the unit cell and followed by the collapse of the structure above 775 degrees C. The insertion of cobalt ions within the CHA framework was monitored by FTIR spectroscopy, which showed that bridged Co(2+)-O(H)-P hydroxyls are present after morpholine removal.

Temperature-Induced Structural Changes in Acidic L-Zeolite: An In Situ Synchrotron Time-Resolved Powder Diffraction Study

“…Considering that neutron diffraction data from acidic L-zeolites indicate the presence of a Brønsted acid site on O5, which points toward the center of the 8MR channel, 21 this phenomenon can reasonably be attributed to the formation of a Lewis acid site on this framework oxygen atom upon heating. Similar structural evidence (i.e., formation of Lewis sites) from X-ray diffraction studies has also been reported for a zeolite H-Y, 34 CoAPO, 35 and borosilicates. 36 At the same time, the antirotation of the T2 polyhedron determines the progressive shrinkage of the T1−O4−T2 angle, and it is associated with the corotation of the T1 site.…”

In Situ XAS and XRPD Parametric Rietveld Refinement To Understand Dealumination of Y Zeolite Catalyst

“…Because both methods can be performed in situ, a complete picture of the evolution of the Al species as well as of their framework and extraframework characteristics can be determined. The value of combining diffraction and complementary in situ techniques has been widely demonstrated. − …”

“…This enhanced the reliability of the results . Standard Rietveld refinement , of time-resolved XRPD patterns is performed by considering each individual pattern as an independent acquisition. ,,,,,− ,,− This means that all of the refined parameters, such as scale factor, background factors, and position and occupancy of the atom, in two subsequent patterns are refined independently. This approach is ideal when dealing with single crystal data, which have very high data/parameter ratio, but can be problematic when referring to time-resolved XRPD data, where the S/N quality of a pattern is significantly lower with respect to static acquisition.…”

“…The value of combining diffraction and complementary in situ techniques has been widely demonstrated. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] The time-resolved synchrotron XRPD yields many consecutive patterns, which we analyzed simultaneously by means of parametric analysis. This enhanced the reliability of the results.…”