SAPO-37 microporous catalysts: revealing the structural transformations during template removal

Abstract

We have studied the structural behavior of SAPO-37 during calcination using simultaneous in situ powder X-ray diffraction (PXRD) and mass spectroscopy (MS) in addition to ex situ thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). A spike in the unit cell volume corresponding to template removal (tracked using the occupancy of the crystallographic sites in the SAPO-37 cages) is revealed from the XRD data and is strongly correlated with the DSC curve. The occupancy of the different template molecules in the faujasite (FAU) and sodalite (SOD) cages is strongly related to the two mass loss steps observed in the TGA data. The templates act as a physical stabilizing agent, not allowing any substantial unit cell response to temperature changes until they are removed. The FAU cages and SOD cages have different thermal response to the combustion of each template. The FAU cages are mainly responsible for the unit cell volume expansion observed after the template combustion. This expansion seems to be related with residual coke from template combustion. We could differentiate between the thermal response of oxygen and T-atoms. The TO -T angle between two double 6-rings and a neighboring TO -T linkage shared by SOD and FAU had different response to the thermal events. We were able to monitor the changes in the positions of oxygen and T-atoms during the removal of TPA + and TMA +. Large changes to the framework structure at the point of template removal may have a significant effect on the long-term stability of the material in its activated form.

In Situ Flow MAS NMR Spectroscopy and Synchrotron PDF Analyses of the Local Response of the Brønsted Acidic Site in SAPO‐34 during Hydration at Elevated Temperatures

“…suggested that if Al−O−P bonds were broken, a 31 P peak would appear at δ =−15 ppm from hydrolyzed P atoms . Thus, it appears that no Al−O−P bonds are broken at RT, in contrast to other template‐free SAPO frameworks such as SAPO‐37 . Upon increasing the temperature to 100 °C, all changes occur within 1 h. The two 27 Al NMR and 31 P NMR spectra at 100 °C were acquired after stabilization of the sample.…”

“…[12b] Thus, it appears that no AlÀOÀPb onds are broken at RT,i nc ontrast to other template-free SAPO frameworks such as SAPO-37. [16] Upon increasing the temperature to 100 8C, all changes occur within 1h.T he two 27 Al NMR and 31 PNMR spectra at 100 8Cw ere acquired after stabilization of the sample. The Al and PTatomsh ave now lost the strongly coordinating water molecules:t he Al peak at d = À15 ppm disappears and the skew peak at d = 44 ppm moves to d = 36 ppm.…”

“…The atomicf orm factors of the atoms of the respectivei nteratomic distances (Z number)a re contained in the peak intensity.B ya pplyingp roper calculation of difference-PDFs, the contributiono fp retty weak scatterers can be interpreteda sw ell. In contrast to traditional diffraction studies, in which the Bragg diffraction peaks correspond to crystalline long-range order, [16] and NMR spectroscopy,w hich probest he local electronic environmento fs electedn uclei, [12a] PDF analysis provides an overall characterization ranging from local bond lengths (1-2 )t om edium-and long-range order ( Figure 2). Reports using the PDF methodt os tudy zeolitesa re rather scarce.…”

Deactivation of Zeolite Catalyst H-ZSM-5 during Conversion of Methanol to Gasoline: Operando Time- and Space-Resolved X-ray Diffraction

“…Difference Fourier maps were used to assign the positions of dummy carbon atoms to each coke position in the framework channels, see S.I. Their individual occupancies were refined (with symmetry constraints) during subsequent cycles 14,[20][21] . This is related to the changes in intensity upon deactivation mentioned above.…”

Synthesis, Structure and Properties of an Extra‐Large‐Pore Aluminosilicate Zeolite NUD‐6

“…However, sometimesc alcination destroys the pore structure, thus limiting the application of the materials.F or instance, the structure of FAU-types ilicoaluminophosphate zeolite SAPO-37 collapsed after the SDA tetramethylammonium hydroxide (TMAOH) was removed. [19] Solvent extractioni sa na lternative method to remove neutral and ion-paired templates in porous materials. [21] It is often used in producing mesoporous materials such as MCM-41 [22] and SBA-15.…”