In situ single-crystal structural approach to study CO2 adsorption in Y zeolite

https://doi.org/10.1107/S2053273318017618

“The in situ single-crystal structural approach to study CO₂ adsorption in Y zeolite is unprecedented; in the literature there are only reports of a study by XRPD (Arletti et al., 2016) and a few single-crystal studies of CO₂ adsorption on other types of zeolite performed under ex situ conditions (Fujiyama et al., 2013; Nguyen et al., 2014). Structural studies of the adsorption in Y zeolite of organic molecules can also be found in the literature (Martucci et al., 2015; Gigli et al., 2018). In this study traditional structural refinement (both manual and automatic) and PCA-based approaches are thus explored and the results compared to assess potentialities and limitations of PCA applied to single-crystal data. The manual structure refinement is able to locate extra-framework atoms in an accurate way after structure solution but requires a model structure and is very time consuming. The refinement of a data set of 50 structures takes many working hours and a protocol has to be defined in order to treat all the structures consistently. The automatic (batch) refinement is faster, but still needs the structure to be solved and careful checking of results and refined variables. In contrast, PCA can be executed on the full data set; it does not need structural information; and can provide information about the trends in the data in a few minutes. The trends extracted by PCA can be coupled with structural information obtained from one or more data sets to gain a better insight into their meaning (i.e. to link the changes to the relevant part of the structure).”

“A suitable crystal of Y zeolite for single-crystal measurements was obtained by the hydrothermal method described in the literature (Warzywoda et al., 1999; Ferchiche et al., 2001) and detailed in the supporting information. The experiments were performed at the ESRF Synchrotron in Grenoble, on the Swiss–Norwegian Beam Line (SNBL; BM01A) equipped with a 2D Pilatus 2M detector. The single crystal was mounted on a 0.2 mm capillary and sealed inside a 0.3 mm capillary. The external capillary was connected to a gas line and a vacuum pump and left at 300 K under vacuum for the outgassing. One first data set, to test the sample and to be used as a reference, was collected under vacuum at 300 K. CO₂ was injected into the capillary to a pressure of 10 kPa and the temperature was lowered to 200 K, while measuring a complete single-crystal data set (360° φ scan with an exposure time of 2 s per frame) every 2 K. Between two data sets the dead time was 2 min to allow the cryostream to reach and stabilize at the temperature and the sample to reach its equilibrium.”