Synthesis and Characterization of Silicoaluminophosphate CIT-16P and Its Transformation to SAPO-17

Creators: Alshafei, Faisal H.; Kang, Jong Hun; Cho, Sung June; Davis, Mark E.¹

1. California Institute of Technology

Abstract

A silicoaluminophosphate molecular sieve, CIT-16P, is synthesized using butane-1,4-bis(quinuclidinium) [(C₇H₁₃N)-(CH₂)₄-(NC₇H₁₃)]²⁺ dihydroxide (DiQ-C₄-(OH)₂) as an organic structure-directing agent (OSDA). Upon the removal of the OSDA, either by thermal treatment in air at temperatures exceeding 490 °C or by extended ozone treatment at 150 °C, CIT-16P transforms to SAPO-17 (ERI topology). The structure solution of CIT-16P in its as-synthesized form is obtained using a Rietveld refinement of the powder X-ray diffraction pattern. The primary composite building units (CBUs) of CIT-16P are highly distorted cancrinite (can) CBUs that transform into stable can units of the ERI-type framework as a result of the OSDA removal. The distortion of can CBU is maintained without transformation by the presence of tightly bound DiQ-C₄ dications in the as-synthesized form of CIT-16P. The transformed material is characterized and evaluated as a catalyst in the methanol-to-olefins (MTO) reaction. The catalytic behavior of the formed SAPO-17 (Si/T-atom = 0.022) (T = Si + Al + P) at 400 °C and WHSV of 1.3 h^–1 produces elevated C₃₊ olefin products (i.e., propylene, butenes, and pentenes) in early stages of the reaction. However, as the reaction proceeds, the C₃₊ fraction decreases in favor of more ethylene.

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Acknowledgement

This work was supported by the New Faculty Startup Fund from Seoul National University (Grant Number 0668-20200245). The Chevron Energy and Technology Company also provided financial support for this research. The authors gratefully acknowledge Dr. Sonjong Hwang for assistance with solid-state NMR, and Dr. Stacey Zones and Dr. Dan Xie for valuable technical discussions. F.H.A. thanks Aramco R&D for financially supporting his graduate studies. The authors acknowledge the Pohang Accelerator Laboratory (PAL) for beamline use. High-resolution powder diffraction experiments at PAL were supported by the Ministry of Science & ICT, Republic of Korea.

Contributions

The manuscript was written through the contributions of all authors. All authors have given approval to the final manuscript.

Data Availability

Synthesis details; PXRD profiles; NMR spectroscopy data; and crystallographic information of CIT-16P based on the Rietveld refinement (PDF)

Accession Codes:CCDC 2233461 contains the supplementary crystallographic data for this paper.

Conflict of Interest

The authors declare the following competing financial interest(s): A US patent application related to this work has been submitted, and the co-inventors are J.H.K., F.H.A., and M.E.D.

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