Abstract
SAPO-34 is widely used as a catalyst for important industrial reactions, such as the methanol-to-olefin (MTO) reaction and selective catalytic reduction (SCR) of nitrogen oxides (NOx). The internal structure of SAPO-34 has a great influence on the catalytic performance. Two-dimensional (2D) images of the SAPO-34 particle surfaces from scanning electron microscopy (SEM) show clearly well-faceted cube morphologies, which suggest they should be quite uniform perfect crystals. However, Bragg coherent X-ray diffraction imaging (BCDI) of the SAPO-34 particles shows a rich internal structure existing within these crystals. In this work, we investigated the internal structure of a SAPO-34 zeolite by serial block-face scanning electron microscopy (SBFSEM). The internal structure observed in the backscattered electron (BSE) micrographs from SBFSEM and the energy dispersive spectroscopy (EDS) measurements is found to be consistent with the BCDI results. From the three-dimensional (3D) structural images of SAPO-34 crystals obtained by SBFSEM, the domains within the individual SAPO-34 were visualized and quantified.
Highlights
Zeolites are of great scienti c and technological importance because the petroleum-re ning and petrochemical industries rely on their catalytic activity and shape selectivity.[1,2] SAPO-34, a crystalline silico-aluminophosphate, is a member of the ALPOn zeolite family.[3]
A single particle of SAPO-34 zeolite was investigated by Bragg coherent X-ray diffraction imaging (BCDI)
A complicated single-centred diffraction pattern from BCDI indicates SAPO-34 has internal domain structures, which are hidden from the simple cube shapes observed by 2D scanning electron microscopy (SEM) observation
Summary
Zeolites are of great scienti c and technological importance because the petroleum-re ning and petrochemical industries rely on their catalytic activity and shape selectivity.[1,2] SAPO-34, a crystalline silico-aluminophosphate, is a member of the ALPOn zeolite family.[3]. SBFSEM was rst introduced by Kuzirian and Leighton[22,23] and largely-improved by Denk and Horstmann.[24] Gatan company commercialized it under the name “3View” It is exploited mostly for biological materials,[25,26] light alloys,[27] and organic coatings.[28] Due to the SBFSEM method being much less used in inorganic crystalline materials, there are lots of challenges for using it on measuring SAPO-34 zeolite, such as possible imaging artefacts generated by epoxy and electron charging.[29] In the work reported in this paper, AGAR 100 RESIN was modi ed with conductive carbon particles to reduce the charging effects while collecting BSE signals. An improved sample preparation method is provided which will help using SBFSEM to measure other non-conductive inorganic hard condensed matters and materials in the future
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