Three-dimensional imaging and analysis of the internal structure of SAPO-34 zeolite crystals†
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.