Controllable preparation of various crystal size and nature of intra-crystalline diffusion in Cu/SSZ-13 NH3-SCR catalysts

Abstract

In this work, we report a facile technique to prepare crystalline Cu/SSZ-13 particles with uniform and controllable sizes. Samples with varying particles sizes (0.4–2 µm) with 1–2 wt% Cu were synthesized by carefully controlling the amount of zeolite seeds and by adjusting the pH values, with larger seed amounts and higher pH values resulting in smaller particle sizes. Various techniques (SEM, XRD, BET, H2-TPR etc.) were used to characterize these samples and the results confirm that despite the varying particle sizes, these Cu/SSZ-13 catalysts have similar Si/Al ratio, acidity and Cu distributions. Hence, these catalysts provided the perfect sample sets to probe the role of intra-crystalline diffusion in NH3 SCR reactions. The kinetic experiment results indicate that turnover frequencies (TOFs) of the catalysts with different particle sizes and copper loadings are identical, therefore NH3-SCR reaction rate over Cu/SSZ-13 catalysts is not limited by intra-crystalline diffusion.