It has been possible to efficiently synthesize high-silica ERI and AFX zeolites with nano-sized primary crystallites (30-200 nm). This was achieved by using a dicationic and rigid organic structure directing agent (OSDA) that fits within the large cavities of these zeolites, and the use of FAU zeolites as initial Si and Al-sources. Cu- and Fe-based ERI and AFX materials were prepared following both post-synthetic cation exchange and direct synthesis methodologies, showing good activity for the selective catalytic reduction (SCR) of nitrogen oxide using ammonia. Accelerated hydrothermal ageing of the zeolites at high temperature (i.e. 750 degrees C) shows the necessity of removing the alkali cations remaining in the zeolites to obtain stable materials. Furthermore, the catalytic performance of the prepared Cu- and Fe-containing AFX catalyst, both before and after ageing treatment, approaches the catalytic activity of Cu- and Fe-CHA. (C) 2017 Elsevier B.V. All rights reserved.