Enhancing nucleation to synthesize Al-rich CHA zeolites under ultra-low OSDA contents: Application for heavy-duty NH3-SCR of NOx

Abstract

The crystallization of Al-rich CHA zeolites with an ultra-low organic structure directing agent (OSDA) content and without using pre-crystallized FAU zeolites as Si and/or Al sources has been accomplished by controlling the nucleation step. Indeed, the use of “gel-type” seeds containing discrete nanosized CHA nanoparticles (i.e. below 100 nm) combined with the understanding of the seed-assisted crystallization mechanism has allowed the efficient preparation of Al-rich CHA materials using ultra-low methyltriethylammonium (MTEA) contents (MTEA/Si molar ratios ∼ 0.03–0.04), making this synthetic route very cost-competitive compared to recent synthesis improvements for CHA using substoichiometric contents of expensive OSDAs (i.e. N,N,N-trimethyladamantammonium, TMAda). The optimized Al-rich CHA materials, after incorporating the catalytically active copper cations, perform as ideal catalysts for the selective catalytic reduction (SCR) of NOx with ammonia relevant for heavy-duty applications.