Coaxial 3D printing of zeolite core–shell structured catalysts for integrated NOx adsorption and selective catalytic reduction in cold start application

Abstract

NH₃ selective catalytic reduction (NH₃-SCR) is the most effective technology to alleviate NO_x emission from diesel vehicles but faces the cold start problem. Ideally, integrating passive NO_x adsorption (PNA) and NH₃-SCR could achieve a cost-effective and space-friendly tandem of these two units, but designing effective catalysts to achieve both high adsorption capacity and superior catalytic activity remains a challenge. Herein, we have successfully developed an integrated PNA-SCR catalyst system based on the Pd-SSZ-13@Cu-SSZ-13 core–shell structured zeolite composite via coaxial 3D printing, which affords ultra-high NO_x removal efficiency (96%) over the entire PNA and NH₃-SCR process. Over the core–shell structure with spatially confined effects, NO_x can be effectively adsorbed in the Pd-SSZ-13 core at low temperature (<170 °C) with less H₂O competition, which is subsequently released at 200–350 °C to react completely with NH₃ over the Cu-SSZ-13 shell without excessive side reactions. Based on the optimal component of composite catalysts, Pd-SSZ-13@Cu-SSZ-13 displays high adsorption capacity (NO_x/Pd = 0.54), high adsorption rate, optimized desorption temperature (∼250 °C), and excellent NH₃-SCR activity, providing a potential solution to the cold start challenge in NO_x elimination.