Coaxial 3D printing of zeolite core–shell structured catalysts for integrated NO x adsorption and selective catalytic reduction in cold start application

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.