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.