Excellent stability for catalytic oxidation of methane over core–shell Pd@silicalite-1 with complete zeolite shell in wet conditions

Supported palladium is the most promising catalyst for catalytic combustion/oxidation of unburned methane generated in vehicles and thermal power generation. The development of a stable catalyst in the presence of high concentrations of water vapor is a challenging task. Herein, core–shell Pd@silicalite-1 catalysts were synthesized with a two-step seed-directed hydrothermal growth method. Firstly, we demonstrate that Fourier transform infrared spectroscopy of CO adsorption (CO-FTIR) is a facile, sensitive, and definite method to probe the completeness of the zeolite shell for metal@zeolite materials. CO-FTIR method is based on the CO access to metal surface because the structure directing agent (SDA) retained in the pores of zeolite shell in the fresh metal@zeolite materials will block the transport of CO. More importantly, for catalysts with complete shell, Pd@S-x (x = 1.5, 2.0) catalyst show no deactivation for 200 h in practical wet conditions (10% H2O, 500 °C). To the best of our knowledge, this is one of the scare Pd catalysts which show 200 h stability in these practical conditions. Pd@S-2.0 shows negligible low temperature water absorption which lead to its high catalytic stability in wet conditions.