Understanding the catalytic properties for synthesizing NOx derivative NH3 by an alternate gas-switching process†

Abstract

Reactive nitrogen compounds like NO_x are not environment-friendly but have potential as some of the chemical sources for the low-energy synthesis of NH₃ and value-added chemicals. Our recent initiatives have revealed catalytic conversion to NH₃via a gas-switching NO_x storage and reduction process. This concept was demonstrated absolutely by using nanocomposite catalysts based on mesoporous metal oxides with noble metal catalysts and NO_x storage components like BaO/Pt@mAl₂O₃ and BaO/Pt@mTiO₂. Here, we investigate and compare the properties of another BaO/Pt@mCeO₂-type nanocomposite catalyst. After stabilization by zirconium doping, BaO/Pt@mCe_0.8Zr_0.2O₂ exhibited acceptable NO_x storage properties at temperatures higher than 250 °C with extra NO_x storage by the CeO₂-based support in addition to the major capacity of BaO. However, Pt nanoparticles were made to be very fine by a strong metal–support interaction to CeO₂ and possibly worked very well, which was not preferable for the formation of NH₃. From this viewpoint, the hydrogenation property was suppressed by lowering the reaction temperature, leading to an improvement in the NH₃ selectivity from less than 10% to more than 70% even in the low NO_x storage state.