Adsorption-Dependent Surface Nonradical Pathway Toward Selective Catalysis: Nh4+ Oxidation Over Zeolite Based Catalyst

Abstract

Ammonium ions (NH4+) are widely present in drinking water and do not meet the health standards in many countries and regions. To selectively convert NH4+ into gaseous nitrogen other than nitrate and nitrite remains a great challenge. Herein, an adsorption-dependent surface reactive oxygen species (ROS) reaction process is proposed with a novel catalyst of Na-rich Mn anchored zeolite (Na/Mn@Beta) designed for the selective removal of NH4+. Compared to pure ozonation, this process achieves a 15.5-fold increase in the oxidation rate of NH4+, demonstrating high selectivity toward gaseous N2 with a 95.7% yield ̶ surpassing nearly all known O3-based methods. The high promotion of NH4+ removal and gaseous nitrogen selectivity benefits from the enhancing proximity of confined NH4+ with surface-adsorbed atomic oxygen (*Oad) and singlet oxygen (1O2) generated through electron transfer. When applied to real drinking water, Na/Mn@Beta catalytic ozonation efficiently eliminates NH4+ with an oxidation rate of 0.0724 min-1 and presents excellent stability. This underscores the feasibility of reducing ammonia nitrogen pollution and almost avoids toxic nitrate and nitrite formation with adsorption-dependent nonradical pathway, thereby supporting sustainable clean water development.

Keywords: Ammonia nitrogen, drinking water, adsorption-dependent nonradical pathway, selective catalytic ozonation, zeolite based catalyst