Potential Risk of NH 3 Slip Arisen from Catalytic Inactive Site in Selective Catalytic Reduction of NO x with Metal-Free Carbon Catalysts.

Ammonia emissions from industrial processes have rapidly increased in the past years. Recent advances have used carbon-based selective catalytic reduction (SCR) technology combined with a reaction-regeneration process to reduce NO x from sintering flue gas, while NH 3 slip is seldom accounted for in this process. This study demonstrates that although the electrophilic carboxyl groups (-COOH) on metal-free carbon catalysts exhibit strong adsorption toward NH 3 , they do not participate in the SCR reaction. As a result of the competitive adsorption of NH 3 in the reaction step, these catalytic inactive carboxyl groups not only prolong the time to the SCR steady state, but also result in the potential risk of NH 3 slip. A linear relationship with the equimolar ratio between carboxyl groups and slipped NH 3 was established in the regeneration steps. The slip of NH 3 could be alleviated by the decomposition of carboxyl groups, and special attention should be paid to the presence of inactive sites with strong NH 3 adsorption on industrial-employed carbon catalysts. In addition to advancing the understanding of the NH 3 -SCR mechanism, this work also provides valuable opportunities for the control of ammonia emissions from industrial processes.