Highly Efficient RuO<sub><i>x</i></sub>/NbO<sub><i>x</i></sub>-ZrO<sub><i>x</i></sub> Catalysts for Ammonia Removal via Tuning Acidic Active Species
Linna Li, Xuan He, Danrui Zhu, Huimin Wang, Jianjun Chen, Qiulin Zhang, Ping Ning
Abstract
NH 3 elimination is highly desired during hazy pollution periods. However, the enhanced low-temperature activity and in-depth understanding of the reaction mechanism remain a tough challenge for NH 3 selective catalytic oxidation (NH 3 –SCO) to N 2 . Here, a zirconium–niobium composite oxide-supported 0.2 wt % RuO x component (R/Z-N) was synthesized and systematically investigated. Compared with its counterparts (RuO x /ZrO 2 and RuO x /Nb 2 O 5 ), R/Z-N presented superior NH 3 removal performance, obtaining complete conversion of NH 3 at 300 °C and 90% N 2 selectivity at a wide temperature window of 175–300 °C, followed by a lower apparent activation energy (79.2 kJ/mol). Thorough structural and surface property analysis revealed that the unique amorphous Nb 2 Zr 6 O 17 structure was formed over R/Z-N through strong zirconia–niobium oxide interaction, resulting in its highest fraction of medium strong acid, surface adsorbed oxygen, and RuO 2 catalytic active sites among these samples. Detailed situ DRIFTS studies further revealed that NH 4 + species adsorption on Bro̷nsted acid sites exhibited higher activity compared to NH 3 on Lewis. Thus, the plentiful Bro̷nsted acid sites over R/Z-N could accelerate the activation and dehydrogenation of NH 3, further promoting the fast NH 3 –SCO process via the i-SCR mechanism, thereby improving activity. This work could guide the development of a high-efficiency catalyst for NH 3 purification via tuning acidic active species.