Co-exchange of Mn ions:A Simple Method to Improve Performance of Cu-SSZ-13 Catalyst

Zhenguo  Li, The Automotive Engineering Research Institute (AERI)

Ammonia selective catalytic reduction is an effective NOX purification technology for diesel exhaust. As the core of SCR technology, Cu/SSZ-13 has become the hot research topic. High low temperature catalytic activity, hydrothermal stability and resistance to poisoning are critical for the application of Cu-SSZ-13 catalysts [1-3]. Simply changing the copper ion content is limited for catalyst activity enhancement: high Cu loading is beneficial to low-temperature NOx conversion, but detrimental to catalyst hydrothermal stability. Alkali and alkaline earth co-cation additives to Cu/SSZ-13 to improve the catalytic performance have been deeply researched [2]. And It has also been extensively studied to improve the performance of catalysts by combining metal oxides with zeolites [1]. However, the researches of Mn ions as the co-cation additives are still lack.

Based on the excellent low temperature activity and the substitution of B acid sites in zeolite of Mn species, we used a co-exchange of Mn ions to improve the catalyst performance. We prepared 0.2Cu0.1Mn-SSZ-13 catalyst, 0.2Cu-SSZ-13 and 0.2Cu-SSZ-13 catalysts and detailed studied the effect of added Mn ions as the co-cation. The low-temperature activity, hydrothermal stability and anti-C3H6 ability were improved. Combined with SCR, NH3 oxidation, NO oxidation reaction tests and ammonia temperature-programmed desorption, X-ray diffraction analysis, solid state nuclear magnetic resonance analysis, low-temperature N2 absorption and desorption, the effects of co-exchanged Mn ions were divided into two aspects. On the one hand, the addition of Mn ions replaced parts of H+ and different ions play a similar role in this factor. On the hand, the unique properties of Mn ions and the interaction of Cu ions provide excellent catalytic performance for the catalyst. The specific research are as follows: (1) The replacement of H+ can reduce the decrease of crystallinity and the dealumination of the skeleton during the hydrothermal aging of the catalyst. (2) The interaction between Mn ions and Cu ions leads to an increase in its low temperature activity and the presence of Mn ions could effectively inhibit the formation of CuxOy during hydrothermal aging of the catalyst. (3) The addition of Mn ions is capable of repressing the formation of carbon deposition and improve its activity.

References:

[1] Liu Q, Fu Z, Ma L, Niu H, Liu C, Li J, Zhang Z. 2017. MnOx -CeO2 supported on Cu-SSZ-13: A novel SCR catalyst in a wide temperature range[J]. Applied Catalysis A: General, 547: 146-154.

[2] Gao F, Wang Y, Washton N M, Kollár M, Szanyi J, Peden C H F. 2015. Effects of Alkali and Alkaline Earth Cocations on the Activity and Hydrothermal Stability of Cu/SSZ-13 NH3–SCR Catalysts[J]. ACS Catalysis, 5(11): 6780-6791.

[3] Ma L, Su W, Li Z, Li J, Fu L, Hao J. 2015. Mechanism of propene poisoning on Cu-SSZ-13 catalysts for SCR of NOx with NH3[J]. Catalysis Today, 245: 16-2