Efficient abatement of NOx emitted from automotive engines via adsorption on the Ba-CMK-3 adsorbents.

Abstract

The Ba-CMK-3(x) (x was the Ba(NO3)2:CMK-3 mass ratio and equals to 5, 10, and 15 wt%) samples were prepared by the incipient impregnation method, which were used for the adsorption of NO + O2 at room temperature. The samples were characterized by the XRD, BET, TEM, TPD, TG, and DRIFTS techniques. The results showed that the CMK-3 and Ba-CMK-3(x) samples possessed an ordered two-dimensional hexagonal mesoporous structure, and Ba was uniformly dispersed on the surface of CMK-3. After Ba doping, the surface areas and pore size distributions of the Ba-CMK-3(x) samples were altered due to the synergistic effect of partial blocking of the channels by Ba and partial etching of the carbon materials by O2 produced from Ba(NO2)3 decomposition at high temperatures. The sequence in NO adsorption capacity was Ba-CMK-3(10) (108.1 ± 0.55 mg/g) > Ba-CMK-3(15) (106.2 ± 0.72 mg/g) > Ba-CMK-3(5) (102.3 ± 1.33 mg/g) > CMK-3(88.8 ± 1.15 mg/g), with the Ba-CMK-3(10) sample showing the best (NO + O2) adsorption performance. We proposed the two main adsorption pathways in the process of NO adsorption: (i) NO reacted with O2 to form NO2, part of NO2 were weakly adsorbed on the surface hydroxyl groups, part of NO2 were adsorbed to form the nitrite and nitrate species, and the left NO2 was disproportionated to the NO, NO2-, and NO3- species; and (ii) NO was directly oxidized to the NO2- species by the oxygen-containing functional groups in carbon, and then some of the NO2- species were transformed to the NO3- species directly or via disproportionation. The regeneration efficiencies of the Ba-CMK-3(x) samples were slightly inferior to that of the CMK-3 sample.