Runping Wu,Qing Ye,Kai Wu,Shuiyuan Cheng,Tianfang Kang,Hongxing Dai
The alkali metal (M = Na, K, Rb, and Cs)-modified C-FDU-15 (M-C-FDU-15( x ); x was the M/C-FDU-15 M ratio, and equal to 0.01–0.03) samples were prepared through an in situ process, and characterized by means of the TG, XRD, TEM, EDS, N 2 adsorption–desorption, O 2 -TPD, and CO 2 -TPD techniques. The (NO + O 2 ) adsorption mechanism was investigated using the (NO + O 2 )-TPD and DRIFTS techniques. The results show that the sequence of (NO + O 2 ) adsorption performance was Na-C-FDU-15(0.01) (104.1 mg/g) > K-C-FDU-15(0.01) (92.4 mg/g) > C-FDU-15 (76.2 mg/g) > Rb-C-FDU-15(0.01) (65.1 mg/g) > Cs-C-FDU-15(0.01) (62.3 mg/g). The alkali metal was uniformly distributed in C-FDU-15 and its doping enhanced the amount of the basic sites in the sample. Moreover, the optimal Na/C-FDU-15 M ratio was 0.02. (NO + O 2 ) were chemically adsorbed mainly in the forms of nitrite (NO 2 − ) and nitrate (NO 3 − ) on M-C-FDU-15( x ). A more amount of NO was converted to nitrate than to nitrite. There were three key factors of enhancing the (NO + O 2 ) adsorption capacity of C-FDU-15 due to alkali metal doping: the first factor was the increasing of surface area and pore volume of the sample, the second one was the enhancement in amount of the active sites in the sample, and the third one was the smaller alkali metal ionic radius in the sample.
To improve the removal capacity of NO + O 2 effectively, the alkaline earth metal-doped order mesoporous carbon (A-C-FDU-15(0.001) (A = Mg, Ca, Sr and Ba)) and Mg-C-FDU-15( x ) ( x = 0.001−0.003) samples were prepared, and their physicochemical and NO + O 2 adsorption properties were determined by means of various techniques. The results show that the sequence in (NO + O 2 ) adsorption performance was as follows: Mg-C-FDU-15(0.001) (93.2 mg/g) > Ca-C-FDU-15(0.001) (82.2 mg/g) > Sr-C-FDU-15(0.001) (76.1 mg/g) > Ba-C-FDU-15(0.001) (72.9 mg/g) > C-FDU-15 (67.1 mg/g). Among all of the A-C-FDU-15(0.001) samples, Mg-C-FDU-15(0.001) possessed the highest (NO + O 2 ) adsorption capacity (106.2 mg/g). The species of alkaline earth metals and basic sites were important factors determining the adsorption of NO + O 2 on the A-C-FDU-15( x ) samples, and (NO + O 2 ) adsorption on the samples was mainly chemical adsorption. Combined with the results of (NO + O 2 )-temperature-programmed desorption ((NO + O 2 )-TPD) and in situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization, we deduced that there were two main pathways of (NO + O 2 ) adsorption: one was first the conversion of NO and O 2 to NO 2 and then part of NO 2 was converted to NO 2 − and NO 3 − ; and the other was the direct oxidation of NO to NO 2 − and NO 3 − .
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