Abstract
Carbon nanotubes are a promising adsorbent for desulfurization and denitrification. In this paper, Cu- and Cr-doped TiO2 supported by multi-walled carbon nanotubes (MWCNTs/Cu-Cr-TiO2) were synthesized by the sol-gel method. Characterizations of the samples were performed by TEM, XPS, XRD, DRS, and BET. The experiments of simultaneous desulfurization and denitrification were conducted in a fixed-bed reactor. The results showed that the adsorbent with a Cu to Cr molar ratio of 3 displays excellent adsorption property. The SO2 and NO adsorption capacity of MWCNTs/Cu-Cr-TiO2 (Cu/Cr = 3) were 36.83 and 12.34 mg/g under the optimal experimental operating parameters (SO2 content: 1575 mg/m3, NO content 736 mg/m3, O2 content 8%, H2O content 5%, and space velocity 1003 h−1). The adsorption capacity of MWCNTs/Cu-Cr-TiO2 was significantly better than that of the adsorbent doped with Cu or Cr alone (MWCNTs/Cu-TiO2 and MWCNTs/Cr-TiO2). Compared with single metal doping, bimetallic multivalent states accelerate the electron migration and separation from holes, which increase the number of oxygen vacancies and enhance the adsorption of SO2 and NO. The kinetic models and the reaction mechanism of the desulfurization and denitrification were also analyzed in this work.
Highlights
Desulfurization and denitrification are independent in most industrial applications, in which NO is removed by selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR) located at the entrance of the electrostatic precipitator [2]
Yang et al [28] synthesized Cr-doped MWCNTs/TiO2 for SO2 removal; the results showed that Cr-doped MWCNTs/TiO2 displayed a better adsorption property than MWCNTs/TiO2
The rupture signs were observed at the end of MWCNTs because of acid treatment [30]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Carbon nanotubes loaded with TiO2 and doped with metal(s) improved the adsorption property of such materials. Wang et al [22] introduced metal Au on CNT-TiO2 , which showed higher activity and adsorption capacity than CNT-TiO2 to degrade methylene blue in water. In the study of Zhang et al [23], Ag-doped CNT/TiO2 showed a good catalytic degradation efficiency (76%) for methylene blue illuminated with visible light. Metal doped carbon nanotubes loaded with TiO2 were used for flue gas desulfurization and denitrification. Liu et al [26] investigated the adsorption of SO2 and NO on Cu-doped Multi-Walled Carbon Nanotubes/TiO2 (MWCNTs/TiO2 ), with the removal efficiency of 62% and 43%, respectively. Bao et al [27] prepared MWCNTs/TiO2 doped with Mn to remove SO2 , which showed a good desulfurization efficiency (66%). The kinetic models for the desulfurization and denitrification were studied, and the reaction mechanism of MWCNTs/Cu-Cr-TiO2 for SO2 removal and NO was analyzed
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