Ruoyuan Li,Aixia Li,Junhua Li,Yao Wang,Zhiming Liu
Selective catalytic reduction of NO x by CO (CO-SCR) in the presence of O 2 is challenging because in this process CO is prone to being oxidized by O 2 , thus inhibiting NO x reduction by CO. Furthermore, SO 2 typically leads to the deactivation of the CO-SCR catalyst. Herein, a significant promoting effect of SO 2 on Ir/SiO 2 catalyst for the CO-SCR of NO x in the presence of O 2 is reported. In-situ X-ray Absorption Fine Structure (XAFS) and X-ray photoelectron spectroscopy (XPS) analysis showed that SO 2 does not affect the chemical nature of Ir 0 under reaction conditions. However, SO 2 can be oxidized to sulfate and deposit on the catalyst surface. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis demonstrated that the presence of SO 2 can inhibit the CO + O 2 reaction, thus leaving more CO available to reduce NO x over the active Ir 0 sites. As a result, the reduction of NO x is remarkably promoted even in the presence of O 2 and SO 2 .
Lele Jin,Wenzhi Li,Qiying Liu,Longlong Ma,Chao Hu,Ajibola T. Ogunbiyi,Mingwei Wu,Qi Zhang
In this study, the Mo-promoted Ir/SiO 2 (Ir-MoO x /SiO 2 ) catalysts combined with the zeolite HZSM-5 were used for the direct conversion of microcrystalline cellulose (MCC) to liquid fuel (C 5 /C 6 alkanes) in n-dodecane/H 2 O system. A synergistic effect was formed between the partially reduced MoO x species and the Ir particles, which effectively promoted the catalytic activity of Ir/SiO 2 catalyst. When the Mo/Ir molar ratio was 0.5, a high yield of C 5 /C 6 alkanes (91.7%) was achieved at 210 ℃ for 12 h. In addition, the main component of C 5 /C 6 alkanes was n-hexane, which was proven to be obtained by the hydrogenolysis of the key intermediate, sorbitol, formed from the hydrolysis and hydrogenation of MCC.
Controlling both CO and NOx pollutants without additional cost is necessary but challenging, especially in industrial flue gas with complex components. Previous studies mainly focused on the effect of O 2 and SO 2 on the CO oxidation side reaction and valence state of Ir species on various catalysts, while neglecting the impact on NO conversion pathway. Herein, we propose an "ineffective reaction pathway" in the presence of O 2 with nitrate as an intermediate according to the results of in situ DRIFTS and DFT. And we also reveal the contribution of SO 2 in inhibiting the adsorption of O 2 and promoting the selective adsorption of NO and CO even at lower injection concentrations, based on the oxidation of SO 2 on Ir(111). This is quite a favorable characteristic for the treatment of industrial flue gas, resolving the long–standing dispute on the involvement of these components in the CO–SCR reaction. Under specific conditions (CO/NO=20, O 2 =5%, SO 2 =200 ppm) at 250 °C, the NOx conversion is as high as 78%. These results will contribute to the development of more efficient catalysts in the future for simultaneously controlling two pollutants (CO and NOx).
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