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The Roles of Sulfur-Containing Species in the Selective Catalytic Reduction of NO with NH3 over Activated Carbon

Li, Yuran, Guo, Yangyang, Xiong, Jin, Zhu, Tingyu, Hao, Junke
Industrial & Engineering Chemistry Research 2016 v.55 no.48 pp. 12341-12349
Fourier transform infrared spectroscopy, Raman spectroscopy, activated carbon, ammonia, desorption, engineering, gases, graphene, moieties, nitric oxide, physicochemical properties, sulfates, sulfur dioxide, temperature
In the selective catalytic reduction (SCR) of NO with NH₃ over activated carbon (AC), deactivation occurs over time in the presence of SO₂. This work distinguishes the multiple roles of SO₂ in the gas phase versus the solid deposition product and clarifies the effects of the physicochemical properties of AC on NO conversion. The deposition products were detected using temperature-programmed desorption (TPD) coupled with mass spectrum (MS) analysis and Fourier transform infrared (FTIR) spectrometry. The results showed that the activated carbon loses less de-NOₓ activity when it has more CO- and CO₂-containing groups with decomposition temperatures over 900 K. The Raman spectra revealed that the disorder of the microcrystalline structure of the graphite has a positive linear correlation with NO conversion regardless of the presence of functional groups. The deposition products were analyzed by Gaussian-Lorentz deconvolution of the TPD spectra, and it was discovered that the sulfur-containing species included sulfate and strongly adsorbed SO₂/SO₃; the NH₃-containing species included NH₄HSO₄ and freely adsorbed NH₃; and the ratios of SO₂/SO₃, NH₄HSO₄ and NH₃ were approximately 31 mol %, 42 mol %, and 26 mol %, respectively. NH₄HSO₄ does not notably inhibit NO conversion, even with a high loading amount. The inhibitory effect of gaseous SO₂ on NO conversion is reversible, and this inhibitory effect is greater than that caused by the loss of functional groups. Increasing the disorder of the microcrystalline structure of the graphite and reducing the gaseous SO₂ were identified as ways to improve activated carbon activity for NO conversion.