Journal
CHEMICAL ENGINEERING JOURNAL
Volume 361, Issue -, Pages 820-829Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.cej.2018.12.149
Keywords
NH3-SCR; Fe-2(SO4)(3); Thermal deactivation; In situ recovery; DFT calculations
Categories
Funding
- National Natural Science Foundation of China [21477095, 21677114, 21876139]
- National Key Research and Development Program [2016YFC0204201]
- Natural Science Foundation of Fujian Province, China [2016J05048]
- China Postdoctoral Science Foundation [2016M602831]
- Fundamental Research Funds for the Central Universities [xjj2017113]
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Due to high catalytic activity and excellent resistance to SO2 and H2O, sulfate materials are considered to be promising vanadium-free catalysts for selective catalytic reduction of NOx with NH3 (NH3-SCR). Despite this, investigations about thermal stability of sulfate SCR catalysts are limited, which is surprising given that sulfates are typically susceptible to thermal decomposition. In this work, the thermal stability of Fe-2(SO4)(3)/TiO2 catalysts was investigated. It was determined that the thermal decomposition of Fe-2(SO4)(3) resulted in NOx conversion decreased from 90% to 60% at 350 degrees C. Interestingly however, the introduction of SO2 into the gas stream was found to reverse the effects of the thermal deactivation and the NOx conversion of 90% (350 degrees C) was once again observed. Extensive characterization of each catalyst sample and density functional theory (DFT) calculations were subsequently conducted. The reduction in catalytic activity after the thermal treatment was attributed to the transformation of Fe-2(SO4)(3) to alpha-Fe2O3, which reduced the quantity of Bronsted acid sites on the catalyst. The presence of SO2 in the gas stream was found to reverse this phase transformation which ultimately led to the recovery of Bronsted acid sites. DFT calculations indicated that SO2 adsorbed selectively on Fe atoms of the thermal deactivated catalysts and S-Fe bond should mainly be formed by electrons from p orbitals of S and Fe atoms. Then NH3 could be adsorbed on the surface by N-S bond with SO2. The recoverable property of this catalyst provides a promising outlook for the commercial application, especially given that industrial flue gas streams regularly contain SO2.
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