Performance and reaction mechanism for low-temperature NOx catalytic synergistic Hg-0 oxidation of catalytic polyphenylene sulfide filter materials

An in situ method (ISM), impregnation calcination method, and coating method were proposed to prepare catalytic polyphenylene sulfide (PPS) filter materials, and the low-temperature catalytic activities for nitrogen oxides (NOx) and Hg-0 were investigated in fixed bed system. Furthermore, the surface morphology characteristics, crystalline structure, and NOx interaction mechanisms were studied by scanning electron microscopy, energy dispersive X-ray, Fourier transform infrared, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy. The results showed that the maximum NOx and Hg-0 conversions decreased in the sequence of Mn-Ce-Fe-Co-O-x/PPS@ ISM> Mn-Ce-Fe-Co-O-x/PPS@ impregnation calcination method > Mn-Ce-Fe-Co-O-x/PPS@ coating method. The best catalyst reduced 84.6% NOx and oxidized 93.2% Hg-0 at 170 degrees C. NO obviously affected the conversions through a homogeneous reaction. As the reaction temperature was increased from 120 to 170 degrees C, NOx and Hg-0 conversions increased significantly but decreased from 170 to 300 degrees C. In addition, the maximum oxidation activity of NO to NO2 on Mn-Ce-Fe-Co-O-x/PPS@ ISM was 8.6% at 170 degrees C. NO-TPD and Hg-TPD respectively indicated that NOx was mainly stored by nitrite/nitrate and NO2, and HgO/Hg-2(NO3)(2) and HgSO4 were the thermal stable forms of mercury presented in PPS catalyst after reaction in simulated selective catalytic reduction flue gases. The microstructure characterizations of scanning electron microscopy-energy dispersive X-ray and Fourier transform infrared results suggested that the active metal oxides were uniformly supported on the PPS surface as the proportion of the catalyst preparation process. X-ray photoelectron spectroscopy spectra results indicated that Mn, Ce, Fe, and Co mainly existed in the form of Mn4+, Ce4+, Fe3+, and Co3+, respectively, which had the best catalytic activity to achieve flue gas NOx and mercury removal. The reaction mechanisms were further discussed on the basis of the results.