| NOx that emitted from coal-fired flue gas is one of the most atmospheric pollutants, so efficacious control is necessary to stop serious atmosphere environmental pollution caused by NOx. Low-temperature SCR device is arranged after the dust removal and desulfurization, it can be not only avoid the flue gas preheat energy consumption and reduce the operating cost, but also ease the congestion and the poison of dust and SO2. Based on the review of the current situation of SCR technology, Ce-Mn mixed oxides has widely paied attention to domestic and foreign researchers, but TiO2, Al2O3and Activated Carbon were the main support, this could not solve the problem of retrieve and particulate matter controling. In order to solve these problems, a new technology that cerium-manganese oxides supported on modified glass-fiber was proposed to achieve removing NO and particles in low-temperature.Firstly, high temperature inorganic glass fiber was selected as the catalyst carrier in this study, and the glass fiber was modified to reach the best effect of loading. In addition to the necessary grouping comparative experiments, the pretreatment experiments design of glass fiber fabric using response surface methodology was used to identify the optimal pretreatment conditions from the theoretical analysis of existing experimental theoretical analysis.Secondly, samples of cerium-manganese oxides supported on modified glass-fiber with different molar Ce/Mn ratios (Ce-Mn/GF) were prepared by an impregnation method and tested for low-temperature (80-180℃) selective catalytic reduction (SCR) of NO with ammonia. This brand-new technology could remove NO and particles matter from coal-fired flue gas. The surface properties of the catalysts were examined using Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The experimental results showed that the catalyst with a molar Ce/Mn ratio of0.2 obtained high activity of87.4%NO conversion at150℃under a high space velocity of50,000h-1. Deactivation poisoned by SO2still occurred, but the Ce-Mn/GF(0.2) catalyst performed desirable tolerance to SO2with decreasing50%in40min and then maintaining at about30%NO conversion. Characterization results indicated that the excellent low-temperature catalytic activity is related to the high specific surface area, pore structure, and amorphous phase.Furthermore, the effect of temperature, O2, NH3, NO and SO2on the SCR activity of Ce-Mn/GF(x) catalysts as well as its mechanism were investigated detailed. The influence of sulfur poisoning on the SCR performance of Ce-Mn/GF(x) was investigated at150℃for60min by adding550ppm SO2to feed gases. For the Mn/GF catalyst the NO conversion dropped from77.4%to3%during20minute, which means that a severe deactivation occurred to the catalyst after exposure to SO2. Clearly, sulfur resistance of the Ce-Mn/GF(x) catalysts strengthened with the increasing of Ce loading. The reason is that a portion of the Ce4+transformed into Ce3+ions as the SO2acted as a reducing agent on sample surface.On the basis of this study, it can be concluded that the Ce-Mn/GF(0.2) catalyst showed high activity without SO2existed. Above87%NO conversion was obtained at150℃under a space velocity of50,000h-1.Characterization results indicate that the catalytic activity is related to the specific surface area, pore volume, and the amorphous phase. In case of Ce-Mn/GF(0.2), BET surface area and pore volume were relatively high. It was known from XPS analysis that Mn valence state on the surface of the Ce-Mn/GF(x) catalysts(x≠0) were in Mn4+state. XRD showed that Ce-Mn mixed oxides were well-dispersed throughout the support structure. In future work, the regeneration of Ce-Mn/GF catalysts, the de-dusting capability, and the interaction between Ce and Mn oxides are worthy of detailed investigation. |
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