| The selective catalytic reduction (SCR) is one of the widely-used technology treatment, while the development of highly active SCR catalysts working at low temperatures (<250℃) is the key to control the exhaust gas of NOx from fired power plants. The use of activated carbon (AC) as catalyst for NH3-SCR has been recognized as one of the advanced technologies due to its unique and versatile characteristics that adsorb gas/liquid into internal pore surface, and its high degree of surface reactivity. Compared with the metal-based catalysts, the post-treatment of these catalysts is easier, cleaner and more environmental.As we know, sargassum is an advantageous biomass source over land-based plants, including lower price, higher yields without requiring arable land, high contents in carbon and nitrogen (40.24% and 2.52%). This novel utilization of AC derived from sargassum, normally disposed as waste, shows an effective approach of combining waste disposal, biomass energy recovery and air pollution control (NOx) in one process.This work aims to investigating the potential of urea or metal modified activated carbon derived from sargassum as a novel NH3-SCR catalyst in the temperature range of 50～250℃. The impacts of water (H2O) and sulfur dioxide (SO2) on the SCR activity of the catalyst were also discussed. An array of analytical techniques, including Brunauer-Emmett-Teller method (BET); Elemental Analysis (EA); Fourier Transform infrared spectroscopy (FTIR); X-ray Photoelectron spectroscopy (XPS); H2 Temperature-programed reaction (H2-TPR) and NH3Temperature-programed desorption(NH3-TPD) were also employed to study the structural properties, elemental content, the role of chromium ions and distribution of nitrogen-containing groups of the catalyst prepared.Firstly, the influence of important process variables, such as preparation methods, and phosphoric acid impregnation ratios, were investigated. The experimental results showed that Co/SAC-2 showed the best SCR activity with a maximum NOx conversion of 82.05% at 125℃ and high N2 selectivity over 95%. In addition, Co/SAC-2 had an excellent water-tolerance and sulfur-tolerance. However, the reaction temperature window of catalyst was too narrow.Secondly, in order to broaden the reaction temperature window of SAC in SCR, urea modification by impregnation method was employed. Experimental results suggested that the urea modified sample (C/SAC-2/U-6) exhibited higher NOx conversion (with a maximum 87%), better N2 selectivity and broader operation temperature window(over 75% during 50～250℃) than all the SAC samples and the commercial activated carbon sample at the GHSV of 80000 h-1. Moreover, it has good water and sulfur tolerance, making the sargassum derived catalyst as a promising NH3-SCR catalyst for NOx emission from fired power plant. From the XPS results, the N-containing groups (especial N-6) had a great improve on the SCR activity.Lastly, various metals (Ce, Mn, Cu and Cr) have been selected as the active components to improve the catalytic performance of sargarsum-based activated carbon catalyst with a high GHSV of 80000 h-1 and the effect of different CrO3 doping amounts on the SCR activity of SAC catalyst was studied. Experimental results suggested that Cr/SAC catalyst showed the highest NOx conversion compared with the others. At temperature above 125℃, the order of NOx conversion is Cr/SAC> Cu/SAC> Ce/SAC^Mn/SAC. With the introduction of Cr species, a remarkable promotional effect is observed within the temperature range of 50～250℃ and the NOx conversion increased from 56.91% to 92.3% at 125℃. Moreover, it has good water and sulfur tolerance, making the sargassum derived catalyst as a promising NH3-SCR catalyst for NOX emission from fired power plant. |
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