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標題: 活性碳擔持銅觸媒對二氧化硫吸附特性之研究
作者: 曾惠馨
Tseng, Hui-Hsin
關鍵字: 活性碳
出版社: 環境工程學系
摘要: 活性碳由於其特殊的孔洞結構與表面化學組成,而能對催化反應所需之性質提供相當靈活且具有彈性的修正空間。因此,為改善傳統鋁擔體於除硫時所遭遇之問題,本研究選用活性碳為銅觸媒之擔體,期能建立一具有:(1)可降低銅觸媒的吸附溫度;(2)擔體不參與反應,或參與反應的硫酸化擔體其再生容易且結構穩定性佳;(3)擔體表面酸度低,可降低積碳性等特點之可再生的金屬氧化物除硫試劑。實驗藉由不同的酸溶液預處理碳擔體,並輔以BET、XRPD、EA、TPD、FTIR與SEM等分析,以觀察碳擔體的氧表面複合物與活性金屬分散性及二氧化硫吸附量之關係。 研究結果指出,酸溶液預處理碳擔體由於可於擔體表面形成不同的含氧官能基位而降低其表面酸度(pHslurry);當含浸溶液之pH值大於pHslurry值時,將有利於前驅物金屬離子於孔洞中的擴散行為,並進而改善活性相之分散性、提升對SO2的吸附能力。然以HNO3溶液預處理時,雖可大幅地降低碳擔體的表面酸度,但硝酸根的殘留及某些氧表面官能基位所產生的立體效應,都將抑制銅離子與擔體間的交互作用,而使其座落於外孔洞中產生團聚現象。 此外,經由動力實驗之數據分析與反應產物之紅外光吸收光譜驗證,活性碳擔持銅觸媒於低溫250℃時對SO2之吸附能力為最佳,且由於碳擔體與SO2間之吸附行為屬於低溫物理程序,因此並不參與除硫反應而無擔體硫酸化之虞。該觸媒之再生亦可以熱處理方式於不含還原氣體的高溫(360-380℃)環境中進行,藉由鄰近硫酸銅的碳表面含氧官能基位於碳擔體表面與CuSO4反應後將其還原並生成CO與CO2等產物。此外,硫酸化之活性碳擔持銅觸媒於NO/NH3=1之含氧環境中,對NO亦有極佳的催化還原能力。
Activated carbon (AC), the materials with specific porous structure and oxygen surface groups, has been used in heterogeneous catalysis for a long time, because it can act as direct catalyst or satisfy most of the desirable properties required for a suitable support. To improve the disadvantages of participation of alumina support in sulfation reaction, activated carbon as catalyst support which pre-treated with HCl and HNO3 and the effects of acid treatments on the properties of the activated carbon support was studied by pH, BET, FTIR, XRPD, EA, TPD and SEM. Desirable advantages of such catalysts would be: (1) savings in operating costs by lowering the SO2 catalytic oxidation temperature, without the worry of ammonium sulfate production and deposition; (2) the spent catalyst could be regenerated easily and without causes a detrimental effect on stability; and (3) a lower surface acidity of the catalyst supports in order to lower their coking propensity. It was found that acid treatment significantly changed the surface chemical properties of the activated carbon. At pH>pHslurry the carbon surface are covered by deprotonated carboxyl groups; the negatively charged surface then attracts and adsorbs cations from solution. However, due to the fact that the acidic groups introduced following HNO3 treatment causes cubic effect, CuO may crystallize and can be present on the external surface of the HNO3 treated AC support and increases the crystallite size of the active site. The kinetics of SO2 removal from flue gas and adsorption in the form of regenerable surface sulfate species on a Cu/AC catalyst were analyzed according to spectroscopic evidence showing the formation of one sulfae specie linked ot Cu site. The spent catalysts could be regenerated by neighboring surface oxygen functional groups and generated Cu, SO2, CO and CO2. Furthremore, under the NO/NH3=1 the NO could be selective catalytic reduction (SCR) with NH3 in the presence of O2, which catalyzed by fresh and spent AC-supported catalyst.
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