• 关键词：MnO_x/PG催化剂  硫酸铵盐  MnSO₄  热处理

• 基金项目：国家自然科学基金(No.40902020,51002042);高等学校博士学科点专项科研新教师基金(No.20090111120019);中央高校基本科研业务费专项资金(No.2011HGQL1003)

• 张翠平
• 合肥工业大学化学工程学院, 合肥 230009

• 张先龙
• 合肥工业大学化学工程学院, 合肥 230009

• 吴雪平
• 合肥工业大学化学工程学院, 合肥 230009

• 张连凤
• 合肥工业大学化学工程学院, 合肥 230009

• 张恒建
• 合肥工业大学化学工程学院, 合肥 230009

• 杨保俊
• 合肥工业大学化学工程学院, 合肥 230009

• 摘要：采用等体积浸渍法制备了锰氧化物负载凹凸棒石(MnO_x/PG)低温SCR催化剂,通过SO₂暂态响应、程序升温表面反应(TPSR)等实验技术研究了烟气中SO₂对催化剂SCR脱硝活性的影响行为.采用程序升温脱附(TPD)、BET比表面及孔径分布测定、XPS等表征技术对催化剂硫中毒的机理及化学本质进行了深入分析.结果表明,低温下烟气中SO₂对MnO_x/PG催化剂的SCR脱硝活性存在显著的抑制作用,催化剂中毒主要由烟气中SO₂的催化氧化引起.一方面SO₂氧化为SO₃后与NH₃及H₂O竞争反应形成复杂的硫酸铵盐堵塞催化剂孔道,另一方面与活性组分MnO₂结合形成MnSO₄使得部分活性组分形态发生变迁.其中硫酸铵盐的形成可通过适当的热处理得以去除,而MnSO₄则不可恢复,但催化剂SCR活性却显著增加,表明MnSO₄的形成不是催化剂失活的主要因素.吸附态的硫可显著增加催化剂表面酸性,因此对SCR活性有促进作用.催化剂失活主要机理为:由气相SO₂的连续氧化并与NH₃相结合形成硫酸铵盐,并且在低温下难以分解,以致堵塞催化剂活性中心.

• Abstract：MnO_x/PG, as low temperature SCR catalysts, were prepared by means of pore volume impregnation. Influences of SO₂ on the MnO_x catalysts at low temperature were investigated by transient response of SO₂ and temperature programmed surface reaction (TPSR). Catalysts were characterized by TPD, BET surface area and XPS, and the mechanism of SO₂ deactivation was discussed. The results indicated that SO₂ in the flue gas obviously inhibited the catalyst's activities for SCR at low temperature. Catalytic oxidation of SO₂ to SO₃ was mainly responsible for the poisoning of the MnO_x/PG catalysts. On one hand, SO₂ was oxidized to SO₃ and then reacted with NH₃ and H₂O to form complicated ammonium sulfates, which were then deposited on the surface of catalysts and blocked the pore; On the other hand, MnSO₄ was formed due to the combination of SO₃ and MnO₂, which partly changed the morphology of active species. The ammonium sulfates can be removed by appropriate heat treatment, while MnSO₄ cannot be recovered in the SCR. SCR activity of the MnO_x/PG catalyst was enhanced obviously after heat treatment for the poisoned catalysts, which indicated that the formation of MnSO₄ was not the key factor for the deactivation of catalysts. The adsorbed sulfur can enhance the surface acidity of catalysts significantly and thus improve the catalyst's activity. The main mechanism of the deactivation for MnO_x/PG catalysts was that SO₂ in the flue gas was oxidized continuously and formed ammonium sulfate with NH₃. The ammonium sulfates were difficult to decompose in low temperature, which resulted in the blocking of active sites.

• Key words：MnO_x/PG catalysts  ammonium sulfates  MnSO₄  heat treatment

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