以非均相沉淀法制备了凹凸棒石(PG)载体上负载锰氧化物催化剂Mn/PG,并用于低温选择性催化还原法(SCR)脱硝反应.采用X射线衍射、透射电子显微镜和H_2-程序升温还原方法对催化剂进行了表征;通过NH_3吸脱附实验考察了催化剂的锰负载量和煅烧温度对NH_3吸附和脱附量及吸附位的影响.结果表明,锰氧化物高度分散于PG晶体表面,其存在状态取决于催化剂煅烧温度.煅烧温度低于550℃,锰氧化物为Mn_2O_3和Mn_3O_4,煅烧温度为550℃时,锰氧化物为Mn_3O_4.NH_3主要吸附在PG载体上,锰氧化物的担载基本不影响催化剂吸附NH_3的能力,但促进了吸附NH_3的活化,这是催化剂SCR活性显著增加的直接原因.
A Mn/palygorskite catalyst for low-temperature selective catalytic reduction (SCR) of NO by NH_3 was prepared by heterogeneous co-precipitation followed by drying and calcination. NH_3 adsorption capacity of the catalyst, which is generally considered to be a key property of SCR catalysts, was investigated by experiments of ammonia adsorption and temperature-programmed desorption (TPD). Physico-chemical properties of the catalyst were characterized by X-ray diffraction, transmission electron microscopy, temperature-programmed reduction in H_2. The results showed that manganese oxides are highly dispersed on the surface of the palygorskite support. The surface manganese species exist as Mn_2O_3 and Mn_3O_4 at calcination temperature lower than 550 ℃ and as Mn_3O_4at 550 ℃. Adsorption of ammonia on the catalyst occurs mainly on the palygorskite support. The manganese oxide loading does not promote the NH_3 adsorption on the catalyst but increases the activation of the adsorbed NH_3. This is the main reason for the remarkable increase in catalytic activity of the palygor-skite-based catalyst.
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