石墨烯基介孔锰铈氧化物催化剂:制备和低温催化还原NO

Graphene Based Mesoporous Manganese-Cerium Oxides Catalysts:Preparation and Low-temperature Catalytic Reduction of NO

锰铈氧化物由于较强的氧化还原活性、优良的低温脱硝性能,已被广泛用于选择性催化还原(SCR)脱硝反应,但是锰铈氧化物存在活性组分易团聚、比表面积较低等问题,限制其催化剂活性的提高。本研究以介孔结构的石墨烯基SiO_(2)(G@SiO_(2))纳米材料为模板,采用水热法制备了系列石墨烯基介孔锰铈氧化物(G@MnO_(x)-CeO_(2))催化剂,并考察了该催化剂在低温下(100~300℃)的SCR脱硝性能。结果表明,与石墨烯基铈氧化物(G@CeO_(2))相比,G@MnO_(x)-CeO_(2)催化剂具有较高脱硝活性。当Mn、Ce与模板G@SiO_(2)质量比分别为0.35、0.90时,G@Mn(0.35)Ce(0.9)催化剂的脱硝活性最佳,220℃下NO转化率达到最高(80%)。添加适量MnO_(x),提高了G@MnO_(x)-CeO_(2)催化剂的比表面积、孔容,降低了催化剂的结晶度;并且MnO_(x)-CeO_(2)以纳米尺度(2~3 nm)较为均匀地分散于石墨烯片层表面。此外,由于MnO_(x)与CeO_(2)之间存在协同作用,Mn原子可以部分替代Ce原子掺杂于CeO_(2)的晶体结构中形成MnO_(x)-CeO_(2)固溶体,使G@Mn(0.35)Ce(0.9)催化剂表面存在较高含量的高价态Mn^(3+)和Mn^(4+)、Ce^(4+)以及较高的化学吸附氧浓度,从而展现出较高的脱硝性能。该工作为MnO_(x)-CeO_(2)基催化剂在低温NH3-SCR中的实际应用提供了基础数据。

Manganese and cerium oxides are extensively used for selective catalytic reduction(SCR)in denitrification reaction due to their high redox ability and excellent low-temperature SCR activities.However,these catalysts still face problems such as easy aggregation of active components and low specific surface area,which restricts the enhancement of catalytic activity.Here,graphene based SiO_(2) nanocomposites(G@SiO_(2))with mesoporous structure was used as the template to prepare series of graphene based mesoporous manganese-cerium oxides(G@MnO_(x)-CeO_(2))catalysts by hydrothermal method.The obtained catalysts were investigated for selective catalytic reduction(SCR)of NO at low temperature(100–300℃).The results indicate that G@MnO_(x)-CeO_(2) catalyst exhibits better SCR activity than graphene based cerium oxides(G@CeO_(2)).With the mass ratio of Mn and Ce to G@SiO_(2) of 0.35 and 0.90,respectively,the G@Mn(0.35)Ce(0.9)catalyst shows the best NO removal activity with the maximum conversion of 80%at 220℃.It is found that the addition of appropriate amount of MnO_(x) increases specific surface area and pore volume but decreases crystallinity of the catalyst G@MnO_(x)-CeO_(2).Furthermore,MnO_(x) and CeO_(2) are uniformly distributed on the surface of graphene sheets in the form of nanoparticles.In addition,partial replaced Ce atoms is actually doped with Mn atoms into the structure of CeO_(2) to form MnO_(x)-CeO_(2) solid solution,resulting in higher percentage of Mn^(3+) and Mn^(4+) with higher valance states and Ce^(4+),and higher concentration of surface chemisorbed oxygen on the surface.These results contribute to higher SCR activity of the G@Mn(0.35)Ce(0.9)catalyst.This work provides promising basic data for the practical application of MnO_(x)-CeO_(2) based catalysts in low temperature NH3-SCR.