CAJ | 학술논문

采用水热法合成了两种具有相同形貌但是不同物相结构的MnO2纳米棒,分别为隧道状和层状结构,考察其低温NH3选择性催化还原NOx(NH3-SCR)的性能.结果表明MnO2纳米棒的比表面积不是影响活性的主要因素,催化剂的晶相结构和表面性质对催化活性有很大影响,隧道状α-MnO2纳米棒的低温NH3-SCR活性明显高于层状δ-MnO2纳米棒.结构分析和NH3程序升温脱附(NH3-TPD)实验表明,α-MnO2纳米棒的暴露晶面(110)面存在大量的配位不饱和Mn离子,形成较多的Lewis酸性位点,而且α-MnO2较弱的Mn-O键和隧道结构都有利于NH3的吸附;而δ-MnO2纳米棒的暴露晶面(001)面上的Mn离子已达到配位饱和,所以其表面Lewis酸性位点较少.X射线光电子能谱(XPS)和热重(TG)分析表明α-MnO2纳米棒的表面更有利于NH3和NOx的活化.具有有利于吸附NH3和活化NH3和NOx的表面性质和晶型结构,是α-MnO2纳米棒活性高的主要原因.
채용수열법합성료량충구유상동형모단시불동물상결구적MnO2납미봉,분별위수도상화층상결구,고찰기저온NH3선택성최화환원NOx(NH3-SCR)적성능.결과표명MnO2납미봉적비표면적불시영향활성적주요인소,최화제적정상결구화표면성질대최화활성유흔대영향,수도상α-MnO2납미봉적저온NH3-SCR활성명현고우층상δ-MnO2납미봉.결구분석화NH3정서승온탈부(NH3-TPD)실험표명,α-MnO2납미봉적폭로정면(110)면존재대량적배위불포화Mn리자,형성교다적Lewis산성위점,이차α-MnO2교약적Mn-O건화수도결구도유리우NH3적흡부;이δ-MnO2납미봉적폭로정면(001)면상적Mn리자이체도배위포화,소이기표면Lewis산성위점교소.X사선광전자능보(XPS)화열중(TG)분석표명α-MnO2납미봉적표면경유리우NH3화NOx적활화.구유유리우흡부NH3화활화NH3화NOx적표면성질화정형결구,시α-MnO2납미봉활성고적주요원인.
Two manganese oxides with the same nanorod-shaped morphology but different crystal structures,tunnel and layer structures,were synthesized and investigated for selective catalytic reduction of NOx with NH3 (NH3-SCR) at low temperature.Tunneled α-MnO2 had much higher catalytic activity than layered δ-MnO2 under the same reaction conditions.Experiment results revealed that the surface area was not the main factor to affect the NH3-SCR activities over the MnO2 nanorods and that the activities were structure sensitive.Structure analysis and temperature-programmed desorption experiments of NH3 (NH3-TPD) suggested that the exposed (110) plane of α-MnO2 had many Mn cations in coordinatively unsaturated environment,while all of the Mn cations on the exposed (001) plane of δ-MnO2 were in coordinatively saturated environment.Thus,α-MnO2 possessed many more Lewis acid sites.Furthermore,α-MnO2 has weaker Mn - O bonds and an efficient tunnel structure,which are favorable characteristics for NH3 adsorption.Moreover,X-ray photoelectron spectroscopy (XPS) and thermal gravimetric (TG) analysis indicated that α-MnO2 obtained a higher capability for NH3 and NOx activation than δ-MnO2.The crystal structure and surface properties of α-MnO2 are more suitable to the adsorption of NH3 and activation of NH3and NOx,which accounts for the higher catalytic activity of the α-MnO2 nanorods.