Ag修饰La0.6Sr0.4MnO3基催化剂氧物种的谱学表征

采用柠檬酸溶胶-凝胶法制备钙钛矿型La0.6Sr0.4MnO3 氧化物, 并用Ag 对其进行修饰,制得Ag/La0.6Sr0.4MnO3 催化剂.活性评价结果显示, Ag 的修饰能显著提高原基质催化剂La0.6Sr0.4MnO3 对低浓度CH3OH和CO完全氧化的催化活性, 相应于95% CH3OH和CO转化所需反应温度T95分别可低至421 和370 K. 催化剂的XPS和LRS谱学表征结果揭示, 在6% Ag/La0.6Sr0.4MnO3上, 具高度反应活性的表面氧物种O22- (a)和O-(a)在总表面氧中所占克分子百分数(m ol% )几近未经Ag 修饰的基质体系La0.6Sr0.4MnO3 的两倍. O2-TPD测试结果证实,Ag 对La0.6Sr0.4MnO3基质的修饰、掺杂和部分取代使其对O2 的低温吸附能力大为提高,诱生出一类数量可观具有低温吸-脱附性能的吸附氧物种. 本文结果表明, Ag/La0.6Sr0.4MnO3 催化剂对CH3OH和CO完全氧化高的催化活性与Ag 的修饰提高了催化剂对氧的低温吸附活化能力, 并使催化剂上对CHX, CH3OH, HCHO和CO具高度反应活性的表面氧物种O22- (a)和O-(a)的相对含量明显增加密切相关.

Characterization of Oxygen Species on Ag/La0.6Sr0.4MnO3 Catalyst for Oxidation of CH3OH and CO at Low Concentrations

A highly active Ag-m odified La0.6Sr0.4MnO3 catalyst with the perovskite- type structure forcom plete oxidation ofCH3OHand COatlow concentrations was prepared by using a citricacid sol-gelm ethod. Theresultsofactivity assay show ed thattheincorporation of Ag2O to the La0.6Sr0.4MnO3 hostcatalystresulted in significantenhancem entofthe catalystac- tivity. Over the 6% Ag/La0.6Sr0.4MnO3 catalyst, the reaction tem perature needed for 95% con- version ofCH3OH and CO, T95, can be aslow as 421K and 370Krespectively. Thecharacteri- zation ofthecatalystby XPSand LRSspectroscopiesrevealed thatm odification ofthe Ag2Oto the surface ofLa0.6Sr0.4MnO3 resulted in a significantincrease in relative contentofthe surface O22- /O- specieshighly reactivetow ard CH3OHand CO, with the m olarfraction (% ) ofthe ad- sorbed O22- /O-species in the totalsurface oxygen on the 6% Ag/ La0.6Sr0.4MnO3 being alm ost tw ice as m uch asthaton the La0.6Sr0.4MnO3. The O2-TPDresults indicated thatthe doping of Ag2O in the La0.6Sr0.4MnO3 hostcatalystled to enhancing adsorbability ofthe catalysttow ard oxygen and generating plenty ofoxygen ad-species w hich can be desorbed underthe relatively low tem perature. This m eans that the quantity of adsorbed and non-stoichiom etric oxygen- species being able to participate in the CH3OH and CO oxidation reactions would greatly in- crease. Allthesefactors would contributeto the pronounced im provem entofthecatalystactiv- ity.