物理化学学报
物理化學學報
물이화학학보
Acta Physico-Chimica Sinica
2015年
9期
1761-1770
,共10页
范丰奇%孟明%田野%郑黎荣%张静%胡天斗
範豐奇%孟明%田野%鄭黎榮%張靜%鬍天鬥
범봉기%맹명%전야%정려영%장정%호천두
NOx%储存%还原%氧化铜%碳酸钾
NOx%儲存%還原%氧化銅%碳痠鉀
NOx%저존%환원%양화동%탄산갑
NOx%Storage%Reduction%Copperoxide%Potassiumcarbonate
采用连续浸渍法制备了一系列非贵金属稀燃NOx阱(LNT)催化剂CuO-K2CO3/TiO2,考察了Cu负载量对催化剂结构和NOx储存还原性能的影响.发现8%(w) CuO-K2CO3/TiO2催化剂的催化性能最佳,其对NOx的储存量达到1.559 mmol g–1,对NOx的还原效率高达99%,且在NOx还原过程中无副产物N2O产生.应用粉末X射线衍射(XRD),高分辩透射电子显微镜(HR-TEM), CO2程序升温脱附(CO2-TPD),扩展X射线吸收精细结构(EXAFS),氢气程序升温还原(H2-TPR)和原位漫反射红外光谱(in-situ DRIFTS)等技术详细表征了催化剂的结构.结果表明,不同Cu负载量的催化剂中,铜物种均主要以CuO相存在.铜的负载量直接影响铜物种、钾物种的存在状态,高分散的CuO相与表面K2CO3之间存在较强相互作用,这种相互作用不仅有利于NOx的储存,而且有利于增强催化剂的稳定性. in-situ DRIFTS结果表明, NOx储存过程中产生的两个负峰(1436和1563 cm–1)缘于碳酸盐的分解,这间接证明了碳酸盐作为储存介质参与到NOx储存反应中. EXAFS结果表明,经过15个稀燃/富燃循环测试,催化剂中的CuO相仍保持稳定.基于以上表征结果,提出了CuO和K2CO3在催化剂表面的分布模型,并探讨了NOx储存还原的可能机理.
採用連續浸漬法製備瞭一繫列非貴金屬稀燃NOx阱(LNT)催化劑CuO-K2CO3/TiO2,攷察瞭Cu負載量對催化劑結構和NOx儲存還原性能的影響.髮現8%(w) CuO-K2CO3/TiO2催化劑的催化性能最佳,其對NOx的儲存量達到1.559 mmol g–1,對NOx的還原效率高達99%,且在NOx還原過程中無副產物N2O產生.應用粉末X射線衍射(XRD),高分辯透射電子顯微鏡(HR-TEM), CO2程序升溫脫附(CO2-TPD),擴展X射線吸收精細結構(EXAFS),氫氣程序升溫還原(H2-TPR)和原位漫反射紅外光譜(in-situ DRIFTS)等技術詳細錶徵瞭催化劑的結構.結果錶明,不同Cu負載量的催化劑中,銅物種均主要以CuO相存在.銅的負載量直接影響銅物種、鉀物種的存在狀態,高分散的CuO相與錶麵K2CO3之間存在較彊相互作用,這種相互作用不僅有利于NOx的儲存,而且有利于增彊催化劑的穩定性. in-situ DRIFTS結果錶明, NOx儲存過程中產生的兩箇負峰(1436和1563 cm–1)緣于碳痠鹽的分解,這間接證明瞭碳痠鹽作為儲存介質參與到NOx儲存反應中. EXAFS結果錶明,經過15箇稀燃/富燃循環測試,催化劑中的CuO相仍保持穩定.基于以上錶徵結果,提齣瞭CuO和K2CO3在催化劑錶麵的分佈模型,併探討瞭NOx儲存還原的可能機理.
채용련속침지법제비료일계렬비귀금속희연NOx정(LNT)최화제CuO-K2CO3/TiO2,고찰료Cu부재량대최화제결구화NOx저존환원성능적영향.발현8%(w) CuO-K2CO3/TiO2최화제적최화성능최가,기대NOx적저존량체도1.559 mmol g–1,대NOx적환원효솔고체99%,차재NOx환원과정중무부산물N2O산생.응용분말X사선연사(XRD),고분변투사전자현미경(HR-TEM), CO2정서승온탈부(CO2-TPD),확전X사선흡수정세결구(EXAFS),경기정서승온환원(H2-TPR)화원위만반사홍외광보(in-situ DRIFTS)등기술상세표정료최화제적결구.결과표명,불동Cu부재량적최화제중,동물충균주요이CuO상존재.동적부재량직접영향동물충、갑물충적존재상태,고분산적CuO상여표면K2CO3지간존재교강상호작용,저충상호작용불부유리우NOx적저존,이차유리우증강최화제적은정성. in-situ DRIFTS결과표명, NOx저존과정중산생적량개부봉(1436화1563 cm–1)연우탄산염적분해,저간접증명료탄산염작위저존개질삼여도NOx저존반응중. EXAFS결과표명,경과15개희연/부연순배측시,최화제중적CuO상잉보지은정.기우이상표정결과,제출료CuO화K2CO3재최화제표면적분포모형,병탐토료NOx저존환원적가능궤리.
A series of non-platinic lean NOx trap (LNT) CuO-K2CO3/TiO2 catalysts with different Cu loadings were prepared by sequential impregnation, and they showed relatively good performance for lean NOx storage and reduction. The catalyst containing 8%(w) CuO showed not only the largest NOx storage capacity of 1.559 mmol g–1 under lean conditions, but also the highest NOx reduction percentage of 99%in cyclic lean/rich atmospheres. Additionally, zero selectivity of NOx to N2O was achieved over this catalyst during NOx reduction. Multiple techniques, including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), temperature-programmed desorption of CO2 (CO2-TPD), extended X-ray absorption fine structure (EXAFS), temperature-programmed reduction of H2 (H2-TPR), and in-situ diffuse reflectance Fourier-transform infrared spectroscopy (DRIFTS), were used for catalyst characterization. The results indicate that highly dispersed CuO is the main active phase for oxidation of NO to NO2 and reduction of NOx to N2. The strong interaction between K2CO3 and CuO was clearly revealed, which favors NOx adsorption and storage. The appearance of negative bands at around 1436 and 1563 cm–1, corresponding to CO2 asymmetric stretching in bicarbonates and -C=O stretching in bidentate carbonates, showed the involvement of carbonates in NOx storage. After using the catalysts for 15 cycles of NOx storage and reduction in alternative lean/rich atmospheres, the CuO species in the catalysts showed little change, indicating high catalytic stability. Based on the results of in-situ DRIFTS and the other characterizations, a model describing the NOx storage processes and the distribution of CuO and K2CO3 species is proposed.
