物理化学学报
物理化學學報
물이화학학보
ACTA PHYSICO-CHIMICA SINICA
2013年
4期
723-730
,共8页
王晨%魏子章%吕永康*%邢斌%王贵昌*
王晨%魏子章%呂永康*%邢斌%王貴昌*
왕신%위자장%려영강*%형빈%왕귀창*
苯乙烯%选择性氧化%结构敏感%银催化剂%密度泛函理论计算
苯乙烯%選擇性氧化%結構敏感%銀催化劑%密度汎函理論計算
분을희%선택성양화%결구민감%은최화제%밀도범함이론계산
Styrene%Selective oxidation%Structure sensitivity%Ag catalyst%Density functional theory calculation
采用密度泛函理论(DFT)对苯乙烯在Ag(110)表面和Ag(111)表面的环氧化反应进行了计算研究.经计算,在Ag(110)表面预吸附氧原子更易吸附在3重穴位(3h),吸附能为-3.59 eV;在Ag(111)表面预吸附氧原子的最稳定吸附位是fcc位,吸附能为-3.69 eV.苯乙烯的环氧化反应过程首先经过一个金属中间体,然后再进一步反应变为产物,其中经过直链中间体较支链中间体更加有利. Ag(110)面的反应活化能一般大于Ag(111)面的,并且微观动力学模拟结果表明, Ag(111)表面生成环氧苯乙烷的选择性要明显高于Ag(110)表面(0.38与0.003),原因是Ag(111)面环氧化反应活化能小于苯乙醛及燃烧中间体的活化能,而在Ag(110)上正相反.
採用密度汎函理論(DFT)對苯乙烯在Ag(110)錶麵和Ag(111)錶麵的環氧化反應進行瞭計算研究.經計算,在Ag(110)錶麵預吸附氧原子更易吸附在3重穴位(3h),吸附能為-3.59 eV;在Ag(111)錶麵預吸附氧原子的最穩定吸附位是fcc位,吸附能為-3.69 eV.苯乙烯的環氧化反應過程首先經過一箇金屬中間體,然後再進一步反應變為產物,其中經過直鏈中間體較支鏈中間體更加有利. Ag(110)麵的反應活化能一般大于Ag(111)麵的,併且微觀動力學模擬結果錶明, Ag(111)錶麵生成環氧苯乙烷的選擇性要明顯高于Ag(110)錶麵(0.38與0.003),原因是Ag(111)麵環氧化反應活化能小于苯乙醛及燃燒中間體的活化能,而在Ag(110)上正相反.
채용밀도범함이론(DFT)대분을희재Ag(110)표면화Ag(111)표면적배양화반응진행료계산연구.경계산,재Ag(110)표면예흡부양원자경역흡부재3중혈위(3h),흡부능위-3.59 eV;재Ag(111)표면예흡부양원자적최은정흡부위시fcc위,흡부능위-3.69 eV.분을희적배양화반응과정수선경과일개금속중간체,연후재진일보반응변위산물,기중경과직련중간체교지련중간체경가유리. Ag(110)면적반응활화능일반대우Ag(111)면적,병차미관동역학모의결과표명, Ag(111)표면생성배양분을완적선택성요명현고우Ag(110)표면(0.38여0.003),원인시Ag(111)면배양화반응활화능소우분을철급연소중간체적활화능,이재Ag(110)상정상반.
@@@@The selective oxidation of styrene on oxygen-covered Ag(110) and Ag(111) surfaces is studied by density functional theory (DFT) calculations with the periodic slab model. On the Ag(110) surface, a pre-adsorbed oxygen atom prefers the 3-fold hol ow site (3h) with an adsorption energy of-3.59 eV. On the Ag(111) surface, the most stable adsorption site for a pre-adsorbed oxygen atom is the fcc site, and the adsorption energy is-3.69 eV. The reaction process of the selective oxidation of styrene includes two steps: the formation of surface intermediates (branched oxametal acycle and linear oxametal acycle) and the subsequent formation of different products. The calculated results show that the formation of styrene oxide via the linear oxametal acycle (i.e., the pre-adsorbed atomic oxygen bound to the methylene group in styrene) is the favorable reaction mechanism on both Ag(110) and Ag(111) surfaces. The reaction barriers for the different reaction steps of styrene epoxidation on the Ag(110) surface are general y higher than those on the Ag(111) surface. Moreover, the micro-kinetic simulation results indicate that the relative selectivity towards the formation of styrene oxide on the Ag(111) surface is much higher than that on the Ag(110) surface (0.38 vs 0.003) because the energy barrier for the styrene epoxidation is smal er than that for the formation of phenyl acetaldehyde and its combustion intermediate on Ag(111) surface. The reverse trends occurred on the Ag(110) surface.
