摘要
用ESR表征了几种Cu(Ⅱ)-A沸石中Cu^(2+)离子物种,发现在铜含量较高(5.20wt%)的样品中,偶极-偶合的Cu^(2+)离子对占压倒优势,而孤立的Cu^(2+)离子则很少.样品还原后的ESR结果表明,偶极-偶合的Cu^(2+)离子对至少存在着两种不同类型的物种.结合ESR、XPS和XRD方法,研究了Cu(Ⅱ)-A沸石中共存阳离了Mn^(2+)的效应,并讨论了Cu^(2+)和Mn^(2+)两种离子间的氧化还原反应.
The Cu2+ species in Cu ( Ⅱ ) -A zeolites has been characterized by ESR.It was found that the dipole-coupled Cu2+ pairs are the predominate species and the isolated Cu2+ ions are the minor one in the Cu ( Ⅱ ) -A sample with higher copper content ( 5.21wt% ) .As compared with the dipole-coupled Cu2+ pairs, the isolated Cu2+ ions are reduced more difficultly by carbon monoxide, but they can easily be reduced by hy drogen .The existence of two kinds of dipole-coupled Cu2+ pairs was suggested on the basis of the results of ESR measurement of samples after reduction .The reversal of g values (g2I (2.083)>gu2 (2. 049) was observed when the sample with lower copper content (3.0 wt%) was heated at 310℃, which may be attributed to the formation of [Cu ( O2 ) 3 ( H2O ) 2 ] 2+ species . Combining the results of ESR with those of XPS and XRD,the effects of coexisting cation Mn2+ onCu(Ⅱ)-A zeolites were investigated. The ESR signal of Mn2+ ion was observed in the fresh MnCuA sample and disappeared during dehydration of the sample. The decrease in binding energy of Cu2p3/2 for the dehydrated MnCuA sample revealed that the addition of Mn2+ ions to Cu ( Ⅱ )-A zeolites leads to the reduction of Cu2+ to Cu+ .The possibility of auto-reduction of Cu2+ ions with O2- ions in lattice was excluded due to the rather perfect crystal of MnCuA sample. The redox reaction between Cu2+ and Mn2+ ions was discussed.
出处
《分子催化》
EI
CAS
CSCD
1989年第3期230-234,共5页
Journal of Molecular Catalysis(China)
