Umamaheswari V, Hartmann Martin, Pöppl Andreas
Faculty of Physics and Geoscience, University of Leipzig, D-04103 Leipzig, Germany.
J Phys Chem B. 2005 Jun 2;109(21):10842-8. doi: 10.1021/jp0502914.
The local environments of Cu(I)-NO adsorption complexes formed in zeolites Cu-L and Cu-ZSM-5 were studied by electron spin resonance (ESR), pulsed electron nuclear double resonance (ENDOR), and hyperfine sublevel correlation spectroscopy (HYSCORE). Cu(I)-NO complexes have attracted special interest because they are important intermediates in the catalytic decomposition of nitric oxide over copper exchanged zeolites. Recently, detailed structures of the complexes in Cu-ZSM-5 zeolites, O2-Al-O2-Cu(I)-NO, have been proposed on the basis of quantum chemical calculations (Pietrzyk, et al. J. Phys. Chem. B 2003, 107, 6105. Dedecek, et al. Phys. Chem. Chem. Phys. 2002, 4, 5406). 27Al pulsed ENDOR and HYSCORE experiments allowed the hyperfine coupling parameters of an aluminum nuclei found in the vicinity of the Cu(I)-NO complex formed in zeolite Cu-L to be estimated. The data indicate that the aluminum atom is located in the third coordination sphere of the adsorbed NO molecule in agreement with the suggested geometry of the adsorption sites. Broad distributions of aluminum nuclear quadrupole and hyperfine coupling parameters and short electron spin relaxation times of the Cu(I)-NO species prevented the determination of the 27Al hyperfine couplings for zeolite Cu-ZSM-5.
通过电子自旋共振（ESR）、脉冲电子核双共振（ENDOR）和超精细亚能级相关光谱（HYSCORE）研究了在Cu-L和Cu-ZSM-5沸石中形成的Cu（I）-NO吸附络合物的局部环境。Cu（I）-NO络合物引起了特别的关注，因为它们是铜交换沸石上一氧化氮催化分解的重要中间体。最近，基于量子化学计算（Pietrzyk等人，《物理化学杂志B》2003年，107卷，6105页。Dedecek等人，《物理化学化学物理》2002年，4卷，540页），提出了Cu-ZSM-5沸石中络合物O2-Al-O2-Cu（I）-NO的详细结构。27Al脉冲ENDOR和HYSCORE实验可以估算出在Cu-L沸石中形成的Cu（I）-NO络合物附近发现的铝核的超精细耦合参数。数据表明，铝原子位于吸附的NO分子的第三配位球中，这与所建议的吸附位点几何结构一致。铝核四极矩和超精细耦合参数的广泛分布以及Cu（I）-NO物种的短电子自旋弛豫时间阻碍了对Cu-ZSM-5沸石中27Al超精细耦合的测定。
