Kolyagin Yuriy G, Ivanova Irina I, Pirogov Yuri A
Department of Chemistry, Moscow State University, Lenin Hills 1/3, 119991 Moscow, Russia.
Solid State Nucl Magn Reson. 2009 Apr;35(2):104-12. doi: 10.1016/j.ssnmr.2009.01.005. Epub 2009 Feb 12.
The early stages of methane, ethane and propane conversion were studied by in situ (1)H and (13)C MAS NMR techniques over fully exchanged Zn(2+)/MFI catalyst obtained by the reaction with zinc vapour. The in situ techniques revealed strong interaction of alkanes with Zn(2+) cations evidenced by significant shift of the corresponding NMR lines. Besides that, the formation of methyl zinc, ethyl zinc and n-propyl zinc species along with bridging and silanol surface OH-groups was detected already at the ambient temperature. These results pointed to dissociative adsorption of alkanes over (ZO)-Zn(2+)-(OZ) and (ZO)-Zn(2+)-(OSi) active sites of the catalyst. The dissociative adsorption was shown to be a dead-end surface reaction in the case of methane starting reactant, while in the case of ethane and propane, it appeared to be responsible for the initiation of the catalytic cycle leading to alkenes and dihydrogen formation and regeneration of zinc containing catalytic sites.
通过原位¹H和¹³C MAS NMR技术，对与锌蒸汽反应制得的完全交换的Zn²⁺/MFI催化剂上甲烷、乙烷和丙烷转化的早期阶段进行了研究。原位技术揭示了烷烃与Zn²⁺阳离子之间的强相互作用，这由相应NMR谱线的显著位移证明。除此之外，在室温下就已检测到甲基锌、乙基锌和正丙基锌物种以及桥连和硅醇表面OH基团的形成。这些结果表明烷烃在催化剂的(ZO)-Zn²⁺-(OZ)和(ZO)-Zn²⁺-(OSi)活性位点上发生解离吸附。对于甲烷起始反应物，解离吸附是一种终端表面反应，而对于乙烷和丙烷，它似乎是催化循环引发的原因，导致烯烃和二氢的形成以及含锌催化位点的再生。
