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为了探明在NiX沸石催化剂上乙烯二聚反应诱导期的成因和活性中心的本质,考察了在反应过程中镍离子与乙烯分子的相互作用。发现诱导期随催化剂的预处理温度的提高而缩短,也随Ni_(2+)离子交换度的增加及反应温度的升高而缩短。用H_2进行NiX催化剂预还原,且在ESR谱中证实Ni~+存在的情况下反应诱导期并不消失,而在反应条件下用乙烯进行样品预处理后则没有诱导期。并且伴随着诱导期的消失和二聚反应的开始,在NiX的ESR谱上出现一组新信号。这组新信号可能是Ni~+离子与乙烯相互作用形成的表面活性物种引起的,它的生成导致了诱导期的消失。提出了在乙烯二聚反应过程中催化剂的活化图式。
In order to find out the origin of the induction period and the active center of the ethylene dimerization reaction on the NiX zeolite catalyst, the interaction between nickel ions and ethylene molecules during the reaction was investigated. It was found that the induction period shortened with the increase of the catalyst pretreatment temperature and also shortened with the increase of the ion exchange degree of Ni 2+ and the reaction temperature. HX was used to pre-reduce the NiX catalyst, and the reaction induction period did not disappear in the presence of Ni ~ + in the ESR spectrum. However, there was no induction period after sample pretreatment with ethylene under the reaction conditions. And along with the disappearance of the induction period and the start of the dimerization reaction, a new set of signals appear on the ESR spectrum of NiX. This new set of signals may be caused by the surface active species formed by the interaction of Ni ~ + ions with ethylene, and its formation leads to the disappearance of the induction period. Proposed catalyst in the ethylene dimerization reaction activation scheme.