【摘要】 用XPS、ESR及高分辨固体NMR考察了在PdY沸石上乙烯双聚反应中活性中心钯离子的价态和位置。XPS的实验结果表明,双聚反应的活性价态为一价的Pd~+离子。同时,ESR的结果表明,用乙烯对样品进行预处理,在诱导期消失,双聚反应开始时,ESR谱上出现一新信号,它可能是乙烯与Pd~+配位形成的表面活性物种所引起的,它的生成导致诱导期的消失。NMR的结果证实了PdY沸石中阳离子在沸石笼之间的迁移现象,而XPS的实验结果又证实了钯离子在催化剂体相和表面间的迁移。提出了乙烯双聚反应中PdY催化剂的活化图式。更多还原

【Abstract】 The valent state and the location of the palladium ions in PdY zeohte for ethylene dimerization have been studied with the aid of XPS, ESR and high resolution NMR. The XPS results showed that the binding energy of Pd was gradually decreased with raising the evacuation temperature from 100℃ to 500℃,while the activity of PdY gave a maximum. It was suggested that the intermediate-valent state of Pd might be the active state for ethylene dimerization.The ESR results showed that the Pd+ ions were formed during evacuation, therefore the intermediate-valent state or active state was Pd+. A new signal appeared on the ESR spectra of PdY catalyst after pretreatment of PdY with ethylene which eliminated the induction period,it was suggested that the new species characterized by the new signal was probably catalytically active intermediate formed by the coordination of Pd+ with ethylene molecules. The 23NaNMR studies indicated there was cation migration among zeolite cages during calcination and evacuation of PdY zeolites and their activation by ethylene, while the XPS studies also indicated there was a migration of palladium ions between bulk and surface of the catalyst. An activation pattern of PdY zeolite in ethylene dimerization was proposed,the complex formed by the coordination of Pd+ located in supercage of the catalyst with ethylene might be the active site for ethylene dimerization.更多还原