载镍沸石上NH3-TPD脱附峰的非酸性探讨

NH_3-TPD技术表征固体催化剂的酸性似乎已很成熟,其实不然。如该技术表征HZSM-5沸石时,有作者观察到773K左右的高温脱氨峰,而有些作者则检测不到。诚然,各作者间所用试样及预处理条件等存在差异,但实验装置和实验操作条件不同带来的影响也不可忽视。此外,该技术在用于表征一些新的较复杂的催化剂时,其程脱谱也会呈现出新现象,这些现象有时是不能通过酸性来解释的,这是因为NH_3作为探针分子不仅具有碱性,同时还有还原性和配位性。本文对载镍沸石上NH_3-TPD谱图中出现的某些新峰进行了剖析和归属。

PROBE INTO NH_3-TPD CURVE OF Ni-CONTAINING ZEOLITE OUT THE VIEW OF ACIDITY

Two peaks, appeared respectively at Ca. 900 K and 800 K on the NH_3-TPD curve of Ni-containing Y zeolite, have been investigated. These two peaks can't be simply explained by means of acidity. One peak observed at Ca. 90O K, has been contributed to the water gas resulted from the dehydroxylation of zeolite. Another peak, appeared at Ca. 800 K, has been proved to be due to NH_3, formed by decomposation of a complex with the suggested formula Ni~(2+)(NH)_x(OH~-)_(6-x). This complex resulted from the interaction of adsorbed NH_3, the supported Ni~(2+) species and the skeleton OH groups under suitable conditions and decomposed at Ca. 800 K by a first order reaction with an activation energy of about 90.74 kJ·mol~(-1).