金属卟啉在石油加氢脱硫催化剂表面吸附机理的ESR研究

MECHANISM OF THE ADSORPTION OF METALLO-PORPH YRIN ON THE SURFACE OF HDS (Co-Mo-A1_2O_3)

本文用ESR方法研究了金属卟啉在石油加氢脱硫催化剂表面的吸附机理。金属卟啉的模型化合物是VO-TPP,加氢脱硫催化剂是Co-Mo-Al_2O_3体系。VO-TPP在催化剂表面吸附时,由于中心VO^(2+)离子相对于表面有两种不同取向,从而可能发生两种不同模式的吸附:中心1吸附和中心2吸附。一般情况下由于催化剂表面化学吸附了供电基团H_2O、OH^-等,只可能发生中心1吸附。催化剂经高温灼烧后,脱除了表面吸附的供电基团,隔绝空气吸附VO-TPP,这时会出现中心2吸附。中心2吸附中卟啉分子与表面的作用比中心1吸附中卟啉分子与表面的作用强。样品暴露空气后,中心2吸附会逐渐转化为中心1吸附。

This article studies the mechanism of the adsorption of metallo-porphyrin on the surface of HDS catalysts. The model compound used, metallo-porphyrin, is VO-TPP and the HDS catalysis used are Co-Mo-Al2O3 systems. When VO-TPP is adsorbed on the surface of the catalysts, the central ion VO2- has two different orientations to the surface, and will lead to two kinds of adsorptions: center 1 and center 2. In most cases only center 1 can occur because of the adsorption of eletron donor ( H2O, OH-, etc. ) on the cational spots of the surface. When the catalysts are calcined the adsorbed electron donor will be desorbed, and when the calcined catalysts are used to adsorb VO-TPP center 2 will occur. The interaction in center 2 between VO-TPP and the catalysts surface is much stronger than in center 1. But center 2 is less stable than center 1 when the adsorbed sample is exposed to air. It turns into center 1 in air.