【摘要】 利用红外光谱方法考察了在Pt/Al₂O₃催化剂上Pt晶粒大小和共吸附H₂O对CO吸附态的影响。共吸附H₂O可使CO在Pt/Al₂O₃上的线式吸收带产生远大于文献报道过的红移(△vco=40厘米^-1 ),谱带宽化和强度增加,而在Pt/SiO₂催化剂上则没有发现类似的效应。还发现CO的吸收带位置因Pt粒子大小不同而异,当D_pt足够大时,在共吸附H₂O的作用下,CO在Pt/Al₂O₃上的线式吸收带分裂成双峰,其中高波数峰对H₂O的作用不敏感,低波数峰对H₂O的作用敏感。提出了Al₂O₃表面羟基可以和CO吸附态之间形成氢键的观点,可用以解释在Al₂O₃上高分散的Pt上和纯Pt金属表面上CO吸附态的不同特征。更多还原

【Abstract】 Pt/Al2O3 catalysts of different dispersion with adsorbed CO have been studied by infrared spectroscopy. A remarkable effect of particle size on the absorption band of linear CO was observed both in the presence or absence of co-adsorbed water. For catalysts of higher dispersion, only a single absorption band of linear CO emerged with its peak position at lower wave number, which was further shifted to the red side by co-adsorbed water. The red shift(v=40cm-1) results from the co-adsorbed water is much higher than that (v-15cm-1) reported in literature.?In the case of catalysts of lower dispersion, the co-adsorbed water splitted up clearly the absorption band of linear CO into two bands, a nonshifted band at high wave number and a shifted one at low wave number. But such effect is not observed in the case of Pt/SiO2 catalysts. A H-bonding model for explanation of the profound effect of co-adsorbed water on the absorption band of linear CO is proposed, it is suggested that in addition to the d-n back-donating bond between Pt site and adsorbed species of CO, a hydrogen bond between the adsorbed CO on Pt and the co - adsorbed water on alumina will be operative on Pt/Al2O3 catalysts.更多还原