【摘要】 用量子化学近似方法研究了HY,HM和HZSM-5,HM的Bronsted酸性质,解释了氨吸附时产生吸附热及羟基振动向低频位移等实验现象,从而讨论了各酸位的相对酸强度,并对HY沸石内四种结构羟基的相对稳定性作了估计.更多还原

【Abstract】 Using quantum chemical method, CNDO/2 scheme, the diagram of the potential energy surface for ammonia adsorption on O_x, site of straight channel was obtained by both adsorption distance and bond length of hydroxyl group. In diagram it was shown that a stable adsorption region is 2.80A>R_ON>2.45A and adsorption heat is 153.6kJ/ mol. On the other hand, when the NH₃ is adsorbed on the acidic OH group of sinusoidal channel of HZSM-5, and on the acidic OH group of straight pockot channel of H⁺-Mordenite zeolite, and on the hydroxyl group of supercage of HY zeolite, the magnitude of adsorbion heats are 163.8, 138.8, 139 and 132kJ/mol respectively. At the same time, the shifts of vibrational frequencies of acidic hydroxyl groups and the protonic degree of adsorbing NH₃ are also calculated when NH₃ is adsorbed on these sites of acidic hydroxyl. All these results are in agreement with the change of acid strength and also in agreement with the experimental values published.For HY zeolite, the order of stability for protons on framework oxygen atoms has been obtained by calculation, it is O₃H≈O₁H>O₂H>O₄H.更多还原