原位红外光谱法研究脱铝Y型沸石表面羟基及异丙苯裂解反应

In-Situ IR Spectra Studies of the Surface Hydroxyl Groups and Cumene Craccking on Dealuminated Y Zeolites

本文用原位红外光谱法,以自行设计的红外池,采用流动体系研究了NH_4Y及用EDTA配位脱铝的Y型沸石上的表面羟基,苯及异丙苯在不同温度下的吸附,以及用脉冲进样原位红外研究了异丙苯裂解反应,发现在脱铝Y型沸石(DAlY)中除Y型沸石原有的3620和3535cm^(-1)表面羟基峰外,在3724cm^(-1)处又出现一个与脱铝“空穴”Si—OH有关的吸收峰,且此峰随脱铝量增加而增加,脱氨过程的研究表明超笼中羟基具有酸性,苯及异丙苯在Y型或DAlY型沸石上均与超笼中羟基作用,在360℃时异丙苯裂解反应的活性中心主要是超笼中羟基,催化剂失活主要是由于炭沉积在活性位上所致。

The process of deammonation and the characteristics of surface hydroxyl groups of NH_4Y and DAlY, the H_4EDTA dealuminated produce, were examined by in-situ IR spectra. The adsorption of benzene and cumene, as well as the cumene cracking reaction on theses amples were also studied by the same method. There are two OH frequencies at 3620 and 3535 cm^(-1) on Y zeolite, corresponding to the OH groups situated in supereage and sodalite cage, respectively. While on DAlY a new band at 3724 cm^(-1) appeared which was assigned to the frequencies of Si—OH located in the empty hole resulted from the dealumination. After the adsorption of benzene and cumene on the Y and DAlY zeolites, the 3620cm^(-1) band disappeared, which implies that the adsorption occurred in the supercages. The acidic OH groups absorbed at 3620 cm^(-1) are the main active sites of the cumene cracking.