铁锆混合交联蒙脱土的酸性和催化性能研究

^STUDY OF THE ACIDITY AND ACID-CATALYTIC PROPERTY OF Fe-Zr-PILLARED CLAYS

制备了锆交联蒙脱土（Ｚｒ─ＰＩＬＣ）和铁锆混合交联蒙脱土（Ｆｅ─Ｚｒ─ＰＩＬＣ─１／４，Ｆｅ─Ｚｒ─ＰＩＬＣ－１／５），并用吡啶吸附红外光谱和氨程序升温脱附等方法对其酸性进行了研究。结果表明：Ｆｅ－Ｚｒ－ＰＩＬＣ－１／４，Ｆｅ－Ｚｒ─ＰＩＬＣ－１／５与Ｎａ─原土相比，中强酸和强酸酸量均增加，而与Ｚｒ─ＰＩＬＣ相比，中强酸和强酸酸量均减少，且中强酸强度减弱。以甲醇胺化反应为探针研究了样品酸催化活性。结果表明：Ｆｅ－Ｚｒ－ＰＩＬＣ─１／４和Ｆｅ－Ｚｒ－ＰＩＬＣ－１／５活性比Ｎａ─原土高，但低于Ｚｒ－ＰＩＬＣ。起酸催化作用的主要是Ｌ酸中心。

Hydroxy Zr pillared(Zr-PILC)and hydroxy-Fe-Zr pillared clays (Fe-Zr-PILC-1/4,Fe-Zr-PILC-1/5) hare been prepared by the reaction of Na-montmorillonite with base-hydrolyzed solution of Zr and Fe salts.The acid properties of the samples were studied using infrared spectroscopy of pyridine adsorption and temperature-programmed des orption of ammonia techniques. For Na-montmorillonite, two pyridine adsorbed IR peaks at 1447cm-1 the 1489cm-1 characteristic of Lewis acid site are observed, after pillaring with ZrO2a new peak at 1545cm-1 contributed to Bronsted acid appears and the peak intensity of 1447cm-1 is increased.While introducing iron oxide as the second component of the pillar,the 1447cm-1 peak indensity is decreased.From the IR specra of pyridine desorbed at different temperaures,it can be seen that all these peaks are weakened with increasing of the desorption temperature.After being desorbed at 400℃, the 1545 cm-1 IR peak disappears;it reveals that the strength of Bronsted acid is weaker than that of Lewis acid.NH3 TPD results show that there are mainly two desorption peaks; the first peak is located at the temperature range of 185￣203℃ and the second one is at a temperature region higher than 350℃.Compared to Na-montmorillonite,for Zr-PILC the desorption peak intensity is stronger the the amount of desorbed NH3 is much larger. Introducing iron oxide as the second component of the pillar would cause the decrease of the peak intensity the the amount of desorbed NH3 as well.The TPD pattern shows that for Fe-Zr-PILC there is a shoulder appearing at 300℃;it suggests that a new acid-site is formed.Methanol amination is used as a probe reaction to determine the acid catalytic activity of PILC.At the temperature lower than 400℃ the catalytic activity for methanol amination is very low for all the samples. Over Zr-PILC,the methanol conversion reaches 97. 6% at 400℃,which is much higher than that of 32. 8% OVer Na-montmorillonite. For the Fe-Zr-PILC-1/5 and Fe-zr-PILC-1/4 samples the methanol conversion is 72. 2% and 49.7% respectively. Apparently, the catalytic activity increases with increasing of the total amount of the acid determined by TPD of NH3.Since the IR results show that the B acid site disappears beyond 400℃,the catalytic activity of methanol conversion should be related to the L acid site.At 400℃ the DMA selectivity is very low over all the samples,and it increases with the reaction temperature.On the other hand, for all the samples the greatest DMA selectivity is similar and although the total acid amount is different the ratio of the medium strong acid the strong acid amount is similar. According to the above results,we suggest that there is a certain correlation between the DMA selectivity and the ratio of medium strong to srong acid amount.