共沉淀法制备无络铁系催化剂的沉淀剂

Precipitants Used in Preparation of Non chromium Iron Based Catalyst by Coprecipitation

通过对离子生成氢氧化物沉淀完全性的理论和实验结果分析，指出用氨水作沉淀剂，共沉淀法制备主组分为铁、镁和锌的无铬铁系丁烯氧化脱氢制丁二烯催化剂时，重现性较差的主要原因在于锌和镁的沉淀不完全。从催化剂组成的稳定性、制备的经济性以及反应性能等方面阐明了氢氧化钠是比氨水更优选的制备无铬铁系催化剂的沉淀剂。通过对催化剂的晶相分析和酸度测定，指出催化剂中的钠是降低催化剂的酸度使其活性和选择性下降的主要原因，大量钠的存在会阻碍催化剂活性晶相的形成。

It was discussed theoretically and tested experimentally that Fe 3+ , Mg 2+ and Zn 2+ could be precipitated completely by ammonium hydroxide and sodium hydroxide, respectively. When ammonium hydroxide was used as precipitant in the catalyst preparation by coprecipitation method, the main components of non chromium iron based catalyst, Fe 3+ , Mg 2+ and Zn 2+ , could not be coprecipitated completely under the same conditions. And this was why the catalyst could not be duplicated easily. As an alternative precipitant,sodium hydroxide was used to prepare non chromium iron based catalyst for oxidative dehydrogenation of n butene to butadiene in co precipitation method. When the precipitate was washed properly, the catalyst prepared by sodium hydroxide showed higher conversion and selectivity than that by ammonium hydroxide used usually. Using cheaper feed and eliminating the feed loss, the cost of the catalyst was reduced in sodium hydroxide technology. The crystal structure and acidity of the catalysts were determined, It was discovered that the sodium in the catalyst reduced its acidity, and this resulted in the decrease of its conversion and selectivity. If the amount of sodium in the catalyst reached a relatively high level, the active crystal structure of the catalyst could not be formed.