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一、导言: 乙烯在负载银催化剂上直接氧化生产环氧乙烷是一个重要的催化过程。银的微晶粒大小对乙烯的氧化存在着影响。Wu和Harriott以及Xenophon等人的研究表明,乙烯在载银催化剂上的氧化反应是结构灵敏反应,比催化活性和选择性与银的微晶粒大小成强烈的函数关系。国内对银催化剂的晶粒形态与催化活性和选择性之间的关系的研究尚未见到详细报导,一般认为银是以二次聚集态的多晶颗粒分布在载体上。钡做为银催化剂的助剂已在工业上广泛应用,但对其作用机理尚有争议。Spath将钡的作用归结为两个方面;一方面是稳定催化剂母体,另一方面是钡盐复盖在银母体上形成以银原子作为施主的半导体膜而发挥催化作用。本文研究了本院一室制备的负载银催化剂上银的晶粒形态及助催化剂钡对银的晶粒形态的影响,并与催化反应的活性和选择性进行了关联。
I. INTRODUCTION: Direct oxidation of ethylene to ethylene oxide over supported silver catalysts is an important catalytic process. The crystallite size of silver has an effect on the oxidation of ethylene. Studies by Wu and Harriott and Xenophon et al. Show that the oxidation of ethylene on a silver-supported catalyst is a structurally sensitive reaction that is more strongly functional than the catalytic activity and selectivity with the silver crystallite size. Domestic studies on the relationship between the morphology of the silver catalyst and the catalytic activity and selectivity have not been reported yet. It is generally believed that the silver is distributed on the carrier by the second aggregation state of polycrystalline particles. Barium as a silver catalyst additives has been widely used in industry, but its mechanism of action is still controversial. Spath boils down the barium effect to two aspects; on the one hand stabilizes the catalyst matrix, on the other hand, the barium salt covers the silver matrix to form a semiconducting membrane on which the silver atom acts as a donor and exerts catalytic action on the silver matrix. In this paper, the effects of the grain morphology of silver on the supported silver catalyst prepared in our laboratory and the effect of barium promoter on the grain morphology of silver were studied, and the relationship between the activity and selectivity of the catalytic reaction was also studied.