Au/HZSM-5沸石催化剂的正丁烷异构化反应性能的研究

采用脉冲微反装置评价了纯正丁烷、含有不同比例异丁烷的混合丁烷在Au改性的纳米HZSM-5催化剂上的反应活性和异构化选择性。结果表明,在300℃时,载金量为1.31%的催化剂上纯正丁烷原料的转化率可达7.0%,异丁烷选择性可达80%以上。相比之下,在纳米HZSM-5载体上正丁烷的转化率只有0.55%,异丁烷选择性仅为11.67%。在Au负载量为0.12%~1.91%,随着Au负载量的增加,正丁烷转化率先增后减,异丁烷选择性在低负载量时增加明显。在反应温度低于400℃时,纯正丁烷在载金催化剂上主要发生异构化反应;高于400℃时,主要发生裂解和芳构化等反应,即400℃是正丁烷在脉冲微反条件下异构化和裂解等反应的分水岭。另外,混合丁烷的组成对正丁烷异构化反应有一定影响,但在适当温度下正丁烷异构化时裂解产物很少,表现出金属-酸双功能催化特征。Au⁺在反应中发挥了脱氢和加氢作用。

Performance of Au/HZSM-5 catalysts for the isomerization reaction of n-butane

The activity and selectivity to isomerization of pure n-butane and mixed butane (with different proportions of iso-butane) of Au/HZSM-5 catalysts were evaluated using a micro-scale pulse reactor. Results showed that the conversion of pure n-butane was above 7.0% and the selectivity to iso-butane could be as high as 80% on Au/HZSM-5 catalysts with 1.31% Au loading at 300℃. By contrast, the conversion of n-butane and the selectivity to iso-butane was only 0.55% and 11.67% on the HZSM-5 supporter. The conversion of n-butane increased firstly and then decreased with the increase of Au loading at a range of 0.12%~1.91%. The selectivity to iso-butane increased with increase of Au loading apparently when Au loading was at a low level. When reaction temperature was lower than 400℃, the main reaction on Au/HZSM-5 catalyst was isomerization of pure n-butane. When the temperature was higher than 400℃, the main reactions were dissociation and aromatization. 400℃ was the watershed of dissociation and aromatization under the reaction conditions of micro-scale pulse reaction. Additionally, the composition of mixed butane had certainly influence on the isomerization reaction of n-butane. But the products in the isomerization reaction of n-butane were very rare at proper reaction temperature, showing a metal-acid bifunctional catalytic character. The species of Au⁺ possibly played an important role in the dehydrogenation and hydrogenation reactions.