在常压同定床反应器上考察了不同载体担载的Rh催化剂上的甲烷溴氧化反应,发现在惰性载体SiC和SiO_2担载的Rh催化剂上溴代甲烷选择性较高,而以金属氧化物ZrO_2和TiO_2为载体的Rh催化剂上易发生深度氧化.程序升温还原实验表明,惰性载体担载的Rh催化剂更难还原.热力学数据分析表明,在所考察的温度区间内,提高反应温度有利于-溴甲烷水汽重整反应的进行.惰性载体担载的Rh催化剂活性高可归因于Rh适中的氧化还原能力,抑制了溴甲烷水汽重整反应的进行.由于Rh/SiC显示出较高的甲烷转化率和溴代甲烷选择性,因此对该催化剂的Rh载量和反应条件进行了优化.结果表明,在620℃,气、液空速分别为900和3.0ml(g·h)条件下,甲烷单程转化率和溴代甲烷总选择性分别保持在20%和90%以上,并且连续反应100h未发生催化剂失活.
Oxidative bromination of methane over Rh-based catalysts supported on different carriers was studied using a conventional fixed-bed reactor at atmosphere pressure. It was found that inert supports such as SiC and SiO_2 were in favor of the selectivity for bromomethanes, whereas deep oxidation occurred over ZrO_2 and TiO_2 oxides. H_2-temperature-programmed reduction experiments confirmed that inert carrier-supported Rh catalysts were more difficuR to be reduced than the metal oxide-supported Rh catalysts. Thermodynamic analysis revealed that the steam reforming of bromomethanes was promoted at higher reaction temperatures. It was concluded that the supe-rior performance of the inert carrier-supported catalysts could be ascribed to the medium redox ability, which suppressed the steam reforming reaction. Among the catalysts studied, Rh/SiC showed the highest methane conversion and selectivity for bromomethanes, and therefore the key parameters of catalyst preparation and reaction conditions were optimized on this catalyst. About 20% methane conversion and 90% total selectivity for bromomethanes were achieved on a single pass at 620 ℃ with the gas hourly space velocity and liquid hourly space velocity of 900 and 3.0 ml/(g·h),respectively.No deactivation happened during 100 h time-stream.
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