钾助剂对Rh/Al_2O_3催化富氢条件下CO选择氧化反应性能的影响

Effect of Potassium Promoter on Reaction Performance of Rh/Al_2O_3 Catalyst for CO Selective Oxidation in H_2-Rich Streams

采用程序升温与原位FT-IR,CO程序升温脱附和X射线衍射等技术研究了钾对Rh/Al2O3催化剂上CO吸附态和表面吸附物种的影响.结果表明,钾未改变金属铑上CO吸附的形态,但削弱了CO的吸附强度;在程序升温(真空中)的动态过程中,120℃时CO线式吸附完全脱除,180℃时CO桥式吸附完全脱除;助剂钾明显促进了表面甲酸盐和碳酸盐物种的形成,同时减弱了Al-Rh的相互作用.讨论了钾存在时甲酸盐和碳酸盐物种的形成机理.

It is indispensable to remove CO to less than 50 × 10^- 6 from a H2-rich feed gas for proton exchange membrane fuel cells. The promoting effect of potassium on the Rh/Al2O3 catalyst has been found in the CO preferential oxidation with O2 under H2-rich streams, CO conversion as high as 99.82% can be achieved, and methanation can be restrained. In this paper, the effect of potassium promoter on CO adsorption states and surface chemisorbed species in the CO selective oxidation process under H2-rich streams over Rh/Al2O3 was investigated by in situ temperature-programming and FT-IR, CO-TPD and XRD. The results indicate that CO adsorption states on Rh/Al2O3 are not changed, but the CO adsorption intensity is weakened when potassium is added. The linear and bridged CO adsorbed on active sites of Rh-K/Al2O3 is fully desorbed at 120 and 180 ℃ , respectively. The mechanism of formate and carbonate species formation is also discussed. The experimental resuits of catalytic activity show that there exists an optimum loading of potassium on the Rh/Al2O3 catalyst to obtain both higher CO conversion and less methane product.