富氢气氛下CO选择性氧化催化剂Pt/γ-Al_2O_3中添加钴的作用

Effect of Cobalt in Modifying Pt/γ-Al_2O_3 Catalyst for Preferential Oxidation of CO in Hydrogen rich Stream

研究了Pt/γAl2O3催化剂上添加Co对降低Pt负载量的效应,同时通过XRD,COTPD,H2TPR和FTIR等手段对Co助催的Pt/γAl2O3催化剂进行了表征,藉此探讨了Co的改性作用.实验结果表明,在Pt/γAl2O3催化剂中添加Co可显著降低Pt的用量和改善低温活性.在Pt负载量为wPt=0.01,Co添加量为wCo=0.015～0.03时,在φO2/φCO=1.0和120℃的较低温度下,CO转化率和O2选择性分别高达99%和47%以上.在Pt/γAl2O3催化剂中添加的Co以不完全还原的CoOx形态存在,不仅可以提供活泼氧与CO反应生成CO2,而且影响Pt的电子性能,使之较难还原.Co的引入还削弱了CO在Pt上的吸附,使CO线式吸附物种消失,同时使碳酸氢盐和甲酸盐吸附物种增加.随温度升高,Co/Pt/γAl2O3催化剂上碳酸氢盐物种消失并转化成CO2.

Carbon monoxide is a poison to the Pt anode in proton exchange membrane fuel cell (PEMFC). Preferential oxidation (PROX) over Pt/ γ Al 2O 3 catalyst is an effective method to reduce CO in hydrogen rich gas streams to a tolerant level. In this paper, the effect of adding Co to Pt/ γ Al 2O 3 catalyst on lowering Pt loading and improving catalytic properties was investigated. Experimental results showed that the addition of Co to Pt/ γ Al 2O 3 could not only improve the activity at low temperature but also reduce significantly the Pt loading in the catalysts. Over the catalysts with Pt loading of w Pt =0.01 and Co loading of w Co =0.015～0.03 and in the conditions of temperature at 120 ℃ and φ O 2 / φ CO =1.0, the conversion of CO could reach over 99% and the selectivity of O 2 was 47%. The results of characterization by XRD, CO TPD, H 2 TPR and FTIR revealed that in the promoted catalyst there existed incompletely reduced cobalt oxides, which not only provided active oxygen to CO to the formation of CO 2 but also affected the electronic property of Pt, leading to a more difficult reduction of Pt. Furthermore, the addition of Co weakened the adsorption of CO on Pt, inhibited the linear adsorption of CO on Pt, and increased the surface adsorption of bicarbonate and formate species. Bicarbonate species diminished quickly and turned into CO 2 over Co/Pt/ γ Al 2O 3 with increasing temperature.