Catalytic Activity Of Transition Metal Nitrides For The Eferential Oxidation Of CO In H₂Rich Stream

Proton exchange membrane fuel cell （PEMFC） is a new type a clean and efficient greenbattery, which is pollution-free and has high energy conversion when used as power. However,the H2-rich feed gas applied in the anode pole of PEMFC contains trace amount of CO thatwould poison the platinum electrode. Therefore, the trace CO must be removed. Among thevarious ways available to remove CO, preferential CO oxidation （PROX） has been regardedas the most promising method. The commercial PROX catalyst is based on the precious metalof platinum. Due to the similar catalytic properties as platinum, transition metal nitrides andphosphides have attracted much interest. In this paper, transition metal nitrides andphosphides have been first studied in the PROX reaction. Some preparation conditions suchas synthesis temperature, preparation method and metal loading were investigated. Thecatalysts were characterized by means of XRD, BET, XPS, chemisorption, etc.The γ-Al₂O₃supported transition metal nitrides （Co₄N, Mo₂N, Fe₃N and W₂N） wereprepared with impregnation method. The results showed the best PROX activity ofCo₄N/γ-Al₂O₃catalyst. With synthesis temperature of700oC, the CO convertion of3wt%Co₄N/γ-Al₂O₃at200oC and220oC were⁹6%and¹00%, respectively, as well as goodstability.The supported cobalt-platinum catalysts for PROX reaction were investigated in thispaper. By investigating the conditions of synthesis temperature, the metal loading of cobaltand platinum and so on, the results suggested that20wt%Co₄N/2wt%Pt/γ-Al₂O₃catalysthad the best activity with synthesis temperature of700oC. The CO convertion reached almost100%at80oC and had good stability. When10%H2O and15%CO₂were added to the feedgas, the CO convertion maintained above90%with good stability. Through the O₂and COchemisorption results, it was deduced that, low-temperature oxidation of CO onCo₄N/Pt/γ-Al₂O₃catalyst would obey a dual-site non-competitive mechanism, where Pt actedas a CO adsorption site and Co served as an O₂activation site, respectively. Hence,Co₄N/Pt/γ-Al₂O₃catalyst exhibited a high CO-PROX activity at low temperatures and mayhas a promising prospect for application.Transition metal phosphides were studied in PROX reaction. The results showed that,unsupported Co₂P catalyst had preferable activity. The CO convertion reached almost100%at200oC and had good stability. While as to γ-Al₂O₃supported Co₂P catalyst, the COconvertion was about98%at220oC.