| Polymer electrolyte membrane fuel cells (PEMFC), which have better energy efficiency than the conventional combustion engines and a zero-emission of air pollutants, have received much attention as a potential power source of electric vehicles. Restricted by the distribution and storage of hydrogen, the H2 feed gas of PEMFC is usually produced by steam reforming, partial oxidation or combination of the above techniques from methanol, natural gas. Since the PEMFC is operated at relatively low temperatures (80℃), its Pt-anode catalyst is extremely sensitive to CO contaminant (1%) in reformed gases, which will poison the catalyst and decrease the performance. Therefore, it is essential to remove the trace CO in Ha feedgas. Among the currently available methods for removing CO from H2-rich feedgas, the selective catalytic oxidation of CO with molecular oxygen is undoubtedly the most straightforward, simplest, and the most economic one. Catalysts so far proposed for this process are mainly noble metals, such as Pt, Rh, Au. However, decreasing the reaction temperatures and seeking for more economic catalysts for CO selective oxidation are the research focuses of the near future. It is well known that silver catalysts are unique for partial oxidation reactions and is not so precious as other noble metals used currently.Based on this idea, silver catalyst is a good candidate for CO selective oxidation in H2 feedgas. The effects of supports, silver loading, and reaction temperatures et al. on the activities of silver catalysts, as well as the correlation between the surface structure of silver and reaction activity, are investigated. The surface restructuring, redispersion model and the reaction mechanism for CO oxidation over silver surfaceare proposed. The following research works have been conducted:1. SiO2 is a good support of silver catalysts for CO selective oxidation. An appropriate content and distribution of silanol favors the silver particles dispersion. For zeolite support, the catalytic activity increases with the increasing of Si/Al ratio of the zeolites. The strong interaction between Ag and Al decreases the catalysts activity. Mesoporous silica materials as SB A-15, MCM-41 zeolites are also found to be better supports of silver catalysts for CO selective oxidation at low temperatures.2. Ag/SiO2 catalysts have a good performance for CO selective oxidation at low temperatures, and are quite stable. With the increasing of silver loading, the reaction rate increases and reaction temperature decreases. TPD and CO-TPSR results show that the amount of sub-surface oxygen increases with the silver loading. Thus more active [O] species will be supplied, and react with CO at much lower temperatures (-10) over silver catalyst with higher loading.3. The surface oxygen species formed by oxygen treatment at low temperatures (100-300) following H2 treatment at 500 block the adsorption of gas oxygen species, and further deactivate the silver catalysts, indicating that it is very essential to obtain a clean silver surface for CO selective oxidation. However, pretreatment with O2 at higher temperatures (>350) distinctly improves the catalytic performance at low temperatures. The stability of silver particles decreases at higher temperatures than 350, and more sub-surface oxygen species are formed. Reduction with H2 at low temperatures following the oxygen treatment at high temperatures increases the catalytic activity due to the further dispersion of silver particles; however, hydrogen reduction at higher temperatures decreases the activity and selectivity. Oxygen treatment at high temperatures will reactivate the silver catalysts. Interestingly, the changes in activity are mostly reversible.4. It is firstly observed that the reaction of CO and oxygen over silver catalysts treated by H2 at low temperatures (100-300℃) following oxygen treatment at 500℃ may occur at -75 by In-situ FTIR technique. Adsorbed CO gives a lower frequency after H2 reduction due to an increase in elec...
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