Controllable Construction Of Copper-cerium Catalysts And Their Deactivation Performances For Preferential Oxidation Of Carbon Monoxide

As the feeding gas of proton exchange membrane fuel cells?PEMFCs?,hydrogen produced by industry requires the extremely low CO content?<100 ppm?,otherwise it will poison the Pt electrode of the fuel cell.The preferential oxidation of carbon monoxide?CO-PROX?is an important way to purify carbon monoxide in hydrogen.Copper-cerium catalysts become the preferred materials for CO-PROX reactions with low cost and high activity.The Cu⁺species and the synergistic effect between copper and cerium have been proven to promote the oxidation of CO.However,the comparison between the reported results is different due to the difference between the catalysts and the reaction conditions in the long-term research,so the deactivation mechanism of the catalysts is inconclusive.Therefore,it is very important to theoretically investigate the origin of deactivation mechanism.In view of this,CeO₂material with high oxygen storage capacity is selected as the support,and the catalysts with high Cu⁺species content and strong copper-cerium synergy are designed and prepared to improve the CO-PROX performance.Through experiments and calculations,the catalysis and deactivation mechanism of copper-cerium-based catalysts are clarified.The specific research contents are as follows:Au@CuO_x/CeO₂ catalysts with different Au core sizes were prepared by the sodium citrate reduction method.In this work,Au@CuO_x core-shell nanometer microreactors can perform a restricted effect on Au.The experimental results show that the difference in Au core size greatly affects the catalytic activity.Au cores with large size can promote the interaction between Au-Cu and Cu-Ce species,and thus promote the increase of CO-PROX activity.A series of CuO/CeO₂ catalysts were prepared by the hydrothermal method.By changing the content of CuO on the surface of the CeO₂ support,experimental and calculation results show that 10%-CuCe performs best in the catalytic performance,which is derived from the higher Cu⁺species and Ce³⁺content.In addition,comparing the chemical state of the surface of 10%-CuCe before and after the reaction,it is found that after undergoing three test cycles and stability tests of up to38 hours,the 10%-CuCe catalyst had a slight decrease in Ce³⁺and O?%contents on the surface and the production of Cu⁰ reduced the active sites,which are the main cause of activity loss.On the other hand,both H₂O and CO₂ resistance performance tests and DFT calculations show that under the conditions of simultaneous addition of CO₂ and H₂O,CO₂ adsorbs on the surface of the catalyst and occupies the active sites,resulting in the reduction in the adsorption sites of CO and catalytic activity,which makes the catalyst show poor resistance to CO₂ and strong resistance to H₂O.In order to promote the valence diversity of copper oxide species on the surface of copper-cerium catalysts,a series of CuO_x/CeO₂ catalysts were prepared by adding hydrazine hydrate.The sources of Cu⁺and Ce³⁺active species that affect the catalytic process and the changes of copper and cerium species during the calcination process were further explored.The experimental results show that the addition of reducing agent effectively promotes the diversity of copper species on the catalyst surface,thereby affecting the performance of CO-PROX.It is found that the addition of reducing agents resulted in the production of a large number of low-valent copper species,which weakened the synergy between Cu-Ce species.Combined with XPS and Raman results,it is proved that the strong interaction between copper and cerium also promotes the generation of more oxygen vacancies and enhances the surface oxygen cycle.