Study On The Conversion Performance Of Carbon Monoxide Supported Gold Catalysts By Praseodymium Complex Oxide

Due to the unique electronic layer structure and lanthanide shrinkage,rare earth metals show excellent performance in enhancing the thermal stability and mechanical strength of the support,improving the oxygen storage capacity of catalyst and adjusting the acidity and alkalinity of catalyst surface.However,the study on the rare earth element praseodymium as a carrier or promoter in the field of catalysis is less.Therefore,this paper starts from the ability of anti-carbonate and oxygen activation.A series of different mole ratio of praseodymium–titania mixed oxides（denote as Pr_aTi_bO_x）and praseodymium–zirconium mixed oxides（denote as Pr_aZr₁O_x）are synthesized by using rare earth metal praseodymium as additives.Subsequently,the CO conversion,activation energy and reaction rate are investigated in two reactions of water gas shift and CO oxidation in CO₂-rich feed at different reaction temperatures（50～400℃）.Meanwhile,the influence of praseodymium-based catalyst on stability is also explored under different reaction conditions,and the following conclusions are obtained:（1）A serious of Pr_aTi_bO_x support were prepared via a sol–gel method.Au/Pr₁Ti₂O_xcatalyst shows the high reaction rate(0.327 mol _CO·mol _Au^-1)and TOF(4.02 s^-1).The long-term stability of Au/Pr₁Ti₂O_x catalyst was tested with time-on-stream for WGSR.The CO conversion rate only decreases 8%in 40 hours.The catalyst of Au/Pr₁Ti₂O_x shows the easy release of surfaceO at low temperature.It was found that the valence composition of Au,Pr and Ti was changed by modulating the mole of praseodymium and the chemical environment of oxygen atoms was affected too,resulting in the change the adsorption and dissociation ability of oxygen vacancies to H₂O.This can be attributed to electronic interaction between gold and support and the electronic compensation between praseodymium and titanium atoms.（2）Rare earth metal praseodymium was introduced to improve the reaction rate and stability for CO oxidation in CO₂-rich feed.It was found that the molar ratio between praseodymium and titanium has a great impact on the reaction activity,the reaction rates follow the trend:Au/Pr₁Ti₂O_x(10.6 mol _CO·mol _Au^-1)>Au/TiO₂(9.6 mol _CO·mol _Au^-1)>Au/Pr₁Ti₄O_x(6.3 mol _CO·mol _Au^-1)>Au/Pr₂Ti₁O_x(0.16 mol _CO·mol _Au^-1)>Au/Pr₁Ti₁O_x(0.13mol _CO·mol _Au^-1).Comparied with the catalysts with less Pr content,excessive praseodymium elements strengthened the electronic interaction between gold and support,resulting in the majority of Au⁺species in Au/Pr₂Ti₁O_x and Au/Pr₁Ti₁O_x catalysts and thus lowering the activity.In addition,compared with Au/TiO₂,the catalyst of Au/Pr₁Ti₂O_xpresented not only higher activity but also better stability in high concentration CO₂ steam due to easy desorption of CO₂from it.（3）A series of Pr_aZr₁O_x is prepared via hydrothermal method by adjusting mole ratio of praseodymium to zirconium,in which Pr/Zr=0.005 is optimal.It is found that the Au/Pr_0.005Zr₁O_x catalyst can adsorb more oxygen molecules at low temperature.The characterizations demonstrate that the crystal constant and average pore diameter gradually increase with the increase of Pr content.The chemical state of Au and the content of oxygen species were changed in reaction,which is the key factor causing the difference in catalytic activity.In addition,according to the stability test results,we find that neither Au/ZrO₂ nor Au/Pr_aZr₁O_x catalysts are affected by high concentration CO₂ in feed.