Promoted Multi-metal Catalysts For Several Reactions Of Hydrogen Production

The design and development of highly effective catalysts have always been the central topic of catalytic researches.Water gas shift(WGS)is of massive significance to the whole chemical engineering industry.On the other hand,ammonia decomposition(AD)has also shown great potentials in on-line H2 production.The development of fuel cell applications has brought higher demand of the catalyst performances for both reactions.Preparation and improvement towards these catalysts have attracted attentions of many researchers.Due to the complicated structure and lack of in-situ characterizations,the important scientific issues in bulk catalysts,such as mutual interaction,in-situ structural change,determination of active sites and mechanisms,are still not solved.In this thesis,we have thoroughly studied former literatures.And with the add of promoters(CeO2,Al2O3,Fe3O4),highly promoted bulk Cu-based WGS catalysts and Ni-based AD catalysts were developed.Through careful selection and tuning of the promoters,the catalytic activity and stability was largely improved.Active sites were accuratedly identified with multiple in-situ techniques.The structure-funtion relationship for the catalysts was also clarified.These efforts could give useful guiding and exploration to the design strategies of highly promoted catalysts.1.Cu has often been used as promoter of Fe3O4 high-temperature WGS catalyst,while Cu-Fe3O4 catalysts for low-temperature WGS have rarely been reported.If Cu-based catalysts could be promoted to match commercial Cu-Zn-Al catalyst with Cu-Fe3O4 interaction,it will bring great economic benefits to the industry.In the study of promoted Cu-Fe-Al catalyst for low-temperature WGS reaction,we took advantage of sufficient active sites in bulk catalyst.A series of Cu-Fe3O4 catalysts with different Cu-Fe ratio was prepared via aerosol-spray method.The catalysts were carefully characterized with XRD,SEM,TEM,N2 sorption,XPS and TPR.We found pronounce Cu-Fe3O4 interaction,which helped improve Cu dispersion and reducibility.During the catalytic tests,Cu0.3Fe0.7Ox showed the highest activity,with conversion>70%and 90%under 200 0C and 300 ℃,respectively(GHSV=42000 mL g-1 h-1).By using in-situ DRIFTS,XRD and TPD measurements,we confirmed the enhancement of CO,H2O,CO2 adsorption after Fe addition.Besides,metallic Cu has been identified as active sites.Minor amount of Al2O3 could significant improved the stability of the catalyst,resuting in Cu0.3Fe0.6Al0.1Ox catalyst with highly promoted WGS activity and stability.2.In the study of promoted inverse CeO2-Cu catalyst for low-temperature WGS reaction,we combined aerosol spray with in-situ reduction,and successively dispersed many CeO2 nanoparticles(2-5 nm)on bulk Cu(>100 nm).Through characterizations of HR-TEM,XRD,XPS,Raman,UV-vis and H2-TPR,we confirmed Cu-CeO2 interaction and bulk-nano CeO2-Cu interfaces.With abundant bulk-nano interfaces,the inverse CeO2-Cu catalyst showed great WGS activity.The reaction rate(r)under 300 ℃ was as high as 47.3 × 10-6 mol g-1 s-1,which is almost 5 times of that for normal Cu-CeO2 catalyst(9-10×10-6 mol g-1 s-1).The CeO2 nanoparticles showed great anti-sintering property,as shown in the in-situ XRD results,leading to high stability of inverse CeO2-Cu catalyst.With very high GHSV(600000 mL g-1 h-1),the inverse CeO2-Cu catalyst showed no decay in the 50 h stability test at 250 ℃.The results of TPSR,CO-TPD and in-situ DRIFTS showed that CeO2 nanoparticles were easily oxided by CO,forming oxygen vacancies.H2O dissociated at the vacancies and H2 was generated,convincing the combination of redox and associative mechaninsms on the inverse catalyst.3.In the study of multi-metal catalyst for ammoia decomposition,we chose Fe and Ni as active metals.CeO2 and Al2O3 served as promoters,respectively.The catalysts with different ration were prepared via aerosol-spray method.XRD,SEM,N2 sorption and XPS experiments were conducted。CeO2 proved to be effective promoter to the activity,while Al2O3 could enhance the stability.By studying structural change with SEM and in-situ XRD,metallic Ni has been confirmed as active site.The size effect of Ni was directly observed to determine the activity,showing structure sensitivity in the system.On the other hand,though Fe catalysts went through severe sintering during reaction,the activity seemed not affected by the structural change.