Pd-Doped Ni-Co Spinel Catalysts For H₂-SCR Denitrification Performance

Nitrogen oxides?NO_x?are one of the major air pollution,and more harmful for a variety of crops,the ecological environment and human health.Effectively control the atmospheric NO_x content has become an imminent problem.In this paper,the non-polluting H₂ was selected to be used to selectively reduce the NO reaction.The effects of noble metal Pd and Ce-doped nickel cobalt spinel oxides on NO_x removal of H₂-SCR were studied.And the H₂-SCR catalytic activities of Pd-doped spinels were studied by their physical and chemical characteristics.The effects of the different preparation methods,Pd doping amount,Ce doping amount on the SCR activity were also investigated.Moreover,the effects of NO/H₂ ratios,oxygen concentration,reaction temperature,gas hourly space velocity,SO₂ and H₂O on the SCR performance were also considered.We studied the H₂-SCR denitrification performance of Pd0/LaMnO3,ACo1.95Pdo.05O₄?A=Ni,Mn,Zn,Cu?catalysts,then selected the better one with good SCR activity,NiCo,.95Pdo.05O₄ spinel,as object for the follow-up study.Compared the SCR activity of NiCo_1.95Pd_0.05O₄ spinel obtained by three different kinds of preparation methods?sol-gel method,coprecipitation method and hydrothermal method?,and the results showed that the catalyst prepared by sol-gel method had good DeNO_x performance,therefore,in the following studies,the preparation method will adopt sol-gel method.Through the study of NiCo_1-xPd_xO₄?x=0.00,0.05?,we found that the doping of Pd can effectively improve the SCR activity,especially the NiCo_1.95Pd_0.05O₄ catalyst shows a better SCR denitrification performance.An increase in the O2 concentration from 0%to 6%and the NO/H₂ ratio from 1:10 to 1:1 resulted a slight decrease of the NO conversion,which indicated that the O2 content and H₂ concentration can affect the SCR activity.The addition of water vapor had a weak effect on the catalytic activity of NiCo_1.95Pd_0.05O₄ catalyst,indicating that the catalyst had a good water resistance.Moreover,after the addition of 100 ppm SO₂,the NO conversion decreased 4.88%,indicating that the doping of Pd can improve the sulfur resistance of the catalyst.In order to improve the SO₂-resistance of NiCo_1.95Pd_0.05O₄ spinel,we studied the Ni_1-xCe_xCo_1.95Pd_0.05?x=0.00,0.03,0.05,0.07,0.1,0.2?catalysts,the results showed that the doping of a small amount of Ce did not only improve the sulfur resistance of catalysts,but also enhance the SCR activity,especially the Ni_0.93Ce_0.07Co_1.95Pd_0.05O₄ catalyst had better denitration activity.The NO/H₂ ratio changed from 1:1 to 1:10,the NO conversion increased greatly,while the O2 content changed from 0%to 6%,the decreasing amplitude of NO conversion was not significant,which indicated that the addition of Ce can effectively improve the oxygen resistance of the catalyst.In addition,this catalyst also showed better water resistance,the effect of water on its catalytic activity was weak.For the purpose of improving the use ratio of hydrogen,the denitrification performance of H₂-SCR with nickel-supported nickel-cobalt spinel catalyst was studied.Through the SCR activity test,and that the 0.03g Ni_0.93Ce_0.07Co_1.95Pd_0.05O₄ catalyst was supported on foam-nickel by soaking method,we found that the maximum conversion of the foam nickel supported nickel-cobalt catalyst was about 30 times than the unused foam nickel catalyst under the conditions of the unit mass catalyst,which means that the foam nickel has good effect of local hydrogen strengthening.At high GHSV,the foam nickel supported nickel cobalt spinel catalyst still has a high catalytic activity,an increase of NO/H₂ ratio froml:10 to 1:5 and O2 concentration from 0%to 4%resulted in a weak effect on SCR activity,which NO conversion rate can reach 90%,indicating that the foam nickel can enhance the local enrichment of hydrogen.In addition,the passivation of sulfur dioxide to this type of catalyst was partially reversible.In conclusion,the doping of Pd can effectively improve the SCR denitrification performance of nickel-cobalt spinel catalyst,and a small amount of Ce doping can not only improve its catalytic activity,but also enhance its sulfur resistance,foam nickel supported a small amount of nickel cobalt catalyst can enhance the adsorption of hydrogen and denitrification performance.In addition,adjusting the NO/H₂ ratio,oxygen concentration,gas hourly space velocity and other experimental parameters,can affect the catalyst SCR activity.While the effect of water on the spinel catalytic activity was relatively weak.