Study On AB Site Substitution Of La₂NiO₄for Simultaneous Removal Of NOx And PM

A series of La₂NiO₄-type complex oxides were prepared by the citric acidcomplexation, the catalyst was modified by A-site and B-site substitution, theircatalytic performance for simultaneous removal of NO_x and PM was investigated.According to these investigations, we found that:All samples shows show La₂NiO₄--type structure through the citric acidcomplexation method, the structure of La₂NiO₄does not change by partialsubstitution of A and B site within the proper degree. La₂NiO₄showed good catalyticactivity at low temperature range, the NO conversion rate is42%at300℃.The oxygen play an important role for the whole reaction, for La₂NiO₄, thecatalytic activity is very low when reaction gases does not contain oxygen, the NOconversion rate is9%at650℃, oxygen could promote the formation of intermediatespecies CO*, which could smooth the reaction process, decrease the reactiontemperature and increase the catalytic efficiency.When substituted amount of La for Sr Ba at A site, the mobility of adsorbedoxygen will change, the mobility of adsorbed oxygen would mainly influence theactivity, selectivity, the higher the mobility of adsorbed oxygen, the lower theselectivity and activity, and vice versa. For Sr-doped La_1.8Sr_0.2NiO₄, the mobility ofadsorbed oxygen decreased, the NO conversion rate increased from42%to64%, theselectivity increased form54%to69%.The B site substitution would change the mobility of lattice oxygen. Themobility of lattice oxygen would mainly influence the reaction temperature, thelower the mobility of lattice oxygen, the higher the reaction temperature. ForLa₂Ni_0.8Mn_0.2O₄and La₂Ni_0.8Fe_0.2O₄, the mobility of lattice oxygen decreased largely,their reaction temperature increased to500℃and600℃, respectively, meanwhile,their catalytic activity and selectivity almost maintain the similar level.