Promoting NO_(x)reduction via in situ activation of perovskite supported Pd catalysts under alternating lean-burn/fuel-rich operating atmospheres

Herein,we report the excellent De-NO_(x)performance of La0.7Sr0.3MnO3(LSM)perovskite-supported Pd catalysts(Pd-LSM)in alternating lean-burn/fuel-rich atmospheres using C3H6 as reductant and describe the in situ activation of the Pd catalysts via metal-support interaction(MSI)tuning.The NO_(x)reduction conversion of the Pd-LSM catalyst increased significantly from 56.1%to 90.1%and the production of N2O was suppressed.Our results demonstrated that this behavior was mainly attributed to the in situ transformation of Pd2+into Pd0 during the reaction.The generated Pd0 species could readily activate the C3H6 reductant and achieve an eight-fold higher turnover frequency than Pd2+for the reduction of NO_(x).Moreover,excessive MSIs inhibited the in situ generation of Pd0,and thereby,lowered the De-NO_(x)activity of the catalyst even at high Pd dispersion.In addition,the Pd-LSM catalysts exhibited much higher S tolerance than conventional Al_(2)O_(3)-supported catalysts.Our study provides a new approach for analyzing and designing highly active metal catalysts operated under dynamic alternating oxidizing/reducing atmospheric conditions.

Metal-Support Interactions on Ag/Co_(3)O_(4)Nanowire Monolithic Catalysts Promoting Catalytic Soot Combustion

Tuning metal-support interactions(MSIs)is an important strategy in heterogeneous catalysis to realize the desirable metal dispersion and redox ability of metal catalysts.Herein,we use pre-reduced Co_(3)O_(4)nanowires(Co-NWs)in situ grown on monolithic Ni foam substrates to support Ag catalysts(Ag/Co-NW-R)for soot combustion.The macroporous structure of Ni foam with crossed Co_(3)O_(4)nanowires remarkably increases the soot-catalyst contact effi ciency.Our characterization results demonstrate that Ag species exist as Ag 0 because of the equation Ag^(+)+Co^(2+)=Ag^(0)+Co^(3+),and the pre-reduction treatment enhances interactions between Ag and Co_(3)O_(4).The number of active oxygen species on the Ag-loaded catalysts is approximately twice that on the supports,demonstrating the signifi cant role of Ag sites in generating active oxygen species.Additionally,the strengthened MSI on Ag/Co-NW-R further improves this number by increasing metal dispersion and the intrinsic activity determined by the turnover frequency of these oxygen species for soot oxidation compared with the catalyst without pre-reduction of Co-NW(Ag/Co-NW).In addition to high activity,Ag/Co-NW-R exhibits high catalytic stability and water resistance.The strategy used in this work might be applicable in related catalytic systems.

A-site defects in LaSrMnO_(3) perovskite-based catalyst promoting NOx storage and reduction for lean-burn exhausts

Herein,we report the high De-NOx performance of the A-site defective perovskite-based Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst.The formation of the defective perovskite structure can be proved by both the increased Mn^(4+)/Mn^(3+) ratio and serious lattice contraction due to cationic nonstoichiometry.It promotes the Sr doping into perovskite lattice and reduces the formation of the SrCO_(3) phase.Our results demonstrate that below 300℃ the A-site defective perovskite can be more efficiently regenerated than the SrCO_(3) phase as NOx storage sites due to the latter’s stronger basicity,and also exhibits the higher NO oxidation ability than the A-site stoichiometric and excessive catalysts.Both factors promote the lowtemperature De-NOx activity of the Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst through improving its NOx trapping efficiency.Nevertheless,above 300℃,the NOx reduction becomes the determinant of the De-NOx activity of the perovskite-based catalysts.A-site defects can weaken the interactions between perovskite and Pd,inducing activation of Pd sites by in-situ transformation from PdO to metallic Pd in the alternative leanburn/fuel-rich atmospheric alternations,which boosts the De-NOx activity of the Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst.The Pd/L_(0.5)Sr_(0.3)MnO_(3) catalyst exhibits the high sulfur tolerance as well.These findings provide insight into optimizing the structural properties and catalytic activities of the perovskite-based catalysts via tuning formulation,and have potential to be applied for various related catalyst systems.