Preparation And Characterization Of Alkal Metal (K, Cs) Based Nanocrystal Catalysts For Soot Oxidation

In this study, the nanometer particle catalysts based on the alkali metals (K, Cs)were prepared by direct coating method. The effects of calcination temperature andlong time aging on the catalytic activity as well as moisture absorption characteristicsand poison resistance to Pb and S were studied. The compositions, thermal changesand morphologies of the catalysts were studied by XRD, TG-DSC and SEMseparately.Al/K catalysts prepared using various precursors were studied, and the resultsshowed that the ignition temperature of Al/K catalysts for soot was almost all under350℃. Moreover, the oxidation rate of soot was high, and hence the conglomeration ofsoot could be avoided. It was proved that Al₂O₃ filter material would have nodetrimental effect on the catalytic activity of soot catalysts containing K element. Thedeficiency of the Al/K catalysts was the weak ability resisting to high temperature,long time aging and S poisoning. Adding Sm into Al/K catalysts could increase theresistance to S poison, but had no effect on increasing the anti-deterioration ability tohigh temperature and long time aging.It was founded that PbO_x has good oxidation activity for soot. The resistingability for Pb poisoning for Sm/K catalysts was better than those of Nd/K and Y/Kcatalysts. The activity of Pb/K catalysts was good with the ignition temperature ofabout 320℃. The activity of M/Pb/K catalysts prepared by adding rare earth andtransition metals to Pb/K catalysts was obviously higher than that of Pb/K catalyst, andthe activity was further enhanced by higher K content. It is obvious that metal M has important effect on M/Pb/K catalysts. The water and CO2 absorption ability of M/Pb/Kcatalysts increased with the increase of K content, while the addition of metal elementcan efficiently decrease the water absorption ability of the catalysts. With the increaseof K content, the resistance of Pb/K based catalysts for S poisoning decreasedgradually, with only the catalyst with Nd:Pb:K=2:1:10 while the perovskite likecompound was not destroyed in the catalyst exhibiting a high soot oxidation activityafter sulfuration.It was found that the activity of Sm/Cs/M catalysts were also high with the Tm(maximum temperature) of only 384℃when Sm: Cs-1:1.5 and Sm:Cs=1:3. But theirresistance to Pb and S poisoning and rust degradation were not satisfied. As the K saltCs salt can improved the activity of catalysts through increasing the contact betweencatalysts and soot. Besides, the K salt can improve the activity of catalysts through theformation of medium carbonate by absorbing the water and CO₂ in air, but Cs-basedcatalysts neither absorb the water and CO₂ in air nor form the medium carbonate, andhave the good stability.The soot oxidation catalysts prepared by direct coating method, because of theuniformity of mixed precursors, have a small catalysts particle, commonly at about 20nm, which is favorable for the contact between catalysts and soot.