Preparation Of Honeycomb Ceramic Perovskite-type Catalyst And Its Characteristic Of Catalytic Combustion Of Vocs

Catalytic combustion was a simple and effective way for the treatment of VOCs, which avoided the yield of NO_x, CO, etc. Due to the complex reaction conditions, the catalyst had to be able to suffer from the high temperature and the poison, which made the noble metals monolithic catalysts can not fulfill the demand of environmental protection. Therefore, the dissertation, the honeycomb ceramic monolith catalyst was studied using perovskite type oxides La_0.8Sr_0.2MnO₃ (LSM) as active pahse, and its catalytic activities on the VOCs combustion were investigated.Two honeycomb ceramics supports, cordierite and mullite, were discussed first. It was found that the LSM supported on the two supports were both deactivated obviously after calcined at 850℃(total conversation temperature increased from 280℃to 350℃). By XRD, EDS and TPR, the results were originated from the interaction between the LSM and the supports, forming La₂MgO_x and destroying the LSM crystal structure. Because of performance-price ratio,cordierite were taken as support during subsequent studiesSecond, Al₂O₃, La-Al₂O₃,Ce_0.5Zr_0.5O₂ and hexaaluminat (HA) were employed as washcoat (Second Support) of monolithic LSM catalysts. After calcined at 850℃, visible cracks were observed on the Al₂O₃, La-Al₂O₃,Ce_0.5Zr_0.5O₂ and the LSM was sintered by SEM, thus caused the activity decrease. While after calcined at 850℃for 6hour, the Sr_0.3La_0.2Ba_0.5MnAl₁₁O₁₉ hexaaluminat was not sintered and the LSM particles were still well dispersed on the washcoat surface. The results indicated that the HA washcoat had very well thermal stability and it could prevent the aggregation of the LSM phase, thus maintained the activity of the catalyst.By over investigation, monolithic LSM, which was precoated with hexaaluminate, were prepared and its catalytic performance on the various VOCs (aromatic, alkane, ester, ketone, and aldehyde were discussed). It showed that the monolithic LSM exhibited very well catalytic activity for these VOCs, especially for the oxygenated-volatile organic compounds (OVOCs). The order of the VOCs combustion activity over the monolithic LSM was as follows: acetone=EtAc > ethanol>acetaldehyde>xylene> toluene > n-hexane> benzene> cyclohexane.Considering the excellent performance of the monolithic LSM for the OVOC combustion, we combined the noble catalyst and monolithic LSM to deal with the waste gas from painting factory, which contained much OVOCs, i.e. EtAc and NOVOCs, i.e. toluene. It was found that the total converted temperature of the VOCs over the monolithic LSM or the noble metal catalyst were 270℃and 300℃respectively, while the total converted temperature was decreased to 250℃over the combined catalyst.