Cu-ZSM5/Alumina 촉매필터 제조 및 De-NOx 특성에 관한 연구

Abstract

기존의 허니컴 필터를 대신한 비드형 세라믹 촉매필터 Cu-ZSM5/Alumina를 제조하여 Urea SCR(Selective Catalyst Reduction) system으로의 적용을 고려한 NOx 저감특성에 대해 연구하였다. 제조된 세라믹 비드 필터 지지체는 기공율 75~83%, 기공크기 130㎛, 비표면적이 2.8㎡/g되는 3차원 망상구조로 이루어져 있다. Pt, Cu-ZSM5촉매는 80℃에서 24시간동안 이온교환하여 제조하였다. 제조된 촉매를 10w% 약산의 조건하에서 비드 필터 지지체에 워시코팅하였다. 워시코팅한 결과 워시코팅 층의 두께는 약 20~30㎛ 정도 였으며, 이후 제조된 촉매 필터의 압력손실을 측정한 결과 비드사이즈와 기공율이 커질수록 압력손실특성이 좋은결과를 나타내었다. 제조된 Cu-ZSM5/Alumina 필터는 NH3/Urea를 환원제로 사용하여 De-NOx 특성을 평가하였다. 파우더 테스트 결과 Cu의 최적담지량은 4.2w%였으며 제올라이트종류에 따른 NOx제거 성능은 ZSM5 >zeolite Y >Mordernite >Ferrierite 순이었다. Pt 촉매필터의 경우에는 고온(>250℃)에서의 산화력으로 인해 150 ~ 230℃에서, Cu 촉매필터의 경우에는 고온(>250℃)에서의 높은 활성으로 인해 250 ~ 400℃에서 우수한 NOx제거성능을 보였으며 비드 type의 촉매필터 지지체는 발포율과 크기가 증가함에 따라 NOx의 전환율이 증가하였고 하니컴 type의 촉매필터 지지체에 비해 저온에서 우수한 전환율을 보였다. 운전 조건은 Cu 담지량 4.2w%, 반응온도 250~400℃, NH3/NO =0.6 ~ 1.0 공간속도 20000h-1에서 가장 높은 De-NOx제거율로 매우 넓은 활성 온도범위를 나타내었다. 환원제의 주입량에 따라 NOx의 전환율은 환원제와 NOx의 몰비율을 0.6에서 1로 증가 했을 때, 증가율은 약 20%증가 하였다.; The diesel vehicle is relatively superior to gasoline vehicle on the fuel consumption, durability and combustion efficiency. However, exhaust emission from diesel vehicles are known to be harmful to human health and environment. The treatment technologies for the diesel exhaust gases are classified as replacement of fuel, quality control of diesel fuel, improvement of engine and aftertreatment system, and this research is continuously conducted by many groups. At present, the main technologies for the removal of NOx are as follows. 1) Application of the commercialized stationary SCR of NOx to mobile system using Urea as reductant.(Urea SCR) 2) Advanced lean NOx catalyst using HC as reductants.(LNC) 3) Alternately by a two-stage operation whereby NOx are trapped upon a selective sorbent, and then reduced by a short fuel excursion (LNT) In this research, as mentioned above, the application to the Urea SCR system was considered using the foam filter to reduce NOx from the diesel vehicle. Porous media with constant pore size of 130㎛ and porosity of 75~83% were prepared using foaming and gel-casting method from alumina. A washcoating process was applied to coat 20vol% Cu-ZSM5 on porous support with 20-30㎛ layer. After the Cu-ZSM5-coated supports were coated by using VEI(Vacuum Evaporation Impregnation) method. The characterization and the feasibility as a catalytic supports were investigated. The NOx conversion of prepared (Cu, Pt)-ZSM5 filter was conducted by using NH3/Urea as reductants under laboratory test. The following results are summary of this experiment. (1) Carrier type; ZSM5, Y, Ferrierite, Modernite was consideres of and ZSM5 shows the highest NOx conversion (2) Pt loading; Cu loading was considered of 2.5~5.5wt% and 4.2wt% shows the highest NOx conversion (3) Bead size and Porosity; The result shows Porosity is the higher, NOc conversion is the better. Porosity is effective than bead size in NOx conversion (4) Reaction Temp; De-NOx test was observed in the temperature range of 1500-500℃, indicating that the best operation temperature of the catalytic filter is 250~400℃. (5) NH3/NO Ratio; The experiment was considered active system and passive system then the range of NH3/NO is determined between 0.6 and 1. The result shows NH3/NO ratio is the higher, NOx conversion is the better. The NOx conversion increased Max. 138% at 250~400℃ (6) NH3 slip; The result shows NH3/NO ratio is the higher, NH3 is the larger (5) Space Velocity; The experimental is focused on general driving mode (SV=20000~30000h-1), NOx conversion at SV=20000h-1 shows Max.18% higher than 30000h-1 If this approach could be utilized as a catalytic filter, active system should be considered.