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알칼리 토금속/희토류 금속 원소의 첨가가 백금 : 로듐 삼원촉매의 내열성에 미치는 영향
Effect of Alkaline Earth/Rare Earth Addition on the Heat Resistance of Pt : Rh Three Way Catalysts
아주대학교 화학공학과, 수원 590-170 1한국가스공사 연구개발원, 안산 425-150 2산업자원부 기술표준원, 과천 427-760
Dept. of Chem. Eng., Ajou Univ., Suwon Kyunggi 590-170, Korea 1Korea Gas Corporation R&D Center, Ansan Kyunggi 425-150, Korea 2Agency for Technology and Standards, MOCIE, Kyunggi, 2 Joongang, Kwacheon 427-760, Korea
HWAHAK KONGHAK, April 2001, 39(2), 131-137(7), NONE
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Abstract
기본 삼원촉매인 PtRh/Al2O3에 세륨을 첨가하여 표준 삼원 촉매인 PtRh-Ce/Al2O3를 만들고, 표준 삼원촉매인 PtRh-Ce/Al2O3에 알칼리 토금속/희토류 금속 원소를 각각 참가하였을 때 이들 첨가 원소들이 촉매의 내열성에 미치는 영향에 대해 조사하였다. 이 시험을 위해 촉매 시료를 950 ℃에서 100 hr동안 열화시킨 후 자동차 모의가스 반응시험을 통해 Light-off온도(T(50%))와 CO, HC(탄화수소), NO(χ)의 전환율 변화를 시험하였고, BET, SEM을 이용하여 특성변화를 관찰하였다. PtRh/Al2O3에 세륨을 첨가한 경우 고온에 노출되면 세륨이 귀금속과 소결되는 현상 및 알루미나와 화합물(CeAlO3)을 형성함으로 인하여 희박 조건 (λ=1.03)에서 CO와 HC의 활성과, 과농 조건(λ=0.97) 및 양론 조건 (λ=1.00)에서 NO(χ)의 활성이 심하게 감소되는 것으로 나타났다. PtRh-Ce/Al2O3에 알칼리 토금속(Mg, Ca, Sr, Ba)과 희토류 금속(La, Nd)원소를 첨가하여 열화시킨 경우, 바륨의 열 안정성이 가장 우수하였으며 네오디뮴, 스트론튬, 란타늄의 순서로 내열효과가 있었다. 그러나 칼슘은 소결 방지에 거의 기여를 못하였고, 마그네슘은 열에 의한 귀금속 및 알루미나와의 소결이 가속되어 활성이 이들 원소의 첨가 전보다 오히려 저하되었다.
The effect on the heat resistance of the catalysts has been studied upon the addition of cerium to basic three way catalyst(PtRh/Al2O3) and of alkaline earth/rare earth metal to the standard three way catalyst(PtRh-Ce/Al2O3). Light-off temperature and three way conversion rate were evaluated with the simulated automotive exhaust gas mixture of H2, CO, C3H6, C3H8, NO, CO2, O2, H2O and N2 over fresh catalyst and over the aged one at 950℃ for 100 hours. The prepared catalysts were characterized utilizing BET and SEM. The addition of cerium to the PtRh/Al2O3 catalyst severely reduced the oxidation of CO and hydrocarbon under the lean condition(λ=1.03) and the reduction of NO(x) under the rich(λ=0.97) or stoichiometric condition(λ=1.00) due to sintering of cerium with the precious metals and producing of CeAlO 3 compound with alumina. When alkaline earth(Mg, Ca, Sr or Ba) or rare earth metal(La or Nd) was added to PtRh-Ce/Al2O3 and aged, catalyst with barium showed the highest catalytic activity with the best thermal stability, and neodymium, strontium and lanthanum added catalysts had the higher activities in the order. However, calcium addition to the catalyst had little effect on the thermal stability, showing a little higher catalytic activity with the standard catalyst. Magnesium added catalyst was extremely deactivated compared to the standard catalyst due to the enhanced sintering with precious metal and alumina.
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