CeO2가 졸겔법으로 합성한 CeO2-TiO2계 SCR용 촉매의 활성에 미치는 물리화학적 영향
Physico-chemical effects of cerium oxide on catalytic activity of CeO2-TiO2prepared by sol-gel method for NH3-SCR
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CeO2의 첨가가 CeO2-TiO2계 SCR촉매 활성에 미치는 영향을 구조적, 형상학적, 물리화학적 분석을 통해 규명하였다. 순수한 TiO2 분말과 10, 20, 30 wt%의 CeO2를 첨가한 CeO2-TiO2 분말을 졸겔법으로 합성한 결과, 분말 모두 TiO2의아나타제 (anatase)상을 나타내었고 CeO2를 첨가할수록 TiO2 표면에 결정성이 낮은 CeO2가 분산되어 피크강도가 낮아짐을확인하였다. 순수한 TiO2의 비표면적이 60.6306 m2/g인데 반해 CeO2-TiO2의 비표면적은 30 wt%의 CeO2를 첨가한 경우116.2791 m2/g으로 비표면적이 증가하였고 따라서 첨가된 CeO2가 TiO2의 응집을 억제한 것으로 예상된다. NOx 제거효율은30 wt% CeO2-TiO2 촉매가 300oC에서 98 %로 다른 분말보다 높은 효율을 나타내는데 이는 FT-IR을 이용하여 촉매의 산점변화를 확인한 결과 30 wt% CeO2-TiO2 분말의 경우가 다른 분말들에 비해 산점이 상대적으로 많았기 때문이다. 따라서 졸겔법으로 합성한 SCR용 CeO2-TiO2계 촉매에서 CeO2의 첨가는 TiO2의 입성장을 억제하여 비표면적을 증가시키고 BrΦnsted 및 Lewis 산점을 증가시킴으로써 촉매 효율을 향상시켰다고 판단된다.
Abstract
The effects of CeO2 on catalytic activity of CeO2-TiO2 for the selective catalytic reduction (SCR) of NOx were investigated in terms of structural, morphological, and physico-chemical analyseis. CeO2-TiO2 catalysts were synthesized with three different additions, 10, 20, and 30 wt% of CeO2, by the sol-gel method. The XRD peaks of all specimens were assigned to a TiO2 phase (anatase) and the peaks became broader with the addition of CeO2 because it was dispersed as an amorphous phase on the surface of TiO2 particles. The specific surface area of TiO2 increased with the addition of CeO2from 60.6306 m2/g to 116.2791 m2/g due to suppression of TiO2 grain growth by CeO2. The 30 wt% CeO2-TiO2 catalyst,having the strongest catalytic acid sites (BrΦnsted and Lewis), showed the highest NOx conversion efficiency of 98 % at 300oC among the specimens. It was considered that CeO2 contributes to the improvement of the NOx conversion of CeO2-TiO2 catalyst by increasing specific surface area and catalytic acid sites.
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