메탄의 oxidative coupling(OCM)은 산소를 산화제로 하여 메탄을 직접 에탄, 에틸렌으로 전환시키는 반응이다. 본 연구에서는 Li₂CO₃-Sm₂O₃ 혼합 산화물 촉매를 이용하여 메탄의 oxidative coupling 반응에 대해 BiOCl의 첨가 효과를 미분형 고정층 흐름 반응기에서 연구하였다. Sm₂O₃에 BiOCl이 첨가되지 않은 Li₂CO₃-Sm₂O₃ 촉매의 경우 반응 시간이 지남에 따라 활성이 감소하였는데 이는 OCM반응의 활성점인 리튬이 반응 도중 소실되기 때문이었다. BiOCl이 첨가된 Li₂CO₃-Sm₂O₃ 촉매의 경우 첨가되지 않은 경우와 비교해 볼 때, 메탄의 전환율은 비슷하였으나, C₂ 선택도가 크게 증가하였으며, 촉매의 안정성도 증가하였는데, 이는 BiOCl이 반응의 활성점인 리튬을 안정화시켜 소실을 억제하였다. 또한 Sm₂O₃ 촉매상의 산점의 양은 Li₂CO₃ 또는 BiOCl의 첨가량이 증가할수록 감소하였는데, 산점의 감소는 CO 및 CO₂로의 완전산화를 억제해 C₂ 선택도의 증가를 나타내었다. Li₂CO₃-Sm₂O₃ 혼합산화물에 BiOCl 대신 Bi₂O₃가 첨가되면, 큰 효과가 없는 것으로 나타났는데, 이는 리튬을 안정화시키는 것이 Bi가 아니라 BiOCl 화합물이라는 것을 의미한다. Li₂CO₃가 첨가되지 않은 BiOCl-Sm₂O₃ 촉매는 OCM 반응에 좋은 활성을 나타내지 못하였다.

Addition effect of BiOCl to Li₂CO₃-Sm₂O₃, a mixed oxide catalyst, on oxidative coupling of methane(OCM) was studied in a differencial fixed bed reactor. When Li₂CO₃-Sm₂O₃ catalyst in absence of BiOCl was used for OCM reaction, it showed severe deactivation with the reaction time. This may be due to the loss of an active lithium during the reaction. On the other hand, however, Li₂CO₃-Sm₂O₃ catalyst promoted with BiOCl showed almost the same conversion of methane, higher selectivity to C₂, and the enhancement of catalyst stability. It was found from the catalyst characterization by means of XRD and FT-IR that BiOCl stabilized the acitive lithium and supressed its loss. TPD of ammonia on Sm₂O₃ showed that acidity of Sm₂O₃ decreased with the addition of Li₂CO₃ or BiOCl. Decrease of acidity was found to be closely related to the inhibition of total oxidation to CO and CO₂ and to the enhancement of the C₂ selectivity. When Bi₂O₃ in place of BiOCl was added to Li₂CO₃-Sm₂O₃, it showed no promotion. This suggests that promotor is not Bi but BiOCl. If BiOCl was added to Sm₂O₃ in absence of Li₂CO₃, activity change was negligible. From these results, it is concluded that BiOCl promotes OCM reaction by suppressing the loss of the active lithium and by reducing the acidity of Sm₂O_3.

Oxidative Coupling of Methane(OCM) Li₂CO₃-BiOCl-Sm₂O₃ C₂ Selectivity

Kim SC, Yu EY, HWAHAK KONGHAK, 28(5), 536 (1990)
Kim CS, Lee WY, HWAHAK KONGHAK, 31(1), 62 (1993)
Kim SC, Sunwoo CS, Yu EY, Korean J. Chem. Eng., 7(4), 279 (1990)
Kim SH, Cho SM, Yoon KJ, Korean J. Chem. Eng., 14(1), 69 (1997)
Keller GE, Bhasin MM, J. Catal., 73, 9 (1982) 
Amnemoniya Y, Birrs VI, Goledzinowski M, Galuszka J, Sanger AR, Catal. Rev.-Sci. Eng., 32, 163 (1990)
Lee JS, Oyama ST, Catal. Rev.-Sci. Eng., 30(2), 242 (1988)
Otsuka K, Jinno K, J. Catal., 100, 353 (1986) 
Matir W, Lunsford JH, J. Am. Chem. Soc., 103, 3728 (1981) 
Campbell KD, Zhang H, Lunsford JH, J. Phys. Chem., 92, 750 (1988) 
Burch R, Squire GD, Tsang SC, Appl. Catal., 43, 105 (1988) 
Chung JS, M.S. Thesis, Seoul National Univ. (1993)
Khan AZ, Ruckenstein E, J. Catal., 138, 322 (1992) 
Weissman M, Benson SM, Int. J. Chem. Kinet., 16, 307 (1984) 
Otsuka K, Hatano M, Komatsu T, Stud. Surf. Sci. Catal., 36, 383 (1988)