Abstract: The catalytic performance of commonly used heteropolyacids (H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀ and H₃PMo₁₂O₄₀) for the synthesis of 4,4'-methylenedianiline (4,4'-MDA) from aniline and formaldehyde was evaluated and the result showed that H₄SiW₁₂O₄₀ with moderate acid strength exhibited the best catalytic performance. Then H₄SiW₁₂O₄₀@MIL-100(Fe) was prepared by encapsulating H₄SiW₁₂O₄₀ within the pores of MIL-100(Fe) to facilitate its recovery and reuse. The prepared H₄SiW₁₂O₄₀@MIL-100(Fe) was characterized by means of FT-IR, N₂ adsorption-desorption, XRD, TG and then the catalytic performance was evaluated. The result showed that H₄SiW₁₂O₄₀ was highly dispersed in the pores of MIL-100(Fe), and both the Keggin structure of H₄SiW₁₂O₄₀ and the crystal skeleton structure of MIL-100(Fe) could be effectively preserved. Furthermore, H₄SiW₁₂O₄₀@MIL-100(Fe) showed excellent catalytic performance under the following reaction conditions:a molar ratio of aniline to formaldehyde=5, a mass ratio of catalyst to formaldehyde=1.2, a reaction temperature of 120℃ and a reaction time of 6 h. Under the above reaction conditions, the conversion of aniline was 41.1%, and the yield and selectivity of 4,4'-MDA were 81.6% and 79.2%, respectively. Unfortunately, an appreciable loss in the catalytic activity of the recovered H₄SiW₁₂O₄₀@MIL-100(Fe) was observed because of the blocking of the pores and the change of the acidity resulted from the adsorption of alkaline organics such as aniline and 4,4'-MDA. The adsorbed alkaline organics could be cleaned up when the recovered catalyst was washed by methanol and DMF. Then the catalyst was effectively reused up to three cycles without much loss in its activity.

Key words: H₄SiW₁₂O₄₀@MIL-100(Fe), Catalyst activation, 4,4'-Methylenedianiline synthesis, Multiphase reaction, Stability

摘要： The catalytic performance of commonly used heteropolyacids (H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀ and H₃PMo₁₂O₄₀) for the synthesis of 4,4'-methylenedianiline (4,4'-MDA) from aniline and formaldehyde was evaluated and the result showed that H₄SiW₁₂O₄₀ with moderate acid strength exhibited the best catalytic performance. Then H₄SiW₁₂O₄₀@MIL-100(Fe) was prepared by encapsulating H₄SiW₁₂O₄₀ within the pores of MIL-100(Fe) to facilitate its recovery and reuse. The prepared H₄SiW₁₂O₄₀@MIL-100(Fe) was characterized by means of FT-IR, N₂ adsorption-desorption, XRD, TG and then the catalytic performance was evaluated. The result showed that H₄SiW₁₂O₄₀ was highly dispersed in the pores of MIL-100(Fe), and both the Keggin structure of H₄SiW₁₂O₄₀ and the crystal skeleton structure of MIL-100(Fe) could be effectively preserved. Furthermore, H₄SiW₁₂O₄₀@MIL-100(Fe) showed excellent catalytic performance under the following reaction conditions:a molar ratio of aniline to formaldehyde=5, a mass ratio of catalyst to formaldehyde=1.2, a reaction temperature of 120℃ and a reaction time of 6 h. Under the above reaction conditions, the conversion of aniline was 41.1%, and the yield and selectivity of 4,4'-MDA were 81.6% and 79.2%, respectively. Unfortunately, an appreciable loss in the catalytic activity of the recovered H₄SiW₁₂O₄₀@MIL-100(Fe) was observed because of the blocking of the pores and the change of the acidity resulted from the adsorption of alkaline organics such as aniline and 4,4'-MDA. The adsorbed alkaline organics could be cleaned up when the recovered catalyst was washed by methanol and DMF. Then the catalyst was effectively reused up to three cycles without much loss in its activity.

关键词: H₄SiW₁₂O₄₀@MIL-100(Fe), Catalyst activation, 4, 4'-Methylenedianiline synthesis, Multiphase reaction, Stability