On the influence of pore geometry and acidity on the activity of parent and modified zeolites in the synthesis of methylenedianiline

Methylenedianiline synthesis from formaldehyde and aniline is catalyzed by solid acid catalysts, such as zeolites, which offer strong acidity and high acid site density. Critical parameters for catalyst activity were explored using materials with MFI, BEA, MOR and FAU structure. While materials with MOR and MFI structure hardly show activity, BEA and FAU type zeolites are active and selective. The higher activity for the latter materials is related to their larger pore structure. Nevertheless, the reaction is limited by pore diffusion over parent BEA- and FAU-type zeolites. Mesoporous materials, such as dealuminated FAU, offer significantly higher activity as pore diffusion limitation can be overcome. Therefore, we synthesized and tested other mesoporous aluminosilicates such as desilicated BEA and the delaminated MWW materials ITQ-2 and MCM-36. It was shown that desilication increases the activity of parent BEA type zeolites for MDA formation, yet not to the same extend as dealumination in case of FAU. ITQ-2 shows promising results, but MCM-36 surpasses ITQ-2 in terms of activity by a factor of two displaying activities similar to the dealuminated FAU materials.

Figure optionsDownload high-quality image (70 K)Download as PowerPoint slideResearch highlights▶ Pore size and geometry have an pronounced impact on catalyst activity. ▶ MFI and MWW type materials are inactive. ▶ BEA and FAU type materials are active, but the reaction is limited by pore diffusion. ▶ Mesoporous materials offer increased activity by avoiding mass transport limitation. ▶ MCM-36 and dealuminated FAU type materials display the highest TOFs.