Organosilanesulfonic acid-functionalized Zr-TMS catalysts: Synthesis, characterization and catalytic applications in condensation reactions

Organosilanesulfonic acid (–Si–R3S–R4SO3H, OSA)-functionalized mesoporous Zr-TMS (Zr-TMS–Si–R3S–R4SO3H, Zr-TMS–OSA) was synthesized either by post-synthetic modification of Zr-TMS (zirconia-based transition metal oxide mesoporous molecular sieves) with 3-mercaptopropyltrimethoxysilane (3-MPTS) and further with 1,4-butanesultone (1,4-BS) or by in situ one-pot synthesis procedure. A number of physico-chemical characterization techniques have been used to show that the organosilanesulfonic acid groups were anchored on to the walls of Zr-TMS. MCM-41–Si–R3S–R4SO3H-20 (MCM-41–OSA-20) was also prepared by post-synthesis procedure for comparison. Physico-chemical properties of in situ made A-Zr–OSA-20, Zr-TMS–SO3H-20 and MCM-41–OSA-20 were compared with Zr-TMS–OSA catalysts. The catalytic activity of the materials was tested in liquid phase condensation of aniline with p-formaldehyde to 4,4′-diaminodiphenylmethane (4,4′-DADPM). Results showed that Zr-TMS–OSA catalysts were more active than Zr-TMS–SO3H-20, MCM-41–OSA-20 and A-Zr–OSA-20 and more selective than Zr-TMS–SO3H-20 and A-Zr–OSA-20 catalysts.