Direct Crystallization of Silicoaluminophosphates onto the Surface of Open-Celled SiC Foam

Silicoaluminophosphates of the framework types CHA (SAPO-34) and AFI (SAPO-5) are deposited onto the surface of open-celled ceramic SiC foam monoliths by direct crystallization. Therefore, a conventional hydrothermal synthesis is carried out in the presence of SiC foam monoliths with pore densities of 10 and 30PPI, respectively. Moreover, the crystallization time is varied to determine its effect on the coating produced. In all cases, the direct crystallization of the respective SAPO material is successful. Irrespective of the pores density of the ceramic foam a variation of the crystallization time (SAPO-5: 20h/30h, SAPO-34:30h/45h) does not show any influence on the thickness of the layers produced as suggested by optical microscopy. However, in the case of SAPO-34 these layers are clearly thicker than the layers of SAPO-5, which leads to a partial blockage of the pores of the ceramic foam with a pore density of 30PPI. As proved by N-2-sorption measurement, the coatings offer BET surface areas comparable with those reported for pure powder samples.