Organosilane-assistant synthesis of hierarchical SAPO-34 aggregates with superior MTO performance

Hierarchical SAPO-34 aggregates were hydrothermally synthesized with the assistance of organosilane N-[3-(Trimethoxysilyl)propyl]ethylenediamine (TPED), during which the morpholine was used as the template. The resultant products were characterized by XRD, SEM, ICP-OES, NH3-TPD, N-2 adsorption-desorption and TGA, and a possible formation mechanism was proposed. As the amount of added TPED varies, the morphologies, compositions and acid properties of the resultant hierarchical SAPO-34 aggregates differ. The hierarchical SAPO-34 aggregates possessed higher external surface areas, lower Si content, weaker strength and lower concentration in the strong acid sites than the conventional SAPO-34. The investigation of formation process showed that the addition of the TPED had a pivotal role for the formation of hierarchical SAPO-34 aggregates. Compared to conventional SAPO-34, the hierarchical SAPO-34 aggregates exhibited a significant improvement in methanol to olefin reaction (MTO) reactions due to their hierarchical structure and mild acid properties.