Size control of SSZ-13 crystals with APAM and its influence on the coking behaviour during MTO reaction

Abstract

Anionic polyacrylamide (APAM) was first introduced for the synthesis of SSZ-13 crystals. The SSZ-13 crystal size could be manipulated from 110 nm to 1.21 μm by changing the amount of APAM being added to the synthesis precursor solution and the hydrothermal temperature. The SEM and XRD techniques were used to investigate the crystallization process, and APAM showed an efficacy in preventing crystallite assembly. The catalytic performance of the SSZ-13 crystal of different sizes was tested, and the nano-sized SSZ-13 crystals showed the most extended catalyst lifetime in the methanol-to-olefins (MTO) reaction. An in situ TGA revealed that the coke formation rate decreased with the reduction in crystal size. The evolution of coke species on SSZ-13 of different crystal sizes during the MTO reaction was propped by the GC-MS technique. The generation of phenanthrenes was depressed evidently and more naphthalenes were involved in the MTO reaction as the SSZ-13 crystal size decreased.