Synthesis of Chainlike ZSM-5 with a Polyelectrolyte as a Second Template for Oleic Acid and Ethanol Cracking into Light Olefins

Chainlike ZSM-5 was synthesized in a tetrapropylammonium hydroxide (TPAOH) and poly(diallydimethylammonium chloride) (PDDA) dual-template system. The synthesis parameters and formation mechanism of chainlike zeolites were investigated. The optimized composition of the synthesis mixture was as follows: the PDDA/SiO2, TPAOH/SiO2, SiO2/Al2O3, and H2O/SiO2 molar ratios are, respectively, 0.16, 0.4, 50, and 40, with tetraethyl orthosilicate and aluminum nitrate as silicon/aluminum sources. The resultant ZSM-5 showed a cross-linked chainlike morphology, mesopore-dominated pore structure, and mild acidity. The formation of the chainlike zeolite was attributed to synergistic actions between PDDA and TPAOH. TPAOH acted as an alkali source and helped to induce nucleation and control the crystal size. PDDA acted as a soft template to promote crystal nucleation, and a hard template to form a three-dimensional mesoporous structure. Light olefin (C2–4=) selectivities from cracking of ethanol and oleic acid over the present chainlike ZSM-5 at 400 °C reached 90 and 75.7%, respectively, which were much higher than those from commercial ZSM-5 (75 and 52.3%, respectively), demonstrating the excellent hydrothermal stability and catalytic performance of the synthesized chainlike zeolite.