Vapor-phase transport (VPT) modification of ZSM-5/SiC foam catalyst using TPAOH vapor to improve the methanol-to-propylene (MTP) reaction

Tetrapropylammonium hydroxide (TPAOH) was introduced in the vapor phase to perform the vapor-phase transport (VPT) modification of the structured ZSM-5 supported on SiC foam (ZSM-5/SiC foam) catalyst. An optimum precursor concentration of 0.5 M TPAOH could effectively convert the amorphous aluminosilicate binder to the zeolitic phase with improved intracrystal mesopores, nanosized crystals (ca. 100 nm), high concentration of acidity sites (83 mmol g⁻¹) as well as a high value of the relative acidity (0.7). Combined with the intrinsic property of macroscopic SiC foams such as the low pressure drop and the high thermal conductivity (14 W m⁻¹ K⁻¹ at 773 K), TPAOH VPT modified ZSM-5/SiC foam catalyst demonstrated an excellent activity in the catalytic methanol-to-propylene (MTP) reaction, surpassing the state-of-the-art hierarchal ZSM-5 monolith catalyst. The catalyst showed an extended activity for ca. 970 h (>95% methanol conversion) with the high selectivity to the propylene (>45%). The coke formation was significantly retarded (ca. 2.1 × 10⁻² wt.% h⁻¹) due to the enhanced transport phenomena within the developed structured catalyst.