Mesoporous low silica X (MLSX) zeolite: Mesoporosity in loewenstein limit?

Abstract

Synthesis of Low Silica X zeolite (LSX) with hierarchical porosity was achieved. The low silicon/aluminum ratio of this zeolite allowed to increase the number of active sites, as cationic positions (>25%) respect to the previous mesoporous X zeolite. Mesoporosity was induced by using sodium dodecylbenzene sulfonate (SDBS) during the synthesis. A dissolution time of 24 h for SDBS improved the zeolite crystallinity, maintaining the FAU characteristic framework, with a silicon/aluminum molar ratio near the unity (<1.1), limit of the Lowenstein’ rule. The surfactant removal at 773 K promoted the development of a wider pore size distribution. The heating rate highly determined the pore size distribution, resulting in a bimodal distribution (maxima at 80 Å and 290 Å) at low heating rate (1.3 K/min) and a unimodal distribution, with a maximum at 230 Å, at higher heating rate (8 K/min). The analysis by Transmission Electronic Microscopy (TEM) showed the mesoporous cavities in the zeolite nanoparticles. These cavities were generated by the SDBS spherical micelles removal. Mesoporous Low Silica X zeolite (MLSX) showed higher catalytic activity than the same zeolite without mesoporosity in the deoxygenation of oleic acid. The conversion reached a constant value around 100% with higher yield toward C9–C18 hydrocarbons, representative fraction of sustainable aviation fuel (SAF). Therefore, this new mesoporous low silica X zeolite (MLSX) has a significant potential use as catalyst in the processing of bulky molecules.