Transition-Metal-Free Aluminosilicate Small-Pore Zeolites Upgrade Methane to Light Olefins.

Upgrading methane to value-added chemicals is significant but still challenging. Well-designed catalysts are required to activate methane. Extensive efforts have been dedicated to the catalytic conversion of methane over transition-metal-containing catalysts. A simple aluminosilicate FER-type zeolite has been found to activate methane and nitrous oxide to methanol stably. To further diversify the catalytic properties, zeolites with different topologies were screened in the methane oxidation reaction. Here, we show that small-pore zeolites have unique advantages in the direct upgrading of methane to light olefins. Among them, the CHA-type zeolite (SSZ-13) exhibited an outstanding performance, with a total selectivity of 90.5% to light olefins and a CH4 conversion of 5.3% at 350 °C, accompanied by excellent regeneration. Penta-coordinated Al species as one of the active centers was figured out for methane activation and further identified as a non-framework tetra-coordinated Al species by density functional theory (DFT) calculations. The acidity of the zeolite was confirmed to influence the tandem conversion of methanol to light olefins. Our study revealed a novel possibility that transition-metal-free aluminosilicate small-pore zeolites can serve as bifunctional catalysts directly and continuously upgrade methane to light olefins via methanol as the intermediate. This approach avoided energy consumption and cumbersome operations and achieved high-efficiency and low-energy production of light olefins.