Isomerization of n-Butane over Cost-Effective Mordenite Catalysts Fabricated via Recrystallization of Natural Zeolites

The as-received natural zeolites showed a mordenite (MOR) dominant phase with impurity phases and low total surface area (ca. 133 m²/g) as indicated by X-ray diffraction and nitrogen physisorption analysis, respectively. High-quality MOR, i.e., high crystallinity and large surface area (ca. 327 m²/g), was obtained through hydrothermal recrystallization of the low-grade natural mordenite followed by a microwave-assisted acidic ion-exchange. The time of hydrothermal recrystallization affected the physical and chemical properties of the recrystallized natural mordenite. The n-butane isomerization in a fixed bed reactor was selected as a model reaction to evaluate the samples. The n-butane conversion was boosted from 3.5% over the parent natural MOR (H-P-H) to 25% over the recrystallized natural MOR (H-R26-H). The yield of isobutane over the recrystallized natural MOR was 8%, which was far higher than the one over parent natural MOR with only 1%. The recrystallized natural MOR also exhibited a comparable isobutane yield with the synthetic mordenite (ca. 7%).