Olefin Upgrading over Ir/ZSM-5 catalysts under methane environment

•Alkene can be converted to cycloalkane under methane environment over Ir/ZSM-5.•Highly dispersed Ir/IrO2 species benefits methane activation.•Strength and amount of surface acidity play important role on olefin upgrading.•Methane has potential to act as alternative hydrogen donor for olefin saturation.

Upgrading olefin in the synthetic oil to alkane is highly desired due to its high volatility and thermal unstability as well as low energy density. Unlike conventional hydrotreating, methane (CH4) was used in this study as the novel hydrogen donor for olefin saturation. The significant increase of H/C atomic ratio of product oil from 1.69 ± 0.02 (over pure ZSM-5) to 2.04 ± 0.02 (over Ir/ZSM-5 (10.0)) and the alkane content up to 83.8 ± 2.1% in the upgraded oil indicated that methane could exhibit comparable catalytic performance to what hydrogen (H2) did for olefin (1-Decene) upgrading over the developed bifunctional catalysts with low Ir loadings. The HRTEM and XPS data revealed that the highly dispersed metallic Ir particles with average size of 1.32 nm was coexisting with IrO2 species. The synergic effects of Ir/IrO2 obviously promoted the activation of methane, which supplied sufficient hydrogen for the saturation and stabilization of olefin. The results from BET indicated that the pore size and volume of the ZSM-5 support were increased upon Ir introduction, which provided more active sites for cracking olefin (1-decene). NH3-TPD results suggested that the presence of highly dispersed Ir increased the amount of surface acidity, which enhanced the formation and stabilization of carbenium ion intermediates. As a result, the produced alkanes were mainly composed of cyclopentane-derived compounds, like propylcyclopentane, 3-methylbutyl-cyclopentane and 1,2,4-trimethyl-cyclopentane, which has great application potential as immersion fluid and additive in the field of optics and petroleum.

Graphical abstractOlefin gets converted into cycloalkane with high efficiency under the facilitation of Ir/ZSM-5 under methane environment.Download high-res image (195KB)Download full-size image