A Novel Two-stage CO₂ Conversion for Methanol and Dimethyl Ether Formations

Chao-Lung Chiang^1*, Kuen-Song Lin², Yan-Gu Lin¹

¹Material Science Group, Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu City, Taiwan
²Department of Chemical Engineering and Materials Science/Environmental Technology Research Center, Yuan Ze University, Taoyuan City, Taiwan

* Presenter:Chao-Lung Chiang, email:chiang.cl@nsrrc.org.tw

The co-precipitation prepared Ni₅Ga₃/SiO₂ and CuO–ZnO–Al₂O₃/protonated Y-type zeolite (CZA/HYZ) catalysts for a two-stage CO₂ conversion were well-characterized. Catalytic components of Ni₅Ga₃/SiO₂ and CZA/HYZ were gallium and copper that have been confirmed with X–ray photoelectron spectroscopy (XPS). Notably, the stable oxidation states of metal atoms in Ni₅Ga₃/SiO₂ and CZA/HYZ with slight bond distance shifts were demonstrated with X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra. The optimal catalytic performances (CO₂ conversion=100.0%, CH₃OH selectivity=84.7%, CH₃OH yield=84.7%) of Ni₅Ga₃/SiO₂ were obtained at 250 °C. In terms of CZA/HYZ, the catalytic temperature with optimal catalytic performances (CH₃OH conversion=78.0%, CH₃OCH₃ selectivity=91.7%, CH₃OCH₃ yield=71.5%) was also 250 °C. Rate constants and activation energies of CH₃OH and CH₃OCH₃ formations at various catalytic temperatures were evaluated with pseudo-first-order/second-order models and Arrhenius equation, respectively. Extremely low Gibbs energies of CH₃OH (2.720 kJ/mol) and CH₃OCH₃ (1.160 kJ/mol) formations revealed that their spontaneities were significantly enhanced using Ni₅Ga₃/SiO₂ and CZA/HYZ, respectively.

Keywords: Two-Stage CO₂ Conversion, Hydrogenation-Dehydration, Methanol-Dimethyl Ether, Ni-Ga/Cu-Based Catalyst