Oxidative Fluorination of a Ternary Cu/ZnO/FeOx Methanol Catalyst─A Proof of Principle

Abstract

Oxidative fluorination is reported to increase methanol (MeOH) productivity of binary copper–zinc oxide (CZ) catalyst systems yet is incompatible with all the hitherto tested ternary support materials. Here, we show that the oxidative fluorination with F₂ gas of CZ MeOH catalysts including iron oxide as a support material improves catalytic performances. A systematic variation of the compositions of the investigated ternary CZFe (copper, zinc, and iron) catalyst system led to a total of 13 different systems. The subsequent oxidative fluorination of all systems with a low F₂ pressure of 200 mbar showed significant improvement in the MeOH productivity and selectivity for almost all systems tested. High-iron systems benefited most from oxidative fluorination. In addition, selected systems were exposed to higher F₂ amounts and were studied. Further measurements showed that the crystallinity, surface area, and high-temperature carbonate content of the CZFe systems are very well tunable. Kinetic investigations indicated that fluorination leads to an increase in the number of active sites for the MeOH synthesis and at the same time increases the apparent activation energy for the RWGS reaction. In addition, oxidative fluorination at total F₂ pressures of and higher than 1250 mbar shuts down the iron-induced parasitic Fischer–Tropsch-type hydrogenation to hydrocarbons and results in the highest MeOH production rates.