PNNL

Abstract

The Cu/ZnO/Al2O3 catalyst was screened with a series of primary, secondary and tertiary amines and alcohols under 60 bar H2/CO2 pressure at 170 °C. Use of amine and alcohol mixture was found to be necessary for the formation of CH3OH. Particularly, tertiary amines such as NEt3 in combination with EtOH formed CH3OH with 100% yield with respect to the amine. The NEt3, EtOH and catalyst can be recovered after the reaction and reused. Unlike the traditional gas-phase heterogeneous metal catalyzed CO2-to-CH3OH reactions, no CO is used in the feed gas mixture in this method. In addition, the hydrogenation gives good selectivity for CH3OH and only trace amounts of CO and CH4 are formed. The presence of CO in the gas mixture was attributed to the decomposition of CH3OH product, which was confirmed by high temperature MAS NMR. In addition, since the reaction was performed in the condensed phase at relatively lower temperature 120-170 °C, the RWGS reaction was significantly reduced. We also present here the first in situ spectroscopic evidence for the condensed phase hydrogenation of alkylcarbonate or CO2 to CH3OH via ammonium formate and alkylformate intermediates.