Condensed-phase low temperature heterogeneous hydrogenation of CO 2 to methanol

A low-temperature CH 3 OH synthesis was achieved at 120–170 °C using tertiary amine and alcohol in the presence of a Cu/ZnO/Al 2 O 3 catalyst by CO 2 hydrogenation. A series of 1°, 2° and 3° amines and alcohols were screened to study their influence on the formation of CH 3 OH. Particularly, 3° amines such as NEt 3 in combination with EtOH formed CH 3 OH with 100% yield with respect to the amine. Unlike the traditional gas-phase heterogeneous metal catalyzed CO 2 -to-CH 3 OH reactions, no CO is used in the feed gas mixture in this method. In addition, the hydrogenation gives good selectivity (>95%) to CH 3 OH and only trace amounts of CO and CH 4 are formed. The presence of CO in the gas mixture was attributed to the decomposition of the CH 3 OH product, which was confirmed by high-temperature and high-pressure MAS NMR. The reaction was performed in the condensed phase at relatively lower temperatures, thus the RWGS reaction, which typically operates at >250 °C, was significantly reduced at these temperatures (120–170 °C). The first in situ spectroscopic evidence for the condensed phase hydrogenation of alkylcarbonate to CH 3 OH via ammonium formate and alkylformate intermediates was also presented under the experimental conditions.