| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 60559 | Journal of Catalysis | 2016 | 8 Pages |
•Prepared and characterized La-promoted Co–Cu catalyst for higher oxygenate synthesis.•CO linearly adsorbs on Co2C phase on the catalyst surface during syngas exposure.•Cu promoted catalyst reduction and the formation of ethanol and acetaldehyde.•The catalyst with Cu:Co = 1:2 showed the highest selectivity to alcohols.
A series of La-promoted cobalt–copper catalysts with various Co:Cu ratios have been used to study the conversion of syngas to oxygenates and hydrocarbons. In particular, the effect of the Co:Cu composition on the selectivity to oxygenates versus hydrocarbons has been examined.Three bulk catalysts were synthesized by coprecipitation, reduced in H2/He flow, and then cobalt carbide was formed during CO hydrogenation. The composition of the catalysts was as follows: Cu:Co = 12:9, 7:13, and 0:21 (cobalt only). CO hydrogenation tests were performed at differential conversions and 30 bar, H2/CO = 2/1 and 250 °C.The C1 selectivity (methane + methanol + CO2) was ∼64% for the two catalysts containing Co and Cu, and slightly less for the Co-only catalyst (52%). These products are formed by three mechanisms: (1) CH4: hydrogenation of dissociatively adsorbed CO at metallic cobalt sites, (2) CH3OH: hydrogenation of associatively adsorbed CO at copper sites, and (3) CO2: water gas shift, also at the copper sites. C2+ alcohol selectivity for the two Cu-containing catalysts is greater than for the Co-only catalyst, while the Co-only catalyst has the highest selectivity to acetaldehyde. The formation of C2+ oxygenates is consistent with the CO insertion mechanism, in which associatively adsorbed CO is inserted into the CHx species and forms the first C–C bond, producing a CHxCO intermediate that can be hydrogenated into ethanol or acetaldehyde.
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