Methanol Production and Higher Alcohols from Syngas

3 Methanol Production and Higher Alcohols from Syngas 

The nature of the outer-layer of the Cu-Zn based catalysts and the role of the different active sites are still a topic of investigation. Metallic copper is implicated as being the dominant oxidation state of the metal during the reaction. However, the presence of Cu+ is also important as a small amount of oxygen increases the reaction rate.51,66 Shen et al.67 found on ceria supported copper catalyst that in spite of the reductive reaction atmosphere, metallic copper particles on cerium oxide were oxidised during reaction and the catalyst was activated. The formation of the copper oxide species was considered indispensable for the onset of high catalytic activity. Synergy between Cu and ZnO in the catalysis of methanol synthesis 

The mechanism of methanol synthesis from syngas over Pd catalysts has been studied with Ca-doped Pd catalysts supported on silica.90 It was found that basic metal oxides are needed to give a Pd catalyst with high activity for methanol formation. The authors proposed that the Ca-doped Pd/SiC 2 catalysts acted as a bifunctional catalyst in the methanol synthesis reaction. Sites on the metal oxide are responsible for the formation of the formate 

Finally, it should be noted that different reaction engineering approaches are being investigated to further increase the activities and selectivities of higher alcohol synthesis. A review of these approaches has recently been published by Herman.99 

4 Hydrogenation Reactions and Other Possibilities Aimed to Reuse C02 

Such mechanism has been postulated mainly on the basis of isotope-labelling studies. Methanol is formed from CO2 that is produced during the water-gas shift reaction. Under normal operating conditions, carbon dioxide is added to the feed gas. There appears to be a limit to the amount of CO2 that can be present in the feed, since water produced during methanol synthesis from 

The high surface concentration of these surface species interact with CO2 from the feed gas, producing an inhibition of the water-gas shift side-reaction. In the second case it is proposed that two cat-alytical species (CoO(OH)/Co304 and Mo ) synergisticallyperform the formation of C2+ alcohols. 

Technologically the evaluation of catalysts under realistic conditions is relevant. Thus in a detailed study of the effect of HgS in the syngas feed over alkali promoted cobalt-molybdenum sulphide catalysts, it is raised that the presence of hydrogen sulphide lowers the alcohol selectivity enhancing the hydrocarbon formation, even if the production of higher alcohols is enhanced at adequate HgS concentration levels. 

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