Studies On Rh-based Catalysts For CO Hydrogenation To C₂-oxygenates

As the substitution for crude oil, the production of chemicals and transportation fuels from abundant coal and natural gas has attracted much attention in the world. Rh-Mn-Li/SiO2 catalyst is proved to be one of the most promising catalyst systems for the synthesis of C2-oxygenates from syngas. However, the activity and the selectivity of C2 oxygenates produced is still needed to be improved.Relative catalytic activities for CO adsorption and dissociation, hydrogenation and CO insertion, as well as Rh particle size on catalyst surface are regulated by addition of promoter, and/or selection of silica, reduction and reaction conditions and preparation process to promote the formation of C2 oxygenates over Rh-Mn-Li/SiO2 catalyst.The addition of trace amount of Ti (0.0025～0.02wt%) as a promoter in Rh-Mn-Li/SiO2 and the regulation of calcination temperature of TiOx/SiO2 alter Rh-Mn interaction, and thus increase the STY and selectivity of C2 oxygenates. The results show that the presence of H2 promotes the desorption of weakly adsorbed CO and its re-adsorption. In addition, the dissociation of strongly adsorbed CO is enhanced; the adsorption CO is strengthened and Rh dispersion increases.When large pellet size of silica is used to prepare Rh-Mn-Li/SiO2 catalyst(Rh=1 %)without calcination, Rh particle size formed on the catalyst surface is 2~4 nm with sharp distribution. As expected, when CO hydrogenation reaction is operated at 593K, 3Mpa and 12500h-1, the STY and selectivity of C2+ oxygenates reach up to 618.4 g/kg-cat.h and 54.6% (on carbon basis), respectively.Catalytic hydrogenation activity is correctly suppressed over...