The promotion effects of Mn, Li and Fe on the selectivity for the synthesis Of C-2 oxygenates from syngas on rhodium based catalysts

Rh-based catalysts with the promoters of Mn, Li and Fe were prepared. The activity of the catalyst for C, oxygenates formation enhanced with the addition of additives. The promotion effects of these additives were investigated by means of FT-IR, CO-TPD and TPSR of adsorbed CO with H-2,. IR results suggested that Fe, Mn and Li might be in close contact with Rh, and formed new active sites, which promoted CO activation on Rh surface and favored the formation of C-2 oxygenated intermediates. The results of CO-TPD and TPSR showed that only a part of adsorbed CO on the catalyst could be hydrogenated into CH4. The ratio of CH4 quantity in TPSR to that of desorbed CO in CO-TPD on various catalysts was calculated, and it decreased in the order: Rh/SiO2 >Rh-Mn/SiO7 >Rh-Mn-Li/SiO >Rh-Mn-Li-Fe/SiO2, which implied that non-dissociated CO increased in the reverse order. Which was consistent with the catalytic activity of C, oxygenates formation sequence. The improvement of the space-time yield (STY) and selectivity towards C-2 oxygenates could be explained based on that the increase of the nondissociative CO and the decrease of dissociative CO on the catalyst favored the insertion of CO into CHx