Unveiling the Structure Sensitivity for Direct Conversion of Syngas to C2-Oxygenates with a Multicomponent-Promoted Rh Catalyst

Abstract

Mn and Li promoted Rh catalysts supported on SiO 2 with a thin TiO 2 layer were synthesized by stepwise incipient wetness impregnation approach. The thin TiO 2 layer on the surface of SiO 2 was proved to stabilize those small Rh nanoparticles and hinder their agglomeration. The reducibility of Rh on these catalysts depends on Rh particle size as well as the position of manganese oxide, and large Rh nanoparticles with MnO on Rh nanoparticles can be only reduced at an elevated temperature. Catalyst with large Rh particles exhibits a higher CO conversion and higher products selectivity towards long chain hydrocarbons and C2-oxygenates at the expense of decreasing methane formation than a similar catalyst with smaller Rh particles. This was attributed to the synergistic effect of Mn and Li promotion and molar ratio between Rh 0 and Rh δ+ sites on the surface of Rh nanoparticles. Moreover, Rh nanoparticles on MnO are proved to be more efficient in promoting hydrogenation of acetaldehyde to ethanol than its counterpart with MnO on Rh nanoparticles. Finally, in order to target high C2-oxygenates selectivity, low reaction temperature together with a low H 2 /CO ratio in the feed is recommended.

A Systematic Approach to Study Complex Ternary Co-Promoter Interactions: Addition of Ir, Li, and Ti to RhMn/SiO2 for Syngas Conversion to Ethanol

“…Various experimental studies have shown that all three promoters are capable of increasing selectivity towards C 2+ oxygenates [13,28,29]. Additionally, the role of Ti has been associated with increasing activity and stability due to its interaction with silica support [30][31][32][33][34][35][36], and Li has been reported to alter catalytic activity via the formation of oxygen vacancy sites and also to be capable of suppressing methane formation [34,35].…”