Abstract
Mn and Li promoted Rh catalysts supported on SiO2 with a thin TiO2 layer were synthesized by stepwise incipient wetness impregnation approach. The thin TiO2 layer on the surface of SiO2 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 Rh0 and Rhδ+ 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 H2/CO ratio in the feed is recommended.Graphic
Highlights
The synthesis of renewable fuels such as ethanol has received extensive attention in recent years for its application both as a fuel additive and an energy carrier [1,2,3]
Prepared supported rhodium catalysts were further studied by transmission electron microscopy technique (TEM) combined with energy-dispersive X-ray spectroscopy (EDX)
Further raising the calcination temperature to 773 K leads to an increase of Rh nanoparticle size to 2.8 nm, with some large clusters consisting of small Rh2O3 crystals (Fig. 1c)
Summary
The synthesis of renewable fuels such as ethanol has received extensive attention in recent years for its application both as a fuel additive and an energy carrier [1,2,3]. Catalyst synthesis is composed of several steps: (i) depositing a thin layer of TiO2 on SiO2; (ii) introducing Mn on Rh or other way around by stepwise incipientwetness-impregnation (IWI) on the prepared TiO2/SiO2; (iii) impregnating Li by a further IWI With this strategy, we demonstrate that the thin TiO2 layer on the surface of SiO2 plays a crucial role in stabilizing Rh nanoparticles in right dispersion. Rh on MnO is more efficient in promoting the hydrogenation of acetaldehyde to ethanol compared to its counterpart with MnO on Rh. the catalytic performance of the multicomponent Rh-based catalyst depends on Rh particle size, and catalyst with a larger Rh nanoparticle size exhibits a higher activity and C2-oxygenates selectivity, but lower methane selectivity than its counterpart with smaller Rh nanoparticles. This approach will provide new insight for the rational design of highly active and selective Rh based catalysts for C2-oxygenates production
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