CO Hydrogenation to C2-oxygenates over Rh–Mn–Li/SiO2 Catalyst: Effects of Support Pretreatment with nC1–C5 Alcohols

Abstract

The effects of support pretreatment with nC 1 -C 5 alcohols on the performance of Rh-Mn-Li/SiO 2 catalyst in the synthesis of C 2 -oxygenates from syngas have been investigated by CO hydrogenation reaction, transmission electron microscopy (TEM), pulse adsorption of CO and H 2 , and Fourier Transform infrared (FT-IR) spectroscopy. The catalysts prepared from the pretreated silica supports exhibited higher space time yields of C 2 -oxygenates (STY C2-oxy ) and selectivities towards C 2 -oxygenates (S C2-oxy ) than that prepared from the untreated silica support. The enhancement in the hydrophobicity of the pretreated silica supports would be favorable for increasing Rh dispersion and ratio of Rh + /Rh 0 sites, therefore increasing the number of active sites, especially the active sites for CO insertion. Such variations are responsible for the improvements in the catalytic performance of the Rh-Mn-Li/SiO 2 catalyst.

Effect of secondary additives (Li, Mn) in Fe-promoted Rh/TiO2 catalysts for the synthesis of ethanol from syngas

“…Mn was a favorite additive for Rh-based catalysts to produce C 2? oxygenates on the supports of SiO 2 and Al 2 O 3 [4,19]. As shown in Table 1, by introducing Mn in 2%Rh-5%Fe/TiO 2 , the CO conversion increased but the selectivity slightly decreased.…”

“…The catalytic activity and the product distribution over Rhsupported catalysts can be significantly influenced by changing either the support or promoter for the synthesis of ethanol from syngas [13][14][15][16][17]. Most previous reports have studied the SiO 2 support with relatively less literature on carbon or Al 2 O 3 supports, and several on TiO 2 support [1][2][3][4][5][6][13][14][15][16][17][18][19]. The TiO 2 support has high density of surface hydroxyls and thus may have an effect on the interaction between neighboring cations or atoms of the supported metals [3,5].…”

Insights into structure and dynamics of (Mn,Fe)Ox-promoted Rh nanoparticles

“…66 The promoter effect of manganese oxide has been frequently attributed to a stabilization of Rh + sites. 11,19,37,38,73 However, no Rh + carbonyl species were detectable at reaction temperature excluding these species from being the active sites in CO hydrogenation. The present experiment clearly demonstrates that Rh + does not exist on the surface of the promoted catalyst under reaction conditions (Fig.…”

The Promoting Effect of Fe Doping on Rh/CeO2 for the Ethanol Synthesis

“…The intensity ratio of dicarbonyls to monocarbonyls band on the catalysts increased slightly with the rise in Fe content. Generally the CO(gdc) species can only be formed on highly dispersed rhodium [51]. It can be inferred from the IR results that the Fe doping decreases the Rh particle size.…”