EXAFS and FT-IR Characterization of Mn and Li Promoted Titania-Supported Rh Catalysts for CO Hydrogenation

Abstract

The effect of Li and Mn promoters on the structure and selectivity of supported Rh catalysts for CO hydrogenation reaction was examined. Infrared spectroscopy and X-ray absorption were used to investigate the adsorption of reactants and local structure of Rh. These techniques were used in combination with reactivity, H2 chemisorption, and temperature programmed studies to correlate structural characteristics with activity and selectivity during CO hydrogenation of unpromoted Rh/TiO2 and three promoted Rh catalysts: Rh–Li/TiO2, Rh–Mn/TiO2, and Rh–Li–Mn/TiO2. The presence of a promoter slightly decreases the Rh clusters size; however, no evidence for an electronic effect induced by the presence of Li and Mn was found. Higher turnover frequencies were found for the promoted catalysts, which also showed the lower dispersion. The Li promoter introduces a weakened CO adsorption site that appears to enhance the selectivity to C2+ oxygenates. The selectivity to C2+ oxygenates varies inversely with the reducibility of Rh metal, that is, the lower the Rh reducibility, the higher the selectivity.

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

“…1, le middle). 23,37,49 The peak shi suggests that Mn is in close contact with Rh, which apparently impedes the reduction of Rh oxide species. The second peak located at 500 K is increased in intensity compared to the unpromoted catalyst indicating that Mn has an impact on the nanostructure of the calcined precursor.…”

Kinetics study of C 2+ oxygenates synthesis from syngas over Rh–MnO x /SiO 2 catalysts

“…Two peaks at 49 and 84 1C were observed for pure Rh. The first one can be resulted from the reduction of surface RhO x , while the second one should be caused by the reduction of bulk RhO x (Luo et al, 2001;Schwartz et al, 2011). With the addition of Mn, the reducibility of RhO x was decreased, leading to a continuous shift to higher temperature and broadened from 50 to 100 1C.…”

Synthesis of higher alcohols over highly dispersed Cu–Fe based catalysts derived from layered double hydroxides

“…Rh-based catalysts [14,15], and Mo-based catalysts [16,17]. Among those catalytic systems available for HAS reaction, Cu-based catalysts containing active metal towards F-T synthesis (Fe, Co, or Ni), such as Cu-Fe based catalysts, are considered very promising catalysts [18,19].…”