Deactivation of the water–gas-shift activity of Pd/ceria by Mo

Abstract

The effect of surface Mo on the water-gas-shift (WGS) activity of Pd/ceria was studied. A series of 1-wt% Pd catalysts, with varying Mo content, were prepared from supports obtained by aqueous impregnation of (NH 4 ) 2 MoO 4 onto ceria. Rates were found to decrease linearly with Mo coverage up to 1.8 Mo/nm 2 and were 10% of that on Pd/ceria after the addition of this amount of Mo. TPD studies with 2-propanol on the Mo-containing ceria demonstrate a relationship between the loss of WGS activity and ceria sites that decompose the alcohol to propene and water. FTIR measurements suggest that Mo ions exchange with surface hydroxyls on ceria and that carbonates are not formed on ceria surfaces that have 1.8 Mo/nm 2 . The results from CO-O 2 pulse measurements suggest that the Mo-containing surface is much harder to reduce than pure ceria. Raman spectra of the Mo-containing ceria show features associated with molybdena only for Mo coverages greater than 1.8 Mo/nm 2 . The implications of these results for understanding WGS activity on Pd/ceria are discussed. KeywordsCeria, Pd, Molybdena, Water-gas-shift reaction, 2-propanol

The dynamic surface chemistry during the interaction of CO with ceria captured by Raman spectroscopy

“…However, the more than 90% decrease the intensities of these two bands after exposure to flowing O 2 for 12 h at room temperature (figure 3) provides a strong driving force to consider alternative assignments to carbonate for the 1582-1600 and 1331-1340 cm )1 bands observed in this investigation, even though their formation under conditions similar to those used in the present work has been reported [3,41]. Carbonates of ceria are notoriously stable [10], and no apparent change in the spectra of CO adsorbed on CeO 2 occurs after dosing O 2 on CeO 2 preadsorbed with CO according to Li et al [26].…”

Study on the carbon deposition in steam reforming of ethanol over Co/CeO2 catalyst

“…3 [5,13,15,[37][38][39][40][41]. The one route is dehydrogenation of ethanol to produce CH 3 CHO, then CH 3 CHO is decomposed and then the steam reforming of CH 4 , and so on.…”

“…Sketch map of reaction pathway for catalytic steam reforming of ethanol[5,13,15,[37][38][39][40][41].…”

Effect of Mo and Re Promoters on the Activity and Stability of a Pt/ZrO2 Water-Gas Shift Catalyst (Part 1)

“…The effect of Mo addition to Pd/Ceria catalysts was studied by Zhao et al [17]. The authors found a reduction in WGS activity with increasing Mo loading.…”