Metal-ceria catalysts

Table 69 Kinetic parameters from fixed bed testing of metal/ceria catalysts at 300 °C386... 

Table 73 CO conversion data over metal/ceria catalysts with equivalent molar amounts of metal (l%Pt by weight as basis). GHSV = 21.7 L/g, per hour. BET SA ceria = 105.5 m2/g410 ... 

The metal/ceria catalyst was suggested to possibly follow the simplified mechanism in Scheme 83, with H20 activation on ceria, CO adsorption on the metal, with reaction across the metal-ceria interface. 

Catalyst systems for the WGS reaction that have recently received significant attention are the cerium oxides, mostly loaded with noble metals, especially platinum 42—46]. Jacobs et al. [44] even claim that it is probable that promoted ceria catalysts with the right development should realize higher CO conversions than the commercial Cu0-Zn0-Al203 catalysts. Ceria doped with transition metals such as Ni, Cu, Fe, and Co are also very interesting catalysts 37,43—471, especially the copper-ceria catalysts that have been found to perform excellently in the WGS reaction, as reported by Li et al. [37], They have found that the copper-ceria catalysts are more stable than other Cu-based LT WGS catalysts and at least as active as the precious metal-ceria catalysts. 

While both base metal and precious metal catalyst formulations performed well in a simulated high temperature WGS feed stream (-15% CO), precious metal catalysts were clearly superior when tested with a low temperature WGS feed stream (-5% CO). Results for a Siid-Chemie copper zinc catalyst (T2650) and a Siid-Chemie precious metal-ceria catalyst (PMS5) are shown in Figure 5, tested in a simulated low temperature WGS feed stream. Equilibrium was achieved for the PMS5 catalyst for... 

Figure 5. Conversion of CO versus temperature for engineered forms of Sud-Chemie T2650 (copper-zinc) and PMS5 (precious metal ceria) catalysts. Results correspond to a simulated low temperatme WGS feed stream at a steam to gas ratio of 0.5.

The greater activity of Pd for methanol decomposition reaction was also found by using the steady state isotopic transient kinetic analysis (SSITKA) method over noble metal (Pt, Pd, Rh)/ceria catalysts. Their activity increased in the order Rh < Pt < Pd, while the by-products were (i) methane, carbon dioxide, water, methyl formate and formaldehyde in most cases and (ii) ethylene and propylene, formed only over Rh/Ce02, at 553 K. SSITKA measurements indicated that two parallel pools exist for the formation of CO (via formation and decomposition of formaldehyde and methyl formate). The difference in the activity order of noble metal/ceria catalysts seems to correlate with the surface coverage of active carbon containing species, which followed the same order. The latter implies that a part of these species is formed on the ceria surface or/and metal-ceria interface. ... 

Metal/ceria catalysts have received great interest for their reactions involving steam conversion, including CO for low-temperature water-gas shift, and the conversion of chemical carriers of hydrogen, among them methanol and ethanol. The mechanism by which ROH... 

Jacobs G, Ricote S, Davis BH (2006) Low temperature water-gas shift type and loading of metal impacts decomposition and hydrogen exchange rates of pseudo-stabilized formate over metal/ceria catalysts. Appl Catal A 302 14—21... 

Figure 8.25 Methanol conversion vs. reaction temperature over IB metal/ceria catalysts prepared by (A) DP and (B) CP. Reprinted from Scird et with permission from Elsevier.

Design and Modeling of Active Sites in Metal-Ceria Catalysts... 

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