Catalyst copper/ceria

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. 

The copper-ceria catalysts in WGS were found to be nonpyrophoric and stable, showing little or no deactivation during the experiments. The Civ,2Ce(J802 y catalyst prepared by coprecipitation method showed good catalytic activity for the WGS reaction. The Cu0, Ce0 902 v catalysts prepared by the sol-gel method were found to be less active, which could be due to the lower number of active... 

The [MSR 6] reactor type (see below) was applied for methanol steam reforming over Cu/Ce02/Al203 catalysts by Men et al. [34, 35], Wash coating of the alumina was performed, followed by subsequent impregnation steps with ceria and copper salt solutions. At 250 °C reaction temperature and a water/methanol molar ratio of 0.9, the copper/ceria atomic ratio was varied from 0 to 0.9, revealing the lowest conversion for pure ceria and a sharp maximum for a ratio of 0.1 (see Figure 2.13). 

Liu YY, et al. Highly active copper/ceria catalysts for steam reforming of methanol. Appl Catal A Gen. 2002 223(l-2) 137-45. 

A patent was granted to Shore et al.42 for a process utilizing a Cu/Ce02 catalyst that also contained Pt. It was found that the precious metal lowered the temperature necessary for the reduction of the base metal from its inactive oxide to the active metal form. The operating temperature is 100°C, compared with the minimum of 140°C required for the reduction of Pt-free copper/ceria in the reformate. One limitation of the copper Prox catalyst is that it is CO inhibited CO shifts the reduction temperature of the catalyst. 

The reactivity profiles shown by the samples suggest on their own that copper-ceria interactions lead to a large promotion of CO oxidation. The activity observed for CuA can be interpreted in terms of the formation of important amounts of more active [12] metallic copper by interaction of the catalyst with the reactant mixture, as evidenced by the FTIR experiment of Figure 6b, for a temperature close to 573 K. At lower temperature, the presence of less active dispersed Cu ions [17] or of smaller amounts of reduced copper entities leads to low activity levels for this sample. The important decrease of isoconversion temperatures observed already upon addition of a relatively small amount of ceria must be due to changes in the nature of the active centers and/or in the reaction mechanism involved. 

Since classical Cu/ZnO catalysts exhibited a poor stability while the addition of alumina resulted in much better systems, it was tempting to add alumina to Cu-Ce intermetallic compounds. Jennings et al. (1992a), prepared ternary Cu-Ce-Al alloys of various compositions and also tried a variety of other metals (Ca, Cr, Mn, Pd, Zn). Among these ternary alloys aluminum-containing catalysts were the best. In spite of lower initial activities as compared to binary alloys, they exhibited a much better long-term stability. It is believed that the role of aluminum is to stabilize the disperse copper-ceria phases responsible for methanol synthesis activity, although the mechanism for such a process remains unclear. 

H. Kusar, S. Hocevar, J. Levee, Kinetics of the water-gas shift reaction over nanostractured copper-ceria catalysts, Appl. Catal. B Environ. 63 (2006) 194-200. 

Gamarra, D., Belver, C., Fernandez-Garcra, M., etal. (2007). Selective CO Oxidation in excess H2 over copper-ceria catalysts Identification of active entities/species, J. Am. Chem. Soc., 129, pp. 12064-12065. 

Martinez-Arias, A., Cataluna, R., Conesa, J.C., and Soria, J. Effect of copper-ceria interactions on copper reduction in a Cu/Ce02/Al203 catalyst subjected to thermal treatments in CO. J. Phys. Chem. B 1998,102, 809-817. 

In Fig. 9.1, the results of in situ time-resolved XRD show diffraction lines for CuO and CeOg in a freshly prepared copper-ceria nano-catalyst. Once the catalyst is exposed to the reactants of the WGS at temperatures above 200 °C, the diffraction lines for CuO disappear and new lines appear for metallic Cu. Significant catalytic activity is... 

Of the ceria-based oxide catalysts, mixed ceria cobalt and mixed ceria-copper have been the most extensively investigated. 

This equilibrium has a buffer-like effect stabilizing the presence of cationic copper species in the structure even in a highly reductive atmosphere. The above scheme of copper oxide-ceria interactions indicates clearly that the catalyst is mutually promoted, i.e., both copper and ceria cooperate in the redox mechanism. 

Alloying the nickel of the anode to improve tolerance for fuel contaminants has been explored. Gold and copper alloying decreases the catalytic activity for carbon deposition, while dispersing the anode with a heavy transition metal catalyst like tungsten improves sulfur resistance. Furthermore, ceria cermets seem to have a higher sulfur tolerance than Ni-YSZ cermets [75],... 

---