TAILORING,GOLD-MIXED LA/CE-OXIDE CATALYSTS FOR WATER-GAS SHIFT

摘要

The water gas shift reaction (WGS) is one of the key reactions in the production of liquid fuels or hydrogé? from fossil and renewable resources. It is widely used to adjust the CO:H_2 ratio in synthesis gás for the production of chemicals and liquid fuels, and to reduce the carbon monoxide content in order to produce hydrogen-rich streams for fuel cells. While WGS is at high temperatures limited only by thermodynamic equilibrium limitations, at lower temperatures (<400°C) the activity and stability of the catalysts is currently the limiting factor. In recent years, supported Au catalysts have widely been reported as a potentially highly active WGS catalyst, in particular in combination with a CeO_2-based support. Building onto these reports, we are currently working on the synthesis of Au supported on mixed La/Ce oxides with wide range of La content (from 10% to 90%). Both CeO_2 and La_2O_3 oxides have previously been shown to be effective (and active) support materials for noble metal-based catalysts in WGS. Moreover, some previous work also showed that the addition of rare earth additives can improve the properties of CeO_2. However, very few systematic studies of La-doped CeO_2 for WGS are available in the published literature. Here we report the synthesis of gold catalysts on mixed CeO_2- and La_2O_3-based oxide supports with variable Ce:La ratio. By utilizing a reverse microemulsion-templated sol-gel synthesis route, nanostructured oxides with high surface area and good thermal stability were obtained. Mixed La/Ce- oxides solid solutions with cubic structures were obtained over the entire range of La-dopings up to 90% La content without phase separation. Au nanoparticles were deposited on these oxides by deposition-precipitation, and the resulting catalysts were characterized by a wide range of methods (XRD, I CP, TEM, TPR and BET). Water gas shift catalytic tests showed that appropriate addition of La can result in significantly increased activity of Au/CeO_2. Correlations between structure and reducibility of the oxide support and catalytic properties of Au/CeO_2-La_2O_3 catalysts will be discussed in detail in the presentation.