Nanostructured Noble Metal Catalysts udfor Water-Gas Shift Reaction

摘要

The water-gas shift (WGS) reaction (CO + H2O = CO2 + H2) has attracted great research attention because of its applications in adjusting H2/CO ratio for the Fischer-Tropsch process, providing hydrogen-rich streams for fuel cells and processing exhaust gases from automobiles. However, the current WGS process suffers from certain drawbacks of traditional catalysts, such as the toxicity of Fe-Cr-based catalysts and the instability/low space velocity of Cu-based catalysts. In the search for alternative catalysts to overcome these drawbacks, novel metal-based catalysts have been the focal point of most recent studies. The structures and properties of CeO2, on which the rate determining step proceeds (i.e. water dissociation), are believed to fundamentally impact the performance of this catalyst.udIn this project, the objective is to develop a rational design of novel metal-based WGS catalyst which combines high activity with stability against sintering and poisoning. In order to achieve this objective, we have prepared pure and mixed lanthanum-cerium oxide supports, and investigated the effects of these compositions and morphologies to the material’s reducibility and catalytic activity. For the composition, it was found that a proper amount of La doping can improve the WGS activity by tailoring the Ce4+/Ce3+ ratio. When we change the morphology, the CeO2 nanorods were observed to be a better support for Au than the CeO2 nanoparticles. The outstanding performance of the CeO2 nanorods were attributed to its predominantly exposed crystal plane {110}, which is more active to be reduced and to form oxygen vacancies than the {111} exposed by CeO2 nanoparticles. udAfter obtaining the high activity WGS catalysts, we have improved our catalysts against particle sintering and S-poisoning. Surface decoration technique has been applied to prepare layered La2O3/M/CeO2 (M = Au, Pt) with sulfur resistance and regeneration ability during cyclic sour WGS. On one hand, La2O3 has been demonstrated as a protective overlayer against H2S in syngas feedstocks in addition to its stabilizing effect to prevent Au nanoparticles sintering. On the other hand, reducible CeO2 supports enable complete regeneration of sulfur-poisoned Pt catalysts due to the strong metal support interaction (SMSI).