Activity, durability and microstructural characterization of ex-nitrate and ex-chloride Pt/Ce0.56Zr0.44O2 catalysts for low temperature water gas shift reaction

Ex-nitrate and ex-chloride Pt over Ce0.56Zr0.44O2 have been prepared by a single-step solution combustion synthesis (SCS) and are compared with the corresponding catalyst prepared by incipient wetness impregnation (IWI) of platinum over the bare support for the water gas shift reaction under a simulated reformate gas composition. All the catalysts have similar surface areas (23-27 m(2) g(-1)). Structural and microscopic characterization shows the presence of metallic Pt in all the catalysts. Ex-nitrate catalyst prepared by solution combustion synthesis shows an interesting epitaxial bonding between Pt and the support that has an effect on the WGS activity. It is found that the catalysts prepared by solution combustion method are sensitive to pretreatment atmosphere, with the oxidized catalysts more active than the reduced and as-synthesized catalysts. The impregnated catalysts behave similarly in all the three forms. The stability of these materials under reformate atmosphere at 563 K has also been compared. The catalysts experience different degrees of deactivation related to the method of preparation and the precursors used. Sintering of Pt associated with the formation of carbonate is responsible for the decay of activity (10-12%) in SCS catalysts. For the impregnated catalyst from nitrate precursor, there is no sintering effect, but a strong embedding of Pt by the support reduces the activity (overall loss 34%) together with carbonate formation. The behaviour of the impregnated catalyst from chloride precursor is unusual since it shows an overall gain in activity (8%). The removal of chlorides during durability test and long-term stabilization of Pt crystallize size around 3 nm have been attributed as the controlling factors for this catalyst. Recovery of all the catalysts except the impregnated catalyst from nitrate precursor is found to be reversible. (C) 2010 Elsevier Inc. All rights reserved.