Highly Effective Pt-Based Water–Gas Shift Catalysts by Surface Modification with Alkali Hydroxide Salts

Herein, we describe an economical and convenient method to improve the performance of Pt/alumina catalysts for the water-gas shift reaction through surface modification of the catalysts with alkali hydroxides according to the solid catalyst with ionic liquid layer approach. The results are in agreement with our findings reported earlier for methanol steam reforming. This report indicates that alkali doping of the catalyst plays an important role in the observed catalyst activation. In addition, the basic and hygroscopic nature of the salt coating contributes to a significant improvement in the performance of the catalyst. During the reaction, a partly liquid film of alkali hydroxide forms on the alumina surface, which increases the availability of H2O at the catalytically active sites. Kinetic studies reveal a negligible effect of the KOH coating on the rate dependence of CO and H2O partial pressures. TEM studies indicate an agglomeration of the active Pt clusters during catalyst preparation; restructuring of Pt nanoparticles occurs under reaction conditions, which leads to a highly active and stable system over 240 h time on stream. Excessive pore fillings with KOH introduce a mass transfer barrier as indicated in a volcano-shaped curve of activity versus salt loading. The optimum KOH loading was found to be 7.5 wt %.