Quantification of Reactive CO and H2 on CuOx-CeO2 during CO Preferential Oxidation by Reactive Titration and Steady State Isotopic Transient Kinetic Analysis

The molar quantity of adsorbed CO and H 2 present on the surface of a mixed CuO x -CeO 2 catalyst during CO preferential oxidation in H 2 at 353 K was quantified using both the reactive titration method and the steady-state isotopic-transient kinetic analysis (SSITKA). For the reactive titration method, either CO or H 2 was replaced by He during steady state reaction while monitoring the residual transient product formation of CO 2 or H 2 O produced from the surface adsorbed CO or H 2 via catalytic oxidations. For SSITKA, 12 CO was replaced by 13 CO during steady state reaction while monitoring the transient product formation of 12 CO 2 . The amount of adsorbed reactive CO increases with increasing CO partial pressure or decreasing H 2 partial pressure, while the amount of reactive H 2 decreases with increasing CO partial pressure or decreasing H 2 partial pressure, showing that the adsorbed CO and H 2 compete for active redox sites and prohibit the other’s adsorption. Using reactive CO and H 2 amounts, two models of coverage were defined with trends providing insight into the competitive redox mechanism between adsorbed CO and H 2 . CO oxidation is kinetically preferred over CuO x -CeO 2, and the relative CO to H 2 coverage is shown to be the determiner for CO 2 selectivity. This new depiction of selectivity parameters provides a useful principle for the design of selective PROX catalysts.