Abstract
Cu-based catalysts are promising for CO oxidation applications with catalyst deactivation being a major barrier. We start with a CuO/Al2O3 catalyst and find that while the CO conversion decreases, CO2 accumulates and the average Cu chemical state stays the same. It suggests CO2 self-poisoning, i.e., CO2 desorption is the rate-determining step. Subsequently, experiments are performed to prove this hypothesis by showing (1) CO2 adsorption inhibits O2 adsorption, (2) complete desorption of CO2 regenerate the catalyst, (3) pre-adsorbed CO2 quenches catalyst activity which recovers during the reaction and (4) the apparent activation energy is consistent with CO2 desorption. It is further evidenced by using a stronger CO2 adsorbing support CeO2 to speed up CO2 desorption from the CuO sites resulting in a superior CuO/CeO2 catalyst. It provides an example for experimentally deciding and speeding up the rate-determining step in a catalytic reaction.
Highlights
Catalytic CO oxidation is an important reaction in automotive exhaust catalysis [1,2,3,4,5].The current commercial catalysts are mainly noble metal (Pt, Pd and Rh) containing catalysts
Catalyst Deactivation Occurs on a CuO/Al2 O3 Catalyst in CO Oxidation
With the initial show of correlation between CO2 adsorption and the catalyst performance, we experimentally proved the inferences from the CO2 self-poisoning hypothesis, including (1) CO2 adsorption inhibits
Summary
Catalytic CO oxidation is an important reaction in automotive exhaust catalysis [1,2,3,4,5]. The current commercial catalysts are mainly noble metal (Pt, Pd and Rh) containing catalysts. Due to the high prices and the limited resources of noble metals, noble metal-free catalysts are much more desired. Among all base metal oxides, cobalt and copper-based oxides are potential candidates [6,7,8,9,10]. A major drawback of Cu based catalysts is high susceptibility to deactivation by water and sulfur, which hinders their applications [11,12]. There is no consensus on what the active sites and deactivation mechanism are for Cu based catalysts
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