The role of the substrate porosity, Cu loading and redox state of CuO/CeO2/Al2O3 catalysts in the CO Preferential Oxidation in H2-rich mixtures

The Preferential Oxidation of carbon monoxide (CO-PROX) reaction is meaningful processes for CO removal in trace amounts from a reformate stream rich in H2 to be further utilized in Fuel Cell applications. Catalysts based on transition metal oxides (e.g CuO/CeO2/Al2O3) were identified as potential candidates for CO-PROX in H2-rich reformate gas thanks to their high activity towards CO oxidation and their crucial role in the reduction or replacement of platinum-group metal (PGMs)- based catalysts. In this work, six catalytic matirial were provided by National Center for Scientific Research “Domokritos” (NCSRD) as a part f an active collaboration. The catalyst were synthesised with two methods(ADP and EISA), which differ in the methodology employed for the deposition of CuO-Cu on the surface of the catalytic substrate. ADP catalysts differed according to the loading of copper oxide (15,20 and 30%), while EISA catalysts were calcined at different temperatures (400,550 and 900°C). A fixed GHSV value (20000h−1) and a specific thermal ramp (up to 280°C) were taken into account for the verification of the catalytic activity. Activity experiments in a standard plug-flow reactor showed that 20% CuO loading has the highest performance among the ADP samples, with a maximum CO conversion of 80% at 185°C and 100% selectivity for CO oxidation up to 170°C. However, the 20% sample synthesized with EISA and calcined at 900°C showed the highest activity among all the samples, with 90% of CO conversion at 210°C and H2 conversion lower than 0.5% from 250°C. A weak deactivation of the 20% CuO/CeO2/Al2O3-ADP sample was obtained as higher temperatures were needed to achieve the same performance of the fresh catalyst. In the operational range of the reaction, the catalyst is subjected to a continuous cycle of reduction and oxidation, due to the high presence of hydrogen (a strong reducing agent) and the fact that the most stable form of the catalyst is the oxidized state. This redox cycle causes the catalyst to consume some of the oxygen in the mixture and thus reduce the possible conversion of CO WGS reaction cannot take place for temperature below to 155°C because the catalyst is not active towards the hydrogen oxidation.