NOx storage and reduction over copper-based catalysts. Part 1: BaO + CeO2 supports

The performance of noble metal-free copper-based NSR catalysts was studied by rapid-scan operando DRIFTS, using CeO2, BaO and BaO + CeO2 mixtures with different ratios as supports. The maximum temperature for CuO/CeO2 utilization as NSR catalyst was 400 °C, as the stored NOx species decomposed above this temperature. At 400 °C, CuO/CeO2 showed high NO oxidation capacity and NOx were stored on the catalyst mainly in the form of nitrates and lower populations of nitro groups. CuO/BaO was not suitable for NSR below 250 °C, because its oxidation activity was very low and its NOx storage capacity was negligible, but it did not exhibit upper temperature restrictions until 500 °C. The effect of temperature on NOx chemisorption on copper catalysts with BaO + CeO2 mixed oxide supports was between those of CuO/CeO2 and CuO/BaO. NSR experiments performed with high frequency H2 or CO pulses (micropulses every 120, 60 or 30 s) at 400 °C showed that regeneration with H2 was more effective than with CO, and this was attributed to the higher reactivity of H2 rather than to the poisoning effect of the reaction products (H2O and CO2 respectively). Nitrates were the main form of chemisorbed nitrogen oxides on all catalysts in NSR experiments at 400 °C, and NOx chemisorption and desorption rates were faster for CuO/CeO2 than for CuO/BaO. The general behavior of all catalysts tested for NSR at 400 °C was quite similar, and only certain differences were observed during the highest frequency pulses of CO, where CuO/CeO2 showed the best resistance to deactivation. For all catalysts, N2 was the only NOx reduction product detected during H2 regeneration.The authors thank the financial support of Generalitat Valenciana (Project PROMETEOII/2014/010 and grant BEST/2014/250), the Spanish Ministry of Economy and Competitiveness (Projects CTQ2015-67597-C2-2-R, MAT2014-61992-EXP, and grant PRX14/00249), and the UE (FEDER funding)