Enhancing the catalytic properties of a biochar-supported copper oxide in nitric oxide selective reduction with hydrogen

Copper oxide supported on a biochar could suffer from a low nitrogen-selectivity and carbon combustion, despite the sustainability prospect it provides in replacing the utilization of non-renewable materials as the catalyst support to reduce nitric oxide. Bimetallic catalysis is a means to improve catalytic properties including conversion and selectivity. Therefore, this work investigates the enhancement of carbon-supported copper oxides in nitric oxide selective reduction using hydrogen by co-impregnating iron or manganese with copper. The bimetallic catalysts were prepared via sequential incipient wetness method where copper oxide was impregnated and calcined prior to the impregnation and calcination of the co-catalyst. As iron was paired with copper, the nitrogen selectivity was enhanced by 20% (almost 100% selective) at 200 °C while reducing the carbon combustion rate by 20% at a higher temperature (300 °C). This improvement was regarded as the synergistic effects obtained by the bimetallic oxide catalysts as a result of the altered elemental composition (from 60% carbon content to 50%), catalyst acidity (from 12 mmol NH₃ desorbed/g to 16 mmol NH₃d/g) and redox properties (from 5 mmol H₂ consumed/g to 3 mmol H₂/g). Flash elemental analyser showed that this catalyst has lower carbon content but higher oxygen amount (30% compared to 19%) which is correlated to the higher acidic sites, as confirmed via temperature-programmed desorption analysis and Fourier-Transform infra-red spectroscopy. Varying the ratio between the two catalysts revealed that different mechanisms govern the reaction that could be the key to understanding the enhancement of the nitrogen-selectivity. Nevertheless, further studies are required to ensure the applicability of this catalytic system in the industry.