Methanol interaction with NO2: An attempt to identify intermediate compounds in CH4-SCR of NO with Co/Pd-HFER catalyst

The objective of this work is the study of fundamental common aspects of NOx catalytic reduction over a Co/Pd-HFER zeolite catalyst, using methanol or methane as reducing agent. Temperature Programmed Surface Reaction (TPSR) studies were performed with reactant mixtures comprising NO2 and one of the reducing agents. The formation of formaldehyde was detected in both studied reactions (NO2–CH4 and NO2–CH3OH) in the temperature range between 100 and 220 °C. At higher temperature, when the NOx reduction process effectively begins, formaldehyde starts to be consumed. Using methanol as reducing agent, nitromethane and nitrosomethane, are detected. At 300 °C these species are consumed and cyanides and iso-cyanides formation occurs. On the contrary, with methane, these last species were not detected; however, there are strong evidences for CH3NO and CH3NO2 formation. Thus, using methanol or methane, similar phenomena were detected. In both cases, common intermediary species seem to play an important role in the NOx reduction process to N2. These results suggest that methanol can be considered as a reaction intermediate species in the mechanism of the reduction of NO2 with methane, over cobalt/palladium-based ferrierite catalysts.