Direct Spectroscopic Evidence of CO Spillover and Subsequent Reaction with Preadsorbed NOx on Pd and K Cosupported Mg-Al Mixed Oxides

The CO adsorption and subsequent reaction with preadsorbed NOx on Pd and K cosupported Mg-Al mixed oxides (Pd-K/MgAlO, 1/8/100 w/w) were investigated using in situ FTIR spectroscopy. During CO adsorption, a peculiar and well-defined IR band at 2160 cm(-1) was observed. Several elaborately designed experiments such as the competitive adsorption of CO and CO2 demonstrated that the 2160 cm(-1) band was exclusively assigned to a carbonyl species on K sites due to the CO spillover from Pd to K, which results from a strong Pd-K interaction based on temperature-programmed reduction with H-2 experiments. Importantly, the spillover of CO is found to be involved in the reduction of preadsorbed NOx from temperature-programmed surface reactions with CO. Thus, all adsorbed NOx can be reduced by CO before desorption. Like the process of pumping CO by Pd from the atmosphere to irrigate the field of the nitrates/nitrites, the adsorbed NOx at not only K sites adjacent to Pd but also at the remote K sites can be reduced into N-2 and N2O effectively.