NO reduction by CH(4) over La(2)O(3): temperature-programmed reaction and in situ DRIFTS studies

The chemistry between NO(x) species adsorbed on La(2)O(3) and CH(4) was probed by temperature-programmed reaction (TPR) as well as in situ DRIFTS. During NO reduction by CH(4) in the presence of O(2), NO(3)(-) does not appear to activate CH(4), thus either an adsorbed O species or an NO(2)(-) species is more likely to activate CH(4). In the absence of O(2), a different reaction pathway occurs and NO(-) or (N(2)O(2))(2-) species adsorbed on oxygen vacancy sites seem to be active intermediates, and during NO reduction with CH(4) unidentate NO(3)(-), which desorbs at high temperature, behaves as a spectator species and is not directly involved in the catalytic sequence. Because reaction products such as CO(2) or H(2)O as well as adsorbed oxygen cannot be effectively removed from the surface at lower temperatures, steady-state catalytic reactions can only be achieved at temperatures above 800 K, even though formation of N(2) and N(2)O from NO was observed at much lower temperature during the TPR experiments.