Annealing Strategies for the Improvement of Low-Temperature NH3-Selective Catalytic Reduction Activity of CrMnOx Catalysts

Annealing strategies for the citrate complexation-combustion method have been explored as a simple approach for improving the catalytic activity of mixed Cr-Mn oxides for the NH 3 -selective catalytic reduction of NO x . Materials prepared at 300 and 400 °C possess largely amorphous structures, consistent with highly dispersed Cr/Mn components. Annealing at 300 °C for 10 h facilitates the formation of catalysts possessing the largest surface area, reducibility, acidity, and activity window (92-239 °C), while areal activity is measured at 3.8 nmol s -1 m -2 and is comparable to values obtained for materials prepared at 400 °C. Conversely, shorter annealing times of 1 and 5 h at 300 °C produce materials that transform NO x about 2-3 times faster at equivalent surface area. Characterization demonstrates that simple annealing strategies have significant impact on the physiochemical and textural properties of these materials. Moreover, reducibility, O α species, and acidity were correlated against areal activity, but only the latter exhibited a near-linear correlation, indicating its dominance in controlling surface reaction rates.