Annealing Strategies for the Improvement of Low-Temperature NH(3)-Selective Catalytic Reduction Activity of CrMnO (x) 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.