| Summary: | In this work, single-crystalline large-scale LaCO<sub>3</sub>OH nanoprism morphologies were synthesized by controlling La and Ca molar ratio and the hydrothermal reaction conditions. The nanoprism morphologies of LaCO<sub>3</sub>OH were unique in nature with a sharp corner and smooth surfaces. The hydrothermal reaction was carried out in the absence of organic additives or templates and (NH<sub>4</sub>)<sub>2</sub>CO<sub>3</sub> was used as a precipitation agent. The molar ratio of La:Ca was varied over the following values (the sample shorthand is given in parentheses): 75:25 mol% (LC-1), 50:50 mol% (LC-2), and 25:75 mol% (LC-3). Phase-pure LaCO<sub>3</sub>OH nanoprisms formed at a La:Ca molar ratio of 75:25 mol% without any assistance of catalysts or template. The photoluminescence (PL) properties of the as-synthesized powders showed one broad emission band centered at 394 nm after excitation of the pure LC-3 LaCO<sub>3</sub>OH nanoprisms at λ = 280 nm. The PL intensities were decreased in the order of LC-1 < LC-2< LC-3. The LC-1 and LC-2 samples had almost the same PL intensities probably due to their unique and smooth particle morphology. The calcination result of three samples treated for two hours at 800 °C, shows a reduction in NO activities over highly distributed CaO comprising La<sub>2</sub>O<sub>3</sub>. Further, under the presence of H<sub>2</sub>O and O<sub>2</sub> vapor<sub>,</sub> CaO comprising La<sub>2</sub>O<sub>3</sub> catalysts shows higher stability for the reduction of NO with CH<sub>4</sub>.
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