Effect of the synthesis method and pre-treatment conditions on the catalytic performance of lanthanum manganite in preferential oxidation of CO

Abstract LaMnO 3 perovskite catalysts were synthesized via four methods, co-precipitation (CP), glycol-thermal (GT), sol–gel (SG), and reactive ball milling (BM), to systematically investigate how synthesis-controlled defect engineering governs CO preferential oxidation (CO-PrOx) performance. XRD, STEM-EDX, H 2 -TPR, and O 2 -TPD characterization revealed that the BM catalyst exhibits a uniquely high concentration of oxygen vacancies and grain boundary defects, arising from mechanochemical energy input during synthesis. Despite possessing the lowest BET surface area (3.0 m 2 g −1 ), BM 700 delivered the highest CO-PrOx activity under both air and H 2 -reduced pretreatments, achieving a surface-area-specific activity of 20.29 × 10 –6 mol CO m −2 min −1 at 200 °C under air pretreatment, 5.3–9.0 times higher than CP, GT, and SG analogues. This demonstrates unambiguously that intrinsic active site density, rather than textural surface area, governs catalytic performance. The GT method yielded the most phase-pure LaMnO 3 , while CP and SG produced phase-pure materials with intermediate defect densities. These findings establish synthesis-method-controlled defect engineering as the primary design lever for optimizing low-temperature CO-PrOx catalysts.