Synthesis of high surface-area perovskite-type oxides by reverse homogeneous precipitation method and their catalytic property

摘要

Single-phase perovskite-type oxides in the La/Fe and La/ Mn families could be synthesized after air-calcining the corresponding hydroxide precursors above 550 and 650 deg C, respectively. The precursors were easily obtained by dropping a mixed aqueous solution of metal nitrates into highly basic aq. NH_3 without (RHP) and with (R-RHP) the presence of R_4N~+ cations (R=Me, Et, n-Pr). As a consequence of lowering the synthesis temperature, oxides obtained by the RHP and R-RHP methods had higher specific surface areas than those obtained by the conventional methods. The weight-normalized catalytic activity for the propane combustion reaction increased monotonically with increasing specific surface area, indicating that increasing surface area directly results in the promotion of the catalytic property. The perovskite particles obtained by the RHP and R-RHP methods fairly uniform in size with a narrow distribution and kept from being heavily agglomerated. The addition of R_4N~+ was effective in increasing the specific surface area of the products as well as in stabilizing the colloidal solution of the hydroxide precursor in the synthesis of La/Mn-based perovskites.