Catalytic combustion of methane on nano-structured perovskite-type oxides fabricated by ultrasonic spray combustion

The synthesis of perovskite-type oxides using ultrasonic spray combustion (USC) was investigated by adjusting the composition of the precursor solution and the temperature of synthesis and calcination. LaMnO3 was chosen as model perovskite to systematically analyze the effect of USC operating parameters. XRD, IR spectroscopy, TG-TPD, SEM, TEM and BET were used to characterize the samples with respect to phase composition, thermal stability, morphology and surface area. The catalytic properties were evaluated with respect to methane combustion as such materials are potential catalysts in the control of exhaust gases from mobile and stationary sources. Addition of citric acid to the precursor solution and calcination in air appeared to be the crucial parameters to produce spherical hollow particles composed of nano-sized LaMnO3 crystallites (down to 30 nm) with high catalytic activity and durability. Calcination was required in order to remove uncombusted precursors and to improve both the crystallinity of the materials and their catalytic activity. LaFeO3, LaCoO3 and La(M,Pd)O3 (M = Mn, Fe) with pure perovskite-phase were synthesized in a single step under the optimal conditions selected for LaMnO3. Though the order of catalytic activity within the two series of samples (with and without Pd) agreed with reported trends, the production of each single perovskite composition by USC may require further optimization around these synthesis conditions. We demonstrate that USC is a simple, versatile and reliable method with potential application in the one-step synthesis of heterogeneous catalysts.