PMMA-templating preparation and catalytic properties of high-surface-area three-dimensional macroporous La 2CuO 4 for methane combustion

Abstract

The three-dimensional (3D) macroporous orthorhombically crystallized perovskite-like oxides La 2CuO 4 were prepared using the polymethyl methacrylate (PMMA) microsphere-templating strategy with nitrates of lanthanum and copper as metal source and a mixed solution of methanol and ethylene glycol as solvent in the absence or presence of citric acid and after calcination at various atmospheres. The as-prepared materials were characterized by means of X-ray diffraction, N 2 adsorption-desorption, scanning electron microscopy, X-ray photoelectron spectroscopy, and hydrogen temperature-programmed reduction. Catalytic activities of the materials were evaluated for the combustion of methane. The catalyst (La 2CuO 4-1) prepared with PMMA and citric acid possessed a 3D ordered macroporous (3DOM) structure and a surface area up to 46 m 2/g, whereas the one (La 2CuO 4-2) prepared with PMMA but without citric acid exhibited a 3D wormhole-like macroporous structure and a surface area of 39 m 2/g. There was the presence of a trace amount of La 2O 2CO 3 phase in the La 2CuO 4-1 and La 2CuO 4-2 catalysts. The calcination procedure (first in N 2 flow at 700 °C and then in air flow at 300 and 800 °C, respectively) was crucial in forming the 3D porous structure of La 2CuO 4. The as-obtained catalysts had overstoichiometric oxygen. The La 2CuO 4-1 catalyst showed better low-temperature reducibility than the La 2CuO 4-2 and La 2CuO 4-Citrate (derived from the conventional citric acid-complexing route) catalysts. The 3D porous La 2CuO 4 materials performed well in catalyzing the oxidation of methane, with the La 2CuO 4-1 catalyst showing the best performance (the temperature for 90% CH 4 conversion = 672 °C (reaction rate = ca. 40 mmol/(g h)) at CH 4/O 2 molar ratio = 1/10 and space velocity = 50,000 mL/(g h). It is concluded that the excellent catalytic performance of La 2CuO 4-1 was mainly related to the higher surface area, better low-temperature reducibility, and 3DOM architecture.