Chemical looping methane partial oxidation: The effect of the crystal size and O content of LaFeO3

The site requirements for the methane total combustion, partial oxidation, and decomposition on LaFeO3 perovskite catalysts during the chemical looping process were addressed by a kinetic study through varying the O content and the crystal size. The exchange between the surface oxygen and lattice oxygen is rapid, and the active sites of Fe associated with the surface oxygen are highly dynamic in nature, which depends on the amount of O in the perovskite during reaction and the O binding energy. Three types of active sites are identified where Fe atoms highly coordinated with O lead to total combustion of methane, Fe moderately coordinated with O leads to partial oxidation, and Fe highly coordinated with vacancy sites leads to carbon formation. The crystal size of LaFeO3 perovskite plays a significant role in determining the O binding energy and their catalytic properties on the partial oxidation of methane by the chemical looping process. Different crystal sizes of perovskites have been obtained using various preparation methods. Larger crystal has a high selectivity to synthesis gas and high capacity of O removal, due to a lower O–Fe bond energy, as indicated by a smaller band gap measured by UV–Vis absorption spectroscopy. Nearly pure synthesis gas was produced by methane partial oxidation using chemical looping on LaFeO3 by tuning the surface O coverage through controlling the oxidation degree in the oxidation step.

The Fe coordination number with oxygen on LaFeO3 surface governs the selectivity to total and partial oxidation as well as methane decompositionFigure optionsDownload high-quality image (51 K)Download as PowerPoint slideHighlights
► Selective methane partial oxidation on LaFeO3 perovskites.
► Strong dependence of the activity and selectivity on LaFeO3 crystal size.
► Three different active Fe sites related to the coordination number with oxygen.
► Higher oxygen binding energy on smaller crystals.
► Control the selectivity to syngas through adjusting oxidation degree of perovskites.