Ga-Doped LaCoO 3 Featured with a Macroporous Morphology as a Superior Oxygen Carrier for Chemical Looping Dry Reforming of Methane

Perovskite oxides have emerged as promising oxygen carriers for chemical looping dry reforming of methane (CL-DRM) due to their potentially larger oxygen storage capacity (OSC), easily tunable compositions, and redox properties. However, it is still very challenging to properly modulate the activity of surface and lattice oxygen species in perovskite-type oxygen carriers to well balance their capability of C(sp3)–H bond activation and syngas selectivity. Herein, Ga-doped LaCoO3 (LaGa0.5Co0.5O3) featured with a three-dimensionally ordered macroporous (3DOM) morphology was discovered to show a superior syngas yield of 10.60 mmol gmaterial–1 with ∼85% selectivity that is about 7- and 1.7-fold those of unmodified LaCoO3 (1.40 mmol gmaterial–1) and LaGa0.5Co0.5O3 (5.74 mmol gmaterial–1) oxygen carriers, respectively, combined with an improved CO productivity of 3.84 mmol gmaterial–1 in the CL-DRM. The incorporation of the Ga dopant was proven to be useful to further suppress the formation of coke from CH4 cracking during the partial oxidation of methane (POM) half-reaction, leading to enhanced CO selectivity. The XPS results revealed that the chemical looping reactions based on the LaGa0.5Co0.5O3 oxygen carrier were driven by both the Co0/Co2+/Co3+ and Ga0/Ga3+ redox pairs. As further proven by the CH4-TPR and H2-TPR characterizations, the constructed 3DOM morphology can effectively promote redox reactions between different valence cobalt species and gallium species due to its increased surface anchoring sites for redox-active centers and facilitated mass transfer (e.g., gas diffusion and ion migration) within the internal pores and skeleton. Our work demonstrates that lattice modification coupled with surface engineering through doping and morphology control can effectively enhance the CL-DRM performance of LaGaxCo1–xO3 oxygen carriers, which provides a promising strategy to design other high-performance oxygen carriers beyond the cobalt-based perovskite oxygen carriers discussed in our work.