In-depth understanding of the crystal-facet effect of La2O2CO3 for low-temperature oxidative coupling of methane

• Published in: Fuel (Guildford) 2022-01, Vol.308, p.121848, Article 121848
• Main Authors: Feng, Ru, Niu, Pengyu, Wang, Qiang, Hou, Bo, Jia, Litao, Lin, Minggui, Li, Debao
• Format: Article
• Language: English
• Subjects: Adsorbed oxygen specie; Carbon dioxide; Catalysts; Coupling; Crystal facet; Dehydrogenation; Free energy; Hydrothermal crystal growth; La2O2CO3; La3+–O2− site; Lanthanum; Low temperature; Low-temperature oxidative coupling of methane; Methane; Methyl radicals; Nanoparticles; Oxidation; Oxides; Oxygen; Selectivity
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2021.121848

•Shaped La2O2CO3 exposed different ratio of {001} and {100} surfaces have been successfully synthesized.•The origin of oxygen species on irreducible lanthanum-based oxide surface were illustrated.•The {001} facets, with more La3+–O2− pair sites, give higher methane conversion activity at 410 °C.•The as-formed methyl radical can be easily successively dissociated and deeply oxidized on La2O2CO3{001}. Facet effect of lanthanum-based oxides on low-temperature oxidative coupling of methane (OCM) reaction have attracted great attention. In the present work, La2O2CO3 nanoparticles in the morphologies of triangular nanoplate and triangular nanocube with different ratio of {001} and {100} facets were prepared by facile hydrothermal method. The {001} facets exhibited higher OCM activity than {100} facets at 410 °C due to larger number of La3+–O2− sites, which could adsorb CO2 to form bidentate carbonate, and then reacting with oxygen to form adsorbed oxygen species. However, the higher methyl radical adsorption energy and the lower free energy of methane successive dehydrogenation of La2O2CO3{001} surface caused the excessive dissociation and deep oxidation of methyl radical, thus {001} facets show poor selectivity than {100} facets. Our findings will get a better understanding the facet effect of lanthanum-based oxides and provide guidance for the design of efficient low-temperature OCM catalysts.