Effect of rare earth element (Ln = La, Pr, Sm, and Y) on physicochemical properties of the Ni/Ln2Ti2O7 catalysts for the steam reforming of methane

• Published in: Molecular catalysis 2019-05, Vol.468, p.130-138
• Main Authors: Fang, Xiuzhong, Xu, Luoji, Zhang, Xianhua, Zhang, Kunfeng, Dai, Hongxing, Liu, Wenming, Xu, Xianglan, Wang, Xiang, Zhou, Wufeng
• Format: Article
• Language: English
• Subjects: Coke-resistant ability; Ln2Ti2O7; Monoclinic layered perovskite; Oxygen vacancies; Pyrochlore; Steam reforming of methane
• ISSN: 2468-8231; 2468-8231
• DOI: 10.1016/j.mcat.2019.02.022

[Display omitted] •The change in A-site element influences the rA/rB ratio of A2B2O7 (A = Ln; B = Ti).•Ln2Ti2O7 alters from monoclinic layered perovskite to pyrochlore with a rise in rA/rB.•Pyrochlore has a stronger interaction with Ni species than monoclinic layered perovskite.•Ni dispersion and surface oxygen determine catalytic performance of Ni/Ln2Ti2O7.•Ni/Y2Ti2O7 shows the best catalytic performance and coke-resistant ability. Ln2Ti2O7 (Ln = La, Pr, Sm, and Y) and Ni/Ln2Ti2O7 catalysts were prepared using the co-precipitation and incipient wetness impregnation methods, respectively. XRD and Raman results reveal that with the decrease in rA/rB ratio of A2B2O7 (A = La, Pr, Sm, and Y; B = Ti), the crystal structure transformed from the monoclinic layered perovskite (La2Ti2O7 and Pr2Ti2O7) to the ordered pyrochlore (Sm2Ti2O7 and Y2Ti2O7). H2-TPR results demonstrate that the active Ni species had a stronger interaction with Sm2Ti2O7 or Y2Ti2O7 than with La2Ti2O7 or Pr2Ti2O7. Therefore, smaller Ni crystallites with larger active metallic surface areas could be formed in the Ni/Sm2Ti2O7 and Ni/Y2Ti2O7 catalysts. XPS results indicate that the oxygen vacancies and oxygen mobility were also gradually enhanced with the decrease in rA/rB ratio. As a consequence, the Ni/Y2Ti2O7 sample exhibited the highest catalytic activity and the best coke-resistant ability in the steam reforming of methane for hydrogen production among all of the catalysts. It is concluded that the change in A-site element influenced the structures of Ln2Ti2O7 significantly, which ultimately affected catalytic performance of Ni/Ln2Ti2O7 for the steam reforming of methane.