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

Abstract Ln 2 Ti 2 O 7 (Ln = La, Pr, Sm, and Y) and Ni/Ln 2 Ti 2 O 7 catalysts were prepared using the co-precipitation and incipient wetness impregnation methods, respectively. XRD and Raman results reveal that with the decrease in r A / r B ratio of A 2 B 2 O 7 (A = La, Pr, Sm, and Y; B = Ti), the crystal structure transformed from the monoclinic layered perovskite (La 2 Ti 2 O 7 and Pr 2 Ti 2 O 7 ) to the ordered pyrochlore (Sm 2 Ti 2 O 7 and Y 2 Ti 2 O 7 ). H 2 -TPR results demonstrate that the active Ni species had a stronger interaction with Sm 2 Ti 2 O 7 or Y 2 Ti 2 O 7 than with La 2 Ti 2 O 7 or Pr 2 Ti 2 O 7 . Therefore, smaller Ni crystallites with larger active metallic surface areas could be formed in the Ni/Sm 2 Ti 2 O 7 and Ni/Y 2 Ti 2 O 7 catalysts. XPS results indicate that the oxygen vacancies and oxygen mobility were also gradually enhanced with the decrease in r A / r B ratio. As a consequence, the Ni/Y 2 Ti 2 O 7 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 Ln 2 Ti 2 O 7 significantly, which ultimately affected catalytic performance of Ni/Ln 2 Ti 2 O 7 for the steam reforming of methane.