Mössbauer Study of the Ni/Ca_0.8Sr_0.2Ti_1−x Fe _x O_3−α Catalyst System for Partial Oxidation of Methane to Synthesis Gas

Abstract

The Ni/Ca_0.8Sr_0.2TiO₃ catalyst system prepared by the citrate method shows high activity in partial oxidation of methane to synthesis gas. It is assumed that the interaction of Ni with the perovskite lattice may be responsible for the increased catalytic activity. 1% ⁵⁷Fe dopant substituted for Ti was used in order to see if the presence of Ni has any perturbation effect on the structure of the perovskite. One may expect systematic changes in the Mössbauer parameters of the substitutional Fe impurity as a function of the NiO content if the bulk properties of the perovskite are affected. Samples with different Ni/Ca_0.8Sr_0.2Ti_0.99 ⁵⁷Fe_0.01O_3−α ratios from 0:1 to 1:1, and others having Fe substitutions for Ti up to 30%, all prepared by the citrate method, have been investigated. The Mössbauer spectra contained doublets of paramagnetic Fe³⁺ and Fe⁴⁺ species as well as paramagnetically relaxed Fe³⁺. These species were assigned to the bulk perovskite, the perovskite surface and the NiO/perovskite interface. The perturbation of the perovskite structure by Ni could not be verified.