Partial oxidation of methane to synthesis gas using LnCoO3 perovskites as catalyst precursors

In this work Co supported catalysts have been prepared by the reduction of the perovskites LnCoO(3) (Ln = La, Pr, Nd, Sm and Gd)to produce Co-n/Ln(2)O(3). Detailed TPR and XRD studies showed that the perovskite NdCoO3 is reduced in two steps, first to NdCoO2.5 and further to Co-o/Ln(2)O(3) and in both stages it was demonstrated that the reoxidation with O-2 is capable to recover the perovskite structure. TPO experiments with reduced Ln-Co-O (Ln = La, Nd, Sm and Gd) catalysts indicated that reoxidation takes place in two steps: first oxidation of the supported Co-o to the spinel Co3O4 (Co2+Co23+O4) and further the oxidation of the Co2+ to Co3+ with a simultaneous solid state reaction with Ln(2)O(3) regenerating the perovskite structure, It was observed that the temperature for the second oxidation step is strongly dependent on the nature of the lanthanide increasing in the following order La > Nd > Sm > Gd. This trend seems to be determined by the thermodynamic stability of the parent perovskite. These catalysts (Co-o/Ln(2)O(3)) have been tested for the partial oxidation of methane to synthesis gas showing remarkable differences in activity [1], The system Gd-Co-O showed exceptionally better performance for CO and H-2 production whereas the activity for the other catalysts decreased in the following order Sm-Co-O > > Nd-Co-O > Pr-Co-O. The catalyst La-Co-O was active for methane combustion and only traces of CO and H-2 were observed, It was found that these differences are determined by the lanthanide which plays a fundamental role on the stability of the catalyst.