Perovskite as catalyst precursors in the partial oxidation of methane: The effect of cobalt, nickel and pretreatment

Perovskites with formula LaNi1-xCoxO3 (x = 0.0, 0.2, 0.5 and 1.0) were investigated in the Partial Oxidation of Methane (POM) reaction. In situ XRD results suggest that the reduction of the perovskites under H-2 lead to the formation of La2B2O5 (B = Ni and Co) which is further transformed to Ni1-xCox/La2O3. The phase structure evolution when increasing the temperature of LaNi0.8Co0.2O3 without pre-reduction with H-2 but submitted to a mixture CH4 + O-2 allows the formation of a spinel phase La2BO4 (B = Ni and Co) before obtaining Ni and Co over La2O3. On the other hand LaNi0.8Co0.2O3 presented a different behavior after previous reduction with H-2 and the spinel phase is not detected. The H-2 pre-reduction favored lower mean crystallite size of Ni on La2O3. The catalytic tests suggest that H-2 pretreatment promotes the production of the syngas with a H-2/CO = 2 close to the stoichiometry. Without pretreatment, the H-2/CO ratio is lower (1.6) indicating the occurrence of parallel reactions such as RWGS. The sample Ni0.8Co0.2/La2O3 pretreated with H-2 presented a higher molar rate H-2/CO = 2.2. Deactivation was not observed after 24 h run test but graphitic carbon was detected on all samples. In the case of Ni0.8Co0.2/La2O3 less carbon formation was detected.