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

Abstract Perovskites with formula LaNi 1-x Co x O 3 (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 La 2 B 2 O 5 (B = Ni and Co) which is further transformed to Ni 1-x Co x /La 2 O 3 . The phase structure evolution when increasing the temperature of LaNi 0.8 Co 0.2 O 3 without pre-reduction with H 2 but submitted to a mixture CH 4  + O 2 allows the formation of a spinel phase La 2 BO 4 (B = Ni and Co) before obtaining Ni and Co over La 2 O 3 . On the other hand LaNi 0.8 Co 0.2 O 3 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 La 2 O 3 . 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 Ni 0.8 Co 0.2 /La 2 O 3 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 Ni 0.8 Co 0.2 /La 2 O 3 less carbon formation was detected.