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

Abstract

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 H2 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 H2 but submitted to a mixture CH4+O2 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 H2 and the spinel phase is not detected. The H2 pre-reduction favored lower mean crystallite size of Ni on La2O3. The catalytic tests suggest that H2 pretreatment promotes the production of the syngas with a H2/CO=2 close to the stoichiometry. Without pretreatment, the H2/CO ratio is lower (1.6) indicating the occurrence of parallel reactions such as RWGS. The sample Ni0.8Co0.2/La2O3 pretreated with H2 presented a higher molar rate H2/CO=2.2. Deactivation was not observed after 24h run test but graphitic carbon was detected on all samples. In the case of Ni0.8Co0.2/La2O3 less carbon formation was detected.