Influence of metal composition on the catalytic performance of half-substituted LaB’0.5B0.5O3 (B’, B: Fe, Co, Ni) exsolved perovskites catalysts in m-cresol hydrogenation

Abstract

Half-substituted perovskites LaFe_0.5Ni_0.5O₃, LaFe_0.5Co_0.5O₃ and LaCo_0.5Ni_0.5O₃ were used as precursors to synthesize, by an exsolution process, reduced catalysts for the liquid-phase hydrogenation of m-cresol at 200 °C and 30 bar H₂ pressure. The calcined perovskites and exsolved catalysts were characterized by AAS, H₂-TPR, N₂ physisorption, XRD, XPS, TEM and NH₃-TPD techniques. The characterization results show large differences in the reducibility of perovskites in the presence or absence of Fe. In the case of the exsolved catalyst without Fe content (LaCo_0.5Ni_0.5O₃), the formation of metallic Co⁰ and Ni⁰ is detected, while the exsolved catalysts containing Fe (LaFe_0.5Co_0.5O₃, LaFe_0.5Ni_0.5O₃) were not reducible in H₂ below 500 °C. The higher m-cresol conversion, initial reaction rate and hydrogenation (HYD) activity of the exsolved LaCo_0.5Ni_0.5O₃ catalyst were attributed to the presence of highly dispersed surface species of metallic Co⁰ and Ni⁰. The formation of the major product, 3-methylcyclohexanol, over the LaCo_0.5Ni_0.5O₃ catalyst was independent of the reaction temperature in the range of 150 – 200 °C. However, the hydrogenation activity increased with increasing H₂ pressure between 20 and 50 bar. The exsolved LaCo_0.5Ni_0.5O₃ catalyst shows no loss of catalytic activity after 5 cycles without regeneration, and post-reaction characterization demonstrates that the surface composition remains stable after five reaction cycles, with no detectable leaching of nickel and cobalt.