Estudo de precursores tipo perovskitas LaNi1-xFexO3 e La1- xCexNiO3 na obtenção de gás de síntese a partir da reforma seca do CH4 em presença de O2

Abstract

In the present work perovskite materials La1-xCexNiO3 (x = 0.0; 0.3; 0.7) and LaNi1-xFexO3 (x = 0.0; 0.3; 0.7; 1.0) were synthesized, characterized and evaluated in the dry reforming of CH4 in the presence of O2 (Oxi-CO2). The perovskites were synthesized by citrate method and characterized by the TGA techniques, XRD, XRF, SEM, BET, TPR-H2, TPSR and TPO. The XRD patterns of the materials presented the perovskite phase and that high crystallinity materials were obtained indicating that the synthesis method was successful. Formation of phase segregated phases, La2O3, Fe2O3, NiO, CeO, was also observed. XRF analysis showed that the desired perovskite stoichiometry was also achieved and BET results showed that the samples presented small areas, typical of perovskite materials. TPR-H2 profiles showed that Ni substitution by Fe hinders the reducibility of species, increasing the materials reduction temperature and the substitution of La by Ce improves the reducibility of the materials, shifting the reduction to lower temperatures. TPSR analysis indicated that the materials are active for Oxy-CO2 and that the reaction occured in two main steps: Total combustion followed by reforming of methane. Long term catalytic activity tests showed that the materials presented good conversion and selectivity to synthesis gas, obtaining H2/CO ratio according to the reaction stoichiometry. It was found that all materials were stable and active during 10h of reaction. It was also found that the materials activation method was effective to obtain the active phase, as evidenced by DRXT results and catalytic perfomance. TPO analysis post-TPSR and catalytic tests demonstrated a reduction on carbon deposition by adding Ce or Fe in LaNiO3 structure, showing that the partial substitution of La by Ce or Ni for Fe improved the stability and resistance to carbon deposition on the catalyst surface. It was concluded that the incorporation of Ce and Fe in LaNiO3 structure coupled to appropriate conditions decreases the formation of carbonaceous species in the Oxy-CO2 being evaluated promising catalysts to obtain synthesis gas.