The modification of Gd₂O₃ with BaO for the oxidative coupling of methane reactions

It was found that BaO could significantly improve the catalytic performance of Gd₂O₃ for the OCM reaction. For the 30 mol% BaO/Gd₂O₃ catalyst at 750°C, with CH₄:O₂:N2=2.5:1.0:11.4 and contact time=0.6 g s ml^-1, the CH₄ conversion, C₂ selectivity and C₂ yield stayed at around 32%, 54%, and 17%, respectively, within a reaction time of 40 h. The results of XRD studies indicated that ionic substitution between Ba²⁺ and Gd³⁺ ions had occurred during the preparation of the BaO/ Gd₂O₃ catalysts as well as in the OCM reaction. TPR, O2-TPD, O2-pulse, and Raman results showed that such ionic substitution could lead to an increase in the amount of oxygen adsorbed on the BaO/Gd₂O₃ catalysts. We observed that at 750°C both mono-oxygen and di-oxygen species could react with methane, but the O^2-₂ species was more suitable for forming C₂ hydrocarbons. Based on the XRD, XPS, and Raman results, we know that barium oxide was transformed to BaCO₃ during the OCM reaction. The combined results of CO₂-TPD and Raman investigations suggested that there were BaCO₃ decomposition and regeneration in the OCM reaction, and O^2-₂ species were formed as a result of O₂ interaction with the O^2- species generated in BaCO₃ decomposition.