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 degrees C, with CH4:O-2:N-2=2.5:1.0:11.4 and contact time=0.6 g s ml(-1), the CH4 conversion, C-2 selectivity and C-2 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 degrees C both mono-oxygen and di-oxygen species could react with methane, but the O-2(2-) species was more suitable for forming C-2 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 O-2 interaction with the O(2-)species generated in BaCO3 decomposition. (C) 1998 Elsevier Science B.V.