THE MODIFICATION OF GD2O3 WITH BAO FOR THE OXIDATIVE COUPLING OF METHANE REACTIONS

It was found that BaO could significantly improve the catalytic perfor mance of Gd2O3 for the OCM reaction. For the 30 mol% BaO/Gd2O3 catalys t 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 4 0 h. The results of XRD studies indicated that ionic substitution betw een 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 a n 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 spe cies could react with methane, but the O-2(2-) species was more suitab le for forming C-2 hydrocarbons. Based on the XRD, XPS, and Raman resu lts, we know that barium oxide was transformed to BaCO3 during the OCM reaction. The combined results of CO2-TPD and Raman investigations su ggested that there were BaCO3 decomposition and regeneration in the OC M reaction, and O-2(2-) species were formed as a result of O-2 interac tion with the O(2-)species generated in BaCO3 decomposition. (C) 1998 Elsevier Science B.V.