The nonoscale Er2O3 and 30 mol% BaCl2/Er2O3 catalysts prepared by a modified sol-gel method have been compared with their large-size counterparts for the oxidative dehydrogenation of ethane (ODE) to ethylene. The nanoscale catalysts showed better catalytic performance than the corresponding large-size ones, especially at lower reaction temperatures and shorter contact times. X-ray diffraction results revealed that the extent of cubic Er2O3 lattice expansion in nanoscale BaCl2/Er2O3 was larger than that in the large-size one and that more defects were formed in the nanoscale catalyst. We detected further enlargement of the cubic Er2O3 lattice in the nanoscale 30 mol% BaCl2/Er2O3 catalyst during the first 40 h of on-stream reaction. The results of X-ray photoelectron spectroscopic investigation demonstrated that after 40 h surface chlorine composition on nanoscale 30 mol% BaCl2/Er2O3 increased slightly, while that on the large-size catalyst decreased. O2 temperature-programmed desorption studies illustrated that, compared to the large-size catalysts, there were more oxygen species desorbed from the nanoscale ones. In situ Raman studies indicated that the reduction in particle size was beneficial for the activation of oxygen molecules. Taking into consideration the catalytic activity and Raman results, we suggest that dioxygen species such as O2δ- (0<δ<1), O2-, O2n- (1<n<2), and O22- are responsible for the selective oxidation of C2H6 to C2H4.
Scopus Subject Areas
- Process Chemistry and Technology