| Popis: |
Thermal analysis and X-ray diffraction techniques were used to investigate the preparation of TiO 2 -based catalysts. It was found that anatase can transform to rutile, a highly stable modification, at high temperature (⪢ 1000 K), but with anatase alone the transformation is slow and not completed at 1273 K. An La promoter has little effect on the transformation. However, an Li promoter dramatically accelerates the transformation and decreases the transformation temperature to 853 K. The effect of an Li promoter on the transformation is possibly due to the substitution of Li + ions for lattice Ti 4+ ions. The catalytic activity was measured at 1073 K in a fixed-bed reactor and the results showed that rutile has a preference over anatase for the coupling of CH 4 . The addition of an Li promoter greatly improves the selectivity of C2 hydrocarbons which suggests a new form of active center on the surface of TiO 2 . |
