摘要
HMCM-22 catalysts modified with La203 （5% La） and MgO （≈0.87% Mg） were prepared respectively by impregnation method, and were characterized by scanning electron microscopy, X-ray diffraction, N2 physical ad- sorption-desorption and temperature-programmed desorption of NH3. The effect of supported metallic oxides （La203, MgO） on catalytic performance in xylene isomerization of C8 aromatics （ethylbenzene, m-xylene and o-xylene） was investigated in detail. The experimental results showed that 5% LaJHMCM-22 catalyst had higher isomerization activity and stronger shape-selectivity than 0.87% Mg/HMCM-22 catalyst, owing to its more acid sites and smaller pore size. And the loading amount of La was optimized to be about 7%. Moreover, supporting metal over 7% La/HMCM-22, respectively with 0.3% Pt, 3% Ni and 3% Mo, was carried out to prepare bifunction- al isomerization catalysts. In comparison, 3% Mo/7% La/HMCM-22 showed the best catalytic performance with both high activity and high selectivity, with the low hydrocracking of m-xylene and o-xylene. Besides, the op- timal reaction conditions were found： 340℃, 1.5 MPa H2, WHSV 4 h^-1 and H2/C8 4 mol/mol. Under the above conditions, ethylbenzene conversion was up to 20%, para-selectivity was over 23% with low xylene loss of 2.9%.
HMCM-22 catalysts modified with La203 （5% La） and MgO （≈0.87% Mg） were prepared respectively by impregnation method, and were characterized by scanning electron microscopy, X-ray diffraction, N2 physical ad- sorption-desorption and temperature-programmed desorption of NH3. The effect of supported metallic oxides （La203, MgO） on catalytic performance in xylene isomerization of C8 aromatics （ethylbenzene, m-xylene and o-xylene） was investigated in detail. The experimental results showed that 5% LaJHMCM-22 catalyst had higher isomerization activity and stronger shape-selectivity than 0.87% Mg/HMCM-22 catalyst, owing to its more acid sites and smaller pore size. And the loading amount of La was optimized to be about 7%. Moreover, supporting metal over 7% La/HMCM-22, respectively with 0.3% Pt, 3% Ni and 3% Mo, was carried out to prepare bifunction- al isomerization catalysts. In comparison, 3% Mo/7% La/HMCM-22 showed the best catalytic performance with both high activity and high selectivity, with the low hydrocracking of m-xylene and o-xylene. Besides, the op- timal reaction conditions were found： 340℃, 1.5 MPa H2, WHSV 4 h^-1 and H2/C8 4 mol/mol. Under the above conditions, ethylbenzene conversion was up to 20%, para-selectivity was over 23% with low xylene loss of 2.9%.
