Structure and basicity of γ-Al2O3-supported MgO and its application to mercaptan oxidation

gamma -Al2O3-supported MgO samples with different MgO loading have been prepared by impregnating gamma -Al2O3 with magnesium nitrate solution and then calcining at 773 K. Resultant MgO/Al2O3 samples have been characterized with XRD, CO2-TPD, XPS, surface area and pore size distribution measurements, and compared with hydrotalcite-derived Mg-Al mixed oxide (Mg(Al)O) samples. Results show that the utmost dispersion capacity (threshold) of MgO on gamma -Al2O3 is 0.17 gMgO/gAl(2)O(3); the base amount of MgO/gamma -Al2O3 increases with MgO loading and reaches a maximum at the threshold loading; the base strength of MgO/gamma -Al2O3 with the threshold loading ((Mg/Al)O) is similar to that of Mg(Al)O (Mg/Al = 3), but its base site density is almost twice as much as that of Mg(Al)O; the pore size distributions of (Mg/Al)O and Mg(Al)O are quite different from each other. The pore size of (Mg/Al)O concentrates on a relatively narrow meso-pore range (between 30 and 60 A). When treating the real jet fuel, the catalyst of (Mg/Al)O-supported CoPcS shows a little higher conversion and much longer lifetime than Mg(Al)O-supported CoPcS. The former's lifetime is almost three times as long as the latter's and reaches over 800 h. The better performance of MgO/gamma -Al2O3 is attributed to its proper pore size distribution and to more basic sites being available. (C) 2001 Elsevier Science B.V. All rights reserved.