Stabilization of supported platinum nanoparticles on γ-alumina catalysts by addition of tungsten

摘要

The thermal stabilization of Al_2O_3 using W~(6+) ions has been found useful to the synthesis of Pt/Al_2O_3 catalysts. The simultaneous and sequential methods were used to study the effect of W~(6+) upon Pt/γ-Al_2O_3 reducibility, Pt dispersion, and benzene hydrogenation. The W/Pt atomic ratios were from 0.49 to 12.4. In the first method we found that the W~(6+) ions delayed reduction of a fraction of Pt~(4+) atoms beyond 773 K. At the same time, W~(6+) inhibited sintering of the metallic crystallites once they were formed on the surface. For the sequential sample with a W/Pt atomic ratio of 3.28 W~(6+) did not inhibit the H_2 reduction of Pt oxides even below of 773 K, the Pt oxides were reduced completely. After reduction at 1073 K, sequential samples impregnating Pt on WO_x-γ-Al_2O_3 were more active and stable during benzene hydrogenation. TOF of the reaction did not change when the W/Pt atomic ratio, preparation technique and reduction temperature changed and its value was of 1.1 s~(-1). W~(6+) ions promoted high thermal stability of Pt crystallites when sequential catalysts were reduced at 1073 K and decreased their Lewis acidity.