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

The thermal stabilization of Al₂O₃ using W⁶⁺ ions has been found useful to the synthesis of Pt/Al₂O₃ catalysts. The simultaneous and sequential methods were used to study the effect of W⁶⁺ upon Pt/γ-Al₂O₃ 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 W⁶⁺ ions delayed reduction of a fraction of Pt⁴⁺ atoms beyond 773 K. At the same time, W⁶⁺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 W⁶⁺ did not inhibit the H₂ 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-Al₂O₃ 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. W⁶⁺ ions promoted high thermal stability of Pt crystallites when sequential catalysts were reduced at 1073 K and decreased their Lewis acidity_.