Spherical-like Pd/SiO₂ catalysts for n-butylamine efficient combustion: Effect of support property and preparation method

Two types spherical-like SiO₂ with different specific surface area (SSA) and porosity were synthesized and used as support for Pd catalysts, which were prepared by various protocols (in situ synthesis (IS, Pd/S-1_IS, and Pd/S-2_IS), wet impregnation (WI, Pd/S-1_WI, and Pd/S-2_WI), and grafting (GA, Pd/S-1_GA, and Pd/S-2_GA)) and adopted in n-butylamine combustion. Results suggest that Pd dispersion is positive correlation with support SSA and GA method is the most favorable approach to obtain highly dispersed Pd active sites. Pd/S-1_IS, Pd/S-1_WI, and Pd/S-1_GA catalysts with small SSA show inferior activity and higher NO_x yield than those of Pd/S-2_IS, Pd/S-2_WI, and Pd/S-2_GA with large SSA, irrelevant with the preparation methods. Amongst, Pd/S-2_GA possesses the smallest Pd average diameter (ca. 1.72 nm) and highest activity with 90% of n-butylamine destructed at 234 °C; however, the yield of NO_x over Pd/S-2_GA is much higher than the other catalysts (except Pd/S-1_GA) as the GA approach provides high concentration of active sites and the preparation procedure sacrifices the SSA and porosity of supports to some extent. In situ DRIFTS results reveal that the developed porosity of catalyst promotes nitrogen-containing by-products (NH_x) transfer and diffusion and avoids their further oxidizing to NO_x. The activity of samples prepared by the WI process is lower than that prepared by the IS or GA method due to limited active sites. Comparatively, the Pd/S-2_IS prepared by the IS method has relative high activity (T₉₀ of 240 °C) and low NO_x yield (0.99% at T₉₀) in n-butylamine oxidation among all materials, exhibiting an attractive prospective in nitrogen-containing VOC environment-friendly elimination.