Synthesis of Hydroxylamine Sulfate via NO Hydrogenation over Pt/Graphite Catalysts. I: Physicochemical State of Platinum Particles and the Surface of the Support in the Catalysts

Resumo

The physicochemical state of supported platinum and the surface of the support is studied for a number of industrial 0.5 wt % Pt/graphite (freshly prepared, after the synthesis of hydroxylamine sulfate via NO hydrogenation in sulfuric acid, and regenerated) by scanning electron microscopy (SEM), transmission electron microscopy(TEM), X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and CO chemisorption. It is shown that platinum particles agglomerate in a catalyst during operation, and its regeneration results in finer dispersity of the supported metal. Despite the common opinion that a platinum surface is modified by sulfur during the synthesis or regeneration of such catalysts, no evidence of this is found via XPS. Data showing that the surface nitrogen-containing graphite groups formed during the preparation of a catalyst are responsible for the modification of the absorption properties of platinum particles with respect to CO are obtained for the first time. The latter seems to be one of the factors that influence the catalytic properties of platinum in NO hydrogenation.