Influence of Graphite as a Shaping Agent of Bi Molybdate Powders on Their Mechanical, Physicochemical, and Catalytic Properties

The influence of using graphite (G) as a shaping agent for bismuth molybdate (BiMo) catalysts was analyzed. Shaping was done by tableting, with addition of different loadings of graphite (0, 0.5, 1, 3, 5, 7, and 10 wt %). The use of graphite during the pressing of bismuth molybdate powders eases tableting because of the lubricating properties of the former. Furthermore, the compressive strength of BiMo-G tablets is higher than that of pure BiMo. Concerning the physicochemical properties of BiMo-G, XRD and XPS showed that graphite changes neither the relative distribution of the crystallographic phases of bismuth molybdate nor the oxidation state of bismuth and molybdenum in the tableted powders. Consequently, the shaped BiMo-G catalysts displayed similar, or slightly better, performances in the selective oxidation of propylene to acrolein. TGA analysis of samples of BiMo-G confirmed the thermal stability of the catalysts under oxidative conditions. Graphite was observed to experience crystallization into the hexagonal 2H phase during the catalytic tests. The results reported herein demonstrate that graphite is an effective shaping agent for bismuth molybdate powders.