Preparation of molybdenum carbides using butane and their catalytic performance

The synthesis of high surface area molybdenum carbides from molybdenum oxid e and butane has been studied via temperature-programmed reaction (TPRe), X -ray diffraction (XRD), scanning electron microscopy (SEM), C-13 solid-stat e NMR, infrared (IR), and Raman spectroscopy (LR). The molybdenum oxygen/ca rbon system passes through four phase transitions before transforming into the pure Mo2C carbide. Carbon exists in two forms within high surface area molybdenum carbide. The initially produced molybdenum carbide has a face-ce ntered-cubic (fcc) structure but is gradually converted into the hexagonal- close-packed (hcp) structure with increasing carburization temperature, and eventually at high temperature coke is deposited. During the early stages, MoO3 is reduced by H-2, but at higher temperatures, butane also takes part in the reduction and, besides being consumed in the formation of carbide, is catalytically converted into methane, ethane, propane, and benzene. The high surface area of the molybdenum carbide materials is a consequence of p reliminary cracking of oxide crystallites during reduction with hydrogen an d later from the deposition of amorphous carbon. Catalytic activity tests i ndicate that molybdenum carbide material, prepared at 823 K, is a good cata lyst for the dehydrogenation of butane. The carbide obtained between 923 an d 973 K has excellent performance for pyridine HDN with good selectivity.