A highly active and stable bimetallic Ni-Mo2C catalyst for a partial oxidation of jet fuel

Abstract

Mo2C is an attractive catalyst for fuel reforming reactions because it possesses both a high activity and a high coking resistance. However, Mo2C catalysts cannot guarantee sufficient long-term stability during fuel reforming reactions that operate at a high fuel flow rate due to their phase instability. The present investigation is focused on improving the phase stability and the performance of Mo2C by addition of Ni for the partial oxidation (POX) of jet fuel. Mo2C and Ni-Mo2C were first prepared from CH4/H2 carburization of synthesized MoO3 and NiMoO4, respectively. To investigate the catalytic activity of carburized catalysts for the POX of jet fuel, tests were conducted at 750 °C and 1 atm, with a weight-hourly-space-velocity (WHSV) of 42 h−1 and O2/C ratio of 0.6. The Mo2C sample without Ni shows a performance similar to that of a blank run (in the absence of catalyst) with 70% conversion, 12% H2 yield, and 53% CO yield. The poor performance of Mo2C is due to its partial phase transformation into the MoO2 phase at the high WHSV. For Ni-Mo2C, the catalyst exhibits excellent stability over the 24 h test period with carbon conversion of 90% and H2 and CO yields of 56 and 63%, respectively. There were no indications of bulk oxidation or surface coking. Temperature-programmed reaction and isotopic exchange experiments showed that Ni-Mo2C follows the “catalytic oxidation and re-carburization cycle.” In this cycle, molecular oxygen is activated over the Mo2C surface, and the activated oxygen species react with lattice carbons from Mo2C to produce both CO and carbon vacancies. Hydrocarbons are decomposed into H2 and surface carbons over the metallic Ni sites. To sustain the catalytic cycle, the Mo2C1-x phase (i.e., non-stoichiometric Mo2C with carbon vacancies) is re-carburized by the surface carbons deposited on the metallic Ni sites. Finally, our results also showed that NiMoO4 can be rapidly carburized in-situ to form a high performance Ni-Mo2C catalyst under a flowing mixture of n-dodecane and air.