(544fw) Ni-Mo2C: A Highly Active Catalyst for Partial Oxidation of Jet Fuel

Authors: 
Bkour, Q., Washington State University
Ha, S., Washington State University
Norton, M. G., Washington State University
The reforming of logistic liquid fuels for fuel cell applications is a challenging proposition, because of the severe carbon deposition on the surface of the reforming catalyst and sulfur problems. It becomes more challenging for a catalyst to be able to reform fuels within realistic operation conditions that are compatible with fuel cells and tolerate the influence of various aromatic and poison compounds present in these fuels. Therefore, the successful reforming of these hydrocarbons will largely depend on the development of a catalyst. Transition metal carbides (TMCs) have attracted considerable attentions because of the unique chemical and physical properties and their affordable prices. Mo2C is an attractive catalyst for methane reforming because it does not require excess oxidant to operate without coke deposition. However, Mo2C catalysts cannot guarantee sufficient long-term stability under liquid fuel reforming conditions at 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 prepared from CH4/H2 carburization of prepared MoO3 and NiMoOfrom combustion method. Our results showed that the carburization temperature of Mo2C is lowered by the presence of Ni. Our results suggests that hydrocarbons reduces NiMoO4 to Ni metal and MoO2 and then Ni species enhances hydrocarbons dissociation and hence promote the transformation of MoO2 into Mo2C. On the other side, Pure MoO2 needs higher temperature and higher concentration of hydrocarbons to have full carburization to Mo2C. T

To investigate the catalytic activity of carburized catalysts for the partial oxidation of jet fuel, tests were conducted at 750 °C and 1 atm, with a high weight-hourly-space-velocity (WHSV) of 42 h-1 and O2/C ratio of 0.6. Mo2C has a performance similar to that of blank run (in the absence of the catalyst) with 12% H2 yield, 53% CO yield and 70% conversion. The inactivity of Mo2C is due to its partially transformation to MoO2 phase due to the high fuel flow rate. Over Ni-Mo2C, the catalyst exhibits excellent stability over the 24 h test period without indication of oxidation or coking with carbon conversion of 90% and H2 and CO yields of 56 and 63%, respectively. Our temperature-programmed reaction and isotopic exchange experiments showed that In the case of Ni-Mo2C with higher hydrocarbons dissociation rate, there is the establishment of the “catalytic oxidation and re-carburization cycle” due to the synergistic effects between Mo2C and metallic Ni. In which O2 dissociation occurs on Mo2C surface forming oxygen that is able to oxidize Ni-Mo2C to Ni and MoO2,which can react with hydrocarbon fragments to generate Ni-Mo2C through carbothermal process. Moreover, the results indicated that NiMoO4 could be carburized to Ni-Mo2C in a flow of dodecane/air mixture in short time. While MoO2 cannot be carburized to Mo2C in same conditions.