Application of Ti-doped MoO2 microspheres prepared by spray pyrolysis to partial oxidation of n-dodecane

Abstract

The present investigation is focused on improving the performance of molybdenum dioxide (MoO2) by doping with Ti for the partial oxidation (POX) of n-dodecane. Ti-doped MoO2 nanoparticles were synthesized via solvothermal cracking of polycrystalline MoO3 microparticles prepared by ultrasonic spray pyrolysis in the presence of a Ti precursor. Partial oxidation of n-dodecane was conducted at 850 °C with an O2/C ratio of 0.5. The 6 at% Ti-doped MoO2 was fully converted into orthorhombic carbide phase (β-Mo2C) during the reaction. This carbide sample showed high catalytic activity and stability with conversion and H2 yield of 94.4% and 86.3% after 24 h on stream, respectively. On the other hand, un-doped MoO2 was partially converted into the carbide phase during the reaction, which led to mixed oxide and carbide phases. This mixed phase showed poor catalytic activity and rapid deactivation after only 6 h of operation. Our ammonia temperature programmed desorption (TPD) and pyridine diffuse reflectance infrared Fourier transform (DRIFT) tests suggest that the addition of Ti to MoO2 improves both the density and strength of Lewis acid sites, and hence improves hydrocarbon activation. This increased surface carbon activation would enhance the carburization process of the Ti-doped MoO2 catalyst and retain the carbide phase under the POX condition.