Synthesis, characterization, and thiophene desulfurization activity of unsupported gamma-Mo2N macrocrystalline catalysts

Macrocrystals of gamma-Mo2N were synthesized by temperature-programmed reac tion of macrocrystalline MoO3 and NH3 or N-2/H-2 mixtures, X-ray diffractio n analyses indicate macrocrystalline Mo2N is an aggregate of particles in c rystallographic alignment with diameters ranging from 4.6 to 18 nm, dependi ng on synthesis conditions. Scanning tunneling microscopy (STM) supports th ese observed diameters. Based on diffraction data and surface area measurem ents, it is concluded that the particles in each sample are found with a ra nge of diameters, each flattened in the [200] direction with either an amor phous surface phase or polycrystalline interior. The highest crystal BET su rface area achieved is 44 m(2)/g. TGA was used to monitor the temperature-p rogrammed reaction of MoO3 and N-2/H-2 mixtures. The lowest reduction tempe ratures were observed in syntheses employing high H-2 concentrations and sl ow temperature ramping rates. The rate of the Mo2N macrocrystal synthesis r eaction was observed to be slower than the equivalent powder reaction, whic h could possibly be attributed to the effects of solid-state diffusion. The specific thiophene hydrodesulfurization (HDS) activity (units of mol/s m(2 )) of the Mo2N macrocrystalline catalyst at 673 K was found to be higher th an the powder form by a factor of 2.5. Weight-specific HDS activities and r eaction product fractions over Mo2N macrocrystal and powder catalysts were roughly the same. An analysis of reaction products over a range of conversi ons indicates thiophene desulfurizes to form predominantly 1-butene with sm aller amounts of other C-4 hydrocarbons also present. (C) 1999 Academic Pre ss.