Highly Dispersed MoO3/Al2O3 Shell-Core Composites Synthesized by CVD of Mo(CO)6 under Atmospheric Pressure

MoO3/gamma-Al2O3 composites are synthesized by CVD under atmospheric pressure using Mo(CO)(6) as the precursor and porous gamma-Al2O3 particles in a horizontal, rotating, hot-wall reactor, which is also used for calcination in air. The composites are characterized by N-2 physisorption, atomic absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and laser Raman spectroscopy (LRS). The synthesized samples exhibit excellent porosity, even at high Mo loadings. A much higher Mo yield is achieved when applying sublimation-adsorption in static air instead of using flowing N-2. A high degree of Mo dispersion on alumina is confirmed by XRD, LRS, and TEM; with a Mo surface density as high as 5.2 atoms nm(-2), the sample is X-ray amorphous, there are no polymeric molybdate species detectable by LRS, and the island size of the molybdate species is about 1 nm according to TEM. The XPS analysis shows that exclusively Mo-VI species are present on all synthesized samples. Thus, the applied rotating, hot-wall reactor achieves efficient mixing and homogeneous deposition.