A comparative study on the dispersion behaviors and surface acid properties of molybdena on CeO2 and ZrO2 (Tet).

Dispersion of molybdena on CeO(2), ZrO(2) (Tet), and a mixture of CeO(2) and ZrO(2) (Tet), was investigated by using laser Raman spectroscopy (LRS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and temperature programmed reduction (TPR). The results indicate that molybdena is dispersed on both individual oxide support and mixed oxide support at the adopted molybdena loadings (0.2 and 0.8 mmol Mo(6+)/100 m(2)) and the structure of the supported molybdena species is intimate association with its loading amount. Two molybdena species are identified by Raman results, i.e. isolated MoO(4)(2-) species at 0.2 mmol Mo(6+)/100 m(2) and polymolybdate species at 0.8 mmol Mo(6+)/100 m(2). IR spectra of ammonia adsorption prove that isolated MoO(4)(2-) species are Lewis acid sites on the Mo/Ce and/or Zr samples, and the polymolybdate species are Brönsted acid sites on the Mo/Ce and/or Zr samples. Moreover, a combination of the Raman, IR and TPR results confirms that at 0.2 mmol Mo(6+)/100 m(2) Ce+Zr, molybdena is preferentially dispersed on the surface of CeO(2) when a mixed oxide support (CeO(2) and ZrO(2)) is present, which was explained in term of the difference of the surface basicity between CeO(2) and ZrO(2) (Tet). Surface structures of the oxide supports were also taken into consideration.