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

Dispersion of molybdena on CeO2, ZrO2 (Tet), and a mixture of CeO2 and ZrO2 (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 Mo6+/100 m2) 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 MoO2−4 species at 0.2 mmol Mo6+/100 m2 and polymolybdate species at 0.8 mmol Mo6+/100 m2. IR spectra of ammonia adsorption prove that isolated MoO2−4 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 Mo6+/100 m2 Ce + Zr, molybdena is preferentially dispersed on the surface of CeO2 when a mixed oxide support (CeO2 and ZrO2) is present, which was explained in term of the difference of the surface basicity between CeO2 and ZrO2 (Tet). Surface structures of the oxide supports were also taken into consideration.

IR spectra of ammonia adsorption indicate that isolated MoO2−4 species are corresponding to Lewis acid sites and polymolybdate species are corresponding to Brönsted acid sites over the Mo/Ce and/or Zr samples.Figure optionsDownload as PowerPoint slide