ausblenden:
Schlagwörter:
MoVTeNb oxide; propane adsorption; differential heat
Molybdenum-Vanadium compounds in C3 and C4 selective oxidation
Zusammenfassung:
Polycrystalline, mixed MoVTeNb oxides have been reported to show high selectivity and activity in the oxidation of propane to acrylic acid. The most relevant crystal structure in C-H activation of propane is the orthorhombic, bronze-like M1 phase. In the present work, the adsorption of propane on the surface of M1 has been studied by microcalorimetry. The investigation is aimed at a deeper understanding of the mechanism of propane activation. A series of highly crystalline, phase-pure M1 catalysts was prepared. The M1 catalysts were tested in propane oxidation to acrylic acid. At propane conversion of approximately 50%, the selectivity to acrylic acid differs by an order of magnitude. Highly selective M1 is characterized by comparatively strong adsorption of propane (∆Hads~60 kJ/mol). The heat of adsorption is independent of the coverage suggesting homogeneous distribution and uniformity of adsorption sites. Nano-structuring of M1 results in weaker adsorption (∆Hads~45 kJ/mol) and inhomogeneity, which may be connected with low the selectivity.
