Oxidative dehydrogenation of ethanol on modified OMS-2 catalysts

Modified MnO catalysts with a cryptomelane (OMS-2) structure are prepared by a redox reaction between manganese sulfate and potassium permanganate solutions with different Mn/M molar ratio (10/1, 20/1), where M is Fe or Sn. Fe- or Sn-containing salts are used as precursors added at the stage of redox co-deposition. XRD, TEM, H-TPR, TPO, XPS, and Raman spectroscopy techniques are used to study the features of the modified OMS-2 catalysts. It has been shown that the modifier cations can enter into the cryptomelane crystalline lattice, probably by substitution of Mn and K ions into the tunnels or can be distributed on the surface of OMS-2 samples. Segregation of Sn ions on the surface and in the subsurface layers of the modified Sn-OMS-2 catalysts preferentially takes place with a noticeable distortion of the initial OMS-2 structure. While, Fe cations are homogeneously distributed between the surface and the crystalline structure of the Fe-OMS-2 samples. According to the H-TPR data, the addition of Fe or Sn modifiers leads to an increase in the strength of oxygen binding with the catalyst surface. Under the TPO conditions, a shift of the O consumption to low temperatures (by >100 °C) is observed for the Sn-containing samples due to an increase of the amount of oxygen-deficient SnO species that are formed as a result of SnO disproportionation. The modified sample Fe-OMS-2 (20/1) shows the highest selectivity towards acetaldehyde formation (>82%) at the ethanol conversion of 80% at 157 C. The increase in the Fe content in the composition of the Fe-OMS-2 (10/1) sample results in the increase of T up to 180 °C, while keeping high selectivity towards acetaldehyde of 83%.