Oxidative dehydrogenation of ethane on promoted VPO catalysts

Me-doped VPO (Me = Zr, Bi, and La-Bi) catalysts have been prepared, characterized and tested in the oxidation of ethane. The main of these catalysts present a high selectivity in the oxidative dehydrogenation (OXDH) of ethane to ethylene. However, O-containing partial reaction products were not observed. The addition of Bi or Zr to VPO catalyst leads to an important increase in both the catalytic activity and the selectivity to ethylene, especially in case of Zr-containing catalysts. (VO)(2)P(2)O(7) was the main crystalline phase observed in most selective catalysts. Doping by Bi and Zr was also associated with an increase of the surface area. However, a drop in both the ethane conversion and the selectivity to ethylene was observed in La-Bi-containing VPO catalysts (in which beta-VOPO(4) was the main crystalline phase). The addition of Bi or Zr ions to VPO favours a decrease of the O 1s-electron binding energies as observed by XPS, which could favour the proton abstraction of the ethane molecule and the enhancement of the rate of ethane oxidation. On the other hand, the variation of the selectivity to ethylene was related to the modification of acid-base properties of the catalyst surface. In this way, the decrease of the strength of Lewis acid centres favours an increase of the selectivity to ethylene. Yields of ethylene of 18-19 mol% and productivities of about 80 gC(2)H(4) kg(cat)(-1) h(-1) were obtained on synthesized catalysts. (C) 2003 Elsevier B.V. All rights reserved.