Srg. Carrazan et al., CATALYTIC SYNERGY IN THE OXIDATIVE DEHYDROGENATION OF PROPANE OVER MGVO CATALYSTS, Journal of catalysis, 158(2), 1996, pp. 452-476
Synergetic effects in the oxidative dehydrogenation of propane have be
en studied over magnesium vanadate catalysts containing three differen
t Mg/V ratios: 1/2, 2/2, and 3/2, denoted as MgV(1/2), MgV(2/2), and M
gV(3/2). Four types of catalysts were analysed: (a) pure magnesium van
adate oxides, (b) mechanical mixtures of the pure magnesium vanadate o
xides, (c) mechanical mixtures of the magnesium vanadate oxides with a
lpha-Sb2O4, and (d) impregnated MgV(2/2) and MgV(3/2) with Sb ions. Sy
nergetic effects are observed in MgV(3/2) and in MgV(2/2) oxides when
they are in presence of (alpha-Sb2O4. In the mixtures of MgV(3/2) with
alpha-Sb2O4, the principal effect is an increase in the selectivity w
ith a corresponding decrease in propane conversion, whereas in the mix
tures of MgV(2/2) with alpha-Sb2O4, there is a strong increase in prop
ane conversion with a moderate increase in propene yield. Concerning t
he mixtures of MgV(3/2) and MgV(2/2), synergetic effects in the conver
sion, in the yield, and in the selectivity are observed. However, no s
ynergetic effects in selectivity or conversion are exhibited by MgV(2/
2) and MgV(3/2) when they are mixed with MgV(1/2). Highly dispersed (S
bxOy), formed on impregnated MgV(2/2) and MgV(3/2), sinters and detach
es from MgV(2/2) and MgV(3/2) surfaces. No formation of a new phase or
contamination in the presence of alpha-Sb2O4 takes place when MgV(3/2
) is used. Thus, these catalysts contain two separate phases in contac
t. In MgV(2/2) + alpha-Sb2O4 mechanical mixtures a new phase, MgSb2O6,
(formed during the test) is also present in small quantities. The mix
tures of MgV(3/2) with MgV(2/2) reveal neither formation of a new phas
e nor contamination. The synergetic effects in the selectivity exhibit
ed by MgV(3/2) mixed with MgV(2/2) and with alpha-Sb2O4 is explained b
y a remote control mechanism. MgSb2O6, formed in MgV(2/2)-containing c
atalysts, is responsible for the increase in complete oxidation and th
e strong decrease in selectivity. (C) 1996 Academic Press, Inc.