Basic catalysis on MgO: generation, characterization and catalytic properties of active sites - Catalysis - page 6

high temperature (1023 K), the relative distribution of surface low-
coordination O 2 anions is shifted toward the less coordinated ions
along the series MgO-CVD o MgO-hydration MgO-precipitation o MgO-

sol-gel. The same order was observed for MgO activity to convert
2-methylbut-3-yn-2-ol into acetone and acetylene, a base-catalyzed
reaction [50]. The density and strength of base sites on MgO may also
be regulated by controlling both the Mg(OH) 2 decomposition and MgO
activation conditions. For example, Vidruk et al. [51] reported that
densification of Mg(OH) 2 before its dehydration to obtain MgO generates
a significant increase of surface basicity. We have recently investigated
[52] the effect of calcination temperature of MgO obtained by Mg(OH) 2
decomposition on its base and catalytic properties.

E

3.1.1.1 Thermal decomposition of Mg(OH) 2 . The thermal de-
composition of Mg(OH) 2 precursor was studied by XRD. The diffracto-
grams in Fig. 1 showed that the Mg(OH) 2 brucite structure was stable up
to about 573 K, but then, between 573 and 673 K, decomposed to MgO.
Figure 1 also shows that the MgO stabilized at 773 K during 18 h is more
crystalline than that obtained by dynamic heating up to the same
temperature. Consistently, characterization by DTA technique showed
that the Mg(OH) 2 heating exhibits an endothermic peak between 573 and
673 K arising from the solid decomposition [52]. On the other hand,
TPDe experiments revealed the presence of evolved CO 2 in the 573-673 K

Mg(OH) 2

MgO

stabilized at
773 K for 18 h

773 K

673 K

573 K

298 K

30 35 40 45 50

2 θ (°)

Fig. 1 XRD diffraction patterns of Mg(OH) 2 decomposition.