The oxides used were reagent grade commercial products (V2O5, MgO, ZnO,
Fe2O3, La2O3, CuO) or from appropriate salts. Mn3O4, NiO and
Co3O4 is obtained from basic carbonates by heating at 803 K
3 hours, identified by infrared spectroscopy [11]. Decompose to get Cr20 3
Hydroxide Cr(OH) 3 at 673 K. calcium pantothenate
2.2. Catalyst test
Catalytic experiments were performed in a flow system on a fixed bed of 2 g
catalyst. The catalyst was activated under a gas flow of 723 K and used
Argon before the experiment. Reagent grade cyclohexanol vapor
Introduce using a calibrated syringe and evaporator. concentrated reaction
Product analysis by GC on a 2 m silanized chromosorb W column
60-80 mesh, 15% DC 550, 403K.
All experiments were performed at 673 K and WHSV 2 hr −1 . Some
Oxides (e.g. Mn3O4) are inactive to cyclohexanol below 673
K. Results are summarized in Table 1.
3. Results and discussion
Microcalorimetric studies [3] allow the classification of oxides
Divided into 3 groups: acidic oxides A; basic oxides B; acidic and basic oxides A-B.
CP Bezouhanova, M.A. Al-Zihari / Test reactions for acid-base properties
Table 1
Conversion of cyclohexanol over oxide catalysts. Temperature 673 K, LHSV 2 h-1
247
Catalyst product (wt.%)
C-Hexene C-Hexanol C-Hexanone Phenol
Magnesium Oxide - 64.0 30.6 1.4
Zinc oxide 3.9 26.1 67.6 -
Iron dioxide 3 8.9 65.9 22.7 1.0
Manganese 304 3.3 75.0 18.0 1.2
Zirconia 5 99.7 - - -
Cr20 3 16.5 42.1 36.4 -
Copper oxide - 17.7 65.3 11.3
Co3O4 11.7 50.3 26.5 4.3
Nickel oxide 3.7 46.6 40.2 6.3
La20 3 1.2 79.9 16.6 -
Our experiments with cyclohexanol showed that V2O5 is a typical acid,
And MgO is a typical base. This is consistent with the results in [3].
Considering that the heterogeneous dissociation of hydrogen can
occurs on MgO [12], hydrogen extraction from cyclohexanol can be
Assumptions:
Hydrogen +
Mg----~O Magnesium
> +
H + HMg--d--lVlg
Metal cations serve as Lewis active sites.
No Broensted acid sites are found in CuO. NiO and Mn3O4 show small
dehydration activity.
According to the results in [3], V205 has only Brunsted acid
site, since the only reaction product is cyclohexene. Acid sites also occur in
Cr2O3, C03O4, Fe2O3, ZnO, Mn3O4, NiO, La20 3 in order
Activity.
ZnO is considered as a solid base [3,13], but some acidic properties have been
also established [14]. The most active materials in dehydrogenation are ZnO and
Copper oxide. It is well known [15] that Zn- and Cu-catalysts find industrial application
Dehydrogenation of cyclohexanol to cyclohexanone at 673-723 K and atmospheric pressure. Under our experimental conditions, CuO and NiO also dehydrogenated cyclohexanol to phenol.
Although dehydrogenation of alcoholic hydroxyl groups may proceed
Hydrogen accepting sites with fundamental features - oxygen atoms from oxides
248 C.P. Bezuhanuwa, AIM. Al-Zihari / Acid-Alkaline Properties Test Reaction
lattice, the dehydrogenation of rings appears to be related to
transition metals.
In conclusion, most of the metal oxides studied possess acidic sites and hydrogen
Accepted sites, i.e. they must be considered members of group A-B
(according to [3]). Not only metal ions but also basic oxygen atoms have
Hydrogen acceptability. Simple and rapid conversion of cyclohexanol
Methods for determining the functionality of oxide catalysts.