The electronic absorption spectra of 2-hydroxy-l,4-naphthoquinone (HNQ) in one- and
two-component solvents are discussed. The visible absorption of this reagent has been shown to arise
from a charge-transfer transition of the zwitterionic tautomer stabilized by a hydrogen bond donating
solvent. The formation constant of the 1 : 1 hydrogen bonded complex with methanol, ethanol, and
n-propanot has been determined at 25 °C from the spectral behaviour in mixed solvents. The
tautomerization equilibrium of HNQ in aqueous ethanol is demonstrated and characterized. The
dependence of the absorbance maximum of HNQ on the hydrogen bond donor ability of the solvent in
the visible spectrum, as measured by the Taft-Kamlet ~ parameter, has been established. Experimentally derived evidence is supplied to justify the recommendation of HNQ as a novel probe for hydrogen
bond donor ability in pure solvents and in mixed aqueous solvents.

The electronic absorption spectra of 2-hydroxy-l,4-naphthoquinone (HNQ) in one- and
two-component solvents are discussed. The visible absorption of this reagent has been shown to arise
from a charge-transfer transition of the zwitterionic tautomer stabilized by a hydrogen bond donating
solvent. The formation constant of the 1 : 1 hydrogen bonded complex with methanol, ethanol, and
n-propanot has been determined at 25 °C from the spectral behaviour in mixed solvents. The
tautomerization equilibrium of HNQ in aqueous ethanol is demonstrated and characterized. The
dependence of the absorbance maximum of HNQ on the hydrogen bond donor ability of the solvent in
the visible spectrum, as measured by the Taft-Kamlet ~ parameter, has been established. Experimentally derived evidence is supplied to justify the recommendation of HNQ as a novel probe for hydrogen
bond donor ability in pure solvents and in mixed aqueous solvents.

The electronic absorption spectra of 2-hydroxy-l,4-naphthoquinone (HNQ) in one- and
two-component solvents are discussed. The visible absorption of this reagent has been shown to arise
from a charge-transfer transition of the zwitterionic tautomer stabilized by a hydrogen bond donating
solvent. The formation constant of the 1 : 1 hydrogen bonded complex with methanol, ethanol, and
n-propanot has been determined at 25 °C from the spectral behaviour in mixed solvents. The
tautomerization equilibrium of HNQ in aqueous ethanol is demonstrated and characterized. The
dependence of the absorbance maximum of HNQ on the hydrogen bond donor ability of the solvent in
the visible spectrum, as measured by the Taft-Kamlet ~ parameter, has been established. Experimentally derived evidence is supplied to justify the recommendation of HNQ as a novel probe for hydrogen
bond donor ability in pure solvents and in mixed aqueous solvents.

The electronic absorption spectra of 2-hydroxy-l,4-naphthoquinone (HNQ) in one- and
two-component solvents are discussed. The visible absorption of this reagent has been shown to arise
from a charge-transfer transition of the zwitterionic tautomer stabilized by a hydrogen bond donating
solvent. The formation constant of the 1 : 1 hydrogen bonded complex with methanol, ethanol, and
n-propanot has been determined at 25 °C from the spectral behaviour in mixed solvents. The
tautomerization equilibrium of HNQ in aqueous ethanol is demonstrated and characterized. The
dependence of the absorbance maximum of HNQ on the hydrogen bond donor ability of the solvent in
the visible spectrum, as measured by the Taft-Kamlet ~ parameter, has been established. Experimentally derived evidence is supplied to justify the recommendation of HNQ as a novel probe for hydrogen
bond donor ability in pure solvents and in mixed aqueous solvents.

The complexation equilibria of zinc(lI) with 2-hydroxy-1,4-naphthoquinone, 5-hydroxy- 1,4-naphthoquinone and 5.8-dihydroxy- 1,4-naphthoquinone have been studied spectrophotometrically as a function of pH in 50% (v/v) ethanol-water medium at 25°C and an ionic strength of 0.1M NaClO4. The spectral study of the complexation reactions has been carried out in solutions containing equimolar concentrations or an excess of one component in the pH range of study. The chelation capabilities of these hydroxynaphthoquinones with zinc(II) have been examined. The complexation equilibria have been demonstrated and characterized by analysis of the absorbance versus pH graphs. The composition, molar absorptivities, equilibrium constants and stability constants of zinc(II) complexes with these reagents have been determined. The fundamental conditions favouring direct spectrophotometric determination of trace amounts of zinc(II) using naphthazarin have been investigated.

The complexation equilibria of zinc(lI) with 2-hydroxy-1,4-naphthoquinone, 5-hydroxy- 1,4-naphthoquinone and 5.8-dihydroxy- 1,4-naphthoquinone have been studied spectrophotometrically as a function of pH in 50% (v/v) ethanol-water medium at 25°C and an ionic strength of 0.1M NaClO4. The spectral study of the complexation reactions has been carried out in solutions containing equimolar concentrations or an excess of one component in the pH range of study. The chelation capabilities of these hydroxynaphthoquinones with zinc(II) have been examined. The complexation equilibria have been demonstrated and characterized by analysis of the absorbance versus pH graphs. The composition, molar absorptivities, equilibrium constants and stability constants of zinc(II) complexes with these reagents have been determined. The fundamental conditions favouring direct spectrophotometric determination of trace amounts of zinc(II) using naphthazarin have been investigated.

The complexation equilibria of zinc(lI) with 2-hydroxy-1,4-naphthoquinone, 5-hydroxy- 1,4-naphthoquinone and 5.8-dihydroxy- 1,4-naphthoquinone have been studied spectrophotometrically as a function of pH in 50% (v/v) ethanol-water medium at 25°C and an ionic strength of 0.1M NaClO4. The spectral study of the complexation reactions has been carried out in solutions containing equimolar concentrations or an excess of one component in the pH range of study. The chelation capabilities of these hydroxynaphthoquinones with zinc(II) have been examined. The complexation equilibria have been demonstrated and characterized by analysis of the absorbance versus pH graphs. The composition, molar absorptivities, equilibrium constants and stability constants of zinc(II) complexes with these reagents have been determined. The fundamental conditions favouring direct spectrophotometric determination of trace amounts of zinc(II) using naphthazarin have been investigated.

The complexation equilibria of zinc(lI) with 2-hydroxy-1,4-naphthoquinone, 5-hydroxy- 1,4-naphthoquinone and 5.8-dihydroxy- 1,4-naphthoquinone have been studied spectrophotometrically as a function of pH in 50% (v/v) ethanol-water medium at 25°C and an ionic strength of 0.1M NaClO4. The spectral study of the complexation reactions has been carried out in solutions containing equimolar concentrations or an excess of one component in the pH range of study. The chelation capabilities of these hydroxynaphthoquinones with zinc(II) have been examined. The complexation equilibria have been demonstrated and characterized by analysis of the absorbance versus pH graphs. The composition, molar absorptivities, equilibrium constants and stability constants of zinc(II) complexes with these reagents have been determined. The fundamental conditions favouring direct spectrophotometric determination of trace amounts of zinc(II) using naphthazarin have been investigated.

Lanthana–zirconia supported chromium oxide and magnesium chromium mixed oxide catalysts were studied in the dehydrocyclization of n-octane and characterized by temperature-programmed desorption of NH3, temperature-programmed reduction, XPS and DRIFTS. The Mg-free catalyst shows the highest activity, but suffers from rapid deactivation due to coke formation. The addition of Mg decreases the initial activity of the supported chromium oxide and retards its deactivation. The characterization results reveal that the deactivation retarding effect of Mg species not only consists in the deletion of strong acid sites but also in the decoration and/or dilution of Cr3+ oxide cluster, supposedly due to the formation of Mg–Cr surface compounds and, thus, in preventing the formation of coke.

Alumina and zirconia supported Pt and Pt–Sn catalysts have been tested in the dehydrocyclization (DHC) of n-octane at 823 K to alkylaromatics as desired products using pure hydrogen (H2) and water vapour containing hydrogen (WVH2) atmospheres. The materials were characterized by nitrogen adsorption, NH3-TPD, TPR, XRD, XPS, TEM and EDX. The characterization results reveal the formation of PtSn alloys on alumina support after a catalyst precursor reduction in H2 at 873 K. This observation enables an interpretation of the higher on-stream stability of Pt–Sn/Al2O3 catalyst in H2 as well as in WVH2 compared to the monometallic sample, using the well-known concept of the ensemble effect of Sn by alloying to Pt. The alumina supported Pt and Pt–Sn catalysts act bifunctionally in H2 atmosphere, producing a mixture of benzene, mono- and dialkylaromatics, near the chemical equilibrium. In WVH2