Transition Metal-Substituted Potassium Silicotungstate Salts as Catalysts for Oxidation of Terpene Alcohols with Hydrogen Peroxide

• Published in: Catalysis letters Vol. 151; no. 7; pp. 2094 - 2106
• Main Authors: da Silva, Marcio Jose, da Silva Andrade, Pedro Henrique, Sampaio, Vinicius Fernando Coelho
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-07-2021; Springer; Springer Nature B.V
• Subjects: Alcohol; Alcohols; Analysis; Aqueous solutions; Catalysis; Catalysts; Catalytic activity; Chemical precipitation; Chemical synthesis; Chemistry; Chemistry and Materials Science; Cobalt; Hydrogen peroxide; Industrial Chemistry/Chemical Engineering; Infrared spectroscopy; Manganese; Nickel; Organometallic Chemistry; Oxidation; Oxidation-reduction reaction; Oxidizing agents; Physical Chemistry; Potassium; Sodium silicates; Spectrum analysis; Substitutes; Substrates; Titration; Transition metals; X-rays; Zinc compounds; Heteropoly acids; Heterogeneous catalysis; Oxidation; Green chemistry; Alcohols
• ISSN: 1011-372X; 1572-879X
• DOI: 10.1007/s10562-020-03449-9

In this work, the catalytic activity of the transition metal-substituted potassium silicotungstate salts (i.e. K
8-n
SiM
n+
W
11
O
39
(M
n+
 = Cu
2+
, Co
2+
, Ni
2+
, Zn
2+
and Fe
3+
) was investigated on the oxidation reactions of the terpene alcohols with H
2
O
2
aqueous solution. The metal-substituted silicotungstate salts were easily synthesized in one-pot reactions of the precursor metal solutions (i.e. Na
2
WO
4
, Na
2
SiO
3
and MCl
n
) with KCl added in stoichiometric amount; after this precipitation step, the solid heteropoly salts were filtered and dried in an oven. This procedure of synthesis avoids multi-step processes that starts from the pristine heteropolyacid. The substituted metal heteropoly salts were characterized by infrared spectroscopy, measurements of the specific surface area (BET) and porosimetry by isotherms of adsorption/desorption of N
2
, X-rays diffraction, thermal analyses, dispersive X-rays spectroscopy, scanning electronic microscopy. The acidity strength was estimated by potentiometric titration with
n
-butylamine. All the salts were evaluated as catalysts in terpenic alcohols oxidation reactions with H
2
O
2
. The K
5
SiFeW
11
O
39
was the most active and selective catalyst toward oxidation products. The impacts of the main reaction variables such as catalyst concentration, temperature, oxidant load, and nature of the terpene substrate were assessed. The highest activity of the K
5
SiFeW
11
O
39
catalyst was assigned to the highest Lewis acidity.
Graphic Abstract