Unraveling the role of the lacunar Na₇PW₁₁O₃₉ catalyst in the oxidation of terpene alcohols with hydrogen peroxide at room temperature

Abstract

The Na7PW11O39 lacunar salt was the most active among Keggin lacunar salts (Na8SiW11O39 and Na7PMo11O39), a saturated salt (Na7PW12O40) and heteropolyacid catalysts.

How the Cobalt Position in the Keggin Anion Impacts the Activity of Tungstate Catalysts in the Furfural Acetalization with Alkyl Alcohols

“…Due to their structural versatility, various modifications on the Keggin anion have improved their catalytic activity. These are the main changes performed: (i) to convert HPAs to salts after exchange their protons by metal or organic cations, resulting in catalysts highly active in esterification, etherification, acetalization, and hydrolysis reactions; [21–29] (ii) to transform the Keggin HPAs to lacunar salts, removing one MO unit (M=W or Mo), leading to the highly active catalysts in oxidation reactions with hydrogen peroxide of olefins, alcohols, and aldehydes; [30–35] and (iii) to doping lacunar Keggin anion with a transition metal cation, resulting in efficient catalysts in oxidative transformations [36–41] …”

“…[18][19][20] Due to their structural versatility, various modifications on the Keggin anion have improved their catalytic activity. These are the main changes performed: (i) to convert HPAs to salts after exchange their protons by metal or organic cations, resulting in catalysts highly active in esterification, etherification, acetalization, and hydrolysis reactions; [21][22][23][24][25][26][27][28][29] (ii) to transform the Keggin HPAs to lacunar salts, removing one MO unit (M=W or Mo), leading to the highly active catalysts in oxidation reactions with hydrogen peroxide of olefins, alcohols, and aldehydes; [30][31][32][33][34][35] and (iii) to doping lacunar Keggin anion with a transition metal cation, resulting in efficient catalysts in oxidative transformations. [36][37][38][39][40][41] An important aspect is that the size of cation can modulate the solubility of these salts (i. e., lacunar, metal-doped); while salts containing highly charged counterions such as small-sized metal cations are soluble in a polar solvent, those having large radium cations are almost insoluble.…”

Vanadium-doped sodium phosphomolybdate salts as catalysts in the terpene alcohols oxidation with hydrogen peroxide

“…The purication, spectroscopic characterization, and identication of all the products was previously published. 31 The vibrations of these chemical bonds generate typical bands in the region 500 to 1200 cm À1 of the infrared spectrum, recognized as the ngerprint region. If vanadium atoms replace molybdenum atoms in the Keggin anion, may occur a decrease in the symmetry of the anion, leading to the changes in the bands noticed in the infrared spectrum of salts.…”

“…A simple protons exchange by metal cations allows that their properties such as acidity strength, porosity, and surface area can be adequately tuned, making them efficient catalysts in redox or acid-catalyzed reactions. [28][29][30][31][32] In addition, if the protons are exchanged by large ionic radius cations such as cesium, potassium, or ammonium, they become insoluble catalysts in polar solvents. 33,34 This modication keeps untouched the Keggin anion, which is the primary structure of these catalysts.…”

Na4PMo11VO40-catalyzed one-pot oxidative esterification of benzaldehyde with hydrogen peroxide

“…33,34 Alternatively, Keggin HPAs can be converted to solid salts, exchanging their protons by larger radium cations as cesium or potassium. 35,36 Two other interesting approaches may improve the performance of Keggin HPAs in catalytic oxidation reactions: the removal of an MO unit (i.e., M ¼ W or Mo), generating lacunar catalysts, 37,38 and the exchange of an addenda atom (i.e., tungsten or molybdenum) by vanadium atom. 39,40 Lacunar Keggin HPA catalysts were successfully used in the oxidation of aldehydes with hydrogen peroxide.…”