Gold Nano-size Effect in Au/SiO2 for Selective Ethanol Oxidation in Aqueous Solution

Abstract

Narrowly sized colloidal Au particles of varying average sizes (3-30 nm) were immobilized on an inert support (SiO 2 ) to study the Au size effect on the aerobic oxidation of ethanol in aqueous solution. Au particles with an average diameter of 5 nm showed an areal activity that was about three times that of the smaller (3 nm), and 15 times that of larger (10-30 nm) Au particles. Investigation on the dependence of product yields on ethanol conversion over these differently sized Au particles clearly uncovered that the yield of acetic acid increased always with the ethanol conversion, while that of acetaldehyde passed a maximum at an ethanol conversion of 20-30%, therefore well demonstrating that acetaldehyde is the intermediate product in the oxidation of ethanol to acetic acid.

Synthesis of Acetoaldehyde, Acetic Acid, and Others by the Dehydrogenation and Oxidation of Ethanol

“…Figure 7 shows that over MgAl 2 O 4 support the oxidation of ethanol with air proceeds deeper to yield acetic acid in the order of Pd, Pt, and Au [26]. Later Au/TiO 2 [27], Au/SiO 2 [28], Au/ZnO, Au/TiO 2 , and Au/Al 2 O 3 [29] are reported to be also selective to acetic acid. Our screening of support materials for gold catalysts proved that among simple metal oxides NiO, Al 2 O 3 and TiO 2 provide higher conversion and higher acetic acid selectivity [30].…”

“…Coprecipitated Au/NiO doped with Cu calcined at 573 K shows good activity even at 393 K with selectivities to acetic acid above 90%. Figure 8 shows that acetic acid selectivity increases with an increase in ethanol conversion whereas acetaldehyde selectivity decreases, indicating that acetic acid is produced from acetaldehyde in liquid phase [28]. The rate determining step is oxygen assisted dehydrogenation of ethanol to acetaldehyde.…”

Ab initio studies of ethanol dehydrogenation at binary AuPd nanocatalysts

“…One particularly interesting case is the selective production of aldehydes; various studies suggest that the main reaction mechanism involves two steps: dissociation of the alcohol O-H bond with formation of a metal-alkoxy intermediate, followed by breaking of the C-H bond, forming the aldehyde and a metal-hydride intermediate [6][7][8] . One trivial consequence of such complex reaction mechanism is that very diverse characteristics of the catalyst can dramatically influence both reactivity and selectivity: size and type of support currently being the most carefully analyzed 9,10 . Very recently, the study of bimetallic nanocatalysts has added even more complexity and richness to the problem.…”

Gold Nanoparticles Stabilized by Task-Specific Oligomeric Ionic Liquid for Styrene Epoxidation Without Using VOCs as Solvent

“…Since Haruta's [1] pioneering work in 1987 on the extraordinary catalytic activity of nanoscale gold particles for CO oxidation, gold nanoparticles have been shown to be highly active catalysts for many important industrial reactions, such as low temperature CO oxidation [2][3][4], alcohol oxidation [5][6][7][8][9][10], hydrogenation of a,b-unsaturated aldehydes [11], direct formation of hydrogen peroxide [12,13], and epoxidation/oxidation of alkenes [14][15][16][17][18][19][20]. Owing to easy agglomeration of nanoparticle, these gold nanoparticles are generally stabilized by solid supports in catalytic reactions, especially in liquid-phase epoxidation/ oxidation.…”

“…Owing to easy agglomeration of nanoparticle, these gold nanoparticles are generally stabilized by solid supports in catalytic reactions, especially in liquid-phase epoxidation/ oxidation. Although the supported solid catalysts show good activity in some liquid-phase reactions [5][6][7][8][9][10][14][15][16][17], the potential inaccessibility of the substrate to the catalytic active sites in the reaction system involving solid catalyst has stimulated researchers to use liquid stabilizer as an alternative solution [21][22][23][24]. On the other hand, liquidphase epoxidation/oxidation catalyzed by solid gold nanoparticle catalysts usually employ volatile organic compounds (VOCs) as solvents, such as benzene [14][15][16], methylcyclohexane [17], and 1,2,3,5-tetramethylbenzene [18].…”