Aerobic Oxidation of Alcohols over Gold Catalysts: Role of Acid and Base

Abstract

Gold nanoparticles are deposited on potassium titanate nanowires and used as heterogeneous catalysts in the aerobic oxidation of benzyl alcohol in methanol to methyl benzoate at ambient conditions. The presence of a catalytic amount of base promotes the reaction and the formation of free benzoic acid during the reaction poisons the catalyst. The activity however, of the catalyst can be restored again by addition of base.

Ab initio studies of ethanol dehydrogenation at binary AuPd nanocatalysts

“…Once ethanol is adsorbed at a Pd site, surrounded by other Pd atoms and with the Au atoms relatively far away, the main features of the reaction pathway are quite similar to the results found for pure Pd 10 . The first reaction barrier is moderate (0.75 eV), and the second one, C-H bond breaking, is also quite low (0.56 eV), with height very similar to the corresponding one for Pd 10 . Also, we find a highly stable doubly-bonded acetaldehyde intermediate.…”

“…In the case of Au 2 Pd 8 , all the main reaction steps take place at Pd sites, which have local environments analogous to the ones of the pure Pd 10 cluster. This causes the reaction pathway to be very similar to the one for Pd 10 . The Au 5 Pd 5 cluster is characterized by a uniform mixing of Pd and Au atoms, resulting in each site being surrounded by a mixture of Pd and Au sites.…”

“…It is, in fact, lower than the corresponding barriers on Pd 10 and Au 10 . Then, the intermediate state with dissociated ethanol is characterized by a binding energy of -0.21 eV, which is approximately halfway between the -0.8 eV value for Pt 10 and the +0.4 eV for Au 10 . The second reaction barrier, of 0.23 eV, is now much smaller than the first one, and it involves reaction of the second hydrogen atom with a Pd atom.…”

“…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.…”

Palladium Nanoparticles Supported on Titanate Nanobelts for Solvent‐Free Aerobic Oxidation of Alcohols

“…For example, Au-Pd bimetallic catalysts supported on ZnO and MgO resulted in no formation of toluene. [30] The basic nature of the titanate nanobelts makes the catalyst particularly useful, especially compared with the extensive and more complicated efforts involving base addition [31][32][33] and support modification. [8][9][10]34] After full water removal by calcination, partial hydrolysis and Na + exchange in the titanate nanobelts could be completely inhibited to strengthen the basicity of the support.…”