Environmentally benign aqueous oxidative catalysis using AuPd/TiO2 colloidal nanoparticle system stabilized in absence of organic ligands

Abstract

The use of nanoparticles (NPs) for efficient, environmentally benign catalysis is receiving increasing attention, with gold and palladium NPs being an important area of research. Herein we present a simple, reliable and cost-effective preparation of a catalytically active gold-palladium NP system that is stabilized by an aqueous titania dispersion (AuPd/TiO 2 ) in the absence of organic ligands. The major advantages of this system are that it is catalytically active in the as-prepared colloidal state, eliminating the need for drying and sintering before use and is colloidally stable in oxidative conditions. The AuPd/TiO 2 system exhibits efficient oxidative catalysis in both the presence of hydrogen peroxide and atmospheric oxygen, even at ambient temperatures for our model aqueous phase reaction of 1-phenylethanol oxidation. The preparation and characterization of the AuPd/TiO 2 system is described with respect to the effects of colloidal stability, particle size and morphology on aqueous oxidative catalysis. The major finding is that NPs with a gold core and thin palladium shell (70 mol% gold, 30 mol% palladium, Au 70 Pd 30 /TiO 2 ) provides the most catalytically active system. The ability of the catalyst to use atmospheric oxygen at ambient temperatures in aqueous media highlights the strong potential of the developed catalytic system for green oxidative processes. The presented approach provides a new platform of all-inorganic colloidal nanoparticle systems for future development of industrially viable, environmentally friendly catalysts.

Theoretical Studies on the Synergetic Effects of Au–Pd Bimetallic Catalysts in the Selective Oxidation of Methanol

“…Among them, Au-Pd catalysts usually show enhanced activity and selectivity in catalyzing alcohols to corresponding aldehydes or ketones compared to pure Au or Pd catalysts. [20][21][22][23][24] Moreover, alloying Au and Pd improves the resistance to the deactivation. 19,21,22 Despite superior properties of Au-Pd catalysts, the knowledge of the intrinsic catalytic mechanisms and the nature of the synergetic effect between Au and Pd is still elusive.…”

“…1,2 Utilization of O 2 or air as oxidizing agents to replace conventional stoichiometric d 0 -metal oxides is the final goal for environmentally benign oxidation reactions. To achieve this goal, tremendous efforts have been made to develop new catalysts, including monometallic Au, [3][4][5][6][7][8][9][10][11][12][13][14] Pd, [15][16][17][18] and bimetallic Au-Pd, [19][20][21][22][23][24][25][26][27] Au-Cu, 28, 29 Au-2 Ir 30 catalysts. Among them, Au-Pd catalysts usually show enhanced activity and selectivity in catalyzing alcohols to corresponding aldehydes or ketones compared to pure Au or Pd catalysts.…”

Synthesis of Nanoparticles for Biomass Conversion Processes

“…They have been used for advances in fuel cell technology. These types of NPs are also important in other biorenewable transformations, such as hydrogenation (110) and small molecule oxidation (111)(112)(113)(114)(115)(116)(117)(118)(119)(120)(121)(122)(123)(124)(125)(126)(127)(128)(129)(130).…”

A Review: The Uses of Various Nanoparticles in Organic Synthesis

“…Au-Pd nanoparticles are preared in the absence of organic ligands and adsorbed onto TiO 2 supports and is found to be stable in oxidative catalysis conditions [84]. It was investigated that 70% gold, 30% Pd composition of the bimetallic nanoparticles show the highest catalytic activity for the oxidative catalysis.…”