Water-Enhanced Catalysis of CO Oxidation on Free and Supported Gold Nanoclusters

Abstract

The enhancement by water molecules of the catalytic activity of gas-phase and supported gold nanoclusters toward CO oxidation is investigated with first-principles calculations. Coadsorption of H(2)O and O(2) leads to formation of a complex well bound to the gold cluster, even on a defect-free MgO(100) support. Formation of the complex involves partial proton sharing between the adsorbates, that in certain configurations results in proton transfer leading to the appearance of a hydroperoxyl-like complex. The O-O bond is activated, leading to a weakened peroxo or superoxolike state, and consequently the reaction with CO to form CO2 occurs with a small activation barrier of approximately 0.5 eV. A complete catalytic cycle of the water-enhanced CO oxidation is discussed.

Factors in Gold Nanocatalysis: Oxidation of CO in the Non‐Scalable Size Regime

“…For the gold octamer, bound to a defect-free MgO(100) surface, two spatial regions for oxygen adsorption may be identified in the calculations: (i) the top facet of the cluster, where O 2 adsorbs weakly (adsorption energies up to 0.1eV), in agreement with [18,27,30] [65]. The distance between the O atoms sharing the proton takes a value of about 2.49 Å , while the O-O hydroperoxyl bond length reaches a value of about 1.48 Å (that is 21% larger than in a free molecule), reflecting a very high degree of bond activation.…”

“…As mentioned in the introduction, for certain supports, moisture is able to increase the activity of gold nanocatalysts by about two orders of magnitude [24] Thus, the influence of water on the chemical activity of gold clusters was recently investigated with the use of quantum mechanical ab-initio calculations for Au 8 adsorbed on a defect-free MgO(100) surface [65], i.e. a system that does not exhibit charging effects and is inert for CO oxidation (see above).…”

Effects of solvation shells and cluster size on the reaction of aluminum clusters with water

“…8 Nanotechnology has opened new avenues toward solving this problem. For example, the surfacearea to volume ratio is drastically increased, 11 quantum effects on the atomic scale often lead to novel catalytic activities 12 and enhanced reaction rates, 1,7,[13][14][15][16] and surfaces can be tailored at the nanometer scale to prevent oxidation. 17 Metal clusters have been found to react chemically in unusual ways.…”

“…A remarkable example is an Al superatom, i.e., a cluster consisting of a magic number of Al atoms. 18,19 Hydrogen molecules were produced through gas-phase reaction of Al superatoms with water molecules, where Al 12 and Al 17 showed particularly higher reactivity compared with other cluster sizes. 20,21 The size selectivity of superatoms for gas-phase reaction with water molecules has been explained through geometric factors.…”

Structure, reactivity, and electronic properties of V-doped Co clusters

“…7,8 Considering the huge possibility of using nanoclusters in catalysis, the study of cluster reactivity has become an interdisciplinary topic of present day research. [9][10][11][12] About 2 decades ago, Nonose et al measured the reactivity toward H 2 of bimetallic Co n V m ͑n Ͼ m͒ clusters using laser-vaporization technique and reported strong cluster size and composition dependence. 13 Both V and Co are 3d transition metals.…”