Metallic Corner Atoms in Gold Clusters Supported on Rutile Are the Dominant Active Site during Water−Gas Shift Catalysis

Abstract

Au/TiO(2) catalysts used in the water-gas shift (WGS) reaction at 120 °C, 7% CO, 22% H(2)O, 9% CO(2), and 37% H(2) had rates up to 0.1 moles of CO converted per mole of Au per second. However, the rate per mole of Au depends strongly on the Au particle size. The use of a nonporous, model support allowed for imaging of the active catalyst and a precise determination of the gold size distribution using transmission electron microscopy (TEM) because all the gold is exposed on the surface. A physical model of Au/TiO(2) is used to show that corner atoms with fewer than seven neighboring gold atoms are the dominant active sites. The number of corner sites does not vary as particle size increases above 1 nm, giving the surprising result that the rate per gold cluster is independent of size.

CO Oxidation Mechanism on CeO2-Supported Au Nanoparticles

“…A Bader charge analysis, 46,47 presented in Figure S4, shows that electrons from the Au atom binding CO were redistributed over all of the Au atoms in Au 13 @CeO 2 -3VAC, whereas on Au 13 @CeO 2 -STO the electrons (0.29 e) were largely transferred to the empty 4f-band of Ce atoms, leading to more positively charged Au 13 (see Figure S4a). The same amount of charge was transferred to the adsorbed O 2 molecule in both Au 13 65 as reactive species. The complete CO oxidation pathway and rate presented in Figure 7 and Table 1 show that charged Au ions play no direct role in CO oxidation, because CO and O 2 preferentially bind to noncontacting Au atoms with low-coordination numbers.…”

Sour water–gas shift reaction over Pt/CeZrO2 catalysts

“…Table 6 compares the catalyst performance in terms of forward turnover frequency (TOF), measured in the temperature range 150-400°C. We have used the total amount of surface metal to estimate TOF, as recommended in the literature [73,74]. The changes in the observed TOF allowed comparing the effect of the catalyst surface composition on the WGSR.…”

“…We have also calculated specific reaction rates based on the perimeter of the Pt-support interface as reported before [75,76]. In the calculation of the length of the Pt-support interface (I 0 ), Pt nanoparticles were considered hemispherical, mean particle sizes were estimated based on CO chemisorption, and the number of particles was calculated using the Pt content in the catalysts (1%) and a density of Pt of 21.3 g/cm 3 [73,74]. Metal-support interface sites may be playing a role in the case of ceria-containing catalysts, and the perimeter of the Pt-support interface could be a better descriptor than the number of surface metal sites.…”

Water–Gas Shift on Pd/α-MnO2 and Pt/α-MnO2

“…including Au and Pt impregnated on reducible oxides such as CeO 2 and TiO 2 , have been extensively studied [9,[15][16][17][18][19]. It is generally acknowledged that surface of metal particles adsorbs CO and oxygen vacancies of reducible oxides dissociate H 2 O molecules to form OH groups [11,14].…”