Ag Adsorption on Reduced CeO₂(111) Thin Films

Abstract

The adsorption energies and growth morphology of silver on reduced CeO 2 (111) thin films at 300 K have been studied using adsorption microcalorimetry in combination with low energy ion scattering (ISS), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), sticking probability measurements, low energy electron diffraction (LEED), and scanning tunneling microscopy (STM). Thin films (4 nm thick) of CeO 2-x (111), with x ) ∼0.1, were grown on a Pt(111) singlecrystal. The AES and ISS signals varied with Ag coverage in a manner indicative of 3D Ag particle growth, with a density of ∼4 × 10 12 particles/cm 2 . The initial heat of adsorption of Ag vapor was ∼200 kJ/mol, which is much lower than the heat of sublimation of Ag (285 kJ/mol). Further reduction of the surface by heating in vacuum (to reach x ) ∼0.2) resulted in a slight increase in the initial heat of adsorption to ∼220 kJ/mol; subsequently, higher heats of adsorption were observed until the heat of sublimation of bulk Ag was reached on both films. This increase was attributed to stronger bonding of Ag particles to oxygen vacancies. The initial adsorption energy of Ag on a thinner film (1 nm thick) of CeO 1.9 (111) was ∼250 kJ/mol, ∼50 kJ/mol higher than the 2, 3, and 4 nm films. This is probably due to an interaction of the Ag particles with the underlying Pt(111) surface. The sticking probability of Ag was measured to be near unity (>0.98) on all these reduced CeO 2 (111) films between 1-4 nm thick at 300 K and at all Ag coverages.

Energetics of Cu Adsorption and Adhesion onto Reduced CeO2(111) Surfaces by Calorimetry

“…The results are compared to similar measurements of Cu adsorption on MgO(100) 11 and Ag adsorption on the same reduced CeO 2 (111) surfaces. 8,9 Copper supported on ceria has shown promise as a catalysts for a variety of reactions such as CO oxidation, 12,13 water gas shift reaction, 14,15 and methanol synthesis. 16,17 For methanol synthesis, the perimeter of copper nanoparticles at the interface with ceria was found to be the most catalytically active sites, 17 and Cu was only catalytically active when it is in the neutral form rather than oxidized.…”

Shape-dependent interplay between oxygen vacancies and Ag–CeO2 interaction in Ag/CeO2 catalysts and their influence on the catalytic activity

“…Theoretical calculation studies showed that CeO 2 {1 1 1} is the least active surface, followed by {1 0 0} and {1 1 0} [35]. However, besides the surface composition and surface structure determined by the exposed crystal plane, oxygen vacancies also play a decisive role in the surface reactivity and catalytic performance of CeO 2 nanoparticles [9,10,21,22,[36][37][38] and the concentration and structure of oxygen vacancies have been reported to depend on the preparation process and structure of CeO 2 nanoparticles [21,39,40]. Esch et al [39] reported that small size surface oxygen vacancies were immobile on CeO 2 (1 1 1) at room temperature, but could form linear clusters at high temperatures.…”

The effect of Ag as a promoter for Ru/CeO2 catalysts in ammonia synthesis

“…But it can be accepted by considering that Ag promoter loading could result in the reduction of the adsorbed sites and surface area. Though the O vacancy created by reduced ceria can adsorb hydrogen, Ag could interacted with O vacancy of CeO 2−x [41][42][43], occupied O vacancy would not adsorb hydrogen, so the intensity of hydrogen desorption peak reduced with Ag loading. Additionally, it is well known that suppression of H 2 chemisorption is an important property for the mental/oxides systems with SMSI effect [44].…”