Experimental Microkinetic Approach of the Surface Reconstruction of Gold Particles during the Adsorption of CO at 300 K on 1% Au/Al₂O₃

Abstract

The adsorption of CO at 300 K on a 1% Au/Al2O3 solid leads to the formation of a linear CO species adsorbed on the Au° particles (denoted L1) characterized by an IR band at 2095 cm−1 at high coverage. For an adsorption pressure PCO< 1 kPa the position and the intensity of this IR band is independent of the duration of the adsorption ta (ta < 30 min). For PCO ≥ 5 kPa, it is shown that there is a progressive decrease in the intensity of the IR band of the L1 CO species with the increase in ta (without modification of its position) in parallel with the progressive increase in an IR band at 2070 cm−1 ascribed to a new linear CO species (denoted L2). According to literature data, these modifications are ascribed to the reconstruction of the gold particles leading to the transformation of the Au° sites adsorbing CO. The rate of the L1 → L2 transformation allows studying the elementary steps involved in this reconstruction process according to an experimental microkinetic approach that considers the impacts of different experimental parameters in particular ta, PCO and the dispersion of the gold particles. This work shows that (a) the rate constant at 300 K of the elementary step controlling the reconstruction is dependent on the coverage θL1 of the L1 CO species that is a function of PCO and (b) the higher heat of adsorption of the L2 CO species as compared to the L1 CO species constitutes one of the driving force of the reconstruction of the gold surface and explains the stabilization of the reconstructed surface during out degassing at 300 K. It is shown that the conclusions of the present study are consistent with literature data on DFT calculations.