CO Adsorption Behavior on Au/TiO2 and Associated Size Effects Under the Influence of Ni Contamination

The dynamic changes of metals and supports under CO atmosphere combined with the potential undetected Ni impurities frequently complicates the attribution of CO species and leads to controversial mechanism interpretations in Au/TiO2 catalysis. The influence of Ni contamination on the CO adsorption on Au nanoparticles supported on TiO2 has been investigated by Fourier transform infrared spectroscopy. On the 2.8 nm Au nanoparticles, the impurity Ni(CO)4 in the CO atmosphere dissociates on the surface of Au particles and diffuses into the bulk of Au to form an alloy. Upon subsequent CO exposure, Ni segregates to the Au surface and bonds with CO. The apparent activation energy of ~37 kJ/mol for Ni segregation in the presence of CO was measured. The presence of Ni significantly decreases the adsorption enthalpy of CO on Au due to the electron transfer from Ni to Au. In contrast, on the 6.6 nm Au nanoparticles, the Ni contamination remains on the Au particle surface and no bulk phase penetration occurs. These findings highlight the critical yet often overlooked influence of trace Ni contamination when characterizing Au/TiO2 catalytic systems under CO atmospheres.