On the reality of negatively charged supported gold nanoparticles

[Display omitted] •CO adsorption on Au/TiO2 was monitored in a system free of Ni-contamination.•IR bands around 2070 cm−1 were assigned to negatively charge Au following reduction.•Two positively charged Au species were identified in the presence of O2. The presence of negatively charged gold species on Au surfaces or supported Au nanoparticles has widely been reported based on the appearance of IR bands of adsorbed CO located below 2090 cm−1. However, others have proposed that these bands may be solely due to the presence of Ni-CO species contaminating the sample surfaces. CO adsorption was monitored here using a CO supply, DRIFTS reaction cell and lines in which contamination by nickel could be excluded. Our data show that a band at 2067 cm−1 appeared without the involvement of Ni carbonyls, the observed band being assigned to CO adsorbed on negatively charged Au.