Fig. 2: Structure and quantification of atomic Cu(II) site.
From: Adsorption and activation of molecular oxygen over atomic copper(I/II) site on ceria
a HAADF-STEM images of CuO–CeO2 at 1 wt% CuO loading. b EDS mapping of the CuO-CeO2 at 1 wt% CuO loading with red for Ce and green for Cu. c, d The coordination numbers (C.N.) of Cu–O, Cu–Ce(1), Cu–Ce(2), Cu–Cu(1) and Cu–Cu(2) scattering as a function of Cu loading, derived from the EXAFS spectra. Purple line: The Cu–O coordination number is 4 in the CuO standard. The standard error of the mean (s.e.m.) is labelled according to the EXAFS fitting results listed in Supplementary Table 1. e The peak position of 1s → 3d and 1s → 4p electron transitions in the first derivative of Cu K-edge XANES, showing changes of absorption energy as a function of Cu loading compared to metallic Cu (purple line), Cu2O (pink line) and CuO (black, orange and blue lines) as standard materials. f X-band cw EPR spectra for CuO–CeO2 with CuO loading from 0 to 1 wt%. g EPR spectra for CuO–CeO2 with CuO loading from 1 to 20 wt%. h Quantification of atomic Cu(II) site. Black: molar proportion of atomic Cu(II) site within all Cu species in CuO–CeO2. Red: absolute loading of atomic Cu(II) site showing the optimal content at 1 wt%. Scale bars: 2 nm in (a) and 10 nm in (b).
