A coordinatively unsaturated single iron site confined in a graphene matrix shows an ultrahigh activity for catalytic oxidation.

Copper−ceria as one of the very active catalysts for oxidation reactions has been widely investigated in heterogeneous catalysis. In this work, copper oxide (1 wt % Cu loading) deposited on both ceria nanospheres with a {111}/{100}-terminated surface (1CuCe-NS) and with nanorod exposed {110}/{100} faces (1CuCe-NR) have been prepared for the investigation of crystal plane effects on CO oxidation. Various structural characterizations, especially including aberration-corrected scanning transmission electron microscopy (Cs-STEM), X-ray absorption fine structure (XAFS) technique, and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), were used to precisely determine the structure and status of the catalysts. It is found that the copper oxides were formed as subnanometer clusters and were uniformly dispersed on the surface of the ceria support. The results from XAFS combined with the temperatureprogrammed reduction technique (H 2 -TPR) reveal that more reducible CuO x clusters with only Cu−O coordination structure exclusively dominated in the surface of 1CuCe-NS, while the Cu species in 1CuCe-NR existed in both CuO x clusters and strongly interacting Cu-[O x ]-Ce. In situ DRIFTS results demonstrate that the CeO 2 -{110} face induced a strongly bound Cu-[O x ]-Ce structure in 1CuCe-NR which was adverse to the formation of reduced Cu(I) active sites, resulting in low reactivity in CO oxidation (r CO = 1.8 × 10 −6 mol CO g cat −1 s −1 at 118 °C); in contrast, CuO x clusters on the CeO 2 -{111} face were easily reduced to Cu(I) species when they were subjected to interaction with CO, which greatly enhanced the catalytic reactivity (r CO = 5.7 × 10 −6 mol CO g cat −1 s −1 at 104 °C). Thus, for copper−ceria catalyst, in comparison with the well-known reactive {110} CeO2 plane, {111} CeO2 , the most inert plane, exhibits great superiority to induce more catalytically active sites of CuO x clusters. The difference in strength of the interaction between copper oxides and different exposed faces of ceria is intrinsically relevant to the different redox and catalytic properties.

Copper-ceria is one of the very active catalysts for the preferential oxidation of carbon monoxide (CO-PROX) reaction, which is also a typical system in which the complexity of copper chemistry is clearly exhibited. In the present manuscript, copper−ceria catalysts with different Cu contents up to 20 wt % supported on CeO 2 nanorods were synthesized by a deposition−precipitation (DP) method. The as-prepared samples were characterized by various structural and textural detections including X-ray diffraction (XRD), Vis-Raman, transmission electron microscopy (TEM), ex situ/in situ X-ray absorption fine structure (XAFS), and temperatureprogrammed reduction by hydrogen (H 2 -TPR). It has been confirmed that the highly dispersed copper oxide (CuO x ) clusters, as well as the strong interaction of Cu-[O x ]-Ce structure, were the main copper species deposited onto the ceria surface. No separated copper phase was detected for both preoxidized and prereduced samples with the Cu contents up to 10 wt %. The fresh copper−ceria catalysts were pretreated in either O 2 -or H 2 -atmosphere and then tested for the CO-PROX reaction at a space velocity (SV) of 60 000 mL. The prereduced 5 and 10 wt % Cu samples exhibited excellent catalytic performance with high CO conversions (>50%, up to 100%) and O 2 selectivities (>60%, up to 100%) within a wide temperature window of 80−140 °C. The in situ XAFS technique was carried out to monitor the structural evolution on the copper−ceria catalysts during the PROX experiments. The X-ray absorption near edge spectra (XANES) profiles, by the aid of linear combination analysis, identified the oxidized Cu(II) were the dominant copper species in both O 2 -and H 2 -pretreated samples after CO-PROX at 80 °C. Furthermore, the extended X-ray absorption fine structure (EXAFS) fitting results, together with the corresponding H 2 -TPR data distinctly determined that the highly dispersed CuO x (x = 0.2−0.5) cluster, other than the Cu−[O x ]−Ce (x = 0.7−3.2) structure, were the crucial active species for the studied CO-PROX reaction.

The design of catalysts that are both highly active and stable is always challenging. Herein, we report that the incorporation of single metal active sites attached to the nitrogen atoms in the basal plane of graphene leads to composite materials with superior activity and stability when used as counter electrodes in dye-sensitized solar cells (DSSCs). A series of composite materials based on different metals (Mn, Fe, Co, Ni, and Cu) were synthesized and characterized. Electrochemical measurements revealed that CoN4 /GN is a highly active and stable counter electrode for the interconversion of the redox couple I(-) /I3 (-) . DFT calculations revealed that the superior properties of CoN4 /GN are due to the appropriate adsorption energy of iodine on the confined Co sites, leading to a good balance between adsorption and desorption processes. Its superior electrochemical performance was further confirmed by fabricating DSSCs with CoN4  /GN electrodes, which displayed a better power conversion efficiency than the Pt counterpart.