Crystal Plane Effect of Ceria on Supported Copper Oxide Cluster Catalyst for CO Oxidation: Importance of Metal–Support Interaction

Abstract

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.

Effective Strain Engineering of IrO2 Toward Improved Oxygen Evolution Catalysis through a Catalyst‐Support System

“…Between the primary and secondary IrÀ O shells, the IrÀ M (M = metal, refers to Ir and Mn here) contribution at a distance of 2.7-3.2 Å (Figure 6d and S17, uncompensated). The IrÀ M bond distance of IrO 2 /MnÀ Co(2 : 1)-Bir is 3.113 Å (shorter than 3.146 Å of IrO 2 ), corresponding to the creation of a IrÀ OÀ Mn interaction, which is similar to the previous reports on AuÀ OÀ Ce [34] , FeÀ OÀ Ce [35] , CeÀ OÀ Cu [36] systems. The shorten IrÀ M distance agrees well the TEM results displaying the catalyst-support interface, and further confirms a distorted octahedron geometry.…”

Influence of the Hydrothermal Parameters on the Physicochemical Characteristics of Cu−Ce Oxide Nanostructures

“…[53,66,70] As it can be seen from Table 2, the effect of hydrothermal parameter is obvious in this case, too. 464, 600 and 1174 cm À 1 (I (600 + 1174) /I 464 ) can roughly reflect the amount of lattice defects (oxygen vacancies) in the obtained materials.…”

“…The diffraction peaks are well-defined and correspond to the cubic fluorite phase of CeO 2 (space group: Fm-3 m, JCPDS: 00-043-1002, α = 0.54113 nm). [6,[52][53][54] Moreover, no significant shift of the main peak of CeO 2 is indicated. The presence of highly dispersed copper species over ceria, the formation of CuÀ OÀ Ce solid solutions, the detection limitations of XRD technique, the poor crystallization and/or a combination of these, could be the possible reasons for the absence of CuO phase.…”

“…The strong band at ca. [37,53,55,68,69] Interestingly, the absence of Raman peaks (at ca. [59][60][61] According to several studies, this band appears at ca.…”

Pretreatment Effect on Ceria‐Supported Gold Nanocatalysts for CO Oxidation: Importance of the Gold–Ceria Interaction

“…Theb andsc entered at 2360 and2 340 cm À1 attributed to gaseousC O 2 and the band at circa 2173 cm À1 to gaseous CO were detected at the indicated temperature. [2,54] Beyond that, the bands at circa 2125 and 2118 cm À1 for Au d + ÀCO andA u 0 ÀCO can be observed in the spectrao fO 3a nd C3. [7,17,55] Theb and assigned to Au d + ÀCO decreased in concentration with the increase of the temperature up to 80 8Ca nd practically disappeareda bove 60 8C ( Figure 10 a, c, e, g), most likely because of the productiono fC O 2 and thermal stability effects.…”