Role of ZnO and CeO_x in Cu-Based Model Catalysts in Activation of H₂O and CO₂ Dynamics Studied by in Situ Ultraviolet–Visible and X-ray Photoelectron Spectroscopy

Abstract

Flat model and powder Cu, ZnO/Cu, and CeO x /Cu catalysts were studied by focusing on the role of the oxide phase as a promoter in the water gas shift (WGS) and its reverse reaction (RWGS). Activity measurements of the powder catalysts showed that both oxides enhance Cu reactivity, with CeO x /Cu being more active than ZnO/Cu in the WGS reaction. In situ ultraviolet–visible spectroscopy, exploiting the localized surface plasmon resonances of metallic Cu nanoparticles, together with X-ray photoelectron spectroscopy was then used to elucidate the origin of the enhanced reactivity on flat model catalysts. These experiments showed that ZnO and CeO x promote H2O and CO2 dissociation, leading to oxidation of the Cu nanoparticles. CeO x performs better in this respect than ZnO. This is important because the reactivity in the WGS and RWGS reactions is related to the ability to activate H2O and CO2. The Ce3+ ions are identified as the most efficient sites for H2O and CO2 dissociation, while Cu0 keeps Ce3+ stable by promoting reduction of Ce4+ during the dissociation process. In this sense, the CeO x /Cu catalyst forms a bifunctional catalyst, which is more active in the (R)­WGS than CeO x and Cu catalysts separately.

The most active Cu facet for low-temperature water gas shift reaction

“…The apparent activation energy of ZnO/c-Cu catalyst is smaller than those of commercial Cu/ZnO/Al 2 O 3 catalyst, Cu/ZnO(0001) (52 kJ mol −1 ) 11 , and ZnO/Cu (46 kJ mol −1 ) 36 model catalysts, and is similar to those acquired on CeO x /Cu(111) (30 kJ mol −1 ) 37 and Cu/CeO 2 (111) (37 kJ mol −1 ) 11 model catalysts. It is noteworthy that the activity of CeO x /Cu(111) model catalyst was evaluated between 573 and 673 K 37 under which the Cu(111) surface might restructure.…”

Metal/semiconductor interfaces in nanoscale objects: synthesis, emerging properties and applications of hybrid nanostructures

“…3D tomography would allow answering intriguing questions regarding surface structure, as pointed out in a review by Miao and co-workers. 428 Since intermediate characterization is vital in mechanistic studies, it will not be limited to electron microscopy, and we expect other in situ techniques (e.g., X-ray, 429,430 optical spectroscopy [431][432][433][434] ) to gain traction alongside the growing use of multimodal imaging. 435 The integration of hybrid nanostructures in various devices and applications depends tremendously on the progress that is achieved in two directions: simplifying and reducing the synthesis costs and also developing heavy metal-free (abundant and nontoxic elements) and stable hybrid nanostructures; these are yet to emerge.…”

Artificial Photosynthesis of Alcohols by Multi‐Functionalized Semiconductor Photocathodes

“…[6,7] On the other hand, photocatalytic and electrocatalytic CO 2 reduction have turned into promising strategies to store energy in chemical bonds of carbon-based fuels as they are environmentally benign processesr esulting in sustainable energy. [15][16][17][18][19][20][21][22][23] However, their large band gap of 3.2 eV confines the absorption in visible light and the catalytic performance for CO 2 reduction within al arge number of recombination of photoinduced electron-hole pairs. [15][16][17][18][19][20][21][22][23] However, their large band gap of 3.2 eV confines the absorption in visible light and the catalytic performance for CO 2 reduction within al arge number of recombination of photoinduced electron-hole pairs.…”

“…[8][9][10][11][12][13][14] As the most frequently studied photocatalysts, titaniumd ioxide (TiO 2 )a nd zinc oxide (ZnO) have many advantages such as abundance, low-cost,l ow-toxicity,a nd chemical stability. [15][16][17][18][19][20][21][22][23] However, their large band gap of 3.2 eV confines the absorption in visible light and the catalytic performance for CO 2 reduction within al arge number of recombination of photoinduced electron-hole pairs. There have been many studies on looking for suitable metal co-catalysts,s uch as Pt, Rh, Au, Ag, Cu, and Pd coatedo nT iO 2 ,t oi mprovet he catalytic properties of TiO 2 for CO 2 reduction, nonetheless, these reported strategies are very restricted to enhance the catalytic abilities of semiconductors.…”