Surface Segregation in CuNi Nanoparticle Catalysts During CO₂ Hydrogenation: The Role of CO in the Reactant Mixture

Abstract

Surface segregation and restructuring in size-selected CuNi nanoparticles were investigated via near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at various temperatures in different gas environments. Particularly in focus were structural and morphological changes occurring under CO 2 hydrogenation conditions in the presence of carbon monoxide (CO) in the reactant gas mixture. Nickel surface segregation was observed when only CO was present as adsorbate. The segregation trend is inverted in a reaction gas mixture consisting of CO 2 , H 2 , and CO, resulting in an increase of copper concentration on the surface. Density functional theory calculations attributed the inversion of the segregation trend to the formation of a stable intermediate on the nanocatalyst surface (CH 3 O) in the CO-containing reactant mixture, which modifies the nickel segregation energy, thus driving copper to the surface. The promoting role of CO for the synthesis of methanol was demonstrated by catalytic characterization measurements of silica-supported CuNi NPs in a fixed-bed reactor, revealing high methanol selectivity (over 85%) at moderate pressures (20 bar). The results underline the important role of intermediate reaction species in determining the surface composition of bimetallic nanocatalysts and help understand the effect of CO cofeed on the properties of CO 2 hydrogenation catalysts.

Electrocatalytic CO2 Reduction to Fuels: Progress and Opportunities

“…This has been observed for alloys of Cu under CO 2 hydrogenation conditions. [51,52] Consistent with this proposition, most alloys of Cu with reactive metals have yielded product distributions much more representative of the reactive metal (i.e., high selectivity to HER) than the product distribution associated with Cu. [53] For Cu mixed with oxophilic metals (such as Zn, Sn, In) the enthalpy of formation of a monometallic oxide of the oxophilic metal is much larger than the alloy formation energy of the metals.…”

Chemical Batteries with CO2

“…It has been shown [88a, 106a] that the interaction energy between Cu and ZnO differs depending on the degree of reduction of the ZnO.This interaction can modify the morphology of ap ure copper cluster.Defective ZnO 1Àx can "creep" onto and around aCu cluster that has been, for example,c ontaminated with and roughened by dissolved oxygen. [61] It is questionable whether the functionality of copper in the electroreduction of CO 2 can be further clarified if another element, [111] such as Co [66b,c,e] or Ni, is added to the copperbased catalyst because they change the reactivity in acomplex way.T he chemistry of the support is likewise critical. Avery different reactivity of copper was demonstrated with respect to hydrogen depending on whether diamond or oxygencontaining sp 2 -hybridized carbon was used.…”

Efficient non-noble Ni–Cu based catalysts for the valorization of palmitic acid through a decarboxylation reaction

“…Figure 3a For the bimetallic catalysts after activation under hydrogen, a shoulder at higher angle was observed in all cases, indicating a second peak. This might be related to the segregation of Ni in the Ni-Cu alloy, which, according to literature, is promoted upon annealing in H2 [58]. By 3.…”