Size‐Tunable Ni–Cu Core–Shell Nanoparticles—Structure, Composition, and Catalytic Activity for the Reverse Water–Gas Shift Reaction

Abstract

A facile and efficient methodology is described for the solvothermal synthesis of size‐tunable, stable, and uniform NiCu core–shell nanoparticles (NPs) for application in catalysis. The diameter of the NPs is tuned in a range from 6 nm to 30 nm and to adjust the Ni:Cu ratio from 30:1 to 1:1. Furthermore, the influence of different reaction parameters on the final NPs is studied. The NPs are structurally characterized by a method combination of transmission electron microscopy, anomalous small‐angle X‐ray scattering, X‐ray absorption fine structure, and X‐ray photoelectron spectroscopy. Using these analytical methods, it is possible to elucidate a core–shell–shell structure of all particles and their chemical composition. In all cases, a depletion from the core to the shell is observed, with the core consisting of NiCu alloy, surrounded by an inner Ni‐rich shell and an outer NiO shell. The SiO2‐supported NiCu core–shell NPs show pronounced selectivity of >99% for CO in the catalytic reduction of CO2 to CO using hydrogen as reactant (reverse water–gas shift reaction) independent of size and Ni:Cu ratio.

A 3D-printed CuNi alloy catalyst with a triply periodic minimal surface for the reverse water-gas shift reaction

“…Considering the RWGS reaction at 500 °C as an example, the CuNi/Al 2 O 3 catalyst yielded 79.7% selectivity for CO, similar to the previously reported CuNi catalysts. [39][40][41][42] Notably, with a similar CO 2 conversion, 93.5% selectivity for CO was obtained by DL2-RD20 at 500 °C. A more efficient mass transfer for the DL2-RD20 catalysts could promote the desorption of CO from the catalyst surface, improving CO selectivity.…”

Small Angle Scattering Techniques for the Study of Catalysts and Catalytic Processes

“…For example, Heilmann et al . described the synthesis NiCu core‐shell NPs (see Figure 6a) for the reverse water‐gas shift reaction [48] . From SAXS patterns analysis, shown in Figure 6b, they concluded that NPs diameter was 6.8 nm with a distribution of 14 % using a Weibull distribution.…”

“… (a) TEM images of spherical 16 nm diameter NiCu nanoparticles and (b) SAXS curve of the same particles (black circles) and the fitted curve using a core‐shell‐shell model (red line). Adapted, with permission, from reference [48] . (c) TEM image of hollow porous AuPt nanostructures (top), scanning TEM images and elemental mapping images of distribution of Pt (red) and Au (green) in those nanostructures (middle and bottom) and (d) SAXS curves of hollow Au nanoshells (red line), hollow porous AuPt nanoshells (black line) and Pt NPs (green line), respectively; and their respective SAXS patterns (insets from left to right).…”

“…[47] For example, Heilmann et al described the synthesis NiCu core-shell NPs (see Figure 6a) for the reverse water-gas shift reaction. [48] From SAXS patterns analysis, shown in Figure 6b, they concluded that NPs diameter was 6.8 nm with a distribution of 14 % using a Weibull distribution. While SAXS allowed the integral modelling of the core-shell structure, ASAXS enabled to perform element specific structural analysis.…”

“…Adapted, with permission, from reference. [48] (c) TEM image of hollow porous AuPt nanostructures (top), scanning TEM images and elemental mapping images of distribution of Pt (red) and Au (green) in those nanostructures (middle and bottom) and (d) SAXS curves of hollow Au nanoshells (red line), hollow porous AuPt nanoshells (black line) and Pt NPs (green line), respectively; and their respective SAXS patterns (insets from left to right). Adapted, with permission, from reference.…”