Catalytically efficient Ni-NiOx-Y2O3 interface for medium temperature water-gas shift reaction

Abstract

The metal-support interfaces between metals and oxide supports have long been studied in catalytic applications, thanks to their significance in structural stability and efficient catalytic activity. The metal-rare earth oxide interface is particularly interesting because these early transition cations have high electrophilicity, and therefore good binding strength with Lewis basic molecules, such as H₂O. Based on this feature, here we design a highly efficient composite Ni-Y₂O₃ catalyst, which forms abundant active Ni-NiO_x-Y₂O₃ interfaces under the water-gas shift (WGS) reaction condition, achieving 140.6 μmol_CO g_cat^-1 s^-1 rate at 300 °C, which is the highest activity for Ni-based catalysts. A combination of theory and ex/in situ experimental study suggests that Y₂O₃ helps H₂O dissociation at the Ni-NiO_x-Y₂O₃ interfaces, promoting this rate limiting step in the WGS reaction. Construction of such new interfacial structure for molecules activation holds great promise in many catalytic systems.

Fig. 1. Catalytic performance test of the Ni_aY_bO_x catalysts.

a Temperature-dependent activities of the catalysts (Ni₁Y₉O_x, Ni₉Y₁O_x, pure Ni catalyst, the reaction gas content was 2%CO, 10%H₂O, and the rest was N₂); b temperature-dependent activity and selectivity of Ni₉Y₁O_x under different pretreatment conditions; c comparison of reaction rates with other Ni-based catalysts; d the long-term stability at a high GHSV (Ni₉Y₁O_x: 300 °C, GHSV = 420,000 cm³ g_cat⁻¹ h⁻¹; pure Ni catalyst: 280 °C, GHSV = 168,000 cm³ g_cat⁻¹ h⁻¹).

Fig. 2. The aberration-corrected HAADF-STEM images and elemental mappings.

a−d Ni₉Y₁O_x-fresh; f−i Ni₉Y₁O_x-used; electron energy-loss spectroscopy (EELS) elemental mapping results of (e) Ni₉Y₁O_x-fresh or (j) Ni₉Y₁O_x-used.

Fig. 3. Phase change and surface electronic structure.

a XRD patterns of the fresh and used Ni₉Y₁O_x catalysts; b, c XPS results of the fresh and used Ni₉Y₁O_x catalysts; d, e quasi in situ XPS results of Ni₉Y₁O_x-used; f Y K edge X-ray absorption near edge spectra profiles and g Y K edge EXAFS of the fresh and used Ni₉Y₁O_x catalysts for experiment data (solid) and fitted lines (dotted).

Fig. 4. In situ characterizations to monitor the interfacial structure changing.

a In situ XRD patterns in 5% H₂/Ar for the Ni₉Y₁O_x catalyst; in situ Raman spectra under the WGS reaction conditions for (b, c) Ni₉Y₁O_x catalyst and (d) pure Ni sample.

Fig. 5. The WGS mechanism study and DFT calculation of the Ni₉Y₁O_x catalyst.

a Surface reaction on the Ni₉Y₁O_x catalyst at 250 °C under 2%CO/Ar atmosphere; b cyclic CO-TPR experiments for CO consumed and CO₂ evolved against temperature for the Ni₉Y₁O_x catalyst (Between CO-TPR-1 and CO-TPR-2, the catalyst was treated in the WGS atmosphere at room temperature); c the ∆G of H₂O adsorption and dissociation process at three Y atom sites in the Y₃O₄/NiO_x/Ni{111} model, the reaction temperature was set to 300 °C and the partial pressure of water vapor was set to 10 kPa, i.e., the inlet pressure; d the simulated WGS reaction pathways (the reaction temperature: 300 °C, the partial pressure of CO, H₂O, CO₂ and H₂: 1, 8000, 2000 and 2000 Pa, i.e., the outlet pressure of the reactor).