Correlations between the catalyst properties and catalytic activity of Au on ZrO₂-CeO₂ in the hydrogenation of CO₂

Highlights

• Cost-effective synthesis procedure of Au on amorphous ZrO₂ modified with Ce.

• Tunable acidic/basic properties of Au/ZrO₂-CeO₂ via Ce content.

• Close correlation of acidic/basic properties and methanol selectivity.

• Enhanced reducibility of Au/ZrO₂-CeO₂ is not beneficial for CO₂ hydrogenation.

• Excellent stability as ${\mathit{r}}_{{\mathit{C}\mathit{H}}_3\mathit{O}\mathit{H}}$ = 3.32 g⋅(g_Au⋅h)^-1 remained for 93 h time on stream.

Abstract

To exploit the potential of both ZrO₂ and CeO₂, the mixed oxides with Ce content up to 5 wt.% were prepared via the simple coprecipitation method, subsequently loaded with Au catalysts, and investigated in the hydrogenation of CO₂. The obtained catalysts, namely Au/ZrCex (x = n_Ce/n_Zr = 0.0–0.1), exhibit similar Au content (0.7 wt.%), structural and textural properties, however, considerably different acidic/basic properties and great surface oxygen vacancy. The introduction of Ce leads to slightly decreased CO₂ conversion, which was found proportional to the Ce content. Interestingly, it is evidenced that the methanol selectivity is closely related to the acidic/basic properties of the catalysts employed. Over the broad range of acid site density (ASD) ranging from 400 to 700 μmol g⁻¹, the highest methanol selectivity of 27 % was recorded at 250 °C and 40 bar over the catalyst exhibiting an ASD of 600 μmol g⁻¹, which decreased with further increasing ASD. The volcano-shape trend was also discovered for the base site density showing the critical point at 120 μmol g⁻¹ over the range from 90 to 210 μmol g⁻¹. These findings suggest that the acidic/basic properties can be tuned, e.g., via thermal treatment, to tailor the product distribution of the CO₂ hydrogenation. Above all, the Au catalysts supported on ZrO₂–CeO₂ mixed oxides exhibit excellent catalytic stability, e.g., a methanol formation rate of 3.32 $g_{{\mathrm{C}\mathrm{H}}_3\mathrm{O}\mathrm{H}}\bullet {\left(g_{\mathrm{A}\mathrm{u}}\bullet h\right)}^{-1}$ is remained over the reaction course of 93 h at 250 °C and 40 bar for Au/ZrCe0.025 sample.