Application of Au/TiO2 catalysts in the low-temperature water–gas shift reaction

• Three different synthesis methods of nanosized Au-based catalysts are reported.
• Activity in water–gas shift reaction strongly depends on both Au loading and dispersion.
• Au/TiO2-DP-3 and Au/TiO2-LPRD-3 catalysts showed higher conversions/TOF values.
• Au/TiO2-WGC (from World Gold Council) was more stable.

Au/TiO2 catalysts were synthesized by three different methods, with different gold loadings, and tested for the low temperature water–gas shift (WGS) reaction. Gold was loaded by a Double Impregnation Method (DIM), Deposition–Precipitation (DP) and Liquid Phase Reductive Deposition (LPRD). For each procedure, catalysts were synthesized with three different loadings of gold, up to ca. 2.5 wt.%, identified as 1, 2 or 3 for low, intermediate or high amounts of nanosized gold, respectively. The prepared materials were characterized by High-Resolution Transmission Electron Microscopy (HR-TEM), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Temperature Programmed Reduction (TPR) and Absorption Atomic Spectroscopy (AAS).The performance of the catalysts was compared based on the CO conversions (XCO) and turnover frequencies (TOFs) obtained in the WGS reaction. The two best catalysts obtained were Au/TiO2-DP-3 and Au/TiO2-LPRD-3. Both showed XCO and TOF values higher than that of the commercial Au/TiO2-WGC (supplied by the World Gold Council). Although TOF was higher for Au/TiO2-LPRD-3 (at 250–300 °C), this sample suffers deactivation. The Au/TiO2 DP-3 material was thus selected as the best synthesized catalyst, with a XCO ≈ 85% at 300 °C (XCO of the WGC sample was ≈52% at 300 °C). The Au/TiO2 DP-3 material has small gold nanoparticles before and after use, which can account for the improved catalytic activity, well known to be related with gold nanoparticle size. However, stability was found to be better for the WGC sample.

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