Crystal-Plane-Dependent Guaiacol Hydrodeoxygenation Performance of Au on Anatase TiO2

TiO2-supported catalysts have been widely used for a range of both liquid-phase and gas-phase hydrogenation reactions. However, little is known about the effect of their different crystalline surfaces on their activity during the hydrodeoxygenation process. In this work, Au supported on anatase TiO2, mainly exposing 101 or 001 facets, was investigated for the hydrodeoxygenation (HDO) of guaiacol. At 300 °C, the strong interaction between the Au and TiO2-101 surface resulted in the facile reduction of the TiO2-101 surface with concomitant formation of oxygen vacancies, as shown by the H2-TPR and H2-TPD profiles. Meanwhile, the formation of Auδ−, as determined by CO-DRIFT spectra and in situ XPS, was found to promote the demethylation of guaiacol producing methane. However, this strong interaction was absent on the Au/TiO2-001 catalyst since TiO2-001 was relatively difficult to be reduced compared with TiO2-101. The Au on TiO2-001 just served as the active site for the dissociation of hydrogen without the formation of Auδ−. The hydrogen atoms spilled over to the surface of TiO2-001 to form a small amount of oxygen vacancies, which resulted in lower activity than that over Au/TiO2-101. The catalytic activity of the Au/TiO2 catalyst for hydrodeoxygenation will be controlled by tuning the crystal plane of the TiO2 support.

Sinter-Resistant and Highly Active Sub-5 nm Bimetallic Au-Cu Nanoparticle Catalysts Encapsulated in Silica for High-Temperature Carbon Monoxide Oxidation

A novel gold-copper-based silica-encapsulated mixed metal oxide (MMO) core-shell catalyst-with sub-5 nm MMO particles-was successfully synthesized via a reverse micelle process. The SiO₂-encapsulated MMO catalyst was reduced under hydrogen flow to produce an Au-Cu@SiO₂ catalyst. X-ray diffraction and X-ray photoelectron spectroscopy characterization confirmed the presence of Au-Cu nanocomposites in the catalyst, while transmission electron microscopy characterization revealed the core-shell structure of the catalyst with the presence of sub-5 nm Au-Cu nanoparticle cores inside SiO₂ shells. Brunauer-Emmett-Teller surface characterization identified that the catalyst is porous and bimodal in nature. The effects of promoter metal ion, catalyst pretreatment (calcination), and the presence of CO₂ in the feed stream on carbon monoxide (CO) oxidation over the Au-Cu@SiO₂ catalyst were examined in the temperature range of 50-400 °C. A catalyst stability test was performed at 300 °C by conducting a CO oxidation reaction for 116 h on stream. The catalyst exhibited excellent efficacy for CO oxidation, with ∼100% conversion to CO₂ achieved at 400 °C. While the presence of Cu enhanced the CO conversion at low to intermediate temperatures (50-300 °C), silica encapsulation of the Au-Cu nanocomposites facilitated remarkable stability of the catalyst. The activity of the Au-Cu@SiO₂ catalyst is suitable for its application in automotive after-treatment devices, especially in low-temperature combustion engine exhausts.

Pt-Au/MOx-CeO₂ (M = Mn, Fe, Ti) Catalysts for the Co-Oxidation of CO and H₂ at Room Temperature

A series of nanostructured Pt-Au/MO_x-CeO₂ (M = Mn, Fe, Ti) catalysts were prepared and their catalytic performance for the co-oxidation of carbon monoxide (CO) and hydrogen (H₂) were evaluated at room temperature. The results showed that MO_x promoted the CO oxidation of Pt-Au/CeO₂, but only the TiO₂ could enhance co-oxidation of CO and H₂ over Pt-Au/CeO₂. Related characterizations were conducted to clarify the promoting effect of MO_x. Temperature-programmed reduction of hydrogen (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) results suggested that MO_x could improve the charge transfer from Au sites to CeO₂, resulting in a high concentration of Ce³⁺ and cationic Au species which benefits for the CO oxidation. In-situ diffuse reflectance infrared Fourier transform spectroscopy (In-situ DRIFTS) results indicated that TiO₂ could facilitate the oxidation of H₂ over the Pt-Au/TiO₂-CeO₂ catalyst.

Pt–Au/CeO2 catalysts for the simultaneous removal of carbon monoxide and formaldehyde

A series of Pt–Au/CeO₂ catalysts were prepared via the impregnation deposition–precipitation (IDP) and reduction–deposition precipitation (RDP) methods.

Investigation of oxygen vacancies on Pt- or Au-modified CeO2 materials for CO oxidation

Metal (Au or Pt)-modified CeO₂ materials with excellent redox ability for the oxidation of CO to CO₂ were prepared by a redox precipitation method and a certain amount (4.2%) of oxygen vacancies was necessary to improve the CO oxidation on Pt-CeO₂.

Promoting effects of lanthanum on the catalytic activity of Au/TiO2 nanotubes for CO oxidation

TEM image of Au/La₂O₃–TiO₂-NTs. Gold particles were distributed homogeneously on La modified TiO₂ NTs.

Synthesis of MCF-supported AuCo nanoparticle catalysts and the catalytic performance for the CO oxidation reaction

AuCo/MCF calcined at 500 °C for 1 h was found to produce the most active and stable catalyst for CO oxidation. In situ FTIR results of AuCo/MCF catalysts with different treatments.