Epoxidation of propene using Au/TiO₂: on the difference between H₂ and CO as a co-reactant

Abstract

The role of the reducing gas in the direct epoxidation of propene to propene oxide (PO) using O2 over a Au/TiO2 catalyst was studied through experiments and density functional theory calculations.

Adsorption, Dissociation, and Spillover of Hydrogen over Au/TiO2 Catalysts: The Effects of Cluster Size and Metal–Support Interaction from DFT

“…Au nanoparticles supported on oxides are catalytically active for many important reactions such as low-temperature CO oxidation, − water–gas shift (WGS) reaction, − direct propylene epoxidation − and some typical hydrogenation processes. − The catalytic activity of Au catalysts strongly depends on the size and structure of the Au particles supported on oxides. − The particular catalytic properties of Au catalysts are closely related to the electronic structures of the Au/oxide surfaces and the metal–support interactions have been unraveled to play an important role in affecting the catalytic properties of Au catalysts. − Experimental and theoretical studies have demonstrated that the catalytic activity of Au nanoparticles can be influenced by the presence of defects on the support, charge transfers from the support, doping, as well as the adsorbates on the surface such as H 2 O species or the metal cluster per se. − Therefore, the metal–support interaction is very important and sometimes becomes the decisive factor for the catalytic activity of gold.…”

“…Titanium dioxide (TiO 2 ) has been widely used in the field of environmental protection and energy conservation such as photocatalysis, , heterogeneous catalysis, ,, gas sensors, − and dye-sensitized solar cells − due to its excellent photoelectric properties, nontoxic nature, physical chemical stability, high catalytic activity, and low costs. Au nanoparticles supported on TiO 2 have been widely used in many important catalytic reactions. ,− The structures of Au nanoparticles on TiO 2 have been studied using high-resolution electron microscopy (HREM), and researchers found that the catalytic activity strongly depends on the size of Au particles as well as the crystalline structure of TiO 2 supports. , Density functional theory (DFT) calculations were employed to investigate the interactions between Au and TiO 2 support − as well as the reaction mechanisms for reactions catalyzed by Au/TiO 2 catalysts. ,− Catalytic hydrogenation is an important type of reaction in which Au nanoparticles supported on TiO 2 exhibit their particular catalytic capability such as in CO 2 reduction, ,,− the hydrogenation of unsaturated C–C bonds, ,, the selective hydrogenation of α,β-unsaturated carbonyl compounds such as aldehydes and ketones, ,,− and the hydrodeoxygenation of biomass-derived compounds. ,,, In these hydrogenation processes, the adsorption and dissociation of hydrogen on the supported metal particles are crucial steps and sometimes rate-limiting . Interactions between hydrogen molecule and Au atoms/small gold clusters have been theoretically studied − which show that the flexibility of the cluster structure and the size of Au cluster play important roles for H 2 adsorption and dissociation.…”

Theoretical Insights into Propene Epoxidation on Au7/Anatase TiO2–x(001) Catalysts: Effect of the Interface and Reaction Atmosphere

“…Most of the reported experimental results have indicated that the presence of H 2 in the reaction system can greatly increase the selectivity toward PO during the epoxidation of propene with O 2 . ,, When H 2 is present, O 2 can react with H 2 to produce an OOH intermediate in situ, which can also act as an oxidant to epoxidize propene. In this subsection, we describe a study of the formation of OOH.…”

Unravelling CO Activation on Flat and Stepped Co Surfaces: A Molecular Orbital Analysis

“…The supported nanoclusters and rods were created as follows. As supports for the nanoclusters and nanorods, we used γ-Al 2 O 3 (110) and rutile-TiO 2 (110) surfaces because these are reported to be thermodynamically the most stable. , Four layers of the support material were placed in a supercell; the bottom two layers were frozen. After adding the nanocluster or nanorod, we enlarged the vacuum space above the slab to accommodate adsorbates, leaving a distance of at least 12 Å between neighboring super cells.…”