Uncalcined TS‐2 immobilized Au nanoparticles as a bifunctional catalyst to boost direct propylene epoxidation with H₂ and O₂

Abstract

Developing stable yet efficient Au-Ti bifunctional catalysts is important but challenging for direct propylene epoxidation with H 2 and O 2. This work describes a novel strategy of employing uncalcined titanium silicalite-2 (TS-2-B) to immobilize Au nanoparticles as a bifunctional catalyst for the reaction. Under no promoter effects, the Au/TS-2-B catalyst compared to the referenced Au/TS-1-B catalyst delivers outstanding catalytic performance, that is, exceptionally high stability over 100 hr, propylene oxide (PO) formation rate of 118 g PO Áhr −1 Ákg cat −1 , PO selectivity of 90% and hydrogen efficiency of 35%. The plausible relationship of catalyst structure and performance is established by using multiple techniques, such as UV-vis, high-angle annular dark-field scanning transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. A unique synergy of Au-Ti 4+-Ti 3+ triple sites is proposed for our developed Au/TS-2-B catalyst with the higher stable PO formation rate and hydrogen efficiency. The insights reported here could shed new light on the rational design of highly stable and efficient Au-Ti bifunctional catalysts for the reaction.

Combining trace Pt with surface silylation to boost Au/uncalcined TS‐1 catalyzed propylene epoxidation with H2 and O2

“…The two peaks in Au 4f spectrum shown in Figure 4A were observed for all samples, which can be ascribed to the metallic Au 4f 5/2 and 4f 7/2 , respectively 7 . The Ti 2p spectra in Figure 4B were deconvoluted with Ti 4+ and Ti 3+ peaks according to the previous studies 21,30 . It can be seen that both the binding energies of Au 4f 7/2 and Ti 2p 3/2 shift to the lower energy regions, and the deconvoluted peak areas ratio of Ti 3+ /Ti 4+ slightly increases when the Pt was introduced into the Au/TS‐1‐B catalyst.…”

“…Au, Pt, and bimetallic Au‐Pt catalysts were prepared with deposition‐precipitation‐urea (DPU) method, which could give high capture efficiencies of Au and Pt species because of the increased isoelectric point with 7.1 5,20 . This method has been widely employed in the preparation of uncalcined TS‐1 and TS‐2 supported Au catalysts to better control the Au loading in the previous studies 7,21,22 . Specifically, a gram of TS‐1‐B was suspended in 40 mL ultrapure water under stirring followed by the addition of HAuCl 4 and/or H 2 PtCl 6 solution and urea.…”

Size-Dependent Structures and Catalytic Performances of Au/TiO2-{001} Catalysts for Propene Epoxidation

“…The electronic states of the Au NPs in the Au/TiO 2 -{001} catalysts were characterized by XPS (Figure B). On the basis of the deconvolution of Au 4f spectra, all Au/TiO 2 -{001} catalysts show only one component, with the Au 4f 7/2 binding energy at 83.2 eV, assigned to the metallic Au supported on Ti-based supports during propene epoxidation with H 2 and O 2 . − …”

Advances in Designing Au Nanoparticles for Catalytic Epoxidation of Propylene with H2 and O2

“…Some studies focused on designing isolated and highly dispersed tetrahedral-coordinated Ti-oxide centers in the ligand-to-metal charge-transferred state ((Ti 4+ −O 2− )*), which is associated with the adsorption of propylene [5,48] and the nucleation sites for Au nanoparticles [49]. In previous studies, Au nanoparticles were deposited on Ti-modified mesoporous silica supports, such as SiO 2 [27,28], TUD [29], SBA-15 [30,31], MCM-41 [19,32,33], MCM-48 [15], MCM-36 [34], YNU-1 [34], MWW [34,35], TS-1 [20][21][22][23][37][38][39][40][41][42][43][44][45][46]50], and TS-2 [47], to enhance the epoxidation of propylene. In the last, support materials play a key role in slowing the deactivation.…”