Surface Engineering and Kinetics Behaviors of Au/Uncalcined TS-1 Catalysts for Propylene Epoxidation with H₂ and O₂

Abstract

Uncalcined TS-1-immobilized Au bifunctional catalysts have been demonstrated to be highly active yet stable for the propylene epoxidation with H2 and O2. The objective of this study is to further engineer the surface properties of uncalcined TS-1 toward enhanced bifunctional catalysis. A strategy by increasing the reduction temperature is proposed to remove the residual TPA+ template on the external surfaces, and the resultant Au/TS-1-B-300 catalyst gives rise to simultaneously enhanced activity, propylene oxide (PO) selectivity, and H2 efficiency. These phenomena are explained by more exposed Ti-active sites and targeted catalysts’ electronic properties based on high-angle annular dark-field scanning transmission electron microscopy, thermal gravimetric analysis, UV–vis, Fourier transform infrared spectra, and X-ray photoelectron spectroscopy measurements. Furthermore, kinetics analysis demonstrates a much lower activation energy for the main reaction to form PO, suggesting the existence of an appropriate reaction temperature for the PO yield. The obtained insights could shed new light on rationally designing and optimizing the catalysts by engineering the surface properties.

Synthesis of titanium silicalite‐1 with high titanium content and its catalytic performance of propylene epoxidation

“…PTS-1 has smaller particle size, higher Ti content, and thus better catalytic performance for gas phase propylene epoxidation. Hong et al [31] Au/TS-1-B(40) a 83 158 473 Feng et al [28] Au/TS-1 6.7 78.1 95 443 Lu et al [21] Au/TS-1 10 84 320 437 Li et al [32] Au/TS-1-B-300 a 95 150 473 Wang et al [33] Au/TS-1-Na 8.3 84 127 473 Huang et al [34] Au/TS-1-Na 7.4 85 119 473 Huang et al [35] Au/TS-1-Cs 9.9 85 285 473 Lee et al [36] a…”

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

“…Uncalcined TS‐1 zeolite with blocked micropores by tetrapropylammonium hydroxide (TPAOH) template, denoted as TS‐1‐B, was synthesized with hydrothermal method according to the reported procedures 5,7 . 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 .…”

“…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.…”

“…Direct gas‐phase epoxidation of propylene with H 2 and O 2 over Au‐Ti catalysts has attracted considerable interests for clean and economical production of propylene oxide (PO) compared to the traditionally industrial processes 1–4 . Among the tested catalysts, the Au nanoparticles immobilized on uncalcined TS‐1 have exhibited state‐of‐the‐art PO formation rate and stability by avoiding the deactivation caused by micropore blocking 5–7 . The collaboration between the formation of hydroperoxide species over the Au sites and the desorption of PO from the TS‐1 surfaces has been revealed to be the key to gaining the high PO activity, selectivity, and H 2 efficiency 8–11 .…”

“…The objective of this study is to develop highly efficient catalysts for PO production from propylene epoxidation with H 2 and O 2 by combining the addition of Pt into Au particles to enhance hydroperoxide species formation with the surface silylation to promote PO desorption. Uncalcined TS‐1 with blocked micropores (TS‐1‐B) was employed to immobilize Au nanoparticles because of its excellent stability 5–7 . The catalyst structure–performance relationship was established by using theoretical calculations and multiple characterization techniques, including high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM), X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FT‐IR), and inductively coupled plasma (ICP) analysis.…”