Vapor-Phase Propylene Epoxidation with H₂/O₂ over Bioreduction Au/TS-1 Catalysts: Synthesis, Characterization, and Optimization

Abstract

Au/TS-1 catalysts could be prepared by immobilizing the biosynthesized Au sol on TS-1 supports. A variety of techniques, such as N 2 physisorption, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectorscopy, UVÀvisible diffuse reflectance, and thermogravimetric analysis, were employed to characterize both the supports and the bioreduction catalysts. The influence of various parameters (Si/Ti molar ratio, Au loading, immobilization pH, reaction temperature, and space velocity) on the catalytic performance in vapor phase propylene epoxidation with H 2 /O 2 was systematically analyzed. Parameter optimization results manifested that the optimum catalytic activity and stability of bioreduction Au/TS-1 catalysts were obtained under optimum operation conditions of Si/Ti molar ratio of 35, Au loading of 1 wt %, immobilization pH of 2, reaction temperature of 573 K, and space velocity of 4000À8000 mL g cat À1 h À1 . Furthermore, efforts were also made to clarify the plausible reaction routes over the bioreduction catalysts.

Kinetics of liquid phase oxidation of benzyl alcohol with hydrogen peroxide over bio-reduced Au/TS-1 catalysts

“…The titanium silicate-1 (TS-1) supports with a Si/Ti molar ratio of 35 were prepared according to the established procedure reported in the literature [19]. The resulting material has a specific surface area of 388 m 2 g −1 , a pore volume of 0.31 cm 3 g −1 and a pore diameter of 4.5 nm.…”

“…The mean diameter of the catalyst is very small (∼162 nm) as such it is difficult to investigate the effect of the size of catalyst particles on the rate of reaction [19,22]. Therefore, we adopt the Mears criterion [28] (Eq.…”

“…On the other hand, different preparation procedures result in variations in the particle sizes of Au nanoparticle catalysts and the reduction method is a more advantageous way to prepare Au particles with narrow size distributions and desired diameters [18]. Our group has paid continuing effort to exploit the plant extract as bio-reducing agents for preparation of Au catalysts [19][20][21], and we recently reported the first example of Au/TS-1 catalysts designed via bioreduction method, which shown excellent performance for the selective oxidation of BzOH to BzH with aqueous H 2 O 2 achieving simultaneous high activity, high recyclability and remarkable stability [22].…”

The effects of impregnation of precious metals on the catalytic activity of titanium silicate (TS-1) in epoxidation of propene using hydrogen peroxide

“…Recently, plenty of attention has been paid to the characteristics of Au and bimetallic Au-Pd, which have been known to be highly active for the direct synthesis of hydrogen peroxide from H 2 and O 2 [37][38][39][40][41][42][43][44][45][46][47] when supported on TS-1 for the liquid-or gas-phase epoxidation, and the improvement of precious metals distribution on the surface of TS-1. The homogeneous distribution of Au is an important factor for epoxidation activity of Au/TS-1 catalyst: Delgass and colleagues studied the optimum conditions of deposition-precipitation (DP) to prepare Au/TS-1 catalyst on which Au is uniformly dispersed in nanoscale [42,43].…”

“…Mennemann and Claus claimed that the uptake and distribution of Au could be enhanced by adding 0.2 -0.5 wt% of Co when the catalyst was prepared via DP method [44]. Zahn et al published a few papers about a new preparation route for Au/TS-1 catalyst based on biomass-reduction, in which an important issue was also the distribution and stabilization of Au nanoparticles [45,46].…”