24.02.2013 Views

Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

Chapter 3<br />

Selective Liquid-Phase <strong>Oxidation</strong> of Alcohols<br />

<strong>Catalyzed</strong> by a Silver-Based Catalyst Promoted by<br />

the Presence of Ceria<br />

Abstract<br />

A number of impregnated silver catalysts supported on SiO2,<br />

Al2O3, celite, CeO2, kaolin, MgO and activated carbon were<br />

screened for their catalytic activity in the selective liquid<br />

phase oxidation of benzyl alcohol using a special screening<br />

approach. For this purpose 5‐6 catalyst samples were mixed<br />

and tested simultaneously. When a high catalytic conversion<br />

(> 30 % over 2 h) was found the number of catalyst<br />

1Alcohol oxidation by components was reduced in the following tests. Thereby, a<br />

Ag/SiO2 – CeO2.<br />

collaborative effect between a physical mixture of ceria nanoparticles and silver‐impregnated silica<br />

(10 wt.‐% Ag/SiO2) was found. The catalytic activity was highly dependent on the silver loading, the<br />

amount of ceria and especially the calcination procedure. Transmission electron microscopy (TEM),<br />

X‐ray diffraction (XRD) and X‐ray absorption spectroscopy (XANES, EXAFS) demonstrate that silver is<br />

mainly present as metallic particles. This is also supported by in situ XAS experiments. Silver‐oxygen<br />

species appear to be important for the catalytic oxidation of the alcohol for which a preliminary<br />

mechanism is presented. The application of the catalyst was extended to the oxidation of a wide<br />

range of primary and secondary alcohols. Compared to Pd and Au catalysts, the new Ag catalyst<br />

performed similarly or even superior if CeO2 was present. In addition, the presence of ceria increased<br />

the catalytic activity of all investigated catalysts.<br />

77

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!