Nanodisperse gold catalysts in oxidation of benzyl alcohol: comparison of various supports under different conditions

Gergely Nagy, A. Beck, G. Sáfrán, Z. Schay, Shaofeng Liu, Tianbo Li, Botao Qiao, Junhu Wang, K. Lázár

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Abstract

Monodisperse gold particles (ca. 2 nm) were prepared and deposited on various supports (SiO2, Al2O3, HAP, MgAl2O4 and MgO). The acid/base properties of supports were characterized by NH3 and CO2 sorption. The size of the gold nanoparticles spans in the 1.7–6.5 nm mean diameter range after calcination as determined from TEM measurements. The amounts of accessible surface sites were estimated by binary concentration pulse chromatography of CO with Kr adsorption. The data are in agreement with the results of CO adsorption obtained by DRIFT spectroscopy. The activities of the catalysts were compared in the oxidation of benzyl alcohol in stirred batch reactors under two different conditions: in xylene solvent with atmospheric oxygen at 60 °C (in presence and in absence of K2CO3), and in a solvent-free mixture at elevated pressure and temperature (5 bar O2, 150 °C, 5 h). The activities of catalysts in benzyl alcohol conversion are described in two variants, namely related to (i) active catalytic sites (ASNA), and (ii) number of Au atoms on the geometric surface of particles (GSNA). The activities of catalysts in xylene solvent at 60 °C were excellent, with 0.28–1.11 s−1 characteristic GSNAini values (initial reaction rates related to surface Au atoms, Ausurf) in presence of K2CO3. The observed order of activities under these conditions is Au/SiO2 < Au/Al2O3 < Au/HAP < Au/MgAl2O4 < Au/MgO. In the experiments performed at 150 °C under solvent-free conditions, the reaction partners are depleted in greater extents (with the exception of Au/Al2O3), thus the obtained average GSNAave (average reaction rate during 5 h reaction related to Ausurf) values are less reliable, however selectivity data provide useful information as well. These estimated average GSNAave values (0.14–0.83 s−1) attest still good activities. For the interpretation of the obtained data, the roles of active sites on gold nanoparticles of various dispersion and the accessibility of their surfaces as well as the acid–base properties and surface hydroxyl concentration of supports, water ad- and desorption phenomena are considered simultaneously.

Original languageEnglish
JournalReaction Kinetics, Mechanisms and Catalysis
DOIs
Publication statusPublished - Jan 1 2019

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Keywords

  • Acid/base support effects
  • Benzyl alcohol oxidation
  • Binary concentration pulse chromatograohy
  • Distinction of active sites
  • Supported gold catalysts

ASJC Scopus subject areas

  • Catalysis
  • Physical and Theoretical Chemistry

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