The Dynamic Structure of Gold Supported on Ceria in the Liquid Phase Hydrogenation of Nitrobenzene

Abstract

With regard to heterogeneous catalysis by gold and, in particular, hydrogenation reactions, there is no consensus on the oxidation state of the catalytically active species. By means of high‐resolution X‐ray absorption spectroscopy, we determined in situ the oxidation state of gold in the functioning catalyst Au/CeO2 in the slurry phase of the hydrogenation of nitrobenzene at high pressure. The conversion of nitrobenzene was monitored simultaneously by means of online attenuated total reflectance–Fourier transform infrared spectroscopy. We found that catalysts without measurable amounts of cationic gold were more active than catalysts with cationic gold. Any cationic gold that remained after pretreatment was reduced under reaction conditions, without any loss of activity. No evidence was found that the cationic gold contributed to the catalytic activity.

Reaction Monitoring in Multiphase Systems: Application of Coupled In Situ Spectroscopic Techniques in Organic Synthesis

“…[11] Oxidation of veratryl alcohol with Co(salen) and oxygen [12] ATR-FTIR/calorimetry Hydrogenation of 5-(2-methoxy-4-nitrophenyl) oxazole over a bimetallic Pt/V/C catalyst [13] ATR-FTIR/Raman Synthesis of tributyltin azide and hydrogenation of 1-chloro-2-nitrobenzene to 2-chloroaniline [14] ATR-FTIR/ATR-FTIR Hydrogenation of nitrobenzene over Au/ Pioneering work establishing the application of ATR-FTIR technique in catalysis research was done by the Baiker group [27][28][29]. Further interesting developments in terms of combining ATR-FTIR with other methods were published recently by the Hungerbühler group [15,19,26,[30][31][32] also in cooperation with the Baiker group. Selected studies are discussed in more detail later.…”

“…The coupling of spectroscopic methods, in particular, ATR-FTIR, with X-ray methods, is an important field to elucidate the mechanisms of heterogeneously and homogeneously catalyzed reactions in the liquid phase [19][20][21]. Reactant conversion is monitored by ATR-FTIR spectroscopy, while changes in the electronic and geometric structures of the catalyst during reaction are followed by XAS.…”

“…Reactant conversion is monitored by ATR-FTIR spectroscopy, while changes in the electronic and geometric structures of the catalyst during reaction are followed by XAS. Using this combination, the liquid-phase hydrogenation of NB on Au/CeO 2 was studied [19,32]. For this purpose, a special batch reactor cell was developed as described later.…”

Synthesis of mesoporous γ-Fe2O3 supported palladium nanoparticles and investigation of their roles as magnetically recyclable catalysts for nitrobenzene hydrogenation

“…When the catalyst was ready, nitrobenzene (2.5 mmol) was injected into the solution to start the reaction. During the reaction, the vessel was kept at 50 • C and 1 atm under reflux, very mild conditions as compared with those in the literature [3,18,[35][36][37]. Samples were taken every 20 min to analyze the conversion of nitrobenzene and concentration of reaction intermediates and products.…”

Scientific Opportunities for Heterogeneous Catalysis Research at the SuperXAS and SNBL Beam Lines

“…During the latter process only Au°was determined to be present and is thus considered the active phase. [36] Simultaneously to the registration of HERFD XANES at the Au L 3 edge the reactor allowed the conversion and selectivity to be monitored in situ using an integrated probe for attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy measurements. The final example illustrates the capabilities of SuperXAS for the studies of industrially relevant catalytic processes under extreme conditions.…”