In situ infrared monitoring of the solid/liquid catalyst interface during the three-phase hydrogenation of nitrobenzene over nanosized Au on TiO2

Abstract

The three-phase hydrogenation of nitrobenzene catalysed by nanosized gold over titania was investigated in a slurry. Simultaneous in situ ATR-FTIR monitoring of the liquid phase and at the solid/liquid catalyst interface identified the species adsorbed on the catalyst and those in the liquid phase during the reaction. Nitrosobenzene was not detected analytically while the spectroscopic measurements strongly indicated phenylhydroxylamine as an intermediate reacting before desorbing from the catalyst surface. Under the same reaction conditions, azobenzene and hydrazobenzene were identified as intermediates during the hydrogenation of azoxybenzene to aniline. When nitrosobenzene or phenylhydroxylamine was alternately fed as reactant, azoxybenzene was produced via a disproportionation route. With the former, azoxybenzene was not further reduced by hydrogen because nitrosobenzene deactivated the catalyst. Combined with H(2) uptake, the spectroscopic measurements provided new insights into the reaction mechanism of the gold catalysed hydrogenation of nitrobenzene and an update of the corresponding kinetics.

Gold catalysts for the synthesis of aromatic azocompounds from nitroaromatics in one step

“…NC: nitrocompound, NSC: nitrosocompound, AHA: aromatic hydroxylamine, AN: aniline, AOC: azoxycompound, AC: azocompound, HAC: hydrazocompound. Adapted from Richner et al [15] In the present work we show that it is possible to produce azocompounds with more than 98% yield from nitrobenzene in a single pass with a catalyst able to preferentially direct the process towards the coupling of nitrosobenzene intermediate (condensation route a.1 in Scheme 2). In this way the azoxycompound is formed that selectively evolves to the desired azocompound.…”

“…In opposite, nitrosobenzene adsorbs differently on both catalyst ( Figure 7). On Au/TiO 2 nitrosobenzene is found to be coordinated to a surface metal site by a -N bonding (characterized by the 1485 cm -1 N=O stretching IR band [15,17] ), while on Au/CeO 2 , in addition to an interaction of the N=O group by -N (IR band at 1485), a -O bonding (IR bands at 1520-1508 cm -1 ) and an interaction of the N=O group with surface oxygen ions (IR band at 1540 cm -1 ) is observed [17] . The higher basicity of the oxygen ions in the ceria nanoparticles explains the former stabilization mode of nitrosobenzene on the catalysts surface.…”

Hydrogenation of Nitrobenzene Over Au/MeOx Catalysts—A Matter of the Support

“…Because of earlier results, which showed that a high nitrosobenzene concentration poisoned the reaction, [6] we decreased the concentration of nitrosobenzene in this experiment from 0.8 to 0.4 mmol, which did not result in catalyst poisoning. All other reaction conditions were the same as in Figure 1.…”

“…The direct route dominates over Au/TiO 2 , [17b, 18] and accumulation of phenylhydroxylamine on the surface of the catalyst has been observed. [6] We found that hydrogenation was sufficiently fast over Au/TiO 2 to prevent condensation of phenylhydroxylamine with nitrosobenzene, which was formed either from nitrobenzene or by phenylhydroxylamine decomposition, but slower than over Au/CeO 2 . Phenylhydroxylamine has been found as an intermediate on the surface of the catalyst during the liquid-phase hydrogenation of nitrobenzene by using liquid-phase attenuated-total-reflectance (ATR) IR measurements.…”

Tuning the Chemoselective Hydrogenation of Nitrostyrenes Catalyzed by Ionic Liquid-Supported Platinum Nanoparticles

“…A more detailed scheme on NO 2 group hydrogenation can be found elsewhere. 39 Under the reaction conditions used, the IL-supported Pt NP catalyst retained its preferential activity for the CC double bond. The selectivity for ENB of this catalyst was only moderate and continuously decreased with conversion (Figure 1), reaching a value of 61% at around 90% conversion.…”