Selective Liquid-Phase Hydrogenation of a Nitro Group in Substituted Nitrobenzenes over Au/Al 2 O 3 Catalyst in a Packed-Bed Flow Reactor

Chempluschem. 2015 Dec;80(12):1741-1749. doi: 10.1002/cplu.201500310. Epub 2015 Aug 28.

Abstract

A series of substituted nitrobenzenes with the general formula XC6 H4 NO2 (X=Cl, CH=CH2 , or C(O)CH3 ) dissolved in toluene were reduced with hydrogen over the 1.9 % Au/Al2 O3 catalyst at 60-110 °C and 10-20 bar in a three-phase packed-bed reactor operating in up-flow mode. Under these conditions, hydrogenation of isomeric ClC6 H4 NO2 gives exclusively chloroanilines. Hydrogenation of 3-CH2 CHC6 H4 NO2 and 4-CH3 C(O)C6 H4 NO2 leads to the formation of 3-CH2 CHC6 H4 NH2 and 4-CH3 C(O)C6 H4 NH2 with selectivities of up to 93 and 97 % at substrate conversions of 98 and 100 %, respectively. Smooth catalyst deactivation was observed regardless of which substituted nitrobenzene was taken for hydrogenation. According to the results obtained by temperature-programmed oxidation of the spent catalyst, a carbonaceous deposit formed that might block the catalyst surface. Almost complete regeneration of the supported gold catalyst with retention of its high selectivity to hydrogenation of a nitro group was achieved in a flow of air at temperatures up to 400 °C to eliminate carbonaceous deposits.

Keywords: gold; hydrogenation; nitrobenzenes; supported catalysts; three-phase flow reactor.