Characterization and reactivity of Pd supported on ZnAl₂O₄catalysts for direct coupling of ethylbenzene dehydrogenation with nitrobenzene hydrogenation

Abstract

The ZnAl₂O₄supported palladium catalysts have been described for the first time in the direct coupling of dehydrogenation of ethylbenzene with hydrogenation of nitrobenzene, in a fixed bed catalytic reactor at atmospheric pressure in the temperature range of 673−823 K. The former reaction is reversible, endothermic, thermodynamically limited and also supplies hydrogen to produce styrene. However, the latter is irreversible, exothermic and consumes<i style="mso-bidi-font-style:normal"> in situ</i> hydrogen to produce aniline, thereby making the coupling reaction slightly exothermic and additionally overcoming thermodynamic constraints. A series of palladium (0.25−4.0 wt%)<span style="mso-bidi-font-weight:bold"> catalysts supported on crystalline ZnAl₂O₄ have been prepared and their catalytic activities studied in the coupling reaction. The catalyst samples are characterized by X-ray diffraction, H₂-temperature programmed reduction, CO chemisorption and BET surface area data. The metal dispersion and particle size are obtained by CO chemisorption method. The reaction profile shows that 0.5 wt% palladium is an optimum loading to obtain maximum conversions of ethylbenzene (52.3%) and nitrobenzene (43.9%) to give 88.3% and 100% selectivity of styrene and aniline products respectively.<b> </b>

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