Hydrogenation of 4-chloronitrobenzenes over palladium and platinum catalysts supported on beta zeolite and γ-alumina

Abstract

Liquid-phase hydrogenation of 4-chloronitrobenzene (4-CNB) to 4-chloroaniline (4-CAN) under mild reaction conditions (0.6 MPa, 25 °C, methanol-diethyl ether, 1:1 vol.) over palladium and platinum catalysts containing 1 mass% of metal supported on beta zeolite (M/B) or γ-alumina (M/A) was studied. The catalysts were prepared by the incipient wetness method using amino nitrate complexes and hydrogen as the reducing agent. SEM, adsorption–desorption nitrogen isotherms, XRD, TEM, and hydrogen chemisorption techniques were used for their characterization. The techniques employed revealed the presence of relatively large metal particles (approximately 15 nm; about 3% of metal dispersion). Stability of the catalysts during the hydrogenation was high; no catalyst changes were observed after two recycle runs. Hydrogenation over M/A catalysts was found to be faster than that over M/B catalysts in the methanol–diethyl ether mixture. Selectivity of only about 75% to 4-CAN was achieved over the M/A catalyst in methanol. Positive effect of the acid support (beta zeolite) and low polarity of the reaction environment (diethyl ether) are reflected in the high selectivity to 4-CAN; of about 99% at virtually 100% conversion of 4-CNB.