Amination of phenols with ammonia over palladium supported on alumina

The amination of phenol with ammonia in the presence of hydrogen over palladium supported on alumina gives aniline effectively at 250 °C. The presence of hydrogen is essential. The following reaction scheme is proposed: The reaction rate is approximately first order with respect to the partial pressure of hydrogen, and zeroth order with respect to the partial pressure of ammonia. The rate-determining step of the reaction is concluded to be in the hydrogenation of phenol into cyclohexanone. The catalytic behavior of palladium is improved by making an alloy with gold or by cosupporting La3+ or Al3+ ions. The improvement may be caused by better dispersion of palladium.