Influence of the reaction conditions and catalytic properties on the liquid-phase hydrodebromination of bromobenzene over palladium supported catalysts: activity and deactivation

The liquid-phase hydrodebromination of bromobenzene with molecular hydrogen over palladium supported catalysts was studied. The reaction was found to be structure-sensitive as regards both the initial activity and the final c onversion (deactivation). The influence of the palladium content and the ca talytic support effect on the initial activity were negligible in catalysts of similar metal dispersion. The supports tested, viz. SiO2/AlPO4, ZrO2 an d MgO, significantly affected the catalyst deactivation. On the other hand, the addition of NaOH to the reaction medium had no effect on the initial a ctivity, but clearly helped the reaction to be completed and avoided passiv ation of the catalyst. In summary, the activity of the catalyst depends alm ost solely on its metal particle size, whereas the deactivation of the acti ve phase is decisively influenced in addition to metal particle size, by th e nature of the catalyst support and the presence of a base in the reaction medium. (C) 1999 Elsevier Science B.V. All rights reserved.