Chlorinated Alumina Catalyst for Isobutane / 2-Butene Alkylation :Influence of Added Noble Metals

Abstract

Many solids with a high surface acidity have been tested as catalysts for alkylation of isobutane with butene [1]. All of them suffer a rapid deactivation, which is generally ascribed to secondary reactions leading to carbonaceous deposit. Rejuvenation has been attempted through hydrogenation of the deposit, catalyzed by a small amount of a noble metal [2]. We found that chlorinated alumina when prepared in a proper way, was an effective catalyst when alkylation was performed at 0°C and olefin dilution α = 20 [3]. Accordingly, a fast deactivation occurs, although carbon deposition is rather limited. Furthermore, the lifetime of the catalyst is markedly improved upon doping with alkaline cation. This points to a different mechanism of deactivation. Indeed, when chlorinated alumina doped with platinum is used in alkane isomerization, its chlorine content is permanently renewed by adding chloroalkanes to the feed. Therefore, in the alkylation catalyzed by Al₂O₃-Cl some loss of HCl may be a further cause of deactivation, and addition of a metallic phase (Pt or Pd) was expected to assist the rejuvenation of the acidic surface, either through hydrogenation of the adsorbed carbonaceous species, or through decomposition of a chloroalkane yielding HCl.