Laboratory and industrial results are used to elucidate the general features of the deactivation of supported copper metal catalysts in hydrogenation reactions. Hydrogenations with copper catalysts are milder than with their nickel or platinum counterparts, and they have selectivities that are exploited commercially. They are used in single stream plants for production of hydrogen via the low-temperature water shift gas reaction, and for methanol manufacture from synthesis gas, and also in hydrogenation of speciality organic compounds. Common catalyst types are based on Cu/Cr 2 O 3 (copper chromite) or Cu/ZnO formulations that contain stabilisers and promoters such as alkaline earth oxides and Al 2 O 3 . These have several roles, including inhibition of sintering, and poison traps that prevent poisoning of the active metal surface. The best understood are Cu/ZnO formulations that have improved sulphur resistance due to formation of thermodynamically stable ZnS. Copper catalysts are susceptible to thermal sintering via a surface migration process and this is markedly accelerated by the presence of even traces of chloride. Care must be, therefore, taken to eliminate halides from copper catalysts during manufacture, and from the reactants during use. Operating temperatures must be restricted, usually to below 300°C when catalyst longevity is important with large catalyst volumes. Water can soften some Cu/ZnO formulations during use, and cause particle breakage that leads to high-pressure drop and maldistribution of flow through large catalyst beds and impaired performance. Commercial copper catalysts are not acidic, and since they operate under mild conditions, carbon deposition (coking) is uncommon. However, conventional site blocking poisoning with sulphur compounds, and particularly by H 2 S, is common. The initial phase involves interaction with surface hydroxyl groups and elimination of water. Sulphur is retained strongly on the catalyst, and when partially sulphided they can exhibit selectivity in hydrogenation of organic hydrogenations. A variety of other sulphur compounds, and some chlorinated organic compounds, can cause complete deactivation or enhanced selectivity.

Deactivation of supported copper metal catalysts for hydrogenation reactions

Hydrogenation and Dehydrogenation of Organic Compounds

The influence of macromolecular carbon deposits, catalytic poisons, sintering, and destruction of pellets both on the deactivation and life of a copper catalyst used for the selective gas-phase catalytic reduction has been discussed. The catalyst applied in an industrial tube non-isothermic reactor is deactivated mainly by carbon deposits and sintering. The contribution of catalytic poisons is in fact negligible if their concentration in the processed raw material is lower than 0.5 ppm. It has been proved that the support composition, the presence of poisons, and the amount of 1, 3-dinitrobenzene in the raw material can have the major influence on the formation of carbon deposits. The catalyst sintering occurs nearly exclusively in the starting period of the operational cycle. The slow destruction of pellets has a positive influence on the catalyst life.

P. Pavlas

Papers

Deactivation of a Supported Copper Catalyst in the Industrial Aniline Plant