Deactivation of supported copper metal catalysts for hydrogenation reactions

Laboratory and industrial results are used to elucidate the general feature s 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 explo ited 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 or ganic compounds. Common catalyst types are based on Cu/Cr2O3 (copper chromi te) or Cu/ZnO formulations that contain stabilisers and promoters such as a lkaline earth oxides and Al2O3. These have several roles, including inhibit ion of sintering, and poison traps that prevent poisoning of the active met al 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 pro cess and this is markedly accelerated by the presence of even traces of chl oride. Care must be, therefore, taken to eliminate halides from copper cata lysts during manufacture, and from the reactants during use. Operating temp eratures must be restricted, usually to below 300 degreesC when catalyst lo ngevity is important with large catalyst volumes. Water can soften some Cu/ZnO formulations during use, and cause particle br eakage 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 deposi tion (coking) is uncommon. However, conventional site blocking poisoning wi th sulphur compounds, and particularly by H2S, 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 sulphide d they can exhibit selectivity in hydrogenation of organic hydrogenations. A variety of other sulphur compounds, and some chlorinated organic compound s, can cause complete deactivation or enhanced selectivity. (C) 2001 Elsevi er Science B.V. All rights reserved.