SUPPORTED PALLADIUM CATALYSTS FOR METHANATION

Pd/Al2o3 catalysts exhibit specific activities (molecules-s-1-site-1) in the methanation reaction 70-fold greater than those for unsupported Pd and ~ 35-fold greater than Pd/Sio2 catalysts. Most surprising is the finding that the specific activities of Pd/Al2o3 are only a factor of 3 less than those for typical nickel methanation catalysts. A much lower activity reported previously for a Pd/Al2o3 catalyst cannot be attributed to poisoning by sodium, since the behavior of a Pd/Al2o3 catalyst containing 0.7 wt % Na was virtually identical with that with no Na added. Activity maintenance studies indicate that at high conversions and temperatures of 623-673 K, these Pd/Al2o3 catalysts deactivate rapidly. However, at lower conversions and 573 K Pd/Al2o3 catalysts exhibit stable activity and an activity per unit weight which is comparable to nickel catalysts because Pd/Al2o3 can be prepared and maintained with a higher fraction exposed than Ni. Even though the costs of Pd catalysts are significantly greater than those of Ni, their use in methanation may be justified when other attributes such as absence of bulk carbide and volatile carbonyl formation, in situ regeneration and redispersion capability, and anticipated better sulfur tolerance than nickel catalysts are considered. © 1979, American Chemical Society. All rights reserved.