Egg-shell membrane reactors for nitrite hydrogenation: Manipulating kinetics and selectivity

A method to fabricate catalytic membrane contactor reactors with a Pd-egg-shell distribution has been developed on α-alumina tubes, allowing excellent control over the distribution of the active phase through the wall of the alumina tube. The performance of these catalytic membrane reactors has been assessed for nitrite hydrogenation. We have shown that manipulation of the thickness of the zone containing active phase induces different diffusion lengths for nitrite and hydrogen, strongly influencing activity and selectivity. Thick active layers have proved to be more selective to nitrogen, the desired product for purification of drinking water. Surprisingly, a thick layer with active phase also induced a negative apparent order in hydrogen, which is tentatively assigned to the fact that the ratio of concentrations of reactants, hydrogen and nitrite, varies extremely in the active zone.