Temperature gradients and activation energies on catalytic wires

Abstract

The steady-state temperature distribution has been determined along a 9 cm 32 SWG Pd wire axially stretched in a reaction vessel and electrically heated in vacuo and in 26 Pa oxygen. The results have been used to calculate reaction velocity for the model rate k_m=B_m exp (–E/RT), with B_m= 10²⁵ molecule m^–2 s^–1, and with E= 80–180 kJ mol^–1. ‘Experimental’E′ and B″ values were then calculated using the maximum (central) wire temperatures T′ and E″ and B″ values using the computed average wire temperatures T″. For the range of E, the E′ and B′ values correspond more closely for the gaseous ambient to the true (E and 10²⁵) values. If we assume a simple linear extrapolation to lower E values than 80 kJ mol^–1, then below E= 30 kJ mol^–1, E″ will correspond more closely to the true E values. The generalisation of these conclusions is discussed in relation to some earlier studies on catalytic wires.