TPSR(Temperature-Programmed Surface Reaction) study of sulfur-poisoned nickel catalyst

Abstract

Nickel is easily poisoned by sulfur even when the ambient stream contains very low levels of sulfur. For example, a study {1] shows that the hydrogen stream containing only 1 ppb of H2S readily forms a monolayer of nickel sulfide on the surface at 390~ Many studies therefore have been made of the sulfur effects on the catalytic properties of nickel [2,3] and of the methods to protect nickel from sulfur poisoning [4]. The sulfur-poisoned nickel, however, is very difficult to regenerate. Thus, few works have been reported on the catalyst regeneration at least in the open literature. A common method to regenerate po:Lsoned metal catalysts is to treat them in ':eactive gas streams such as H 2 [5] and O:, [6]. But, this method has not been efficient in regenerating the sulfur-poisoned nickel. Regeneration in H 2 has been unsuccessful because the surface nickel sulfides are relatively s~.able under the reducing atmosphere. McCarty and Wise [7] have indicated that the H 2 stream in equilibrium with the sulfur-covered nickel surface, at 89% saturation covetage, contains only 4.4 ppb of H2S at 350~ This means that regeneration of poisoned nickel even with extremely pure H 2 would take a very long time, and therefore the regeneration method is impractical. Regeneration in 02 is acceptable only when care is taken of the reaction conditions. That is, the 02 partial pressure in the gas stream is maintained extremely