Absorption kinetics and mechanisms of carbon monoxide in liquid niobium

Abstract

Absorption kinetics and mechanisms of carbon monoxide in liquid niobium were investigated in the temperature range of 2700 to 3000 K in samples levitated in a CO/Ar stream. The carbon and oxygen dissolution in liquid niobium from CO gas is an exothermic process, and the solubilities of carbon and oxygen (Ce, Oe in at. pct) are related to temperature (T in kelvin) and partial pressure of CO (P co in atm) as follows:ln Ce ϩ ln Oe Ϫ P co ϭ 2.32 ⅐ 10 4 /T Ϫ 2.35The reaction CO → [C] ϩ [O], which occurs along with the evaporation of niobium oxide during the absorption of carbon and oxygen, is a second-order process with a first-order dependence on C and O concentrations, respectively. The absorption mechanism implies that the overall reaction rate is controlled by the substep of dissociation of surface-adsorbed CO molecules. The rate equations for C and O absorption are given as follows:where C and O are carbon and oxygen concentrations in atomic percent, respectively, A is the surface area of the sample in cm 2 , and V is the volume in cm 3 .

Photoionization of Nb3CO and Nb3(CO)2: Is CO Molecularly or Dissociatively Adsorbed on Niobium?

“…Adsorption of CO as a poisoning process, a side reaction, or as part of a catalytic cycle is a ubiquitous concern in heterogeneous catalysis. , With increased usage of Nb as a performance-enhancing dopant of industrial catalysts, , the number of scientific studies of the fundamental reactivity associated with Nb-containing surfaces is on the rise and multiple review articles have been published recently. ,,, From this work, there is evidence to support the presence of both dissociatively and molecularly adsorbed CO on Nb surfaces, , but there are no conclusions regarding the conditions under which these species are formed. Thermodynamically, dissociative adsorption is thought to be strongly favored.…”