| How catalyst modifiers influence the catalytic behavior of metals is of great importance in the design of new catalysts. This work addresses the chemical modification of Ru/SiO{dollar}sb2{dollar} by chlorine and potassium.; CO hydrogenation over Cl-modified Ru/SiO{dollar}sb2{dollar} was studied using steady-state Fischer-Tropsch synthesis and steady-state isotopic transient kinetic analysis (SSITKA) of methanation. The results illustrate how the presence of Cl acted to decrease catalytic activity and enhance selectivity for methane formation even though it was present on the catalyst only during the initial stages of the reaction. The deactivation results for F-T as well as the SSITKA results suggest that structural rearrangements induced by the presence of Cl may be the primary mechanism of Cl modification of catalytic properties of ruthenium-catalyzed CO hydrogenation.; Potassium modification of CO hydrogenation over chlorine-free and chlorine-contaminated Ru/SiO{dollar}sb2{dollar} was studied using SSITKA of methanation. It was found that residual Cl worked to partially mask the effects of added K{dollar}sp+{dollar} but that there were no apparent Cl-induced changes in the alkali's mechanism of modification.; A study of potassium dispersion in a series of Ru/SiO{dollar}sb2{dollar} catalysts sequentially doped with potassium indicates that, the alkali was apparently atomically dispersed on the Ru surface. Using a preferential-poisoning model, a study of the structure-sensitive ethane hydrogenolysis reaction suggests that at high potassium levels alkali dispersion became nonuniform in these catalysts.; A new technique for the nonparametric estimation of reactivity distributions from in-situ kinetic information was applied to study the series of K{dollar}sp+{dollar}-promoted Ru/SiO{dollar}sb2{dollar} catalysts. The results indicate that during steady-state CO hydrogenation carbidic carbon evolved into methane via a high-reactivity (C{dollar}sb{lcub}1alpha{rcub}{dollar}) and a low-reactivity (C{dollar}sb{lcub}1beta{rcub}{dollar}) trajectory. Upon K{dollar}sp+{dollar} promotion, the average intrinsic turnover frequency of both these carbidic pools decreased steadily, as did their surface abundance. Relative to C{dollar}sb{lcub}1beta{rcub}{dollar}, the C{dollar}sb{lcub}1alpha{rcub}{dollar} pool was affected more, both in terms of reactivity and abundance. With time, deactivation by inactive carbon did not significantly affect the product distribution or the methane rate constant; instead, deactivation was attributed to a decreasing abundance in carbon-containing surface intermediates. |
