Decomposition of nitric oxide by rhodium cluster cations at high temperatures

Abstract

Decomposition reactions of NO molecules on gas-phase Rhn+ (n = 6–9) clusters were investigated by gas-phase thermal desorption spectrometry and density functional theory calculations.

Size-dependent reactivity of Rh cationic clusters to reduce NO by CO in the gas phase at high temperatures

“…For n = 7 and 8, several O-rich clusters, including Rh 7 NO 3 + , Rh 7 NO 5 + , Rh 7 O 4 + , Rh 8 NO 3 + , Rh 8 NO 5 + , and Rh 8 N 2 O 4 + , were produced by thermal desorption in the absence of CO, which is consistent with our previous study. 18 These O-rich clusters were formed by N 2 released from Rh 7 N x O x + and Rh 8 N x O x + . We expected that these clusters would be effectively reduced by CO, forming clusters with fewer O atoms and increasing the N-rich clusters.…”

“…24 Here, the number of N atoms, x , was assumed to be the same as the number of O atoms, y , because NO molecules were adsorbed onto Rh n + . However, few O-rich clusters ( y > x ) were generated, 18 likely because of the pre-oxidation of the Rh rod surface. The mass flow and pressure controllers maintained the NO concentration at the desired level.…”

“…Indeed, the release of the N 2 molecule from Rh n N x O x + requires the NO molecule to dissociate, forming two or more N atoms, which then migrate to form an N-N bond. 18 The presence of the N-O bond in the NO-attached Rh metal clusters was observed using vibrational spectroscopy. 19,20 When Rh metal clusters react with NO gas, the prominent products obtained are Rh n (NO) m + .…”

“…Previous studies on rhodium metal clusters have shown a size dependence of the reaction rate. 15,18 Information regarding the temperature dependence of the reaction is essential for further understanding. Therefore, it is important to analyze the reactivity of clusters under high-temperature conditions using mass spectrometry.…”

Zooming in on the initial steps of catalytic NO reduction using metal clusters

“…The thermally driven evaporation of ligands off Rh n + N k O k was studied using thermal desorption spectrometry. 104,117 In the He-filled copper extension tube following the reaction gas cell, the clusters reach a thermal equilibrium with the tube wall due to collisions with surrounding He atoms. The NO reduction, which was probed by mass spectrometry, was driven by heat at high temperature.…”