Adsorption Forms of NO on Rh_n⁺ (n = 6–16) Revealed by Infrared Multiple Photon Dissociation Spectroscopy

Abstract

The adsorption of NO on cationic Rh clusters, Rhn + (n = 6−16), was studied by IRMPD spectroscopy using FELIX in combination with DFT calculations. The IRMPD spectra show that NO adsorbs molecularly on an on-top site of Rhn + for all n studied, while for n = 7, 12, 13 and 14 evidence is found for second, bridging, adsorption site. Indeed, the DFT calculations suggest that molecular NO adsorption on a bridge site is more stable than on an on-top site for n = 7. Part of the NO adsorbs dissociatively on Rhn + , and the ratio of dissociative adsorption depends on the size, n. For Rhn + (n = 6, 8, 9), the dissociative form of NO is predicted more favorable than the molecular form by the DFT calculations, but experimentally observed ratios of dissociative adsorption were less than the prediction. The activation barrier existing between the molecular and dissociative adsorption was considered to hinder the NO dissociation. 20 ASSOCIATED CONTENT Supporting Information The supporting information is available free of charge on the ACS Publication website at DOI:_.

IR spectroscopic characterization of the co-adsorption of CO2 and H2 onto cationic Cun+ clusters

“…This approach assumes that no direct loss of multiple H 2 or CO 2 occurs from [Cu n , m CO 2 , p H 2 ] + ( m , p > 1) induced by IR absorption, and was used previously. 53 By employing it, ingrowth effects from higher order complexes are reduced, as are shot-to-shot fluctuations in cluster production.…”

Tuning the Dissociative Action of Cationic Rh Clusters Toward NO by Substituting a Single Ta Atom

“…15 Computational steps were almost the same as the previous studies. 12 For Rh5Ta + NO, more than one hundred initial geometries, prepared randomly, were calculated using Becke's Vibrational spectra were constructed by convoluting the (unscaled) harmonic frequencies and intensities with a Gaussian line shape functions. To reflect the changing bandwitdh of the FEL, the spectral width (FWHM) was chosen 5 cm −1 in the range below 300 cm −1 , and 20 cm −1 above.…”

“…In our previous work, we also found a preference of the N atom for a hollow site on Rhn + (n = 6, 8−10). 12…”

“…All clusters studied exhibited intense vibrational bands around 1800 cm −1 , characteristic for molecularly adsorbed NO. 12 Concurrent DFT calculations suggested that dissociation of NO on Rhn + is energetically as stable as molecular adsorption, pointing to the presence of a substantial activation barrier for the NO molecule towards dissociation on Rhn + .…”

Catalytic conversion of NO and CO into N2 and CO2 by rhodium–aluminum oxides in the gas phase

“…9 Confining individual active species on isolated gas-phase atomic clusters that can be studied under well-controlled and reproducible conditions is an important way to reveal the nature of active sites on related catalysts. 10–14 In the field of gas phase studies, the elementary reactions of Rh x 0,± , 15–17 Rh x M + (M = Ta, Al, V, and Co), 18,19 Rh x O y , 20 and RhAl 2 O 6 + 21 species with NO or CO have been extensively investigated, while the catalysis of NO reduction by CO mediated by Rh-containing species has not been established. Herein, benefiting from a homemade time-of-flight mass spectrometer (TOF-MS) coupled with a vacuum ultraviolet (VUV) laser system, 22 the catalytic conversion of NO and CO into N 2 and CO 2 by neutral rhodium-aluminum oxides RhAlO 0–3 and RhAl 2 O 1–4 has been identified for the first time in the gas phase.…”