Photochemical Activation of CO₂ on Rh^I(CO)₂/Al₂O₃−CO₂ Dissociation and Oxygen Atom Exchange

Abstract

The ultraviolet (3.8 eV) photolysis of atomically dispersed RhI(13C18O)2 species supported on an Al2O3 surface in the presence of CO2 at 256 K has been studied by infrared spectroscopy (FTIR). Carbon dioxide is activated on photochemically produced RhI(13C18O) sites to produce various isotopically labeled rhodium gem-dicarbonyl species. The two major products of CO2 activation exhibit infrared bands at 2077 and 1958 cm-1 assigned to RhI(12C16O)(13C18O) species and bands at 2036 cm-1 and near 1958 cm-1 assigned to RhI(13C16O)(13C18O). The infrared band assignments for the isotopic rhodium gem-dicarbonyl species are supported by a thermally driven isotopic exchange experiment with 13C16O(g) and by a comparison to the frequencies predicted with frequency calculations based on known force constants. Two dissociation pathways are proposed for CO2 coordinated on RhI(13C18O) sites. Path I involves direct dissociation of the C−O bond in CO2 and Path II involves oxygen atom exchange between CO2 and CO ligands, followed by C−O bond dissociation in the CO2 ligand which was produced by the O exchange process. The lack of formation of oxidized rhodium carbonyl species during CO2 activation suggests that CO2 temporarily coordinates to RhI(CO) with η1 bonding. This work demonstrates the first steps of a potential low-temperature route for the conversion of CO2 into other molecules on catalyst sites using ultraviolet light as an energy source.

Infrared Spectra of RhCO+, RhCO, and RhCO- in Solid Neon: A Scale for Charge in Supported Rh(CO) Catalyst Systems

“…Clearly, bands in the 2200-2165 cm -1 region are enhanced by CCl 4 , products in the 2040-2010 cm -1 region are little affected, but bands in the 1920-1800 cm -1 region are markedly decreased. Experiments were also done with 13 CO, C 18 O, and a mixture of 12 CO and 13 CO, and the product absorptions are listed in Table 1. Calculations were performed on the monocarbonyl and dicarbonyl neutrals, cations and anions, and the isotopic carbonyl frequencies are listed in Tables 2 and 3 for comparison with experiment.…”

“…[1][2][3][4][5][6][7][8][9] This gem-rhodium dicarbonyl species is usually designated Rh I (CO) 2 because of agreement with the C-O stretching modes of the (OC) 2 Rh(Cl) 2 Rh(CO) 2 molecule, where the oxidation state of rhodium is +1. 6,7,9 The rhodium dicarbonyl on alumina, silica, and zeolites is widely used as a catalyst system for activation of many molecules including H 2 , N 2 , CO 2 , and alkanes [10][11][12][13][14][15] through a coordinatively unsaturated Rh I (CO) center, which absorbs near 2096 cm -1 on zeolites, 16 2070 cm -1 on silica, 17 and 2060 cm -1 on alumina. 4,11 Furthermore, the activation of C-H bonds in alkanes by a transient CpRh(CO) species absorbing near 1985 cm -1 in the gas phase readily occurs.…”

Photoinduced activation of CO2 on Ti-based heterogeneous catalysts: Current state, chemical physics-based insights and outlook

“…66 As an example, a study by Wovchko and Yates demonstrated the activation of CO 2 by a metal complex (Rh I (CO) 2 ) immobilized on an alumina support. 57 Similar studies should lead to the rational design of photocatalysts mediating CO 2 reduction. The surface chemistry of CO 2 on metals and oxide surfaces was reviewed by Freund and Roberts.…”

“…Some recent developments in this field have been moved towards rational photocatalyst design, the use of highly active isolated Tispecies in mesoporous and microporous materials, 11,14,15,[36][37][38]55,56 metal-doping of TiO 2 , development of catalysts active at longer wavelengths than can be achieved with commercially available titania, and the elucidation of reaction mechanisms through in situ spectroscopic studies. 14,57 A comparison of the CO 2 conversion rates from various studies is shown in Fig. 3.…”

Anchoring Sites Engineering in Single‐Atom Catalysts for Highly Efficient Electrochemical Energy Conversion Reactions

“…[ 27 ] In the 1990s to 2000s, more studies established that a single‐metal atom is capable of driving catalytic reactions (e.g., Pt SAs on MgO). [ 28–31 ] Flytzani‐Stephanopoulos’ group in 2003 studied single‐site Au and Pt catalysts, showing that they exhibited high performance, despite after removing the corresponding nanoparticles, suggesting the residual Au/Pt species were the active sites toward water–gas shift reaction. [ 32 ] Pd SAs and Ir SAs on Al 2 O 3 and MgO supports were directly observed by Lee and co‐workers and Gates and co‐workers.…”