RESUMEN
CO oxidation represents an important model reaction in the gas phase to provide a clear structure-reactivity relationship in related heterogeneous catalysis. Herein, in combination with mass spectrometry experiments and quantum-chemical calculations, we identified that the RhMn2O3- cluster cannot oxidize CO into gas-phase CO2 at room temperature, while the NO preadsorbed products RhMn2O3-[(NO)1,2] are highly reactive in CO oxidation. This discovery is helpful to get a fundamental understanding on the reaction behavior in real-world three-way catalytic conditions where different kinds of reactants coexist. Theoretical calculations were performed to rationalize the crucial roles of preadsorbed NO where the strongly attached NO on the Rh atom can greatly stabilize the products RhMn2O2-[(NO)1,2] during CO oxidation and at the same time works together with the Rh atom to store electrons that stay originally in the attached CO2- unit. The leading result is that the desorption of CO2, which is the rate-determining step of CO oxidation by RhMn2O3-, can be greatly facilitated on the reactions of RhMn2O3-[(NO)1,2] with CO.
RESUMEN
Catalytic conversion of toxic nitrogen oxide (NO) and carbon monoxide (CO) into nitrogen (N2) and carbon dioxide (CO2) is imperative under the weight of the increasingly stringent emission regulations, while a fundamental understanding of the nature of the active site to selectively drive N2 generation is elusive. Herein, in combination with state-of-the-art mass-spectrometric experiments and quantum-chemical calculations, we demonstrated that the rhodium-cerium oxide clusters RhCe2O3-5- can catalytically drive NO reduction by CO and give rise to N2 and CO2. This finding represents a sharp improvement in cluster science where N2O is commonly produced in the rarely established examples of catalytic NO reduction mediated with gas-phase clusters. We demonstrated the importance of the unique chemical environment in the RhCe2O3- cluster to guide the substantially improved N2 selectivity: a triatomic Lewis "acid-base-acid" Ceδ+-Rhδ--Ceδ+ site is proposed to strongly adsorb two NO molecules as well as the N2O intermediate that is attached on the Rh atom and can facilely dissociate to form N2 assisted by both Ce atoms.
RESUMEN
A fundamental understanding on the dynamically structural evolution of catalysts induced by reactant gases under working conditions is challenging but pivotal in catalyst design. Herein, in combination with state-of-the-art mass spectrometry for cluster reactions, cryogenic photoelectron imaging spectroscopy, and quantum-chemical calculations, we identified that NO adsorption on rhodium-cerium bimetallic oxide cluster RhCeO2 - can create a Ce3+ ion in product RhCeO2 NO- that serves as the starting point to trigger the catalysis of NO reduction by CO. Theoretical calculations substantiated that the reduction of another two NO molecules into N2 O takes place exclusively on the Ce3+ ion while Rh behaves like a promoter to buffer electrons and cooperates with Ce3+ to drive NO reduction. Our finding demonstrates the importance of NO in regulating the catalytic behavior of Rh under reaction conditions and provides much-needed insights into the essence of NO reduction over Rh/CeO2 , one of the most efficient components in three-way catalysts for NOx removal.
RESUMEN
Identifying the structural configurations of precursors for CO dissociation is fundamentally interesting and industrially important in the fields of, e.g., Fischer-Tropsch synthesis. Herein, we demonstrated that CO could be dissociated on polynuclear vanadium nitride V4N5- clusters at room temperature, and a key intermediate, with CO in a N-assisted tilted bridge coordination where the C-O bond ruptures easily, was discovered. The reaction was characterized by mass spectrometry, photoelectron spectroscopy, and quantum-chemistry calculations, and the nature of the adsorbed CO on product V4N5CO- was further characterized by a collision-induced dissociation experiment. Theoretical analysis evidences that CO dissociation is predominantly governed by the low-coordinated V and N atoms on the (V3N4)VN- cluster and the V3N4 moiety resembles a support. This finding strongly suggests that a novel mode for facile CO dissociation was identified in a gas-phase cluster study.
RESUMEN
The discovery of compounds containing transition metals with an unusual and well-established oxidation state is vital to enrich our horizon on formal oxidation state. Herein, benefiting from the study of the water-gas shift reaction (CO + H2O â CO2 + H2) mediated with the iridium-vanadium oxide cluster IrVO2-, the missing -II oxidation state of iridium was identified. The reactions were performed by using our newly developed double ion trap reactors that can spatially separate the addition of reactants and are characterized by mass spectrometry and quantum-chemical calculations. This finding makes an important step that all the proposed 13 oxidation states of iridium (+IX to -III) have been known. The iridium atom in the IrVO2- cluster features the IrâV double bond and resembles chemically the coordinated oxygen atom. A reactivity study demonstrated that the flexible role switch of iridium between an oxygen-atom like (Ir-IIVO2-) and a transition-metal-atom like behavior (Ir+IIVO3-) in different species can drive the water-gas shift reaction in the gas phase under ambient conditions. This result parallels and well rationalizes the extraordinary reactivity of oxide-supported iridium single-atom catalysts in related condensed-phase reactions.
RESUMEN
Gas-phase studies on catalytic CO oxidation by O2 mediated with gold-containing heteronuclear metal oxide clusters are vital to obtain the structure-reactivity relationship of supported gold catalysts, while it is challenging to trigger the reactivity of clusters with closed-shell electronic structure in O2 activation. Herein, we identified that CO oxidation by O2 can be catalyzed by the AuTi2 O4-6- clusters, among which AuTi2 O4- with closed-shell electronic structure can effectively activate O2 . The reactions were characterized by mass spectrometry and quantum chemical calculations. Theoretical calculations showed that in the initial stage of O2 activation, the Ti2 O4 moiety in AuTi2 O4- contributes dominantly to activate O2 into superoxide (O2- â ) without participation of the Au atom. In subsequent steps, the intimate charge transfer interaction between Au and the Ti2 O4 moiety drives the direct dissociation of the O2- â unit.
RESUMEN
Water (H2O) is ubiquitous in the environment and inevitably participates in many surface reactions, including CO oxidation. Acquiring a fundamental understanding of the roles of H2O molecules in CO oxidation poses a challenging but pivotal task in real-life catalysis. Herein, benefiting from state-of-the-art mass-spectrometric experiments and quantum chemical calculations, we identified that the dissociation of a H2O molecule on each of the cerium oxide cluster anions (CeO2)nO- (n = 1-4) at room temperature can create a new atomic oxygen radical (Oâ¢-) that then oxidizes a CO molecule. The size-dependent reactivity of H2O-mediated CO oxidation on (CeO2)nO- clusters was rationalized by the orbital compositions (O2p) and energies of the lowest unoccupied molecular orbitals of active Oâ¢- radicals modified by H2O dissociation. Our findings not only provide new insights into H2O-mediated CO oxidation but also demonstrate the importance of H2O in modulating the reactivity of the Oâ¢- radicals.
RESUMEN
Herein, by using state-of-the-art mass spectrometry, we demonstrated experimentally that the bimetallic copper-vanadium oxide cluster anions CuVO3,4- can catalyze the reduction of NO by CO into N2O and CO2. Note that the catalysis of NO reduction by CO has been rarely established in the gas phase and noble-metal containing clusters were commonly emphasized. Benefiting from quantum-chemical calculations, the Cu-V synergistic effect that both metal atoms work energetically to favor NO adsorption, N-N coupling, and CO oxidation by facilitating electron transfer can be understood at a strictly molecular level. Theoretical results demonstrated that the precaptured NO molecule encourages the adsorption of the second NO by electron donation. This finding deepens our understanding on NO reduction that NO functions not only as a reactant but also as a promoter during the reactions. This discovery could be helpful to permeate the nature and mechanism of active sites on related copper-vanadium heterogeneous catalyst used in real-life NO reduction.
RESUMEN
By using state-of-the-art mass spectrometry and guided by the newly discovered single-electron mechanism (SEM; e.g., Ti3+ + 2NO â Ti4+-Oâ¢- + N2O), we determined experimentally that the vanadium-aluminum oxide clusters V4-xAlxO10-x- (x = 1-3) can catalyze the reduction of NO by CO and substantiated theoretically that the SEM still prevails in driving the catalysis. This finding marks an important step in cluster science in which a noble metal had been demonstrated to be indispensable in NO activation mediated by heteronuclear metal clusters. The results provide new insights into the SEM in which active V-Al cooperative communication favors the transfer of an unpaired electron from the V atom to NO attached to the Al atom on which the reduction reaction actually takes place. This study provides a clear picture for improving our understanding of related heterogeneous catalysis, and the electron hopping behavior induced by NO adsorption could be a fundamental chemistry for driving NO reduction.
RESUMEN
Noble metals dispersed on transition-metal carbides exhibit extraordinary activity in CO2 catalytic conversion and bimetallic carbides generated at the interface were proposed to contribute to the observed activity. Heteronuclear metal carbide clusters (HMCCs) that compositionally resemble the bimetallic carbides are suitable models to get a fundamental understanding of the reactivity of the related condensed-phase catalysts, while the reaction of HMCCs with CO2 has not been touched in the gas phase. Herein, benefiting from the newly designed double ion trap reactors, the reaction of laser-ablation generated and mass-selected RhTaC2- clusters with CO2 was studied. The experimental results identified that RhTaC2- can reduce four CO2 molecules consecutively and generate the product RhTaC2O4-. The pivotal roles of Rh-Ta synergy and the C2 ligand in driving CO2 reduction were rationalized by theoretical calculations. The presence of an attached CO unit on the product RhTaC2O4- was evidenced by the collision-induced dissociation experiment, providing a fundamental strategy to alleviate carbon deposition under a CO2 atmosphere at elevated temperatures.