Consecutive C-C Coupling of CH and CO Mediated by Heteronuclear Metal Cations CuTa.

The conversion of methane and carbon dioxide to form C products is of great interest but presents a long-standing grand challenge due to the significant obstacle of activating the inert C-H and C═O bonds as well as forming the C-C bonds. Herein, the consecutive C-C coupling of CH and CO was realized by using heteronuclear metal cations CuTa, and the desorption of HC═C═O molecules was evidenced by state-of-the-art mass spectrometry. The CuTa reaction system is significantly different from the homonuclear metal systems of Cu and Ta.

Dry Reforming of Methane to Syngas Mediated by Rhodium-Cobalt Oxide Cluster Anions RhCoO.

Dry reforming of methane (DRM) to syngas is an important route to co-convert CH and CO. However, the highly endothermic nature of DRM induces the thermocatalysis to commonly operate at high temperatures that inevitably causes coke deposition through pyrolysis of methane. Herein, benefiting from the mass spectrometric experiments complemented with quantum chemical calculations, we have discovered that the bimetallic oxide cluster RhCoO can mediate the co-conversion of CH and CO at room temperature giving rise to two free H molecules and two adsorbed CO molecules (CO).

Role of HO Adsorption in CO Oxidation over Cerium-Oxide Cluster Anions (CeO)O ( = 1-4).

Water (HO) is ubiquitous in the environment and inevitably participates in many surface reactions, including CO oxidation. Acquiring a fundamental understanding of the roles of HO 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 HO molecule on each of the cerium oxide cluster anions (CeO)O ( = 1-4) at room temperature can create a new atomic oxygen radical (O) that then oxidizes a CO molecule.

Catalytic Conversion of NO and CO by Noble-Metal-Free Copper-Vanadium Oxide Cluster Anions CuVO.

Herein, by using state-of-the-art mass spectrometry, we demonstrated experimentally that the bimetallic copper-vanadium oxide cluster anions CuVO can catalyze the reduction of NO by CO into NO and CO. 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.

Reactivity of Atomic Oxygen Radical Anions in Metal Oxide Clusters.

Atomic oxygen radical anion (O⋅) represents an important type of reactive centre that exists in both chemical and biological systems. Gas-phase atomic clusters can be studied under isolated and well controlled conditions. Studies of O⋅-containing clusters in the gas-phase provide a unique strategy to interpret the chemistry of O⋅ radicals at a strictly molecular level.

Experimental Reactivity of (MoO)O ( = 1-21) Cluster Anions with C-C Alkanes: A Simple Model to Predict the Reactivity with Methane.

Metal oxide clusters with atomic oxygen radical anions are important model systems to study the mechanisms of activating and transforming very stable alkane molecules under ambient conditions. It is extremely challenging to characterize the activation and conversion of methane, the most stable alkane molecule, by metal oxide cluster anions due to the low reactivity of the anionic species. In this study, using a ship-lock type reactor that could be run at relatively high pressure conditions to provide a high number of collisions in ion-molecule reactions, the rate constants of the reactions between (MoO)O ( = 1-21) cluster anions and the light alkanes (C-C) were measured under thermal collision conditions.

Conversion of Methane at Room Temperature Mediated by the Ta-Ta σ-Bond.

Metal-metal bonds constitute an important type of reactive centers for chemical transformation; however, the availability of active metal-metal bonds being capable of converting methane under mild conditions, the holy grail in catalysis, remains a serious challenge. Herein, benefiting from the systematic investigation of 36 metal clusters of tantalum by using mass spectrometric experiments complemented with quantum chemical calculations, the dehydrogenation of methane at room temperature was successfully achieved by 18 cluster species featuring σ-bonding electrons localized in single naked Ta-Ta centers. In sharp contrast, the other 18 remaining clusters, either without naked Ta-Ta σ-bond or with σ-bonding electrons delocalized over multiple Ta-Ta centers only exhibit molecular CH-adsorption reactivity or inertness.

Toward Designing Reactive Metal Clusters for Dinitrogen Activation: A Guideline Based on N Initial Adsorption.

Gas-phase metal clusters are ideal models to explore transition-metal-mediated N activation mechanism. However, the effective design and search of reactive clusters in N activation are currently hindered by the lack of clear guidelines. Inspired by the Sabatier principle, we discovered in this work that N initial adsorption energy (Δ) is an important parameter to control the N activation reactivity of metal clusters in the gas phase.

Size-dependent reactivity of VO ( = 1-9) clusters with ethane.

Cost-effective and readily accessible 3d transition metals (TMs) have been considered as promising candidates for alkane activation while 3d TMs especially the early TMs are usually not very reactive with light alkanes. In this study, the reactivity of V and VO ( = 1-9) cluster cations towards ethane under thermal collision conditions has been investigated using mass spectrometry and density functional theory calculations. Among V ( = 1-9) clusters, only V can react with CH to generate dehydrogenation products and the reaction rate constants are below 10 cm molecule s.

Reverse water-gas shift catalyzed by RhVO ( = 3-7) cluster anions under variable temperatures.

A fundamental understanding of the exact structural characteristics and reaction mechanisms of interface active sites is vital to engineering an energetic metal-support boundary in heterogeneous catalysis. Herein, benefiting from a newly developed high-temperature ion trap reactor, the reverse water-gas shift (RWGS) (CO + H → CO + HO) catalyzed by a series of compositionally and structurally well-defined RhVO ( = 3-7) clusters were identified under variable temperatures (298-773 K). It is discovered that the RhVO clusters can function more effectively to drive RWGS at relatively low temperatures.

Machine Learning for Experimental Reactivity of a Set of Metal Clusters toward C-H Activation.

Understanding the mechanisms of C-H activation of alkanes is a very important research topic. The reactions of metal clusters with alkanes have been extensively studied to reveal the electronic features governing C-H activation, while the experimental cluster reactivity was qualitatively interpreted case by case in the literature. Herein, we prepared and mass-selected over 100 rhodium-based clusters (RhVO and RhCoO) to react with light alkanes, enabling the determination of reaction rate constants spanning six orders of magnitude.

Spectroscopic Characterization of Thermal Methane Activation by Lewis-Acid-Base Pair in a Gas-Phase Metal Nitride Anion TaN.

Activation and transformation of methane is one of the "holy grails" in catalysis. Understanding the nature of active sites and mechanistic details via spectroscopic characterization of the reactive sites and key intermediates is of great challenge but crucial for the development of novel strategies for methane transformation. Herein, by employing photoelectron velocity-map imaging (PEVMI) spectroscopy in conjunction with quantum chemistry calculations, the Lewis acid-base pair (LABP) of [Ta-N] unit in TaN acting as an active center to accomplish the heterolytic cleavage of C-H bond in CH has been confirmed by direct characterization of the reactant ion TaN and the CH-adduct intermediate TaNCH .

CO Oxidation Promoted by NO Adsorption on RhMnO Cluster Anions.

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 RhMnO cluster cannot oxidize CO into gas-phase CO at room temperature, while the NO preadsorbed products RhMnO[(NO)] 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.

Activation of Methane by Rhodium Clusters on a Model Support CH.

Supported metals represent an important family of catalysts for the transformation of the most stable alkane, methane, under mild conditions. Here, using state-of-the-art mass spectrometry coupled with a newly designed double ion trap reactor that can run at high temperatures, we successfully immobilize a series of Rh ( = 4-8) cluster anions on a model support CH. Reactivity measurements at room temperature identify a significantly enhanced performance of large-sized RhCH toward methane activation compared to that of free Rh.

Selective Reduction of NO into N Catalyzed by Rh-Doped Cluster Anions RhCeO.

Catalytic conversion of toxic nitrogen oxide (NO) and carbon monoxide (CO) into nitrogen (N) and carbon dioxide (CO) 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 N 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 RhCeO can catalytically drive NO reduction by CO and give rise to N and CO. This finding represents a sharp improvement in cluster science where NO is commonly produced in the rarely established examples of catalytic NO reduction mediated with gas-phase clusters.

Size-Dependent Reactivity of Co ( = 5-25) Cluster Anions toward Carbon Dioxide.

A fundamental understanding of the reactivity evolution of nanosized clusters at an atomically precise level is pivotal to assemble desired materials with promising candidates. Benefiting from the tandem mass spectrometer coupled with a high-temperature ion-trap reactor, the reactions of mass-selected Co ( = 5-25) clusters with CO were investigated and the increased reactivity of Co was newly discovered herein. This finding marks an important step to understand property evolution of subnanometer metal clusters (Co, ∼0.

Activation of Dinitrogen Promoted by Adsorption of CH on FeVC Cluster Anions.

The introduction of organic ligands is one of the effective strategies to improve the stability and reactivity of metal clusters. Herein, the enhanced reactivity of benzene-ligated cluster anions FeVC(CH) with respect to naked FeVC is identified. Structural characterization suggests that CH is molecularly bound to the dual metal site in FeVC(CH).

Superior Reactivity of Molybdenum-Sulfur Cluster Anions MoS and MoS toward Dinitrogen.

Inspired by the fact that Mo is a key element in biological nitrogenase, a series of gas-phase MoS cluster anions are prepared and their reactivity toward N is investigated by the combination of mass spectrometry, photoelectron imaging spectroscopy, and density functional theory calculations. The MoS and MoS cluster anions show remarkable reactivity compared with the anionic species reported previously. The spectroscopic results in conjunction with theoretical analysis reveal that a facile cleavage of N≡N bonds takes place on MoS and MoS.

Catalytic NO Reduction by Noble-Metal-Free Vanadium-Aluminum Oxide Cluster Anions.

By using state-of-the-art mass spectrometry and guided by the newly discovered single-electron mechanism (SEM; e.g., Ti + 2NO → Ti-O + NO), we determined experimentally that the vanadium-aluminum oxide clusters VAlO ( = 1-3) can catalyze the reduction of NO by CO and substantiated theoretically that the SEM still prevails in driving the catalysis.

Filtration of the preferred catalyst for reverse water-gas shift among Rh ( = 3-11) clusters by mass spectrometry under variable temperatures.

The key to optimizing energy-consuming catalytic conversions lies in acquiring a fundamental understanding of the nature of the active sites and the mechanisms of elementary steps at an atomically precise level, while it is challenging to capture the crucial step that determines the overall temperature of a real-life catalytic reaction. Herein, benefiting from a newly-developed high-temperature ion trap reactor, the reverse water-gas shift (CO + H → CO + HO) reaction catalyzed by the Rh ( = 3-11) clusters was investigated under variable temperatures (298-783 K) and the critical temperature that each elementary step (Rh + CO and RhO + H) requires to take place was identified. The Rh cluster strikingly surpasses other Rh clusters to drive the catalysis at a mild starting temperature (∼440 K).

Enhancing the Performance of Global Optimization of Platinum Cluster Structures by Transfer Learning in a Deep Neural Network.

The global optimization of metal cluster structures is an important research field. The traditional deep neural network (T-DNN) global optimization method is a good way to find out the global minimum (GM) of metal cluster structures, but a large number of samples are required. We developed a new global optimization method which is the combination of the DNN and transfer learning (DNN-TL).