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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 (CO2 + H2 → CO + H2O) reaction catalyzed by the Rhn− (n = 3–11) clusters was investigated under variable temperatures (298–783 K) and the critical temperature that each elementary step (Rhn− + CO2 and RhnO− + H2) requires to take place was identified. The Rh4− cluster strikingly surpasses other Rhn− clusters to drive the catalysis at a mild starting temperature (∼440 K). This finding represents the first example that a specifically sized cluster catalyst that works under an optimum condition can be accurately filtered by using state-of-the-art mass spectrometric experiments and rationalized by quantum-chemical calculations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract Background The timed-sequential chemotherapy regimen consisting of etoposide, mitoxantrone and cytarabine (EMA) is an effective therapy for relapsed or refractory acute myelogenous leukemia (AML). We postulated that granulocyte colony-stimulating factor (G-CSF) might enhance the cytotoxicity of EMA by increasing the proportion of leukemic blasts in S-phase. We added G-CSF to EMA (EMA-G) for therapy of advanced high-risk AML patients. Methods High-risk AML was defined as refractory, relapsed or secondary to either an antecedent hematologic disorder or exposure to cytotoxic agents. The patients were treated with one course of EMA-G consisting of mitoxantrone and cytarabine on days 1–3, and etoposide and cytarabine on days 8–10. G-CSF was started on day 4 and continued until absolute neutrophil count recovered. Results Thirty patients were enrolled. The median age was 51 years (range, 25–75). Seventeen (61%) patients had unfavorable cytogenetic karyotypes. Twenty (69%) patients had secondary AML. Ten (34%) had relapsed disease. Four (14%) had refractory AML. Three (10%) patients died from febrile neutropenia and sepsis. Major non-hematologic toxicity included hyperbilirubimenia, renal insufficiency, mucositis, diarrhea, nausea and vomiting, skin rash. A complete remission was achieved in 13 (46%) patients. Median overall survival was 9 months (range, 0.5–66). Median relapse-free survival (RFS) for those who had a CR was 3 months (range, 0.5–63) with RFS censored at the time of allogeneic bone marrow transplantation or peripheral stem cell transplantation for 6 of the patients. Conclusions EMA-G is a safe and efficacious option for induction chemotherapy in advanced, high-risk AML patients. The activity of EMA may be increased if applied in patients with less advanced disease.

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 n - ( n = 5-25) clusters with CO 2 were investigated and the increased reactivity of Co 20-25 - was newly discovered herein. This finding marks an important step to understand property evolution of subnanometer metal clusters (Co 25 - , ∼0.8 nm) atom-by-atom. The reasons behind the increased reactivity of Co 20-25 - were proposed by analyzing the reactions of smaller Co 6-8 - clusters that exhibit significantly different reactivity toward CO 2 , in which a lower electron affinity of Co n contributes to the capture of CO 2 while the flexibility of Co n - could play vital roles to stabilize reaction intermediates and suppress the barriers of O-CO rupture and CO desorption.

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 2 + H 2 → CO + H 2 O) reaction catalyzed by the Rh n - ( n = 3-11) clusters was investigated under variable temperatures (298-783 K) and the critical temperature that each elementary step (Rh n - + CO 2 and Rh n O - + H 2 ) requires to take place was identified. The Rh 4 - cluster strikingly surpasses other Rh n - clusters to drive the catalysis at a mild starting temperature (∼440 K). This finding represents the first example that a specifically sized cluster catalyst that works under an optimum condition can be accurately filtered by using state-of-the-art mass spectrometric experiments and rationalized by quantum-chemical calculations.

Noble metals dispersed on transition-metal carbides exhibit extraordinary activity in CO 2 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 CO 2 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 RhTaC 2 - clusters with CO 2 was studied. The experimental results identified that RhTaC 2 - can reduce four CO 2 molecules consecutively and generate the product RhTaC 2 O 4 - . The pivotal roles of Rh-Ta synergy and the C 2 ligand in driving CO 2 reduction were rationalized by theoretical calculations. The presence of an attached CO unit on the product RhTaC 2 O 4 - was evidenced by the collision-induced dissociation experiment, providing a fundamental strategy to alleviate carbon deposition under a CO 2 atmosphere at elevated temperatures.