Pt-Assisted Carbon Remediation of Mo2C Materials for CO Disproportionation

Multiple CO2 reduction mediated by heteronuclear metal carbide cluster anions RhTaC2. Dalton Trans 2022;51:11491-11498. [PMID: 35833563 DOI: 10.1039/d2dt01612e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

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.

Formation of Surface Impurities on Lithium-Nickel-Manganese-Cobalt Oxides in the Presence of CO2 and H2O

Surface impurities involving parasitic reactions and gas evolution contribute to the degradation of high Ni content LiNi_xMn_yCo_zO₂ (NMC) cathode materials. The transient kinetic technique of temporal analysis of products (TAP), density functional theory, and infrared spectroscopy have been used to study the formation of surface impurities on varying nickel content NMC materials (NMC811, NMC622, NMC532, NMC433, NMC111) in the presence of CO₂ and H₂O. CO₂ reactivity on a clean surface as characterized by CO₂ conversion rate in the TAP reactor follows the order: NMC811 > NMC622 > NMC532 > NMC433 > NMC111. The capacity of CO₂ uptake follows a different order: NMC532 > NMC433 > NMC622 > NMC811 > NMC111. Moisture pretreatment slows down the direct CO₂ adsorption process and creates additional active sites for CO₂ adsorption. Electronic structure calculations predict that the (012) surface is more reactive than the (1014) surface for CO₂ and H₂O adsorption. CO₂ adsorption leading to carbonate formation is exothermic with formation of ion pairs. The average CO₂ binding energies on the different materials follow the CO₂ reactivity order. Water hydroxylates the (012) surface and surface OH groups favor bicarbonate formation. Water creates more active sites for CO₂ adsorption on the (1014) surface due to hydrogen bonding. The composition of surface impurities formed in ambient air exposure is dependent on water concentration and the percentage of different crystal planes. Different surface reactivities suggest that battery performance degradation due to surface impurities can be mitigated by precise control of the dominant surfaces in NMC materials.