Low Activation Energy Barrier Research Articles

Electrospinning Fiber Membrane‐Derived Gel Polymer Electrolytes with High Mechanical Strength and Low Swelling Effect for High‐Safety Lithium Metal Batteries

AbstractThe practical application of lithium metal batteries (LMBs) is hindered by the issues of flammable electrolytes, lithium dendrites and the resulting thermal runaway. Designing flame‐retardant electrolytes with high performance is a valid strategy to break the current dilemma. In this work, the flame retardant of triphenyl phosphate (TPP) is elaborately encapsulated into the polymer shell of polyacrylonitrile (PAN) and polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP) to realize the controllable release of TPP during the soaking process. The resulting TPP@PAN/PVDF‐HFP fiber membrane holds high thermal stability, high mechanical strength, and low swelling rate, which is essential for the preparation of flame‐retardant gel polymer electrolyte (GPE). As demonstrated, the TPP@PAN/PVDF‐HFP GPE can deliver high Li+ transference number of 0.877, low interfacial activation energy barrier of 26.6 kJ mol−1 and heterogeneous SEI composition of Li3PO4/Li2CO3/LiF. The corresponding Li||Li cells achieve stable voltage polarization over 1000 h, and the Li||Cu cells display high plating/stripping CE of 99.1%. Meanwhile, the optimized Li||LiFePO4 batteries exhibit high reversible capacity of 158 mAh g−1 after 200 cycles at 0.5 C, and present outstanding fire resistance through the thermal runaway and puncture test. This study will open window for the design of high‐safety electrolytes to promote the practical application of LMBs.

Mo-Induced Surface Reconstruction in Ni/Co-OOH Prickly Flower Clusters for Improving the Hydrogen Production in Alkaline Seawater Splitting.

Seawater electrolysis is the most promising technology for hydrogen production, in which surface reconstruction on the interface of electrode/electrolyte plays a crucial role in activating the catalytic reactions with a low activation energy barrier. Herein, an efficient Mo modifying NiCoMo prickly flower clusters electrocatalyst supported on nickel foam (Mo-doped Ni/Co-OOH prickly flower clusters) is obtained, which serves as an eminently active and durable catalyst for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) due to the surface reconstruction during the alkaline seawater electrolysis with ultralow overpotentials. It just requires a cell voltage of 1.52V to achieve the current density of 10mAcm-2 for water electrolysis along with robust durability over 30h. Mo doping effectively regulates the surface reconstruction of Ni/Co-OOH, which facilitates the adsorption of oxygen-containing intermediates on the active center, and the nonhomogeneous interface induces charge rearrangement for the catalytic process to improve efficiency, providing a new strategy for revealing the seawater electrolytic mechanism.

Metal-enhanced carbon-nitrogen material for selective detection of hazardous gases: Insights from interface electronic states

In this study, utilizing density functional theory, the C3N1 monolayer modified by Ir, Pd, Pt, and Rh atoms (Ir/Pd/Pt/Rh-C2N1) was chosen for selective adsorption of C2H2 amidst multiple gases (H2O, C2H2, and C4H10O2). According to the results of cohesive energy and ab initio molecular dynamics simulations, it is indicated that precious metal atoms can be stably anchored on the monolayer while enhancing the conductivity of the material The analysis of the electrostatic potential and work function determined the highly active sites and electron release capacity. In addition, the adsorption energy and distance disclosed the gas-solid interface structure of multiple gases on the Ir/Pd/Pt/Rh-C2N1 monolayer. Importantly, C2H2 exhibits strong responses to p-type semiconductor Pt-C2N1 and n-type semiconductor Ir-C2N1, respectively. Crystal Orbital Hamilton Population reveals the difference in adsorption energy due to modifications involving four precious metals. Interestingly, for the first time, the density of states calculation reveals that under the coexistence of multiple gases, the Pt/Ir-C2N1 monolayer effectively eliminates the interference of other gases and has a unique response only to C2H2. In real situations, with the basis of Gibbs free energy and Einstein's law of diffusion, it was determined that Pt-C2N1 and Ir-C2N1 showed excellent hydrophobicity, a wider temperature range, and a low diffusion activation energy barrier. In summary, Pt-C2N1 and Ir-C2N1 detect C2H2 without interference, maintaining fundamental principles, responsiveness, stability, and versatility unaffected by external factors.

Single Atom Catalyst Anchored on Nitrogen-Doped Porous Carbon As an Effective Sulfur Host for Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are considered highly promising for next-generation energy storage due to their high theoretical specific capacity and energy density. However, challenges such as the insulating nature of sulfur cathodes, the detrimental shuttle effect of lithium polysulfides (LiPSs), and sluggish conversion kinetics of LiPSs during charge/discharge cycles impede their commercial viability. In this study, we employed a facile ‘dissolution-carbonization’ approach to synthesize nitrogen-coordinated monometallic atomic catalysts anchored on mesoporous carbon to promote surface-mediated reactions of LiPSs. The hierarchical porous carbon support physically confines the sulfur species, while the introduction of single atoms efficiently captures polysulfide intermediates and facilitates their redox conversion kinetics with a lower activation energy barrier. The synergistic effect of the single atom and nitrogen-rich porous carbon (NC) significantly enhances reaction kinetics and sulfur species utilization. Consequently, LSBs incorporating single-atom catalysts (SACs) demonstrate remarkable performance metrics, including high-capacity retention (824.2 mAh g−1), superior Coulombic efficiency (>98.5%), low-capacity decay rate (0.042% per cycle) after 500 cycles at 1 C, and excellent rate capability (776 mA h g–1 at 3 C). This work presents an effective strategy that combines the functions of a nanoporous material host and SACs for lithium-sulfur batteries.

Mechanistic investigation of methanol-to-olefins conversion catalyzed by H-ZSM-5 zeolite: a DFT study.

The mechanisms for the formation of the first C - C bond and lower olefins on methanol to olefins (MTO) conversion on H-ZSM-5 had been focused in dispute. In this paper, density functional theory has been used to study the reaction mechanisms of methanol to olefins on ZSM-5. The configurations of reactants, intermediates, products and transition state of the numerous reactions involved in such a process have been optimized, as well as the elementary reactions related to these configurations were determined by the calculation of corresponding activation energy barriers and reaction heats. Here, two different kinds of the mechanisms were proposed for the formation of dimethylether (DME), one involving an associative interaction of two methanol molecules with the zeolite Brønsted acid sites and the other occurring via a surface methoxy species and a methanol molecule. A critical intermediate of the methoxy methyl cation was theoretically verified by the reaction of the methoxy species and dimethylether. Besides, it was found that the first intermediates containing a C - C bond were 1,2-dimethoxyethane and 2-methoxy-ethanolare, in which the former was formed from methoxy species with dimethyl ether and the latter was formed from methanol by onium ions((CH3)2O+CH2CH2OCH3), respectively. For the whole reaction mechanism, the results in this paper indicated that the ethene formation is more favorable than propylene formation due to the low activation energy barrier for ethene formation (123.49 vs. 162.09kJ.mol-1). From these calculations, it would be concluded that ethene is the first alkene product that induces the occurrence of the hydrocarbon pool mechanism. All the periodic density function theory (DFT) calculations were performed by the Vienna Ab Initio Simulation package (VASP). The interaction between nucleus and valence electron was described using the pseudopotentials found in the projector augmented wave (PAW) method. PBE-D3 was used in the whole DFT calculations and CI-NEB was used to locate transition state.

Mullite Mineral-Derived Robust Solid Electrolyte Enables Polyiodide Shuttle-Free Zinc-Iodine Batteries.

Zinc dendrite, active iodine dissolution, and polyiodide shuttle caused by the strong interaction between liquid electrolyte and solid electrode are the chief culprits for the capacity attenuation of aqueous zinc-iodine batteries (ZIBs). Herein, mullite is adopted as raw material to prepare Zn-based solid-state electrolyte (Zn-ML) for ZIBs through zinc ion exchange strategy. Owing to the merits of low electronic conductivity, low zinc diffusion energy barrier, and strong polyiodide adsorption capability, Zn-ML electrolyte can effectively isolate the redox reactions of zinc anode and AC@I2 cathode, guide the reversible zinc deposition behavior, and inhibit the active iodine dissolution as well as polyiodide shuttle during cycling process. As expected, wide operating voltage window of 2.7V (vs Zn2+/Zn), high Zn2+ transference number of 0.51, and low activation energy barrier of 29.7kJ mol-1 can be achieved for the solid-state Zn//Zn cells. Meanwhile, high reversible capacity of 127.4 and 107.6 mAh g-1 can be maintained at 0.5 and 1 A g-1 after 3000 and 2100 cycles for the solid-state Zn//AC@I2 batteries, corresponding to high-capacity retention ratio of 85.2% and 80.7%, respectively. This study will inspire the development of mineral-derived solid electrolyte, and facilitate its application in Zn-based secondary batteries.

Study on the key factors affecting the aerosol release characteristics of closed-ended heated tobacco products: 1. Heating temperature

Two Heated Tobacco Products (HTPs) with different airflow pathways were tested in this study to give insight into the aerosol formation and transfer. One permit the puffing air to flow through the tobacco rod and known as the open-ended system, while the other one sealed the tobacco rod and known as the closed-ended system. Results showed that in both systems, with the heating temperature rising, the aerosol transfer rates of nicotine, 1,2-propylene glycol (PG), and glycerol (VG) increased linearly, meanwhile the residual rates in the tobacco section decreased exponentially. In particular, lower residual rates of nicotine and PG were observed in the closed-ended system compared to open-ended system from 200 to 300 ℃, indicating a higher releasing efficiency in close-ended system. However, higher aerosol transfer rates of nicotine in the closed-ended system were noted merely among 200–260 ℃. Additionally, the transfer rates for PG remained basically the same in both systems. For nicotine, the closed-ended system exhibited lower retention rates between 200 and 240 ℃, but reversed between 260 and 300 ℃. Furthermore, the closed-ended system showed significantly higher retention rates for PG compared to the open-ended system from 200 to 300 ℃. Regarding puff-by-puff aerosol release pattern, both systems showed similar trend of increase-decrease for the same key component at identical temperature. While the single-puff release amount differed between them, for example, 3.8 mg for close-ended and 3.0 mg for open-ended of water at the second puff. Furthermore, apparent release kinetics parameters were obtained based on the first-order reaction kinetic model and the Arrhenius Equation. In the closed-ended system, lower activation energy of nicotine (26.255 KJ·mol−1 compared to 34.896 KJ·mol−1 in open-ended) resulted in lower activation energy barrier, and therefore a more efficient release and transfer rate for nicotine.

Highly selective regulation of non-radical and radical mechanisms by Co cubic assembly catalysts for peroxymonosulfate activation

Peroxymonosulfate (PMS) activation on efficient catalysts is a promising strategy to produce sulfate radical (SO4−) and singlet oxygen (1O2) for the degradation of refractory organic pollutants. It is a great challenge to selectively generate these two reactive oxygen species, and the regulation mechanism from non-radical to radical pathway and vice versa is not well established. Here, we report a strategy to regulate the activation mechanism of PMS for the selective generation of SO4− and 1O2 with 100 % efficiency by sulfur-doped cobalt cubic assembly catalysts that was derived from the Co-Co Prussian blue analog precursor. This catalyst showed superior catalytic performance in activating PMS with normalized reaction rate increased by 87 times that of the commercial Co3O4 nanoparticles and had much lower activation energy barrier for the degradation of organic pollutant (e.g., p-chlorophenol) (18.32 kJ⋅mol−1). Experimental and theoretical calculation results revealed that S doping can regulate the electronic structure of Co active centers, which alters the direction of electron transfer between catalyst and PMS. This catalyst showed a strong tolerance to common organic compounds and anions in water, wide environmental applicability, and performed well in different real-water systems. This study provides new opportunities for the development of metal catalyst with metal-organic frameworks structure and good self-regeneration ability geared specifically towards PMS-based advanced oxidation processes applied for water remediation.

Accelerating Anhydrous Proton Transport in Covalent Organic Frameworks: Pore Chemistry and its Impacts

AbstractProton conduction is important in both fundamental research and technological development. Here we report designed synthesis of crystalline porous covalent organic frameworks as a new platform for high‐rate anhydrous proton conduction. By developing nanochannels with different topologies as proton pathways and loading neat phosphoric acid to construct robust proton carrier networks in the pores, we found that pore topology is crucial for proton conduction. Its effect on increasing proton conductivity is in an exponential mode other than linear fashion, endowing the materials with exceptional proton conductivities exceeding 10−2 S cm−1 over a broad range of temperature and a low activation energy barrier down to 0.24 eV. Remarkably, the pore size controls conduction mechanism, where mesopores promote proton conduction via a fast‐hopping mechanism, while micropores follow a sluggish vehicle process. Notably, decreasing phosphoric acid loading content drastically reduces proton conductivity and greatly increases activation energy barrier, emphasizing the pivotal role of well‐developed proton carrier network in proton transport. These findings and insights unveil a new general and transformative guidance for designing porous framework materials and systems for high‐rate ion conduction, energy storage, and energy conversion.

Accelerating Anhydrous Proton Transport in Covalent Organic Frameworks: Pore Chemistry and its Impacts.

Proton conduction is important in both fundamental research and technological development. Here we report designed synthesis of crystalline porous covalent organic frameworks as a new platform for high-rate anhydrous proton conduction. By developing nanochannels with different topologies as proton pathways and loading neat phosphoric acid to construct robust proton carrier networks in the pores, we found that pore topology is crucial for proton conduction. Its effect on increasing proton conductivity is in an exponential mode other than linear fashion, endowing the materials with exceptional proton conductivities exceeding 10-2 S cm-1 over a broad range of temperature and a low activation energy barrier down to 0.24 eV. Remarkably, the pore size controls conduction mechanism, where mesopores promote proton conduction via a fast-hopping mechanism, while micropores follow a sluggish vehicle process. Notably, decreasing phosphoric acid loading content drastically reduces proton conductivity and greatly increases activation energy barrier, emphasizing the pivotal role of well-developed proton carrier network in proton transport. These findings and insights unveil a new general and transformative guidance for designing porous framework materials and systems for high-rate ion conduction, energy storage, and energy conversion.

High-Voltage Long-Cycling All-Solid-State Lithium Batteries with High-Valent-Element-Doped Halide Electrolytes.

All-solid-state batteries (ASSBs) have garnered considerable attention as promising candidates for next-generation energy storage systems due to their potentially simultaneously enhanced safety capacities and improved energy densities. However, the solid future still calls for materials with high ionic conductivity, electrochemical stability, and favorable interfacial compatibility. In this study, we present a series of halide solid-state electrolytes (SSEs) utilizing a doping strategy with highly valent elements, demonstrating an outstanding combination of enhanced ionic conductivity and oxidation stability. Among these, Li2.6In0.8Ta0.2Cl6 emerges as the standout performer, displaying a superionic conductivity of up to 4.47 mS cm-1 at 30 °C, along with a low activation energy barrier of 0.321 eV for Li+ migration. Additionally, it showcases an extensive oxidation onset of up to 5.13 V (vs Li+/Li), enabling high-voltage ASSBs with promising cycling performance. Particularly noteworthy are the ASSBs employing LiCoO2 cathode materials, which exhibit an extended cyclability of over 1400 cycles, with 70% capacity retention under 4.6 V (vs Li+/Li), and a capacity of up to 135 mA h g-1 at a 4 C rate, with the loading of active materials at 7.52 mg cm-2. This study demonstrates a feasible approach to designing desirable SSEs for energy-dense, highly stable ASSBs.

TiO2 thermal stress deformation induced to promote photocatalytic CO2 reduction

Semiconductor photocatalytic reduction of CO2 is an effective means to achieve the goal of double carbon. TiO2 has received extensive attention as an excellent photocatalyst, but the adsorption of CO2 on the surface of TiO2 is not stable, which greatly inhibits the yield and selectivity of reduction products. In this work, wollastonite was used to reduce the melting temperature of TiO2 and in turn induce thermal stress deformation on the surface of the TiO2 lattice. Characterization and DFT results certified that the lattice stress deformation caused by the contraction of oxygen vacancy enables TiO2 to obtain better carrier transport efficiency and lower activation energy barrier, and also stabilizes the adsorption state of CO2 on the surface of TiO2 crystal, which effectively improved the reduction yield and selectivity of CO2. The CO yield is increased by 5.1 times, reaching up to 2.09 μmolg-1h−1, and the CO selectivity is as high as 91 %. These findings provide valuable insights for the development of efficient and selective photocatalysts for carbon dioxide transformation and pave the way for novel avenues in this research field.

Direct and efficient catalytic conversion of biomass-derived 2-methyltetrahydrofuran to 1,3-pentadiene via acid-base coupling of lanthanum phosphate

It is critical to increase the reaction selectivity and atom economy, avoid side reactions during the catalytic process, and achieve the desired single-target product. Here, an efficient and novel method of producing 1,3-pentadiene via the acid-base coupling of rare-earth phosphate-catalyzed dehydra-decyclization of 2-methyltetrahydrofuran (2-MTHF) is reported, resulting in a previously unreported 1,3-pentadiene yield of 97.2% at 350 ℃. This method efficiently addresses two significant problems encountered in the dehydra-decyclization of 2-MTHF to generate 1,3-pentadiene research: the occurrence of retro-Prins condensation and the competitive reaction of 1,4-pentadiene. Density-Functional-Theory calculations demonstrated that 2-MTHF was adsorbed on the surface of rare-earth phosphate catalysts in a multi-site parallel mode, resulting in a lower apparent activation energy and ring-opening energy barrier. Space-time investigations and in situ diffuse reflectance infrared Fourier transform spectroscopy provided evidence for direct synthesis of pentadiene on rare-earth phosphate catalysts with Lewis acid-base sites. The acid-base coupling catalysis was demonstrated by poisoning experiments. In-situ self-regeneration of Brønsted acid sites was confirmed by infrared spectroscopy of adsorbed pyridine, facilitating the isomerization of 1,4-pentadiene to 1,3-pentadiene. Therefore, a unique reaction pathway for the dehydra-decyclization of 2-MTHF on the surface of rare-earth phosphates was proposed, and a new rotational isomer was discovered.

Dearomative [2 + 1] Spiroannulation of Bromophenols with Electron-Deficient Alkenes.

A base-assisted dearomative [2 + 1] spiroannulation of p/o-bromophenols with activated olefins (methylenemalonates) to construct various cyclopropyl spirocyclohexadienone skeletons is reported. Furthermore, several other halophenols (X = Cl, I) were also tolerated in this process. Control experiments reveal a dearomative Michael addition of phenols at their halogenated positions to methylenemalonates, followed by intramolecular radical-based SRN1 dehalogenative cyclopropanation. However, according to the density functional theory (DFT) calculations, an SN2 dehalogenative cyclopropanation with the same low activation energy barrier should not be excluded. The utility of this method is showcased by gram-scale syntheses and transformations of the dearomatized products.

Synergetic Manipulation Mechanism of Single-Atom M-N4 and M-OH (M = Mn, Fe, Co, Ni) Sites for Ozone Activation: Theoretical Prediction and Experimental Verification.

Carbon-based single-atom catalysts (SACs) have been gradually introduced in heterogeneous catalytic ozonation (HCO), but the interface mechanism of O3 activation on the catalyst surface is still ambiguous, especially the effect of a surface hydroxyl group (M-OH) at metal sites. Herein, we combined theoretical calculations with experimental verifications to comprehensively investigate the O3 activation mechanisms on a series of conventional SAC structures with N-doped nanocarbon substrates (MN4-NCs, where M = Mn, Fe, Co, Ni). The synergetic manipulation effect of the metal atom and M-OH on O3 activation pathways was paid particular attention. O3 tends to directly interact with the metal atom on MnN4-NC, FeN4-NC, and NiN4-NC catalysts, among which MnN4-NC has the best catalytic activity for its relatively lower activation energy barrier of O3 (0.62 eV) and more active surface-adsorbed oxygen species (Oads). On the CoN4-NC catalyst, direct interaction of O3 with the metal site is energetically infeasible, but O3 can be activated to generate Oads or HO2 species from direct or indirect participation of M-OH sites. The experimental results showed that 90.7 and 82.3% of total organic carbon (TOC) was removed within 40 min during catalytic ozonation of p-hydroxybenzoic acid with MnN4-NC and CoN4-NC catalysts, respectively. Phosphate quenching, catalyst characterization, and EPR measurement further supported the theoretical prediction. This contribution provides fundamental insights into the O3 activation mechanism on SACs, and the methods and ideals could be helpful for future studies of environmental catalysis.

Mechanistic insights into the incorporation of higher alpha-olefins into acrylate copolymers via photoATRP

Visible light-driven SR & NI photoATRP with CuIIBr2/L yielded acrylate-α-olefin copolymers (Đ ≤ 1.13) incorporating up to 30% α-olefins. DFT revealed low activation energy barriers (14.3 kcal mol−1 and 17.8 kcal mol−1) for PCA2 and PCB2 formation.

Advancing Gold Redox Catalysis: Mechanistic Insights, Nucleophilicity-Guided Transmetalation, and Predictive Frameworks for the Oxidation of Aryl Gold(I) Complexes.

Gold redox catalysis, often facilitated by hypervalent iodine(III) reagents, offers unique reactivity but its progress is mainly hindered by an incomplete mechanistic understanding. In this study, we investigated the reaction between the gold(I) complexes [(aryl)Au(PR3 )] and the hypervalent iodine(III) reagent PhICl2 , both experimentally and computationally and provided an explanation for the formation of divergent products as the ligands bonded to the gold(I) center change. We tackled this essential question by uncovering an intriguing transmetalation mechanism that takes place between gold(I) and gold(III) complexes. We found that the ease of transmetalation is governed by the nucleophilicity of the gold(I) complex, [(aryl)Au(PR3 )], with greater nucleophilicity leading to a lower activation energy barrier. Remarkably, transmetalation is mainly controlled by a single orbital - the gold dx 2 -y 2 orbital. This orbital also has a profound influence on the reactivity of the oxidative addition step. In this way, the fundamental mechanistic basis of divergent outcomes in reactions of aryl gold(I) complexes with PhICl2 was established and these observations are reconciled from first principles. The theoretical model developed in this study provides a conceptual framework for anticipating the outcomes of reactions involving [(aryl)Au(PR3 )] with PhICl2 , thereby establishing a solid foundation for further advancements in this field.

Unlocking power of neighboring vacancies in boosting hydrogen evolution reactions on two-dimensional NiPS3 monolayer

This study investigates the effect of defect engineering on the catalytic activity of a NiPS3 monolayer catalyst for the hydrogen evolution reaction (HER). Three different types of vacancies on the basal plane of the monolayer are explored through a multi-step mechanism involving the dissociative adsorption of a water molecule and subsequent electrochemical adsorption of the dissociated proton. Co-formation of vacancies in both Ni and S sites is found to be the most effective in enhancing the catalytic performance of the monolayer. A key resource for the reaction thermodynamics is the S-substitution-like physisorption of a water molecule on a vacant S site, followed by the dissociative occupation of OH and H into vacant sites of S and Ni elements, boosted by the NiS di-vacancy configuration with low activation energy barriers. Investigation reveals the highest contribution of bonding orbitals to the monolayer-H bond makes it the most desirable defect engineering approach for transition metal phosphorus chalcogenides with high HER activities. Overall, this study highlights the significance of controlled defect engineering in augmenting the catalytic performance of NiPS3 monolayer catalysts for HER.

Contributions of CO2, O2, and H2O to the Oxidative Stability of Solid Amine Direct Air Capture Sorbents at Intermediate Temperature.

Aminopolymer-based sorbents are preferred materials for extraction of CO2 from ambient air [direct air capture (DAC) of CO2] owing to their high CO2 adsorption capacity and selectivity at ultra-dilute conditions. While those adsorptive properties are important, the stability of a sorbent is a key element in developing high-performing, cost-effective, and long-lasting sorbents that can be deployed at scale. Along with process upsets, environmental components such as CO2, O2, and H2O may contribute to long-term sorbent instability. As such, unraveling the complex effects of such atmospheric components on the sorbent lifetime as they appear in the environment is a critical step to understanding sorbent deactivation mechanisms and designing more effective sorbents and processes. Here, a poly(ethylenimine) (PEI)/Al2O3 sorbent is assessed over continuous and cyclic dry and humid conditions to determine the effect of the copresence of CO2 and O2 on stability at an intermediate temperature of 70 °C. Thermogravimetric and elemental analyses in combination with in situ horizontal attenuated total reflection infrared (HATR-IR) spectroscopy are performed to measure the extent of deactivation, elemental content, and molecular level changes in the sorbent due to deactivation. The thermal/thermogravimetric analysis results reveal that incorporating CO2 with O2 accelerates sorbent deactivation using these sorbents in dry and humid conditions compared to that using CO2-free air in similar conditions. The in situ HATR-IR spectroscopy results of PEI/Al2O3 sorbent deactivation under a CO2-air environment show the formation of primary amine species in higher quantity (compared to that in conditions without O2 or CO2), which arises due to the C-N bond cleavage at secondary amines due to oxidative degradation. We hypothesize that the formation of bound CO2 species such as carbamic acids catalyzes C-N cleavage reactions in the oxidative degradation pathway by shuttling protons, resulting in a low activation energy barrier for degradation, as probed by metadynamics simulations. In the cyclic experiment after 30 cycles, results show a gradual loss in stability (dry: 29%, humid: 52%) under CO2-containing air (0.04% CO2/21% O2 balance N2). However, the loss in capacity during cyclic studies is significantly less than that during continuous deactivation, as expected.

CO2 methanation over Ni nanoparticles inversely loaded with CeO2 and Cr2O3: Catalytic functions of metal oxide/Ni interfaces

Interfaces between active metal and metal oxide in a heterogenous catalyst often play an important role in catalysis. In this work, we intentionally synthesized a series of inverse CeO2-Cr2O3/Ni model catalysts with the formation of controlled CeO2-Ni and Cr2O3-Ni interfacial structures and investigated the roles of the oxide-metal interfaces in CO2 methanation performance through excluding the normal support effect. Experimental and DFT calculation results reveal that the formate pathway tends to occur on the catalyst with only CeO2-Ni interfaces. The Cr2O3-Ni interface formed after introducing Cr oxide alters the nearby CeO2-Ni interface by electron transfer through Ni, which brings an additional reaction pathway (CO pathway) on CeO2-Cr2O3/Ni. Furthermore, it shows a relatively lower CO2 absorption energy and activation energy barrier for CO2 dissociation to CO at the Cr2O3-Ni interface, favorable for CO2 activation and further hydrogenation, thus leading to excellent low-temperature activity.