Cooperative Catalysis of Vibrationally Excited CO2 and Alloy Catalyst Breaks the Thermodynamic Equilibrium Limitation

Layered Na2Ti3O7-supported Ru catalyst for ambient CO2 methanation

The methanation of CO2 offers a practical solution for storing renewable energy and mitigating global climate risks. However, the primary challenge lies in achieving efficient CH4 production at lower temperatures. Here, we report a layered Na2Ti3O7-supported Ru catalyst as a stabilizer of low-valence Ru that enables CO2 activation at low temperatures. This catalyst leads to a CH4 production rate of 33.6 and 139.1 mmol gcat-1 h-1 at 140 and 180 °C, respectively, with a gas hourly space velocity of 24,000 mL g-1 h-1 at ambient pressure (1 bar), significantly surpassing state-of-the-art catalysts performance. Moreover, the catalyst demonstrates robustness to on-off intermittency and 220-hour long-term stability tests, indicating its reliability under challenging conditions. The catalyst is also successfully synthesized at the gram scale and on a 3D-printed metal self-catalytic reactor by a facile ion-exchange method, confirming its excellent scalability. This study marks a significant step forward in the design of catalysts for the low temperature CO2 hydrogenation.

Plasma-Derived Atomic Hydrogen Enables Eley-Rideal-Type CO2 Methanation at Low Temperatures

Activating H2 molecules into atomic hydrogen and utilizing their intrinsic chemical reactivity are important processes in catalytic hydrogenation. Here, we have developed a plasma-catalyst combined system that directly provides atomic hydrogen from the gas phase to the catalytic reaction to utilize the high energy and translational freedom of atomic hydrogen. In this system, we show that the temperature of CO2 methanation over Ni/Al2O3 can be dramatically lower compared to thermal catalysis. Using a detailed mechanistic study with kinetic studies, laser plasma diagnostics, in situ plasma surface characterization, and theoretical calculations, we revealed that plasma-derived atomic hydrogen (PDAH) plays a crucial role in reaction promotion. In particular, PDAH effectively lowers the energy barrier of bidentate formate hydrogenation by translating from the Langmuir-Hinshelwood to the Eley-Rideal-type reaction.

Designing Carbon-Foam Composites via Molten-State Reduction for Multifunctional Electromagnetic Interference Shielding

Advanced electromagnetic interference (EMI) shielding materials are in great demand because of the severe electromagnetic population problem caused by the explosive growth of advanced electronics. Besides superior EMI shielding properties, the mechanical strength of the shielding materials is also critical for some specific application scenarios (e.g., shielding cases and shielding frames). Although most reported EMI shielding materials possess good shielding properties and lightweight characteristics, they usually exhibit a poor mechanical strength. Concurrently, multifunctionality is also essential for the application of the EMI shielding material. This study develops a molten-state-based in situ reduction strategy to fabricate an efficient EMI shielding composite, enabling the uniform dispersion of Co-nanoparticles on the carbon form matrix while featuring a high density of defects. This ensures the high mechanical strength of the composite due to the presence of a huge interface and significantly enhances the EMI shielding performance. The composite achieves an optimal shielding effectiveness of 32.6 dB and compressive strength of 38.31 MPa, respectively, improved by 65.4 and 123.4% compared to the pristine carbon foam. Simultaneously, the composite also exhibits desirable electrochemical and photothermal conversion properties. This research offers insights into the design of composites that excel in electromagnetic interference shielding, mechanical robustness, and multifunctionality.

Plasma-Driven Conversion of 2D Graphene into 3D Pouch for Improved Electromagnetic Absorption Performance

Graphene-based materials are ideal for electromagnetic wave-absorbing materials (EAMs) due to their strong electrical and dielectric losses with reduced thickness and weight. To enhance the electromagnetic wave absorption performance of these materials, additional components are often incorporated. However, this approach not only increases the complexity of the synthesis process but also complicates and destabilizes the control of the material properties. In this study, we successfully employed a one-step method to reduce graphene oxide and transform 2D graphene into a 3D pocket-like structure through plasma treatment. This unique 3D structure is induced by the formation of uneven defects on the surface due to plasma treatment. The distinctive pouch-like structure of the reduced graphene oxide achieved remarkable electromagnetic wave absorption properties. Specifically, the material demonstrated a minimum reflection loss of -38.65 dB at 7.14 GHz, with an effective absorption bandwidth of 5.13 GHz and a thickness of just 1.9 mm. These results highlight the potential of plasma processing as a rapid, efficient, and environmentally friendly approach for the continuous production of advanced EAMs, paving the way for greener manufacturing practices in the industry.

Nonthermal Plasma Activation of Adsorbates: The Case of CO on Pt

Nonthermal plasmas provide a unique approach to electrically driven heterogeneous catalytic processes. Despite much interest from the community, fundamental activation pathways in these processes remain poorly understood. Here, we investigate how exposure to a nonthermal plasma sustained in an argon nonreactive atmosphere affects the desorption of carbon monoxide (CO) from platinum nanoparticles. Temperature-programmed desorption measurements indicate that the plasma reduces the effective binding energy (BE) of CO to Pt surfaces by as much as ∼0.3 eV, with the reduction in the BE scaling linearly with the plasma density. We find that the effective CO BE is most strongly reduced for under-coordinated sites (steps and edges) compared to well-coordinated sites (terraces). Density functional theory calculations suggest that this is due to plasma-induced charging and electric fields at the catalyst surface, which preferentially affect under-coordinated sites. This study provides direct experimental evidence of plasma-induced nonthermal activation of the adsorbate-catalyst couple.

Plasma Chemical Looping: Unlocking High-Efficiency CO2 Conversion to Clean CO at Mild Temperatures

We propose a plasma chemical looping CO2 splitting (PCLCS) approach that enables highly efficient CO2 conversion into O2-free CO at mild temperatures. PCLCS achieves an impressive 84% CO2 conversion and a 1.3 mmol g-1 CO yield, with no O2 detected. Crucially, this strategy significantly lowers the temperature required for conventional chemical looping processes from 650 to 1000 °C to only 320 °C, demonstrating a robust synergy between plasma and the Ce0.7Zr0.3O2 oxygen carrier (OC). Systematic experiments and density functional theory (DFT) calculations unveil the pivotal role of plasma in activating and partially decomposing CO2, yielding a mixture of CO, O2/O, and electronically/vibrationally excited CO2*. Notably, these excited CO2* species then efficiently decompose over the oxygen vacancies of the OCs, with a substantially reduced activation barrier (0.86 eV) compared to ground-state CO2 (1.63 eV), contributing to the synergy. This work offers a promising and energy-efficient pathway for producing O2-free CO from inert CO2 through the tailored interplay of plasma and OCs.

Generation of High-Lying Vibrational States in Carbon Dioxide through Coherent Ladder Climbing

Mid-infrared laser excitation of molecules into high-lying vibrational states offers a novel route to realize controlled ground-state chemistry. Here we successfully demonstrate vibrational ladder climbing in the antisymmetric stretch of CO2 in the condensed phase by using intense down-chirped mid-infrared pulses. Spectrally resolved pump-probe measurements directly observe excited-state absorptions attributed to vibrational populations up to the v = 9 state, whose corresponding energy of 2.5 eV is 46% of the dissociation energy. By the use of global fitting analysis, important spectroscopic parameters in the high-lying vibrational states, such as transition frequencies and relaxation times, are quantitatively characterized. Remarkably, our analysis shows that 40% of the molecules are excited above the typical activation barriers in the metal-catalyzed CO2 conversions. These results not only demonstrate the promising ability of infrared excitation to produce elevated vibrational states but also represent a significant step toward accelerating CO2 conversions and other chemical processes via mode-specific vibrational excitation.

Using Surface-Enhanced Raman Spectroscopy to Probe Surface-Localized Nonthermal Plasma Activation

Low-temperature, nonthermal plasmas generate a complex environment even when operated in nonreactive gases. Plasma-produced species impinge on exposed surfaces, and their thermalization is highly localized at the surface. Here we present a Raman thermometry approach to quantifying the resulting degree of surface heating. A nanostructured silver substrate is used to enhance the Raman signal and make it easily distinguishable from the background radiation from the plasma. Phenyl phosphonic acid is used as a molecular probe. Even under moderate plasma power and density, we measure a significant degree of vibrational excitation for the phenyl group, corresponding to an increase in surface temperature of ∼80 °C at a plasma density of 2 × 1010 cm-3. This work confirms that surface-localized thermal effects can be quantified in low-temperature plasma processes. Their characterization is needed to improve our understanding of the plasma-induced activation of surface reactions, which is highly relevant for a broad range of plasma-driven processes.