Zhenhua Xie

The direct conversion of methane to aromatics offers a promising route for liquefying natural gas and biogas, thereby generating higher-value chemicals and reducing transportation costs. However, conventional methane dehydroaromatization (MDA) is severely hindered by thermodynamic limitations, high temperature requirements, and catalyst instability. Here, we report a tandem chemical looping catalysis strategy that integrates chemical looping oxidative coupling of methane (CL-OCM) with dehydroaromatization (DHA), overcoming these challenges. The CL-OCM route generates more readily convertible C2+ intermediates while consuming hydrogen, the equilibrium-limiting byproduct, as water. This shifts the equilibrium and renders the overall reaction exothermic, achieving a single-pass aromatic yield of 27.1%, 2.5 to 3 times the single-pass yields of conventional MDA. Independent regeneration of the two catalyst beds maintains stable performance over repeated reaction-regeneration cycles. Process analysis projects ~75% lower levelized costs and ~77% lower cradle-to-gate emissions than direct MDA.

Pt-based electrocatalysts are effective for the hydrogen evolution reaction (HER); however, their limited ability to facilitate water dissociation and suboptimal hydrogen binding energy (HBE) in alkaline electrolytes result in slow reaction kinetics, which hinders their cost-efficiency and practical applications. This study reports the synthesis of Co2P-Pt heterostructure nanorods using a seed-mediated growth method, producing a high density of Co2P-Pt interfacial sites. Density functional theory (DFT) calculations indicate that electronic interactions at these interfaces optimize HBE on Pt, while the interfacial sites promote water dissociation. The Co2P-Pt nanorods demonstrate an overpotential of 14 mV at 10 mA cm−2 for the HER, highlighting the potential of precisely engineered metal-metal phosphide interfaces for enhancing electrocatalytic efficiency.

Plastic hydrogenolysis is an attractive approach for producing value-added chemicals due to its mild reaction conditions, but controlling product distribution is challenging due to the formation of undesired CH_4. This work reports several bimetallic RuM₃/CeO₂ (M = Fe, Co, Ni) catalysts that shift the product of low-density polyethylene hydrogenolysis toward longer-chain hydrocarbons. These catalysts were characterized by using X-ray absorption fine structure spectroscopy, electron microscopy imaging, and H₂ temperature-programmed reduction. The combined catalytic evaluation and characterization results revealed that the product distribution was regulated by the formation of bimetallic alloys. A model compound, n-hexadecane, was selected to further understand the differences in hydrogenolysis over the Ru-based catalysts. Although a longer reaction time shifted the product toward smaller molecules, the bimetallic (RuCo₃/CeO₂) catalyst limited the further conversion of C2-C5 into CH₄. This work highlights the role of bimetallic alloys in tailoring the interaction with hydrocarbons, thereby controlling the product distribution of polymer hydrogenolysis.

ConspectusIn recent years, the simultaneous upgrading of CO₂ and ethane has emerged as a promising approach for generating valuable gaseous (CO, H₂, and ethylene) and liquid (aromatics and C3 oxygenates) chemicals from the greenhouse gas CO₂ and large-reserved shale gas. The key challenges for controlling product selectivity lie in the selective C-H and C-C bond cleavage of ethane with the assistance of CO₂. Bimetallic-derived catalysts likely undergo alloying or oxygen-induced segregation under reaction conditions, thus providing diverse types of interfacial sites, e.g., metal/support (M/M'O_x) interface and metal oxide/metal (M'O_x/M) inverse interface, that are beneficial for selective CO₂-assisted ethane upgrading. The alloying extent can be initially predicted by cohesive energy and atomic radius (or Wigner-Seitz radius), while the preference for segregation to form the on-top suboxide can be approximated using the work function, electronegativity, and binding strength of adsorbed oxygen. Furthermore, bimetallic-derived catalysts are typically supported on high surface area oxides. Modifying the reducibility and acidity/basicity of the oxide supports and introducing surface defects facilitate CO₂ activation and oxygen supplies for ethane activation.Using in situ synchrotron characterization and density functional theory (DFT) calculations, we found that the electronic properties of oxygen species influence the selective cleavage of C-H/C-C bonds in ethane, with electron-deficient oxygen over the metal (or alloy) surface promoting nonselective bond scission to produce syngas and electron-enriched oxygen over the metal oxide/metal interface enhancing selective C-H scission to yield ethylene. We further demonstrate that the preferred structures of the catalyst surfaces, either alloy surfaces or metal oxide/metal inverse interfaces, can be controlled through the appropriate choice of metal combinations and their atomic ratios. Through a comprehensive comparison of experimental results and DFT calculations, the selectivity of C-C/C-H bond scission is correlated with the thermodynamically favorable bimetallic-derived structures (i.e., alloy surfaces or metal oxide/metal inverse interfaces) under reaction conditions over a wide range of bimetallic catalysts. These findings not only offer structural and mechanistic insights into bimetallic-derived catalysts but also provide design principles for selective catalysts for CO₂-assisted activation of ethane and other light alkanes. This Account concludes by discussing challenges and opportunities in designing advanced bimetallic-derived catalysts, incorporating new reaction chemistries for other products, employing precise synthesis strategies for well-defined structures with optimized site densities, and leveraging time/spatial/energy-resolved in situ spectroscopy/scattering/microscopy techniques for comprehensive structural analysis. The research methodologies established here are helpful for the investigation of dynamic alloy and interfacial structures and should inspire more efforts toward the simultaneous upgrading of CO₂ and shale gas.

Electroreduction of carbon dioxide (CO ₂ ) or carbon monoxide (CO) toward C ₂₊ hydrocarbons such as ethylene, ethanol, acetate and propanol represents a promising approach toward carbon-negative electrosynthesis of chemicals. Fundamental understanding of the carbon─carbon (C-C) coupling mechanisms in these electrocatalytic processes is the key to the design and development of electrochemical systems at high energy and carbon conversion efficiencies. Here, we report the investigation of CO electreduction on single-atom copper (Cu) electrocatalysts. Atomically dispersed Cu is coordinated on a carbon nitride substrate to form high-density copper─nitrogen moieties. Chemisorption, electrocatalytic, and computational studies are combined to probe the catalytic mechanisms. Unlike the Langmuir-Hinshelwood mechanism known for copper metal surfaces, the confinement of CO adsorption on the single-copper-atom sites enables an Eley-Rideal type of C-C coupling between adsorbed (*CO) and gaseous [CO(g)] carbon moxide molecules. The isolated Cu sites also selectively stabilize the key reaction intermediates determining the bifurcation of reaction pathways toward different C ₂₊ products.

A hybrid catalyst with integrated single-atom Ni and nanoscale Cu catalytic components is reported to enhance the C-C coupling and ethylene (C₂H₄) production efficiency in the electrocatalytic CO₂ reduction reaction (eCO₂RR). The single-atom Ni anchored on high-surface-area ordered mesoporous carbon enables high-rate and selective conversion of CO₂ to CO in a wide potential range, which complements the subsequent CO enrichment on Cu nanowires (NWs) for the C-C coupling to C₂H₄. In situ surface-enhanced infrared absorption spectroscopy (SEIRAS) confirms the substantially improved CO enrichment on Cu, once the incorporation of single-atom Ni occurs. Also, in situ X-ray absorption near-edge structure (XANES) demonstrates the structural stability of the hybrid catalyst during eCO₂RR. By modulating hybrid compositions, the optimized catalyst shows 66% Faradaic efficiency (FE) in an alkaline flow cell with over 100 mA·cm^-2 at -0.5 V versus reversible hydrogen electrode, leading to a five-order enhancement in C₂H₄ selectivity compared with single-component Cu NWs.