Cobalt catalyzed ethane dehydrogenation to ethylene with CO2: Relationships between cobalt species and reaction pathways

TiO2, ZrO2 and a series of TiO2-ZrO2 (TxZ1, x means the atomic ratio of Ti/Zr = 10, 5, 1, 0.2 and 0.1) composite oxide supports were prepared through co-precipitation, and then 3 wt% Co was loaded through wetness impregnation methods. The obtained 3 wt% Co/TiO2 (3CT), 3 wt% Co/ZrO2 (3CZ) and 3 wt% Co/TxZ1 (3CTxZ1) catalysts were evaluated for the oxidative ethane dehydrogenation reaction with CO2 (CO2-ODHE) as a soft oxidant. 3CT1Z1 catalyst exhibits excellent catalytic properties, with C2H4 yield, C2H6 conversion and CO2 conversion about 24.5 %, 33.8 % and 18.0 % at 650 °C, respectively. X-Ray Diffraction (XRD), in-situ Raman, UV-vis diffuse reflectance spectra (UV-vis DRS), H2 temperature-programmed reduction (H2-TPR), Electron paramagnetic resonance (EPR) and quasi in-situ X-ray Photoelectron Spectroscopy (XPS) have been utilized to thoroughly characterize the investigated catalysts. The results revealed that 3CT1Z1 produced TiZrO4 solid solution with more metal defect sites and oxygen vacancies (Ov), promoting the formation of Co2+-TiZrO4 structure. Furthermore, the presence of Ov and Ti3+can facilitate the high dispersion and stabilization of Co2+, as well as suppressing the severe reduction of Co2+, leading to superior ethane oxidative dehydrogenation activity. Besides, less Co0 is beneficial to ODHE reaction, because of its promotion effects for reverse water gas shift reaction; however, more Co0 results in dry reforming reaction (DRE). This work will shed new lights for the design and preparation of highly efficient catalysts for ethylene production.

Engineering the Co(II)/Co(III) Redox Cycle and Coδ+ Species Shuttle for Nitrate-to-Ammonia Conversion

Electroreduction of waste nitrate to valuable ammonia offers a green solution for environmental restoration and energy storage. However, the electrochemical self-reconstruction of catalysts remains a huge challenge in terms of maintaining their stability, achieving the desired active sites, and managing metal leaching. Herein, we present an electrical pulse-driven Co surface reconstruction-coupled Coδ+ shuttle strategy for the precise in situ regulation of the Co(II)/Co(III) redox cycle on the Co-based working electrode and guiding the dissolution and redeposition of Co-based particles on the counter electrode. As result, the ammonia synthesis performance and stability are significantly promoted while cathodic hydrogen evolution and anodic ammonia oxidation in a membrane-free configuration are effectively blocked. A high rate of ammonia production of 1.4 ± 0.03 mmol cm-2 h-1 is achieved at -0.8 V in a pulsed system, and the corresponding nitrate-to-ammonia Faraday efficiency is 91.7 ± 1.0%. This work holds promise for the regulation of catalyst reactivity and selectivity by engineering in situ controllable structural and chemical transformations.

Theoretical Insights into Amido Group-Mediated Enhancement of CO2 Hydrogenation to Methanol on Cobalt Catalysts

Catalytic reduction of carbon dioxide into high-value-added products, such as methanol, is an effective approach to mitigate the greenhouse effect, and improving Co-based catalysts is anticipated to yield potential catalysts with high performance and low cost. In this study, based on first-principles calculations, we elucidate the promotion effects of surface *NHx (x = 1, 2, and 3) on the carbon dioxide hydrogenation to methanol from both activity and selectivity perspectives on Co-based catalysts. The presence of *NHx reduced the energy barrier of each elementary step on Co(100) by regulating the electronic structure to alter the binding strength of intermediates or by forming a hydrogen bond between surface oxygen-containing species and *NHx to stabilize transition states. The best promotion effect for different steps corresponds to different *NHx. The energy barrier of the rate-determining step of CO2 hydrogenation to methanol is lowered from 1.55 to 0.88 eV, and the product selectivity shifts from methane to methanol with the assistance of *NHx on the Co(100) surface. A similar phenomenon is observed on the Co(111) surface. The promotion effect of *NHx on Co-based catalysts is superior to that of water, indicating that the introduction of *NHx on a Co-based catalyst is an effective strategy to enhance the catalytic performance of CO2 hydrogenation to methanol.

Sunlight-driven CO2utilization over two-dimensional Co-based nanosheets

Reverse water gas shift (RWGS) reaction is an intriguing strategy to realize carbon neutrality, however, the endothermic process usually needs high temperature that supplied by non-renewable fossil fuels, resulting in secondary energy and environmental issues. Photothermal catalysis are ideal substitutes for the conventional thermal catalysis, providing that high reaction efficiency is achievable. Two-dimensional (2D) materials are highly active as RWGS catalysts, however, their industrial application is restricted by the preparation cost. In this study, a series of 2D Co-based catalysts for photothermal RWGS reaction with tunable selectivity were prepared by self-assembly method based on cheap amylum, by integrating the 2D catalysts with our homemade photothermal device, sunlight driven efficient RWGS reaction was realized. The prepared 2D Co0.5Ce0.5Oxexhibited a full selectivity toward CO (100%) and could be heated to 318 °C under 1 kW m-2irradiation with the CO generation rate of 14.48 mmol g-1h-1, pointing out a cheap and universal method to prepare 2D materials, and zero consumption CO generation from photothermal RWGS reaction.

Unleashing the Full Potential of Photo-Driven CO Hydrogenation to Light Olefins over Carbon-Coated CoMn-Based Catalysts

As a nonpetroleum process, photodriven Fischer-Tropsch synthesis provides a practical approach for the synthesis of light olefins. However, maximizing the solar-energy conversion efficiency based on the design of the composite catalyst and understanding the catalytic mechanism remain challenging. Herein, a novel carbon-coated CoMn-based catalyst, a C-coated mixture of Co and MnO, is designed for the efficient conversion of syngas to light olefins under light irradiation. The CoMnC-450 catalyst exhibits a CO conversion of 12.6% with a selectivity to light olefins of 36.5% under light irradiation, showing 5.5-fold the activity of thermocatalysis. Experimental characterizations as certain the CoMnC-450 catalyst can be excited to generate photogenerated carriers under light irradiation and then the electron transfer to metallic Co to form electron-rich active sites with carbon mediation, thereby enhancing the catalytic performance. In situ Fourier transform infrared spectroscopy and theoretical calculation based on density functional theory reveal the unique roles of photogenerated carriers in promoting the adsorption and activation of CO molecules. This study demonstrates a feasible catalyst model to efficiently utilize full-spectral solar light to produce the value-added chemical.

Co-based Catalysts for Selective H2 O2 Electroproduction via 2-electron Oxygen Reduction Reaction

Electrochemical production of hydrogen peroxide (H₂ O₂ ) via two-electron oxygen reduction reaction (ORR) process is emerging as a promising alternative method to the conventional anthraquinone process. To realize high-efficiency H₂ O₂ electrosynthesis, robust and low cost electrocatalysts have been intensively pursued, among which Co-based catalysts attract particular research interests due to the earth-abundance and high selectivity. Here, we provide a comprehensive review on the advancement of Co-based electrocatalyst for H₂ O₂ electroproduction. The fundamental chemistry of 2-electron ORR is discussed firstly for guiding the rational design of electrocatalysts. Subsequently, the development of Co-based electrocatalysts involving nanoparticles, compounds and single atom catalysts is summarized with the focus on active site identification, structure regulation and mechanism understanding. Moreover, the current challenges and future directions of the Co-based electrocatalysts are briefly summarized in this review.

Efficient Hydrogen Generation from the NaBH4 Hydrolysis by Cobalt-Based Catalysts: Positive Roles of Sulfur-Containing Salts

Development of a simple and efficient strategy for improving the catalytic activity of cobalt-based catalysts toward hydrogen evolution from sodium borohydride (NaBH₄) is paramount but remains challenging. Here, we reported a facile and efficient approach to tune the catalytic performance for NaBH₄ hydrolysis with Co-based catalysts prepared by using cobalt sulfate as a precursor or a mixture of sulfur-containing sodium salts/cobalt salts as a raw material. With the use of cobalt sulfate as the precursor, the CoSO₄-doped Co₃O₄ sample was formed and it exhibited excellent activity with the generation of ∼500 mL of hydrogen gas from NaBH₄ hydrolysis under mild conditions. In terms of sulfur-free cobalt salts (e.g., cobalt chloride, cobalt nitrate, and cobalt acetate) as precursors, the obtained Co-based samples were found to be entirely ineffective for hydrogen production. Interestingly, during the cobalt-based catalyst preparation, the introduction of sodium sulfate or sodium sulfide can considerably accelerate hydrogen production. On the contrary, adding sulfur-bearing salts did not inspire any activity improvement only during the hydrogen generation reaction. Control experiments indicate that during catalyst preparation, the presence of Na₂SO₄ and Na₂S is beneficial for the in situ transformation of Co₃O₄ into catalytically active Co-B alloys, accompanying a positive change in surface morphology during the NaBH₄ hydrolysis, thereby inducing an excellent hydrogen generation rate of up to 4425 mL·min^-1·g_cat^-1.

Co-Based Catalysts Derived from Layered-Double-Hydroxide Nanosheets for the Photothermal Production of Light Olefins

Solar-driven Fischer-Tropsch synthesis represents an alternative and potentially low-cost route for the direct production of light olefins from syngas (CO and H₂ ). Herein, a series of novel Co-based photothermal catalysts with different chemical compositions are successfully fabricated by H₂ reduction of ZnCoAl-layered double-hydroxide nanosheets at 300-700 °C. Under UV-vis irradiation, the photothermal catalyst prepared at 450 °C demonstrates remarkable CO hydrogenation performance, affording an olefin (C_2-4⁼ ) selectivity of 36.0% and an olefin/paraffin ratio of 6.1 at a CO conversion of 15.4%. Characterization studies using X-ray absorption fine structure and high-resolution transmission electron microscopy reveal that the active catalyst comprises Co and Co₃ O₄ nanoparticles on a ZnO-Al₂ O₃ mixed metal oxide support. Density functional theory calculations further demonstrate that the oxide-decorated metallic Co nanoparticle heterostructure weakens the further hydrogenation ability of the corresponding Co, leading to the high selectivity to light olefins. This study demonstrates a novel solar-driven catalyst platform for the production of light olefins via CO hydrogenation.