Electrochemical oxidative lignin cleavage and coupled 2-furaldehyde reduction provide a promising approach for producing high-value added products. However, developing efficient bifunctional electrocatalysts with noble-metal-like activity still remains a challenge. Here, an efficient electrochemical strategy is reported for the selective oxidative cleavage of Cα -Cβ bonds in lignin into aromatic monomers by tailoring the electronic structure through P-doped CoMoO4 spinels (99% conversion, highest monomer selectivity of 56%). Additionally, the conversion and selectivity of 2-furaldehyde reduction to 2-methyl furan reach 87% and 73%, respectively. In situ Fourier transform infrared and density functional theory analysis reveal that an upward shift of the Ed upon P-doping leads to an increase in the antibonding level, which facilitates the Cα -Cβ adsorption of the lignin model compounds, thereby enhancing the bifunctional electrocatalytic activity of the active site. This work explores the potential of a spinel as a bifunctional electrocatalyst for the oxidative cracking of lignin and the reductive conversion of small organic molecules to high-value added chemicals via P-anion modulation.
Lignin shows great potential for sustainable production of high-quality fuels and value-added chemicals. The development of efficient and highly stable multifunctional catalysts for the depolymerization of lignin into aromatic chemicals remains a great challenge. In this work, environmentally friendly NiFe2O4 spinel catalyst characterizing with rich oxygen vacancies and porous structures was constructed by introducing Ni to modulate the coordination environment of cations in Fe3O4. Under optimal conditions, the conversion of alkali lignin catalyzed by NiFe2O4 reached 91%, the yield of liquid product reached 83.6% and the yield of aromatic monomer products reached 31.7%. Combined results from catalyst characterization, product analysis and density functional theory calculations showed that the Lewis acidic center of the catalyst was significantly improved by the introduction of Ni, which promoted the C-O bond breaking in lignin. The Ni-O-Fe structure facilitated the adsorption of lignin substrates and reaction intermediates, which resulted in the improved depolymerization efficiency of lignin. The present work provides valuable insights into the depolymerization of lignin by spinel catalysts, and offers ideas for the future design and development of binary or even ternary spinel catalysts for the depolymerization of lignin.
In heterogeneous catalysis, it is crucial to understand the structure sensitivity in order to elucidate the reaction mechanism and rationally design optimal catalysts. In this work, propane dehydrogenation (PDH) and side reactions (cracking and deep dehydrogenation) were studied by density functional theory calculations on Co catalysts with different crystallographic structures: face-centered cubic (FCC) and hexagonal closed packed (HCP). Wulff construction reveals that the most stable facet of each crystallographic structure, viz. Co(111) and Co(0001), cover 76.2% and 19.4% of the exposed surface. Various reaction pathways for PDH, deep dehydrogenation, and cracking were explored on Co(111) and Co(0001). Microkinetic simulation results suggest that PDH proceeds through both dehydrogenation pathways (via 1-propyl or 2-propyl intermediate) on Co(111), while it favors path A (via 1-propyl intermediate) on Co(0001). At typical reaction conditions of PDH, Co(111) is more active than Co(0001) by 1.3 times, while the latter is more selective toward propylene production and more resistive to coke formation. Compared to Pt(111), both Co surfaces are more active for PDH while Co(0001) is also more selective toward propylene formation. This work provides fundamental insights into the crystallographic structure sensitivity of propane dehydrogenation on a Co catalyst and useful guidance to achieve better catalytic performance for a Co catalyst.
Single-atom catalysts have emerged as cutting-edge hotspots in the field of material science owing to their excellent catalytic performance brought about by well-defined metal single-atom sites (M SASs). However, huge challenges still lie in achieving the rational design and precise synthesis of M SASs. Herein, we report a novel synthesis strategy based on the hetero-charge coupling effect (HCCE) to prepare M SASs loaded on N and S co-doped porous carbon (M
Molybdenum nickel alloy has been proved to be an efficient noble-metal-free catalyst for hydrogen evolution reaction (HER) in alkaline medium, but its electrocatalytic activity and stability need to be further improved to meet industrial requirements. In this study, carboxymethylated enzymatic hydrolysis lignin (EHL) was used as a biomacromolecule frame to coordinate with transition metal ions and reduced by pyrolysis to obtain the MoNi4–NiO heterojunction (MoNi4–NiO/C). The oblate sphere structure of MoNi4–NiO/C exposed a large catalytic active surface to the electrolyte. As a result, the hydrogen evolution reaction of MoNi4–NiO/C displayed a low overpotentials of 41 mV to achieve 10 mA cm−2 and excellent stability of 100 h at 100 mA cm−2 in 1 mol L−1 KOH, which was superior to that of commercial Pt/C. Lignin assisted the formation of NiO to construct the MoNi4–NiO interface and MoNi4–NiO heterojunction structure, which reduced the energy barrier by forming a more favorable transition states and then promoted the formation of adsorbed hydrogen at the heterojunction interface through water dissociation in alkaline media, leading to the rapid reaction kinetics. This work provided an effective strategy for improving the electrocatalytic performance of noble-metal-free electrocatalysts encapsulated by lignin-derived carbon.
Abstract Single‐atom catalysts have emerged as cutting‐edge hotspots in the field of material science owing to their excellent catalytic performance brought about by well‐defined metal single‐atom sites (M SASs). However, huge challenges still lie in achieving the rational design and precise synthesis of M SASs. Herein, we report a novel synthesis strategy based on the hetero‐charge coupling effect (HCCE) to prepare M SASs loaded on N and S co‐doped porous carbon (M 1 /NSC). The proposed strategy was widely applied to prepare 17 types of M 1 /NSC composed of single or multi‐metal with the integrated regulation of the coordination environment and electronic structure, exhibiting good universality and flexible adjustability. Furthermore, this strategy provided a low‐cost method of efficiently synthesizing M 1 /NSC with high yields, that can produce more than 50 g catalyst at one time, which is key to large‐scale production. Among various as‐prepared unary M 1 /NSC (M can be Fe, Co, Ni, V, Cr, Mn, Mo, Pd, W, Re, Ir, Pt, or Bi) catalysts, Fe 1 /NSC delivered excellent performance for electrocatalytic nitrate reduction to NH 3 with high NH 3 Faradaic efficiency of 86.6 % and high NH 3 yield rate of 1.50 mg h −1 mg cat. −1 at −0.6 V vs. RHE. Even using Fe 1 /NSC as a cathode in a Zn‐nitrate battery, it exhibited a high open circuit voltage of 1.756 V and high energy density of 4.42 mW cm −2 with good cycling stability.
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