Herein, an effective tandem catalysis strategy is developed to improve the selectivity of the CO2 RR towards C2 H4 by multiple distinct catalytic sites in local vicinity. An earth-abundant elements-based tandem electrocatalyst PTF(Ni)/Cu is constructed by uniformly dispersing Cu nanoparticles (NPs) on the porphyrinic triazine framework anchored with atomically isolated nickel-nitrogen sites (PTF(Ni)) for the enhanced CO2 RR to produce C2 H4 . The Faradaic efficiency of C2 H4 reaches 57.3 % at -1.1 V versus the reversible hydrogen electrode (RHE), which is about 6 times higher than the non-tandem catalyst PTF/Cu, which produces CH4 as the major carbon product. The operando infrared spectroscopy and theoretic density functional theory (DFT) calculations reveal that the local high concentration of CO generated by PTF(Ni) sites can facilitate the C-C coupling to form C2 H4 on the nearby Cu NP sites. The work offers an effective avenue to design electrocatalysts for the highly selective CO2 RR to produce multicarbon products via a tandem route.

Highly Selective Tandem Electroreduction of CO2 to Ethylene over Atomically Isolated Nickel–Nitrogen Site/Copper Nanoparticle Catalysts

Selective transformation of one-carbon (C1) molecules, which are abundant or easily available and inexpensive carbon feedstocks, into value-added multi-carbon (C2+) compounds is a very attractive but highly challenging research target. Photocatalysis and electrocatalysis have offered great opportunities for the activation and controllable C–C coupling of C1 molecules under mild and environmentally benign conditions. This article provides a critical review on recent advances in photocatalytic and electrocatalytic conversions of major C1 molecules, including CO, CO2, CH4, CH3OH and HCHO, into C2+ compounds, such as C2H4, C3H6, ethanol and ethylene glycol, which play essential roles in the current chemical or energy industry. Besides the photocatalysts and electrocatalysts reported for these conversions, the structure–performance relationships and the key factors that control the activity and product selectivity are analysed to provide insights into the rational design of more efficient catalysts for the synthesis of C2+ compounds from C1 feedstocks. The active species, reaction intermediates and reaction or catalyst-functioning mechanism are discussed to deepen the understanding of the chemistry for the activation and selective C–C coupling of C1 molecules in the presence of solar energy or electrical energy.

Photocatalytic and electrocatalytic transformations of C1 molecules involving C–C coupling

Electrochemical reduction of CO2 to multicarbon (C2+) products is desirable because of the higher energy density and economic value of C2+ products and the significant scientific issue for coupling...

Carbon-Based Materials for Electrochemical Reduction of CO2 to C2+ Oxygenates: Recent Progress and Remaining Challenges

Using lignin as the precursor to synthesize Fe3O4@lignin composite for preparing electromagnetic wave absorbing lignin-phenol-formaldehyde adhesive

Electrochemical CO2 reduction reaction (CO2RR) is an attractive pathway for closing the anthropogenic carbon cycle and storing intermittent renewable energy by converting CO2 to valuable chemicals and fuels. The production of highly reduced carbon compounds beyond CO and formate, such as hydrocarbon and oxygenate products with higher energy density, is particularly desirable for practical applications. However, the productivity towards highly reduced chemicals is typically limited by high overpotential and poor selectivity due to the multiple electron-proton transfer steps. Tandem catalysis, which is extensively utilized by nature for producing biological macromolecules with multiple enzymes via coupled reaction steps, represents a promising strategy for enhancing the CO2RR performance. Improving the efficiency of CO2RR via tandem catalysis has recently emerged as an exciting research frontier and achieved significant advances. Here we describe the general principles and also considerations for designing tandem catalysis for CO2RR. Recent advances in constructing tandem catalysts, mainly including bimetallic alloy nanostructures, bimetallic heterostructures, bimetallic core-shell nanostructures, bimetallic mixture catalysts, metal-metal organic framework (MOF) and metal-metallic complexes, metal-nonmetal hybrid nanomaterials and copper-free hybrid nanomaterials for boosting the CO2RR performance are systematically summarized. The study of tandem catalysis for CO2RR is still at the early stage, and future research challenges and opportunities are also discussed.

Tandem catalysis in electrochemical CO2 reduction reaction

Lignin is one of the most important biomacromolecules in the plant biomass and the largest renewable source of aromatic building blocks in nature. Selectively producing value-added chemicals from the catalytic transformation of renewable lignin is of strategic significance and meet sustainability targets owing to the excessive consumption of non-renewable petroleum resource, but remains a long-term challenge owing to the complexity of lignin structure. This Minireview provides a summary and perspective of the extensive research that provides insight into selectively catalytic transformations of lignin and its derived monomers via directed scissor of chemical linkages (C-O and C-C bonds) with product-oriented targets. Furthermore, some challenges and opportunities of lignin catalytic transformation are provided based on existing problems in this field for readers to discuss future research directions.

Product-oriented Direct Cleavage of Chemical Linkages in Lignin.

Efficient electroreduction of carbon dioxide (CO2) to ethanol is of great importance, but remains a challenge because it involves the transfer of multiple proton–electron pairs and carbon–carbon coupling. Herein, we report a CoO-anchored N-doped carbon material composed of mesoporous carbon (MC) and carbon nanotubes (CNT) as a catalyst for CO2 electroreduction. The faradaic efficiencies of ethanol and current density reached 60.1% and 5.1 mA cm−2, respectively. Moreover, the selectivity for ethanol products was extremely high among the products produced from CO2. A proposed mechanism is discussed in which the MC–CNT/Co catalyst provides a relay catalytic platform, where CoO catalyzes the formation of CO* intermediates which spill over to MC–CNT for carbon–carbon coupling to form ethanol. The high selectivity for ethanol is attributed mainly to the highly selective carbon–carbon coupling active sites on MC–CNT.

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Selective electrochemical reduction of carbon dioxide to ethanol via a relay catalytic platform

Electrochemical reduction of CO2 (CO2 RR) to formate is a promising route to prepare value-added chemical. Developing low-cost and efficient electrocatalysts with high product selectivity is still a grand challenge. Herein, a novel Cu anchored on hollow carbon spheres catalysts (HCS/Cu-x, x represents the mass of CuCl2 added in the system) is designed with controllable copper/carbon heterogenous interfaces. Rich copper/carbon heterogenous interfaces and hollow structure of optimized HCS/Cu-0.12 catalyst are beneficial to charge transmission. Compared with the CO2 RR occurred in aqueous electrolyte over Cu-based catalyst that has been reported to date, it exhibits highest formate Faradaic efficiency (FE) of 82.4% with a current density of 26 mA cm-2 and remarkable stability in a H-cell.

Copper/Carbon Heterogenous Interfaces for Enhanced Selective Electrocatalytic Reduction of CO2 to Formate.

The activation and cleavage of C–C bonds remains a critical scientific issue in many organic reactions and is an unmet challenge due to their intrinsic inertness and ubiquity. Meanwhile, it is crucial for the valorization of lignin into high-value chemicals. Here, we proposed a novel strategy to enhance the Caromatic–Cα bond cleavage by pre-functionalization with amine sources, in which an active amine intermediate is first formed through Markovnikov hydroamination to reduce the dissociation energy of the Caromatic–Cα bond which is then cleaved to form target chemicals. More importantly, this strategy provides a method to achieve the maximum utilization of the aromatic nucleus and side chains in lignin or its platform molecules. Phenols and N,N-dimethylethylamine compounds with high yields were produced from herbaceous lignin or the p-coumaric acid monomer in the presence of industrially available dimethylamine (DMA).

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Organic amine mediated cleavage of Caromatic–Cα bonds in lignin and its platform molecules

The selective transformation of chitin into various renewable N-containing chemicals and medicines has attracted increasing attention. However, the N-acetyl groups in chitin construct strong hydrogen bond networks, which restricts its depolymerization and transformation. The selective conversion of robust chitin commonly requires considerable base catalysts to remove the N-acetyl group as a byproduct in advance, which is non-compliance with the principle of atomic economy. Herein, for the first time we demonstrate a novel approach to achieve the selective utilization of the N-acetyl group in chitin for transamidation of chitin with amines. A series of amine derivatives, mainly including aliphatic amine, cyclic amine and functionalized aromatic amine, could be selectively converted into the corresponding amide products frequently found in pharmaceuticals. Furthermore, the solid residue after removing the acetyl group (denoted as De-chitin) with the sufficient exposure of -NH2 groups as a solid base catalyst shows excellent performance in the aldol condensation reaction of furfural and acetone to produce fuel precursors. Our process provides a strategy that exploiting every functional group adequately in substrates to obtain value-added chemicals.

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Yu Xin

Papers

Product-oriented Direct Cleavage of Chemical Linkages in Lignin.

Selective electrochemical reduction of carbon dioxide to ethanol via a relay catalytic platform

Copper/Carbon Heterogenous Interfaces for Enhanced Selective Electrocatalytic Reduction of CO2 to Formate.

Organic amine mediated cleavage of Caromatic–Cα bonds in lignin and its platform molecules

Selective Utilization of N-acetyl Groups in Chitin for Transamidation of Amines