Electroreduction of CO2 to C1 and C2 products on dual active sites

Selective CO2 photoreduction into high-energy-density and high-value-added C2 products is an ideal strategy to achieve carbon neutrality and energy shortage, but it is still highly challenging due to the large energy barrier of the C-C coupling step and severe exciton annihilation in photocatalysts. Herein, strong and localized charge polarization is successfully induced on the surface of melon-based organic semiconductors by creating dual active sites with a large charge asymmetry. Confirmed by multiscale characterization and theoretical simulations, such asymmetric charge distribution, originated from the oxygen dopants and nitrogen vacancies over melon-based organic semiconductors, reduces exciton binding energy and boosts exciton dissociation. The as-formed charge polarization sites not only donate electrons to CO2 molecules but also accelerate the coupling of asymmetric *CO*CO intermediates for CO2 photoreduction into ethanol by lowering the energy barrier of this process. Consequently, an exceptionally high selectivity of up to 97 % for C2H5OH and C2H5OH yield of 0.80 mmol g-1 h-1 have been achieved on this dual active sites organic semiconductor. This work, with its potential applicability to a variety of non-metal multi-site catalysts, represents a versatile strategy for the development of advanced catalysts tailored for CO2 photoreduction reactions.

Selective CO2 photoreduction into high‐energy‐density and high‐value‐added C2 products is an ideal strategy to achieve carbon neutrality and energy shortage, but it is still highly challenging due to the large energy barrier of the C−C coupling step and severe exciton annihilation in photocatalysts. Herein, strong and localized charge polarization is successfully induced on the surface of melon‐based organic semiconductors by creating dual active sites with a large charge asymmetry. Confirmed by multiscale characterization and theoretical simulations, such asymmetric charge distribution, originated from the oxygen dopants and nitrogen vacancies over melon‐based organic semiconductors, reduces exciton binding energy and boosts exciton dissociation. The as‐formed charge polarization sites not only donate electrons to CO2 molecules but also accelerate the coupling of asymmetric *CO*CO intermediates for CO2 photoreduction into ethanol by lowering the energy barrier of this process. Consequently, an exceptionally high selectivity of up to 97 % for C2H5OH and C2H5OH yield of 0.80 mmol g−1 h−1 have been achieved on this dual active sites organic semiconductor. This work, with its potential applicability to a variety of non‐metal multi‐site catalysts, represents a versatile strategy for the development of advanced catalysts tailored for CO2 photoreduction reactions.

The resurgence of visible light photocatalysis for carbon dioxide reduction reaction (CO2RR) has resulted in the generation of various homogeneous and heterogeneous paradigms. Herein, a new system has been established by incorporating dual catalytic sites into porous coordination polymer toward the photocatalysis of CO2RR. A functional ligand, 5,10,15,20-tetrakis[4'-(terpyridinyl)phenyl]porphyrin (TTPP), has been used to assemble discrete divalent nickel ions into the coordination polymer (TTPP-Ni) through metal bis(terpyridine) nodes. Both the porphyrin and terpyridine moieties prefer to bind with nickel ions, giving rise to TTPP-Ni with dual active catalytic sites. By controlling different molar ratios of ligand and metal and the reaction temperature, four samples including TTPP-Ni-n (n = 1, 2, 3, and 4) with different molar ratios of nickel porphyrin and nickel bis(terpyridine) subunits have been fabricated. The predesigned two-dimensional chemical structures of TTPP-Ni samples have been fully characterized using powder X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and IR and UV-vis spectroscopies. The photocatalytic activities of these coordination polymers have been screened using [Ru(bpy)3]Cl2·6H2O as a photosensitizer together with triisopropanolamine as the sacrificial electron donor in CH3CN and H2O. Among these photocatalysts, TTPP-Ni-3 and TTPP-Ni-4 with almost saturated metal sites are able to display extraordinary photocatalytic performance including a CO generation rate of ca. 3900 μmol g-1 h-1 and 98% selectivity. The mechanism associated with dual active sites has been rationalized on the basis of theoretical simulations.

The achievement of bifunctional metal‐organic frameworks (MOFs) remains a huge challenge due to their lack of dual active sites. Herein, dual sites in the Co‐catecholate (Co‐CAT) are created through Ru, Ir, or Rh doping for overall water splitting. Among them, RuCo‐CAT exhibits excellent bifunctional activities, outperforming benchmarked Pt/C for the hydrogen evolution reaction (HER) and RuO2 for the oxygen evolution reaction (OER). The theoretical calculations demonstrate that the doped Ru atoms with optimal absorption energy for the hydrogen intermediate and the Co centers with a reduced energy barrier for the rate‐determining step are the active sites for HER and OER, respectively. Furthermore, the incorporation of Ru atoms can improve the electrical conductivity and capacity of water adsorption of Co‐CAT greatly, synergistically improving the bifunctional activity. This strategy for engineering dual active sites offers novel insights into designing bifunctional MOFs for overall water splitting.

Synergistic interplay of dual active sites on spinel ZnAl2O4 for syngas conversion

CO2 reduction by single copper atom supported on g-C3N4 with asymmetrical active sites

Tuning dual active sites of Cu/CoCeOx catalysts for efficient catalytic transfer hydrogenation of 5-hydroxymethylfurfural to biofuel 2,5-dimethylfuran

For a single-substance catalyst, due to the different adsorption/desorption kinetics of metallic (cationic) and nonmetallic (anionic) sites, it typically catalyzes hydrogen evolution in a single-active-site manner, which greatly limits the activity of catalysts. Thus, herein, we simultaneously activate the anion (P) and cation (Ni) sites in nickel phosphide (Ni2P) and generate highly active P(Ni) dual sites through the substrate effect of NiS2-NiS heterogeneous structures. Theoretical calculation results combined with in situ Raman spectroscopy unveil that the NiS2-NiS substrate effectively regulates the charge distribution to concentrate around the P atom, therefore resulting in Ni and P synergistic dual active sites for water adsorption, water dissociation, and H* adsorption. Accordingly, the dual active site formed enables the Ni2P/NiS2-NiS electrocatalyst to only require an overpotential of 75 mV to achieve a current density of 10 mA cm-2 in alkaline media, very close to the Pt-group noble metal catalyst. This work highlights the critical regulatory role of substrates in activating the anion-cation dual active site in the single metal/intermetallic compound (such as metal phosphides, sulfides, nitrides, carbides, borides, and silicides) that promotes catalytic performance.

The construction of the active site is pivotal in the design of highly efficient catalysts for heterogeneous catalysis. Notably, the synergy between the two active sites can substantially enhance the catalytic efficiency. Nonetheless, fabricating high-density dual active sites on the catalyst surface remains a significant challenge. In this study, the host-guest strategy was employed to construct a dual active site Mo2N@ZrO2 heterostructure catalyst, featuring a significant number of nitrogen sites and oxygen vacancies. The Mo2N@ZrO2 catalyst exhibited near-equilibrium conversion and 100% CO selectivity in a reverse water-gas shift reaction at 350 °C. Density functional theory (DFT) calculations and in situ diffuse reflection infrared Fourier transform (DRIFT) spectroscopy characterization indicate that oxygen vacancies on the Mo2N@ZrO2 catalyst dissociate CO2 into CO, while Mo2N promotes H2 to form NHx species by heterolytic dissociation. The formation of NHx facilitates the desorption of CO and inhibits the further hydrogenation of CO*. This synergistic effect of the dual active site significantly enhances catalytic performance. This strategy of constructing a dual active site offers valuable insights for developing efficient catalysts.

Theoretical considerations on activity of the electrochemical CO2 reduction on metal single-atom catalysts with asymmetrical active sites

Photocatalytic selective upcycling of polyethylene terephthalate (PET) waste into valuable C2 products is an ideal strategy. However, over-oxidation and nonselective activation of C─C/C─O bonds by active sites in the local microenvironment have limited prior studies to produce C2 products. By designing Pt/ZnO-ZIS catalysts that feature a dynamically coupled Pt-In dual-site synergistic interface, this study achieves in situ upcycling of PET wastes via tuning the electronic structure and chemical environment of the Pt-In active sites and optimizing the adsorption configuration of plastic wastes. The dual active sites (Pt-In), which are spatially adjacent yet functionally distinct, achieves an HOAc production rate of 882.46 µmol g-1 h-1 with nearly 100% selectivity. Detailed characterizations and DFT calculations reveal that the high selectivity is attributed to the Pt sites adsorbing and protecting the terminal hydroxyl group (-OH) oxidation, and then activating the C─O bond to undergo proton substitution. The electron-rich Pt sites further inhibit the over-oxidation of C─C bond, ensuring high selectivity of HOAc. Simultaneously, the In sites facilitate oxidation of -OH to form carboxyl species during the reaction. This study provides an insightful understanding of dual sites with dynamic reconstruction toward highly selective photo-reforming of plastic wastes at the atomic scale.

Control of Co0/Co2C dual active sites for higher alcohols synthesis from syngas

Ground-level ozone (O3) pollution has emerged as a significant concern due to its detrimental effects on human health and the ecosystem. Catalytic removal of O3 has proven to be the most efficient and cost-effective method. However, its practical application faces substantial challenges, particularly in relation to its effectiveness across the entire humidity range. Herein, we proposed a novel strategy termed "dual active sites" by employing graphitized carbon-loaded core-shell cobalt catalysts (Co@Co3O4-C). Co@Co3O4-C was synthesized via the pyrolysis of a Co-organic ligand as the precursor. By utilizing this approach, we achieved a nearly constant 100% working efficiency of the Co@Co3O4-C catalyst for catalyzing O3 decomposition across the entire humidity range. Physicochemical characterization coupled with density functional theory calculations elucidates that the presence of encapsulated metallic Co nanoparticles enhances the reactivity of the cobalt oxide capping layer. Additionally, the interface carbon atom, strongly influenced by adjacent metallic Co nuclei, functions as a secondary active site for the decomposition of O3 decomposition. The utilization of dual active sites effectively mitigates the competitive adsorption of H2O molecules, thus isolating them for adsorption in the cobalt oxide capping layer. This optimized configuration allows for the decomposition of O3 without interference from moisture. Furthermore, O3 decomposition monolithic catalysts were synthesized using a material extrusion-based three-dimensional (3D) printing technology, which demonstrated a low pressure drop and exceptional mechanical strength. This work provides a "dual active site" strategy for the O3 decomposition reaction, realizing O3 catalytic decomposition over the entire humidity range.

The electrochemical reduction reaction of NO3- (NO3RR) represents a promising green technology for ammonia (NH3) synthesis. Among various electrocatalysts, Co-based materials have demonstrated considerable potential for the NO3RR. However, the NH3 production efficiency of Co-based materials is still limited due to challenges in the competitive hydrogen evolution reaction (HER) and hydrogenating oxynitride intermediates (*NOx). In this study, tungsten (W) and cobalt (Co) elements are co-incorporated to form cobalt tungstate (CoWO4) nanoparticles with dual active sites of Co2+ and W6+, which are applied to optimize the hydrogenation of NOx and decrease the HER, thereby achieving a highly efficient NO3RR to NH3. Theoretical calculations indicate that the Co sites in CoWO4 facilitate the adsorption and hydrogenation of *NOx intermediates, while W sites suppress the competitive HER. These dual active sites work synergistically to enhance NH3 production from the NO3RR. Inspired by these calculations, CoWO4 nanoparticles are synthesized using a simple ion precipitation method, with sizes ranging from 10 to 30 nm. Electrochemical performance tests demonstrate that CoWO4 nanoparticles exhibit a high faradaic efficiency of 97.8 ± 1.5% and an NH3 yield of 13.2 mg h-1 cm-2. In situ Fourier transform infrared spectroscopy characterizes the enhanced adsorption and hydrogenation behaviors of *NOx as well as a minimized HER on CoWO4, which contributes to the high efficiency and selectivity to NH3. This work introduces CoWO4 nanoparticles as an electrocatalytic material with dual active sites, contributing to the design of electrocatalysts for NH3 synthesis.

Synergistic Co-N/V-N dual sites in N-doped Co3V2O8 nanosheets: pioneering high-efficiency bifunctional electrolysis for high-current water splitting