Structural engineering of 3D hierarchical Cd0.8Zn0.2S for selective photocatalytic CO2 reduction

The solar-driven catalytic conversion of CO2 to useful chemical fuels is regarded as an environmentally friendly approach to reduce the consumption of fossil fuels and mitigate the greenhouse effect.However,it is highly intriguing and challenging to promote the selectivity and efficiency of visible-light-responsive photocatalysts that favor the adsorption of CO2 in photoreduction processes.In this work,three-dimensional hierarchical Cd0.8Zn0.2S flowers(C8Z2S-F)with ultrathin petals were successfully synthesized through an in-situ self-assembly growth process using sodium citrate as a morphology director.The flower-like Cd0.8Zn0.2S solid solution exhibited remarkable photocatalytic performance in the reduction of CO2,generating CO up to 41.4μmol g^−1 under visible-light illumination for 3 h;this was nearly three times greater than that of Cd0.8Zn0.2S nanoparticles(C8Z2S-NP)(14.7μmol g^−1).Particularly,a comparably high selectivity of 89.9%for the conversion of CO2 to CO,with a turnover number of 39.6,was obtained from the solar-driven C8Z2S-F system in the absence of any co-catalyst or sacrificial agent.Terahertz time-domain spectroscopy indicated that the introduction of flower structures enhanced the light-harvesting capacity of C8Z2S-F.The in situ diffuse reflectance infrared Fourier transform spectroscopy unveiled the existence of surface-adsorbed species and the conversion of photoreduction intermediates during the photocatalytic process.Empirical characterizations and predictions of the photocatalytic mechanism demonstrated that the flower-like Cd0.8Zn0.2S solid solution possessed desirable CO2 adsorption properties and an enhanced charge-transfer capability,thus providing a highly effective photocatalytic reduction of CO2.

Defect Engineering on Carbon‑Based Catalysts for Electrocatalytic CO2 Reduction

Electrocatalytic carbon dioxide(CO2)reduction(ECR)has become one of the main methods to close the broken carbon cycle and temporarily store renewable energy,but there are still some problems such as poor stability,low activity,and selectivity.While the most promising strategy to improve ECR activity is to develop electrocatalysts with low cost,high activity,and long-term stability.Recently,defective carbon-based nanomaterials have attracted extensive attention due to the unbalanced electron distribution and electronic structural distortion caused by the defects on the carbon materials.Here,the present review mainly summarizes the latest research progress of the construction of the diverse types of defects(intrinsic carbon defects,heteroatom doping defects,metal atomic sites,and edges detects)for carbon materials in ECR,and unveil the structure-activity relationship and its catalytic mechanism.The current challenges and opportunities faced by high-performance carbon materials in ECR are discussed,as well as possible future solutions.It can be believed that this review can provide some inspiration for the future of development of high-performance ECR catalysts.

Amorphous CoOx coupled carbon dots as a spongy porous bifunctional catalyst for efficient photocatalytic water oxidation and CO2 reduction

Cobalt-based oxides,with high abundance,good stability and excellent catalytic performance,are regarded as promising photocatalysts for artificial photosynthetic systems to alleviate foreseeable energy shortages and global warming.Herein,for the first time,a series of novel spongy porous CDs@CoOx materials were synthesized to act as an efficient and stable bifunctional photocatalyst for water oxidation and CO2 reduction.Notably,the preparation temperatures visibly influence the morphologies and photocatalytic performances of the CDs@CoOx.Under the optimal conditions,a maximum O2 yield of 40.4% and pretty apparent quantum efficiency(AQE)of 58.6% at 460 nm were obtained over CDs@CoOx-300 for water oxidation.Similarly,the optimized sample CDs@CoOx-300 manifests significant enhancement on the CO2-to-CO conversion with a high selectivity of 89.3% and CO generation rate of 8.1μmol/h,which is superior to most previous cobalt-based catalysts for CO2 reduction.The composite CDs@CoOx-300 not only exposes more active sites but also facilitates electron transport,which results in excellent photocatalytic activity.In addition,the boosted photocatalytic behavior is attributed to the synergistic effect between CoOx and CDs,which was verified by the photocatalytic activity control experiments and electrochemical characterization.The work offers a novel strategy to fabricate a high performance bifunctional photocatalyst for water oxidation and CO2 reduction.

Nitrogen and sulfur dual-doped high-surface-area hollow carbon nanospheres for efficient CO2 reduction

The electrochemical reduction of CO2(CO2 RR) can substantially contribute to the production of useful chemicals and reduction of global CO2 emissions. Herein, we presented N and S dual-doped high-surface-area carbon materials(SZ-HCN) as CO2 RR catalysts. N and S were doped by one-step pyrolysis of a N-containing polymer and S powder. ZnCl2 was applied as a volatile porogen to prepare porous SZ-HCN. SZ-HCN with a high specific surface area(1510 m2 g–1) exhibited efficient electrocatalytic activity and selectivity for CO2 RR. Electrochemical measurements demonstrated that SZ-HCN showed excellent catalytic performance for CO2-to-CO reduction with a high CO Faradaic efficiency(~93%) at-0.6 V. Furthermore, SZ-HCN offered a stable current density and high CO selectivity over at least 20 h continuous operation, revealing remarkable electrocatalytic durability. The experimental results and density functional theory calculations indicated that N and S dual-doped carbon materials required lower Gibbs free energy to form the COOH* intermediate than that for single-N-doped carbon for CO2-to-CO reduction, thereby enhancing CO2 RR activity.

Ag-Cu Nanoparticles Supported on N-Doped TiO2 Nanowire Arrays for Efficient Photocatalytic CO2 Reduction

Photocatalytic reduction of CO2 into various types of fuels has attracted great interest,and serves as a potential solution to addressing current global warming and energy challenges.In this work,Ag-Cu nanoparticles are densely supported on N-doped TiO2 nanowire through a straightforward nanofabrication approach.The range of light absorption by N-doped TiO2 can be tuned to match the plasmonic band of Ag nanoparticles,which allows synergizing a resonant energy transfer process with the Schottky junction.Meanwhile,Cu nanoparticles can provide active sites for the reduction of CO2 molecules.Remarkably,the performance of photocatalytic CO2 reduction is improved to produce CH4 at a rate of 720μmol·g-1·h-1 under full-spectrum irradiation.

Recent advances in the utilization of copper sulfide compounds for electrochemical CO2 reduction

Converting carbon dioxide(CO2)into value-added chemicals by CO2 reduction has been considered as a potential way to solve the current energy crisis and environmental problem.Among the methods of CO2 reduction,the electrochemical method has been widely used due to its mild reaction condition and high reaction efficiency.In the electrochemical reduction system,the CO2 electrocatalyst is the most important part.Although many CO2 electrocatalysts have been developed,efficient catalysts with high activity,selectivity and stability are still lacking.Copper sulfide compound,as a low-toxicity and emerging material,has broad prospects in the field of CO2 reduction due to its unique structural and electrochemical properties.Much progress has been achieved with copper sulfide nanocrystalline and the field is rapidly developing.This paper summarizes the preparation,recent progress in development,and factors affecting the electrocatalytic CO2 reduction performance with copper sulfide compound as a catalyst.Prospects for future development are also outlined,with the aim of using copper sulfide compound as a highly active and stable electrocatalyst for CO2 reduction.

Electrochemical Study on Hydrogen Evolution and CO2 Reduction on Pt Electrode in Acid Solutions with Different pH

Hydrogen evolution reaction(HER)is the major cathodic reaction which competes CO2 reduction reaction(CO2 RR)on Pt electrode.Molecular level understanding on how these two reactions interact with each other and what the key factors are of CO2 RR kinetics and selectivity will be of great help in optimizing electrolysers for CO2 reduction.In this work,we report our results of hydrogen evolution and CO2 reduction on Pt(111)and Pt film electrodes in CO2 saturated acid solution by cyclic voltammetry and infrared spectroscopy.In solution with pH>2,the major process is HER and the interfacial pH increases abruptly during HER;COad is the only adsorbed intermediate detected in CO2 reduction by infrared spectroscopy;the rate for COad formation increases with the coverage of UPD-H and reaches maximum at the onset potential for HER;the decrease of COad formation under HER is attributed to the available limited sites and the limited residence time for the reduction intermediate(Had),which is necessary for CO2 adsorption and reduction.

Electrochemical CO2 Reduction on Pd-Modified Cu Foil

Bimetallic catalysts can improve CO2 reduction efficiency via the combined properties of two metals.CuPd shows enhanced CO2 reduction activity compared to copper alone.Using differential electrochemical mass spectrometry(DEMS)and electrochemical infrared(IR)spectroscopy,volatile products and adsorbed intermediates were measured during CO2 and CO reduction on Cu and CuPd.The IR band corresponding to adsorbed CO appears 300 mV more positive on CuPd than that on Cu,indicating acceleration of CO2 reduction to CO.Electrochemical IR spectroscopy measurements in CO-saturated solutions reveal similar potentials for CO adsorption and CO3^2-desorption on CuPd and Cu,indicating that CO adsorption is controlled by desorption of CO3^2-.DEMS measurements carried out during CO reduction at both electrodes showed that the onset potential for reduction of CO to CH4 and CH3OH on CuPd is about 200 mV more positive than that on Cu.We attribute these improvements to interaction of Cu and Pd,which shifts the d-band center of the Cu sites.

Carbon‐based metal‐free catalysts for electrochemical CO2 reduction: Activity, selectivity, and stability

Zero or negative emissions of carbon dioxide(CO2)is the need of the times,as inexorable rising and alarming levels of CO2 in the atmosphere lead to global warming and severe climate change.The electrochemical CO2 reduction(eCO2R)to value‐added fuels and chemicals by using renewable electricity provides a cleaner and more sustainable route with economic benefits,in which the key is to develop clean and economical electrocatalysts.Carbon‐based catalyst materials possess desirable properties such as high offset potential for H2 evolution and chemical stability at the negative applied potential.Although it is still challenging to achieve highly efficient carbon‐based catalysts,considerable efforts have been devoted to overcoming the low selectivity,activity,and stability.Here,we summarize and discuss the recent progress in carbon‐based metal‐free catalysts including carbon nanotubes,carbon nanofibers,carbon nanoribbons,graphene,carbon nitride,and diamonds with an emphasis on their activity,product selectivity,and stability.In addition,the key challenges and future potential approaches for efficient eCO2R to low carbon‐based fuels are highlighted.For a good understanding of the whole history of the development of eCO2R,the CO2 reduction reactions,principles,and techniques including the role of electrolytes,electrochemical cell design and evaluation,product selectivity,and structural composition are also discussed.The metal/metal oxides decorated with carbon‐based electrocatalysts are also summarized.We aim to provide insights for further development of carbon‐based metal‐free electrocatalysts for CO2 reduction from the perspective of both fundamental understanding and technological applications in the future.

An efficient visible-light photocatalyst for CO2 reduction fabricated by cobalt porphyrin and graphitic carbon nitride via covalent bonding

Nanoparticle photosensitizers possess technical advantages for photocatalytic reactions due to enhanced light harvesting and efficient charge transport.Here we report synthesis of semiconductor nanoparticles through covalent coupling and assembly of metalloporphyrin with condensed carbon nitride.The resultant nanoparticles consist of light harvesting component from the condensed carbon nitride and photocatalytic sites from the metalloporphyrins.This synergetic particle system effectively initiates efficient charge separation and transport and exhibits excellent photocatalytic activity for CO2 reduction.The CO production rate can reach up to 57μmol/(g·h)with a selectivity of 79%over competing H2 evolution.Controlled experiments demonstrate that the combination of light harvesting with photocatalytic activity via covalent assembly is crucial for the high photocatalytic activity.Due to effective charge separation and transfer,the resultant nanoparticle photocatalysts show exceptional photo stability against photo-corrosion under light irradiation,enabling for long-term utilization.This research opens a new way for the development of stable,effective nanoparticle photocatalysts using naturally abundant porphyrin pigments.

Selective photocatalytic CO2 reduction over Zn-based layered double hydroxides containing tri or tetravalent metals

Photocatalytic CO2 reduction holds promise as a future technology for the manufacture of fuels and commodity chemicals.However,factors controlling product selectivity remain poorly understood.Herein,we compared the performance of a homologous series of Zn-based layered double hydroxide(ZnM-LDH)photocatalysts for CO2 reduction.By varying the trivalent or tetravalent metal cations in the ZnM-LDH photocatalysts(M=Ti4+,Fe3+,Co3+,Ga3+,Al3+),the product selectivity of the reaction could be precisely controlled.ZnTi-LDH afforded CH4 as the main reduction product;ZnFe-LDH and ZnCo-LDH yielded H2 exclusively from water splitting;whilst ZnGa-LDH and ZnAl-LDH generated CO.In-situ diffuse reflectance infrared measurements,valence band XPS and density function theory calculations were applied to rationalize the CO2 reduction selectivities of the different ZnM-LDH photocatalysts.The analyses revealed that the d-band center(ed)position of the M3+or M4+cations controlled the adsorption strength of CO2 and thus the selectivity to carbon-containing products or H2.Cations with d-band centers relatively close to the Fermi level(Ti4+,Ga3+and Al3+)adsorbed CO2 strongly yielding CH4 or CO,whereas metal cations with d-band centers further from the Fermi level(Fe3+and Co3+)adsorbed CO2 poorly,thereby yielding H2 only(from water splitting).Our findings clarify the role of trivalent and tetravalent metal cations in LDH photocatalysts for the selective CO2 reduction,paving new ways for the development of improved LDH photocatalyst with high selectivities to specific products.

Recent Advances in Photocatalytic CO2 Reduction Using Earth-Abundant Metal Complexes-Derived Photocatalysts

Photochemical reduction of CO2 with H20 into energy-rich chemicals using inexhaustible solar energy is an appealing strategy to simultaneously address the global energy and environmental issues. Earth-abundant metal complexes show promising application in this field due to their easy availability, rich redox valence and tunable property. Great progress has been seen on catalytic reduction of CO2 under visible light illumination employing earth-abundant metal complexes and their hybrids as key contributors, especially for producing CO and HCOOH via the two-electron reduction process. In this minireview, we will summarize and update advances on earth-abundant metal complex-derived photocatalytic system for visible-light driven CO2 photoreduction over the last 5 years. Homogeneous earth-abundant metal complex photocatalysts and earth-abundant metal complex derived hybrid photocatalysts were both presented with focus on efficient improvement strategy.

Degradation of 4-nitrophenol by electrocatalysis and advanced oxidation processes using Co3O4@C anode coupled with simultaneous CO2 reduction via SnO2/CC cathode

Herein,we prepa red novel three-dimensional(3D)gear-s haped Co3O4@C(Co3O4 modified by amorphous carbon)and sheet-like SnO2/CC(SnO2 grow on the carbon cloth)as anode and cathode to achieve efficient removal of 4-nitrophenol(4-NP)in the presence of peroxymonosulfate(PMS)and simultaneous electrocatalytic reduction of CO2,respectively.In this process,4-NP was mineralized into CO2 by the Co3O4@C,and the generated CO2 was reduced into HCOOH by the sheet-like SnO2/CC cathode.Compared with the pure Co0.5(Co3O4 was prepared using 0.5 g urea)with PMS(30 mg,0.5 g/L),the degradation efficiency of 4-NP(60 mL,10 mg/L)increased from 74.5%-85.1%in 60 min using the Co0.5 modified by amorphous carbon(Co0.5@C).Furthermore,when the voltage of 1.0 V was added in the anodic system of Co0.5@C with PMS(30 mg,0.5 g/L),the degradation efficiency of 4-NP increased from 85.1%-99.1%when Pt was used as cathode.In the experiments of 4-NP degradation coupled with simultaneous electrocatalytic CO2 reduction,the degradation efficiency of 4-NP was 99.0%in the anodic system of Co0.5@C with addition of PMS(30 mg,0.5 g/L),while the Faraday efficiency(FE)of HCOOH was 24.1%at voltage of-1.3 V using the SnO2/CC as cathode.The results showed that the anode of Co3O4 modified by amorphous carbon can markedly improve the degradation efficiency of 4-NP,while the cathode of SnO2/CC can greatly improve the FE and selectivity of CO2 reduction to HCOOH and the stability of cathode.Finally,the promotion mechanism was proposed to explain the degradation of organic pollutants and reduction of CO2 into HCOOH in the process of electrocatalysis coupled with advanced oxidation processes(AOPs)and simultaneous CO2 reduction.

Harnessing Vis-NIR broad spectrum for photocatalytic CO2 reduction over carbon quantum dots-decorated ultrathin Bi2WO6 nanosheets

The photocatalytic reduction of CO2 to energy-rich hydrocarbon fuels is a promising and sustainable method of addressing global warming and the imminent energy crisis concomitantly. However, a vast majority of the existing photocatalysts are only capable of harnessing ultraviolet （UV） or/and visible light （Vis）, whereas the near-infrared （NIR） region still remains unexplored. In this study, carbon quantum dots （CQDs）-decorated ultrathin BizWO6 nanosheets （UBW） were demonstrated to be an efficient photocatalyst for CO2 photoreduction over the Vis-NIR broad spectrum. It is noteworthy that the synthesis procedure of the CQDs/UBW hybrid nanocomposites was highly facile, involving a one-pot hexadecyltrimethylammonium bromide （CTAB）-assisted hydrothermal process. Under visible light irradiation, the optimized 1CQDsAJBW （1 wt.% CQD content） exhibited a remarkable 9.5-fold and 3.1-fold enhancement of CH4 production over pristine Bi2WO6 nanoplatelets （PBW） and bare UBW, respectively. More importantly, the photocatalytic responsiveness of CQDs/UBW was successfully extended to the NIR region, which was achieved without involving any rare earth or noble metals. The realization of NIR-driven CO2 reduction could be attributed to the synergistic effects of （i） the ultrathin nanostructures and highly exposed {001} active facets of UBW, （ii） the excellent spectral coupling of UBW and CQDs, where UBW could be excited by the up-converted photoluminescence of CQDs, and （iii） the electron-withdrawing nature of the CQDs to trap the photogenerated electrons and retard the recombination of charge carriers.

Highly Efficient Photoelectrocatalytic Reduction of CO2 to Methanol by a p–n Heterojunction CeO2/CuO/Cu Catalyst

Photoelectrocatalytic reduction of CO2 to fuels has great potential for reducing anthropogenic CO2 emissions and also lessening our dependence on fossil fuel energy.Herein,we report the successful development of a novel photoelectrocatalytic catalyst for the selective reduction of CO2 to methanol,comprising a copper catalyst modified with flower-like cerium oxide nanoparticles(CeO2 NPs)(a n-type semiconductor)and copper oxide nanoparticles(CuO NPs)(a p-type semiconductor).At an applied potential of−1.0 V(vs SCE)under visible light irradiation,the CeO2 NPs/CuO NPs/Cu catalyst yielded methanol at a rate of 3.44μmol cm^−2 h^−1,which was approximately five times higher than that of a CuO NPs/Cu catalyst(0.67μmol cm^−2 h^−1).The carrier concentration increased by^108 times when the flower-like CeO2 NPs were deposited on the CuO NPs/Cu catalyst,due to synergistic transfer of photoexcited electrons from the conduction band of CuO to that of CeO2,which enhanced both photocatalytic and photoelectrocatalytic CO2 reduction on the CeO2 NPs.The facile migration of photoexcited electrons and holes across the p–n heterojunction that formed between the CeO2 and CuO components was thus critical to excellent light-induced CO2 reduction properties of the CeO2 NPs/CuO NPs/Cu catalyst.Results encourage the wider application of composite semiconductor electrodes in carbon dioxide reduction.

A bio-inspired O2-tolerant catalytic CO2 reduction electrode

The electrochemical reduction of CO2 to give CO in the presence of O2 would allow the direct valorization of flue gases from fossil fuel combustion and of CO2 captured from air. However, it is a challenging task because O2 reduction is thermodynamically favored over that of CO2. 5% O2 in CO2 near catalyst surface is sufficient to completely inhibit the CO2 reduction reaction. Here we report an O2-tolerant catalytic CO2 reduction electrode inspired by part of the natural photosynthesis unit. The electrode comprises of heterogenized cobalt phthalocyanine molecules serving as the cathode catalyst with >95% Faradaic efficiency(FE) for CO2 reduction to CO coated with a polymer of intrinsic microporosity that works as a CO2-selective layer with a CO2/O2 selectivity of $20. Integrated into a flow electrolytic cell, the hybrid electrode operating with a CO2 feed gas containing 5% O2 exhibits a FECOof 75.9% with a total current density of 27.3 mA/cm^2 at a cell voltage of 3.1 V. A FECO of 49.7% can be retained when the O2 fraction increases to 20%. Stable operation for 18 h is demonstrated. The electrochemical performance and O2 tolerance can be further enhanced by introducing cyano and nitro substituents to the phthalocyanine ligand.

Tuning the selectivity of photoreduction of CO2 to syngas over Pd/layered double hydroxide nanosheets under visible light up to 600 nm

Photocatalytic reduction of CO2 with H2 O to syngas is an effective way for producing high value-added chemical feedstocks such as methanol and light olefins in industry.Nevertheless,the precise control of CO/H2 ratio from photocatalytic CO2 reduction reaction still poses a great challenge for the further application.Herein,we prepared a series of highly efficient heterostructure based on highly dispersed palladium supported on ultrathin Co Al-layered double hydroxide(LDH).In conjunction with a Ru-complex sensitizer,the molar ratios of CO/H2 can be tuned from 1:0.74 to 1:3 under visible-light irradiation(λ>400 nm).More interestingly,the syngas can be obtained under light irradiation atλ>600 nm.Structure characterization and density functional theory calculations revealed that the remarkable catalytic activity can be due to the supported palladium,which improved the charge transfer efficiency.Meanwhile,more H atoms were used to generate H2 on the supported palladium for further tunable CO/H2 ratio.This work demonstrates a new strategy for harnessing abundant solar-energy to produce syngas from a CO2 feedstock.

Ultra-small Cu nanoparticles embedded in N-doped carbon arrays for electrocatalytic CO2 reduction reaction in dimethylformamide

The development of heterogeneous catalysts with a well-defined micro structure to promote their activity and stability for electrocatalyfic CO2 reduction has been shown to be a promising strategy. In this work, Cu nanoparticles （- 4 nm in diameter） embedded in N-doped carbon （Cu@NC） arrays were fabricated by thermal decomposition of copper tetracyanoquinodimethane （CuTCNQ） under N2. Compared to polycrystalline copper electrodes, the Cu@NC arrays provide a significantly improved number of catalytically active sites. This resulted in a 0.7 V positive shift in onset potential, producing a catalytic current density an order magnitude larger at a potential of -2.7 V vs. Fc/Fc＋ （Fc = ferrocene） in dimethylformamide （DMF）. By controlling the water content in the DMF solvent, the CO2 reduction product distribution can be tuned. Under optimal conditions （0.5 vol.% water）, 64% HCOO^-, 20% CO, and 13% H2 were obtained. The Cu@NC arrays exhibited excellent catalytic stability with only a 0.5% decrease in the steady-state catalytic current during 6 h of electrolysis. The three-dimensional （3D） array structure of the Cu@NC was demonstrated to be effective for improving the catalytic activity of copper based catalysts while maintaining long-term catalytic stability.

Evaluation of the plasmonic effect of Au and Ag on Ti-based photocatalysts in the reduction of CO2 to CH4

Crystalline TiO（P25） and isolated titanate species in a ZSM-5 structure（TS-1） were modified with Au and Ag, respectively, and tested in the gas-phase photocatalytic COreduction under high purity conditions. The noble metal modification was performed by photodeposition. Light absorbance properties of the catalysts are examined with UV–Vis spectroscopy before and after the activity test. In the gas-phase photocatalytic COreduction, it was observed that the catalysts with Ag nanostructures are more active than those with Au nanostructures. It is thus found that the energetic difference between the band gap energy of the semiconductor and the position of the plasmon is influencing the photocatalytic activity.Potentially, plasmon excitation due to visible light absorption results in plasmon resonance energy, which affects the excitation of the semiconductor positively. Therefore, an overlap between band gap energy of the semiconductor and metal plasmon is needed.

Surface composition dominates the electrocatalytic reduction of CO2 on ultrafine CuPd nanoalloys

Preciously tuning the surface composition of noble metal nanoparticles with the particle size of only 2 nm or less by alloying with other metals represents a powerful strategy to boost their electrocatalytic selectivity.However,the synthesis of ultrafine nanoalloys and tuning their surface composition remain challenging.In this report,ultrafine CuPd nanoalloys with the particle size of ca.2 nm are synthesized based on the galvanic replacement reaction between presynthesized Cu nanoparticles and Pd2+precursors,and the tuning of their surface compositions is also achieved by changing the atom ratios of Cu/Pd.For the electrocatalytic reduction of CO2,Cu5Pd5 nanoalloys show the CO Faradaic efficiency(FE)of 88%at−0.87 V,and the corresponding mass activity reaches 56 A/g that is much higher than those of Cu8Pd2 nanoalloys,Cu3Pd7 nanoalloys and most of previously reported catalysts.Density functional theory uncovers that with the increase of Pd on the surface of the ultrafine CuPd nanoalloys,the adsorbed energy of both of intermediate COOH*and CO*to the Pd sites is strengthened.The Cu5Pd5 nanoalloys with the optimal surface composition better balance the adsorption of COOH*and desorption of CO*,achieving the highest selectivity and activity.The difficult liberation of absorbed CO*on the surface of Cu3Pd7 nanoalloys provides carbon source to favor the production of ethylene,endowing the Cu3Pd7 nanoalloys with the highest selectivity for ethylene among these ultrafine CuPd nanoalloys.