Pd Sites Research Articles

Efficient Hole Extraction and *OH Alleviation by Pd Nanoparticles on GaN Nanowires in Seawater for Solar-Driven H2 and H2O2 Generation.

Photocatalytic seawater splitting generates green fuel (H2) and value-added chemicals (H2O2) using earth-abundant resources. In this study, Pd nanoparticles are integrated with one-dimensional gallium nitride nanowires (Pd NPs/GaN NWs) on a silicon wafer to produce H2 and H2O2 from seawater powered by sunlight. In-situ spectroscopic characterizations combined with computational investigations reveal that in this nanohybrid, Pd NPs function as an efficient hole extractor and *OH alleviator during photocatalysis. Meanwhile, the chloride ions in seawater facilitate the H2O→ H2 + H2O2 conversion by improving the charge dynamics and lowering the energy barrier of the key *OH self-coupling step over Pd sites in the catalytic system. As a result, the photocatalyst delivers an appreciable hydrogen production rate of 2.5 mmol·cm-2·h-1 with a light-to-hydrogen (LTH) efficiency of 4.38% in natural seawater under concentrated light irradiation of 3 W·cm-2 without sacrificial agents and external energies. Notably, water oxidation produces 300 µmol/L [[EQUATION]]H_2O_2H2​O2​ in 2 hours under 3 W/cm² light, using 20 mL water and achieving 0.53% light-to-chemical efficiency. The photocatalyst remain stable for 60 hours withturnover number of 1.42 x 107 moles H2 per mole of Pd. The Outdoor tests confirm the potential of solar-driven seawater splitting for green fuels.

Efficient Hole Extraction and *OH Alleviation by Pd Nanoparticles on GaN Nanowires in Seawater for Solar‐Driven H2 and H2O2 Generation

Photocatalytic seawater splitting generates green fuel (H2) and value‐added chemicals (H2O2) using earth‐abundant resources. In this study, Pd nanoparticles are integrated with one‐dimensional gallium nitride nanowires (Pd NPs/GaN NWs) on a silicon wafer to produce H2 and H2O2 from seawater powered by sunlight. In‐situ spectroscopic characterizations combined with computational investigations reveal that in this nanohybrid, Pd NPs function as an efficient hole extractor and *OH alleviator during photocatalysis. Meanwhile, the chloride ions in seawater facilitate the H2O→ H2 + H2O2 conversion by improving the charge dynamics and lowering the energy barrier of the key *OH self‐coupling step over Pd sites in the catalytic system. As a result, the photocatalyst delivers an appreciable hydrogen production rate of 2.5 mmol·cm−2·h−1 with a light‐to‐hydrogen (LTH) efficiency of 4.38% in natural seawater under concentrated light irradiation of 3 W·cm‐2 without sacrificial agents and external energies. Notably, water oxidation produces 300 µmol/L [[EQUATION]]H_2O_2H2​O2​ in 2 hours under 3 W/cm² light, using 20 mL water and achieving 0.53% light‐to‐chemical efficiency. The photocatalyst remain stable for 60 hours with turnover number of 1.42 x 107 moles H2 per mole of Pd. The Outdoor tests confirm the potential of solar‐driven seawater splitting for green fuels.

Effects of Pd site structural changes on Wacker oxidation of ethylene over PdCu/zeolites

Effects of Pd site structural changes on Wacker oxidation of ethylene over PdCu/zeolites

AuPd/TiO2 Catalysts in the CO Oxidation: Insights into the Synthesis Procedure and In-situ Spectroscopy Studies

Abstract A series of bimetallic AuPd/TiO2 catalysts (Au/Pd = 1) were prepared through either the impregnation or the deposition-precipitation in urea (DPU) approach and tested in the CO oxidation reaction. Among these, the sample synthesized through a sequential impregnation (Pd) followed by DPU (Au), with an intermediate thermal treatment in air, presented a remarkable CO conversion at sub-ambient temperatures and an enhanced catalytic stability, compared to the monometallic samples. The ex-situ characterization revealed that the synthesis procedure led to the formation of well-dispersed bimetallic AuPd nanoparticles over the TiO2 support. The in-situ characterization helped to propose that bimetallic NPs were composed of an intermetallic Au-Pd phase with both atoms available in the surface. Both in-situ FTIR and UV-vis spectroscopies helped to recognize the active sites during the reaction: Au in close interaction with the TiO2 at low temperatures, and step/edges Pd sites at high temperatures. Finally, the pivotal role of the TiO2 reducibility in the CO oxidation reaction, promoted by the bimetallic AuPd NPs, was determined through in-situ Raman spectroscopy.

Steering the Absorption Configuration of Intermediates over Pd-Based Electrocatalysts toward Efficient and Stable CO2 Reduction.

Palladium (Pd) catalysts are promising for electrochemical reduction of CO2 to CO but often can be deactivated by poisoning owing to the strong affinity of *CO on Pd sites. Theoretical investigations reveal that different configurations of *CO endow specific adsorption energies, thereby dictating the final performances. Here, a regulatory strategy toward *CO absorption configurations is proposed to alleviate CO poisoning by simultaneously incorporating Cu and Zn atoms into ultrathin Pd nanosheets (NSs). As-prepared PdCuZn NSs can catalyze CO production at a wide potential window (-0.28 to -0.78 V vs RHE) and achieve a maximum FECO of 96% at -0.35 V. Impressively, it exhibits stable CO production of 100 h under ∼95% FECO with no decay. Combined results from X-ray analysis, in situ spectroscopy, and theoretical simulations suggest that the codoping strategy not only optimizes the electronic structure of Pd but also weakens the binding strengths of *CO and increases the proportion of weak-binding linear *CO absorption configuration on catalysts' surfaces. Such targeted adoption of weakly bound configurations abates the energy barrier of *CO desorption and facilitates CO production. This work confers a useful design tactic toward Pd-based electrocatalysts, codoping for steering adsorption configuration to achieve highly selective and stable CO2-to-CO conversion.

Decoding the Hume-Rothery Rule in a Bifunctional Tetra-metallic Alloy for Alkaline Water Electrolysis.

The 90-year-old Hume-Rothery rule was adapted to design an outstanding bifunctional tetra-metallic alloy electrocatalyst for water electrolysis. Following the radius mismatch principles, Fe (131 pm) and Ni (124 pm) are selectively incorporated at the Pd (139 pm) site of Mo0.30Pd0.70 nanosheets. Analogously, Cu (132 pm) alloys with only Pd, while Ag (145 pm) alloys with both Pd and Mo (154 pm). The face-centered cubic Mo0.30Pd0.35Ni0.23Fe0.12 nanosheets with 10-12 atomic layers, featuring in-plane compressive strain along the {111} basal plane, show 1/3 (422) reflection from local hexagonal symmetry. The more electronegative Pd attracts electron density from Ni/Fe in Mo0.30Pd0.35Ni0.23Fe0.12, synergistically boosting the mass activities for hydrogen and oxygen evolution reactions to 89 ± 5 and 38.6 ± 3.1 A g-1 at ±400 mV versus RHE, respectively. Full water electrolysis continues for ≥550 h, requiring cell voltages of 1.51 and 1.63 V at 10 and 100 mA cm-2, delivering 45 mL h-1 green H2.

In Situ Selenization Induced Electron-Rich Pd with Weakened O2 Adsorption for Boosted Photocatalytic H2O2 Production.

Pd cocatalysts show great potential for the photocatalytic production of H2O2. However, the catalytic efficiency of Pd cocatalyst is limited due to the strong adsorption of O2, which promotes O-O bond cleavage and thus reduces selectivity for the two-electron O2 reduction reaction. Considering that adjusting the electron density of Pd can predominately optimize Pd-Oads bond strength, in this work, electron-rich Pd sites are constructed by introducing Bi2Se3 middle layer between Pd cocatalysts and (010) facet of BiVO4 using an in-situ selenization strategy. The photocatalytic results indicate that the designed BiVO4/Bi2Se3-Pd(0.3 %) photocatalyst achieves a high H2O2 yield of 2166 μmol L-1 in 2 h, which is 36 times and 3.75 times higher than BiVO4/Bi2Se3 and BiVO4/Pd photocatalyst, respectively. Additionally, the corresponding AQE value of BiVO4/Bi2Se3-Pd is 6.71 %. The subsequent Density functional theory (DFT) calculations and XPS spectra confirm that the introduction of Bi2Se3 via in-situ selenization increases the electron density of Pd. This enhances the formation of electron-rich Pd sites, reduces O2 adsorption, and ultimately improves the photocatalytic H2O2 yield. This strategy provides insights into designing efficient photocatalysts for H2O2 production through electronic structure modulation.

Atomic Pd Sites on CeO2 Nanorods for Highly Selective Hydrogen Peroxide Generation and Efficient Degradation of Organic Pollutants

Atomic Pd Sites on CeO₂ Nanorods for Highly Selective Hydrogen Peroxide Generation and Efficient Degradation of Organic Pollutants

Local Symmetry-Broken Single Pd Atoms Induced by Doping Ag Sites for Selective Electrocatalytic Semihydrogenation of Alkynes.

Engineering the local coordination environment of single metal atoms is an effective strategy to improve their catalytic activity, selectivity, and stability. In this study, we develop an asymmetric Pd-Ag diatomic site on the surface of g-C3N4 for the selective electrocatalytic semihydrogenation of alkynes. The single Pd atom catalyst, which has a locally symmetric Pd coordination, was inactive for the semihydrogenation of phenylacetylene in a 1 M KOH and 1,4-dioxane solution at an applied potential of -1.3 V (vs RHE). In sharp contrast, doping Ag sites into single Pd atom catalyst to form paired Pd-Ag diatomic sites with asymmetric Pd coordination substantially enhanced the reaction, resulting in a high conversion (>98%) with exceptional time-independent selectivity to styrene under identical conditions. Characterization and theoretical calculations reveal that the introduction of a Ag site into single Pd atoms disrupts their symmetry coordination by forming Pd-Ag bonds with N2-Pd-Ag-N configuration, thereby modulating the electronic and geometric structures of Pd sites, which in turn benefits the adsorption and activation of substrate and lowers energy barrier for the rate-determining step of semihydrogenation, ultimately enhancing the electrocatalytic reaction. This work provides a facile and powerful strategy for the design of advanced catalysts by tuning the local coordination environment for selective catalysis.

DFT Study on Mechanism and Regioselectivity in Pd(II)‐Catalyzed Dehydrogenative Heck Olefination of Selenophenes

AbstractThe present study deals with the theoretical investigation of mechanistic and regiochemical aspects of the Pd(II)‐catalyzed dehydrogenative Heck olefination of selenophenes. The detailed reaction mechanism was established, and the roles of the catalyst and regioselectivity were well rationalized. Our results clearly showed that the whole reaction involves a concerted metalation‐deprotonation (CMD) process between the C2 site of selenophene and Pd(OAc)2 in the first catalytic cycle. Afterward, the olefin coordinates to the palladium, followed by a regioselective 1,2‐migratory insertion to form a C─C bond. Then, β‐hydride elimination would give the final 2‐monoolefinated product. Subsequently, the second catalytic cycle generates the symmetrical 2,5‐diolefinated selenophene product. Another key finding of this study is that selenophene and its monoolefinated product act as nucleophiles, while the catalyst behaves as an electrophile. A global reactivity index (GRI) analysis revealed that the nucleophilicity (Nk) of C2, C3, C4, and C5 atoms in selenophene plays an important role in controlling the reaction selectivity at these sites. However, the distortion energies play a more important role in controlling the selectivity of reactions at the olefin C sites.

Engineering Lattice Dislocations of TiO2 Support of PdZn-ZnO Dual-Site Catalysts to Boost CO2 Hydrogenation to Methanol.

CO2 hydrogenation to methanol using green hydrogen derived from renewable resources provides a promising method for sustainable carbon cycle but suffers from high selectivity towards byproduct CO. Here, we develop an efficient PdZn-ZnO/TiO2 catalyst by engineering lattice dislocation structures of TiO2 support. We discover that this modification orders irregularly arranged atoms in TiO2 to stabilize crystal lattice, and consequently weakens electronic interactions with supported active phases. It facilitates the transformation of metallic Pd into PdZn alloy, effectively suppressing CO production through inhibiting the reverse water-gas shift reaction mediated by the carboxylate pathway on Pd0 sites. Moreover, it enables the efficient transfer of hydrogen species via hydrogen spillover from PdZn alloy to ZnO for compensating the poor hydrogen dissociation ability of ZnO, thereby creating both more oxygen vacancies essential for CO2 activation and a hydroxyl-rich environment conducive to hydrogenation of intermediates. These collective modifications on PdZn-ZnO dual sites synergistically induce the propensity of the formate pathway for methanol synthesis. Consequently, compared to the unmodified catalyst, our as-designed catalyst increases methanol selectivity from 64.2 to 80.0 %, reduces CO selectivity from 35.0 to 19.8 %, and achieves an impressive methanol space-time yield of 9028.0 mgMeOH gPd+Zn -1 h-1 at a similar CO2 conversion (~8.0 %).

Engineering lattice dislocations of TiO2 support of PdZn‐ZnO dual‐site catalysts to boost CO2 hydrogenation to methanol

CO2 hydrogenation to methanol using green hydrogen derived from renewable resources provides a promising method for sustainable carbon cycle but suffers from high selectivity towards byproduct CO. Here, we develop an efficient PdZn‐ZnO/TiO2 catalyst by engineering lattice dislocation structures of TiO2 support. We discover that this modification orders irregularly arranged atoms in TiO2 to stabilize crystal lattice, and consequently weakens electronic interactions with supported active phases. It facilitates the transformation of metallic Pd into PdZn alloy, effectively suppressing CO production through inhibiting the reverse water‐gas shift reaction mediated by the carboxylate pathway on Pd0 sites. Moreover, it enables the efficient transfer of hydrogen species via hydrogen spillover from PdZn alloy to ZnO for compensating the poor hydrogen dissociation ability of ZnO, thereby creating both more oxygen vacancies essential for CO2 activation and a hydroxyl‐rich environment conducive to hydrogenation of intermediates. These collective modifications on PdZn‐ZnO dual sites synergistically induce the propensity of the formate pathway for methanol synthesis. Consequently, compared to the unmodified catalyst, our as‐designed catalyst increases methanol selectivity from 64.2 to 80.0%, reduces CO selectivity from 35.0 to 19.8%, and achieves an impressive methanol space‐time yield of 9028.0 mgMeOH gPd+Zn‐1 h‐1 at a similar CO2 conversion (~8.0%).

In Situ Metal Vacancy Filling in Stable Pd-Sn Intermetallic Catalyst for Enhanced CC Bond Cleavage in Ethanol Oxidation.

A common challenge in electrochemical processes is developing high performance, stable catalysts for specific chemical reactions. In this work, a Pd-Sn intermetallic compound with Pd site deficiency (Pd1.9-xSn) (x = 0.06) and trace amount of SnOx was synthesised by controlled process. Under the electrochemical conditions, the deficient Pd site is filled by metallic Sn, which generates a highly active and stable (Pd1.84Sn0.06)Sn catalyst for ethanol oxidation reaction (EOR). The crystal structure and atomic arrangements for synthesized and in situ generated compound are comprehensively characterized by various spectroscopic techniques. The in situ generated catalyst exhibits excellent performance toward EOR (anodic reaction in fuel cell), which outperforms the state-of-the-art Pd/C catalyst by three times in terms of activity. Furthermore, it is observed that the catalyst preferentially cleaves the CC bond in ethanol, which is a crucial process that enhances the efficiency of the fuel cells. The catalyst retains its superlative activity even after 1500 cycles of continuous operation. The mechanism for EOR and CC bond cleavage is evidenced by operando Infra Red spectroscopyand Differential Electrochemical Mass Spectroscopy (DEMS), and the driving force toward excellent performance has been proposed via theoreticalcalculations.

Interplay Between Metal and Acid Sites Tunes the Catalytic Selectivity Over Pd/Nanodiamond Catalysts.

Metal and acid sites are two of the most crucial catalytically active components in heterogeneous catalysis. While variations in the size, morphology, and heterogeneity of metal species, or the manipulation of the strength, location, and density of acid sites, could significantly impact the catalytic performance, the combination and interplay between these sites are even more critical and have been a recent research focus. To achieve highly efficient and selective synergistic catalysis, it is desired to design a catalyst capable of orchestrating the sequential transformation of all reactants and intermediates at different active sites. In this study, we demonstrate that both acid and metal (Pd) sites can be introduced onto a nanodiamond@graphene (NDG) support particle through simple air oxidation and metal salt deposition-precipitation methods, respectively. The presence and assembly of these two catalytically active sites significantly alter the reaction network for the cyclohexanol conversion reaction. Under this strategy, the selectivity toward designated products─cyclohexene, phenol, and benzene─can be precisely tuned by the presence and patterning of these two sites on the nanodiamond particles. Specifically, we show that the catalyst with both acid sites and Pd ensemble sites, i.e., Pd/NDG, can efficiently convert cyclohexanol through consecutive dehydration and dehydrogenation reactions to form benzene with high selectivity (>80%). These findings underscore the potential of integrating metal and acid sites to design advanced catalysts with tailored reactivity and selectivity, paving the way for more efficient and versatile catalytic processes in industrial applications.

Machine-learning-accelerated density functional theory screening of Cu-based high-entropy alloys for carbon dioxide reduction to ethylene

Computational screening of high-entropy alloy (HEA) catalysts as alternatives to the typical Cu electrocatalyst for CO2 reduction reaction (CO2RR) has been extensively focused on C1 products, but C2+ products have received significantly less attention. This work optimized CuZnPdAgAu HEA catalyst composition for CO2RR to ethylene via density functional theory and supervised machine learning regression techniques. Candidates were identified from 106,045 HEA data for enthalpy of adsorption of *CO2, *H, *HOCCOH, and *C2H4 species, and the Gibbs free energy of *H. The electrocatalytic properties during the reaction were examined on the surface of the optimized HEA candidate – Cu0.36Zn0.18Pd0.10Ag0.18Au0.18 benchmarked to Cu (111). The Pd site of such a candidate functions as the active site for the CO2 activation step. In terms of catalytic activity, it showed lower Gibbs free energy for the potential determining step – the *OCCOH formation step compared to that on the Cu (111). Insight into electronic properties demonstrated that the candidate reduces the uphill reaction energy for *HOCCOH production pathway due to increased electron density in the C–C bond, donated from two Cu sites. It is shown that the HEA catalyst candidate has the potential for CO2RR targeting ethylene, an alternative to a common Cu catalyst.

Operando elucidation of hydrogen production mechanisms on sub-nanometric high-entropy metallenes

Precise morphological control and identification of structure-property relationships pose formidable challenges for high-entropy alloys, severely limiting their rational design and application in multistep and tandem reactions. Herein, we report the synthesis of sub-nanometric high-entropy metallenes with up to eight metallic elements via a one-pot wet-chemical approach. The PdRhMoFeMn high-entropy metallenes exhibit high electrocatalytic hydrogen evolution performances with 6, 23, and 26 mV overpotentials at −10 mA cm−2 in acidic, neutral, and alkaline media, respectively, and high stability. The electrochemical measurements, theoretical simulations, and operando X-ray absorption spectroscopy reveal the actual active sites along with their dynamics and synergistic mechanisms in various electrolytes. Specially, Mn sites have strong binding affinity to hydroxyl groups, which enhances the water dissociation process at Pd sites with low energy barrier while Rh sites with optimal hydrogen adsorption free energy accelerate hydride coupling, thereby markedly boosting its intrinsic ability for hydrogen production.

Facet-dependent spatial separation of dual cocatalysts on MOF photocatalysts for H2O2 production coupling biomass oxidation with enhanced performance

Cooperative coupling of photocatalytic two-electron oxygen reduction reaction (2e-ORR) with oxidative organic synthesis holds great promise for sustainable production of valuable chemicals. To achieve high performance, the rational design of photocatalysts with effective electron-hole separation and redox capability is crucial. Herein, a MOF-based photocatalyst with crystal facet-dependent spatial separation of dual cocatalysts is constructed for photocatalytic 2e-ORR coupled with vanillyl alcohol oxidation reaction (VAOR). The facet-dependent growth of reductive Pd and oxidative CoOx cocatalysts respectively on the {100} and {001} facets of MIL-125-NH2 enables the directional migration of photogenerated carries, facilitating the charge separation for redox reactions. Additionally, the interaction between Pd and MIL-125-NH2 modulates the Pd sites into electron-sufficient state with upshifted d-band center, promoting the O2 activation and *OOH intermediate formation. The rationally designed composite photocatalyst delivers an excellent H2O2 yield of 74.8 mM g−1 h−1 and a high vanillic acid production rate of 80.9 mM h−1 g−1 with the conversion and selectivity of 96.8 % and 91.1 %, respectively.

Mechanistic and Kinetic Analysis of Complete Methane Oxidation on a Practical PtPd/Al2O3 Catalyst

A PtPd/Al2O3 catalyst developed for the complete oxidation of methane from the ventilation air of underground coal mines is compared against a model PdO/Al2O3 catalyst. Although the PtPd/Al2O3 catalyst is substantially more active and stable than the model catalyst, the nature of active sites between the two catalysts is deemed to be fundamentally the same based on their response to different feed gas compositions and the evolution of surface CO adsorption complexes during time-resolved CO adsorption DRIFTS experiment. For both catalysts, coordinatively unsaturated Pd sites are considered the active centers for methane activation and the subsequent oxidation reaction. H2O competes with CH4 for the same active sites, resulting in severe inhibition. Additionally, the CH4 oxidation reaction also causes self-inhibition. Taking both inhibition effects into consideration, a relatively simple kinetic model is developed. The model provides a good fit of the 72 sets of kinetic data collected on the PtPd/Al2O3 catalyst under practically relevant reaction conditions with CH4 concentration in the range of 0.05–0.4%, H2O concentration of 1.0–5.0%, and reaction temperatures of 450–700 °C. Kinetic parameters based on the model suggest that the CH4 activation energy on the PtPd/Al2O3 catalyst is 96.7 kJ/mol, and the H2O adsorption energy is −31.0 kJ/mol. Both values are consistent with the parameters reported in the literature. The model can be used to develop catalyst sizing guidelines and be incorporated into the control algorithm of the catalytic system.

Polarization Electric Field of Tourmaline Promotes Formic Acid Oxidation on Palladium

Direct formic acid fuel cells (DFAFC) use formic acid that is easy to store and transport as fuel, which has the advantages of high energy density and low operating temperature, and has shown broad application prospects in mobile power and other fields. Palladium is recognized as the most effective electrocatalyst for formic acid oxidation (FAO). Unfortunately, palladium nanoparticles are easily dissolved in the acidic environment during fuel cell operation. In addition, the d-band center of Pd is close to the Fermi level, resulting in forming a strong bond between Pd and adsorbed species (e.g., COad-like species). As a direct consequence of the above issues, Pd nanoparticles are continuously lost and poisoned, causing unsatisfactory cycling performance. However, all these previous approaches can only alleviate the issues of Pd poisoning and Pd dissolution, respectively.In this work, by utilizing the polarization electric field of tourmaline minerals to change the adsorption state and energy of formic acid molecules, the electrocatalytic performance of palladium in FAO reactions can be improved. Tourmaline nanoparticles (TNP) are coated with resorcinol-formaldehyde (RF) resin to obtain TNP@RF support (Fig.1a), and Pd nanoparticles are uniformly and partially embedded in the RF carbon layer to generate TNP@RFC@Pd catalysts by in situ carbothermal reduction (Fig.1b). The polarized-electric field from tourmaline (Fig.1c) induces charge transfer from Pd to tourmaline, causing the d-band center to shift away from the Fermi level (Fig.1d). Both the strain effect and ligand effect cause the electron-deficient state of Pd. Consequently, breaking the O-H bond in formic acid is enhanced and the bond strength between Pd and COad is weakened. The polarized-electric field of tourmaline promotes the generation of OHad on Pd to convert COad into CO2 and release the active sites of Pd. The embedded structure of Pd nanoparticles in the carbon layer prevents the dissolution and agglomeration. Benefiting from these results, TNP6.67@RFC@Pd1 catalyst exhibits 3.9 times higher mass activity, greater CO-tolerance and better durability than those of electric-field-free catalysts (Fig.1e). Figure 1

Interface-Engineering-Induced C-C Coupling for C2H4 Photosynthesis from Atmospheric-Concentration CO2 Reduction.

Producing ethylene (C2H4) from carbon dioxide (CO2) photoreduction under mild conditions is primarily restricted by the difficulty of C-C coupling. Herein, we designed highly active metal atom clusters anchored on semiconductor nanosheets, which established heteroatom sites on the interface to steer C-C coupling, realizing air-concentration CO2 photoreduction into C2H4 in pure water. As an example, the Pd nanoclusters loaded on ZnO nanosheets are prepared, demonstrated by the X-ray photoelectron spectroscopy and high-angle annular dark-field image. In situ Fourier transform infrared spectroscopy confirms the C-C coupling step over the Pd-ZnO nanosheets, while quasi in situ X-ray photoelectron spectroscopy illustrates the active sites of Pd and Zn atoms on the Pd-ZnO nanosheets during CO2 photoreduction. Density functional theoretical calculations unveil the transition state energy barrier of C-C coupling of CO* and COH* intermediates are only 0.998 eV, hinting the easy C-C coupling to produce C2 fuels. Therefore, the Pd-ZnO nanosheets realize C2H4 photosynthesis by atmospheric-concentration CO2 reduction with the formation rate of 1.03 μmol g-1 h-1, while the ZnO nanosheets only acquired the carbon monoxide product.