Pd-based Catalysts Research Articles

Unraveling the effect and difference of S or Si atoms modified Pd-based catalysts in tuning catalytic performance of C2H2 semi-hydrogenation

Modifying the spatial scale of active site has been proven a good strategy for enhancing catalytic performance. In this study, the Pd-based catalysts with different spatial scale of active site were constructed via the modification of non-metallic S or Si atoms over Pd, Cu alloyed Pd SACs, PdAg surface alloy and PdM (M=Au, Ag) IMCs catalysts, then, C2H2 semi-hydrogenation catalytic performance was identified based on DFT calculations. The findings indicate that the catalytic performance of C2H2 semi-hydrogenation is greatly influenced by the spatial extent of active site and the electronic effect modified by the S or Si atoms. Geometric effect caused by S or Si atoms reduces the spatial scale of active site over S/Pd-2 × 2, Si/Pd-3 × 3, S/Pd6Ag, S/Pd1Au1, S/Pd1Ag1 and Si/Pd1Ag1, thereby preventing green oil generation. Electronic effect caused by S or Si atoms leads to far away from the Fermi level of d-band center over S/Pd-2 × 2, Si/Pd-3 × 3, S/Pd1Au1, S/Pd1Ag1 and Si/Pd1Ag1 to improve C2H4 production activity and selectivity. Seven catalysts S/Pd-2 × 2, Si/Pd-3 × 3, PdCu-2 × 2, S/Pd6Ag, S/Pd1Au1, S/Pd1Ag1 and Si/Pd1Ag1 are screened out to present high selectivity and activity of C2H4 production, and effectively prevent green oil generation. This study provides valuable structural insights for designing high-performance catalysts by the modification of non-metallic atom in C2H2 semi-hydrogenation.

Heterogeneous activation of self-generated H2O2 by Pd@UiO-66(Zr) for trimethoprim degradation: Efficiency and mechanism

The Fenton reaction is recognized as an effective technique for degrading persistent organic pollutants, such as the emerging pollutant trimethoprim (TMP). Recently, due to the excellent reducibility of active hydrogen ([H]), Pd–H2 has been preferred for Fenton-like reactions and the specific H2 activation of Pd-based catalysts. Herein, a heterogeneous Fenton catalyst named the hydrogen-accelerated oxygen reduction Fenton (MHORF@UiO-66(Zr)) system was prepared through the strategy of building ships in the bottle. The [H] has been used for the acceleration of the reduction of Fe(III) and self-generate H2O2. The systematic characterization demonstrated that the nano Pd0 particle was highly dispersed into the UiO-66(Zr). The results found that 20 mg L−1 of TMP was thoroughly degraded within 90 min in the MHORF@UiO-66(Zr) system under conditions of initial pH 3, 30 mL min−1 H2, 2 g L−1 Pd@UiO-66(Zr) and 25 μM Fe2+. The hydroxyl radical as well as the singlet oxygen were evidenced to be the main reactive oxygen species by scavenging experiments and electron spin resonance. In addition, both reducing Fe(III) and self-generating H2O2 could be achieved due to the strong metal-support interaction (SMSI) between the nano Pd0 particles and UiO-66(Zr) confirmed by the correlation results of XPS and calculation of density functional theory. Finally, the working mechanism of the MHORF@UiO-66(Zr) system and the possible degradation pathway of the TMP have been proposed. The novel system exhibited excellent reusability and stability after six cyclic reaction processes.

Pd nanoparticles supported on silver, zinc, and reduced graphene oxide as a highly active electrocatalyst for ethanol oxidation

In this manuscript, we present a facile approach to synthesize a highly active catalyst for the electro-oxidation of ethanol using Pd nanoparticles supported on a Ag–Zn alloy on reduced graphene oxide. This nanocomposite material was fabricated via a two-step process of incineration followed by sol-gel synthesis. The physical properties of the catalyst were evaluated using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning and transmission electron microscopies. To understand the catalyst's activity for ethanol oxidation, we performed a series of cyclic voltammetry and electrochemical impedance spectroscopy experiments in alkaline medium. The catalyst exhibited good catalytic activity with a current density of 13.01 mA cm−2, a value seven times higher than the commercial standard Pd/C catalyst and higher than any other previously reported Pd-based catalyst. The results were attributed synergistic effects between the Pd and alloy support along with the large electrochemically active surface area of the material. Taken together, these results suggest that ethanol electrocatalysts based on nanocomposites of Pd, Ag, and Zn is promising candidates for future ethanol fuel cells.

Designing nanoporous Pd catalyst with dual enhancement of thermodynamics and kinetics for formic acid oxidation reaction

Conventional strategies for developing highly efficient electrocatalysts involve enhancing thermodynamics to minimize overpotential and improving kinetics to maximize reaction current. However, current research on Pd-based catalysts for formic acid oxidation reaction (FAOR) mainly focuses on accelerating its kinetics to increase the peak current. This study proposes a catalyst design that can simultaneously improve the kinetics and thermodynamics of FAOR. Specifically, the home-made catalyst (NPG-Pt1-Pd1) is obtained by sequentially depositing monolayer Pt and Pd shells on the surface of nanoporous gold (NPG) substrate. Compared with commercial Pd/C, this electrocatalyst exhibits a noticeable negative shift in onset potential (∼100 mV) and a significantly improved peak current (∼6 times). Experimental data and theoretical calculations demonstrate that NPG-Pt1-Pd1 exhibits a comparatively suitable adsorption energy for small molecules, not only reducing the overpotential but also accelerating the reaction rate of FAOR. Moreover, when applied in direct formic acid fuel cells (DFAFC), the NPG-Pt1-Pd1 anode with an exceptionally low Pd loading of 8.5 μg cm−2, achieves a remarkable power density of 141 mW cm−2. The power efficiency of Pd is 230 times that of Pd/C (1 mg cm−2, 73 mW cm−2). Therefore, this work provides a new methodology for developing efficient Pd-based FAOR electrocatalysts.

Construction of H-Doped PdB Nanocrystals as Electrocatalysts to Modulate Formic Acid Oxidation.

The strong ligand effect in B-doped Pd-based (PdB) catalysts renders them a promising anode for constructing formic acid fuel cells (FAFCs) exhibiting high power density and outstanding stability. However, the enhancement of the oxidation barrier is unavoidable in this alloy system owing to the electron transfer (ET) from B to Pd. In this study, a hydrogen doping strategy is employed to open charge freedom in PdB compounds and boost their formic acid oxidation reaction (FAOR) activity by suppressing the ET process. The resulting hydrogen-doped PdB (PdBH) exhibits an ultrahigh mass activity of up to 1.2A mg-1 Pd, which is 3.23 times that of the PdB catalyst and 9.55 times that of Pd black. Detailed experimental and theoretical studies show that the interstitial hydrogen leads to enhanced orbital hybridization and reduced electron density around Pd. This optimized ligand effect weakens the carbon monoxide adsorption and increases the direct pathway preference of PdBH, resulting in its outstanding catalytic activity for the FAOR. The development of this high-performance hydrogen-doped PdB catalyst is an important step toward the construction of advanced light element co-doped metal catalysts.

Ultrasmall Pd nanoparticles supported on a metal–organic framework DUT-67-PZDC for enhanced formic acid dehydrogenation

The highly dispersed ultrasmall palladium nanoparticles (Pd NPs) (1.7 nm) were successfully immobilized on a N-containing metal–organic framework (MOF, DUT-67-PZDC) using a co-reduction method, and it is used as an excellent catalyst for formic acid dehydrogenation (FAD). The optimized catalyst Pd/DUT-67-PZDC(10, 10 wt% Pd loading) shows 100% hydrogen (H2) selectivity and formic acid (FA) conversion at 60 °C, and the commendable initial turnover frequency (TOF) values of 2572 h−1 with the sodium formate (SF) as an additive and 1059 h−1 even without SF, which is better than most reported MOF supported Pd monometallic heterogeneous catalysts. The activation energy (Ea) of FAD is 43.2 KJ/mol, which is lower than most heterogeneous catalysts. In addition, the optimized catalyst Pd/DUT-67-PZDC(10) maintained good stability over five consecutive runs, demonstrating only minimal decline in catalytic activity. The outstanding catalytic performance could be ascribed to the synergistic corporations of the unique structure of DUT-67-PZDC carrier with hierarchical pore characteristic, the metal-support interaction (MSI) between the active Pd NPs and DUT-67-PZDC, the highly dispersed Pd NPs with ultrafine size serve as the catalytic active site, as well as the N sites on the support could act as the proton buffers. This work provides a new paradigm for the efficient H2 production of FAD by constructing highly active heterogeneous Pd-based catalysts using MOF supports.

Ethylenediamine-mediated synthesis of Pd-based catalysts with enhanced electrocatalytic performances towards formic acid oxidation

Pd-based anode catalysts with superior activity are urgent for formic acid oxidation to further boost the direct formic acid fuel cells (DFAFCs) technologies. Herein, a strategy of ethylenediamine (EDA) modified Pd/C catalyst was developed by two main steps of EDA adsorbed on Vulcan XC-72 carbon by impregnation and Pd nanoparticles loaded on the freeze-dried C-EDA supports by liquid reduction method. The effects of sweep rates and concentrations of EDA on the formic acid electrooxidation were systematically studied. Results showed that the above parameter was optimized as the concentration of EDA of 0.1 mol L−1. Pd nanoparticles with even distribution were fabricated and particle sizes were in the range of 3.5–4.2 nm. In addition, Pd particle size became smaller with the addition of EDA, suggesting that EDA could induce the generation of smaller Pd. Electrochemical measurements demonstrated that the electrocatalytic activity of Pd/C-0.22EDA (1021 mA mg−1) with optimized modification concentration was improved as a factor of 3.82 than that of Pd/C (267 mA mg−1). An enhanced stability (about 41 times higher than Pd/C) and faster charge-transfer kinetics of formic acid electrooxidation were observed for Pd/C-0.22EDA catalyst. CV and CA measurements showed that the most active catalyst was made of the smallest (3.5 nm) Pd nanoparticles for Pd/C-0.22EDA catalyst. The better electrocatalytic performances of Pd/C-0.22EDA might be ascribed to evenly dispersed Pd with relatively smaller particle size, electron regulation between Pd and amine group as well as stable Pd structure.

Locally Varying Surface Binding Affinity on Pd-Au Nanocrystals Enhances Electrochemical Ethanol Oxidation Activity.

Noble metal nanocrystals face challenges in effectively catalyzing electrochemical ethanol oxidation reaction (EOR)-represented multistep, multielectron transfer processes due to the linear scaling relationship among binding energies of intermediates, impeding independent optimization of individual elemental steps. Herein, we develop noble metal nanocrystals with a range of local surface binding affinities in close proximity to overcome this challenge. Experimentally, this is demonstrated by applying tensile strain to a Pd surface and decorating it with discrete Au atoms, forming a diversity of binding sites with varying affinities in close proximity for guest molecules, as evidenced by CO probing and density functional theory calculations. Such a surface enables reaction intermediates to migrate between different binding sites as needed for each elemental step, thereby reducing the energy barrier for the overall EOR when compared to reactions at a single site. On these tailored surfaces, we attain specific and mass activities of 32.7 mA cm-2 and 47.8 A mgPd-1 in EOR, surpassing commercial Pd/C by 10.9 and 43.8 times, respectively, and outperforming state-of-the-art Pd-based catalysts. These results highlight the promise of this approach in improving a variety of multistep, multielectron transfer reactions, which are crucial for energy conversion applications.

Interfacial Push-Pull Dynamics Enable Rapid Had Desorption for Enhanced Formate Electrooxidation.

The electrocatalytic conversion of formate in alkaline solutions is of paramount significance in the realm of fuel cell applications. Nonetheless, the adsorptive affinity of adsorbed hydrogen (Had) on the catalyst surface has traditionally impeded the catalytic efficiency of formate in such alkaline environments. To circumvent this challenge, our approach introduces an interfacial push-pull effect on the catalyst surface. This mechanism involves two primary actions: First, the anchoring of palladium (Pd) nanoparticles on a phosphorus-doped TiO2 substrate (Pd/TiO2-P) promotes the formation of electron-rich Pd with a downshifted d band center, thereby "pushing" the desorption of Had from the Pd active sites. Second, the TiO2-P support diminishes the energy barrier for Had transfer from the Pd sites to the support itself, "pulling" Had to effectively relocate from the Pd active sites to the support. The resultant Pd/TiO2-P catalyst showcases a remarkable mass activity of 4.38 A mgPd-1 and outperforms the Pd/TiO2 catalyst (2.39 A mgPd-1) by a factor of 1.83. This advancement not only surmounts a critical barrier in catalysis but also delineates a scalable pathway to bolster the efficacy of Pd-based catalysts in alkaline media.

Easily recyclable pd-decorated hierarchically porous nanofibers for the selective hydrogenation of phenol

The electrospun nanofibers are good candidates for the catalyst carriers, however the fabrication of electrospun nanofibers with well-developed porous structures is still a big challenge. Herein, the SiO2 nanofibers obtained by electrospinning and pyrolysis are functionalized with polydopamine (PDA) and UiO-66-NH2, and after Pd loading the hierarchically porous Pd/UiO-SiO2 nanofiber catalysts were developed. The surface properties and microstructures of the Pd/UiO-SiO2 nanofiber catalysts were regulated by adjusting the concentrations of dopamine (DA) and zirconium tetrachloride (ZrCl4), and the catalytic performance was tested in the selective hydrogenation of phenol to cyclohexanone. The as-prepared Pd/UiO-SiO2-3–21.44 has abundant hierarchical pores and amino groups, high Pd content with good dispersion, and rich Pd(0), thus exhibiting a superior specific activity of 47.3 h−1 higher than most Pd-based catalysts. Most importantly, the Pd/UiO-SiO2-3–21.44 nanofiber catalyst can be directly taken out from the reaction solution and used for the next run, and has good catalytic stability.

Study of size effect of palladium atoms as single-atom and clusters nanoparticle catalysts for Heck reactions

We reported a series of nitrogen-doped carbon-supported palladium (Pd) species with various sizes for the Heck reaction of iodobenzene and methyl acrylate. By precisely controlling the synthesis procedure, we have successfully synthesized a range of Pd-based catalysts, including single Pd atom, sub-nanometer Pd clusters (∼ 0.4 nm, and ∼1.6 nm), and Pd nanoparticles (∼5.8 nm and 10 nm). Remarkably, these catalysts exhibit a distinct size-dependent catalytic activity in the Heck reaction. In the case of the Heck reaction of 4‑methoxy-iodobenzene and methyl acrylate, the Pd-10 site demonstrated the highest site-specific turnover frequency (TOF), reaching 792.5 h−1. This performance is impressively 5.2 and 15.6 times superior to that of the Pd1 site (152 h-1) and Pd-10 site (50.6 h-1), respectively. Significantly better in the Heck reactions with other aryl halides were achieved with Pd-1.6/N-C (comprising of approximately 1.6 nm-sized Pd clusters), compared to those containing 10 nm-sized nanoparticles (Pd-10/N-C) or Pd1/N-C. These findings suggested that Pd clusters of around 1.6 nm may serve as the potential catalytic sites for the Heck reaction.

Rapid synthesis of PdCu nanosheets with enhanced electrocatalytic activity toward polyalcohol oxidation reaction

Reasonable design of Pd-based catalysts with specific composition and morphology is of great importance for promoting the commercial application.of direct alcohol fuel cells (DAFCs). Recently, two-dimension (2D) with high density of defects and massive low-coordinated surface atom has become research highlights in the field of catalysis. Herein, we report a wet chemical method for synthesizing PdCu nanosheets with abundant wrinkles. The ultrathin two-dimensional structure endows catalysts plentiful catalytic active sites and large specific surface area, improving atomic utilization efficiency. The formation of bimetallic PdCu alloy structure leads to the adjustment of Pd electronic structure, resulting in lattice compression effect. Benefitting from the structural and compositional characteristics, PdCu nanosheets (NSs) exhibits excellent electrocatalytic performance for ethylene glycol oxidation reaction (EGOR) and glycerol oxidation reaction (GOR) with the mass activity of 7031 mA mg−1/5117 mA mg−1, which is 4.4/3.9 times higher than that of commercial Pd/C catalysts. Furthermore, the remained mass activity of PdCu NSs is 3991/3851 mA mg−1 after the durability measurement for EGOR/GOR, which confirm PdCu NSs possesses superior stability. We believe that our synthetic strategy could provide robust reference for the development of high-performance eletrocatalysts.

Palladium-modified zirconium dioxide as a selective catalyst for hydrogenation of furfural to furfuryl alcohol

The hydrogenation reaction can effectively promote the upgrading of biomass-derived resources into high value-added products. Currently, constructing metal Pd-based catalysts is one of the effective strategies to promote hydrogenation reactions. In this paper, Pd-ZrO2 catalyst was prepared through electrospinning technology using PdCl2-Zr(acac)4/PVP as a precursor for furfural hydrogenation reaction. The results revealed that the obtained Pd-ZrO2 catalyst could provide 70 % furfural conversion and 76.2 % furfuryl alcohol selectivity at 170 ℃ and 2 MPa 5 % H2/Ar for 12 h. At the same time, nearly complete FAL conversion with 92.9 % FOL selectivity could be achieved under 2 MPa N2 for 12 h in the process of catalytic transfer hydrogenation. In addition, the effects of conditions such as reaction temperature, reaction time, and solvent on the two hydrogenation paths were further evaluated. The cycle test proved that the catalyst can be recycled multiple times without significant decrease in catalytic activity.

Phosphorus-Doping Enables the Superior Durability of a Palladium Electrocatalyst towards Alkaline Oxygen Reduction Reactions.

The sluggish kinetics of oxygen reduction reactions (ORRs) require considerable Pd in the cathode, hindering the widespread of alkaline fuel cells (AFCs). By alloying Pd with transition metals, the oxygen reduction reaction's catalytic properties can be substantially enhanced. Nevertheless, the utilization of Pd-transition metal alloys in fuel cells is significantly constrained by their inadequate long-term durability due to the propensity of transition metals to leach. In this study, a nonmetallic doping strategy was devised and implemented to produce a Pd catalyst doped with P that exhibited exceptional durability towards ORRs. Pd3P0.95 with an average size of 6.41 nm was synthesized by the heat-treatment phosphorization of Pd nanoparticles followed by acid etching. After P-doping, the size of the Pd nanoparticles increased from 5.37 nm to 6.41 nm, and the initial mass activity (MA) of Pd3P0.95/NC reached 0.175 A mgPd-1 at 0.9 V, slightly lower than that of Pd/C. However, after 40,000 cycles of accelerated durability testing, instead of decreasing, the MA of Pd3P0.95/NC increased by 6.3% while the MA loss of Pd/C was 38.3%. The durability was primarily ascribed to the electronic structure effect and the aggregation resistance of the Pd nanoparticles. This research also establishes a foundation for the development of Pd-based ORR catalysts and offers a direction for the future advancement of catalysts designed for practical applications in AFCs.

Metal immobilized in a USY zeolite-supported (4-CB)TPPB: A new strategy of enhanced stability for acetylene hydrochlorination

Palladium (Pd)-based catalysts supported by silicaluminate materials are potential as the efficient non-mercury catalyst for acetylene hydrochlorination, which is a necessary industrial reaction for producing vinyl chloride monomer. A new strategy was employed to improve Pd/USY zeolite catalysts taking advantage of 4-carboxybutyl triphenylphosphonium bromide ((4-CB)TPPB) for acetylene hydrochlorination. The most active catalyst (Pd@20(4-CB)TPPB/USY) with the 0.5 wt% Pd loadings and the 20 wt% (4-CB)TPPB additives could achieve a stable acetylene conversion of 99.9 % and the vinyl chloride selectivity of 99.7 % during more than 50 h, outperforming the Pd/USY catalyst. The additive of (4-CB)TPPB was preferential to stabilize the catalytic active Pd species, inhibit the Pd (II) reduction and change the surface acidic properties during the preparation process and reaction, hence restraining the carbon deposition. Density functional theory (DFT) calculations further indicate that (4-CB)TPPB additives could effectively enhance the adsorption energy of catalyst for reactants and the desorption energy of vinyl chloride monomer (VCM) products, thus inhibiting the carbon deposition for improving the catalytic performance of Pd/USY catalysts. These findings provide guidance for designing efficient Pd-based catalysts as well as their utilization for acetylene hydrochlorination.

Clarifying Glycerol Electrooxidation Studies on Pd-Based Catalysts: Insights Into Catalytic Performance and Practical Challenges.

Escalating biodiesel production led to a surplus of glycerol, prompting its exploration as a valuable resource in industrial applications. Electrochemical systems have been studied, specifically employing noble metal catalysts like palladium for glycerol electrooxidation. Despite numerous studies on Pd-based catalysts for glycerol electrooxidation, a comprehensive analysis addressing critical questions related to the economic feasibility, global sourcing of Pd, and the thematic cohesion of publications in this field is lacking. Moreover, a standardized framework for comparing the results of various studies is absent, hindering progress on glycerol technologies. This critical overview navigates the evolution of Pd-based catalysts for glycerol electrooxidation, examining catalytic activity, stability, and potential applications. It critically addresses the geographical sources of Pd, the motivation behind glycerol technology exploration, thematic coherence in existing publications, and the meaningful comparison of results. It correlates the use of Pd-based catalysts with the natural source of Pd and the origin of glycerol derived from biodiesel. The proposed standardized approach for comparing electrochemical parameters and establishing experimental protocols provides a foundation for meaningful study comparisons. This critical overview underscores the need to address fundamental questions to accelerate the transition of glycerol technologies from laboratories to practical applications.

Regulating the electronic structure by P-doping cobalt-based catalyst for atomic hydrogen mediated electrocatalytic dechlorination

Electrocatalytic dechlorination by atomic hydrogen (H*) is efficient, but limited by the low efficiency of H* production. Herein, a phosphorus-doped cobalt nitrogen carbon catalyst (Co-NP/C) was prepared, which had high catalytic activity in a wide pH range (3−11). The turnover frequency of Co-NP/C (3.54 min−1) was 1.21–59000 times superior to that of current Pd-based and non-noble metal catalysts (0.00006–2.92 min−1). Co-NP/C significantly enhanced H* generation, which was 1.52, 2.44, and 3.77 times stronger than that of Co-N/C, NP/C, and N/C, respectively, since the introduction of phosphorus was found enhanced the electron density of cobalt and regulated the electron transfer. Co-NP/C showed outstanding catalytic performance after ten cycles and could achieve nearly complete chloramphenicol removal. This regulation method was verified to be effective for other non-noble metal (Fe, Mn, Cu, Ni) phosphorus doped catalysts, proposing a general class for efficient electrochemical dechlorination, which would be of great significance for the elimination of chlorinated organic pollutants.

Coordination-induced amidated modified polyacrylonitrile loaded ultrafine palladium nanoparticles for thermocatalytic hydrogen evolution

A promising approach for powering hydrogen fuel cells (HFCs) involves the in-situ production of hydrogen from formic acid decomposition, with Pd-based catalysts recognized as effective for formic acid dehydrogenation. However, the immobilization of ultrafine palladium nanoparticles (Pd NPs) on catalytic supports presents a challenge and necessitates further investigation into their formation mechanism. We propose a coordination-induced strategy to understand the behavior of ultrafine Pd NPs formation based on multi-functional groups. To establish the structure–activity relationship for tunable Pd microenvironment and catalytic performance, we synthesized various polyacrylonitrile (PAN) carriers through hydrolysis and amidation modification. Molecular dynamics simulations confirmed that a stronger coordination-induced microenvironment facilitates the dispersion of Pd2+, suppressing aggregation and enhancing Pd loading. Our experimental results and density functional theory (DFT) calculations demonstrated that the catalytic activity of Pd@APAN(15_1%) with ultrafine Pd NPs (1.5 nm) exhibits over 10 times higher than that of Pd@PAN NPs with the turnover of frequency climbing from 112.6 h−1 to 1309.4 h−1 at 323 K. And Pd-imine and Pd-secondary amine moieties were verified to contribute to the creation of a favorable catalysis microenvironment. This study provides new insights into the design of modified supports with various groups to load well-dispersed and ultrafine Pd for highly efficient catalysts based on a coordination-induced strategy.

Theoretically predicted innovative palladium stripe dopingcobalt(1 1 1) surface with excellent catalytic performance for carbon monoxide oxidative coupling to dimethyl oxalate

Pd-based catalysts are extensively employed to catalyze CO oxidative coupling to generate DMO, while the expensive price and high usage of Pd hinder its massive application in industrial production. Designing Pd-based catalysts with high efficiency and low Pd usage as well as expounding the catalytic mechanisms are significant for the reaction. In this study, we theoretically predict that Pd stripe doping Co(1 1 1) surface exhibits excellent performance than pure Pd(1 1 1), Pd monolayer supporting on Co(1 1 1) and Pd single atom doping Co(1 1 1) surface, and clearly expound the catalytic mechanisms through the density functional theory (DFT) calculation and micro-reaction kinetic model analysis. It is obtained that the favorable reaction pathway is COOCH3–COOCH3 coupling pathway over these four catalysts, while the rate-controlling step is COOCH3+CO+OCH3→2COOCH3 on Pd stripe doping Co(1 1 1) surface, which is different from the case (2COOCH3→DMO) on pure Pd(1 1 1), Pd monolayer supporting on Co(1 1 1) and Pd single atom doping Co(1 1 1) surface. This study can contribute a certain reference value for developing Pd-based catalysts with high efficiency and low Pd usage for CO oxidative coupling to DMO.

3D hollow superstructures endow PdAg electrocatalyst with selective ethanol electrooxidation

Direct ethanol fuel cells (DEFCs) have been considered as future power devices for many portable applications. The ethanol oxidation reaction (EOR), that is, a multielectron process, suffers from low efficiency owing to the high selectivity to the 4e− pathway (C2 pathway) and low selectivity to the 12e− pathway (C1 pathway). The preparation of efficient catalysts with high C1 pathway selectivity is regarded as a promising and fascinating field. Herein, we first advance a one-pot synthesis of 3D PdAg superstructures (SSs) with a hollow interior and ultrathin nanosheet shell. PdAg SSs achieve a mass activity of 5.27 A mg−1 for the alkaline EOR and a Faraday efficiency of 22.7 % for the C1 pathway, which is 5.7 and 7.5 times higher than that of commercial Pd/C, respectively. Mechanism studies confirm that the construction of the Pd-Ag system greatly facilitates the oxidation of the C1 intermediates (*CH3 and *CO) and enhances the CC bond cleavage ability of the catalyst. This work not only highlights an active Pd-based catalyst for the selective EOR, but also sheds light on the formation of 3D open nanostructure via self-assembly of 2D nanosheets.