Pd-based Catalysts Research Articles

Palladium Nanosheet Enables Synergistic Electrocatalytic Dehalogenation via Direct and Indirect Electron Transfer Mechanisms.

Electrocatalytic dehalogenation is a promising method for the remediation of chlorinated organic pollutants. The dehalogenation performance is controlled by catalytic activity, and the underlying electrocatalytic dehalogenation mechanisms need to be carefully investigated for guiding the design of catalyst. Here we report the preparation of a new Pd-based catalyst with a nanosheet structure (Pd NS) by a simple wet-chemical reduction method. This Pd NS catalyst showed a superior electrocatalytic activity toward the reductive dehalogenation of a chlorinated organic pollutant (e.g., 4-chlorophenol) with the dehalogenation rate of 0.324 h-1. Importantly, the obtained Pd NS catalyst had a good durability that could operate well over 30 h under high concentration of 4-chlorophenol with removal efficiency beyond 82%. Experimental results confirmed the simultaneous occurrence of direct electrocatalytic dehalogenation and H*-mediated indirect electron transfer mechanisms in the dehalogenation process, and their quantitative contributions to the dehalogenation performance were established based on the cyclic voltammetry and quenching experiments. This study provides a promising dehalogenation catalyst and sheds light on the mechanism of electrocatalytic dehalogenation as well as the development of a dual-functional electrocatalyst.

Progress in palladium-based bimetallic catalysts for lean methane combustion: Towards harsh industrial applications

<p>Significant volumes of lean methane (0.1–1.0 vol%) are released untreated into the atmosphere during industrial operations, contributing to the greenhouse effect and energy wastage. Catalytic methane combustion presents a promising avenue to mitigate these emissions. Depending on their active components, catalytic systems are predominantly categorized into noble metal-based and non-noble metal-based catalysts, with palladium (Pd)-based catalysts recognized for their superior low-temperature oxidation activity. Nevertheless, enhancing the thermal stability of Pd remains challenging, complicated by impurities such as H<sub>2</sub>O, SO<sub>2</sub> and H<sub>2</sub>S in the lean methane stream, which can cause catalyst poisoning and deactivation. Recent research has focused on the design of Pd-based bimetallic catalysts, offering improved stability, activity, and resistance to poisoning in harsh industrial conditions. This review examines advancements in improving the deactivation resistance of Pd-based bimetallic catalysts for lean methane combustion, covering active site characterization, dispersion and metal-support interactions, the role of auxiliary metals, and structural modulation strategies. It also investigates the impact of harsh industrial environments on Pd-based catalyst performance, focusing on deactivation mechanisms and mitigation strategies. Ultimately, this review identifies current research trends and challenges for Pd-based catalysts in demanding applications. By providing insights into the design of Pd-based catalysts with enhanced stability, activity, and resistance to poisoning, this review aims to guide the development of catalysts that meet industrial demands.</p>

Acetylene semi-hydrogenation catalyzed by Pd single atoms sandwiched in zeolitic imidazolate frameworks via hydrogen activation and spillover.

The semi-hydrogenation of alkynes into alkenes rather than alkanes is of great importance in the chemical industry, and palladium-based metallic catalysts are currently employed. Unfortunately, a fairly high cost and uncontrollable over-hydrogenation impeded the application of Pd-based catalysts on a large scale. Herein, a sandwich structure single atom Pd catalyst, Z@Pd@Z, was prepared via impregnation exchange and epitaxial growth methods (Z stands for ZIF-8), in which Pd single atoms were stabilized by pyrrolic N in a zeolitic imidazolate framework (ZIF-8). Semi-hydrogenation of acetylene was performed and Z@Pd@Z achieved 100% acetylene conversion at 120 °C with an ethylene selectivity of more than 98.3% at an extra low Pd concentration. Z@Pd@Z exhibited a specific activity of 1872.69 mLC2H4 mgPd-1 h-1, surpassing most of the reported Pd-based catalysts. The existence of Pd single atoms coordinated by nitrogen (Pd-N4) was verified by XAS (synchrotron X-ray absorption spectroscopy), which provided active sites for H2 dissociation and the dissociated hydrogen quickly spilled over the surface of the outer ZIF layer to hydrogenate alkyne to ethene; besides, the catalytic activity could be controlled by adjusting the thickness of the outer ZIF layer. The confinement of the ZIF on Pd single-atom sites and the high energy barrier of ethylene hydrogenation were found to be responsible for the superior C2H2 semi-hydrogenation activity. This work opens up valuable insights into the design of ZIF-derived single-atom catalysts for efficient acetylene selective hydrogenation.

Electronic Metal–Support Interaction on Pd/CoNi-hydroxides with enhanced CO adsorption for boosting CO2 methanation

CO2 conversion to value-added chemical products is of significance for carbon cycling. Pd-based catalysts show great potential in CO2 methanation reaction by virtue of synergistic effect between the Pd and...

Integration of Phosphorus in PdCr Metallene for Enhanced CO-Tolerant Alcohol Electrooxidation.

Pd-based alloys are among the most attractive catalysts for direct alcohol fuel cells. However, their widespread use is limited by the high cost of Pd and their susceptibility to deactivation by surface-adsorbed reaction intermediates, particularly CO. In this study, we engineered an ultrathin 2D PdCr metallene to minimize Pd usage and doped it with phosphorus to enhance its CO tolerance. The resulting P-PdCr metallene demonstrated significantly higher activity, stability, and CO tolerance for the electrooxidation of various alcohols compared to PdCr metallene and commercial Pd/C catalysts. Particularly, for the methanol oxidation reaction (MOR), the P-PdCr catalyst achieved a mass activity of 2.64 A mg-1Pd and a specific activity of 5.81 mA cm-2, maintaining remarkable stability over a duration of 27 h. Density functional theory calculations revealed that the enhanced performance is attributed to the incorporation of Cr and P atoms into the Pd metallene structure. This incorporation significantly reduces the energy barriers of the potential-determining step in the MOR process, mitigates CO adsorption on the catalyst surface, and accelerates the conversion of reaction intermediates. The strategic doping of phosphorus into the metallene structure introduces a novel approach for developing Pd-based catalysts with enhanced CO tolerance in alcohol electrooxidation.

Pd-Based Multi-Site Catalysts for Selective CO2-to-Methanol Conversion.

Developing a multi-site Pd-based electrocatalyst for CO2-to-C1 conversion with high performance and selectivity in the hydrogenation pathway for the CO2 electroreduction reaction is both desirable and challenging. Here, we develop triple-site metallene (Pd82Bi11In7), which can achieve an unprecedented Faraday efficiency of 72.6 ± 1% for methanol production. X-ray photoelectron spectroscopy analysis indicates that some electrons transfer from In and Bi to Pd inside Pd82Bi11In7, forming local electron-rich Pd-site, local primary electron-deficient center In-site, and local secondary electron-deficient center Bi-site. Meanwhile, Pd82Bi11In7 has stronger adsorption for *COOH and *CO, which avoids the generation of formic acid and CO. Moreover, Pd82Bi11In7 reduces the potential determining step energy barrier and controls the hydrogenation path for direct methanol production. The synergistic effect of the triple-sites enables efficient CO2 electroreduction to methanol.

Anomalous Role of Carbon in Pd-Catalyzed Selective Hydrogenation.

Carbonaceous species, including subsurface carbidic carbon and surface carbon, play crucial roles in heterogeneous catalysis. Many reports suggested the importance of subsurface carbon in the selective hydrogenation of alkynes over Pd-based catalysts. However, the role of surface carbon has been largely overlooked. We demonstrate that subsurface carbon in Pd is not responsible for the selectivity in acetylene hydrogenation. In contrast, the structure of surface carbonaceous species plays a decisive role in hydrogenation selectivity. Electron microscopy and spectroscopy evidence, along with theoretical modelling, reveal that partial graphitization of surface carbonaceous species results in unique spatial confinement of surface reaction intermediates, thus altering the reaction energy landscape in favour of ethylene desorption as opposed to over-hydrogenation. This mechanism for selectivity control is analogous to enzyme catalysis, where the active centers selectively attract reactants and release products. Similar mechanism might be present in CO/CO2 hydrogenation and alkane dehydrogenation reactions.

Phase Engineering of Zirconia Support Promotes the Catalytic Dehydrogenation of Formic Acid by Pd Active Sites.

The development of Pd-based catalysts with outstanding activity and stability can further promote the hydrogen storage application of formic acid (FA). Regulating the support structure is an effective strategy for enhancing active sites in heterogeneous catalytic systems. This study prepared three types of nanosized ZrO2 through phase engineering to support Pd metal and investigated the implications of support structure on the microenvironment of active sites, thus revealing the structure-activity relationship of the catalysts. The hollow nanoframes like Pd/ZrO2-F with a moderate t-ZrO2 content exhibit remarkable stability and catalytic performance with a TOF of 1348 h-1 at an ambient temperature. Density functional theory (DFT) calculations verify that the crystal phase of ZrO2 can dramatically affect the metal-support interaction and change the Pd electronic state. Moreover, the dehydrogenation energy profiles reveal the synergy effect between ZrO2 phases on Pd active sites in the reaction. Pd/m-ZrO2 is more conducive to the dissociation of FA, and Pd/t-ZrO2 has energy advantages in hydrogen recombination. This work provides a new perspective for understanding the synergistic effect of the zirconia crystal phase on formic acid dehydrogenation by Pd active sites.

Electric Field-Induced Synergetic Enhancement of Local Hydroxyl Concentration and Photogenerated Carrier Density for Removal of COads in Electrocatalytic Formic Acid Oxidation.

Direct formic acid fuel cell (DFAFC) is an efficient power generation device, due to its high energy density, low fuel crossover and low emission. However, the anodic reaction of DFAFC, formic acid oxidation (FAOR), inevitably proceeds through an indirect pathway, adsorbing carbon monoxide intermediate (COads), resulting in a rapid decline of activity for FAOR. Therefore, effectively removing COads is the key to the development of DFAFC. In this work, Pd/CeO2 catalyst is synthesized by in situ growth of Pd nanoparticles on the hollow CeO2. Due to the difference of work function between Pd and CeO2, a built-in electric field from Pd side to CeO2 side is formed, which induces a synergistic enhancement of the photogenerated carrier density and the local high hydroxyl concentration at the Pd/CeO2 interface, thus promoting the oxidative removal of COads and significantly improving the stability of FAOR. Therefore, in photo-assisted electrocatalytic FAOR, Pd/CeO2 not only possessed high mass activity (4161.72 mA mg-1 Pd), and its mass activity decreases by only 20.1% after 40000 s chronoamperometry test, which is superior to most Pd-based catalysts. This work provides a new strategy for efficient removal of COads in FAOR through constructing built-in electric fields, which promotes the DFAFC application.

Thermodynamic Analysis of Size-Dependent Surface Energy in Pd Nanoparticles for Enhanced Alkaline Ethanol Electro-Oxidation.

This work investigates the relationship between the mean diameter of palladium (Pd) nanoparticles and their surface energy, specifically in the context of alkaline ethanol electro-oxidation for fuel cell applications. Employing a recent generalization of the classical Laviron equation, we derive crucial parameters such as surface energy (σ), adsorption-desorption equilibrium constant (Keq), and electron transfer coefficient (α) from linear voltammograms obtained from Pd-based nanoparticles supported on Vulcan carbon. Synthesized using two distinct methods, these nanocatalysts exhibit mean diameters ranging from 10 to 41 nm. Our results indicate that the surface energy of the Pd/C nanocatalysts spans σ ~ 0.5-2.5 J/m2, showing a linear correlation with particle size while remaining independent of ethanol bulk concentration. The adsorption-desorption equilibrium constant varies with nanoparticle size (~0.1-6 × 10-6 mol-1) but is unaffected by ethanol concentration. Significantly, we identify an optimal mean diameter of approximately 28 nm for enhanced electrocatalytic activity, revealing critical size-dependent effects on catalytic efficiency. This research contributes to the ongoing development of cost-effective and durable fuel cell components by optimizing nanoparticle characteristics, thus advancing the performance of Pd-based catalysts in practical applications. Our findings are essential for the continued evolution of nanomaterials in fuel cell technologies, particularly in improving efficiency and reducing reliance on critical raw materials.

Synthesis of stable CeO2-ZrO2/Al2O3 material with abundant oxygen vacancies for Pd-only three-way catalyst through two synergistic lanthanum doping processes

Stable support with abundant surface oxygen vacancies (Ov) is indispensable for robust sintering-resistant heterogeneous catalysts. Herein, a strategy of lanthanum (La) atom selectively doping has been put forward to construct the desirable CeO2-ZrO2/Al2O3 (CZA) support for high-temperature applications with the precise control of its distribution and location through two distinct addition processes. In the first addition process, La3+ was introduced to Al2O3 component by precipitation process to stabilize its structure by occupying the surface –OH sites and forming thermodynamically stabled LaAlO3. In the second addition process, the low-valence La3+ is surface grafted and preferentially captured by CZ component during preparation due to electrostatic attraction, thus generating abundant asymmetric Ov as anchor sites for metal nanoparticles. The resulting CZA supported Pd-based three-way catalyst exhibits superior intrinsic activity even being hydrothermally aged at 900 °C/10 h since the as-prepared CZA could anchor Pd species in smaller size and oxidized state due to the enhanced metal-support interactions. This work provides new insights into doping effects and offers an avenue to design stable and active support material for industrial applications.

Synergistic Interfaces of Pd Nanocrystals and Metal Hydroxides for Ethanol Oxidation Reaction

Introduction As one of the environmentally friendly power generation methods, alcohol fuel cells using bioalcohols have gained attention. Ethanol offers advantages such as low toxicity and an existing distribution network. However, its power generation efficiency is limited by the ethanol oxidation reaction (EOR) at the anode. In an alkaline environment, Pd-based catalysts are regarded as promising candidates due to high intrinsic catalytic activities. Thus, improving the catalytic activity of Pd-based catalysts is a challenging issue to meet the requirements of commercial applications. Several metal hydroxides achieved to improve catalytic activities of Pd nanoparticles for EOR, however, previous studies have not systematically investigated the effects of the kinds of metal hydroxide, structure of the contacting interface, and facets of the materials on catalytic activities of composite catalysts, lacking effective design guide of highly active electrocatalysts. In this study, we synthesize composite electrocatalysts of cubic and octahedral Pd nanoparticles (Pd-NPs) with well-defined facets and monolayer metal hydroxide nanosheets with containing Ni, Fe and Mn, and systematically elucidate highly active interfacial sites between Pd and metal hydroxides for EOR. Experimental The cubic and octahedral Pd (c-Pd, o-Pd) were synthesized by liquid phase synthesis using shape-controlling agents. The multi-metal hydroxide nanosheets were synthesized by exfoliating layered double hydroxides, resulting in FeNi hydroxide nanosheets (FeNi-NS) and MnNi hydroxide nanosheets (MnNi-NS). The suspensions of Pd-NPs and metal hydroxide nanosheets were mixed to synthesize the composite catalysts (Pd/NS). The samples were coated onto a glassy carbon rotating electrode and used as a working electrode. The ethanol oxidation reaction (EOR) was conducted using three electrodes system with a Hg/HgO reference electrode and a Pt wire counter electrode. The catalytic performances were evaluated by a cyclic voltammetry measurement in an Ar-saturated 1.0 mol dm-3 KOH aqueous solution containing 1.0 mol dm-3 ethanol. Results and Discussion SEM and TEM observations confirmed that c-Pd and o-Pd nanoparticles exposed (100) and (111) facets on their surfaces, respectively. Crystallographic diffraction peaks specific to these facets were observed in electron diffraction patterns. STEM observations of Pd/NS revealed that the faceted surface of Pd-NPs was modified with FeNi-NS and MnNi-NS (Fig. 1). The valence states of Pd in the composite catalysts changed to the oxidative states compared to that of the corresponding pristine Pd-NPs due to modification of nanosheets. All catalysts showed anodic peaks originated from ethanol oxidation in the rage of 0.5 and 0.9 V vs RHE. The composite catalysts showed higher current density than that of the pristine Pd-NPs, indicating that nanosheet modification enhanced the catalytic activities of Pd by change in valence states. The Pd/MnNi-NS composite catalysts showed higher activity than Pd/FeNi-NS composite catalysts. This suggests that higher hydroxide ion affinity of MnNi-NS facilitated the dehydrogenation reaction in EOR. While the c-Pd was superior for EOR than the o-Pd in the pristine Pd-NPs, the o-Pd/NS showed higher EOR performances than those of c-Pd/NS. The results suggest that the combination of metal hydroxides and the Pd (111) facet provides highly active interfacial sites for EOR.Fig. 1. The composite catalysts of FeNi-NS and (a)c-Pd and (b)o-Pd. Figure 1

Pd-Based Metal-Support Heterostructure Catalyst for High Performance Electrocatalytic N2 Reduction Reaction

Electrocatalytic nitrogen (N2) reduction reaction (eNRR) is of great interest to produce the green ammonia (NH3). However, the competitive side reaction of hydrogen (H2) evolution reaction (HER) and slow proton-couple electron transfer (PCET) step still become a bottleneck where resulting in poor N2 selectivity and yield of NH3 production. The heterostructures of metal and boron nitride (BN) analogs have been computatively demonstrated and suggested as a potential eNRR catalyst to improve eNRR performance as both suppressing HER and accelerating PCET step. However, experimental demonstration is still challenging due to the complex synthetic method required to achieve a uniform and dense distribution of metal catalysts on the BN surface. Here, we present the facile and uniform formation of the Pd nanoparticles (NPs) on defective boron nitride (BN) using ultrafast radiative Joule-heating within short time (~0.5 s), which is the first-time demonstration on the BN family. Especially, thanks to the strong electronic metal-to-support interaction (EMSI) effect between the defect site of BN surface and Pd NPs, the electron-deficient state of Pd NPs facilitates the significant reduce of free energy during the PCET step which is beneficial to interact with N2 molecules. In particular, we observe that Pd NPs on defective BN support exhibit the high NH3 selectivity of 68% in the neutral aqueous electrolyte and 59% of NH3 selectivity and 53.3 µg/h/cm2 of NH3 yield rate in the acidic media, respectively, which are the highest values of the selectivity and NH3 yield rate among existing Pd-based eNRR catalysts.

Structural Regulation and Advanced Transmission Electron Microscopy Characterization of the Oxygen Reduction Reaction Electrocatalysts

Fuel cells (FCs) are regarded as the most promising green energy conversion technology in the 21st century because of their advantages. However, the industrialization process of FCs is restricted by several key problems, one of which is the cathode catalyst. The Oxygen Reduction Reaction (ORR) of FCs is a complex process involving 4 electrons, which has sluggish kinetics and high over-potential. Therefore, it is usually necessary to use a large number of precious metal platinum (Pt) catalysts to improve the reaction efficiency, but the characteristics of small reserves of Pt, high price, and easy to be poisoned and deactivated increase the operating cost of the whole system. It is imperative to develop substitutes for non-Pt-based ORR catalysts and reveal their structure-activity relationship with advanced characterization techniques.There are two ways to solve this problem: one is to improve the utilization rate of platinum-based catalyst, the other is to develop non-platinum-based catalysts. In terms of improving the utilization rate of Pt, our research group mainly constructed new Pt-based ordered intermetallic compound catalytic materials, and improved the surface structure, alloying degree and electronic structure of Pt-based catalysts by changing the atomic types, proportions and post-treatment temperatures of Pt and transition metals, so as to regulate their electrocatalytic properties. On the other hand, the morphology control of ordered intermetallic compounds has always been a major challenge in this field, and we have made a preliminary attempt in the morphology control. At the same time, with the help of modern characterization techniques, it is of great significance to study the changes of structure and components during the service of Pd-based catalysts, and to understand their failure behavior and performance attenuation mechanism for the subsequent optimization and commercialization of Pd-based catalysts. Among them, visualization technology based on transmission electron microscopy (TEM) has become a research hotspot because it can directly observe the failure process of catalysts in service.

Effect of Cathodic Potential in Electrochemical CO2 Reduction

In this presentation, we will discuss the critical role of cathodic-potential in modulating the selectivity, activity and even stability of electroreduction of CO2 (CO2R). We will first introduce the potential-dependent selectivity in Cu-based CO(2)R, originating from a combination of pH-effect, kinetics of different *CO activation pathways, local field effect, and CO coverage effects, etc. By carefully elucidating the intricate interplays among these effects, we could leverage cathodic potential as an effective lever to steer the CO(2)R selectivity towards multi-carbon-products. Additionally, we will introduce how cathodic-potential plays affects the CO2R stability, particularly in preventing the electrolyte flooding. Specifically, we observed that CO2R kinetic-curves typically enter the mixed-control-region at approximately > 0.75 V, and then quickly transition to the CO2 mass transport-limited-region, regardless of the type of GDE used or the current density achieved. This suggests that GDE flooding is closely associated with the cathodic-potential. Inspired by this understanding, we demonstrate that an intrinsically more active catalyst capable of sustaining a sufficient CO2R current at a low cathodic potential before entering the mixed-controlled region can lead to significantly enhanced CO2R stability and improved energy efficiency.If time allows, we will also briefly introduce two non-Cu-based systems:(1) The potential-dependent structural-evolution of Pd-based catalysts during CO2R to formate. We found that by manipulating the valence state of Pd, one could substantially extend the cathodic-potential window for stabilizing the desired a-Pd phase, achieving robust and efficient CO2-to-formate conversion on Pd-catalysts.(2) The potential-dependent CO2-to-methanol production on Co-Phthalocyanine. Here, the cathodic-potential is critical in inducing the structural-distortion of the Co-N4 plane, influencing the *CO binding mode and strength, which leads to the selectivity change from CO to methanol on Co-Phthalocyanine.Overall, we wish to underscore the importance of considering cathodic potential as a crucial parameter in the design and optimization of electrochemical CO2R systems.

Magnesium oxide-supported potassium hydride as a transition-metal-free catalyst for the selective hydrogenation of alkynes

Catalytic hydrogenation of alkynes to alkenes is pivotal in both petrochemical and fine chemical industries. Its implementation relies on the use of transition metals, especially those precious Pd-based catalysts. In this work, we utilize a melt infiltration method to prepare magnesium oxide-supported potassium hydride (KH/MgO), which is illustrated as a transition-metal-free catalyst for selective hydrogenation of alkynes. H2-D2 exchange experiment proves that dihydrogen activation and dissociation on KH/MgO is plausible at room temperature and ambient pressure. KH/MgO catalyzes hydrogenation of diphenylacetylene (DPA) already at 40 ℃, implying its high intrinsic activity at very mild conditions. Under an optimized condition of 80°C, 2 bar H2, and 40 h, 75 % conversion of DPA is achieved, affording 82 % selectivity to stilbenes. Mechanistic study suggests that surface hydride on KH/MgO plays an important role toward dihydrogen activation, and involved in the hydrogenation step to form stilbenes. This work shows the promise for using light metal hydrides consisting of earth-abundant elements as alternative hydrogenation catalysts.

A Carbon-Particle-Supported Palladium-Based Cobalt Composite Electrocatalyst for Ethanol Oxidation Reaction (EOR)

For the first time, carbon-particle-supported palladium-based cobalt composite electrocatalysts (abbreviated as PdxCoy/CPs) were prepared using a calcination–hydrothermal process–hydrothermal process (denoted as CHH). The catalysts of PdxCoy/CPs prepared using CoC2O4·2H2O, (CH3COO)2Co·4H2O, and metallic cobalt were named catalyst c1, c2, and c3, respectively. For comparison, the catalyst prepared in the absence of a Co source (denoted as Pd/CP) was identified as catalyst c0. All fabricated catalysts were thoroughly characterized by XRD, EDS, XPS, and FTIR, indicating that PdO, metallic Pd, carbon particles, and a very small amount of cobalt oxide were the main components of all produced catalysts. As demonstrated by the traditional electrochemical techniques of CV and CA, the electrocatalytic performances of PdxCoy/CP towards the ethanol oxidation reaction (EOR) were significantly superior to that of Pd/CP. In particular, c1 showed an unexpected electrocatalytic activity for EOR; for instance, in the CV test, the peak f current density of EOR on catalyst c1 was 129.3 mA cm−2, being about 10.7 times larger than that measured on Pd/CP, and in the CA test, the polarized current density of EOR recorded for c1 after 7200 s was still about 2.1 mA cm−2, which was larger than that recorded for Pd/CP (0.6 mA cm−2). In the catalyst preparation process, except for the elements of C, O, Co, and Pd, no other elements were involved, which was thought to be the main contribution of this preliminary work, being very meaningful to the further exploration of Pd-based composite EOR catalysts.

A Nitrogen- and Carbon-Present Tin Dioxide-Supported Palladium Composite Catalyst (Pd/N-C-SnO2)

For the first time, nitrogen- and carbon-present tin dioxide-supported palladium composite catalysts (denoted as Pd/N-C-SnO2) were prepared via an HCH method (HCH is the abbreviation for the hydrothermal process–calcination–hydrothermal process preparation process). In this work, firstly, three catalyst carriers (denoted as cc) were prepared using a hydrothermal-process-aided calcination method, and catalyst carriers prepared using ammonia monohydrate (NH3∙H2O), N,N-dimethylformamide (C3H7NO) and triethanolamine (C6H15NO3) as the nitrogen sources were nominated as cc1, cc2 and cc3, respectively. Secondly, these catalyst carriers were reacted with palladium oxide monohydrate (PdO·H2O) hydrothermally to generate catalysts c1, c2 and c3. As testified by XRD and XPS, besides carbon materials and the N-containing substances, the main substances of all prepared catalysts were SnO2 and metallic palladium (Pd). Above all things, all resultant catalysts, especially c2, showed a prominent electrocatalytic activity towards the ethanol oxidation reaction (EOR). As indicated by the CV (cyclic voltammetry) results, all fabricated catalysts presented a clear electrocatalytic activity towards the EOR. In the CA (chronoamperometry) measurement, the faradaic current density of EOR measured on c2 at −0.27 V vs. an SCE (saturated calomel electrode) after 7200 s was still maintained at about 5.6 mA cm−2. Preparing a novel catalyst carrier, N-C-SnO2, and preparing a new EOR catalyst, Pd/N-C-SnO2, were the principal dedications of this preliminary work, which was very beneficial to the development of Pd-based EOR catalysts.

Engineering Topological and Chemical Disorder in Pd Sites for Record-Breaking Formic Acid Electrocatalytic Oxidation.

Designing palladium-based formic acid oxidation reaction (FAOR) catalysts to achieve significant breakthroughs in catalytic activity, pathway selectivity, and toxicity resistance is both urgent and challenging. Here, these challenges are addressed by pioneering a novel catalyst design that incorporates both topological and chemical disorder, developing a new class of PdCuLaYMnW high-entropy amorphous alloys with a porous network (Net-Pd-HEAA) as a highly active, selective, and stable FAOR electrocatalyst. This novel Net-Pd-HEAA demonstrates record-breaking FAOR performance, achieving the mass and specific activities of 5.94 A mgPd -1 and 8.94mA cm-2, respectively, surpassing all previously reported Pd-based catalysts and showing strong competitiveness against advanced Pt-based catalysts. Simulataneously, Net-Pd-HEAA exhibits extraordinary stability in accelerated durability tests (ADT) and chronoamperometry (CA) tests. Advanced characterization and in situ, spectral analysis reveal that the extremely disordered atomic structure effectively regulates the geometric and electronic structure of the Pd sites, enhancing active intermediate coverage, facilitating dehydrogenation pathway, and inhibiting the production/adsorption of CO. Furthermore, when employed as the anode catalyst in proton exchange membrane water electrolysis (PEMWE), Net-Pd-HEAA only requires a potential of 1.28V to obtain a current density of 1 A cm-2, and operates stably in a highly corrosive electrolyte for over 100 h.

Recycling Sulfur-Poisoned Pd Catalysts via Thermal Atomization for Semi-Hydrogenation of Acetylene.

Palladium catalysts are highly efficient for a variety of chemical industrial processes but are prone to being affected by poisons during practical application. Sulfur is one of the major poisons in Pd-based catalysts. The recycling of deeply poisoned Pd species like Pd sulfides is challenging due to the strong Pd-S bond. Herein, we proposed a top-down strategy to degrade Pd sulfides and create Pd single-atom sites simultaneously by one-step thermal atomization. Pd4S model nanoparticles were successfully converted to Pd single-atom sites supported on nitrogen and sulfur-codoped carbon (Pd1/N, S-C) after loading them on ZIF-8 and thermal treatment. PdZn intermediates were formed during the atomization process. Density functional theory revealed that the formation of PdZn helped the generation of vacancies adjacent to metal nanoparticles, which prompted the atomization process. This strategy can be facilely applied to the atomization of sulfur-poisoned commercial Pd/C, which shows the potential for recycling commercial catalysts. The optimal Pd1/N, S-C catalyst showed good activity and much enhanced selectivity than Pd4S for the semi-hydrogenation of acetylene.