Pd Sites Research Articles

Construction of highly active photocatalytic interfaces through light field modulation and photo-deposition of Pd sites

Anchoring noble metal sites through photo-reduction is an effective way to modulate charge distribution on photocatalytic interfaces, thereby enhancing photocatalytic performance. The irradiation field on the exposed surfaces of photocatalysts has an important influence on the morphology and distribution of noble metal sites. However, non-uniform light field derived from the scattering effects of particle-form photocatalysts hinders the well-distributed photo-deposition of noble metal sites. To address this challenge, we proposed a photo-deposition method utilizing the optical fiber coated with photocatalysts. TiO2 nanorod (NR) array was coated on the optical fiber to achieve a well-distributed irradiation filed across the NR array. This resulted in a concentration of the irradiation field primarily within the NR array, maintaining uniformly distributed light intensities throughout. Palladium (Pd) sites dominated by nanoclusters were well distributed on TiO2 NR array utilizing a photo-reduction method. These Pd sites functioned as electron acceptors, facilitating the effective separation and transfer of photo-generated carriers. Consequently, an highly active photocatalytic reaction interface was constructed, demonstrating the accumulation of a substantial concentration of holes and their efficient conversion into hydroxyl radicals (·OH). Notably, hydroxyl radicals with a concentration of 62.6 μM could be generated within 14.4 min. The construction of this efficient photocatalytic interface offers an optimal platform for accelerating photocatalytic reactions and enhancing photocatalytic efficiency.

Dimensional Reduction of Metal-Organic Frameworks for Photocatalytic Synthesis of Fused Tetracyclic Heterocycles.

Heterogeneous palladium catalysts with high efficiency, high Pd atom utilization, simplified separation, and recycle have attracted considerable attention in the field of synthetic chemistry. Herein, we reported a zirconium-based two-dimensional metal-organic framework (2D-MOF)-based Pd(II) photocatalyst (Zr-Ir-Pd) by merging the Ir photosensitizers and Pd(II) species into the skeletons of the 2D-MOF for the Pd(II)-catalyzed oxidation reaction. Morphological and structural characterization identified that Zr-Ir-Pd with a specific nanoflower-like structure consists of ultrathin 2D-MOF nanosheets (3.85 nm). Due to its excellent visible-light response and absorption capability, faster transfer and separation of photogenerated carriers, more accessible Pd active sites, and low mass transfer resistance, Zr-Ir-Pd exhibited boosted photocatalytic activity in catalyzing sterically hindered isocyanide insertion of diarylalkynes for the construction of fused tetracyclic heterocycles, with up to 12 times the Pd catalyst turnover number than the existing catalytic systems. In addition, Zr-Ir-Pd inhibited the competitive agglomeration of Pd(0) species and could be reused at least five times, owing to the stabilization of 2D-MOF on the single-site Pd and Ir sites. Finally, a possible mechanism of the photocatalytic synthesis of fused tetracyclic heterocycles catalyzed by Zr-Ir-Pd was proposed.

Balancing the Binding of Intermediates Enhances Alkaline Hydrogen Oxidation on D-Band Center Modulated Pd Sites.

Exploring efficient alkaline hydrogen oxidation reaction (HOR) electrocatalysts is of great concern for constructing anion exchange membrane fuel cells (AEMFCs). Herein, d-band center modulated PdCo alloys with ultralow Pd content anchored onto the defective carbon support (abbreviated as PdCo/NC hereafter) are proposed as highly efficient HOR catalyst. The as-prepared catalyst exhibits exceptional HOR performance compared to the Pt/C catalyst, achieving thermodynamically spontaneous and kinetically preferential reactions. Specifically, the resultant PdCo/NC demonstrates a marked enhancement in alkaline HOR performance, with the highest mass and specific activities of 1919.6 mA mgPd-1 and 1.9 mA cm-2, 51.1 and 4.2 times higher than those of benchmark of Pt/C, along with an excellent stability in a chronoamperometry test. In the analysis of in situ Raman spectra, it was discovered that tetrahedrally coordinated H-bonded water molecules were formed during the HOR process. This indicates that the promotion of interfacial water molecule formation and enhancement of HOR activities in PdCo/NC are facilitated by defect engineering and the turning of d-band center in PdCo alloy. The essential knowledge obtained in this study could open up a new direction for modifying the electronic structure of cost-effective HOR catalysts through electronic structure engineering.

Pt1.8Pd0.2CuGa Intermetallic Nanocatalysts with Enhanced Methanol Oxidation Performance for Efficient Hybrid Seawater Electrolysis.

Seawater electrolysis is a potentially cost-effective approach to green hydrogen production, but it currently faces substantial challenges for its high energy consumption and the interference of chlorine evolution reaction (ClER). Replacing the energy-demanding oxygen evolution reaction (OER) with the methanol oxidation reaction (MOR) represents a promising alternative, as the MOR occurs at a significantly low anodic potential, which cannot only reduces the voltage needed for electrolysis but also completely circumvents the ClER. To this end, developing high-performance MOR catalysts is a key. Herein, we report a novel quaternary Pt1.8Pd0.2CuGa/C intermetallic nanoparticles (i-NPs) catalyst, which shows a high mass activity (11.13 A mgPGM -1), a large specific activity (18.13mA cmPGM -2), and outstanding stability toward alkaline MOR. Advanced in-situ surface-enhanced Raman spectroscopy (SERS), online differential mass spectrometry (DEMS) and density functional theory (DFT) calculations reveal that the introduction of atomically distributed Pd in Pt2CuGa intermetallic markedly promotes the oxidation of key reaction intermediates by enriching electron concentration around Pt sites, resulting in weak adsorption of carbon-containing intermediates and favorable adsorption of the synergistic OH- groups near Pd sites. Using Pt1.8Pd0.2CuGa/C i-NPs as anodic catalysts, we demonstrate MOR-assisted seawater electrolysis that continuously operates under 1.23V for 240h in simulated seawater and 120h in natural seawater without notable degradation, showing great potential for energy-saving and cost-competitive hydrogen production from seawater. This article is protected by copyright. All rights reserved.

Creating Atomically Iridium-Doped PdOx Nanoparticles for Efficient and Durable Methane Abatement.

The urgent environmental concern of methane abatement, attributed to its high global warming potential, necessitates the development of methane oxidation catalysts (MOC) with enhanced low-temperature activity and durability. Herein, an iridium-doped PdOx nanoparticle supported on silicalite-1 zeolite (PdIr/S-1) catalyst was synthesized and applied for methane catalytic combustion. Comprehensive characterizations confirmed the atomically dispersed nature of iridium on the surface of PdOx nanoparticles, creating an Ir4f-O-Pdcus microstructure. The atomically doped Ir transferred more electrons to adjacent oxygen atoms, modifying the electronic structure of PdOx and thus enhancing the redox ability of the PdIr/S-1 catalysts. This electronic modulation facilitated methane adsorption on the Pd site of Ir4f-O-Pdcus, reducing the energy barrier for C-H bond cleavage and thereby increasing the reaction rate for methane oxidation. Consequently, the optimized PdIr0.1/S-1 showed outstanding low-temperature activity for methane combustion (T50 = 276 °C) after aging and maintained long-term stability over 100 h under simulated exhaust conditions. Remarkably, the novel PdIr0.1/S-1 catalyst demonstrated significantly enhanced activity even after undergoing harsh hydrothermal aging at 750 °C for 16 h, significantly outperforming the conventional Pd/Al2O3 catalyst. This work provides valuable insights for designing efficient and durable MOC catalysts, addressing the critical issue of methane abatement.

Pd promoted oxygen species activation of ZnO nanosheets for enhanced hydrogen sensing performance and its DFT investigation

The sensing performance of ZnO-based metal oxide semiconductors to H2 can be significantly enhanced after decoration of noble metals, and it is of great significant to understand the mechanism and structure-activity relationship between materials and sensing performance, which facilitate the designation of high-performance sensing materials. Herein, we have synthesized Pd-decorated two-dimensional (2D) ZnO nanosheets. A contrastive study based on H2 gas sensing performance of pristine ZnO and Pd-loaded ZnO (PZO) are carried out. According to the results, PZO exhibit superior sensing performance towards H2 (Ra/Rg=17.6, 160 °C), which is much higher than the pristine ZnO nanosheets. Moreover, the PZO also exhibit robust sensing stability and selectivity, detailed structural investigations illustrate that the electronic and surface properties of Pd-ZnO interface play the vital role in H2 sensing process. Density functional theory (DFT) calculation illustrates that H atoms trend to be dissociated at the surface Pd0 sites and the more surface oxygen vacancies are extremely desirable for H2 sensing. The superior H2 sensing of PZO is mainly attributed to the synergistic mechanism of Pd catalytic site and oxygen vacancy (OV). Our works pave the way for designation of high performance H2 sensing materials for the safety of development and utilization of H2.

Mesoporous Palladium Catalyst for Efficient Electrochemical Semi‐Hydrogenation of Alkynes

AbstractDeveloping robust electrocatalysts for efficient semi‐hydrogenation of alkynes to markedly important alkenes is highly desirable in both research and industry areas. In this work, it is reported that robust palladium mesoporous nanospheres (Pd MSs) with electron‐rich active sites perform perfectly as cathode electrocatalyst for electrochemical semi‐hydrogenation of alkynes in water. In comparison to its counterparts, Pd MSs hold remarkable conversion (97%), superior selectivity (98%), good operation stability in selective semi‐hydrogenation of p‐aminophenylene. High performance is assigned to electron‐rich Pd sites within mesopores that not only favor the formation of active H* but also accelerate the desorption of p‐aminostyrene. Meanwhile, Pd MSs are also highly efficient in selective semi‐hydrogenation of various terminal alkynes with different substituents. It is thus expected that robust Pd MSs can be demonstrated as an alternative catalyst design paradigm for other electrochemical hydrogenation reactions.

Symmetry-Reduction Enhanced Polarization-Sensitive Photoresponse Based on One-Dimensional van der Waals Materials.

Designing high-performance polarization-sensitive photodetectors is essential for photonic device applications. Anisotropic one-dimensional (1D) van der Waals (vdW) materials have provided a promising platform to that end. Despite significant advances in 1D vdW photonic devices, their performance is still far from delivering practical potential. Herein, we propose the design of high-performance polarization-sensitive photodetectors using unique 1D vdW materials. By leveraging the chemical vapor transport technique, we successfully fabricate high-quality 1D vdW Nb2Pd1-xSe5 (x = 0.29) nanowires. The 1D vdW Nb2Pd1-xSe5 photodetector exhibits a high mobility of ∼56 cm2/(V s) and superior photoresponse performance, including a high responsivity of 1A/W and an ultrafast response time of ∼8 μs under 638 nm illumination. Moreover, the 1D vdW Nb2Pd1-xSe5 photodetector demonstrates excellent polarization-sensitive photoresponse with a degree of linear polarization (DOLP) up to 0.85 and can be modulated by adjusting the gate voltage, laser power density, and wavelength. Those exceptional performance are believed to be relevant to the symmetry-reduction induced by the partial occupation of Pd sites. This study offers feasible approaches to enhance the anisotropy of 1D vdW materials and the modulation of their polarization-sensitive photoresponse, which may provide deep insights into the physical origin of anisotropic properties of 1D vdW materials.

Promoting effect of potassium over Pd/SiO2 catalyst for ambient formaldehyde oxidation

Highly dispersed noble metals are acknowledged for its pivotal role in influencing the efficiency of catalysts during the HCHO oxidation process. Interestingly, in this work, an innovative approach was employed to augmenting the stabilization of noble metals on irreducible carriers supported noble metal catalyst (Pd/SiO2) by adding alkali metal potassium (K). A formidable promotion effect was observed when the K doping to Pd/SiO2 catalysts. It achieves a conversion rate of 93% for 270 ppmV of HCHO to harmless CO2 and H2O at a weight hourly space velocity (WHSV) of 300,000 mL/(g·hr) at 25°C. Multiple characterization results illustrated that a strong interaction between added K and Pd species was formed after K addition, which not only stabilized Pd species on the carrier surface but also markedly enhanced its dispersal on the SiO2 carrier. The increasing Pd dispersion induced more oxygen vacancies on the surfaces of the Pd/SiO2 catalysts. The formation of these oxygen vacancies can be attributed to the phenomenon of hydrogen spillover, which also contributed to elevating the electron density on the Pd sites. Meanwhile, the oxygen vacancies favored the O2 activation to form more reactive oxygen species participating in the HCHO oxidation reaction, thus improving the performance of Pd/SiO2 catalysts displayed for HCHO oxidation. This study provides a simple strategy to design high-performance irreducible carriers supported noble metal catalysts for HCHO catalytic oxidation.

The Geometric and Electronic Effects of Ceria on Promoting PdZn Catalyst for Enhanced Acetylene Semi‐Hydrogenation

PdZn intermetallic compounds (IMCs) have been extensively reported for acetylene semi‐hydrogenation due to unique geometric and electronic structure of isolated Pd sites. However, to achieve high ethylene selectivity at high conversion remains challenging. Here we show the promotional role of ceria in modifying the geometric and electronic structure of PdZn IMCs towards enhanced catalytic performance for acetylene semi‐hydrogenation. The Ce (0.1wt%) promoted Pd‐Zn‐Al catalyst shows by far the best catalytic performance among other Pd based catalysts in literature, maintaining high selectivity (>95%) and excellent stability (~130 h) at high acetylene conversion (~ 90%). Using in situ spectroscopic techniques, the geometric and electronic effects of CeOx promotor were clearly elucidated. At low Ce content, the presence of highly dispersed Ce3+ species in the periphery of PdZn alloys enhanced electronic metal‐oxide interaction, resulting in electron‐rich Pd sites that promote hydrogen dissociation and ethylene desorption, and account for the outstanding catalytic performance. At high Ce content, the formation of bulk‐phase CeO2 suppressed the PdHx formation during PdZn alloying and led to phase separation yielding highly dispersed Pd ensembles, consequently lowering ethylene selectivity. Our results provide a new route for the design of PdZn catalyst by applying rare earth promoters towards high‐performance acetylene semi‐hydrogenation.

Highly selective electrocatalytic CO2 reduction to multi-carbon products at CuPd synergistic sites over OD-Cu based catalysts

CO2 reduction is a potential way to kill two birds with one stone by converting greenhouse gas into fuels through clean energy. Cu-based catalysts, with a wide range of products, often have limited selectivity and low activity for specific products. In this study, Cu2O was used as the oxide-derived copper (OD-Cu) substrate, which was loaded with CuPd nanoparticles by using pulsed potential and galvanic replacement. Theoretical calculations revealed that the strong H-affinity Pd sites can reduce the selectivity of formate by stabilizing *COOH and simultaneously lowering the d-band center of neighboring Cu. Additionally, the asymmetric C–C coupling of *CHO+*CO, distributed between Cu and Pd sites, can lower the free energy change of rate-determining step to promote production of the C2+ products. Faradaic efficiency (FE) of the C2+ products over Cu2O-CuPd0.5μM was more than three times higher than that over untreated Cu2O NW, rising from 16.50 % to 54.47 % under −1 V (vs RHE) bias. Moreover, the FE for formate and CO decreased respectively from 28.57 % and 19.30 % to 3.69 % and 11.82 %, accompanied by a simultaneous increase in current density by 71.49 %.

Uniformly Distributed Palladium Nanoparticles on NH2‐MIL‐53 Fabricated by an Equilibrium Adsorption Method for Reduction of Nitrite in Water

Metal particle on a support material should be small and homogeneous in size, which is desirable when using it as a catalyst. In this study, we investigated to introduce Pd nanoparticles (NPs) with narrow size distribution into NH2‐MIL‐53, which was prepared by the reaction of aluminum(III) nitrate with 2‐aminoterephthalic acid. Only by immersing it in an aqueous PdCl2 solution, followed by the reduction with NaBH4, Pd NPs of about 2 nm with unform distribution were formed in NH2‐MIL‐53 up to 3.5 wt.% Pd loadings. Amino group on the linkers in NH2‐MIL‐53 played a critical role for the introduction of (PdCl3)– as a precursor for Pd NPs, while no Pd was introduced into MIL‐53 without amino group. The obtained catalysts (Pd@NH2‐MIL‐53) showed high catalytic performance for reduction of nitrite in water. The specific activity per Pd site exposed on the surface changed greatly depending on the Pd loadings despite the size of Pd NPs unchanged. Pd@NH2‐MIL‐53 with low Pd loadings showed higher specific activity (TOF = 2.9×102 h‐1), which might be due to the preferential exposure of Pd(111) facet on Pd NPs.

Unveiling the roles of distinct active sites over Pd/SSZ-13 for low-temperature NOx adsorption

Pd-based zeolites are attractive candidates for passive NOx adsorbers to reduce NOx emission from vehicle exhausts at low temperature. However, it is not well understood the NO adsorption/desorption mechanism in the presence of H2O and CO, which are constant components in diesel exhaust. In this study, an initial Pd/SSZ-13 sample was treated by reduction in H2 and then oxidation in NO to obtain a hydrophilic Pd/SSZ-13 with mostly Z[Pd2+(OH)] sites, or by thermal aging at 750 °C to prepare a hydrophobic Pd/SSZ-13 dominated by Z2Pd2+ and Z[Pd2+(OH)] sites. The two distinct Pd/SSZ-13 catalysts were characterized by XRD, H2-TPR, 27Al MAS NMR, and in situ DRIFTS spectra of CO adsorption, etc. Furthermore, the NOx adsorption/desorption reaction experiments and in situ DRIFTS studies were carried out on the two Pd/SSZ-13 catalysts under various conditions to explore the role of Z2Pd2+ and Z[Pd2+(OH)] sites in NO adsorption in the presence of H2O or co-existence of H2O and CO. Additionally, the recovery of active Pd sites after NO desorption was studied.

Hydrogenation of olefinic bonds in nitrile butadiene rubber on single-atom Pd1/CeO2−x catalysts with ultrahigh mass activity and stability

As pivotal high-performance elastomers, hydrogenated nitrile butadiene rubber (HNBR) was commonly manufactured by selective hydrogenation of nitrile butadiene rubber (NBR). Nevertheless, the high cost and poor stability of current noble metal-based catalysts seriously limit their large-scale applications. Herein, we report single-atom Pd supported by oxygen vacancies-rich CeO2−x nanorods (Pd1/CeO2−x) as a novel catalyst for selectively hydrogenating the NBR. As a result of strong interaction between single-atom Pd and CeO2−x support, the electrophilicity of Pd sites, and the nucleophilicity of olefinic bonds in NBR, the Pd1/CeO2−x show a very high hydrogenated degree of 97.6 %, an unprecedentedly high Pd mass activity of 93.9 gNBR gPd−1h−1, and outstanding cycling stability, which considerably outperform those for previously reported catalysts. Therefore, this work will promote the low-cost manufacture of HNBR and the exploration of single-atom catalysts for selective hydrogenation.

Pd nanoflakes epitaxially grown on defect MoS2 nanosheets for enhanced nitroarenes hydrogenation to anilines

Hydrogenation of nitroarenes to anilines under mild conditions is attractive from both theoretical and practical viewpoints. Here, high-performance catalyst with layered Pd nanoparticles epitaxially growing on ultrathin MoS2 nanosheets (Pd/MoS2) were prepared. It shows surprisingly high catalytic activity, selectivity and stability for hydrogenation of various nitroarenes to corresponding anilines; the turnover frequency is one or two magnitudes higher than conventional Pd-based catalysts. Surface sulfur vacancies are formed on MoS2 nanosheets with low formation energy barrier. These S vacancies provide efficient positions for adsorbing Pd atoms, which enables facile cleavage of N–O bond as result of strong interfacial electron interaction that decreases activation energy by 0.41 eV in comparison with conventional Pd catalysts. In situ spectroscopy and DFT calculation results reveal a dual-site mechanism, in which surface Pd sites adsorb and dissociate H2 into active H*, and then readily reacts with nearby activated nitroarene to form aniline on interfacial Pd-MoS2 sites.

Synergistic effect of PDA and PVP on nanosized Pd doped graphite felt/Ni electrode for promoting the electrocatalytic degradation of 2,4- dichlorophenoxyacetic acid

Reducing the mass transfer barrier for the diffusion of water and pollutants to Pd sites is an important measure to achieve efficient degradation of chlorinated organic compounds. Herein, a simple electroless deposition method for preparing a superhydrophilic nanosized Pd-loaded graphite felt/Ni electrode with the aid of the dispersibility of polyvinylpyrrolidone (PVP) and adhesiveness of polydopamine (PDA) is proposed. The GF/Ni/PDA/Pd-PVP electrode exhibited high electrocatalytic activity toward 2,4-dichlorophenoxyacetic acid (2,4-D) under the optimized conditions, namely degradation and dechlorination efficiencies of 90.5% and 88.53%, respectively, corresponding to 39% higher than that on the GF/Ni/Pd electrode. Experimental results revealed that PDA and PVP doping enhanced the hydrophilicity of the electrode, promoted the dispersibility of Pd nanoparticles (NPs), and the formation of Pd (111) and Ni (111) crystal facets. Compared to the electron-deficient PVP, the appropriate electron-donating ability of PDA promoted the formation of a suitable ratio of electro-deficient and electron-rich Pd, thus enhancing the production of Hads* and C-Cl scission. Moreover, theoretical calculation indicated that the doping of PDA and PVP optimized the adsorption energies of 2,4-D, Hads*, and the main dechlorination product PA, which was obtained via 4-electron transfer via Hads*. Therefore, this study provides a simple and feasible way to fabricate an efficient cathode for 2,4-D dechlorination.

Deciphering SO2 poisoning mechanisms for passive NOx adsorption: A kinetic modeling approach and development of a high-resistance catalyst

Passive NOx adsorption (PNA) is a promising technology aimed at reducing NOx emissions from vehicles during the cold start phase of the engine. This work investigated the SO2 poisoning mechanism of PNA through a combination of experimental research and kinetic modeling, leading to the development of a novel PNA sample with high resistance to SO2 poisoning. Pd/SSZ-13 samples were synthesized using different drying conditions, revealing that samples dried at room temperature showed lower degradation (10 %) compared to those dried at 80 °C (26 %). Investigation into the degradation revealed that ion-exchanged Pd sites with a hydroxyl group were more resistant to SO2 poisoning than other Pd sites. It is also found that SO2 aids in NOx storage on Pd sites, enhancing the PNA performance. A kinetic model was developed to describe the SO2 poisoning behavior and its influence on NOx storage. The model, which was verified under various conditions, effectively simulated the PNA behavior and SO2 poisoning of Pd/SSZ-13.

Nanoscale intimacy in hierarchical catalytic structures for mediating furfural hydroconversion over Pd/CoxOy/SiAlOz

Precisely controlling nanoscale metal-acid intimacy of bifunctional catalysts is increasingly being exploited to improve the performance toward the tandem reactions. It remains a critical challenge to rationally design the spatial organization of dual-functional sites due to the lack of effective synthesis and material characterization methods at the nanoscale. Here we impose hierarchical structures into bifunctional catalysts, wherein Pd particles are controllably deposited on cobalt oxide (CoxOy) nanoglues, which themselves are dispersed on high-surface-area and acid silica-alumina (SiAlOz). The hydroconversion of furfural demonstrates that the catalytic performance is optimized by tailoring the intimacy between Pd and acid sites, that is, with an appropriate nanoscale rather than the closest intimacy. The conversion from furfural to cyclopentanone on hierarchical catalytic structures in Pd/CoxOy/SiAlOz undergoes the treble-site catalytic mechanism, comprising the dissociation of H2 on Pd, the preferential adsorption and hydrogenation of the carbonyl on CoxOy, followed by the hydrogenative ring-rearrangement of furfuryl alcohol intermediate on SiAlOz via the synergistic effect of acid sites and hydrogen spillover. Besides, the asynchronous catalysis resulting from Pd ensemble isolation from SiAlOz surface profoundly restrains the generation of tetrahydrofurfuryl alcohol by elongating the distance of hydrogen spillover, weakening the hydrogenation of the furan ring flat adsorbed on SiAlOz. Resultant Pd/CoxOy/SiAlOz-40 with an optimal Pd-acid intimacy delivers a conversion of 96% and selectivity toward cyclopentanone of 88%, outperforming most state-of-the-art noble metal catalysts. We anticipate that such a concept and synthesis strategy of hierarchical catalytic structures will extend the understanding of the metal-acid intimacy and provide a feasible approach for delicately regulating the location of functional sites in bifunctional catalysts, the results of which may enable the properties of multifunctional catalysts to be modulated to specific target processes.

Independent Multiple‐Atom‐Site Functionality in Composition Adjustable Immiscible Ru‐Rh‐Pd‐Pt Solid‐Solution High‐Entropy Alloys for NOx Reduction Outperforming Rh

AbstractThe high‐entropy‐alloy (HEA) nanoparticles with four, five or more metals significantly can yield the developments of functional materials with excellent performances in various reactions. However, the underlying reaction mechanisms of heterogeneous catalysis for HEA have been rarely investigated, due to their diverse elements and complex compositions. In this study, we successfully synthesized the homogeneously dispersed Ru−Rh−Pd−Pt HEA with adjustable compositions, as the multiple‐atom‐site catalysts (MASC). In the NOx reduction performance tests, Ru0.4 (Rh0.33Pd0.33Pt0.33)0.6 MASC showed the highest activity, which was significantly improved compared to that of the best monometal Rh, with the light‐off temperature decreasing by ca. 50 °C. The Fourier transform infrared measurements revealed that the outstanding activity of Ru−Rh−Pd−Pt MASC was attributable to the well‐coupled elementary steps of the CO adsorption, NO adsorption, NO dissociation and O spillover on the Ru, Rh, Rh−Pd and Pt sites, respectively, which explained the first clear reaction mechanism in heterogeneous catalysis for HEA.

Pd-Based Bimetallic Electrocatalysts for Hydrogen Oxidation Reaction in 0.1 M KOH Solution.

A series of carbon black-supported 7.5 wt.% Pd-2.5 wt.% M/C (M: Ag, Ca, Co, Cu, Fe, Ni, Ru, Sn, Zn) electrocatalysts, synthesized via the wet impregnation method, and reduced at 300 °C, were compared in terms of their hydrogen oxidation reaction (HOR) activity in a 0.1 M KOH solution using the thin-film rotating-disk electrode technique. Moreover, 10 wt.% Pd/C and 10 wt.% Pt/C electrocatalysts were prepared in the same manner and used as references. The 7.5 wt.% Pd-2.5 wt.% Ni/C electrocatalyst exhibited the highest HOR activity among the Pd-based electrocatalysts, although it was lower than that of the 10 wt.% Pt/C. Its activity was also found to be higher than that of Pd-Ni electrocatalysts of the same total metal loading (10 wt.%) and reduction temperature (300 °C) but of different Pd to Ni atomic ratio. It was also higher than that of 7.5 wt.% Pd-2.5 wt.% Ni/C electrocatalysts that were reduced at temperatures other than 300 °C. The superior activity of this electrocatalyst was attributed to an optimum value of the hydrogen binding energy of Pd, which was induced by the presence of Ni (electronic effect), as well as to the oxophilic character of Ni, which favors adsorption on the Ni surface of hydroxyl species that readily react with adsorbed hydrogen atoms on neighboring Pd sites in the rate-determining step.