Low Noble Metal Loading Research Articles

Constructing CoP/Ni2P Heterostructure Confined Ru Sub-Nanoclusters for Enhanced Water Splitting in Wide pH Conditions.

Developing efficient electrocatalysts for water splitting is of great significance for realizing sustainable energy conversion. In this work, Ru sub-nanoclusters anchored on cobalt-nickel bimetallic phosphides (Ru-CoP/Ni2P) are constructed by an interfacial confinement strategy. Remarkably, Ru-CoP/Ni2P with low noble metal loading (33.1µgcm-2) shows superior activity for hydrogen evolution reaction (HER) in all pH values, whose turnover frequency (TOF) is 8.7, 15.3, and 124.7 times higher than that of Pt/C in acidic, alkaline, and neutral conditions, respectively. Meanwhile, it only requires the overpotential of 171 mV@10mAcm-2 for oxygen evolution reaction (OER) and corresponding TOF is 20.3 times higher than that of RuO2. More importantly, the Ru-CoP/Ni2P||Ru-CoP/Ni2P displays superior mass activity of 4017mAmgnoble metal -1 at 2.0V in flowing alkaline water electrolyzer, which is 105.1 times higher than that of Pt/C||IrO2. In situ Raman spectroscopy demonstrates that the Ru sites in Ru-CoP/Ni2P play a key role for water splitting and follow the adsorption evolution mechanism toward OER. Further mechanism studies disclose the confined Ru atom contributes to the desorption of H2 during HER and the formation of O-O bond during OER, leading to fast reaction kinetics. This study emphasizes the importance of interface confinement for enhancing electrocatalytic activity.

Isolated Pt Atoms Stabilized by Ga2O3 Clusters Confined in ZSM-5 for Nonoxidative Activation of Ethane.

Selective activation of light alkanes is an essential reaction in the petrochemical industry for producing commodity chemicals, such as light olefins and aromatics. Because of the much higher intrinsic activities of noble metals in comparison to non-noble metals, it is desirable to employ solid catalysts with low noble metal loadings to reduce the cost of catalysts. Herein, we report the introduction of a tiny amount of Pt (at levels of hundreds of ppm) as a promoter of the Ga2O3 clusters encapsulated in ZSM-5 zeolite, which leads to ∼20-fold improvement in the activity for ethane dehydrogenation reaction. A combination of experimental and theoretical studies shows that the isolated Pt atoms stabilized by small Ga2O3 clusters are the active sites for activating the inert C-H bonds in ethane. The synergy of atomically dispersed Pt and Ga2O3 clusters confined in the 10MR channels of ZSM-5 can serve as a bifunctional catalyst for the direct ethane-benzene coupling reaction for the production of ethylbenzene, surpassing the performances of the counterpart catalysts made with PtGa nanoclusters and nanoparticles.

Highly Active Oxidation Catalysts through Confining Pd Clusters on CeO2 Nano‐Islands

AbstractCeO2‐supported noble metal clusters are attractive catalytic materials for several applications. However, their atomic dispersion under oxidizing reaction conditions often leads to catalyst deactivation. In this study, the noble metal cluster formation threshold is rationally adjusted by using a mixed CeO2‐Al2O3 support. The preferential location of Pd on CeO2 islands leads to a high local surface noble metal concentration and promotes the in situ formation of small Pd clusters at a rather low noble metal loading (0.5 wt %), which are shown to be the active species for CO conversion at low temperatures. As elucidated by complementary in situ/operando techniques, the spatial separation of CeO2 islands on Al2O3 confines the mobility of Pd, preventing the full redispersion or the formation of larger noble metal particles and maintaining a high CO oxidation activity at low temperatures. In a broader perspective, this approach to more efficiently use the noble metal can be transferred to further systems and reactions in heterogeneous catalysis.

Highly Active Oxidation Catalysts through Confining Pd Clusters on CeO2 Nano-Islands.

CeO2-supported noble metal clusters are attractive catalytic materials for several applications. However, their atomic dispersion under oxidizing reaction conditions often leads to catalyst deactivation. In this study, the noble metal cluster formation threshold is rationally adjusted by using a mixed CeO2-Al2O3 support. The preferential location of Pd on CeO2 islands leads to a high local surface noble metal concentration and promotes the in situ formation of small Pd clusters at a rather low noble metal loading (0.5 wt %), which are shown to be the active species for CO conversion at low temperatures. As elucidated by complementary in situ/operando techniques, the spatial separation of CeO2 islands on Al2O3 confines the mobility of Pd, preventing the full redispersion or the formation of larger noble metal particles and maintaining a high CO oxidation activity at low temperatures. In a broader perspective, this approach to more efficiently use the noble metal can be transferred to further systems and reactions in heterogeneous catalysis.

Experimental study of low-temperature combustion performance in hydrogen/air mixtures over Pt–Cu/HZSM-5/cordierite bimetallic catalysts

Catalytic combustion provides a feasible technology to effectively avoid NOx formation due to the high temperature in the process of hydrogen combustion. Recently, the development of efficient and affordable catalysts has attracted extensive attention as the cost of noble metals remained high. In this study, a list of cordierite monolithic catalysts with low noble metal loading are prepared by introducing the appropriate amount of transition metals (Mn, Cu, Fe, Co, and Ce), and their catalytic performance are further investigated. On this basis, the study on catalytic stability and kinetic is carried out, and the synergistic interaction between the bimetals is revealed with comprehensive characterization methods. The results show that Cu could promote the reaction rate of the Pt-based catalyst which show the best catalytic performance with the Cu loading of 1 g/L. The ignition temperature T10 is 58.5 °C, and the burnout temperature T100 is 100 °C, with activation energy as low as 44.00 kJ/mol. The enhancement of the catalytic performance is attributed to the interaction between the bimetallic elements. On the one hand, the valence state of Cu and Pt is changed, and on the other hand the dispersion of Pt get improved, which contributed to the catalytic reaction rate.

Four-channel catalytic micro-reactor based on alumina hollow fiber membrane for efficient catalytic oxidation of CO

The traditional automotive catalytic converter using commercial ceramic honeycomb carriers has many problems such as high back pressure, low engine efficiency, and high usage of precious metals. This study proposes a four-channel catalytic micro-reactor based on alumina hollow fiber membrane, which uses phase inversion method for structural molding and regulation. Due to the advantages of its carrier, it can achieve lower ignition temperature under low noble metal loading. With Pd/CeO2 at a loading rate of 2.3% (mass), the result showed that the reaction ignition temperature is even less than 160 °C, which is more than 90 °C lower than the data of commercial ceramic substrates under similar catalyst loading and airspeed conditions. The technology in turn significantly reduces the energy consumption of the reaction. And stability tests were conducted under constant conditions for 1000 hours, which proved that this catalytic converter has high catalytic efficiency and stability, providing prospects for the design of innovative catalytic converters in the future.

Metal‐2D Semiconductor Hybrid Nano‐Structure Catalyst: A New Frontier of Heterogeneous Catalysis

AbstractCatalytic hydrogenation of nitroarenes is a type of important reaction to get corresponding amines, the development of catalysts with outstanding catalytic performance is in urgent need. In this review, we summarize the breakthroughs in the development of supported metal catalysts in the past few decades, including the use of different metals and supports, improved metal utilization efficiency, adjustment of the structure, and the interaction. We focus on how to develop and innovate the structure of the catalyst, aiming at the contradiction between conversion and selectivity in selective hydrogenation of nitroarenes, from the perspective of the structure and the interaction to construct a kind of catalyst with low noble metal loading and high activity, stabilize the active components, and design and fabricate hybrid nanostructured catalysts with desired activity and selectivity. The development process and the catalytic performance of metal‐2D semiconductor hybrid nano‐structure catalyst are also discussed and provide a theoretical and practical basis for the precise design of supported metal catalysts.

Regulation of Rate‐Determining Step on (RhxNi1‐x)2P for Enhanced Alkaline Hydrogen Oxidation Reaction

AbstractThe development of cost‐efficient Pt‐group metals (PGM)‐based electrocatalysts with low noble metal loading for alkaline hydrogen oxidation reaction (HOR) remains challenging for practical applications of anion exchange membrane fuel cells (AEMFCs). Here we successfully synthesized a series of (RhxNi1−x)2P catalysts with satisfying HOR performance in alkaline media. Especially, (Rh0.3Ni0.7)2P−C exhibits an excellent mass activity of 1.274 mA μgPGM−1, 7‐times higher than that of Rh−C. Density functional theory (DFT) calculations and experimental results indicate that benefiting from the synergistic effect of Rh sites with Ni2P, the hydroxyl binding energy (OHBE) is enhanced on the optimized P sites of (RhxNi1−x )2P, which, together with the accelerated water desorption behavior derived from the downshifted d‐band center of Rh sites in (RhxNi1−x )2P, contributes to speeding up the water formation step and thus resulting in the translation of rate‐determining step, as well as the enhanced alkaline HOR performance.

Modified cellulose nanocrystals immobilized AuPd nanoalloy for formic acid dehydrogenation

Formic acid (FA) is regarded as a promising liquid organic hydrogen transporter. Herein, carriers for immobilizing ultrafine AuPd nanoparticles with a size of approximately 2 nm were produced using cellulose nanocrystals (CNCs) treated with polydopamine (PDA) and polyethyleneimine (PEI). Even with a low noble metal loading (0.01 mmol), the optimized Au0.4Pd0.6/PEI-PDA@CNCs demonstrated extremely high FA dehydrogenation activity compared with similar products, with 100% hydrogen selectivity and TOFinitial up to 4258 h−1 at 323 K. The modified CNCs can enhance the electron transfer between metal particles, and their optimization of the local electronic structure can improve the adsorption of the key intermediates of the reaction. The density functional theory (DFT) calculations were discovered the optimized local electron environment promotes bi-HCOO* rearrangement and lowers the energy barrier for H* and H* binding. This discovery can be used to develop more effective catalysts in the future.

ZnCo2O4 supported low-loading Pd as an enhanced catalyst for low temperature oxidation of carbon monoxide

We have successfully synthesized a series of Pd/ZnCo2O4 supported catalytic materials with low noble metal loading and high activity by the impregnation method. The Pd/ZnCo2O4 catalysts containing 0.2% Pd have superior performance for oxidizing CO at 80 °C, achieving 100% conversion. There is also no loss of activity after four cycles of tests, with the conversion remaining approximately 100%. Aside from that, various advanced physicochemical characterizations indicate that this excellent catalytic performance stems from the interaction between metal Pd and carrier ZnCo2O4. Pd provides a higher degree of accessibility to the active site, while ZnCo2O4 as a carrier can better stabilize Pd nanoparticles. The 0.2% Pd/ZnCo2O4 exhibits higher levels of Pd2+ species as the electronic interaction between Pd and ZnCo2O4 improves, thus improving CO oxidation catalytic efficiency. Furthermore, the low loading of Pd is crucial for reducing the cost of noble metal catalysts and ameliorating their practicality in industrial applications.

A novel Ir–Ru-based nanoparticle supported on ordered electrochemically synthesized TiO2-nanotube as a highly active and stable oxygen evolution reaction catalyst for water splitting in acidic media

Herein Iridium-Ruthenium-based OER electrocatalysts (Ir: Ru 60:40 at%) supported on electrochemically synthesized TiO2 nanotubes (IrRuOx/TNTs) at 80 wt% have been synthesized by the modified Adams fusion method. Physical and electrochemical characterization of the catalysts is compared with IrRuOx, 80 wt% IrRuOx/TiO2 and commercial RuO2. The total charge and the average diameter of the unsupported IrRuOx are 1655.0 mC mg−1 and 4.98 nm, respectively. The total charge and the average diameter for the IrRuOx/TNT have been obtained at 3647.5 mC mg−1 and 3.77 nm, respectively. IrRuOx/TNT shows a current density of 1000 mA mg−1 at 1.604 VRHE and a Tafel slope of 68.9 mV dec−1. Various methods, such as CV, CP, and CA, have been used to evaluate the stability of the catalysts. The results demonstrate that IrRuOx/TNT is a stable catalyst for use in harsh acidic OER environments and can exhibit good activity in a low noble metal loading.

Dense-Packed RuO2 Nanorods with In Situ Generated Metal Vacancies Loaded on SnO2 Nanocubes for Proton Exchange Membrane Water Electrolyzer with Ultra-Low Noble Metal Loading.

Proton exchange membrane water electrolyzer (PEMWE) is a green hydrogen production technology that can be coupled with intermittent power sources such as wind and photoelectric power. To achieve cost-effective operations, low noble metal loading on the anode catalyst layer is desired. In this study, a catalyst with RuO2 nanorods coated outside SnO2 nanocubes is designed, which forms continuous networks and provides high conductivity. This allows for the reduction of Ru contents in catalysts. Furthermore, the structure evolutions on the RuO2 surface are carefully investigated. The etched RuO2 surfaces are seen as the consequence of Co leaching, and theoretical calculations demonstrate that it is more effective in driving oxygen evolution. For electrochemical tests, the catalysts with 23 wt% Ru exhibit an overpotential of 178mV at 10mA cm-2 , which is much higher than most state-of-art oxygen evolution catalysts. In a practical PEMWE, the noble metal Ru loading on the anode side is only 0.3mg cm-2 . The cell achieves 1.61V at 1 A cm-2 and proper stability at 500mA cm-2 , demonstrating the effectiveness of the designed catalyst.

H2-rich syngas production from biogas reforming: Overcoming coking and sintering using bimetallic Ni-based catalysts

Dry reforming of methane is a very appealing catalytic route biogas (mainly composed by greenhouse gases: carbon dioxide and methane) conversion into added value syngas, which could be further upgraded to produce liquid fuels and added value chemicals. However, the major culprits of this reaction are coking and active phase sintering that result in catalysts deactivation. Herein we have developed a highly stable bimetallic Ni–Rh catalyst supported on mixed CeO2–Al2O3 oxide using low-noble metal loadings. The addition of small amounts of rhodium to nickel catalysts prevents coke formation and improves sintering resistance, achieving high conversions over extended reaction times hence resulting in promising catalysts for biogas upgrading.

The acidic OER activation-decay process of highly active Ir–Ni mixed oxide modified by capping agent for both particle fining and Ir–OH formation

Developing highly active catalyst for oxygen evolution reaction (OER) with low noble metal loading is crucial for the application of proton exchange membrane (PEM) water electrolysis. Ir-transition metal (TM) binary catalyst with chemical leaching was reported to perform excellent activity with TM leaching. However, most of the studies on the activation-decay focused on the final status, and the variation process remains unclear. With cysteamine·HCl, a modified facile molten salt method was applied to prepared highly active Ir–Ni mixed oxide (c-xNiIrMO), which perform 5.5 times higher mass activity than commercial IrO2. The variation of active surface area, intrinsic activity, conductivity of prepared catalyst layer during the activation process are studied to unveil the key factors for the activity enhancement. With further stability test, c-xNiIrMO with Ni content lower than 67% performs decrease intrinsic activity and improved kinetic performance in the first hundred cycles. After obtaining a stable Ir0.95Ni0.05Ox structure, further cycling results in typical activity decay with dissolution of Ir.

Facile and rapid synthesis of ultrafine RuPd alloy anchored in N-doped porous carbon for superior HER electrocatalysis in both alkaline and acidic media

Searching for preeminent electrocatalysts toward hydrogen evolution reaction (HER) is significantly important in transforming renewable electricity to clean hydrogen energy by electrochemical water splitting. Herein, ultrafine RuPd alloy nanoparticles anchored in MOFs-derived N-doped porous carbon dodecahedrons (Ru x Pd 1−x @NPC) were synthesized by microwave-assisted ethylene glycol reduction method. Due to the synergistic promotion by modulating the composition and structure, excellent HER catalytic performance was achieved in both alkaline and acidic media for the as-prepared Ru x Pd 1−x @NPC electrocatalysts with low noble metal loading. In which, Ru 0.7 Pd 0.3 @NPC exhibited significantly enhanced alkaline HER activity with a low overpotential of only 20 mV to reach a current density of 10 mA cm −2 . Meanwhile, Ru 0.3 Pd 0.7 @NPC showed admirable HER activity in acidic media, which delivered an overpotential of 36 mV at 10 mA cm −2 . Additionally, the proposed catalysts demonstrated high mass activity and good long-term stability in both alkaline and acidic condition, remarkably surpassing the commercial Pt/C catalyst. The superior activity of the Ru x Pd 1−x @NPC catalysts is attributed to improved intrinsic activity, fast charge transfer kinetics and distinct electrochemical active surface areas after alloying. This work provides a rapid and facile synthesis of highly efficient, durable and affordable alloy electrocatalysts for hydrogen evolution. With low noble metal loading, the alloying Ru x Pd 1−x @NPC electrocatalysts synthesized by facile and rapid microwave-assisted reduction method exhibit dramatically enhanced performance for sustainable hydrogen evolution. • Series of ultrafine alloying RuPd nanoparticles are dispersedly encapsulated in N-doped porous carbon dodecahedrons. • A facile and rapid microwave-assisted reduction method is proposed to synthesize RuPd alloy catalysts. • Enhanced HER electrocatalytic performance is realized in both alkaline and acidic media .

Understanding the in-plane electron transport in low noble metal proton exchange membrane water electrolyser

Reducing noble metal loading in membrane electrode assembly (MEA) can lower the cost of proton exchange membrane (PEM) water electrolyser, but it always leads to performance decline. In-plane conductivity of catalyst layer is mentioned very critical to the cell performance, and it is necessary to fully understand the role of planar electron transportation of catalyst layer. Herein, a bilayer cathode which consists of catalyst layer and planar electron conductive layer is developed to investigate the role of in-plane electron transportation. The additional planar electron conductive layer can significantly improve the performance of the cathode under low noble metal loading. The ohmic polarization as well as the active overpotential are reduced. The results highlight the benefit of bilayer structure and provide a method for enhancing the performance even though the catalyst layer is less homogeneous. Moreover, it can be also used to guide the design of cost-effective anode.

MnO2-Ir Nanowires: Combining Ultrasmall Nanoparticle Sizes, O-Vacancies, and Low Noble-Metal Loading with Improved Activities towards the Oxygen Reduction Reaction.

Although clean energy generation utilizing the Oxygen Reduction Reaction (ORR) can be considered a promising strategy, this approach remains challenging by the dependence on high loadings of noble metals, mainly Platinum (Pt). Therefore, efforts have been directed to develop new and efficient electrocatalysts that could decrease the Pt content (e.g., by nanotechnology tools or alloying) or replace them completely in these systems. The present investigation shows that high catalytic activity can be reached towards the ORR by employing 1.8 ± 0.7 nm Ir nanoparticles (NPs) deposited onto MnO2 nanowires surface under low Ir loadings (1.2 wt.%). Interestingly, we observed that the MnO2-Ir nanohybrid presented high catalytic activity for the ORR close to commercial Pt/C (20.0 wt.% of Pt), indicating that it could obtain efficient performance using a simple synthetic procedure. The MnO2-Ir electrocatalyst also showed improved stability relative to commercial Pt/C, in which only a slight activity loss was observed after 50 reaction cycles. Considering our findings, the superior performance delivered by the MnO2-Ir nanohybrid may be related to (i) the significant concentration of reduced Mn3+ species, leading to increased concentration of oxygen vacancies at its surface; (ii) the presence of strong metal-support interactions (SMSI), in which the electronic effect between MnOx and Ir may enhance the ORR process; and (iii) the unique structure comprised by Ir ultrasmall sizes at the nanowire surface that enable the exposure of high energy surface/facets, high surface-to-volume ratios, and their uniform dispersion.

Hydrothermal-treated Pt/Al2O3 as an excellent catalyst for toluene total oxidation

The preparation of highly active supported noble metal catalysts with a low noble metal loading has always been the ultimate goal of researchers working on catalysis. Hydrothermally treated Pt/Al2O3 (Pt/Al2O3-H) exhibits better catalytic activity than that (Pt/Al2O3-C) treated via the conventional calcination approach. At the high space velocity of 100,000 mL/(g∙hr), the temperature that correspond to 50% toluene conversion (T50) of Pt/Al2O3-H is 115°C lower than that of Pt/Al2O3-C, and the turnover frequency (TOF) value can reach 0.0756 sec−1. The mechanism by which the hydrothermal approach enhances Pt/Al2O3 activity has been investigated. The structure associated with the high catalytic activity of Pt nanoparticles (NPs) can be retained via hydrothermal treatment. Furthermore, the support is transformed to AlO(OH) with numerous surface hydroxyl groups, which in turn can facilitate the adsorption of toluene. And the synergistic effects of Pt NPs and AlO(OH) increases the contents of Pt in oxidation state and active oxygen, which are beneficial for toluene oxidation.

Cover Feature: Galvanic Deposition of Pt Nanoparticles on Black TiO2 Nanotubes for Hydrogen Evolving Cathodes (ChemSusChem 22/2021)

The Cover Feature shows the spontaneous galvanic deposition of metallic Pt nanoparticles on the top, but also inner TiO2 nanotube surfaces. High-aspect-ratio and heavily reduced TiO2 serves as the sacrificial template during this electroless deposition. A high-performing and stable hydrogen evolution cathode in acidic media is demonstrated and prepared via minimal engineering and low noble metal loadings. More information can be found in the Full Paper by A. Touni et al.

Galvanic Deposition of Pt Nanoparticles on Black TiO2 Nanotubes for Hydrogen Evolving Cathodes.

A galvanic deposition method for the in‐situ formation of Pt nanoparticles (NPs) on top and inner surfaces of high‐aspect‐ratio black TiO2‐nanotube electrodes (bTNTs) for true utilization of their total surface area has been developed. Density functional theory calculations indicated that the deposition of Pt NPs was favored on bTNTs with a preferred [004] orientation and a deposition mechanism occurring via oxygen vacancies, where electrons were localized. High‐resolution transmission electron microscopy images revealed a graded deposition of Pt NPs with an average diameter of around 2.5 nm along the complete nanotube axis (length/pore diameter of 130 : 1). Hydrogen evolution reaction (HER) studies in acidic electrolytes showed comparable results to bulk Pt (per geometric area) and Pt/C commercial catalysts (per mg of Pt). The presented novel HER cathodes of minimal engineering and low noble metal loadings (μg cm−2 range) achieved low Tafel slopes (30–34 mV dec−1) and high stability in acidic conditions. This study provides important insights for the in‐situ formation and deposition of NPs in high‐aspect‐ratio structures for energy applications.