Ultrafine Pd Nanoparticles Research Articles

The engineered interfacial Pd-O-Ti sites on the TiO2 nanobelts to accelerate water dissociation for the alkaline hydrogen evolution

Electrochemical water splitting derived by the renewable electricity is one attractive route to produce the green hydrogen. The hydrogen evolution reaction (HER) at the cathode side under the alkaline condition is relatively difficult compared with the acidic, because there is a rate-determining step of breaking strong H-OH bonding in the water molecular. Herein, the ultrafine Pd nanoparticles are uniformly distributed on the TiO2 nanobelts (PdNPs/TiO2) by the pulsed laser deposition to expose the abundant interfacial sites, showing a lower HER overpotential of 71 mV at the current density of -10 mA cm-2 in 1 M KOH. The interfacial Pd-O-Ti structure on PdNPs/TiO2 provides the direct contact between active phase and the water molecules, contributing to break H-OH bond. At the same time, a selective adsorption of H on Pd and OH intermediate on TiO2 is achieved in the interfacial Pd-O-Ti sites under the alkaline HER, optimizing the whole catalytic dynamic.

Effect of Electric Field on Carbon Encapsulation and Catalytic Activity of Pd for Efficient Formic Acid Decomposition

Utilizing carbon coated ferroelectric materials to introduce polarization‐induced electric field (PIEF) stimulates research of electric field‐assisted catalysts for various reactions. However, effect of PIEF on carbon coating mechanism has not been studied. Herein, tourmaline nanoparticles (TNPs) with spontaneous dipole moments were applied as the PIEF supplier and sucrose was utilized as the carbon precursor to synthesize carbon coated TNPs (TNP@SC) to uncover the influence of PIEF on the carbon coating and catalytic activity of Pd toward formic acid decomposition (FAD). PIEF enhanced the adsorption capacity of TNPs for the caramelized intermediate species and increased H+ concentration by facilitating water ionization. Polymerization of adsorbed caramelized intermediate species on TNPs was accelerated. Uniformly coated carbon layer with more defects, larger specific surface area, and higher porosity was coated on TNP. Such surface properties of the carbon layer were beneficial for strongly anchoring ultrafine Pd nanoparticles. Owing to the specific properties of carbon layer and existence of PIEF, Pd/TNP@SC exhibited higher FAD activity than the catalysts absent of PIEF. Stronger PIEF leaded to higher initial turnover frequency. This study provides guidance to supply electric field for catalysis.

Ultrafine Pd nanoparticles confined in naphthalene-based covalent triazine frameworks for efficient and stable hydrogen production from formic acid

Formic acid (FA) is considered as a kind of promising hydrogen storage materials due to its economic feasibility, safety, stability and high hydrogen density. Nevertheless, it is a challenge to design a high-performance catalyst with high activity, selectivity and stability for the dehydrogenation of FA to generate hydrogen (H2). Herein, a range of covalent triazine frameworks (CTFs including 1,8-CTF, 1,5-CTF and 2,3-CTF) with abundant nitrogen atoms are developed to support palladium nanoparticles for efficiently catalyzing FA dehydrogenation. Ultrasmall palladium nanoparticles with a size of 1.2 ± 0.3 nm showed near 100 % H2 selectivity and high catalytic activity in FA dehydrogenation supported by 1,8-CTF. The activation energy of FA dehydrogenation catalyzed by Pd/1,8-CTF reaches 26.17 kJ·mol−1. In addition, Pd/1,8-CTF exhibits high stability and easy recyclability, and the catalytic activity is maintained even after 6 cycles. This work gives a feasible strategy to develop high-efficiency and selective nanocatalysts for H2 production from FA dehydrogenation.

Ultrafine Pd Nanoparticles Anchored on Spherical Covalent Triazine Frameworks for the Selective Tandem Hydrogenation of Nitrobenzene and Benzaldehyde to Secondary Amines

Ultrafine Pd Nanoparticles Anchored on Spherical Covalent Triazine Frameworks for the Selective Tandem Hydrogenation of Nitrobenzene and Benzaldehyde to Secondary Amines

Enhanced photocatalytic dehydrogenation of formic acid over ultrafine electron-deficient Pd nanoparticles immobilized on amine-functionalized mesoporous titanium dioxide

Formic acid (FA) has been increasingly favored by researchers as an ideal material for the chemical storage of hydrogen. However, the exploration of photocatalytic hydrogen evolution from FA is less extensive compared to conventional thermal catalytic FA decomposition. Therefore, constructing highly active photocatalysts for H2 release from FA presents a challenging issue. Herein, we employed a strategy that involves Pd nanoparticles (NPs) immobilized on amine-functionalized mesoporous titanium dioxide (TiO2–NH2) to promote hydrogen production from FA under full-spectrum light illumination. Impressively, the as-made 2 wt% Pd/TiO2–NH2 catalyst showed remarkable activity under full-spectrum light (Turnover frequency (TOF) of 1380.5 h−1 at 308 K, H2 selectivity: 100%). Characterization results indicated that the unique mesoporous structure of TiO2–NH2, the synergistic interaction of Pd NPs with –NH2, and the Mott-Schottky heterojunction are primarily responsible for the excellent photocatalytic performance of 2 wt% Pd/TiO2–NH2. This study modulates the metal-support interactions through surface engineering and proposes a novel and effective method for the construction of high-performance photocatalysts for H2 production from FA or other photoinduced reactions.

Total hydrogenation of furfural on Pd/COFs under mild conditions

Total hydrogenation of furfural (FAL) is an efficient way to produce the industrially important tetrahydrofurfuryl alcohol (THFOL). However, it is a challenge to obtain highly selective catalysts for this transformation especially under mild reaction conditions. Herein, we report that the β-ketoenamine-linked covalent organic framework (TpBD COF) supported ultrafine Pd nanoparticles exhibit significantly enhanced selectivity for THFOL compared to Pd/C (95% vs. 82 %) at almost full FAL conversion. This heightened selectivity is attributed to the increased electronic density on the Pd surface, resulting from the electron-donating effect of pendant groups in the TpBD COF. Moreover, kinetic investigations reveal that the activity of total FAL hydrogenation on Pd surface is linked to the rate-determining step in its first C = O hydrogenation process. Additionally, Pd/TpBD COF could catalyse various other bio-based furanic compounds to the corresponding furan ring saturated products in high yields. This work provides guidance for the rational design catalysts to improve its tandem hydrogenation efficiency.

Regulating CHO* intermediate pathway towards the significant acceleration of photocatalytic CO2 reduction to CH4 through rGO-coated ultrafine Pd nanoparticles

Tailoring catalytic reaction pathways by using reduced graphene oxide (rGO) to tune the electron-hole separation channels in the active sites of noble metals for achieving ideal yield and selectivity in photocatalytic CO2 reduction of hydrocarbon fuels remains a challenge. Herein, ternary catalyst of rGO-coated SnO2-supported noble metal Pd nanoparticles (Pd4/SnO2@rGO) has been prepared by coassembly between negatively charged graphene oxide and positively charged Pd nanoparticles. By coating with ultrathin rGO, the selectivity can be shifted from CO (44.69 % for Pd4/SnO2) toward CH4 as the prevalent species, in which the Pd nanoparticles acted as catalytic sites and electron capture sites. The rGO coating reduced the recombination of the photogenerated carriers as well as optimized the band gap and reduction potential of the catalyst. The in situ spectroscopic tests and density functional theory calculations revealed that CO2 adsorbed on Pd nanoparticles selectively formed dominant low-energy CHO* intermediates because of the generation of HCOOH* intermediates, thus providing a unique reaction pathway for the reduction of CO2 to CH4. Therefore, under sunlight irradiation, the CH4 selectivity of the catalyst is enhanced to 94.1 % with a production rate of up to 77.8 μmol·g−1·h−1. This work demonstrated the prospect to tune the electronic structure of Pd using rGO, which provided a strategy for enhancing the carbon dioxide reduction reaction and selectively obtaining CH4 products in photocatalytic systems.

Exploiting tripeptide in Pd/C for boosting hydrogen production from formic acid dehydrogenation

Ultrafine Pd nanoparticles with lattice strain induced by the incorporation of tripeptide anchored on XC-72R carbon (Pd/C-TPT) show excellent catalytic activity for formic acid dehydrogenation reaction with a TOF of 2102 h−1 without any additives.

Electron-rich palladium regulated by cationic vacancies in CoFe layered double hydroxide boosts electrocatalytic hydrodechlorination

Palladium (Pd) is regarded as a promising electrocatalytic hydrodechlorination (EHDC) catalyst for the detoxification of halogenated phenols. Nevertheless, its intrinsic EHDC activity is seriously restricted by the hydrogen evolution reaction (HER), consuming the active hydrogen (H*) for EHDC. Here, we report a defect regulation strategy using cationic vacancies rich CoFeV-LDH with coupling ultrafine Pd nanoparticles that induces optimized electron distribution of Pd to promote EHDC. The experimental and theoretical results reveal that superior EHDC performance of Pd@CoFeV-LDH is attributed to the electron-rich Pd regulated by cationic vacancies in CoFeV-LDH support, driving facile adsorption of halogenated phenols, high water activation ability and H* selectivity for EHDC. Our findings provide a versatile defect-regulating strategy to overcome the challenge in efficiency and selectivity of EHDC process.

Enhancing Photocatalytic-Transfer Semi-Hydrogenation of Alkynes Over Pd/C3 N4 Through Dual Regulation of Nitrogen Defects and the Mott-Schottky Effect.

The selective hydrogenation of alkynes is an important reaction; however, the catalytic activity and selectivity in this reaction are generally conflicting. In this study, ultrafine Pd nanoparticles (NPs) loaded on a graphite-like C3 N4 structure with nitrogen defects (Pd/DCN) are synthesized. The resulting Pd/DCN exhibits excellent photocatalytic performance in the transfer hydrogenation of alkynes with ammonia borane. The reaction rate and selectivity of Pd/DCN are superior to those of Pd/BCN (bulk C3 N4 without nitrogen defects) under visible-light irradiation. The characterization results and density functional theory calculations show that the Mott-Schottky effect in Pd/DCN can change the electronic density of the Pd NPs, and thus enhances the hydrogenation selectivity toward phenylacetylene. After 1h, the hydrogenation selectivity of Pd/DCN reaches 95%, surpassing that of Pd/BCN (83%). Meanwhile, nitrogen defects in the supports improve the visible-light response and accelerate the transfer and separation of photogenerated charges to enhance the catalytic activity of Pd/DCN. Therefore, Pd/DCN exhibits higher efficiency under visible light, with a turnover frequency (TOF) of 2002 min-1 . This TOF is five times that of Pd/DCN under dark conditions and 1.5 times that of Pd/BCN. This study provides new insights into the rational design of high-performance photocatalytic transfer hydrogenation catalysts.

Highly Sensitive Ethylene Sensors Based on Ultrafine Pd Nanoparticles-Decorated Porous ZnO Nanosheets and Their Application in Fruit Ripeness Detection

Ethylene is the most common ripening phytohormone in fruits, and excess ethylene can overripen the fruit. However, the in-field detection of ethylene is still limited. In this work, ultrafine Pd nanoparticles-decorated porous ZnO nanosheets (UPNP ZnO nanosheets) were conveniently synthesized through a facile solvent reduction method. The UPNP ZnO nanosheets were characterized using scanning electron microscopy, transmission electron microscopy, energy dispersive spectrum, X-ray diffraction and X-ray photoelectron spectroscopy. The ZnO nanosheets were uniformly coated with Pd nanoparticles. The size of the Pd nanoparticle was very small, with a diameter of approximately 2 nm. Due to the unique structure of the porous ZnO nanosheets and the excellent catalytic properties of the ultrafine Pd nanoparticles, the as-prepared samples showed very high sensing performance in ethylene detection. The lowest detection concentration was 10 ppb, which is the lowest detection limit to our knowledge. It has been proved that the decoration of ultrafine Pd nanoparticles can largely increase the relative percentage of chemisorbed oxygen and deficient oxygen, which are benefits for ethylene oxidation, and actually accelerate the process of the sensing reaction. Furthermore, the UPNP ZnO nanosheets can even be applied in fruit maturity detection. Using mangos as an example, our experiment revealed that the response of UPNP ZnO nanosheets to mangos at different maturity stages was quite different. This result suggests that our product has broad application prospects in monitoring fruit ripening stage.

Ultrafine Pd Nanoparticles Encapsulated in Mesoporous TiO2 Region Selectively Confined in Bamboo Microchannels: An Ultrastable Continuous‐Flow Catalytic Hydrogenation Microreactor

Plant‐based flow microreactors with natural channel structures, renewable properties, and environmental friendliness have increasingly gained popularity in heterogeneous catalysis. However, firmly immobilizing the catalysts simultaneously with ease and adaptability, maintaining great effectivity and long‐term stability, is still a fundamental challenge. Herein, a highly efficient and ultrastable bamboo‐based catalytic microreactor (CMR) containing mesoporous TiO2 (M‐TiO2)‐encapsulating ultrafine Pd nanoparticles (NPs) is constructed for the continuous‐flow hydrogenation of nitroaromatics. The fabrication of the Pd‐TiO2 catalysts in required bamboo microchannels (Pd‐TiO2/B CMR) mainly involves a two‐step region‐selective synthetic strategy with ultra‐low chemical usage, fast preparation, and low catalyst loading (0.007 wt%). The M‐TiO2 films: 1) provide abundant oxygen vacancies and enough open cavities to facilitate the growth of Pd NPs; 2) improve Pd dispersion and reduce particle size; 3) allow diffusion of reactants, and 4) induce strong metal‐support interactions for enhanced catalytic activity and stability. The optimized Pd‐TiO2/B CMR demonstrates high efficiency (>97%) and excellent stability (1,000 h) for the continuous‐flow hydrogenation of nitroaniline, even under intermittent operation (12 h on/12 h off for five cycles) or in a real aqueous matrix (>200 h), making it a promising candidate for Pd‐catalyzed hydrogenation.

Self-reduction synthesis of supported ultrafine Pd nanoparticles with high activity and stability in hydrogenation

Supported ultrafine metal nanoparticles display outstanding catalytic performance in heterogeneous catalysis. Nevertheless, there are limited convenient and practical approaches for synthesizing supported ultrafine metal nanoparticle catalysts, despite the development of advanced fabrication methods. High-temperature reduction is often required for the preparation of metal catalysts for catalytic hydrogenation. However, the use of reductants, such as H2, easily leads to the aggregation of nanoparticles during catalyst preparation. In this work, we developed an effective self-reduction strategy using Pd precursors with organic ligands to prepare supported ultrafine Pd catalysts. Simple calcination under an inert atmosphere leads to the formation of uniform and ultrafine Pd nanoparticles (∼1 nm). These Pd precursors were reduced following the reaction between the −CHx groups on ligands and surface hydroxyl species on oxide supports. CO and oxygen vacancies generated in situ both contributed to the stabilization of ultrafine Pd nanoparticles. The as-prepared ultrafine Pd nanoparticles were highly stable even after the high-temperature treatment at 600°C. The catalysts displayed a turnover frequency as high as 26,910 h−1 for styrene hydrogenation and maintained the catalytic activity for at least 5 test cycles.

Synthesis of ultrafine Pd nanoparticles encapsulated in imidazolium-based porous polymers for semi-hydrogenation of alkynes

Interaction between metal and support can dramatically affect the activity and selectivity of supported metallic nanoparticles. Therefore, the development of novel support is a critical path to achieve advanced catalysis. Here, we report that imidazolium-based porous polymers were prepared through a free-radical cross-linking reaction. These imidazolium-based porous polymers with high specific surface area and abundant imidazonium units were utilized as supports to synthesize ultra-small and narrow dispersed Pd nanoparticles . The optimized catalyst displayed 99% selectivity for styrene at 98% conversion in alkyne semi-hydrogenation under ambient conditions with a general application. Comprehensive characterizations demonstrated that the interaction between cationic imidazolium-based porous polymers and Pd enhanced the alkene selectivity by weakening the adsorption on Pd, as well as stabilized Pd nanoparticles by the anchoring and spatial confining effects. The pivotal roles of the Pd-imidazonium interaction and the mesoporous structure provide valuable guidance for the manufacture of high-performance metallic nanoparticles catalyst for selective hydrogenation.

Strong Electronic Interaction between Amorphous MnO2 Nanosheets and Ultrafine Pd Nanoparticles toward Enhanced Oxygen Reduction and Ethylene Glycol Oxidation Reactions

AbstractStrengthening the interface interaction between metal and support is an efficient strategy to improve the intrinsic activity and reduce the amount of noble metal. Amorphization of support is an effective approach for enhancing the metal‐support interaction due to the numerous surface defects in amorphous structure. In this work, a Pd/a‐MnO2 electrocatalyst containing ultrafine and well‐dispersive Pd nanoparticles and amorphous MnO2 nanosheets is successfully synthesized via a simple and rapid wet chemical method. Differing from the crystal counterpart (Pd/c‐MnO2), the flexible structure of amorphous support can be more favorable to electron transfer and further enhance the metal‐support interaction. The synergism between Pd and amorphous MnO2 results in the downshift of the d‐band center, which is beneficial for the desorption of critical intermediates both in oxygen reduction reaction (ORR) and in ethylene glycol oxidation (EGOR). Due to the lower *.OH desorption energy of Pd/a‐MnO2 surface, the rapid dissociation of *OH from Pd facilitates the formation of H2O in ORR, thus demonstrating superior ORR performance comparable to Pt/C. For EGOR, the presence of amorphous MnO2 promotes the formation of adsorbed OH species, which accelerates the desorption of intermediate CO from Pd sites, and thus exhibits excellent EGOR activity and stability.

“On–off” switch for H2 and O2 generation from HCOOH resp. H2O2

AbstractIn spite of the numerous advances in the development of H2 and O2 evolutions upon water splitting, the separation of H2 from O2 still remains a severe challenge. Herein, the novel dual‐functional nanocatalysts Pd/carbon nanosphere (CNS), obtained via immobilization of ultrafine Pd nanoparticles onto CNS, are developed and employed for both selective H2 generation from HCOOH dehydrogenation and O2 evolution from H2O2 decomposition. In these reactions, the highest activities for Pd/CNS‐800 (i.e., calcinated at 800°C) are 2478 h−1 and 993 min−1 for H2 and O2 evolution, respectively. The highly efficient and selective “on–off” switch for selective H2 generation from HCOOH is successfully realized by pH adjustment. This novel and highly efficient nanocatalyst Pd/CNS‐800 not only provides new approaches for the promising application of HCOOH and H2O2 as economic and safe H2 and O2 carriers, respectively, for fuel cells, but also promotes the development of “on‐off” switch for on‐demand H2 evolution.

Low-temperature control over deposition of ultrafine Pd nanoparticles on porous carbon nanosheets for highly efficient dehydrogenation of ammonia borane

The search for simply synthetic strategies of small-size metal nanoparticles is of significant relevance but still faces challenges. In this paper, a method of lowtemperature regulation (LTR) of ultrafine palladium nanoparticles deposited on porous carbon nanosheets is proposed for efficient dehydrogenation of ammonia borane. The LTR method might relieve the sintering of metal particles, thereby resulting in ultrafine Pd nanoparticles of 1.7 nm and their high dispersion on porous carbon. As suggested by the catalytic experiments hereby, Pd/NPC-LTR contributes to higher turnover frequencies of ammonia borane hydrolysis relative to most Pd-based catalysts reported previously. Furthermore, the catalytic performance could be further enhanced by the addition of NaOH under the same reaction conditions, with the hydrolysis completion time shortened by 2.5 times. Moreover, the recycle tests reveal that Pd/NPC-LTR catalyst has good stability and reusability in the hydrolysis of ammonia borane, preserving 70% of its initial catalytic activity even after 10 recycles. The insights reported here can be easily extended to slick preparation and rational design of Pd-catalysts for practical applications. • Low-temperature control over deposition of Pd NPs without any complicated treatments. • Highly dispersed and ultrafine Pd NPs are well deposited on porous carbon nanosheets. • Good performance for catalytic dehydrogenation of ammonia borane. • Highly stability and reusability even after 10 recycles.

Hierarchical ZrO2@N-doped carbon nano-networks anchored ultrafine Pd nanoparticles for highly efficient catalytic hydrogenation

Hierarchical ZrO2@N-doped carbon nano-networks anchored ultrafine Pd nanoparticles for highly efficient catalytic hydrogenation

Efficiently catalytic transfer hydrogenation and fast separation of unsaturated alkene compounds over Pd/UiO-66 under green conditions

Stable Pd nanoparticles (Pd NPs) have been uniformly dispersed and immobilized into the metal-organic framework of UiO-66, Pd/UiO-66, by a facile impregnation reduction method. Pd/UiO-66 retains the integrity of the UiO-66 crystal structure and incorporated with ultrasmall Pd NPs(1.70 ± 0.32 nm). Using ammonium formate(AF) as a H-donor and water as solvent under green condition, the optimized 1.16 wt% Pd/UiO-66 catalyst exhibits remarkable activity in the catalytic transfer hydrogenation(CTH) of α-methylstyrene(AMS) into cumin(achieving 99.6% conversion of AMS and almost full selectivity to cumin with an extremely high turnover frequency value 456.7 h−1 at 323.15 K). Pd/UiO-66 also show superior catalytic activity in CTH of unsaturated alkene compounds to saturated compounds with excellent stability and recyclability. Furthermore, the as-formed saturated alkanes can be fast and automatic separated easily from the aqueous catalytic media. This study supplies a general method for immobilizing ultrafine Pd nanoparticles into crystalline MOFs and a “green” path for hydrogenation of unsaturated alkene compounds.

Significant Promotion of Carboxyl Groups in Palladium Nanoparticles-Supported Biomass Carbon Catalysts for Efficient Low-Temperature Hydrodeoxygenation of Lignin Derivatives in Water

Selective and efficient low-temperature hydrodeoxygenation (HDO) of lignin derivatives in water for the production of valuable biofuel and chemicals is still challenging. Herein, we reported biomass carbon-supported ultrafine Pd nanoparticles as highly active and stable catalysts for low-temperature HDO of vanillin (a typical lignin-derived compound) to 2-methoxy-4-methylphenol (MMP). We found that the abundant carboxyl groups on the resultant catalyst greatly accelerated the conversion of the generated intermediate (vanillyl alcohol, VAL), and then, the synergistic catalysis between carboxyl groups and Pd nanoparticles promoted the efficient production MMP through a free-radical pathway. Other lignin derivatives with different functional groups were also efficiently converted to the corresponding products over the prepared catalyst. This work may provide a new idea for designing a biomass-derived catalyst for efficient transformation of various lignin derivatives to produce value-added biofuels and chemicals.