Infrared spectroscopy of isomers of C3H4+ in superfluid helium droplets.

Superfluid helium nanodroplets are unique nanomatrices for the isolation and study of transient molecular species, such as radicals, carbenes, and ions. In this work, isomers of C3H4+ were produced upon electron ionization of propyne and allene molecules and interrogated via infrared spectroscopy inside He nanodroplet matrices. It was found that the spectrum of C3H4+ has at least three distinct groups of bands. The relative intensities of the bands depend on the precursor employed and its pickup pressure, which indicates the presence of at least three different isomers. Two isomers were identified as allene and propyne radical cations. The third isomer, which has several new bands in the range of 3100-3200 cm-1, may be the elusive vinylmethylene H2C=CH-CH+ radical cation. The observed bands for the allene and propyne cations are in good agreement with the results of density functional theory calculations. However, there is only moderate agreement between the new bands and the theoretically calculated vinylmethylene spectrum, which indicates more work is necessary to unambiguously assign it.

Deciphering Indirect Nitrite Reduction to Ammonia in High-Entropy Electrocatalysts Using In Situ Raman and X-ray Absorption Spectroscopies.

This research adopts a new method combining calcination and pulsed laser irradiation in liquids to induce a controlled phase transformation of Fe, Co, Ni, Cu, and Mn transition-metal-based high-entropy Prussian blue analogs into single-phase spinel high-entropy oxide and face-centered cubic high-entropy alloy (HEA). The synthesized HEA, characterized by its highly conductive nature and reactive surface, demonstrates exceptional performance in capturing low-level nitrite (NO2 -) in an electrolyte, which leads to its efficient conversion into ammonium (NH4 +) with a Faradaic efficiency of 79.77% and N selectivity of 61.49% at -0.8 V versus Ag/AgCl. In addition, the HEA exhibits remarkable durability in the continuous nitrite reduction reaction (NO2 -RR), converting 79.35% of the initial NO2 - into NH4 + with an impressive yield of 1101.48 µm h-1 cm-2. By employing advanced X-ray absorption and in situ electrochemical Raman techniques, this study provides insights into the indirect NO2 -RR, highlighting the versatility and efficacy of HEA in sustainable electrochemical applications.

Laser-Synthesized Co-Doped CuO Electrocatalyst: Unveiling Boosted Methanol Oxidation Kinetics for Enhanced Hydrogen Production Efficiency by In Situ/Operando Raman and Theoretical Analyses.

The present study details the strategic development of Co-doped CuO nanostructures via sophisticated and expedited pulsed laser ablation in liquids (PLAL) technique. Subsequently, these structures are employed as potent electrocatalysts for the anodic methanol oxidation reaction (MOR), offering an alternative to the sluggish oxygen evolution reaction (OER). Electrochemical assessments indicate that the Co-CuO catalyst exhibits exceptional MOR activity, requiring a reduced potential of 1.42 V at 10 mA cm-2 compared to that of pure CuO catalyst (1.57 V at 10 mA cm-2 ). Impressively, the Co-CuO catalyst achieved a nearly 180 mV potential reduction in MOR compared to its OER performance (1.60 V at 10 mA cm-2 ). Furthermore, when pairing Co-CuO(+)ǀǀPt/C(-) in methanol electrolysis, the cell voltage required is only 1.51 V at 10 mA cm-2 , maintaining remarkable stability over 12 h. This represents a substantial voltage reduction of ≈160 mV relative to conventional water electrolysis (1.67 V at 10 mA cm-2 ). Additionally, both in situ/operando Raman spectroscopy studies and theoretical calculations have confirmed that Co-doping plays a crucial role in enhancing the activity of the Co-CuO catalyst. This research introduces a novel synthetic approach for fabricating high-efficiency electrocatalysts for large-scale hydrogen production while co-synthesizing value-added formic acid.

Laser-Synthesized Ru-Anchored Few-Layer Black Phosphorus for Superior Hydrogen Evolution: Role of Acoustic Levitation.

Electrochemical water splitting, driven by processed catalysts, is the most reasonable method for hydrogen production. This study demonstrates an activation phenomenon with ruthenium (Ru) nanoclusters on few-layered black phosphorus (BP), greatly enhancing the electrocatalytic hydrogen evolution reaction (HER). Efficient BP exfoliation was achieved using acoustic levitators and pulsed laser irradiation in liquids (PLIL), yielding charge-transfer Ru-nanoclusters on modulated surfaces. Various PLIL parameters were examined for the optimal BP sheet size. After ruthenization, Ru's d-band center facilitated hydrogen adsorption via Ru-H bonding. Synergy between BP's charge-carrier properties and Ru's active sites boosted HER kinetics with an ultralow overpotential of 84 mV at 10 mA/cm2 in KOH. Additionally, the RuO2 || RuBP-2 electrolyzer demonstrated remarkable overall water splitting performance at ∼1.60 V at 10 mA/cm2. These results highlight the pivotal role of metal nanoclusters on exfoliated BP surfaces and offer a refined strategy for high-density electrocatalysts in energy conversion.

Aloe vera-derived graphene-coupled phenosafranin photocatalyst for generation and regeneration of ammonia and NADH by mimicking natural photosynthetic route.

Aloe vera-derived graphene (ADG) coupled system photocatalyst, mimicking natural photosynthesis, is one of the most promising ways for converting solar energy into ammonia (NH3 ) and nicotinamide adenine dinucleotide (NADH) that have been widely used to make the numerous chemicals such as fertilizer and fuel. In this study, we report the synthesis of the aloe vera-derived graphene-coupled phenosafranin (ADGCP) acting as a highly efficient photocatalyst for the generation of NH3 and regeneration of NADH from nitrogen (N2 ) and oxidized form of nicotinamide adenine dinucleotide (NAD+ ). The results show a benchmark instance for mimicking natural photosynthesis activity as well as the practical applications for the solar-driven selective formation of NH3 and the regeneration of NADH by using the newly designed photocatalyst.

In-situ monitoring of thiazine molecular aggregation in various solvents via a free-standing acoustic levitator.

In this work, we explored the in-situ reaction modeling of the molecular self-aggregation of methylene blue (MB), which is a cationic thiazine dye, in different solvents via a container-less acoustic levitator by floating of a single droplet. Our in-situ spectroscopic study revealed that the dimer essentially has a sandwich structural geometry with a deviation from parallel stacking and horizontal arrangements in the molecular planes. The real time conversion of the monomer in MB into a dimer and their dynamics in water and ethanol media were monitored using a free-standing acoustic levitator droplet system. The absorption spectra revealed changes in the two resolved peaks (monomer and dimer) and orderliness when water and ethanol were used as the media. Interestingly, the enhancement in the dimerization of MB could be attributed to droplet evaporation, which is difficult to observe in typical reactor containers. Moreover, acidic protonation resulted in a change in the aggregation orientation direction of the MB molecules, forming an unusual J-aggregation. Theoretical DFT calculations revealed that MB underwent typical H-aggregation and J-aggregation in the different solvent environments, and their orientations well matched the spectroscopic data.

Formation of the C4Hn+ (n = 2-5) ions upon ionization of acetylene clusters in helium droplets.

Infrared (IR) spectroscopy using ultracold helium nanodroplet matrices has proven to be a powerful method to interrogate encapsulated ions, molecules, and clusters. Due to the helium droplets' high ionization potential, optical transparency, and ability to pick up dopant molecules, the droplets offer a unique modality to probe transient chemical species produced via photo- or electron impact ionization. In this work, helium droplets were doped with acetylene molecules and ionized via electron impact. Ion-molecule reactions within the droplet volume yield larger carbo-cations that were studied via IR laser spectroscopy. This work is focused on cations containing four carbon atoms. The spectra of C4H2+, C4H3+, and C4H5+ are dominated by diacetylene, vinylacetylene, and methylcyclopropene cations, respectively, which are the lowest energy isomers. On the other hand, the spectrum of C4H4+ ions hints at the presence of several co-existing isomers, the identity of which remains to be elucidated.

Electrochemical detection of arsenic (III) hazardous chemicals using cubic CsPbBr3 single crystals: Structural insights from DFT study.

Long-term exposure to the highly toxic heavy metal arsenic can harm ecological systems and pose serious health risks to humans. Arsenic pollutant in water and the food chain must be addressed, and active prompt detection of As(III) is essential. The development of an effective detection method for As(III) ions is urgently needed to slow the alarming growth of arsenic pollution in the environment and safeguard the well-being of future generations. This study presents the results of our exhaustive investigation into cubic CsPbBr3 single crystals, the glassy carbon (GC) electrode modification with CsPbBr3 single crystals prepared by direct solvent evaporation, as well as our observations of the material's remarkable electrocatalytic properties and exceptional anti-interference sensing of As(III) ions in neutral pH media. The developed CsPbBr3/GC is exceptionally useful for the ultra-sensitive and specific identification of arsenic in water, exhibiting a detection limit of 0.381 µmol/L, a rapid response across a defined range of 0.1-25 µmol/L, and an ultra-sensitivity of 0.296 µA/µmolL-1. CsPbBr3/GCE (prepared without a specific reagent) is superior to other modified electrodes used as sensors in electrocatalytic activity, detection limit, analytical sensitivity, and stability response.

In situ studies on free-standing synthesis of nanocatalysts via acoustic levitation coupled with pulsed laser irradiation.

Acoustic levitation is a distinctive and versatile tool for levitating and processing free-standing single droplets and particles. Liquid droplets suspended in an acoustic standing wave provide container-free environments for understanding chemical reactions by avoiding boundary effects and solid surfaces. We attempted to use this strategy for the production of well-dispersed uniform catalytic nanomaterials in an ultraclean confined area without the addition of external reducing agents or surfactants. In this study, we report on the synthesis of gold and silver nanoparticles (NPs) via acoustic levitation coupled with pulsed laser irradiation (PLI). In situ UV-Visible and Raman spectroscopic techniques were performed to monitor the formation and growth of gold and silver NPs. The PLI was used for the photoreduction of targeted metal ions present in the levitated droplets to generate metal NPs. Additionally, the cavitation effect and bubble movement accelerate the nucleation and decrease the size of NPs. The synthesized Au NPs with âˆ¼ 5 nm size showed excellent catalytic behavior towards the conversion of 4-nitrophenol to 4-aminophenol. This study may open a new door for synthesizing various functional nanocatalysts and for achieving new chemical reactions in suspended droplets.

Moving beyond Ti2C3Tx MXene to Pt-Decorated TiO2@TiC Core-Shell via Pulsed Laser in Reshaping Modification for Accelerating Hydrogen Evolution Kinetics.

Phase engineering of nanocatalysts on specific facets is critical not only for enhancing catalytic activity but also for intensely understanding the impact of facet-based phase engineering on electrocatalytic reactions. In this study, we successfully reshaped a two-dimensional (2D) MXene (Ti3C2Tx) obtained by etching Ti3AlC2 MAX via a pulsed laser irradiation in liquid (PLIL) process. We produced a TiO2@TiC core-shell structure in spheres with sizes of 200-350 nm, and then ∼2 nm ultrasmall Pt NPs were decorated on the surface of the TiO2@TiC core-shell using the single-step PLIL method. These advances allow for a significant increase in electrocatalytic hydrogen evolution reaction (HER) activity under visible light illumination. The effect of optimal Pt loading on PLIL time was identified, and the resulting Pt/TiO2@TiC/Pt-5 min sample demonstrated outstanding electrochemical and photoelectrochemical performance. The photoelectrochemical HER activity over Pt/TiO2@TiC/Pt-5 min catalyst exhibits a low overpotential of 48 mV at 10 mA/cm2 and an ultralow Tafel slope of 54.03 mV/dec with excellent stability of over 50 h, which is hydrogen production activity even superior to that of the commercial Pt/C catalysts (55 mV, 62.45 mV/dec). This investigation not only serves as a potential for laser-dependent phase engineering but also provides a reliable strategy for the rational design and fabrication of highly effective nanocatalysts.

Architecting the High-Entropy Oxides on 2D MXene Nanosheets by Rapid Microwave-Heating Strategy with Robust Photoelectrochemical Oxygen Evolution Performance.

High-entropy oxides (HEO) have recently concerned interest as the most promising electrocatalytic materials for oxygen evolution reactions (OER). In this work, a new strategy to the synthesis of HEO nanostructures on Ti3 C2 Tx MXene via rapid microwave heating and subsequent calcination at a low temperature is reported. Furthermore, the influence of HEO loading on Ti3 C2 Tx MXene is investigated toward OER performance with and without visible-light illumination in an alkaline medium. The obtained HEO/Ti3 C2 Tx -0.5 hybrid exhibited an outstanding photoelectrochemical OER ability with a low overpotential of 331 mV at 10 mA cm-2 and a small Tafel slope of 71 mV dec-1 , which exceeded that of a commercial IrO2 catalyst (340 mV at 10 mA cm-2 ). In particular, the fabricated water electrolyzer with the HEO/Ti3 C2 Tx -0.5 hybrid as anode required a less potential of 1.62 V at 10 mA cm-2 under visible-light illumination. Owing to the strong synergistic interaction between the HEO and Ti3 C2 Tx MXene, the HEO/Ti3 C2 Tx hybrid has a great electrochemical surface area, many metal active sites, high conductivity, and fast reaction kinetics, resulting in an excellent OER performance. This study offers an efficient strategy for synthesizing HEO-based materials with high OER performance to produce high-value hydrogen fuel.

Current trends and prospects in catalytic upgrading of lignocellulosic biomass feedstock into ultrapure biofuels.

Eco-friendly renewable energy sources have recommended as fossil fuel alternatives in recent years to reduce environmental pollution and meet future energy demands in various sectors. As the largest source of renewable energy in the world, lignocellulosic biomass has received considerable interest from the scientific community to advance the fabrication of biofuels and ultrafine value-added chemicals. For example, biomass obtained from agricultural wastes could catalytically convert into furan derivatives. Among furan derivatives, 5-hydroxymethylfurfural (HMF) and 2, 5-dimethylfuran (DMF) are considered the most useful molecules that can be transformed into desirable products such as fuels and fine chemicals. Because of its exceptional properties, e.g., water insolubility and high boiling point, DMF has studied as the ideal fuel in recent decades. Interestingly, HMF, a feedstock upgraded from biomass sources can easily hydrogenate to produce DMF. In the present review, the current state of the art and studies on the transformation of HMF into DMF using noble metals, non-noble metals, bimetallic catalysts, and their composites have discussed elaborately. In addition, comprehensive insights into the operating reaction conditions and the influence of employed support over the hydrogenation process have demonstrated.

Correction: Tailoring the MOF structure via ligand optimization afforded a dandelion flower like CoS/Co-Nx/CoNi/NiS catalyst to enhance the ORR/OER in zinc-air batteries.

Correction for 'Tailoring the MOF structure via ligand optimization afforded a dandelion flower like CoS/Co-Nx/CoNi/NiS catalyst to enhance the ORR/OER in zinc-air batteries' by Mohan Gopalakrishnan et al., Nanoscale, 2022, 14, 17908-17920, https://doi.org/10.1039/D2NR04933C.

Modulating the Combinatorial Target Power of MgSnN2 via RF Magnetron Sputtering for Enhanced Optoelectronic Performance: Mechanistic Insights from DFT Studies.

The unique structural features of many ternary nitride materials with strong chemical bonding and band gaps above 2.0 eV are limited and are experimentally unexplored. It is important to identify candidate materials for optoelectronic devices, particularly for light-emitting diodes (LEDs) and absorbers in tandem photovoltaics. Here, we fabricated MgSnN2 thin films, as promising II-IV-N2 semiconductors, on stainless-steel, glass, and silicon substrates via combinatorial radio-frequency magnetron sputtering. The structural defects of the MgSnN2 films were studied as a function of the Sn power density, while the Mg and Sn atomic ratios remained constant. Polycrystalline orthorhombic MgSnN2 was grown on the (120) orientation within a wide optical band gap range of ∼2.20-2.17 eV. The carrier densities of 2.18× 1020 to 1.02 × 1021 cm-3, mobilities between 3.75 and 2.24 cm2/Vs, and a decrease in resistivity from 7.64 to 2.73 × 10-3 Ω cm were confirmed by Hall-effect measurements. These high carrier concentrations suggested that the optical band gap measurements were affected by a Burstein-Moss shift. Furthermore, the electrochemical capacitance properties of the optimal MgSnN2 film exhibited an areal capacitance of 152.5 mF/cm2 at 10 mV/s with high retention stability. The experimental and theoretical results showed that MgSnN2 films were effective semiconductor nitrides toward the progression of solar absorbers and LEDs.

Atomic layer encapsulation of ferrocene into zeolitic imidazolate framework-67 for efficient arsenic removal from aqueous solutions.

Arsenic (As(V))-contaminated water is a major global threat to human health and the ecosystem because of its enormous toxicity, carcinogenicity, and high distribution in water streams. Thus, As(V) removal in the environmental samples has received considerable attention. Till now, numerous metal-organic framework materials have been used for the As(V) removal from the aqueous medium, but low As(V) removal and instability of the adsorbents have severely cut off their practical applications. In this study, a ferrocene-encapsulated zeolitic imidazolate framework-67 (Fc-ZIF-67) material was synthesized for As(V) removal from an aqueous solution at neutral pH using a simple solution mixing process. The ferrocene encapsulation provides water-stable and structural defects to ZIF-67. Furthermore, the ferrocene molecule and imidazole linker can enhance As(V) adsorption via both chemisorption and physisorption. The novel Fc-ZIF-67 adsorbent exhibited superior As(V) adsorption performance with an adsorption capacity of 63.29 mg/g at neutral pH. The Langmuir and Freundlich isotherm models were also used to analyze adsorption behavior.

Construction of direct FeMoO4/g-C3N4-2D/2D Z-scheme heterojunction with enhanced photocatalytic treatment of textile wastewater to eliminate the toxic effect in marine environment.

A novel FeMoO4/g-C3N4-2D/2D Z-scheme heterojunction photocatalyst was prepared via wet chemical method. The observed structural morphology of FeMoO4/g-C3N4 reveals the 2D-iron molybdate (FeMoO4) nanoplates compiled with the 2D-graphitic carbon nitride (g-C3N4) nanosheets like structure. The photocatalytic activity of the g-C3N4, FeMoO4, and FeMoO4/g-C3N4 composites were studied via the degradation of Rhodamine B (RhB) as targeted textile dye under visible light irradiation (VLI). The optimal FeMoO4/g-C3N4 (1:3 ratio of g-C3N4 and FeMoO4) composite show an enhanced degradation performance with rate constant value of 0.02226 min-1 and good stability even after three cycles. Thus, the h+ and O2•－are the key radicals in the degradation of RhB under VLI. It is proposed that the FeMoO4/g-C3N4 Z-scheme heterojunction effectively enhances the transfer and separation ability of e-/h+ pairs, by the way increasing the photocatalytic efficiency towards the RhB degradation. Thus, the newly constructed Z-scheme FeMoO4/g-C3N4 heterojunction photocatalyst is a promising material for the remediation of wastewater relevant to elimination of toxic effect in marine environment.

Tailoring the MOF structure via ligand optimization afforded a dandelion flower like CoS/Co-Nx/CoNi/NiS catalyst to enhance the ORR/OER in zinc-air batteries.

Due to their affordability and good catalytic activity for oxygen reactions, MOF-derived carbon composites containing metal alloys have piqued interest. However, during synthesis, MOFs have the disadvantage of causing significant carbon evaporation, resulting in a reduction of active sites and durability. This study proposes tailoring the molecular structure of MOFs by optimizing bipyridine and flexible 4-aminodiacetic terephthalic acid ligands, which have numerous coordination modes and framework structures, resulting in fascinating architectures. MOF frameworks having optimized N and O units are coordinated with Co and Ni ions to provide MOF precursors that are annealed at 700 °C in argon. The MOF-derived Co9S8/Co-Nx/CoNi/Ni3S2@CNS-4 catalyst exhibits excellent catalytic activity, revealing an ORR half-wave potential of 0.86 V and an overpotential (OER) of 196 mV at 10 mA cm-2, a potential gap of 0.72 V and a Tafel slope of 79 mV dec-1. The proposed strategy allows for the rational design of N-coordinated Co and CoNi alloys attached to ultrathin N, S co-doped graphitic carbon sheets to enhance bifunctional activity and sufficient active sites. Consequently, the zinc-air battery using the synthesized catalyst shows a high peak power density of 206.9 mW cm-2 (Pt/C + RuO2 116.1 mW cm-2), a small polarization voltage of 0.96 V after 370 h at 10 mA cm-2, and an outstanding durability of over 2400 cycles (400 h). The key contributions to the superior performance are the synergetic effects of the CoNi alloys plus the N,S-incorporated carbon skeleton, due to the small charge transfer resistances and enhanced active sites of CoNi, metal-S, and pyridinic N.

Unraveling the Synergy of Anion Modulation on Co Electrocatalysts by Pulsed Laser for Water Splitting: Intermediate Capturing by In Situ/Operando Raman Studies.

Herein, the authors produce Co-based (Co3 (PO4 )2 , Co3 O4 , and Co9 S8 ) electrocatalysts via pulsed laser ablation in liquid (PLAL) to explore the synergy of anion modulation on phase-selective active sites in the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Co3 (PO4 )2 displays an ultralow overpotential of 230 mV at 10 mA cm-2 with 48.5 mV dec-1 Tafel slope that outperforms the state-of-the-art Ir/C in OER due to its high intrinsic activity. Meanwhile, Co9 S8 exhibits the highest HER performance known to the authors among the synthesized Co-based catalysts, showing the lowest overpotential of 361 mV at 10 mA cm-2 with 95.8 mV dec-1 Tafel slope in the alkaline medium and producing H2 gas with ≈500 mmol g-1 h-1 yield rate under -0.45 V versus RHE. The identified surface reactive intermediates over in situ electrochemical-Raman spectroscopy reveal that cobalt(hydr)oxides with higher oxidation states of Co-cation forming under oxidizing potentials on the electrode-electrolyte surface of Co3 (PO4 )2 facilitate the OER, while Co(OH)2 facilitate the HER. Notably, the fabricated two-electrode electrolyzers using Co3 (PO4 )2 , Co3 O4 , and Co9 S8 electrocatalysts deliver the cell potentials ≈2.01, 2.11, and 1.89 V, respectively, at 10 mA cm-2 . This work not only shows PLAL-synthesized electrocatalysts as promising candidates for water splitting, but also provides an underlying principle for advanced energy-conversion catalysts and beyond.

Sustainable removal of nitrite waste to value-added ammonia on Cu@Cu2O core-shell nanostructures by pulsed laser technique.

The biochemical reduction of nitrite (NO2-) ions to ammonia (NH3) requires six electrons and is catalyzed by the cytochrome c NO2- reductase enzyme. This biological reaction inspired scientists to explore the reduction of nitrogen oxyanions, such as nitrate (NO3-) and NO2- in wastewater, to produce the more valuable NH3 product. It is widely known that copper (Cu)-based nanoparticles (NPs) are selective for the NO3- reduction reaction (NO3-RR), but the NO2-RR has not been well explored. Therefore, we attempted to address the electrocatalytic conversion of NO2- to NH3 using Cu@Cu2O core-shell NPs to simultaneously treat wastewater by removing NO2- and producing valuable NH3. The Cu@Cu2O core-shell NPs were constructed using the pulsed laser ablation of Cu sheet metal in water. The core-shell nanostructure of these particles was confirmed by various characterization techniques. Subsequently, the removal of NO2- and the ammonium (NH4+)-N yield rate were estimated using the Griess and indophenol blue methods, respectively. Impressively, the Cu@Cu2O core-shell NPs exhibited outstanding NO2-RR activity, demonstrating a maximum NO2- removal efficiency of approximately 94% and a high NH4+-N yield rate of approximately 0.03 mmol h-1.cm-2 at -1.6 V vs. a silver/silver chloride reference electrode under optimal conditions. The proposed NO2-RR mechanism revealed that the (111) facet of Cu favors the selective conversion of NO2- to NH3 via a six-electron transfer. This investigation may offer a new insight for the rational design and detailed mechanistic understanding of electrocatalyst architecture for the effective conversion of NO2- to NH4+.

Unveiling the effect of gas treatment on the electronic structure of carbon nanotube-supported Pd catalysts for electroreduction of H2O2 and Heck reaction.

This study explored the impact of gas treatments on the structures of multi-walled carbon nanotubes supported Pd (CNT-Pd) catalysts used for electrocatalytic H2O2 reduction and the Heck cross-coupling reaction. The CNT-Pd catalyst was prepared by anchoring Pd nanoparticles on thiolated CNTs. XPS was conducted to examine the surface composition and electronic structure changes of the CNT-Pd catalyst before and after gas treatment. The XPS results revealed that as-prepared CNT-Pd contains at least two different oxidation states on the surface, whereon their proportions depend on the gas used for treatment. Treatment with H2 leads to Pd(0) enrichment near the surface, while O2 treatment causes Pd(Ⅱ) enrichment of CNT-Pd. All catalysts containing both Pd(0) and Pd(Ⅱ) were active toward H2O2 reduction, and the Heck cross-coupling reaction of n-butyl acrylate and 4-iodotoluene; increased proportion of metallic Pd(0) boosted the catalytic reaction. However, the catalyst stability increased as the amount of Pd(II) increased.