Catalytic Reduction Reaction Research Articles

Evidence of Sulfur Non-Innocence in [CoII (dithiacyclam)]2+ -Mediated Catalytic Oxygen Reduction Reactions.

In many metalloenzymes, sulfur-containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S-ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four-nitrogen bound [Co(cyclam)]2+ (1; cyclam=1,5,8,11-tetraaza-cyclotetradecane) and the S-containing analog [Co(S2 N2 -cyclam)]2+ (2; S2 N2 -cyclam=1,8-dithia-5,11-diaza-cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the CoII centers in 1 and 2 point to the involvement of sulfur in the O2 reduction process as the key for the improved catalytic ORR capabilities of 2.

Beweis von Schwefel‐non‐Innocence in [CoII(Dithiacyclam)]2+‐vermittelten, katalytischen Sauerstoff‐Reduktions‐Reaktionen

AbstractIn vielen Metallenzymen sind Schwefel‐enthaltende Liganden an Elektronen‐Transfer‐Reaktionen beteiligt. In dem hier diskutierten biomimetischen Ansatz wird der Einfluss einer Schwefelkoordination auf eine Kobalt‐katalysierte Sauerstoff‐Reduktionsreaktion (ORR) demonstriert. Ein Vergleich des ORR‐Vermögens eines vierfach Stickstoff‐koordinierten [Co(Cyclam]2+‐Komplexes (1; Cyclam=1,5,8,11‐Tetraaza‐cyclotetradecan) und dessen Schwefel‐Analogons [Co(S2N2‐Cyclam)]2+(2; S2N2‐Cyclam=1,8‐Dithia‐5,11‐diazacyclotetradecan) zeigt verbesserte katalytische Eigenschaften mit dem in die Ligandensphäre am Kobalt eingeführten Chalkogen. Isolierung und Charakterisierung der Intermediate, die sich im Zuge der Sauerstoffaktivierung an den Kobalt(II)‐Zentren von1und2bilden, identifizieren eine Beteiligung des Schwefels am O2‐Reduktionsprozess als entscheidenden Faktor für die verbesserten Eigenschaften von2bei der katalytischen ORR.

Lattice strain and interfacial engineering of a Bi-based electrocatalyst for highly selective CO2 electroreduction to formate

Surface strain tuning in a coupled heterostructure efficiently engineers the catalytic performance of heterogeneous catalysts by altering the electronic structures and boosting electron transport. Generally, Bi-based catalysts are more favorable than ZnO for CO2 electroreduction to formate, but Bi is much more costly than Zn. Herein, a new Bi2O2CO3/ZnO heterojunction catalyst with porous nanoplate morphology is synthesized through a hexadecyl trimethyl ammonium bromide-templated hydrothermal reaction for a highly efficient catalytic CO2 reduction reaction (CO2RR) to produce formate. The Bi2O2CO3/ZnO catalyst shows a maximum Faradaic efficiency of 92% for formate production at −1.0 V vs. reversible hydrogen electrode (RHE) and a large partial current density of −200 mA mgBi−1 at −1.2 V vs. RHE. More importantly, the mass activity of Bi2O2CO3/ZnO normalized by Bi mass is an approximately 3.1-fold enhancement over that of the pristine Bi2O2CO3 at −1.2 V vs. RHE. By coupling X-ray photoelectron spectroscopy and adsorption spectroscopy measurements, the charge transfer from the Zn atom to the Bi atom through a heterogeneous interface results in an electron-enriched Bi2O2CO3 surface, which facilitates CO2 capture and activation. Meanwhile, compressive stress produced on the catalyst surface helps optimize the adsorption energy of the reaction intermediate, synergistically enhancing the catalytic selectivity and activity of Bi2O2CO3/ZnO for electrochemical CO2 reduction to formate.

Microwave-assisted Synthesis, Characterization, Photocatalytic Degradation of Antibiotics, and Fluorometric Selective Sensing Activity of g-C3N4 Supported CuO Composites.

Herein, we have designed for the fabrication of a series of g-C3N4/CuO composite by using one-step microwave-assisted synthesis for the degradation of antibiotics and detection of nano-molar range of toxic heavy metal ions. The synthesized g-C3N4/CuO composites were analyzed and characterized to know the structure, phase, surface area, absorption region, bandgap, and size of the composites. From the observation of TEM and XRD measurements, g-C3N4/CuO composites have hexagonal shape with average diameter of the particles is 25 ± 5nm. The observed band gap values from UV-vis DRS for g-C3N4 nanosheets and CuO NPs are 2.64eV and 1.72eV. The synthesized g-C3N4/CuO composite has prodigious specific surface area (32.47 m2/g), which is the evident for superior heterogeneous catalytic applications. Therefore, the synthesized g-C3N4/CuO composites were tested for the degradation of antibiotics such as tetracycline (TC) and ciprofloxacin (CIP) under UV light illumination, it shows 88.02% and 90.01% degradation was observed within 1h due to the matching optical band gap and internal charge transfer of excitons with in the heterojunction surface among g-C3N4 and CuO in the composite than the individual components (g-C3N4 and CuO) due to the high surface area and tiny particles of CuO were randomly deposited on the surface of g-C3N4 nanosheets. The catalytic reduction reaction follows as pseudo-first order equation and reused for 5 consecutive cycles without remarkable loss of catalytic activity. Moreover, the synthesized CuO NPs and g-C3N4/CuO composites were used as a prominent fluorescence sensing probe for the selective detection of Pb2+ in nano-molar range of concentration with Ksv is 1.38 × 104mol- 1dm3. It was observed as a linear relationship based on the change in intensity, the limit of detection was determined to be 0.184 nM.

μ-Oxo Dimerization Effects on Ground- and Excited-State Properties of a Water-Soluble Iron Porphyrin CO2 Reduction Catalyst

Iron 5,10,15,20-tetra(para-N,N,N-trimethylanilinium)porphyrin (Fe-p-TMA) is a water-soluble catalyst capable of electrochemical and photochemical CO2 reduction. Although its catalytic ability has been thoroughly investigated, the mechanism and associated intermediates are largely unknown. Previous studies proposed that Fe-p-TMA enters catalytic cycles as a monomeric species. However, we demonstrate herein that, in aqueous solutions, Fe-p-TMA undergoes formation of a μ-oxo porphyrin dimer that exists in equilibrium with its monomeric form. The propensity for μ-oxo formation is highly dependent on the solution pH and ionic strength. Indeed, the μ-oxo form is stabilized in the presence of electrolytes that are key components of catalytically relevant conditions. By leveraging the ability to chemically control and spectrally address both species, we characterize their ground-state electronic structures and excited-state photodynamics. Global fitting of ultrafast transient absorption data reveals two distinct excited-state relaxation pathways: a three-component sequential model consistent with monomeric relaxation and a two-component sequential model for the μ-oxo species. Relaxation of the monomeric species is best described as a ligand-to-metal charge transfer (τ1 = ∼500 fs), an ionic strength-dependent metal-to-ligand charge transfer (τ2 = 2-4 ps), and finally relaxation of a ligand field excited state to the ground state (τ3 = 5 ps). Conversely, excited-state relaxation of the μ-oxo species proceeds via cleavage of an FeIII-O bond to generate transient FeIV═O and FeII porphyrin species (τ1 = 2 ps) that recombine to the ground-state μ-oxo species (τ2 = ∼1 ns). This latter lifetime extends to timescales relevant for chemical reactivity. It is therefore emphasized that further consideration of catalyst speciation and chemical microenvironments is necessary for elucidating the mechanisms of catalytic CO2 reduction reactions.

Enhanced bioelectrochemical performance by NiCoAl-LDH/MXene hybrid as cathode catalyst for microbial fuel cell

In this work, NiCoAl-layered double hydroxide (LDH)/MXene was successfully prepared through straightforward hydrothermal method. NiCoAl-LDH was tightly and uniformly coated on MXene, forming a kind of porous structure. NiCoAl-LDH/MXene exhibited the (002) (012) (105) (100) crystal planes of hydrotalcite reflection. NiCoAl-LDH/MXene also showed superior catalytic oxygen reduction reaction (ORR) in response current according to electrochemical test (cyclic voltammetry (CV) etc.). The maximum power density and output voltage of NiCoAl-LDH/MXene as cathode in microbial fuel cell (MFC) was 362.404 mW/m2 and 450 mV, respectively, which was 1.54 times of MXene-MFC (234.256 mW/m2) and 1.71 times of NiCoAl-LDH-MFC (211.56 mW/m2). The results indicated that NiCoAl-LDH/MXene was a kind of potential cathode catalyst for MFC and was full of future application.

Two-Dimensional (2D) TM-Tetrahydroxyquinone Metal-Organic Framework for Selective CO2 Electrocatalysis: A DFT Investigation.

The resource utilization of CO2 is one of the essential avenues to realize the goal of "double carbon". The metal-organic framework (MOF) has shown promising applications in CO2 catalytic reduction reactions due to its sufficient pore structure, abundant active sites and functionalizability. In this paper, we investigated the electrocatalytic carbon dioxide reduction reactions of single-atom catalysts created by MOF two-dimensional coordination network materials constructed from transition metal-tetrahydroxybenzoquinone using density function theory calculations. The results indicate that for 10 transition metals, TM-THQ single levels ranging from Sc to Zn, the metal atom binding energy to the THQ is large enough to allow the metal atoms to be stably dispersed in the THQ monolayer. The Ni-THQ catalyst does not compete with the HER reaction in an electrocatalytic CO2 reduction. The primary product of reduction for Sc-THQ is HCOOH, but the major product of Co-THQ is HCHO. The main product of Cu-THQ is CO, while the main product of six catalysts, Ti, V, Cr, Mn, Fe, and Zn, is CH4. The limit potential and overpotential of Ti-THQ are the highest, 1.043 V and 1.212 V, respectively. The overpotentials of the other monolayer catalysts ranged from 0.172 to 0.952 V, and they were all relatively low. Therefore, we forecast that the TM-HQ monolayer will show powerful activity in electrocatalytic carbon dioxide reduction, making it a prospective electrocatalyst for carbon dioxide reduction.

The Effect of Iron Content on the Ammonia Selective Catalytic Reduction Reaction (NH3-SCR) Catalytic Performance of FeOx/SAPO-34.

Iron-based catalysts are regarded as promising candidates for the ammonia selective catalytic reduction reaction (NH3-SCR) which show good catalytic activity at medium and high temperatures, whereas SAPO-34 molecular sieves have a micro-pore structure and are ideal catalyst carriers. In this paper, four FeOx/SAPO-34 molecular sieve catalysts with different iron contents (Fe = 1%, 2%, 3%, 4%) were prepared using an impregnation method. The effect of iron content on the surface properties and catalytic activity was investigated by a series of characterization techniques including XRD, SEM, BET, XPS, H2-TPR and NH3-TPD. Iron species in the FeOx/SAPO-34 catalysts exist in the form of isolated iron ions or well-dispersed small crystals and iron oxide species clusters. With the addition of iron content, the integrity of CHA (chabazite) zeolite structure remained, but the crystallinity was affected. The FeOx/SAPO-34 catalyst with 3% Fe loading showed a relatively flat surface with no large-diameter particles and strong oxidation-reduction ability. Meanwhile, more acidic sites are exposed, which accelerated the process of catalytic reaction. Thus, the FeOx/SAPO-34 catalyst with 3% Fe showed the best NO conversion performance among the four catalysts prepared and maintained more than 90% NO conversion efficiency in a wide temperature range from 310 °C to 450 °C.

Si/Al Ratio Determines the SCR Performance of Cu-SSZ-13 Catalysts in the Presence of NO2.

A comparative study was performed to investigate the NH3-selective catalytic reduction (SCR) reaction activity of Cu-SSZ-13 zeolites having Si/Al ratios (SARs) of 5, 18, and 30. Remarkably, the Cu-SSZ-13 zeolite catalysts exhibited completely opposite behaviors as a function of SAR under standard SCR (SSCR) and fast SCR (FSCR) reaction atmospheres. Under SSCR conditions, the NOx conversion increased as expected with the decreasing SAR. Under FSCR conditions, however, the NOx conversion decreased as the SAR decreased, contrary to expectations. In this study, based on characterization of the catalysts by X-ray diffraction, transmission electron microscopy, electron paramagnetic resonance, H2-temperature-programmed reduction, temperature-programmed desorption, and diffuse reflectance infrared Fourier transform spectroscopy, together with theoretical calculations, the authors found that the amount of Brønsted acid sites goes up while the SAR goes down, leading to an increase in the accumulation of NH4NO3 under FSCR reaction conditions. Moreover, the accumulated NH4NO3 is of greater stability for those low SAR Cu-SSZ-13 catalysts. These two reasons cause the FSCR performance of Cu-SSZ-13 to decrease with a decrease in SAR. As a result, the NO2 effect on SCR activity changes from promotion to inhibition as the SAR decreases.

A novel low-temperature Fe-Fe double-atom catalyst for a “fast SCR” reaction

Theoretically designing a catalyst with high catalytic activity for ammonia selective catalytic reduction (NH3-SCR) reaction at low temperature to guide the subsequent experimental synthesis, which is of great significance for controlling the emission of NOx. Herein, we examine for the first time Fe2-N6 catalysts as candidates for this application at a theoretical level. The adsorption behavior of various gases, catalytic mechanism of the NH3-SCR reaction, and turnover frequency were analyzed using density functional theory calculations (DFT) and microkinetic modeling. We found that a “fast SCR” reaction is the dominant path of the NH3-SCR reaction. The energy barrier for the rate-determining step (HONO formation) is 1.00 eV, much lower than that of other SCR catalysts. In addition, the Fe2-N6 catalyst exhibits outstanding low-temperature activities in the temperature window from 300 to 500 K.

Nitrogen doping in porous biochar from cotton stalk with H3PO4 activation for reduction of NOx with NH3-SCR at low temperatures: Characteristics and catalytic activity analysis

This study aimed to prepare a series of nitrogen-doped modified biochar using the cotton stalk as the raw material and examine the effect of different nitrogen-containing groups on the NH3-selective catalytic reduction (SCR) reaction. The X-ray photoelectron spectroscopy results and denitration activity analysis revealed that the pyridine nitrogen (N-5) and pyrrole nitrogen (N-6) were the main nitrogen-containing groups determining the denitration activity of the biochar. The NO-temperature-programmed desorption results showed that the surface basicity of the biochar after nitrogen doping increased, and its adsorption capacity for NO improved. The results of the NO oxidation test indicated that the SCR reaction on the biochar existed as both a “fast-SCR” reaction and a “standard-SCR” reaction. That is, the NH3-SCR reaction mainly depended on the “fast-SCR” reaction at low temperatures (50–150℃). The main reaction at high temperatures (150–260℃) was the “standard-SCR” reaction. The O2-TPD results showed that the biochar doped with nitrogen produced a large number of oxygen holes, increasing the O2 activation ability of the biochar. Both E-R and L-H mechanisms existed in the denitrification process of the nitrogen-doped cotton stalk-based biochar, and both gaseous and adsorbed NO were obtained by •NH2 reduction.

Theoretical Study of Oxygen Reduction Reaction Mechanism in Metal-Free Carbon Materials: Defects, Structural Flexibility, and Chemical Reaction.

Metal-free carbon materials are attractive Pt-based catalyst alternatives. However, despite efforts, the reaction mechanism remains elusive. Thus, we investigated the role of defects (dopant nitrogen and carbon vacancy) on the catalytic oxygen reduction reaction in a metal-free carbon material focusing on the effect of structural flexibility. Crucially, defects lower the energy barrier for the sp2/sp3 transition of the carbon-centered O2-adsorption sites by releasing structural strain during the reaction. In particular, low-coordinated pyridinic-N displaces from the carbon plane to release the strain, whereas weak C-C bonds around the carbon vacancy change the bond lengths to release the strain. Defects indirectly promote the adsorption of oxygen by enhancing structural flexibility. Thus, the nonlocal structural environment is as critical as the direct interaction between adsorption sites and adsorbate in the chemical reaction. Molecular dynamics simulations reveal that pyridinic-N doping is a facile route to introduce stable catalytic active sites. Overall, our results provide a deeper understanding of chemical processes on defective carbon materials.

Mesoporous–optimized BaMnO3 perovskite small-scale nanocrystals in SSZ-13 to enhance activity for the selective catalytic reduction reaction of NO

As one of the cores of ammonia-selective catalytic reduction technology (NH3-SCR), conventional microporous Cu-SSZ-13 has developed hierarchical pores in recent years. The reasonable use of newly mesoporous channels to improve catalytic activity has become a new challenge. We designed novel hierarchical Cu-SSZ-13 catalyst supported with BaMnO3 perovskite, which exhibited excellent low-temperature SCR activity. A series of characterizations illustrated that BaMnO3 was introduced into mesopores located in hierarchical Cu-SSZ-13 and form small-scale nanocrystals of 5–10 nm, which significantly improves the ability to oxidize NO to NO2. In addition, the synergistic effect caused by introduced BaMnO3 and Cu species makes BaMnO3-Cu-SSZ-13 have higher Mn4+ proportion and stronger redox ability. In situ DRIFTS experiments revealed that the introduced BaMnO3 enhanced the reactivity of ammonia and NOx species. Different from the monodentate nitrate observed on Cu-SSZ-13, the reaction intermediate bidentate nitrate and ads-NO2 appeared on BaMnO3-Cu-SSZ-13 in the reaction process, which is also a crucial reason for the higher low-temperature activity.

Exploring of catalytic oxygen reduction reaction activity of lattice carbons of vanadium and niobium doped nitrogen codoped carbon nanotubes by density functional theory

AbstractThe oxygen electroreduction mechanism on the V‐ and Nb‐doped nitrogen‐codoped (6,6)armchair carbon nanotube with incorporated MN4 fragment has been studied using the ωB97XD and PBE density functional theory approaches. The metal center in MN4 fragment and the adjacent NCCN double bond (C2 site) of the support have been revealed as active centers. The metal active centers turned out to be irreversibly oxidized at the first step of ORR affording stable O*, 2O*, or O*HO* adsorbates depending on the applied electrode potential U, that makes them no longer active in ORR. Therefore, the C2 site comes at the forefront in ORR catalysis. Among the metal oxidized forms M(O)N4, M(O)(O)N4, and M(O)(OH)N4CNT, the C2 site of the latter turned out to be most active for 4e dissociative ORR. For both metals the last protonation/electron transfer step, HO* + H* → H2O, is the rate‐limiting step. The alternative hydrogen peroxide formation is not only thermodynamically less favorable but also kinetically slower than the 4e dissociative ORR route on the C2 site of model M(O)(OH)N4CNT catalyst.

Ligand Assisted CO2 Activation and Catalytic Valorization by an NHI‐Stabilized Stannylene

AbstractThe aryl(imino)stannylene MesTer[N(IDipp)]Sn could be obtained by treating NHILi (NHI=N(IDipp), IDipp=C[N‐(2,6‐iPr2C6H3)CH]2) with MesTerSnCl (MesTer=2,6‐Mes2C6H3) and offers a unique reactivity pattern compared to conventional single site tetrylene catalyzed CO2 reduction reactions. The Sn(II) center, stabilized by the NHI ligand enabled the sequestration and valorization of CO2 to C1 feedstock stoichiometrically, as well as catalytically, utilizing HBpin (pin=pinacolato) as reductant. The experimental comparison with aryl(amido)stannylene MesTer(NPh2)Sn and aryl(phosphinidene)stannylene MesTer[P(IDipp)]Sn, as well as computational analysis, rationalize the electronic features and key role of the NHI ligand in the CO2 reduction process. In case of the phosphorus congener, Sn−P bonding with pronounced double‐bond character is obtained, which prevents swift dissociation, thus preventing CO2 uptake. Instead, hard/soft mismatch between tin and the NHI induces zwitterionic and single‐bond character, switching on the intermediate dissociation of Sn(II)/NHI, followed by a tin hydride mediated reduction step, and thus allows for efficient catalysis under mild conditions.

Boosting nitrogen reduction reaction with boron sites supported by defective Mo2B2O2 MBene

Developing a novel strategy based on boron centers as active sites for high-efficient catalytic nitrogen reduction reaction (NRR) to produce ammonia is highly desired. Herein, we have systematically investigated the properties of single and double B atoms supported on defective Mo2B2O2 MBene (B@Mo2B2O2 and B2@Mo2B2O2) for efficient N2 capture and reduction. Our results suggest that B@Mo2B2O2 and B2 @Mo2B2O2 show high activity for N2 reduction through the enzymatic pathway with quite low limiting potentials of − 0.42 V and − 0.34 V, respectively. We highlight that B2 @Mo2B2O2 exhibit much higher selectivity to suppress the competitive HER reaction than B@Mo2B2O2, which is illuminated to be originated from the synergistic effect and covalent bonding between the double B atoms. Further analysis on electronic structures suggests that the limiting potentials of NRR can be well described by the p-band center of B atom as well as its overlap position with N2-p orbitals. Finally, we reveal that compared with B@Mo2B2O2, the double B active sites (B2 @Mo2B2O2) can selectively modulate the adsorption free energy of *NH3, further leading to a lower limiting potential. We believe that the present findings provide depth insight into the superior catalytic performance of B center catalysts for NRR and further guide the design of single/double-atom catalysts.

Magnesium tuned triple conductivity and bifunctionality of BaCo0.4Fe0.4Zr0.1Y0.1O3-δ perovskite towards reversible protonic ceramic electrochemical cells

The performance of reversible protonic ceramic electrochemical cells (R-PCECs) was significantly limited, due to lack of suitable air electrode materials specifically designed to match proton conducting electrolyte. Here, we report by doping a small amount of magnesium (5 %), a phase-pure triple conducting Ba(Co0.4Fe0.4Zr0.1Y0.1)0.95Mg0.05O3-δ (BCFZYM) perovskite is developed as an air electrode for R-PCECs. The doping of 5 % Mg effectively enhances oxygen/steam surface exchange, oxygen-ion and proton conductivity, consequently significantly improves catalytic oxygen reduction and evolution reactions (ORR/OER) activities over protonic electrolytes. R-PCECs with the BCFZYM display excellent performances in both fuel cell (850 mW cm-2 at 600 °C) and electrolysis modes (−1244 mA cm-2 at 1.3 V at 600 °C). In addition, the R-PCECs show favorable stability in cycling (110 h), electrolysis (200 h) and fuel cell modes (300 h), demonstrating that BCFZYM air electrode has excellent operating stability.

A density functional theory study of catalytic oxygen reduction reaction on Co-CoO(111)

The demand for clean energy has greatly increased given the current situation of environmental pollution and energy shortages. Fuel cells have attracted much attention because of their high energy density and low pollutant emission. However, the oxygen-reduction reaction (ORR) kinetics of the cathode are slow, and many platinum-based catalysts are needed to drive the reaction. The high platinum price and scarce reserves limit the application of fuel cells. It is therefore urgent to develop cheaper and more efficient non-noble-metal catalysts to drive the ORR. One promising approach is to develop transition-metal-oxide catalysts with high ORR catalytic performance. Here, the structure of CoO was modified, and the surface of partially reduced CoO(111) catalyst [Co-CoO(111)] was simulated via density functional theory (DFT). The catalytic ORR on two kinds of Co (Co-2, Co-3) on the Co-CoO(111) surface were simulated and free-energy diagrams were created. When Co-2 was used as the active site, the Co-CoO(111) catalyst had a low overpotential of 0.34 eV. Besides, when Co-3 site was covered with O and Co-2(*)-Co-3(O*) is used as ORR reaction site, it still had good catalytic performance of ORR. The electronic structure of Co-CoO(111) was used to explain the high level of the ORR.

Promotion of Catalytic Oxygen Reduction Reactions: The Utility of Proton Management Substituents on Cobalt Porphyrins.

Three ABAB-type cobalt meso-tetraarylporphyrins with fluorine (F-CoPor), acetic acid (AC-CoPor), and cyanoacetic acid (CN-CoPor) groups at the para-positions of phenyl rings at the 10,20-positions are synthesized and evaluated as catalysts for oxygen reduction reactions (ORRs). In density functional theory calculations, the frontier molecular orbitals of these complexes were found to be stabilized relative to model complexes with electron-withdrawing atoms or moieties on the meso-aryl rings. Electrochemical measurements suggest that electrodes with CN-CoPor (CN-CoPor/C) exhibit the most positive ORR potential values and the highest limiting current density in both acidic and alkali electrolytes, while the F-CoPor/C electrocatalyst exhibits extremely low ORR performance. The electron transfer numbers for the electrocatalysts are more than 3.0, indicating that a mixture of 2- and 4-electron transfer pathways occurs. The results demonstrate that coupling the hydrogen bonding properties and electron-withdrawing abilities through rational design of the substituent at the meso-position is an efficient way to modify the ORR performance.

Carboxymethyl cellulose nanocolloids anchored Pd(0) nanoparticles (CMC@Pd NPs): synthesis, characterization, and catalytic application in transfer hydrogenation.

Herein, we report on the preparation of novel colloidal system based on carboxymethyl cellulose (CMC) and Pd nanoparticles (CMC@Pd NPs) via an ecofriendly auto-reduction process under mild conditions. In the first step, the follow-up of reduction and preparation of CMC anchored palladium nanoparticles (Pd NPs) in aqueous solution was carried out using UV-Vis spectroscopy. Thereafter, the monodispersed colloids were fully characterized by advanced analytical, structural, and morphological techniques. Based on Scherrer equation, the as-synthesized CMC@Pd NPs crystallite size was about 10.88nm. Accordingly, the detailed microscopic study revealed CMC nanocolloids anchored uniform distribution of Pd NPs and the presence of CMC nanofilm as protective monolayer. To the best of our knowledge, the observed nanoscale properties are reported for the first time for CMC-M system. The performance of the as-synthesized CMC@Pd nanocolloids was first investigated in the reduction of 4-nitrophenol, as a model substrate, to 4-aminophenol using NaBH4 as a hydrogen source. Moreover, the catalytic reduction of various nitroarenes bearing electron withdrawing or donating substituents was carried out and monitored by UV-Vis spectroscopy. The chemo- and regioselectivity of the catalytic reduction in presence of CMC@Pd NPs were also studied. Consequently, the prepared CMC@Pd nanocolloids exhibit remarkable activity, good heterogeneity, and higher reusability and stability for the catalytic reduction reaction under mild conditions.