Size Of Pd Nanoparticles Research Articles

Synthesis of Palladium Nanoparticles on the Surface of Cerium(IV) Oxide under the Action of Ultraviolet Radiation and Their Characterization

Palladium nanoparticles have been synthesized in an aqueous medium by ultraviolet irradiation using complex palladium oxalate as a precursor. The samples were studied by various laboratory methods, including transmission electron microscopy, X-ray fluorescence analysis, X-ray powder diffraction, X-ray absorption fine structure spectroscopy, and diffuse reflectance infrared spectroscopy with the use of CO probe molecules. The microimages obtained by transmission electron microscopy did not allow us to distinguish Pd nanoparticles from the material of the substrate but do not show any effect of ultraviolet irradiation on the sizes of CeO2 nanoparticles. The X-ray fluorescence analysis data show the presence of cerium and palladium atoms in the material. X-ray diffraction patterns indicate the presence of phases of cerium dioxide and metallic palladium, while the analysis of the X-ray absorption fine structure spectra beyond the K-edge of palladium shows the presence of the PdO phase in the system. The approximate size of the palladium nanoparticles was estimated by the infrared spectra after the adsorption of CO and is less than 2 nm, which is significantly smaller than the average size of Pd nanoparticles obtained by a similar method without a CeO2 substrate (1.5–9.5 nm).

Direct synthesis of hydrogen peroxide from hydrogen and oxygen over yolk–shell nanocatalyst Pd@HCS with controlled Pd nanoparticle size

For conventional palladium-coated catalysts, some active sites of the Pd surface are blocked by a shell and all reactants and products are confined in the same channel for diffusion, which reduces the catalytic activity. To solve these problems, a different type of yolk–shell nanocatalyst were prepared to directly synthesize hydrogen peroxide (H2O2): Pd@HCS, with Pd nanoparticles as core and hollow carbon spheres as shell. The shell pore size of the catalyst Pd@HCS was between 1 and 2 nm, which could be beneficial for the diffusion of the reactant and product molecules. Core Pd nanoparticle size decreased with decreasing number of carbon atoms of the oil phase solvent (isooctane (C8), n-heptane (C7), and cyclohexane (C6)) and surfactant polyethylene glycol monocetyl ether (Brij56) concentration. When Pd nanoparticle size was 5.50 ± 1.13 nm, the catalyst PdC6-0.174@HCS had the highest H2O2 selectivity and productivity, which were 94% and 3219 mmol gPd-1 h−1, respectively.

The Influence of Size and Shape of Pd Nanoparticles on the Performances of Pd/Beta Catalysts for n‐Heptane Hydroisomerization

AbstractSeveral Pd/Beta catalysts with cubic (9 nm, 12 nm, 16 nm) and truncated‐octahedral (18 nm) Pd nanoparticles (NPs) were prepared to investigate the effect of size and shape of Pd NPs for n‐heptane hydroisomerization. Characterizations confirmed that the cubic Pd NPs solely exposed {100} crystal plane and truncated‐octahedral Pd NPs were enclosed by {100} and {111} crystal planes, and that the desorption temperature of subsurface hydrogen on Pd NPs showed size and shape dependence. Hydroisomerization results exhibits that the catalyst with 9 nm cubic Pd NPs displayed the higher isomers selectivity compared to the catalyst with 12 nm cubic NPs, 18 nm truncated octahedral NPs and 16 nm cubic NPs at similar conversion. This result suggested the size and shape dependence of (de)hydrogenation activity of Pd NPs, and further revealed the key role of subsurface hydrogen in determining the (de)hydrogenation activity.

Synthesis of Pd(0) Nanoparticles in TiO2–SiO2 Xerogel

Pd/TiO2–SiO2 xerogels containing 0.15–0.75 wt % palladium are prepared from Pd(NO3)2 · 2H2O solutions in a mixture of tetrabutoxytitanium (TBT) and tetraethoxysilane (TEOS) in a desiccator under acetic acid–water vapors in the batch mode at 20°С followed by drying and calcination of the material at 850°С. IR spectroscopy showed that the presence of Pd(NO3)2 · 2H2O has no effect on the amount of newly formed Ti–O–Si bonds in the double oxide TiO2–SiO2 over the range of salt concentrations studied. X-ray powder diffraction showed that palladium present in the xerogel calcined at 850°С is in the form of Pd(0) nanoparticles. The electron-microscopic morphology study showed that the items prepared (Pd(0) nanoparticles) had near-spherical shapes; their sizes fell in the range 20–230 nm. A means for varying Pd(0) nanoparticle size in the material is to vary the palladium(II) salt concentration at the dissolution stage.

Amine-functionalized sepiolite: Toward highly efficient palladium nanocatalyst for dehydrogenation of additive-free formic acid

Formic acid has recently come to be considered as a promising material for chemical storage of hydrogen. To date, highly efficient and low-cost heterogeneous catalysts for formic acid dehydrogenation without additive under mild conditions are still limited. In this work, we employed amine-functionalized sepiolite, a typical natural clay mineral with fibrous structure, as support to synthesize a nanocatalyst by the simple impregnation-reduction method. The amine groups on amine functionalized sepiolite support are shown to significantly reduce the average size of Pd nanoparticles (from 7.60 to 2.80 nm) as well as provide a synergistic effect with the Pd nanoparticles, which boosts the rate of additive-free formic acid dehydrogenation (initial turnover frequency (TOF) values of 5587 h−1 at 60 °C, equal to or even better than the most active heterogeneous catalysts). Compared to current catalyst systems, this catalyst can lead to a brighter prospect of cost-efficient heterogeneous catalysts for formic acid dehydrogenation.

Cage-like hierarchically mesoporous hollow silica microspheres templated by mesomorphous polyelectrolyte-surfactant complexes for noble metal nanoparticles immobilization

In this paper, well-defined CHMSs were synthesized through co-hydrolysis of tetraethylsiloxane (TEOS) and 3-aminopropyltriethoxysilane (APTS) template by mesomorphous complexes of hexadecylpyridinium chloride (CPC) and poly(acrylic acid) (PAA). It was demonstrated that the adding amount of APTS in the reaction system played a key role in the formation of the hollow cage-like structure and a possible formation mechanism of CHMSs was proposed. The synthesized CHMSs presented as uniform microsphers with average diameter of 600 nm and possessed tri-model pore structure that were the ordered mesopores (˜3 nm) originated from CPC micelle, the secondary nanopores (˜55 nm) templated by phase separated PAA chain in the silica shell as well as the hollow cavity (several hundred nanometer). At the same time, the co-hydrolysis of APTS resulted in amino groups functionalized silica framework of the CHMSs. Ascribed to the unique structure and the inherent amino groups, the CHMSs were utilized as scaffold for preparation of heterogeneous noble metal nanoparticle catalysts. By choosing the palladium (Pd) as a typical example, 1-Pd@CHSMs catalysts containing 1.0 wt% Pd and uniform distributed small size Pd nanoparticles (˜2.9 nm) were obtained. The catalytic reduction of 4-nitrophenol demonstrated that the heterogeneous 1-Pd@CHSMs catalyst was efficient and reusable.

Facile Synthesis and in situ TEM Observation of Nanoporous Pd for Enhanced Catalytic Applications

Summary of main observation and conclusionA facile, efficient and green photochemical synthetic approach has been used to prepare sponge‐like porous Pd nanoparticles. Obtained by ultraviolet irradiation using a K2PdCl4 precursor solution, the final products exhibited three dimensionally interconnected porous structures made up of ~3.6 nm sized Pd nanoparticles. In situ liquid cell TEM results indicated such porous structures are in a dynamic stable state when the particles are distributed in aqueous solution. The porous Pd nanoparticles exhibited electrochemical active surface area (ECSA) of up to 43 m2·g–1 and mass activity of 1144 mA·mg–1 in menthol oxidation, kapp of 0.22 min–1 and normalized kapp/m (kn) of 8.3×104 min–1·g–1 in 4‐nitrophenol (4‐NP) reduction reactions. Comparing with the literature, it is demonstrated that our porous Pd nanoparticles with clean surfaces exhibited very high catalytic performances. This work may shed a light on facile and green synthesis of noble‐metal particles with better catalytic performances.

N-Doped CMK-3 Carbons Supporting Palladium Nanoparticles as Catalysts for Hydrodechlorination

The effect of nitrogen doping of a carbon support on the activity of Pd catalysts in the hydrodechlorination of 4-chlorophenol in water has been studied. Highly mesoporous CMK-3 carbons have been synthesized by infiltration of a commercial resol resin into SBA-15 silica followed by pyrolysis at 700 °C and removal of the template with NaOH. Nitrogen doping was achieved by infiltrating 1,10-phenantroline together with the resin. Equivalent porous texture and Pd nanoparticles size were obtained for the catalysts based on undoped and nitrogen-doped CMK-3 carbons. The catalysts allowed fast 4-chlorophenol hydrodechlorination with exclusive selectivity to phenol. A higher activity was observed at 30 °C for the catalyst with the N-doped support (76–81 mmol·gPd–1·min–1), showing the beneficial effect of nitrogen doping of the carbon supports. The different behavior was also evidenced by the activation energies calculated for the catalysts with undoped (53 kJ·mol–1) and N-doped CMK-3 carbon (36 kJ·mol–1) in the 30...

Atmospheric-pressure dielectric barrier discharge cold plasma for synthesizing high performance Pd/C formic acid dehydrogenation catalyst

Abstract HCOOH is a cheap, non-toxic, ease of storage and transportation, and abundant renewable source for generating hydrogen. Activated carbon supported palladium (Pd/C) catalysts have drawn increasing research interest due to their high performance toward HCOOH dehydrogenation and ease of recycle after deactivation. In this work, atmospheric-pressure (AP) dielectric barrier discharge (DBD) cold plasma has been employed to synthesize Pd/C-P catalyst by using PdCl2 as Pd precursor. For comparison, commercial Sigma-Aldrich Pd/C catalyst is adopted as the reference. Both cold plasma synthesized Pd/C-P and commercial Pd/C catalysts exhibit high performance for HCOOH dehydrogenation, and no CO is detected. The total volume of generated H2 and CO2 over Pd/C-P is 317 ml, which is 1.12 times as that of commercial Pd/C (282 ml). The catalytic stability of Pd/C-P is much superior to the commercial Pd/C catalyst. Catalytic activity of Pd/C-P has been decreased to 59.6% and 50.2% after the second and third reaction cycle, respectively, in comparison with the first cycle. However, they have been decreased to 16.3% and 8.9%, respectively, for commercial Pd/C. Various characterization techniques have been adopted to discuss the influence mechanism. The high catalytic activity of Pd/C-P is mainly attributed to the small size of Pd nanoparticles. The high catalytic stability of Pd/C-P is ascribed to the strong metal-support interaction induced by cold plasma and HNO3 pre-oxidation treatment, which leads to less decrease in Pd/C atomic ratio, Pd leaching, and stabilizes the size of Pd nanoparticles. In conclusion, the Pd/C-P catalyst exhibits much higher catalytic activity and stability than the commercial Pd/C, which has theoretical significance and practical application value.

Influence of controlled Pd nanoparticles decorated TiO2 nanowire arrays for efficient photoelectrochemical water splitting

This work depicts the synthesis of controllable Pd nanoparticles decorated TiO2 nanowire arrays by electrospray technique. By varying the substrate temperature and volume of precursor solution, Pd/TiO2 hybrid structure with different sizes and deposition yield was precisely controlled. The highest photocurrent density of the Pd/TiO2 photoanode was 1.4 mA cm−2 at 1.23 V vs. RHE, which was approximately 5 times higher than the pristine TiO2. The onset potential with a significant cathodic shift of 80 mV compared to the pristine TiO2 was also observed. To the best of our knowledge, the obtained photocurrent showed the optimal photocurrent density and high stability compared with previous reports. It is also found that the photoelectrochemical performance is closely related to the size and deposition quantity of Pd nanoparticles. According to the results, the enhanced PEC performance can be attributed to the Schottky junction, charge transfer and the enhancement about the separation efficiency of the photogenerated electrons and holes betweenTiO2 and Pd NPs. This result demonstrated that this method may design a new and green strategy for synthesizing the well-defined morphologies, compositions, and sizes of the hybrid nanomaterial for photocatalytic hydrogen generation, photocatalytic CO2 reduction and photosynthesis of organic molecules.

An Amphiphilic Mesoporous Polymer Comprising a “built‐in” Imidazolium Ionic Liquid via Nanocasting Method as a Novel Catalyst Support with Combined Prospects

AbstractAn imidazolium based ionic liquid bearing triethylene glycol (TEG) tag was employed as a functional monomer together with divinylbenzene to prepare a novel hydrophilic mesoporous polymer containing ionic liquid functionalities via nanocasting method using SBA‐15 as a hard template. The material was characterized using transmission electron microscopy (TEM), N2 sorption analysis, thermo‐gravimetric analysis (TGA), Fourier‐transform infrared spectroscopy (FT‐IR), elemental analysis (CHN), solid‐state NMR spectroscopy and contact angle measurement. It was found that the hydrophobic/hydrophilic properties of initial template, stepwise addition of monomers and initiator as well as amount of carrier solvent are of the important parameters in preparation of the polymer with uniform pore structure. Benefited from the combined properties such as incorporation of ionic liquid within the pore system of a flexible organic matrix together with its hydrophilic character, the material was found as an appropriate support to generate highly dispersed and very small size of Pd nanoparticles inside the pores. The prepared catalyst in this way, demonstrated outstanding activity, recyclability and high durability in the Suzuki cross‐coupling reaction of varied aryl halides with boronic acids in water as a green reaction medium. The beneficial role of imidazolium ionic liquid in the formation of small and highly active Pd nanoparticles was confirmed with comparative experiments.

Regulating the size and spatial distribution of Pd nanoparticles supported by the defect engineered metal–organic framework HKUST-1 and applied in the aerobic oxidation of cinnamyl alcohol

A series of novel Pd@DE-HKUST-1(Cu/Pd) catalysts with different pydc feeding ratios were successfully synthesized. The size regime and the spatial distribution of the Pd NPs can be controlled by the amount of framework incorporated pydc.

Pd local structure and size correlations to the activity of Pd/TiO2 for photocatalytic reforming of methanol.

The interaction between Pd and TiO2 for promoting photocatalytic activity was investigated by tailoring the size of Pd nanoparticles and monitoring the photocatalytic activity of methanol photo-reforming reaction for hydrogen gas production. We show that at 0.6 wt% Pd loading, the catalyst with highly dispersed nanoparticles obtained at 1 °C temperature exhibits superior photocatalytic activity for hydrogen gas production. At different weights of Pd loading, tailoring two sets of catalysts with different structural properties provides correlation between the changes in the Pd local structures and the rate of hydrogen production. The impact of controlling the structural properties of metal nanoparticles on influencing H2 production outweighs the effect of metal loading variation. The differences of Pd/TiO2 activity at the different metal loadings were correlated with the changes in the Pd local structure consequently affecting the electronic transfer and photocatalytic efficiency.

Hydrogenation of carbonyl compounds to alcohols catalyzed by lignin supported palladium nanoparticles

Lignin supported palladium(0) nanoparticles (lignin@Pd-NPs) was synthesized in water by reduction of Pd(II) salt successfully. The influence of the various parameters on the particle size of Pd nanoparticles was studied. This lignin supported Pd-NPs were characterized by UV-Vis., PXRD, SEM, TEM and EDX. The lignin@Pd-NPs is heterogeneous catalyst has been used in the transfer hydrogenation of carbonyl compounds into alcohols. Short reaction times with good to excellent yields (85-95%) of the desired products represent the effectiveness of this catalyst for these reactions. The catalyst was easily separable by simple filtration and reusable several times in repeating cycles without considerable loss in its activity. The lignin@Pd-NPs unveiled a superior hydrogenation catalyst for carbonyl compounds.

Preparation of Pd@Gr Composite Materials and Research on Catalytic Performance

In this work, the preparation of graphene by chemical oxidation reduction method and a series of chemical reactions to get graphene oxide, with the preparation of graphene composites by simply chemical reduction method for the preparation of palladium/graphene composites. Through the chemical reduction method, the small size of Pd nanoparticles is acquired by controlling the content of reducing agent. The Pd nanoparticles on graphene surface is 10nm size and evenly distributed. Pd2+ adsorption on graphene surface and in situ were partially reduced to Pd to Pd2+ nanoparticles by the reducibility of graphene. In the process, the graphene was reduced to graphene and the final compound was thinner and more transparent than the pre-experiment oxide. The oxygen-containing functional groups on the surface of the graphene have influence to the nucleation and growth of metal nanoparticles and KI can control the morphology and size of nanoparticles. The particle size and dispersion uniformity have great influence on the catalytic performance of composites, the smaller particles have better catalytic performance. Keywords:palladium, graphene composites, nanoparticles

Theoretical study of size effects on the direct synthesis of hydrogen peroxide over palladium catalysts

The direct synthesis of H2O2 over Pd catalysts is a promising alternative to the industrial Riedl–Pfleiderer process. We studied the size effects of Pd catalysts ranging from subnano clusters to extended surfaces using first-principles calculations. Compared to the high-coordinated terrace sites of extended Pd surfaces, the low-coordinated terrace and edge sites of clusters showed lower H2O2 selectivities. Bader charge analysis proved that low-coordinated terrace sites of clusters donated more electrons to adsorbed O2 than the extended surfaces, thus enhancing the undesired dissociation of O2. Accordingly, with the decline in the size of Pd nanoparticles (NPs), the increase in low-coordinated active sites results in the drop in H2O2 selectivity. Moreover, both site coordination and site geometry play critical roles in the performance of Pd active sites. Our findings provide a molecular understanding of size effects of Pd NPs on this reaction, which is consistent with the reported experimental results.

Direct Synthesis of H2O2 on Pd Based Catalysts: Modelling the Particle Size Effects and the Promoting Role of Polyvinyl Alcohol

AbstractSol immobilization is a relevant preparation method, particularly for the preparation of Pd‐based catalysts for the direct synthesis of H2O2. In this preparation, polyvinyl alcohol (PVA) acts as capping agent for Pd particles. Modelling the role of PVA on the Pd nanoparticle size and its promoting effect on the selectivity is important to understand better these catalysts. Here, Pd based catalysts prepared by sol immobilization have been tested in a semi‐batch reactor with an H2/O2 ratio ≈1, analysing the influence of the Pd nanoparticle size and the effect of PVA on the rate constants of the reaction network and their change during the reaction. A stepwise testing protocol coupled with transmission electron microscopy characterization as a function of reaction time has been used. These catalysts were compared with other catalysts prepared by hydrazine reduction and impregnation‐decomposition, where PVA is absent. The results are analysed in terms of rate constants for the various rates in the reaction network in relation with the Pd average particle size and related sites distribution, as a function of the changes occurring during extended catalytic tests. The SI‐series of catalysts (prepared by sol‐immobilization) shows enhanced properties, attributed to the effect of PVA capping agent in forming less defective Pd nanoparticles. This induces both a decrease of direct combustion and secondary hydrogenolysis reactions, and an enhancement of the direct synthesis route. The PVA layer limits H2O2 back‐diffusion with a negative influence on the productivity and selectivity, with its removal leading to initial enhanced performances, but in long‐term to a worsening due to sintering of Pd nanoparticles in extended operations.

Particle size effect in liquid-phase hydrogenation of phenylacetylene over Pd catalysts: Experimental data and theoretical analysis

The liquid-phase hydrogenation of phenylacetylene (PA) over 1 wt% Pd/Al2O3 catalysts with the mean palladium cluster size varying from 1.5 to 22 nm was studied at 5 bar H2 pressure and 25 °C. Turnover frequency in hydrogenation of the triple and double bonds displayed a significant increase with an increase of the cluster size, which was more pronounced for the former case.The effect of Pd nanoparticle size on the hydrogenation kinetics was analyzed and discussed using an approach based on a continuous distribution of edges and terraces exhibiting different reactivity. A quantitative description of the concentration dependences with incorporation of Pd particle size in the rate equations demonstrated an excellent correspondence between theory and experiments.

PdNPs@thermo-responsive block copolymers composed of PNIPAM and poly(ionic liquid) via RAFT polymerization

Preparation and identification of block copolymers comprised of PNIPAM and poly(ionic liquid) of pyridinium sulfonate by two different approaches through changing the order of monomer addition has been reported. Controlled synthesis is performed via reversible addition–fragmentation chain transfer polymerization. Pd nanoparticles (PdNPs) are immobilized onto these block copolymers to utilize them as thermo-responsive catalysts. The block copolymers and their corresponding catalysts were characterized by varied techniques, i.e., FTIR, NMR and UV–Vis spectroscopy, ICP, TGA, DLS and X-ray diffraction. SEM and EDAX were applied to analyze the surface of the sample and its composition. Furthermore, TEM was used to obtain the size of PdNPs and their distribution in the polymer matrix. The catalytic efficiency of the catalysts was examined in the Heck coupling reaction for the production of butyl cinnamate.

Facile synthesis of palladium nanoparticles on hierarchical hollow silica spheres and its catalytic properties in Suzuki-reaction.

A novel well-dispersed Pd@HHSS catalyst was synthesized by reduction of Pd(OAc)2 immobilized on HHSS we reported. When the ratios of Pd/SiO2 were 5 : 100 and 10 : 100, the Pd nanoparticles size was about 5–10 nm. The Pd@HHSS catalyst (Pd/SiO2 = 10 : 100) showed high catalytic activity in Suzuki-reaction with yields of 91–99% and the catalyst is reusable after four successive cycles without obvious loss of catalytic activity.