Collagen fiber with surface-grafted polyphenol as a novel support for Pd(0) nanoparticles: Synthesis,characterization and catalytic application

The aim of this study is to use collagen fiber (CF) as a natural polymeric support to synthesize a novel palladium (Pd) nanoparticle catalyst. To achieve a stable immobilization of Pd on CF support, epigallocatechin-3-gallate (EGCG), a typical plant polyphenol, was grafted onto CF surface, acting both as dispersing and stabilizing agent for Pd nanoparticles. Scanning electron microscopy showed that this catalyst was in ordered fibrous state with high flexibility. The presence of EGCG grafted on CF and the interaction mechanism of Pd ions with support was investigated by X-ray photoelectron spectroscopy. X-ray diffraction and transmission electron microscopy offered evidence that the well-dispersed Pd nanoparticles were generated on the outer surface of CF. By using the hydrogenation of allyl alcohol as a model reaction, the synthesized catalyst presented remarkably improved activity, selectivity and reusability as compared with the Pd catalyst supported by CF without grafting of EGCG.     

Advances in carbon nanotubes as efficacious supports for palladium-catalysed carbon–carbon cross-coupling reactions

Since the 1970s, palladium-catalysed carbon–carbon (C–C) bond formation has made a critical impact in organic synthesis. In early studies, homogeneous palladium catalysts were extensively used for this reaction with limitations such as difficulty in separation and recycling ability. Lately, heterogeneous palladium-based catalysts have shown promise as surrogates for conventional homogeneous catalysts in C–C coupling reactions, since the product is easy to isolate, while the catalyst is reusable and hence sustainable. Recently, a better part of these heterogeneous palladium catalysts are supported on carbon nanotubes (Pd/CNTs), that have shown superior catalytic performance and better recyclability since the CNT support imparts stability to the palladium catalyst. This review discusses the wide variety of surface functionalization techniques for CNTs that improve their properties as catalyst supports, as well as the methods available for loading the catalyst nanoparticles onto the CNTs. It will survey the literature where Pd/CNTs catalysts have been utilized for C–C coupling reactions, with particular emphasis on Suzuki–Miyaura and Mizoroki–Heck coupling reactions. It will also highlight some of the important parameters that affect these reactions.     

Ultrafine Nanoparticle‐Supported Ru Nanoclusters with Ultrahigh Catalytic Activity

The design of an ideal heterogeneous catalyst for hydrogenation reaction is to impart the catalyst with synergetic surface sites active cooperatively toward different reaction species. Herein a new strategy is presented for the creation of such a catalyst with dual active sites by decorating metal and metal oxide nanoparticles with ultrafine nanoclusters at atomic level. This strategy is exemplified by the design and synthesis of Ru nanoclusters supported on Ni/NiO nanoparticles. This Ru‐nanocluster/Ni/NiO‐nanoparticle catalyst is shown to exhibit ultrahigh catalytic activity for benzene hydrogenation reaction, which is 55 times higher than Ru–Ni alloy or Ru on Ni catalysts. The nanoclusters‐on‐nanoparticles are characterized by high‐resolution transmission electron microscope, Cs‐corrected high angle annular dark field‐scanning transmission electron microscopy, elemental mapping, high‐sensitivity low‐energy ion scattering, and X‐ray absorption spectra. The atomic‐scale nanocluster–nanoparticle structural characteristics constitute the basis for creating the catalytic synergy of the surface sites, where Ru provides hydrogen adsorption and dissociation site, Ni acts as a “bridge” for transferring H species to benzene adsorbed and activated at NiO site, which has significant implications to multifunctional nanocatalysts design for wide ranges of catalytic reactions.     

Enhancing both selectivity and coking-resistance of a single-atom Pd<Subscript>1</Subscript>/C<Subscript>3</Subscript>N<Subscript>4</Subscript> catalyst for acetylene hydrogenation

Selective hydrogenation is an important industrial catalytic process in chemical upgrading,where Pd-based catalysts are widely used because of their high hydrogenation activities.However,poor selectivity and short catalyst lifetime because of heavy coke formation have been major concerns.In this work,atomically dispersed Pd atoms were successfully synthesized on graphitic carbon nitride (g-C3N4) using atomic layer deposition.Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed the dominant presence of isolated Pd atoms without Pd nanoparticle (NP) formation.During selective hydrogenation of acetylene in excess ethylene,the g-C3N4-supported Pd NP catalysts had strikingly higher ethylene selectivities than the conventional Pd/A12O3 and Pd/SiO2 catalysts.In-situ X-ray photoemission spectroscopy revealed that the considerable charge transfer from the Pd NPs to g-C3N4 likely plays an important role in the catalytic performance enhancement.More impressively,the single-atom Pd1/C3N4 catalyst exhibited both higher ethylene selectivity and higher coking resistance.Our work demonstrates that the single-atom Pd catalyst is a promising candidate for improving both selectivity and coking-resistance in hydrogenation reactions.     

Carbon-supported AuPd bimetallic nanoparticles synthesized by high-energy electron beam irradiation for direct formic acid fuel cell

Nanoparticle catalysts of carbon-supported Pd (Pd/C) and carbon-supported AuPd (AuPd/C) for the direct formic acid fuel cell (DFAFC) anode were synthesized by the reduction of precursor ions in an aqueous solution irradiated with a high-energy electron beam. We obtained three kinds of nanoparticle catalysts: (1) Pd/C, (2) AuPd/C of the core–shell structure, and (3) AuPd/C of the alloy structure. The structures of AuPd nanoparticles were controlled by the addition of citric acid as a chelate agent, and sodium hydroxide as a pH controller. The structures of nanoparticle catalysts were characterized using transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, the techniques of X-ray diffraction and X-ray absorption fine structure. The catalytic activity of the formic acid oxidation was evaluated using linear sweep voltammetry. The oxidation current value of AuPd/C was higher than that of Pd/C. This indicated that the addition of Au to Pd/C improved the oxidation activity of the DFAFC anode. In addition, the AuPd/C of the alloy structure had higher oxidation activity than the AuPd/C of the core–shell structure. The control of the AuPd mixing state was effective in enhancing the formic acid oxidation activity.     

Si/Pd nanostructure with high catalytic activity in degradation of eosin Y

Si/Pd nanostructure was obtained by preparing Pd nanoparticles on the surface of SiNWs, and employed as catalyst in the degradation of eosin Y in the presence of sodium borohydride, which demonstrated high catalytic activity and could be reused. The reaction rate of eosin Y degradation with Si/Pd nanostructure catalyst enhanced ca. 24 times compared with unsupported Pd and ca. 4 times compared with polymer-supported Pd within eosin Y concentration from 5.0 × 10⁻⁵ M to 4.5 × 10⁻⁵ M. The Si/Pd nanostructure still showed high catalytic activity after five times recycle during the whole degradation.     

Influence of physicochemical treatments on spent palladium based catalyst for catalytic oxidation of VOCs

To recycle the spent catalyst for the removal of VOCs, the benzene, toluene, and xylene (BTX) complete oxidations were studied over pretreated palladium based spent catalyst in a fixed bed flow reactor system at atmospheric pressure. Two different pretreatment methods with gas (air and hydrogen) and acid aqueous solution (HCl, H(2)SO(4), HNO(3), H(3)PO(4) and CH(3)COOH) were used to investigate the catalytic activity of spent catalyst. The properties of the spent and pretreated Pd based catalyst were characterized by XRD, BET, TEM, ICP, and XPS. The results of light-off curves indicate that the catalytic activity of toluene oxidation for pretreated samples is in the order of hydrogen>air>HNO(3)>CH(3)COOH>H(2)SO(4)>H(3)PO(4)>HCl. In addition, the air and the acid aqueous pretreated catalyst activities were significantly decreased compared to that of the spent (or parent) catalyst. Moreover, hydrogen pretreated (or reduced) catalysts having mainly metallic form show the best performance in removing the toluene vapours compared to other pretreated samples. The reduction temperature made a significant difference in the catalytic performance of the spent catalyst pretreated with hydrogen. XPS results clearly supported that the palladium state of the spent catalysts pretreated at 300 degrees C was shifted more toward metallic form than other reduced catalysts. Furthermore, the results of a long-term test and catalytic activity of aromatic hydrocarbons also supported that the hydrogen pretreated spent catalyst was a good candidate for removing toxic compounds.     

Pd–Al pillared clays as catalysts for the hydrodechlorination of 4-chlorophenol in aqueous phase

Catalysts based on pillared clays with Pd–Al were synthesized from a commercial bentonite and tested for catalytic hydrodechlorination (HDC) using 4-chlorophenol (4-CPhOH) as target compound and formic acid as hydrogen source. Stable Pd–Al pillared clays, with a strong fixation of the active phase to the solid support were obtained since no Pd was detected in the reaction media. The incorporation of Pd to the pillared clay structure yielded catalysts with high activity in the reaction studied reaching a complete removal of the 4-CPhOH under mild conditions of temperature (50–70 °C). Phenol was not the only reaction product formed, since a more hydrogenated product such as cyclohexanone was detected in the effluent, which indicates additional hydrogenation of phenol. The influence of the method of introduction of Pd in the pillared clay (ion-exchange or impregnation) and Pd concentration in the catalytic activity were studied as well as other important operating variables such as reaction temperature, catalyst concentration, 4-CPhOH initial concentration and formic acid to 4-CPhOH molar ratio. The catalysts prepared suffered deactivation after three consecutive runs, probably due to carboneous deposits formation since no appreciable Pd leaching was observed.     

Aqueous phase reforming of glycerol over the Pd loaded Ni/Al2O3 catalysts

Bifunctional catalysts containing (0.5-1.5 wt%) palladium and 15 wt% of Nickel supported on gamma-Al2O3 were prepared via an impregnation technique and catalysts were characterzed by XRD BET surface area and SEM, respectively. The aqueous phase reforming of glycerol (APR) was conducted over alumina-supported catalysts at different reaction conditions for catalytic activity. Finally, we concluded that the 1.0 wt% Pd 15 wt% Ni/gamma-Al2O3 catalyst evidences higher conversion, hydrogen selectivity, lower alkane selectivity and CO production. This indicate that Pd loaded Ni/gamma-Al2O3 could be a potential catalyst for the APR of glycerol.     

Pt-Pd alloy nanoparticle-decorated carbon nanotubes: a durable and methanol tolerant oxygen reduction electrocatalyst

We describe the decoration of multiwalled carbon nanotubes (MCNTs) with Pt-Pd alloy nanoelectrocatalysts of three different compositions and their electrocatalytic performance toward the oxygen reduction reaction (ORR). The decoration of the MCNTs involves polymer-assisted impregnation of metal precursors [Formula: see text] and [Formula: see text] and the subsequent reduction of the impregnated precursors by a modified polyol route. The composition of the catalyst was controlled by tuning the molar ratio of the precursors during their impregnation. Electron probe microscopic analysis shows that the catalysts have compositions of Pt(46)Pd(54,) Pt(64)Pd(36) and Pt(28)Pd(72). The Pt(46)Pd(54) and Pt(64)Pd(36) catalysts have truncated octahedral and icosahedral shapes with a size ranging from 8 to 10?nm. On the other hand, the catalyst of Pt(28)Pd(72) composition has a spherical/quasispherical shape with a size distribution of 1-2?nm. The XPS measurement confirms the signature of metallic Pt and Pd. The Pt(46)Pd(54) catalyst has a pronounced electrocatalytic activity toward the ORR with a specific and mass activity of 378 [Formula: see text] and [Formula: see text], respectively at 0.8?V. Moreover, the Pt(46)Pd(54) nanoelectrocatalyst is highly durable and it retains its initial catalytic activity even after 1000 extensive cycles. Interestingly, this catalyst has a very high tolerance toward methanol and it does not favor the oxidation of methanol in the potential window of 0.1-1.4?V. The electrocatalytic activity of the alloy electrocatalyst is compared with commercially available Pt black and MCNT-supported spherical Pt nanoparticles. The catalytic activity of the Pt(46)Pd(54) nanoelectrocatalyst is higher than the other catalysts. The Pt(46)Pd(54) catalyst outperforms the electrocatalytic activity of all other catalysts.     

Catalytic properties of silica/silver nanocomposites

The catalytic properties of silver nanoparticles supported on silica and the relation between catalytic activity of silver particles and the support (silica) size are investigated in the present article. The silver nanoparticles with 4 nm diameters were synthesized and were attached to silica spheres with sizes of 40, 78, 105 nm, respectively. The reduction of Rhodamine 6G (R6G) by NaBH4 was designed by using the SiO2/Ag core-shell nanocomposites as catalysts. The experimental results demonstrated that the catalytic activity of silica/silver nanoparticles depends on not only the concentration of catalysts (silver) but also the support silica size. Silver particles supported on small SiO2 spheres (approximately 40 nm) show high catalytic activity. Moreover, by making a comparison between the UV-vis spectra of the catalyst before and after the catalytic reaction, we found that the position of surface plasma resonance (SPR) peak of Ag nanoparticles changes little. The above results suggested that the size and morphology of silver particles were probably kept unchanged after the reduction of R6G and also implied that the catalytic activity of silver particles was hardly lost during the catalytic reaction.     

Degradation of DCE and TCE by Fe–Ni nanoparticles immobilised polysulphone matrix

The reduction of dichloroethane (DCE) and trichloroethylene (TCE) by bimetallic iron–nickel (Fe–Ni) nanoparticles has been studied in this study. The reduction mechanism involves hydrodechlorination at the iron–nickel interface. The Fe–Ni nanoparticles have been synthesised by the chemical reduction method and immobilised on to a polysulphone matrix. The as-synthesised nanoparticles and Fe–Ni immobilied polysulphone support have been characterised to establish the particle size of the nanoparticles, which are of the order of 36–41?nm, and the physical characteristics of the immobilised support. Batch experiments have been performed using gas chromatography-mass spectrometry to study the degradation of DCE and TCE. The studies have shown that the bimetallic system is quite effective in the dechlorination of DCE and TCE. Also, the stability of the nanoparticles in the matrix has been explored with respect to its suitability for use in the degradation of chlorinated hydrocarbons.     

Graphene-Pd composite as highly active catalyst for the Suzuki-Miyaura coupling reaction

The graphene-supported Pd catalyst was synthesized using the graphene-Pd salt as precursor. Transmission electron microscope and powder X-ray diffraction analysis indicated the Pd nanoparticles, which supported on the surface of the graphene sheets possessed a face-centered cubic structure and were with the size of 4-8 nm. The Suzuki-Miyaura reaction was employed to analyze the catalytic activity of the graphene-supported Pd catalyst. HPLC analysis indicated that the yield of biphenyl was 97% when the reaction only lasted 10 min. The experimental results showed the graphene sheets were great support for ligand-free Pd catalyst.     

Catalytic hydrodechlorination of 2,4-dichlorophenol on Pd/Rh/C catalysts

Catalytic hydrodechlorination of 2,4-dichlorophenol was studied over 0.97% Pd/C, 0.98% Rh/C and 0.8% Pd-0.19% Rh/C catalysts. The catalysts were prepared by incipient wetness impregnation of support and characterized by BET surface area, temperature programmed reduction (TPR) and X-ray diffraction (XRD). The 0.97% Pd/C catalyst, which had the largest crystallite size, was the most active and selective towards the formation of 2- and 4-chlorophenols among three catalysts in liquid phase. Hydrodechlorination activity of carbon-supported catalysts were in the order of Pd/C>Pd/Rh/C>Rh/C. The kinetic equation explained experimental data well and kinetic parameters of three catalysts were provided and discussed.     

Liquid phase hydrodechlorination of chlorophenols at lower temperature on a novel Pd catalyst

Pd catalyst supported on mesoporous silica-carbon nano-composite (Pd/MSCN) was prepared by the method of wet impregnation, and its activity for hydrodechlorination (HDC) of 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol was evaluated at 258-313 K under ordinary hydrogen pressure by using triethylamine (Et(3)N) as a base additive. XRD analysis indicates that Pd/MSCN catalyst possesses the ordered mesostructure. Meanwhile, the results from TEM and H(2) chemisorption analysis indicate the high dispersion of Pd on MSCN with Pd nanoparticles whose average size is 3.2 nm. For the first time, the high activity of nano-size Pd on MSCN for HDC of chlorophenols was observed at 258 K. In addition, it was found that the inhibition effect of Et(3)N on HDC existed obviously, and can be efficiently reduced by stepwise addition of Et(3)N. The correlations of the dielectric constants of base and the polarity of solvent to the activity of Pd/MSCN for HDC of chlorophenols were obtained.     

A facile method for preparation of high performance Pt catalyst supported on multi-wall carbon nanotubes for methanol electrooxidation

Due to the inherent inertness of multi-wall carbon nanotubes (MWCNTs), complicated procedures are involved in the preparation of MWCNT-supported catalysts. In this paper, a facile and effective method is introduced to prepare Pt nanoparticles dispersed on the surface of purified MWCNTs. In this method, sodium phthalate (SP) is used as a special additive to function as an effective cross linker between MWCNTs and Pt ions, and ethylene glycol (EG) aqueous solution is used as an effective solvent. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses reveal that the prepared face-centered cubic Pt nanoparticles with the average diameter of 2.2 nm are well dispersed on the surface of the MWCNTs. Cyclic voltammetry and chronoamperometry tests demonstrate that the Pt/MWCNTs catalyst obtained from typical experiment exhibits better catalytic activity and stability for methanol electrooxidation than the Pt catalyst supported on conventional acid-treated MWCNTs (AO-MWCNTs) and JM commercial 20% Pt/C catalyst.     

In Situ Growth of Pd Nanosheets on g‐C3N4 Nanosheets with Well‐Contacted Interface and Enhanced Catalytic Performance for 4‐Nitrophenol Reduction

Loading novel metal nanosheets onto nanosheet support can improve their catalytic performance, but the morphological incompatibility makes it difficult to construct a well‐contacted interface, which is of particular interest in supported catalysts. Herein, Pd nanosheets (Pd NSs) are supported onto graphitic carbon nitride nanosheets (CNNSs) with intimate face‐to‐face contact through an in situ growth method. This method overcomes the limitations of the morphological incompatibility and ensures the intimate interfacial contact between Pd NSs and CNNSs. The nitrogen‐rich nature of CNNSs endows Pd NSs with abundant anchoring sites, which optimizes the electronic structure and improves the chemical and morphological stability of Pd NSs. The supported Pd NSs demonstrate high dispersion and exhibit largely enhanced activity toward the reduction of 4‐nitrophenol. The concentration‐normalized rate constant is up to 3052 min^?1 g^?1 L, which is 5.4 times higher than that obtained by unsupported Pd NSs. No obvious deactivation is observed after six runs of the recycling experiments. It is believed that the supported novel metal nanosheets with the intimately contacted interface may show promising applications in catalysis.     

Electrochemical characterization of nano-sized Pd-based catalysts as cathode materials in direct methanol fuel cells

To improve the catalytic activity of palladium (Pd) as a cathode catalyst in direct methanol fuel cells (DMFCs), we prepared palladium-titanium oxide (Pd-TiO2) catalysts which the Pd and TiO2 nanoparticles were simultaneously impregnated on carbon. We selected Pd and TiO2 as catalytic materials because of their electrochemical stability in acid solution. The crystal structure and the loading amount of Pd and TiO2 on carbon were characterized by X-ray diffraction (XRD) and energy dispersive X-ray microanalysis (EDX). The electrochemical characterization of Pd-TiO2/C catalysts for the oxygen reduction reaction was carried out in half and single cell systems. The catalytic activities of the Pd-TiO2 catalysts were strongly influenced by the TiO2 content. In the single cell test, the Pd-TiO2 catalysts showed very comparable performance to the Pt catalyst.     

Stable and recyclable Pd catalyst supported on modified silica hollow microspheres with macroporous shells for enhanced catalytic hydrogenation of NBR

In this work, a stable and recyclable Pd catalyst supported on N-containing silane coupling agent modified silica hollow microspheres with macroporous shells (Pd/N-SHMs) was successfully prepared and used for the selective hydrogenation of nitrile-butadiene rubber (NBR) with enhanced catalytic performance. The results showed that Pd/N-SHMs possessed small-sized and well-dispersed Pd nanoparticles (NPs) and the macroporous shells were beneficial for the diffusion of macromolecular NBR, and thus with such a catalyst, the reaction could occur under mild conditions and high hydrogenation degree (96.6%) with 100% selectivity to C=C was obtained. The prepared catalyst could be easily recycled and reused with a high efficiency. More importantly, because of the strong coordination between Pd and diamine ligands, Pd NPs could be anchored steadily over the support and only 5.0 ppm Pd residues was detected in products. This reaction was considered as pseudo-first order at high H₂ pressures, and the reaction activation energy was calculated to be as low as 18.1 kJ/mol. Our contribution is to provide an efficient and recyclable supported Pd catalyst, which may promote the development of heterogeneous catalytic systems for unsaturated macromolecular hydrogenation.     

Preparation of platinum nanoparticle and its catalytic activity for toluene oxidation

Colloidal Pt nanoparticles are prepared using H2PtCl6 as a precursor, polyvinylpyrrolidone (PVP: molecular weight = 10,000 and 40,000) and hydrogen as a stabilizing agent and a reducing agent, respectively. The amounts of the precursor and the stabilizing agent and the molecular weight of PVP have an effect on the formation of Pt nanoparticles. Supported Pt catalyst (CSPt) is prepared from colloidal Pt nanoparticles and y-Al2O3. Another supported Pt catalyst (ISPt) is prepared by using the conventional incipient wetness impregnation method with an aqueous H2PtCl6 solution and gamma-Al2O3. The catalytic activities of CSPt and ISPt catalysts are compared for VOC (toluene) oxidation. Transmission Electron Microscopy (TEM), UV-vis, X-ray diffraction (XRD) and temperature programmed reduction (TPR) are used to characterize CSPt and ISPt catalysts. The experimental results reveal that the catalytic activity of CSPt is superior to that of ISPT.