Pd Fe Catalysts Research Articles

Structure, activity, and selectivity of bimetallic Pd-Fe/SiO2 and Pd-Fe/γ-Al2O3 catalysts for the conversion of furfural

The conversion of furfural has been investigated in vapor and liquid phases over a series of supported monometallic Pd and bimetallic Pd-Fe catalysts. Over the monometallic Pd/SiO2 catalyst, the decarbonylation reaction dominates, yielding furan as the main product. By contrast, over the bimetallic Pd-Fe/SiO2 catalyst a high yield of 2-methylfuran is obtained with much lower yield to furan. Interestingly, changing the catalyst support affects the product distribution. For instance, using γ-Al2O3 instead of SiO2 as support of the bimetallic catalyst changed the dominant product from 2-methylfuran to furan. That is, Pd-Fe/γ-Al2O3 behaves more like monometallic Pd/SiO2 than bimetallic Pd-Fe/SiO2. A detailed characterization of the catalysts via XPS, XRD, and TEM indicated that a Pd-Fe alloy is formed on the SiO2 support but not on the γ-Al2O3 support. Theoretical density functional theory calculations suggest that on the Pd-Fe alloy binding of the furan ring to the surface is weakened compared to on pure Pd. This weakening disfavors the ring hydrogenation and decarbonylation paths, while the oxophilic nature of Fe atoms enhances the interaction of the CO and the OH groups with the metal surface, which favors the CO hydrogenation and CO bond cleavage paths. The presence of the solvent has a less pronounced effect, but clearly has a stronger inhibition on CC bond cleavage (decarbonylation to furan) than on CO bond cleavage (hydrogenolysis to methylfuran).

Catalytic conversion of cellulose into polyols using carbon-nanotube-supported monometallic Pd and bimetallic Pd–Fe catalysts

A series of carbon nanotube (CNT)-supported monometallic Pd and bimetallic Pd–Fe catalysts were synthesized and employed for catalytic hydrogenolysis of cellulose into polyols, including hexitol, ethylene glycol (EG), 1,2-propanediol (1,2-PG), and glycerol (Gly). The physicochemical properties of the catalysts were characterized by nitrogen physical adsorption measurements, X-ray diffraction analysis, transmission electron microscopy, and X-ray photoelectron spectroscopy. The total yield of hexitol, EG, 1,2-PG, and Gly in hydrolytic hydrogenation of cellulose was 37, 55, and 53% for Pd/CNTs, Pd–Fe/CNTs (Pd:Fe = 1:1), and Pd–Fe/CNTs (Pd:Fe = 1:2), respectively. Addition of Fe to Pd significantly modified the physicochemical properties of the nanoparticles and their catalytic performance, especially regarding hexitol selectivity. The promoting effect of Fe, especially for hexitol selectivity, compared with the monometallic catalyst is due to the fact that incorporation of Fe may stabilize Pd0 nanoparticles and lead to downshift of the d-band center of Pd metal nanoparticles by charge transfer from Fe to Pd. Recycling experimental results showed that leaching of Fe resulted in a significant decrease in the hexitol yield obtained using the Pd–Fe/CNTs after the first recycle, further demonstrating that Fe element plays a promoting role for hexitol formation.

Upgrading Lignocellulosic Biomasses: Hydrogenolysis of Platform Derived Molecules Promoted by Heterogeneous Pd-Fe Catalysts

This review provides an overview of heterogeneous bimetallic Pd-Fe catalysts in the C–C and C–O cleavage of platform molecules such as C2–C6 polyols, furfural, phenol derivatives and aromatic ethers that are all easily obtainable from renewable cellulose, hemicellulose and lignin (the major components of lignocellulosic biomasses). The interaction between palladium and iron affords bimetallic Pd-Fe sites (ensemble or alloy) that were found to be very active in several sustainable reactions including hydrogenolysis, catalytic transfer hydrogenolysis (CTH) and aqueous phase reforming (APR) that will be highlighted. This contribution concentrates also on the different synthetic strategies (incipient wetness impregnation, deposition-precipitaion, co-precipitaion) adopted for the preparation of heterogeneous Pd-Fe systems as well as on the main characterization techniques used (XRD, TEM, H2-TPR, XPS and EXAFS) in order to elucidate the key factors that influence the unique catalytic performances observed.

PdFe Nanoparticles for Oxygen Reduction Reaction in Polymer Electrolyte Fuel Cells

Carbon-supported PdFe nanoparticles (NPs) were prepared with composition-controlling via a modified chemical synthesis and a heat-treatment at high temperature under a reductive atmosphere. The synthesis combined the polyol reduction method and hydride reduction method, which was used to obtain monodispersed PdFe NPs. In addition, to induce structural modifications, the as-prepared PdFe NPs received heat-treatment under a reductive atmosphere. Results of structural characterizations including highresolution powder diffraction (HRPD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) analysis, indicated that heat-treated PdFe NPs exhibited a higher degree of alloying and surface Pd atomic composition compared with as-prepared ones. Furthermore, new crystalline phases were detected after heat-treatment. Thanks to the structural alterations, heat-treated PdFe NPs showed ~3 and ~18 times higher mass- and area-normalized oxygen reduction reaction (ORR) activities, respectively than commercial Pt/C. Single cell testing with heat-treated PdFe catalysts exhibited a ~2.5 times higher mass-normalized maximum power density than the reference cell. Surface structure analyses, including cyclic voltammetry (CV), COad oxidation, and XPS, revealed that, after heat-treatment, a downshift of the Pd d-band center occurred, which led to a decrease in the affinity of Pd for oxygen species, resulting in more favorable ORR kinetics.

Electro-oxidation of methanol catalysed by porous nanostructured Fe/Pd-Fe electrode in alkaline medium

Nanostructured Fe/Pd-Fe catalysts are prepared first by the deposition of Fe-Zn onto the Fe electrode surface, followed by replacement of the Zn by Pd at open circuit potential in a Pd-containing alkaline solution. The surface morphology and composition of coatings are determined by scanning electron microscopy and energy dispersive X-ray techniques. The results show that the Fe/Pd-Fe coatings are porous structure and the average particle size of Pd-Fe is low, in the range of 30–80 nm. The electrocatalytic activity and stability of Fe/Pd-Fe electrodes for oxidation of methanol are examined by cyclic voltammetry and chronoamperometry techniques. The new Fe/Pd-Fe catalyst has higher electrocatalytic activity and better stability for the electro-oxidation of methanol in an alkaline media than flat Pd and smooth Fe catalysts. The onset potential and peak potential on Fe/Pd-Fe catalysts are more negative than that on flat Pd and smooth Fe electrodes for methanol electro-oxidation. All results show that the nanostructured Fe/Pd-Fe electrode is a promising catalyst towards methanol oxidation in alkaline media for fuel cell applications.

Effect of post heat-treatment of composition-controlled PdFe nanoparticles for oxygen reduction reaction

Composition-controlled and carbon-supported PdFe nanoparticles (NPs) were prepared via a modified chemical synthesis after heat-treatment at high temperature under a reductive atmosphere. This novel synthesis, which combines the polyol reduction method and hydride method, was used to obtain monodispersed PdFe NPs. In addition, to induce structural modifications, the as-prepared PdFe NPs received heat-treatment under a reductive atmosphere. Structural characterization, including high-resolution powder diffraction (HRPD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) analysis, indicated that heat-treated PdFe NPs exhibited a higher degree of alloying and surface Pd atomic composition compared with as-prepared ones. Furthermore, new crystalline phases were detected after heat-treatment. Thanks to the structural alterations, heat-treated PdFe NPs showed ∼3 and ∼18 times higher mass- and area-normalized oxygen reduction reaction (ORR) activities, respectively than commercial Pt/C. Single cell testing with heat-treated PdFe catalysts exhibited a ∼2.5 times higher mass-normalized maximum power density than the reference cell. Surface structure analyses, including cyclic voltammetry (CV), COad oxidation, and XPS, revealed that, after heat-treatment, a downshift of the Pd d-band center occurred, which led to a decrease in the affinity of Pd for oxygen species, resulting in more favorable ORR kinetics.

Catalytic decomposition of phenethyl phenyl ether to aromatics over Pd–Fe bimetallic catalysts supported on ordered mesoporous carbon

A series of bimetallic Pd–Fe catalysts supported on ordered mesoporous carbon (denoted as Pd1–FeX/OMC) were prepared with a variation Fe/Pd molar ratio (X), and they were applied to the catalytic decomposition of phenethyl phenyl ether to aromatics. Phenethyl phenyl ether was used as a lignin model compound for representing β-O-4 linkage in lignin. The effect of Fe/Pd molar ratio on the catalytic activities and physicochemical properties of bimetallic Pd1–FeX/OMC catalysts was investigated. It was found that crystalline phase, reducibility, chemical state, and electronic property of Pd1–FeX/OMC catalysts were strongly influenced by Fe/Pd molar ratio. In particular, modified electronic property derived from the interaction between Pd and Fe significantly changed the hydrogen adsorption ability and bimetallic structure of the catalysts. Conversion of phenethyl phenyl ether continuously decreased with increasing Fe/Pd molar ratio, whereas selectivity for aromatics increased and then became almost constant with increasing Fe/Pd molar ratio. As a consequence, yield for aromatics showed a volcano-shaped trend with respect to Fe/Pd molar ratio. Catalytic performance of Pd1–FeX/OMC catalysts was closely related to the hydrogen adsorption ability and bimetallic structure of the catalysts. Among the catalysts tested, Pd1–Fe0.7/OMC catalyst with moderate hydrogen adsorption ability and with bimetallic structure of Pd1Fe0.7 composition showed the highest yield for aromatics. Thus, an optimal Fe/Pd molar ratio was required to achieve maximum production of aromatics through selective cleavage of CO bond in phenethyl phenyl ether over Pd1–FeX/OMC catalysts.

Selective cleavage of C[sbnd]O bond in benzyl phenyl ether to aromatics over Pd–Fe bimetallic catalyst supported on ordered mesoporous carbon

Bimetallic Pd–Fe catalyst supported on ordered mesoporous carbon (Pd–Fe/OMC) was prepared by a surfactant-templating method and a subsequent incipient wetness impregnation method. The catalyst was applied to the catalytic cleavage of CO bond in benzyl phenyl ether to aromatics. For comparison, monometallic Pd/OMC and Fe/OMC catalysts were also investigated. Benzyl phenyl ether was used as a lignin model compound for representing α-O-4 linkage in lignin. The combined effect of palladium and iron on the physicochemical properties and catalytic activities of Pd–Fe/OMC was investigated. Although Pd/OMC catalyst showed the highest conversion of benzyl phenyl ether, selectivity for aromatics was low due to saturation of aromatic ring. On the other hand, Fe/OMC catalyst showed lower conversion of benzyl phenyl ether than Pd/OMC, but Fe/OMC catalyst showed higher CO bond cleavage selectivity than Pd/OMC catalyst without saturation of aromatics. Bimetallic Pd–Fe/OMC catalyst showed the highest yield for aromatics. The introduction of Fe into Pd/OMC catalyst resulted in the modification of electronic properties of Pd by electron transfer from Fe to Pd, which led to the enhanced yield for aromatics.

Surface texture and physicochemical characterization of mesoporous carbon--wrapped Pd-Fe catalysts for low-temperature CO catalytic oxidation.

In this paper, mesoporous carbon (meso-C) with three-dimensional mesoporous channels was synthesized through a nanocasting route using three-dimensional mesoporous silica KIT-6 as the template. Mesoporous carbon wrapped Pd-Fe nanocomposite catalysts were synthesized by the co-precipitation method. The effects of the experimental conditions, such as pH value, Fe loading content and calcination temperature, on CO oxidation were studied in detail. The prepared Pd-Fe/meso-C catalysts showed excellent catalytic activity after optimizing the experimental conditions. The surface tetravalent Pd content, existing forms of Fe species, surface chemical adsorbed oxygen concentration, and pore channels of mesoporous carbon played vital roles in achieving the highest performance for the Pd-Fe/meso-C catalyst. The reaction pathway was conjectured according to the XPS analysis of the Pd-Fe/meso-C catalysts for CO oxidation, which maybe adhered to the Langmuir-Hinshelwood + redox mechanism. The effect of moisture on CO conversion was investigated, and the superior Pd-Fe/meso-C catalyst could maintain its activity beyond 12 h. This catalyst also showed excellent activity compared to the reported values in the existing literature.

Carbon Supported Pd-Fe Catalyst with Uniform Alloy Structure Prepared with Direct Thermo-decomposition Method for Oxygen Reduction Reaction

Carbon Supported Pd-Fe Catalyst with Uniform Alloy Structure Prepared with Direct Thermo-decomposition Method for Oxygen Reduction Reaction

Synergistic Catalysis between Pd and Fe in Gas Phase Hydrodeoxygenation of m-Cresol

In this work, a series of Pd/Fe2O3 catalysts were synthesized, characterized, and evaluated for the hydrodeoxygenation (HDO) of m-cresol. It was found that the addition of Pd remarkably promotes the catalytic activity of Fe while the product distributions resemble that of monometallic Fe catalyst, showing high selectivity toward the production of toluene (C–O cleavage without saturation of aromatic ring and C–C cleavage). Reduced catalysts featured with Pd patches on the top of reduced Fe nanoparticle surface, and the interaction between Pd and Fe, was further confirmed using X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and X-ray absorption near edge fine structure (XANES). A possible mechanism, including Pd assisted H2 dissociation and Pd facilitated stabilization of the metallic Fe surface as well as Pd enhanced product desorption, is proposed to be responsible for the high activity and HDO selectivity in Pd–Fe catalysts. The synergic catalysis derived from Pd–Fe interaction found in this work was proved to be applicable to other precious metal promoted Fe catalysts, providing a promising strategy for future design of highly active and selective HDO catalysts.

Pd–Fe/SiO2 and Pd–Fe/Al2O3 catalysts for selective hydrodechlorination of 2,4-dichlorophenol into phenol

The effect of iron introduction on the activity and selectivity of chemically precipitated supported palladium catalysts in the hydrodechlorination of 2,4-dichlorophenol in liquid phase at room temperature was studied. Bimetallic Pd–Fe catalysts supported on silica and alumina were characterized by using XPS, XRD, ToF-SIMS and TPR-H2 techniques. The dispersion of active phase in catalytic systems was examined by XRD and chemisorption of CO gas. Bimetallic Pd–Fe/SiO2 and Pd–Fe/Al2O3 catalysts containing 5wt.% of Pd and 1–20wt.% of Fe demonstrated high activity and high selectivity to phenol. However, Pd–Fe/Al2O3 catalysts with higher dispersion of the active phase were less active in the studied reaction than Pd–Fe/SiO2 systems, but selectivity to phenol was comparable for both types of bimetallic catalysts. The stability of Pd–Fe/SiO2 systems was higher than the bimetallic Pd–Fe/Al2O3 catalysts but selectivity to phenol decreases for that system systematically in each cycle of reaction, reaching only about 40% in the tenth cycle. It was also found that the addition of Fe to palladium catalysts limited the formation of cyclohexanone in the reaction medium.

Carbon-supported bimetallic Pd–Fe catalysts for vapor-phase hydrodeoxygenation of guaiacol

Carbon-supported metal catalysts (Cu/C, Fe/C, Pd/C, Pt/C, PdFe/C, and Ru/C) were characterized and evaluated for vapor-phase hydrodeoxygenation (HDO) of guaiacol (GUA), aiming at the identification/elucidation of active catalysts for high-yield production of completely hydrodeoxygenated products (e.g., benzene). Phenol was found to be the major intermediate on all catalysts. Saturation of the aromatic ring is the major pathway over the precious metal catalysts, forming cyclohexanone and cyclohexanol, followed by ring opening to form gaseous products. Base metal catalysts exhibit lower activity than the precious metal catalysts, but selectively form benzene along with small amounts of toluene, trimethylbenzene (TMB), and cresol without forming ring-saturated or ring-opening products. Compared with Fe/C and Pd/C, PdFe/C catalysts exhibit a substantially enhanced activity while maintaining the high selectivity to HDO products without ring saturation or ring opening. The enhanced activity of PdFe/C is attributed to the modification of Fe nanoparticles by Pd as evidenced by STEM, EDS, EXAFS, TPR, and theoretical calculations.

Effect of support and second metal in catalytic in-situ generation of hydrogen peroxide by Pd-supported catalysts: application in the removal of organic pollutants by means of the Fenton process

A catalytic system for the generation of H2O2 from formic acid and oxygen at ambient conditions has been developed. Pd-supported catalysts (Pd/C, Pd/TiO2 and Pd/Al2O3) have been tested, showing that for bulk purposes Pd/Al2O3 is more favourable while for in-situ applications Pd/TiO2 seems to be preferable. However, when these catalysts were tested in the in-situ H2O2 generation for the oxidation of phenol by means of the Fenton process (in the presence of ferrous ion), Pd/TiO2 did not demonstrate the expected results, whereas Pd/Al2O3 showed to be an efficient catalyst. Therefore, Pd/Al2O3 is offered as a good catalyst for Fenton's reactions with in-situ generated H2O2. In order to optimize the operating cost of the process, different initial concentrations of formic acid have been tested with Pd/Al2O3, and it has been seen that lowering the initial amount of formic acid favours the efficiency of the process. The effect of the addition of a second metallic (Pt, Au, Fe, Cu) active phase was studied. Concerning H2O2 generation, best results were obtained with a Pd-Au catalyst for bulk production (long time) while for in-situ application Pd-Fe showed interesting results. The Pd-Fe catalyst also performed similarly to the semi-heterogeneous Fenton system involving Pd/Al2O3 and ferrous ion in the degradation of phenol. Therefore, Pd-Fe catalyst offered an interesting prospect for making a full heterogeneous catalyst for Fenton reaction involving in-situ generation of H2O2.

Chlorophenol degradation using a one-pot reduction–oxidation process

Chlorophenol degradation was achieved using a combination of hydrodechlorination and heterogeneous Fenton-like oxidation. The process was conducted at ambient conditions (25±2°C, atmospheric pressure) as a one-pot reaction involving formic acid as H2 source for both hydrodechlorination of chlorophenols and H2O2 formation. An alumina-supported Pd–Fe catalyst was applied, which is able to decompose formic acid at the Pd sites, forming H2 and CO2, and additionally H2O2 in the presence of O2. At the same time, due to presence of iron sites on the catalyst, the H2O2 formed can be utilized for a Fenton-like oxidation reaction. Three different reaction protocols were tested, including: (i) consecutive reduction–oxidation with an initial oxygen-free phase adjusted by He purging (CRO–He), (ii) consecutive reduction–oxidation with initially oxygen-limited conditions (CRO) and (iii) simultaneous reduction–oxidation where O2 flowing was started at the beginning of the reaction (SRO). 2,4-Dichlorophenol (DCP) and pentachlorophenol (PCP) were selected as representatives for the group of chlorophenols. For DCP degradation, CRO–He and SRO showed similar efficiencies with respect to the mineralization degree (up to 70%), whereas SRO achieved a better detoxification as observed in bioluminescence tests. The CRO–He reaction over the catalyst used showed only a small decrease in its activity during the oxidation stage, with no further change after the catalyst had been recovered twice. For PCP degradation, a self-inhibition effect was observed for the SRO process, indicating that PCP is hardly degradable by catalytic oxidation. In this case, the CRO–He process, which was facilitated by initial transformation of PCP into phenol and its subsequent oxidation, clearly produced a cleaner medium. This was also confirmed by the results of the toxicity measurements. The catalyst indicated a promising stability based upon the Pd and Fe leaching results measured at the end of each run.

Effect of Fe state on electrocatalytic activity of Pd–Fe/C catalyst for oxygen reduction

The carbon-supported Pd–Fe catalyst (Pd–Fe/C) is prepared in the H 2O/tetrahydrofuran (THF) mixture solvent under the low temperature. The homemade Pd–Fe/C catalyst contains two forms of iron species, alloying and non-alloying Fe. The alloying Fe species is hardly dissolved in 0.5 M H 2SO 4 solution, while the non-alloying Fe species is easily dissolved in 0.5 M H 2SO 4 solution. The electrochemical measurements show the electrocatalytic activity of the Pd–Fe/C catalyst with the acid treatment for the oxygen reduction is higher than that of the Pd–Fe/C catalyst without the acid treatment, illustrating that the non-alloying Fe species suppresses the electrocatalytic activity of the Pd–Fe/C catalyst. In contrast, the alloying Fe species promotes the electrocatalytic activity of the Pd–Fe/C catalyst for the oxygen reduction, which is likely attributed to the change of the electron structure of Pd atom and/or bond length of Pd–Pd in the Pd–Fe/C catalyst.

Simultaneous in situ generation of hydrogen peroxide and Fenton reaction over Pd–Fe catalysts

High mineralization degree of organic compounds can be achieved by a novel environmentally-friendly full heterogeneous Pd-Fe catalytic system, which involves in situ generation of hydrogen peroxide from formic acid and oxygen, and oxidation of organic compounds by Fenton process in a one-pot reaction.

Pt-Decorated PdFe Nanoparticles as Methanol-Tolerant Oxygen Reduction Electrocatalyst

The activity and selectivity of carbon-supported Pt-decorated PdFe nanoparticles in the oxygen reduction reaction (ORR) were investigated in the presence and absence of methanol. The Pt-decorated PdFe nanoparticles, which consist of a PdPt surface and a PdFe interior, were prepared by the galvanic reaction between PdFe/C alloy nanoparticles and PtCl4(2-) in aqueous solution. The presence of a Pt-enriched surface after the replacement reaction was independently confirmed by several microstructural characterization techniques and cyclic voltammetry. The catalyst with such heterogeneous architecture is catalytically more active than a bulk PdFePt alloy catalyst with the same overall composition. The observed enhancements in catalyst performance can be attributed to the lattice strain effect between the shell and core components. The Pt-decorated PdFe (PdFe@PdPt/C) catalyst also compares favorably with a commercial Pt/C catalyst with four times as much Pt in terms of ORR activity, cost, and methanol tolerance.

Studies on alumina supported Pd–Fe bimetallic catalysts prepared by deposition–precipitation method for hydrodechlorination of chlorobenzene

The gas phase catalytic hydrodechlorination (HDC) of chlorobenzene was investigated over alumina supported Pd–Fe bimetallic catalysts. A series of Pd–Fe/Al 2O 3 catalysts with various Fe loadings were prepared by deposition–precipitation (DP) method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR), temperature programmed desorption of H 2 (TPD) and pulse CO chemisorption. XPS and TPR analyses suggested the formation of Pd n+ species when the catalysts were prepared by DP method. The TPR results also revealed that, the addition of small amounts of Fe as second metal to Pd/Al 2O 3 preferentially stabilized the lower oxidation state of Pd. The addition of Fe to Pd/Al 2O 3 improves the stability of the catalyst during the hydrodechlorination of chlorobenzene as compared to monometallic Pd catalyst. The high activity and stability of bimetallic Pd–Fe catalysts can be attributed to the formation of active Pd n+ species at the interfaces of Pd–O–Fe.

Oxygen kinetics and mechanism at electrocatalysts on the base of palladium–iron system

Binary nanodispersed carbon XC72 supported PdFe catalysts with different atomic palladium-to-iron ratios are synthesized and studied in oxygen reduction reaction in acid solution at 60 °C. The Pd:Fe ratio was well controlled by the initial concentrations of Pd and Fe in the precursor solutions. The nanoparticles were characterized by transmission electron microscopy, X-ray diffractometry and X-ray photoelectron spectroscopy. The optimum Pd:Fe ratio for this reaction was determined to be 3:1. The comparison of activities of the catalysts with component ratios equaled 3:1 and 10:1 is shown that the activities are differed from each other by 10–15 times in advantage of catalyst with lesser content of palladium. This phenomenon can be related to the different particle size of both catalysts and different distribution of particles by size discovered by TEM method. The achievement of maximum activity near the ratio of Pd:Fe = 3:1 is due to as effect of alloy-forming and the influence of binary system component ratio and synthesis conditions on dispersity degree of metallic phase nanoparticles. Under optimal conditions of precursor mixture high-temperature pyrolysis, iron produces the stabilizing effect palladium. It gives rise to obtaining the uniform and finely divided (7–8 nm) metallic particles.