Pd Fe Bimetallic Catalysts Research Articles

Improved Glycerol Electrooxidation at Carbon-Supported PdFe Bimetallic Catalysts

We have investigated glycerol electrooxidation at Pd/C and PdFe/C catalysts, synthesized by the microwave polyol decomposition method. Five different heating ramps were tested to provide active catalyst nanoparticles and desired metal loadings at 20 wt%. Introducing iron in the Pd/C catalyst composition improved the catalytic activity and stability of the anode. The PdFe/C catalysts presented greater oxidative capacity and contributed efficiently to the keeping of glycerol skeleton reaction products. The analytical techniques composed of liquid chromatography coupled with mass spectrometry (LC-MS) confirmed glycerate, glycolate, formate, tartronate, and oxalate as the main glycerol oxidation products. The bi-metallic catalysts (PdFe/C) harvested electrons from glycerol and produced energy more effectively than the catalyst without iron (Pd/C). Glycerol proved a potential platform for generating high value-added products and can be employed as a renewable clean energy source for electrosynthesis purposes and fuel cell applications.

Green Chemistry for the Transformation of Chlorinated Wastes: Catalytic Hydrodechlorination on Pd-Ni and Pd-Fe Bimetallic Catalysts Supported on SiO2

Monometallic catalysts based on Fe, Ni and Pd, as well as bimetallic catalysts based on Fe-Pd and based on Ni-Pd supported on silica, were synthesized using a sol-gel cogelation process. These catalysts were tested in chlorobenzene hydrodechlorination at low conversion to consider a differential reactor. In all samples, the cogelation method allowed very small metallic nanoparticles of 2-3 nm to be dispersed inside the silica matrix. Nevertheless, the presence of some large particles of pure Pd was noted. The catalysts had specific surface areas between 100 and 400 m2/g. In view of the catalytic results obtained, the Pd-Ni catalysts are less active than the monometallic Pd catalyst (<6% of conversion) except for catalysts with a low proportion of Ni (9% of conversion) and for reaction temperatures above 240 °C. In this series of catalysts, increasing the Ni content increases the activity but leads to an amplification of the catalyst deactivation phenomenon compared to Pd alone. On the other hand, Pd-Fe catalysts are more active with a double conversion value compared to a Pd monometallic catalyst (13% vs. 6%). The difference in the results obtained for each of the catalysts in the Pd-Fe series could be explained by the greater presence of the Fe-Pd alloy in the catalyst. Fe would have a cooperative effect when associated with Pd. Although Fe is inactive alone for chlorobenzene hydrodechlorination, when Fe is coupled to another metal from the group VIIIb, such as Pd, it allows the phenomenon of Pd poisoning by HCl to be reduced.

Enhancement of anodic oxidation of formic acid on Pd–Fe bimetallic nanoparticles by thermal treatment

The surface composition and catalytic properties of Pd–Fe bimetallic catalysts with identical bulk composition can be continuously tuned by treatment at different temperatures. The activity of these catalysts in formic acid oxidation was related to the treatment temperature. The thermal treatment temperatures ranged from 400 to 600 °C. The Pd–Fe nanoparticles are characterized by an array of analytical techniques including TEM (transmission electron microscopy), XRD (X-ray diffraction), ICP (inductively coupled plasma) and HS-LEIS (low energy ion scattering spectroscopy). The electrocatalytic activity is examined using cyclic voltammetric and chronoamperometric measurements. The Pd–Fe/C catalyst with 500 °C shows the highest electrocatalytic activity for formic acid oxidation, with a current activity 3 times higher than that of before treated Pd–Fe/C catalyst, 5.6 times higher than that of commercial Pt/C catalyst. The migration of Pd to the surface on the nanoparticle catalysts as well as the electrochemical active surface area of the PdFe–H catalysts was shown to play a major role in enhancing the electrocatalytic activity for catalyst. These findings provided important insights into the correlation between the electrocatalytic activity and the treatment temperature of the nanoengineered bimetallic catalysts.

Ambient base-free glycerol oxidation over bimetallic PdFe/SiO2 by in situ generated active oxygen species

Low temperature oxidation of alcohols over heterogeneous catalysts is exceptionally challenging, particularly under neutral conditions. Herein, we report on an efficient, base-free method to oxidise glycerol over a 0.5%Pd-0.5%Fe/SiO2 catalyst at ambient temperature in the presence of gaseous H2 and O2. The exceptional catalytic performance was attributed to the in situ formation of highly reactive surface-bound oxygenated species, which promote the dehydrogenation on the alcohol. The PdFe bimetallic catalyst was determined to be significantly more active than corresponding monometallic analogues, highlighting the important role both metals have in this oxidative transformation. Fe leaching was confirmed to occur over the course of the reaction but sequestering experiments, involving the addition of bare carbon to the reactions, confirmed that the reaction was predominantly heterogeneous in nature. Investigations with electron paramagnetic resonance spectroscopy suggested that the reactivity in the early stages was mediated by surface-bound reactive oxygen species; no homogeneous radical species were observed in solution. This theory was further evidenced by a direct H2O2 synthesis study, which confirmed that the presence of Fe in the bimetallic catalyst neither improved the synthesis of H2O2 nor promoted its decomposition over the PdFe/SiO2 catalyst.

Hydrodeoxygenation of Lignin-Derived Aromatic Oxygenates Over Pd-Fe Bimetallic Catalyst: A Mechanistic Study of Direct C–O Bond Cleavage and Direct Ring Hydrogenation

Hydrodeoxygenation of lignin-derived phenols could be achieved generally with three reaction pathways: tautomerization, direct ring hydrogenation and direct C–O bond cleavage. The former pathway has been extensively studied over Pd/Fe catalyst in liquid-phase reaction, however, the contribution of the latter two is yet subject to further investigations. In this report, a comparative study of direct C–O bond cleavage and direct ring hydrogenation reaction pathways is presented on Pd/Fe, Fe and Pd/C catalysts using diphenyl ether as modelling compound. Despite its much higher activation energy than direct ring hydrogenation, direct C–O bond cleavage is dominant over Pd/Fe with much higher rates than the monometallic analogues due to the synergic catalysis of Pd–Fe. Based on this study and our previous results, the detailed reaction network for HDO of diphenyl ether is proposed.

Enhancements in catalytic activity and duration of PdFe bimetallic catalysts and their use in direct formic acid fuel cells

The palladium–iron based bimetallic catalysts (PdxFey/Cs) and facile synthetic method are introduced to enhance the catalytic activity and operational duration for direct formic acid fuel cells. To improve the properties of PdxFey/C catalysts, such as degree of PdFe alloy and its crystallinity, heat treatment is conducted at 600°C. According to results, the Pd–Fe bond and Fe metal particle are formed after the heat treatment, while iron oxides and Pd particles are observed in the untreated samples. Electrochemical evaluations for measuring the formic acid oxidation reaction rate demonstrates heat treated Pd3Fe1/C (HT-Pd3Fe1/C) is the best catalysts of six samples which are synthesized by using different Pd to Fe ratios (3:1, 1:1, 1:3) before and after heat treatment. This is because the HT-Pd3Fe1/C has high Pd–Fe alloying and Pd contents. Through the heat treatment, the indirect formic acid oxidation reaction way is activated and the resistance to CO poisoning is significantly improved. The maximum power density of direct formic acid fuel cells using HT-Pd3Fe1/C whose open circuit voltage is 0.83V is 137mWcm−2, which is 1.6 and 1.9 times higher than that of direct formic acid fuel cells using untreated catalyst and Pd/C.

High activity Pd-Fe bimetallic catalysts for aqueous phase hydrogenations

Palladium-iron bimetallic catalysts were synthesized using carbon-coated silica supports that provided high hydrogenation activity relative to monometallic palladium under condensed-phase hydrothermal conditions. The catalysts were applied to the hydrogenation of carbonyl groups in acetone, 2-pentanone, and propionaldehyde. While Fe incorporation independent of Pd-to-Fe ratio gave enhanced activity, the catalysts having more Fe than Pd gave more than a three-fold increase in hydrogenation activity relative to the Pd only counterpart. The activity enhancement appeared to be related to the influence of Fe on the Pd as Fe under the condensed-phase reaction conditions was inert. The catalysts were also tested for hydrogenation of unsaturated carbon-carbon double bond and aromatic rings in which more moderate activity enhancement was observed. Through evaluating the influence of Pd-to-Fe ratio on catalyst properties and catalytic performance for the range of molecules, it is proposed that the turnover frequency enhancement can be attributed to the formation of Pdδ− via Pd-Fe interaction.

Combining HDC and CWPO for the removal of p-chloro-m-cresol from water under ambient-like conditions

Catalysts supported on aluminium pillared clays (Al-PILCs) using Fe and Pd or Rh as active phases have been prepared and tested for a two-step treatment of p-chloro-m-cresol (PCMC) in water by catalytic hydrodechlorination (HDC) followed by catalytic wet peroxide oxidation (CWPO) under ambient-like conditions (25°C, 1atm). Both processes were first studied independently. HDC was investigated with Pd and Rh monometallic catalysts as well as Pd-Fe and Rh-Fe bimetallic ones. The bimetallic Pd-Fe catalyst showed the best performance, allowing complete dechlorination in less than 1h reaction time. On the other hand, CWPO of PCMC with a monometallic Fe catalyst allowed complete conversion of that pollutant but with only about 33% reduction of total organic carbon (TOC) after 4h. Then, a two-step approach consisting in HDC of PCMC followed by CWPO has been tested for the first time in two different ways. The first one used a Pd-Fe bimetallic catalyst in both steps while in the second approach monometallic Pd and Fe catalysts were used for HDC and CWPO, respectively. The HDC in alkaline medium allowed reducing significantly Fe leaching. This second approach yielded complete dechlorination followed by higher mineralization (>55%) with better efficiency of H2O2 consumption.

Gas phase hydrodechlorination of CCl4 over Pd–Cu and Pd–Fe bimetallic catalysts supported on an AlF3 matrix

Two bimetallic catalytic systems composed of Pd–Cu and Pd–Fe supported over AlF3 were prepared by the sol–gel method and characterised by BET, X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (P-XRD). Analysis of the XPS and P-XRD data showed that the surface of these bimetallic catalysts may be described as Pd0–CuI and Pd0–FeIII hydroxides. The gas phase hydrodechlorination reaction (HDC) of CCl4 over these bimetallic catalysts showed that the presence of CuOH and Fe(OH)3 altered their catalytic activity, selectivity and product distribution compared to their monometallic Pd/AlF3 analogue. The bimetallic catalysts showed a very high selectivity for the formation of C1-products (CHCl3, CH2Cl2 and CH3Cl) in contrast with the tendency shown by the monometallic Pd/AlF3 analogue of forming coupled C2–C5 products. Interestingly, the pore-controlled version of the Pd–Fe*/AlF3 catalyst showed a greater efficiency favouring the formation of CHCl3 and CH2Cl2 compared with its Pd–Fe/AlF3 analogue which predominantly favoured the formation of CH3Cl. The effect of temperature, in the range of 458–513 K, and time on stream on the catalytic performance of the bimetallic catalysts in terms of percentage conversion, reaction rate and product distribution are discussed.

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.

Phenol Deoxygenation Mechanisms on Fe(110) and Pd(111)

The catalytic deoxygenation of phenolic compounds has become a major area of interest in recent years because they are produced during the pyrolysis of lignin and are present in biofuels. Our previous work showed that a PdFe bimetallic catalyst was catalytically active for the deoxygenation of phenolics. To better understand and control the catalytic deoxygenation reaction of phenolics, the detailed surface reaction mechanisms are needed for phenol, a key intermediate in phenolic deoxygeantion. Here, we have examined five distinct reaction mechanisms for the deoxygenation of phenol on the Fe(110) and Pd(111) surfaces so as to identify the most likely deoxygenation mechanism on these surfaces. Our results show that the elementary phenol deoxygenation reaction step for each mechanism was highly endothermic on Pd(111), whereas the same mechanisms are exothermic on Fe(110). On the basis of the reaction energy studies, detailed mechanistic studies were performed on the Fe(110) surface, and it was found that the most energetically and kinetically favorable reaction mechanism occurs via the direct cleavage of the C–O bond.

Carbon-supported Pd–Fe electrocatalysts for oxygen reduction reaction (ORR) and their methanol tolerance

Carbon-supported palladium-iron bimetallic electrocatalysts of different Pd to Fe ratios (1:1, 2:1, 3:1) were prepared by a low temperature single step co-reduction method in alkaline media without any stabilizing agents. The physical characterizations of catalysts were done using XRD and TEM. The electrochemical characterizations were done using underpotential deposition (upd) of hydrogen and copper. Electrocatalytic activities for oxygen reduction reaction (ORR) were investigated and compared to that of standard Pt/C catalyst. The carbon-supported Pd–Fe bimetallic catalysts showed higher surface area than that of pure Pd/C. The half-wave potential of ORR on as-prepared palladium-iron bimetallic catalysts was shifted positively by ∼75–100mV from that of Pd/C in oxygen saturated 0.1M HClO4 solution. The highest catalytic activity was obtained with Pd3Fe/C catalyst and it was close to that of standard Pt/C. XRD analysis did not show any noticeable shift in peak position due to alloying. In presence of methanol, carbon-supported Pd and Pd–Fe bimetallic catalysts showed superior ORR selectivity and activity unlike Pt/C. The peroxide generation on Pd3Fe/C – the best of Pd based electrocatalyst – was comparable to that on Pt/C. These catalysts, prepared at low temperature and without any further heat-treatment, gave activities that were free from effects of crystallite size, segregation, and enrichment of precious metal content that might happen at high temperature.

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.

Structure and activity of microwave irradiated silica supported Pd–Fe bimetallic catalysts in the hydrodechlorination of chlorobenzene

A series of silica supported Pd–Fe bimetallic catalysts were prepared by conventional as well as microwave heating methods. The catalysts were characterised by nitrogen adsorption (for BET surface area), X-ray diffraction (XRD), temperature-programmed reduction (TPR) and hydrogen chemisorption for their physico-chemical properties and were evaluated for chlorobenzene (CB) hydrodechlorination (HDC) activity. The catalysts prepared with microwave irradiation resulted into higher hydrodechlorination activity compared to their conventionally prepared analogues. These results are explained in terms of differences in the Pd morphology observed during the microwave irradiation.

Preparation of supported bimetallic catalysts by means of selective deposition using mobile metal compounds as precursors

The preparation of supported bimetallic catalysts was examined by selective deposition of metal complex precursors on the surface of the first metal particles. A PtRu/SiO 2 catalyst was prepared using Pt/SiO 2 and ruthenocene as starting materials. Analysis of the surface structure by means of O 2CO titration suggested that Ru metals covered the surface Pt atoms without forming separate Ru particles. This technique was applied for the preparation of an egg-shell type of the PdFe bimetallic catalyst supported on alumina, using ferrocene as a precursor of iron. PtSn bimetallic catalysts were prepared by selective deposition of tetramethyl tin on Pt particles. Liquid-phase deposition was tried in the case of PdAg and PdAu catalysts supported on alumina. Selective deposition of Ag and Au on Pd surface was observed, and the selectivity to 1-butene was increased in the partial hydrogenation of 1,3-butadiene.

Heteronuclear CO activation in CO based reactions catalyzed by SiO 2-supported RhFe and PdFe bimetallic clusters

RhFe and PdFe bimetallic catalysts were prepared from carbonyl clusters such as [Fe 2Rh 4(CO) 16] 2− and [Fe 6Pd 6(CO) 24] 3− grafted on SiO 2. They exhibited high activities and selectivities for C 1+C 2 alcohol formation from CO+H 2. The RhFe catalysts also provided high activities for alcohol formation in hydroformylation of ethene and propene. On the H 2-reduced catalyst, Mőssbauer and EXAFS studies suggest that RhFe and PdFe bimetallic sites are dispersed on the SiO 2 surface, with direct MFe 3+O (M = Pd) bondings. In IR spectrum of chemisorbed CO on the Fe 2Rh 4/SiO 2, a band appeared which is reasonably assigned to μ2:η 2CO coordinating to the RhFe 3+ site. Promoting effect of Fe is discussed in terms of the two-site activation of CO insertion on bimetallic RhFe 3+ and PdFe 3+ sites derived from RhFe and PdFe carbonyl clusters.

A Mössbauer study on remarkable changes in chemical states of iron in silica-supported Pd-Fe bimetallic catalysts by varying Fe contents

Fe-57 Mossbauer spectra of silica-supported Pd−Fe bimetallic catalysts show remarkable changes with varying Fe/Pd atomic ratios. From the spectra, the main Fe-component is estimated as highly dispersed Fe in the Fe/Pd range of 0.05–0.3 and α-Fe ensemble and Fe−Pd intermetallics in the Fe/Pd range above 0.3. It is suggested that the chemical state of iron is associated with the catalytic performance in effective CO−H2 conversion to methanol.