Carbon-supported Pd Catalysts Research Articles

Vapor-phase hydrodeoxygenation of guaiacol over carbon-supported Pd, Re and PdRe catalysts

Vapor-phase hydrodeoxygenation (HDO) of guaiacol was investigated over a commercial Pd/C (A) catalyst (Evonik) and Pd/C (B), Re/C and PdRe/C catalysts prepared by incipient wetness impregnation of Norit SX-1 G activated carbon. The Pd/C catalysts had equivalent dispersions after reduction at 300 °C; however, Pd/C (B) had very low dispersion after reduction at 400 °C. CO chemisorption, Re LIII edge extended x-ray absorption fine structure (EXAFS) spectroscopy, and high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM) of the Re/C catalyst after reduction at 400 °C evidenced the formation of supported Re clusters. EXAFS spectroscopy of the PdRe/C catalyst after in situ reduction at 300 °C indicated the presence of Pd nanoparticles and Re clusters; a 2.70 Å Pd-Re contribution was required to adequately fit the Re LIII EXAFS spectrum. HAADF-STEM with energy-dispersive x-ray (EDX) analysis of the PdRe/C catalyst after reduction at 400 °C revealed Re clusters and Pd nanoparticles, some in intimate contact. In guaiacol HDO at 300 °C and 1 atm, Pd/C (A) was selective to phenol and cyclohexan-one/-ol and did not produce significant yields of benzene and cyclohexane, despite its high activity. Turnover frequencies for phenol (and cyclohexan-one/-ol) formation over the Pd/C catalysts were equivalent. Phenol, benzene and anisole were major products over Re/C after in situ reduction at 400 °C. The highest yield (52%) of fully deoxygenated products was obtained over PdRe/C after in situ reduction at 400 °C. We infer that the bimetallic catalyst combines synergistically the demethoxylation and hydrogenation functions of Pd/C with the capability of Re/C to deoxygenate phenol [Ghampson, et al., Catal. Sci. Technol. 2016].

A highly active and stable Pd/B-doped carbon catalyst for the hydrogenation of 4-carboxybenzaldehyde

Abstract Boron had been introduced into the structure of carbon material (BC), which was used as the support of Pd catalyst for hydrogenation of 4-carboxybenzaldehyde (4-CBA). The physical properties and chemical composition of the support and corresponding catalyst were characterized by N2 adsorption–desorption, Raman spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), element analysis (EA), high-resolution transmission electron microscopy (HRTEM), CO-pulse chemisorption and X-ray photoelectron spectroscopy (XPS). The results demonstrate that Pd/BC catalyst exhibits a superior activity and good stability due to the more uniform dispersion of Pd nanoparticles, the presence of mesoporous structure and the enhanced interaction between Pd nanoparticles and the support, compared to carbon and N-doped carbon supported Pd catalysts (Pd/C and Pd/NC, respectively).

High activity heterogeneous catalysts by plasma-enhanced chemical vapor deposition of volatile palladium complexes on biomorphic carbon

Six new palladium complexes based on allyl and alkenolate ligands were synthesized and structurally characterized. Combination of delocalized allylic sp 2 -hybridized carbon centers and a strongly binding NˆO chelating unit (e.g., 3,3,3-trifluoro(pyridin-2-yl)propen-2-ol) offered a promising combination of high volatility and thermal lability not commonly observed in noble metal precursors. Application of the new Pd compounds in thermal metal–organic and plasma-enhanced chemical vapor deposition demonstrated their clean and efficient decomposition pathways, which in conjunction with their intriguing air stability made them efficient precursors for Pd films and clusters. Plasma-enhanced chemical vapor deposition of the palladium compounds on biomorphic carbon used as a porous substrate with high surface area and interconnected channels delivered recyclable carbon-supported Pd catalysts (Pd@BioC), which showed excellent selectivity, stability, and recyclability in C C coupling reactions.

Study on electrochemical properties of Pd-C and Pd-CNT catalysts

ABSTRACTThe catalytic and electrochemical properties of carbon-supported Pd catalysts (Pd-C, Pd-CNT), prepared by the technique of deposition reduction, are presented in this paper. Single-walled and multiwalled (nitrogen doped, carboxylated, noncarboxylated) carbon nanotubes with different specific surface areas as well as activated carbon (NORIT®) were used. Prepared catalysts were evaluated using cyclic voltammetry. Voltammetric characterization of the catalysts evaluated on the basis of nitrobenzene reduction reaction reveals increasing reactivity of catalysts with increasing Pd concentration from 1 up to 5% Pd and decreasing reactivity from 5 to 10% Pd. Influence of support properties on the reactivity of catalyst was also observed. Prepared catalysts were compared with four commercially produced catalysts.

N-doped carbon supported Pd catalysts for N-formylation of amines with CO2/H2

Using mesoporous N -doped carbons (NCs) derived from glucose and melamine as the supports, a series of Pd/NC catalysts were prepared, in which Pd nanoparticles with average size 2.0 nm were uniformly distributed on the supports. It was indicated that the resultant Pd/NC catalysts were effective for N -formylation of amines with CO2 and H2 in ethanol without any additives. Especially, the catalyst Pd/NC-800-6.9% containing quaternary N showed the best performance, affording a series of formylamides in good or even excellent yields. Further investigation reveals that the interaction between the Pd nanoparticles and quaternary nitrogen in the NC support was responsible for the good performance of the catalyst.

Low-Temperature CO Oxidation: Effect of the Second Metal on Activated Carbon Supported Pd Catalysts

Activated carbon (AC) supported monometallic Pd and bimetallic Pd-M (M = Co, Ni, and Cu) catalysts were prepared by impregnation-reduction method and investigated for carbon monoxide (CO) oxidation. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed highly disperse Pd-M nanoparticles (~ 3–5 nm) on the AC support. The addition of the second transition metal in Pd/AC resulted in an increase in the specific surface area and smaller average particle size. CO oxidation experiments were carried out in a vertical fixed-bed quartz reactor at gas hourly space velocity (GHSV) of 30,000 h− 1 under atmospheric pressure. The catalytic order is as follows: Pd–Cu/AC > Pd–Ni/AC > Pd–Co/AC > Pd/AC. The T50 (50% CO conversion) value of Pd–Cu/AC and Pd/AC catalysts are 30 and 70 °C. BET, XRD and TEM analysis of the used Pd-M/AC and Pd/AC catalysts were performed in order to find any change in the specific surface area, structure, morphology, and average particle size of the catalysts after CO oxidation. The results showed that the bimetallic Pd-M/AC catalysts had better catalytic activity and stability than the monometallic Pd/AC catalyst. Pd–Cu/AC showed excellent time-on-stream stability of 50 h. The apparent activation energy of the Pd–Cu/AC is found to be 69.32 kJ mol− 1. Thus, bimetallic Pd-M/AC catalysts have a potential for practical CO oxidation reaction.

氮磷双掺杂碳负载钯催化剂的制备及其对甲酸电催化氧化性能

氮磷双掺杂碳负载钯催化剂的制备及其对甲酸电催化氧化性能

Selective hydrogenation of quinolines into 1,2,3,4-tetrahydroquinolines over a nitrogen-doped carbon-supported Pd catalyst

In this study, we have prepared a nitrogen-doped carbon supported Pd catalyst with abundant porous structures (abbreviated as Pd/CN) for the hydrogenation of quinolines.

Catalysis for Low-Temperature Fuel Cells

Today, the development of active and stable catalysts still represents a challenge to be overcome in the research field of low-temperature fuel cells.[...]

Catalytic Hydrodeoxygenation of Guaiacol over Palladium Catalyst on Different Titania Supports

Pd catalysts supported on TiO2 with different crystalline phases were prepared with formaldehyde as reducing agent and examined for hydrodeoxygenation (HDO) of guaiacol. Their properties were characterized by N2 adsorption, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Compared to the carbon-supported Pd catalysts, TiO2-supported Pd catalysts exhibited higher C–O bond scission ability, which may be attributed to the presence of partially reduced titanium species originating from the reduction of Ti4+ by spillover hydrogen from Pd at 200 °C on the surface of TiO2. Guaiacol was hydrogenated on Pd sites to give 2-methoxycyclohexanol, which diffused to partially reduced titanium species and subsequently reacted with hydrogen from Pd to generate cyclohexane. Anatase TiO2-supported Pd catalyst gave the highest HDO activity of guaiacol among the Pd catalysts supported on three types of TiO2 (anatase, rutile, and their mix, P25), suggesting that more partially reduced ...

Carbon-supported Pd-Ag catalysts with silica-coating layers as active and durable cathode catalysts for polymer electrolyte fuel cells

Carbon-supported Pd catalysts (Pd/CBs) for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs) were modified with transition metals to enhance their catalytic activity. Pd-M/CB(N) (M = Co, Cu, Y, and Ag) was prepared by the reduction of metal precursors with NaBH4 in the presence of ethylene glycol (EG) without heat treatment. Pd-Ag/CB(N) showed the highest catalytic activity for the ORR among all the Pd-based catalysts tested in the present study, and it had twice higher activity than Pd/CB. The Pd-Ag/CB(N) also had the higher ORR activity than the Pd-Ag/CB prepared by a conventional impregnation method (Pd-Ag/CB(I)) due to the formation of smaller Pd-Ag alloy particles with 1–2 nm diameters. Pd-Ag/CB(N) was covered with silica layers (SiO2/Pd-Ag/CB(N)) in order to improve their durability under severe cathode conditions. The SiO2/Pd-Ag/CB(N) had high catalytic activity for the ORR during the durability test because silica layers prevented the diffusion of metal species from the catalysts.

Carbon-Supported Pd and PdFe Alloy Catalysts for Direct Methanol Fuel Cell Cathodes.

Direct methanol fuel cells (DMFCs) are electrochemical devices that efficiently produce electricity and are characterized by a large flexibility for portable applications and high energy density. Methanol crossover is one of the main obstacles for DMFC commercialization, forcing the search for highly electro-active and methanol tolerant cathodes. In the present work, carbon-supported Pd and PdFe catalysts were synthesized using a sodium borohydride reduction method and physico-chemically characterized using transmission electron microscopy (TEM) and X-ray techniques such as photoelectron spectroscopy (XPS), diffraction (XRD) and energy dispersive spectroscopy (EDX). The catalysts were investigated as DMFC cathodes operating at different methanol concentrations (up to 10 M) and temperatures (60 °C and 90 °C). The cell based on PdFe/C cathode presented the best performance, achieving a maximum power density of 37.5 mW·cm−2 at 90 °C with 10 M methanol, higher than supported Pd and Pt commercial catalysts, demonstrating that Fe addition yields structural changes to Pd crystal lattice that reduce the crossover effects in DMFC operation.

Deoxygenation of Fatty Acid Over Three-Dimensionally Ordered Mesoporous Carbon Supported Palladium Catalysts

Two ordered mesoporous carbons (OMCs) possessing three-dimensionally (3-D) well-ordered mesoporosity with different framework configurations were prepared via a hard template route. The OMCs were treated with different surface-oxidation methods for the preparation of OMC supported highly dispersed Pd catalysts (Pd/OMC). Among the different surface oxidation conditions, the 3-D ordered mesoporous structure of CMK-9 is preserved under a mild surface-oxidation condition by an ammonium persulfate solution at 30 °C for 2 h. The Pd/OMCs were introduced as catalysts for the catalytic deoxygenation of a fatty acid without hydrogen or different amounts of hydrogen. The catalytic performance of the deoxygenation of a fatty acid (stearic acid) was investigated in a batch reactor without hydrogen and a continuous fixed-bed reactor with different amounts of hydrogen (H2/stearic acid = 0–3 molar ratios). The Pd/OMC catalysts were found to be less prone to deactivation than a commercially available activated carbon supported Pd catalyst (Pd/AC). This was attributed to the well-ordered 3-D mesoporosity in the OMC supports, which facilitated the facile diffusion of the liquid reactant and product with a long carbon chain length in the catalyst during the deoxygenation reaction, leading to less Pd metal sintering during the deoxygenation reaction as compared to that with Pd/AC catalyst.

Carbon-supported Pd and Pd-Co cathode catalysts for direct methanol fuel cells (DMFCs) operating with high methanol concentration

Carbon-supported 30% Pd-based catalysts such as Pd/C, Pd4Co1/C and Pd10Co1/C were prepared by the sulphite complex route and physico-chemically characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS). The electrochemical investigation was carried out in half cell and direct methanol fuel cell (DMFC) to evaluate the performance, the tolerance to permeated methanol and the durability of the Pd-based electrocatalysts. For comparison, a commercial 30% Pt/C catalyst was also electrochemically investigated. The advantage of using a high methanol concentration in DMFCs is related to a high energy density. Unfortunately, methanol crossover causes a mixed potential at Pt cathode catalysts reducing the overall cell efficiency, which is exacerbated with high methanol concentration (10M) at the anode side. Pd and Pd-Co alloys based electrocatalysts exhibited high methanol tolerance properties, as evidenced in the half cell characterization, which led also to high performances in single cell configuration (DMFC). Thus, Pd-based electrodes represent a reliable way to minimize the cost in low temperature fuel cells, providing a higher performance than that of Pt-based electrodes at high methanol concentration. Moreover, the durability tests highlighted that including a small amount of cobalt in the crystalline structure of Pd resulted in better durability in terms of resistance to corrosion phenomena.

Monometallic Palladium for Oxygen Reduction in PEM Fuel Cells: Particle-Size Effect, Reaction Mechanism, and Voltage Cycling Stability

In this experimental study, we determine the size dependent activity as well as accelerated voltage cycling stability of various carbon supported palladium electrocatalysts for the oxygen reduction in acidic medium. Furthermore, ex-situ transmission electron microscopy studies before and after accelerated voltage cycling provide a deeper understanding regarding particle stability during voltage cycling. Regarding oxygen reduction, a particle size effect on the specific activity is observed, with bulky Pd-black ( ≈ 4 m2 g− 1Pd) exhibiting ≈x6 times higher activity than Pd supported on Vulcan carbon ( ≈ 190 m2 g− 1Pd). Mass activities, however, exhibit a strong correlation with catalyst surface area at small electrochemically active surface area (ECSA) values, but are observed to be nearly constant between ≈ 50 − 200 m2 g− 1Pd. As stability tests during voltage cycling reveal a benefit for smaller surface areas, i.e. bigger particles, a limited gain in stability can be achieved by increasing catalyst particle size at a negligible cost of electrocatalytic mass-based activity. Moreover, we provide a deeper insight regarding the oxygen reduction reaction mechanism and show significant hints that a sequential two-plus-two electron reduction mechanism via intermediate hydrogen peroxide is likely to occur on carbon supported Pd catalysts.

Turbostratic carbon supported palladium as an efficient catalyst for reductive purification of water from trichloroethylene

This work investigates the catalytic properties of turbostratic carbon supported Pd catalyst in hydrodechlorination of trichloroethylene (TCE HDC) in aqueous phase. 1.57 wt% Pd/C was thoroughly characterized by BET, TPHD, CO chemisorption, PXRD, STEM, XPS and used as the catalyst in removal of trichloroethylene from drinking water in batch and continuous-flow reactors. The studies showed that catalytic performance of Pd/C depended on the hydrophobicity and textural properties of carbon support, which influenced noble metal dispersion and increased catalyst tolerance against deactivation by chlorination. Palladium in the form of uniformly dispersed small (~3.5 nm) nanoparticles was found to be very active and stable in purification of water from TCE both in batch and continuous-flow operation.

Enhanced electrocatalytic activity and stability of Pd nanoparticles supported on TiO2-modified nitrogen-doped carbon for ethanol oxidation in alkaline media

TiO2-modified nitrogen-doped carbon (TiO2-NC), prepared by a polymerization-pyrolysis process, is used to support the Pd catalyst for ethanol oxidation reaction (EOR) in alkaline media. X-ray photoelectron spectroscopy characterization indicates that the incorporation of TiO2 and nitrogen into the carbon matrix could improve the percentage of Pd0 in Pd/TiO2-NC catalyst. Electrochemical characterization shows that the Pd/TiO2-NC catalyst presents higher electrocatalytic activity and stability for EOR than the nitrogen-doped carbon-supported Pd (Pd/NC) catalyst and the carbon black-supported Pd (Pd/CB) catalyst, which can be mainly attributed to the high percentage of Pd0 in Pd/TiO2-NC catalyst (65%) than those in Pd/NC (48%) and Pd/CB (31%) catalysts. The results indicate that the Pd/TiO2-NC catalyst holds great potential as high-performance anode catalyst for direct ethanol fuel cells.

A Hybrid of Palladium-Graphitic Carbon Nitride-Reduced Graphene Oxide for Methanol and Formic Acid Electrooxidation

A novel nitrogen-rich support material (CNNF-G) consisting of graphitic carbon nitride (g-C3N4) nanoflakelets (CNNF) and reduced graphene oxide (rGO) is designed and fabricated for loading Pd nanoparticles. Structural characterizations indicates that the CNNF is formed via splitting decomposition of the g-C3N4 polymer on rGO at higher temperatures and the resulting CNNF is intimately coupled to the rGO sheets. The CNNF can provide more exposed edge sites and active nitrogen species for the high dispersion of Pd NPs. It is found that the Pd NPs with an average diameter of 3.92 nm are uniformly dispersed on CNNF-G sheets. DFT computations reveal that CNNF can trap Pd adatom and thus act as a Pd nucleation site at which Pd atoms tend to accumulate to form Pd clusters. The Pd-CNNF-G nanocatalyst exhibits excellent electrocatalytic activity for both formic acid and methanol oxidation reactions, including large electrochemically active surface area (ECSA) values, significantly high forward peak current densities, and reliable stability and durability, far outperforming the Pd-graphene, commercial activated carbon-supported Pd catalyst or Pd-carbon nanotubes. Such a stable Pd/CNNF-G nanocatalyst may bring new design opportunities for high-performance direct formic acid fuel cell (DFAFC) and direct methanol fuel cell (DMFC) in the future. Figure 1

Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation.

The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method.

Microporous Organic Polymers Derived Microporous Carbon Supported Pd Catalysts for Oxygen Reduction Reaction: Impact of Framework and Heteroatom

Electrochemical oxygen reduction reaction (ORR) plays a crucial role in renewable energy applications, such as fuel cells and metal–air batteries.1,2 For proton exchange membrane fuel cells (PEMFCs) and metal–air batteries, the typical electrocatalyst for ORR is the Pt-based precious metal catalyst. Pd is considered as a cheap alternative to the rare Pt catalyst because of its higher electrocatalytic activity and stability than that of other 3d transition metals (such as Ni, Co, and Fe) for ORR.3 Therefore, incorporating Pd NPs into N-doped carbon support matrix with high surface area and regular pore texture can result in a promising fuel cell cathode catalyst material. For this purpose, we have synthesized three types of KAPs (KAPs-Ph, KAPs-PhPh3, and KAPs-NHC) from different monomers via a similar cross-linked reaction. These carbonized products can be used as typical metal supporting models for comparative investigation. Also, we examined Pd NPs loading on commercial Vulcan XC-72 to illustrate the superiority of such KAPs. We synthesized three types of KAPs (KAPs-Ph, KAPs-PhPh3, and KAPs-NHC) from different monomers via a similar cross-linked reaction.4 The microporous carbon materials are obtained through directly pyrolyzing such KAPs at 800 oC for 4 h with a heating rate of 2 oC min-1 and then cooling down to room temperature under N2flow. The corresponding black carbon products are labeled as CKB, CKTB and CKN, respectively. The products from different temperature are also obtained for comparison. The surface areas and pore distributions of products are determined by nitrogen physisorption analysis. The N2 adsorption-desorption isotherms of these samples are typical type I according to the IUPAC classification, indicating their microporous properties. The size and morphology of Pd NPs loading on three carbonized products are investigated by TEM observation. The lattice spacing of d = 0.22 nm in HRTEM images can be ascribed to the Pd(111) planes. As shown in Figure 1, the Pd NPs are well-dispersed on the surface of microporous carbon, the diameter of Pd NPs suppored on Pd/CKN is about 2 nm. Besides the reason of stable carbon skeleton, N-dopant induced defects can act as trapping sites for anchoring Pd NPs to prevent the aggregation. The influences of framework and heteroatom of MOPs on the ORR catalytic activity of microporous carbonized products as well as carbonized products supported Pd composites are investigated. Among these materials, the CKN possesses the most positive half-wave potential (E½) and highest reaction current density because N-dopant altered the electronic property of carbon. The ORR performance of Pd loading on MOPs derived microporous carbon follows the similar order: Pd/CKN>Pd/CKTB>Pd/CKB. The highest catalytic activity is achieved in Pd/C system using CKN as support when compared with other MOPs derived microporous carbon supports (CKB, CKTB) and XC-72. The improvement of reactivity in Pd/CKN catalyst may be ascribed to the influence of N heteroatom on the electronic structure of carbon framework as well as that of metal NPs through metal/support interfacial interactions. Meanwhile, N-doping will facilitate the charge transfer and electronic interactions between supports and metal NPs. In summary, we synthesized different types of MOPs via one-step ‘knitting’ of rigid aromatic building blocks with an external crosslinker and explored as novel carbon precursors to produce microporous carbon materials. The catalytic performance and durability of MOPs-derived carbon supported Pd NPs exhibit superior behaviors to those loading on commercial 5% Pd/C catalyst. Therefore, this work opens up new insights for the rational design and development of novel highly-efficient carbon for supporting metal or metal oxide for ORR by simply modulating the framework as well as electronic structure of such polymers. This work is supported by the National Natural Science Foundation of China (21571071 and 21473064), Hubei Provincial Natural Science Foundation of China (2015CFB313), the Fundamental Research Funds for the Central Universities (2015QN183), and the Special Fund of Harbin Technological Innovation talent (2013RFLXJ011).