Pd Sn Catalysts Research Articles

Highly selective chemical reduction of nitrate in water in carbon-based contactor catalytic membrane reactors

A carbon-based catalytic membrane reactor in a contactor (interfacial) configuration has been used as an approach to control selectivity in the reduction of NO3- in water. Water and hydrogen fed to the reactor circulate tangentially on opposite sides of the membrane, which acts as a separator and contactor, enabling hydrogen transfer to the water phase. Powdered carbons (carbon black, carbon nanofiber, and activated carbon) were used to prepare catalytic membranes that also acted as contactors to transfer H2 from the gas phase to water. The membranes based on the Pd-Cu/carbon black catalyst showed lower selectivity towards unwanted NH4+ than the Pd-Cu and Pd-Sn catalysts supported on carbon nanofibers and activated carbon, due to a good balance among conductivity, external surface area, and particle size. Sensitivity analysis for H2 partial pressure demonstrated that the contactor membrane reactor can be operated with control of H2 mass transfer, hence enabling enhanced control of the selectivity to NH4+. Additional control of selectivity was achieved by reducing the catalytic layer thickness of the membrane, which improved NO3- transport and decreased the H/N ratio at the active centers. With these approaches, NO3- conversion values above 40 % with negligible NH4+ production and NO3- conversions close to 60 % with NH4+ selectivity values around 3 % were achieved.

Synthesis of Carbon Supported Pd-Sn Catalysts by Ethylene Glycol Method for Ethanol Electrooxidation

Synthesis of Carbon Supported Pd-Sn Catalysts by Ethylene Glycol Method for Ethanol Electrooxidation

A Pd-Sn heterobimetallic catalyst for carbonylative Suzuki, Sonogashira and aminocarbonylation reactions using chloroform as a CO surrogate.

Herein, we report a heterobimetallic Pd-Sn catalyst for the carbonylative Suzuki coupling, aminocarbonylation reaction, and carbonylative Sonogashira coupling of aryl halides with boronic acids, amines, and aromatic alkynes leading to a three-component coupling reaction using in situ generated carbon monoxide. Under the optimized reaction conditions, a variety of bisaryl ketones, amides, and aromatic ynones have been synthesized in moderate to good yields in a one-pot fashion. The reported catalyst has wide reaction scope with good functional group tolerance.

Catalytic membrane reactor based on Pd-Sn supported on nanocarbons for the reduction of nitrate in water

This work studies the reduction of NO3- in water using a catalytic membrane reactor in flow-through configuration (FTCMR) for enhanced control of H2 availability and generation of NH4+. The catalytic membrane was prepared with metal catalysts supported on carbon materials with different structural and physicochemical properties (graphite, carbon nanofibers, reduced graphene oxide, activated carbon and carbon black). The catalysts were firstly tested in a batch reactor for screening and assessing influence of regime control on activity and selectivity. Pd-Sn catalysts showed higher production of NH4+ under chemical control than Pd-Cu ones, but equivalent performance was reached for Pd-Sn supported on carbon nanofibers and carbon black in conditions of H2 mass transfer control. Catalytic membranes were prepared with Pd-Sn catalyst according to higher impact of H2 availability in NH4+ generation. FTCMR was less selective to NH4+ compared to the batch reactor due to better control of H2 mass transfer. Reduction of NH4+ generation was achieved at the expense of activity due to lower availability of H2. However, membranes based on Pd-Sn supported on carbon nanofibers and carbon black were able to operate at higher H2 concentration with low selectivity to NH4+, making possible the use of membrane reactors at advantageous conditions.

Oxygen reduction reaction on PdM/C (M = Pb, Sn, Bi) alloy nanocatalysts

In this work three PdM/C bimetallic catalysts were prepared with a second metal being either Bi, Pb or Sn. The synthesised Pd-alloy nanoparticles were supported on Vulcan carbon XC-72R. These catalysts were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HR-TEM) and electrochemically using the rotating disk electrode (RDE) technique. The prepared Pd-based electrocatalysts were compared to pure Pd/C catalyst synthesised using the citrate method. The oxygen reduction reaction (ORR) kinetics on Pd-alloy catalysts in alkaline solution was systematically investigated. Pd content was determined by microwave plasma atomic emission spectroscopy, which was used to calculate the mass activities (MA) for ORR. Mass activities revealed that BiPd had two-fold higher and PbPd showed 1.6-times increase in MA as compared to Pd/C, however SnPd showed lower MA than Pd/C. BiPd/C catalyst showed around 45% increase in specific activity (SA) for ORR, PdSn catalyst showed around 25% increase and PbPd no increase in SA in comparison to the Pd/C catalyst. Methanol tolerance was also studied for the PdM/C alloy catalysts and a higher tolerance was observed for BiPd/C losing 17 mV in the half-wave potential value and even better methanol tolerance was in evidence with the other two catalysts that lost only ∼10 mV in 0.1 M KOH + 0.5 M MeOH.

Hybrid process for nitrates elimination in water

Groundwater contamination with nitrates is a worldwide problem that needs a solution, because these compounds are harmful to health. There are several technologies to reduce the nitrate content in water to values accepted by the W.H.O. (10 mg L−1). Among them, one of the most advantageous is the catalytic reduction. This paper proposes the use of a combined process, using Pd-Sn catalysts supported on an anion exchange resin. First, nitrates are retained at the resin exchange sites, and then reduced over the metal sites in a regeneration stage. Different formulations were studied; the most active and selective catalyst was Pd 2%-Sn 0.5%, reaching conversions of 97%, with 66% selectivity to N2, when the regeneration was performed in H2 flow at room temperature and atmospheric pressure. This catalyst was also remarkably stable, maintaining conversions close to 90% in 28 successive cycles. The variables involved in the regeneration process were investigated. The addition of CO2 to the H2 stream did not improve either the conversion or the selectivity. The increase in temperature accelerated the process, but favored the catalyst deactivation. The regeneration time was optimized being possible to regenerate the catalyst in 12 h.

Enhancing electrochemical nitrate reduction toward dinitrogen selectivity on Sn-Pd bimetallic electrodes by surface structure design

Bimetallic palladium (Pd) and tin (Sn) catalysts were electrochemically deposited on stainless steel mesh support by controlling the metal deposition sequence, total electrical charge, and metal composition. Results showed that the preparation procedure affected the crystal structure of bimetallic Pd-Sn catalysts, which significantly influenced nitrate removal efficiency and dinitrogen selectivity. Electrode with Sn on the outside surface exhibited relatively greater nitrate removal rate constant and nitrate conversion. The Sn to Pd molar ratio and the electrical charge applied during electrode preparation also affected the nitrate reduction performance. The SS/Sn0.2Pd0.8-497 electrode exhibited 88, 89, 79, and 9% of total nitrate removal, dinitrogen selectivity, dinitrogen yield, and NH4+ selectivity, respectively. Among the three major facets, (214), (131) and (420) of Sn3Pd alloy on the electrode surface, (420) exhibited the most critical effect on the dinitrogen yield. Crystal structure of catalysts controls the reactivity and selectivity of electrochemical reduction as exemplified by nitrate.

Selective hydrogenation of acetylene over Pd-Sn catalyst: Identification of Pd2Sn intermetallic alloy and crystal plane-dependent performance

In Pd catalyzed acetylene semi-hydrogenation, high selectivity always comes at the expense of activity while improving both selectivity and activity is challenging. In this work, the performance of Pd alloy catalysts was enhanced by inserting Sn phase to modify both surface Pd ensembles and electronic structures. Compared with Pd/C, the optimal Pd2Sn/C catalyst exhibits higher selectivity at the same acetylene conversion level, with its selectivity increased from 10 % to nearly 95 % at ca 100 % acetylene conversion. Both experimental and DFT calculation results reveal that the specific performance is attributed to the redispersion of surface Pd ensembles by Sn insertion and down-shift of d-band center of catalysts, thus changing the adsorption behavior of the reaction gases. This design principle provides an efficient method for tailoring and optimizing durable Pd-based catalysts with desirable reactivity and ethylene selectivity for selective hydrogenation of acetylene.

Carbon supported PdSn nanocatalysts with enhanced performance for ethanol electrooxidation in alkaline medium

In this work, simple chemical reduction method is used to prepare Pd–Sn nanocatalysts supported on carbon for ethanol electro-oxidation in alkaline environment using ethylene glycol as reductant. The composition, structure and morphologies of PdSn/f-C catalysts are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray and transmission electron microscopy. The electro-chemical activity and durability of as-obtained PdSn/f-C nanocatalysts are investigated and determined by cyclic voltammetry and Chronoamperometric measurements. The obtained results demonstrate that as prepared PdSn/f-C nanocatalysts have uniform dispersion and small particle size. In addition to, the as prepared PdSn/f-C nanocatalysts have higher electro-chemical activity and better stability toward EOR in alkaline environment than those of Pd/f-C and commercial Pd/C (JM) nanocatalysts. Specifically, the electro-catalytic activity of Pd1.5Sn/f-C nanocatalyst (3413.3mAmgPd−1) is almost 8.6 times higher than Pd/C (JM) nanocatalyst (355.2 mAmgPd−1), which has competitive power among reported Pd–Sn catalysts. These results indicate that the uniform carbon supported PdSn nanostructure are promising electrocatalysts for direct ethanol fuel cells.

Development of Nonenzymatic Benzoic Acid Detection on PdSn/GCE/Vulcan XC‐72R Prepared via Polyol Method

AbstractIn this study a PdSn based sensor was developed for the determination of benzoic acid (BA) in foods. A carbon (Vulcan XC‐72R) supported PdSn catalyst was prepared via polyol method and its surface electronic and chemical properties were investigated by advanced surface analytical techniques such as scanning electron microscopy (SEM), X‐ray diffraction spectroscopy (XRD), X‐ray Photoelectron Spectroscopy (XPS), temperature‐programmed reduction with H2 (TPR‐H2) and transmission electron microscopy (TEM). Electrochemical measurements were performed by employing cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques on PdSn/GCE/Vulcan XC‐72R electrode. The developed sensor showed a wide linear range up to 10 mM with a 0.77 μM low limit of detection (LOD) as well as high stability. Further experiments were performed on food samples containing BA to achieve real sample measurements. For real sample measurements, PdSn/GCE/Vulcan XC‐72R electrode was used for the determination of BA in different kinds of samples such as mayonnaise, ketchup and carbonated beverages.

A continuous process for the catalytic reduction of water nitrate

The catalytic reduction of nitrate in drinking water was studied, using bimetallic Pd-Sn catalysts, supported on a macroporous anionic resin (WA30- Mitsubishi), with different Pd and Sn contents. The catalysts were prepared by the controlled surface reduction method, in which the promoter metal (Sn) is deposited on the surface of the previously reduced noble metal (Pd). The solids characterization by XRF, XPS and H2 chemisorption confirmed the effectiveness of the preparation technique. The catalytic evaluation was carried out both in a fixed-bed reactor with hydrogen bubbling and in a batch reactor. In both cases, the most active catalyst was the Pd 2%-Sn 0.5%, and it was observed that the decrease in the Sn content below this ratio hinders activity. Catalysts containing 1% Pd showed the better N2 selectivities. Catalysts did not show deactivation after treating more than 300 water bed volumes, even in the presence of competing anions. The effect of different reaction conditions was investigated, and it was found that a pH decrease does not modify the conversion but strongly improves N2 selectivity. A reaction mechanism was proposed for the different species involved in the reduction on the continuous reactor with H2 bubbling.

A Tunable Pd–Sn Alloy Electrocatalyst for CO2 Reduction to Value Added Products from DFT Study

Conversion of carbon dioxide (CO2) into value added products by electroreduction is one of the attractive means to reduce CO2 and it must trigger a sustainable solar-fuel-based economy. However, achieving this process requires catalysts with high activity, selectivity, and durability. Alloy catalysts can achieve superior performance to single metals while reducing the cost by finely tuning the composition and morphology. Pd–Sn nanoparticles alloy is known currently as the most active electrocatalyst for CO2 electroreduction reaction, but the reaction pathways to produce ethanol are not clear. In this work, we present the results of theoretical studies aimed at elucidating the optimal mechanism and the effects of the reaction environment of gas and liquid on the intrinsic activity and selectivity of alloy catalysts for the reduction of CO2. In addition, through tuning Pd–Sn catalyst with adding oxygen and sulfur atom, the reaction energy can be significantly reduced, eventually reducing the limiting voltage of the electrode reaction to − 0.51 eV. Density functional theory calculations of the reaction free energy diagrams suggest that the rate-determining step is hydrogenation of CO to CHO, this is easier than CO or CHO dimerization. The calculations also illustrate the rationality of the gas phase model compared to the liquid phase.

Coverage Effect on the Activity of the Acetylene Semihydrogenation over Pd–Sn Catalysts: A Density Functional Theory Study

The existence of acetylene impurities in ethylene feedstock is harmful to downstream polymerization reactions. The removal of acetylene can be achieved via semihydrogenation reaction, which is normally catalyzed by Pd-based catalysts. This paper describes the coverage effect on the activity of acetylene hydrogenation reactions over Pd and PdSn alloy surfaces. High-coverage models are presented to construct coverage-dependent adsorption energies of C2H2, C2H4, and H2 on Pd(111) and Pd3Sn(111) surfaces. It has been validated that the downshift of d-band center caused by preadsorbed molecules makes the adsorption weaker along with the increase of coverage, and the geometric effect can be neglected. An iterative method has been applied to predict surface coverages of reaction intermediates. Previous calculations with low-coverage models indicate that alloying Pd with late or post-transition metals, in general, enhances ethylene selectivity, accompanied with lower hydrogenation activity. However, by applying a...

Vapor phase deoxygenation of heptanoic acid over silica-supported palladium and palladium-tin catalysts

Silica-supported Pd and PdSn catalysts were prepared by ion exchange or incipient wetness impregnation and characterized with H2 chemisorption, X-ray diffraction, in situ Sn K-edge X-ray absorption near edge structure (XANES), and scanning transmission electron microscopy. The activity of the catalysts was evaluated in the deoxygenation of vapor-phase heptanoic acid at 0.1MPa and 573K. A Pd catalyst synthesized via ion exchange formed nanoparticles of 1.1±0.4nm and was more stable in heptanoic acid conversion compared to a Pd catalyst synthesized via incipient wetness impregnation having nanoparticles of 2.4±0.5nm. The addition of Sn to a Pd catalyst by either co-impregnation of precursors or physical mixing of supported monometallic catalysts improved the overall catalyst stability. Moreover, Sn addition expanded the reaction network from primarily decarbonylation over Pd to include dehydration and decarboxylative ketonization over PdSn. Electron microscopy confirmed the physical migration of Sn during catalytic reaction. In situ XANES analysis during the deoxygenation of a carboxylic acid suggests that partially reduced SnOx is the active Sn phase associated with Pd nanoparticles under reaction conditions.

ChemInform Abstract: Re‐Entry of Tin in N‐Alkylation: First Example of a Homogeneous Heterobimetallic Pd—Sn Catalyst for Base and Additive Free Alkylation of Amine and Surrogates with Alcohol.

AbstractThe title reaction provides N‐alkylated amines and amides in good yields and is applied to the synthesis of benzazoles.

Synthesis of Carbon Supported Pd-Sn Catalysts by Ethylene Glycol Method for Ethanol Electrooxidation

Synthesis of Carbon Supported Pd-Sn Catalysts by Ethylene Glycol Method for Ethanol Electrooxidation

Re-entry of tin in N-alkylation: first example of a homogeneous heterobimetallic Pd–Sn catalyst for base and additive free alkylation of amine and surrogates with alcohol

The N-alkylation of amines, and amides with benzyl alcohols is catalyzed by bimetallic catalyst [Pd(COD)(SnCl3)Cl] in o-xylene. The reaction does not require additional base, additive or ligand, and is insensitive toward air and moisture and involves minimal work-up. These features make the reaction attractive, simple, and practical.

Hydrogenation of crude terephthalic acid by supported Pd and Pd–Sn catalysts on functionalized multiwall carbon nanotubes

Liquid phase hydro-purification of crude terephthalic acid (CTA) was performed using supported Pd and Pd–Sn catalysts on functionalized multi-wall carbon nanotubes (FMWCNT). Pd/FMWCNT catalysts were prepared by wet impregnation with Pd loadings of 0.05 to 0.6wt.%. Pd–Sn/FMWCNT catalysts were prepared by co-impregnation (CI) and successive impregnation (SI) using 0.3wt.% Pd loading and Sn/Pd molar ratios of 0.1 and 0.35 for the CI method and 0.05 to 0.35 for the SI method. Pd loading of 0.3wt.% for Pd/FMWCNT was sufficient to decrease the 4-carboxybenzaldehyde (4-CBA) content of CTA from 2100ppm to 5.5ppm without excessive hydrogenation of terephthalic acid (TA). The commercial catalyst containing 0.5wt.% Pd on activated carbon decreased the 4-CBA content to 23ppm and showed excessive hydrogenation of TA leading to a lower selectivity. The Pd–Sn/FMWCNT had lower CTA hydrogenation activity compared with Pd/FMWCNT possibly due to alloy formation and palladium surface blocking due to Sn addition. Sn addition also led to a decrease in the decarbonylation rate of 4-CBA thus enhancing the product selectivity. Pd–Sn/FMWCNT prepared by the SI method and Sn/Pd ratio of 0.1 resulted in 99%+ removal of 4-CBA as well as enhanced selectivity compared with Pd/FMWCNT.

One-step synthesis of nitrogen-doped graphene supported PdSn bimetallic catalysts for ethanol oxidation in alkaline media

In this paper, a facile chemical reduction method was employed to synthesize bimetallic PdSn nanocatalysts, and the nitrogen-doped graphene (N-G) has been used as a conductive support material for PdSn catalysts.

Nano-Structured Pd-Sn Catalysts for Alcohol Electro-Oxidation in Alkaline Medium

The study of alcohols electrooxidation is of paramount importance not only for direct fuel cell and/or electrolysis cell applications, but also in order to gain the fundamental knowledge on reaction mechanisms for electrosynthesis applications. Tin is known to be a high performance co-catalyst of noble metal for alcohol oxidation, particularly concerning the ethanol electrooxidation reaction in acidic medium. This property of tin in association with palladium was recently confirmed for the electrooxidation of methanol, ethanol, and ethylene glycol in alkaline medium. Here, the electrocatalytic behavior of Pd1Snxcatalysts towards the electrooxidation of different C1, C2 and C3 alcohols is compared and discussed in terms of activity and reaction pathways: methanol and ethylene glycol since they are the simplest alcohol and polyol, respectively, ethanol and glycerol because they can both be produced from biomass, and isopropanol which only bears a secondary alcohol function, because it can be interesting for the development of “rechargeable” direct fuel cells. Particularly, the occurrence of two possible mechanisms, a base-catalyzed one and a mechanism based on the ability of the catalytic surface to favor the adsorption and desorption of species at low potentials, is discussed, as well as the difference in activity comparing isopropanol and glycerol oxidation reactions. For this purpose, active self-supported Pd1Snx catalysts are synthesized by the Sacrificial Support Method (SSM). Their catalytic activity towards the oxidation of C1 to C3 alcohols was determined in alkaline medium. The comparison of the activity allowed discarding a first base catalyzed deprotonation reaction of alcohols as rate determining step (rds), and spoke up for a mechanism involving a C-adsorption of carbon bearing an alcohol function. By comparing isopropanol and glycerol oxidation voltammograms, and on the basis of in situFTIR spectroscopy measurements, it has been shown that desorption of dihydroxyacetone could be the limiting step for glycerol oxidation at low potentials. Acknowledgement: Anna Zalineeva thanks the Center for Emerging Energy Technologies, Farris Engineering Center (UNM) for assistance and technical support, and the County Council of Poitou-Charentes (France) for financial support.