Small Amount Of Noble Metal Research Articles

Selective electrocatalytic oxidation of C(OH)–C bond in lignin with Pt@CeO2 toward the synthesis of benzoic acid

The synthesis of carboxylic acid compounds by the selective electrooxidation cleavage of the C(OH)-C bond in lignin is significant to biomass conversion to produce high-value-added chemicals. However, it is challenging to selectively cleave the C(OH)-C bond due to its extremely high dissociation energy of 260–300 kJ mol−1. Herein, a simple and effective method of hydrothermal process and wet impregnation is proposed to synthesize Pt@CeO2 catalysts. The cleavage of the C(OH)-C bond by Pt@CeO2, a catalyst loaded with a small amount of noble metal, triggered the electrochemical oxidation of lignin, resulting in the highly selective synthesis of carboxylic acid compounds. Consequently, more reactive oxygen species (ROS) are produced in the electrocatalytic oxidation process, which enhances the cleavage of C(OH)-C bond and the oxidation of benzaldehyde. In addition, Pt@CeO2 can also be used for the electrochemical depolymerization of industrial alkali lignin to produce carboxylic acids. This research proposes an efficient way of producing carboxylic acids of high value by utilizing an electrocatalyst for the electrocatalytic oxidation of lignin.

Au-nanoparticles-decorated CeO2 electrocatalyst synthesized by direct growth and wet impregnation for enhanced oxygen evolution reaction

Water splitting is a promising method for producing pure hydrogen and oxygen electrochemically. However, the sluggish kinetics of the oxygen evolution reaction (OER) at the anode of a water splitting system reduces the efficiency of the reaction. To address this issue, various electrocatalysts have been developed for use in the OER. Among them, transition-metal-based materials (TMBMs) have emerged as promising candidates owing to their abundance, low cost, high redox states, and synergistic effects. The catalytic performance of TMBMs can be further enhanced by incorporating small amounts of noble metals. Based on this underlying principle, we developed trace amounts of gold nanoparticles (AuNPs)-decorated cerium oxide (CeO2) nanostructured electrocatalyst for a highly efficient OER. Previously, these composite materials have been utilized for this purpose; however, our approach is simple and facile: we incorporate noble metal elements on nanostructured catalysts synthesized by hydrothermal synthesis or electrodeposition. Metal salt aqueous solution-based alkali-free two different routes (hydrothermal synthesis or electrodeposition) were used for the direct growth of nanostructured CeO2 on nickel foam, followed by surface modification via the incorporation of gold using a simple wet impregnation method. The hydrothermally synthesized CeO2 electrode showed higher OER performance than the electrodeposited CeO2 electrodes. In both CeO2 nanostructures, AuNPs-decorated on the surfaces exhibited improved OER performance. Among the electrodes synthesized in this work, the hydrothermally synthesized AuNPs-decorated CeO2 nanostructures (termed HCA herein) exhibited a low overpotential 0.31 V at a current density of 10 mA cm−2, a low Tafel slope (30.25 mV dec−1), and a performance retention of 97% after 50 h, indicating excellent and stable OER performance. Hence, this approach for the synthesis of nanostructured composites can be used to produce other effective electrocatalysts for OER applications.

Synthesis of Pt-CeVO4 nanocomposites and their enhanced photocatalytic hydrogen evolution activity under sunlight

The environmental pollution problem caused by fossil fuels, a nonrecyclable resource, becomes more serious every year. Therefore, the development of technology to produce alternative energy in a carbon–neutral way is urgent. In this regard, solar-powered H2 production from water using particulate photocatalysts is considered the most economical and robust approach to producing carbon–neutral H2 fuels. Using Pt-CeVO4 nanocomposites with controllable amounts of Pt nanoparticles (NPs) on CeVO4 as a photocatalyst, a superior H2 production rate of 220.68 mmol g-1h−1 was achieved, which was five times higher than that of Pt NPs. In the Pt-CeVO4 catalyst, CeVO4 affected the electron density of Pt through upward band bending, which dramatically improved the H2 generation ability. Our research is a competent study that satisfies the dual purpose of 1) achieving maximum reaction efficiency using a small amount of noble metal while providing important insights that 2) proper contact of metal and semiconductor materials can exponentially enhance photocatalytic performance.

PRODUCTION OF HYDROGEN BY A WATER GAS SHIFT REACTION ON SOL-GEL BIMETALLIC Co-CONTAINING CATALYSTS

Modern oil refining requires an increasing amount of hydrogen to carry out hydrogenation processes and hydrotreatment of increasingly heavy oil and obtain high-quality products.Water gas shift reaction (WGSR) being the interaction of steam with carbon monoxide is one of the stages of industrial hydrogen production. Despite the sufficient development of the process, the search for more efficient catalysts for this process does not stop.In this work, the bimetallic cobalt-containing alumina supported catalysts modified with small amount of noble metals and prepared by the solgel method were synthesized and tested in WGSR. The total metal content was 5 mass %, a ratio of Co:M=98:2, where M=Rh or Pd. The effect of process temperature and the nature of additives on behavior of synthesized catalysts has been studied. It has been shown that the sol-gel 5% Co-M/ Al2 O3 catalysts have high activity, thus at t=390o C the extent of carbon oxide conversion reaches 96.5-97.5% depending on the nature of the second metal. The main products of the reaction are hydrogen and carbon dioxide. Both catalysts can be considered as high-temperature catalysts for WGSR.

Recent progress in the application of Ni-based catalysts for the dry reforming of methane

ABSTRACT Ni-based catalysts are highly efficient in methane-reforming processes. In the particular case of methane reforming in the presence of carbon dioxide, or dry reforming of methane (DRM), it is necessary to modify and control the initial properties of the catalyst to confer on it resistance to carbon deposition in particular, and to sintering of the Ni metal particles. In this regard, catalytic supports and promoters of different natures have been proposed. Likewise, the addition of small amounts of noble metals to avoid oxidation of the Ni active phase during the reforming reaction has been proposed. Catalyst preparation methods have also been identified as being of particular interest, since they can affect the structure of the Ni metal particles. In this review, the thermodynamic and kinetic aspects of the dry reforming of methane reaction are presented first. The most recent developments in synthetic methods (impregnation, sol-gel, co-precipitation, equilibrium deposition filtration, atomic layer deposition, non-thermal glow discharge plasma, multi-bubble sonoluminescence, “core-shell” structure) aimed at maximizing the dispersion and thermal resistance of Ni particles are then discussed and compared. The catalytic supports used to promote dispersion of the active metallic phase, the oxygen-storage capacity, and the metal/support interaction are also described. The review then addresses the fact that both the nature of the support and the addition of promoters and other metallic phases that modify the surface properties can control the interaction between the metal and the support, the electronic density of the active phase, and the degree of Ni reduction. Finally, new lines of research focused on the DRM process to make the reaction conditions milder and favor the process at low temperatures are also summarized.

Combination of hydrotalcite-like-compound-derived Ni-Fe/Mg/Al and ceria-supported Rh catalysts for fuel reforming in exhaust gas recirculation system of gasoline engine

Hydrotalcite-like-compound-derived Ni-Fe/Mg/Al catalyst, which is known to have high catalytic performance on reforming when activated by pre-reduction with H2, was combined with small amount of noble metal to obtain self-activation ability (startability) in toluene reforming with model exhaust gas of gasoline engine of automobiles. Rh is found to be the most effective noble metal from the viewpoints of the inherent reforming activity, good promotion of reduction of NiFe, and stability. Physical mixing of Rh/CeO2 and Ni-Fe/Mg/Al powders before shaping to granules gave higher activity in the startability test (reaction without pre-reduction) than other combination methods of Rh/CeO2 + Ni-Fe/Mg/Al, although the activity increase from Rh/CeO2 was much smaller than the potential activity of Ni-Fe/Mg/Al catalyst induced by pre-reduction with H2. Direct addition of Rh to Ni-Fe/Mg/Al by impregnation gave inferior performance to the mixture catalyst, because of the lower activity of Rh on hydrotalcite-derived oxide support than that of Rh on CeO2 support. The characterization with XRD, TEM-EDX and XAS showed that the reduction degrees of Ni, Fe and even Rh were small during the startability test. The Ni and Fe species only located near Rh species were probably reduced by reforming products from toluene formed over Rh.

Enhanced hydrogen evolution reaction activity of FeM (M = Pt, Pd, Ru, Rh) nanoparticles with N-doped carbon coatings over a wide-pH environment

The alloy catalyst formed by transition metal and a small amount of noble metal has become the most promising substitute for M-based (M = Pt, Pd, Ru, Rh) catalyst. However, due to the direct exposure of the metal core to the electrolyte, it is vulnerable to corrosion and oxidation, which in turn reduces the catalytic stability and is becoming a major obstacle to sustainable hydrogen production. The present work addresses this issue by developing a one-step immersion-adsorption-pyrolysis strategy for synthesizing FeM alloy nanoparticles with N-doped carbon coatings ([email protected]) for use as electrocatalysts in the HER. The deliberately designed metal-organic framework material was used as the precursor of catalyst synthesis to achieve the carbon coatings and simultaneously the heteroatom in-situ doping for the alloy nanoparticles. The optimal [email protected] demonstrates excellent catalytic stability and HER activity in an acidic electrolyte medium. The reactions obtain a small overpotential of 28 mV to achieve current densities of 10 mA cm−2, which are comparable to a high-performance commercial Pt/C electrocatalyst with a much higher Pt loading. The [email protected] also demonstrates an outstanding performance with an overpotential of only 18 mV to achieve a current density of 10 mA cm−2 in an alkaline medium.

Perovskites Doped with Small Amounts of Noble Metals for IT-SOFCs

Solid oxide fuel cells (SOFCs) have a great potential among the emerging energy conversion technologies because they can efficiently convert various types of fuel (hydrogen, methane, CO, biogas) into electrical energy in the 750-850 °C temperature range. The choice of electrodes remains a challenge because most metal oxides suffer from low chemical stability and low electrocatalytic activity toward oxygen reduction reaction (ORR) in the intermediate temperatures (IT) range (500-700 °C) [1]. In this view, perovskite oxides (ABO3) have shown excellent properties in terms of thermal stability, compatibility with other cell components, low production cost and, most importantly, great flexibility [1]. La0.6Sr0.4FeO3-δ, (LSF) perovskite oxide have been widely investigated for the high electrical conductivity and the electrochemical properties [2]. However, the main drawback is the poor activity towards ORR in the IT range, as most iron-based perovskite oxides [3]. The B-site doping with noble metal catalysts can sensitively improve the properties and make the compounds suitable for electrode application.The addition of small amounts of Ru or Pt into LSF structure can be an effective approach to improve the electrocatalytic properties [4,5]. Specifically, we synthesized B-site doped LSF powders with very low amounts (<5%mol) of Ru and Pt by using solution combustion synthesis (SCS) method. The synthesized powders were calcined at quite low temperature (750 °C) to get as high as possible surface area (>15 m2/g). All compounds showed a single perovskite phase. As reported in Fig. (a), the addition of Ru and Pt in the structure causes a progressive shift of the XRD peaks to lower 2θ angles indicating the perovskite lattice expansion due to the substitution of Fe4+/ Fe3+ sites with larger Ru and Pt ions.To assess the electrocatalytic activity, the compounds were investigated in oxidizing conditions using electrochemical impedance spectroscopy (EIS) analysis. Fig. (b) shows the Arrhenius plot of area specific resistance (ASR) values of LSFRu and LSFPt perovskite oxides. The ASR values were measured on LSFM/La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM)/LSFM (M=Ru, Pt) symmetric cells in the temperature range 550-800 °C. The insertion of a very low amount (1%mol) of Pt or Ru significantly reduces the polarization resistance, confirming the beneficial effect of noble metal ions on ORR activity. All these features suggest that very low Pt and Ru doping positively affects the structural and electrocatalytic properties valuably for cathodic applications.[1] Hwang J, Rao R.R. (2017). Science 358:751-756[2] Hansen KK, Mogensen M (2008). ECS Trans 13:153–160[3] Chavan SV, Singh RN (2013). J Mater Sci 48:6597–6604[4] Fan W, Sun Z. (2016) RSC Adv 6:34564[5]Shaoli G., Hongjing Wu, (2015),Catalysts, 5, 366-391 Figure 1

Perovskites Doped with Small Amounts of Noble Metals for IT-SOFCs

Noble metal-doped lanthanum strontium ferrite (La0.6Sr0.4Fe0.99M0.01O3-d M=Ru, Pt) powders were developed as active electrodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). The as low as 1% mol doping sensitively improved the electrochemical performance. Structural, electrical, and electrochemical properties are discussed in detail. Fuel cell tests in H2 show promising performance in the 700-750°C temperature range.

Palladium Embedded in SnO2 Enhances the Sensitivity of Flame-Made Chemoresistive Sensor

Introduction Palladium is commonly used to enhance the performance of chemoresistive metal-oxide gas sensors [1]. Typically, this enhancement is attributed to the presence of Pd clusters on the surface of their metal oxide support (e.g. SnO2). More specific, small Pd clusters on SnO2 were associated to enhanced sensitivity to H2 due to fermi-level control [2] or spillover effects [1]. However, Pd may not be present in metallic but oxidic form, that is catalytically active as well [3]. E.g. PdO can form during fabrication or upon the typical annealing [4] at 400 - 700 °C [3] for a few hours prior to gas sensing. Furthermore, possible Pd incorporation or embedding into the support rarely has been considered [5].Here, SnO2 particles with different Pd contents were prepared by flame spray pyrolysis (FSP). Their surface Pd was removed through leaching with HNO3 to guaranty the surface and embedded Pd content was measured. Lastly, the influence of surface and embedded Pd on SnO2 gas sensors was evaluated with acetone, ethanol and CO at 350 °C and 50% relative humidity. Method Pristine and Pd-containing (0 - 3 mol%) SnO2 nanoparticles were produced by FSP and annealed for 5 h at 500 °C. To remove all Pd from the surface, the particles were reduced in 5% H2 in Ar at 150 °C for 30 min and then leached in 10% HNO3 in water at 60 °C for 4 h (Figure 1a). Inductively coupled plasma-optical emission spectrometry was used to determine the Pd content in the leached solution, that corresponds to the surface amount. Sensing films were prepared by doctor-blading the particles onto 15 × 13 × 0.8 mm Al2O3 sensor substrates followed by annealing at 300 °C for 30 min. These sensors were then heated to 350 °C and tested with different concentrations (5 - 1000 ppb) of acetone, ethanol and CO in a gas sensing setup described elsewhere [6]. Results and Conclusions Figure 1b displays the fraction of surface (or leachable) Pd over the nominal content of flame-made and annealed particles. Only a fraction of Pd content is on the surface whereas the rest is embedded in the bulk SnO2. For instance, at nominal 0.5 mol% Pd, only 30% of it is leached while at 3 mol% Pd it increased to 45%. Apparently, most Pd is embedded and thereby not exposed to the analytes during sensing.Figure 1c shows the sensor responses at 350 °C to 1 ppm of acetone at 50% RH of annealed Pd-containing SnO2 as a function of the nominal Pd content. Before leaching (triangles), the addition of small amounts of Pd (up to 0.2 mol%) slightly increases the responses to acetone (within the error bar of reproducibility). At higher Pd contents, the responses continuously deteriorate until they are hardly detectable anymore at 3 mol% Pd. The circles in Figure 1c show the analyte responses after leaching the surface Pd as a function of the nominal Pd content. While the responses of pristine SnO2 were hardly affected by leaching, surprisingly, adding only 0.2 mol% Pd almost doubled the acetone response from 4 to 7. Overall, SnO2 containing both surface & embedded Pd (i.e. prior to leaching, triangles) results in lower responses than after leaching (circles).We reveal that flame-made Pd-containing SnO2 contains a significant fraction of Pd embedded in the bulk of (and/or strongly surface-bonded to) SnO2. Furthermore, small amounts of embedded Pd nearly double the responses of SnO2 to acetone at 350 °C. In contrast, the presence of surface Pd deteriorates the sensor performance below that of pure SnO2. This might point out, that small amounts of noble metals embedded in metal oxides can be more effective than on their surface.

Regulating Fe2(MoO4)3 by Au Nanoparticles for Efficient N2 Electroreduction under Ambient Conditions

AbstractAmmonia, as an important chemical, has played an indispensable role in the fields of fertilizer precursors, fuel, and energy carriers over time. The electrocatalytic nitrogen reduction reaction (eNRR) has attracted extensive attention due to the potential availability of clean energy under mild conditions, while electrochemical catalysts still need further optimization and exploration restricted by the strong chemical bonds of NN. In this work, it is proposed that a small amount of noble metal (Au) modified Fe2(MoO4)3 can serve as active sites in eNRR. Density functional theory calculations reveal that the interaction of Au with Fe2(MoO4)3 reduces the reaction energy of the rate determining step and inhibits the hydrogen evolution reaction, which increase the eNRR activity and selectivity of Au/Fe2(MoO4)3. As expected, according to the 1H nuclear magnetic resonance measurement as the exclusive quantitative detection approach, the as‐prepared Au/Fe2(MoO4)3 achieves outstanding eNRR performance with 7.61 µg h−1 mg−1cat. NH3 production rate and 18.79% Faradaic efficiency at −0.4 V versus reversible hydrogen electrode in 0.2 m Na2SO4 under ambient conditions.

Study of the effect of noble metal promotion in Ni-based catalyst for the Sabatier reaction

This paper reports the preparation and the evaluation of the performance of Ni-based powder catalysts with low nickel loading on the CO2 methanation reaction, that is an integral part of the power-to-gas (PtG) technology. CeO2, CeZrO4 and CeO2/SiO2 were selected as possible supports, and the results of this first screening pointed out that 10%Ni/CeO2 catalyst could offer the best reaction performances because of ceria's peculiar characteristics. Moreover, the promotion of this promising formulation with the addition of a small amount of noble metals (Pt, Ru, Rh) was investigated, showing that platinum in particular can enhance the catalyst performances. A further study related to the noble metal loading pointed out that platinum and ruthenium have a different optimum loading condition: this result, together with the activity tests performed on monometallic formulations with only the noble metal, suggested that the two metals are able to catalyse two different reactions, thus promoting two different reaction mechanisms.

Surface Leaching of Pd-Containing SnO2 Gas Sensors Enhances Sensitivity

Introduction Palladium is commonly used to enhance the performance of chemoresistive metal-oxide gas sensors [1]. Typically, this enhancement is attributed to the presence of Pd clusters on the surface of their metal oxide support (e.g. SnO2). More specific, small Pd clusters on SnO2 were associated to enhanced sensitivity to H2 due to fermi-level control [2] or spillover effects [1]. However, Pd may not be present in metallic but oxidic form, that is catalytically active as well [3]. E.g. PdO can form during fabrication or upon the typical annealing [4] at 400 - 700 °C [3] for a few hours prior to gas sensing. Furthermore, possible Pd incorporation or embedding into the support rarely has been considered [5].Here, SnO2 particles with different Pd contents were prepared by flame spray pyrolysis (FSP). Their surface Pd was removed through leaching with HNO3 to guaranty the surface and embedded Pd content was measured. Lastly, the influence of surface and embedded Pd on SnO2 gas sensors was evaluated with acetone, ethanol and CO at 350 °C and 50% relative humidity. Method Pristine and Pd-containing (0 - 3 mol%) SnO2 nanoparticles were produced by FSP and annealed for 5 h at 500 °C. To remove all Pd from the surface, the particles were reduced in 5% H2 in Ar at 150 °C for 30 min and then leached in 10% HNO3 in water at 60 °C for 4 h (Figure 1a). Inductively coupled plasma-optical emission spectrometry was used to determine the Pd content in the leached solution, that corresponds to the surface amount. Sensing films were prepared by doctor-blading the particles onto 15 × 13 × 0.8 mm Al2O3 sensor substrates followed by annealing at 300 °C for 30 min. These sensors were then heated to 350 °C and tested with different concentrations (5 - 1000 ppb) of acetone, ethanol and CO in a gas sensing setup described elsewhere [6]. Results and Conclusions Figure 1b displays the fraction of surface (or leachable) Pd over the nominal content of flame-made and annealed particles. Only a fraction of Pd content is on the surface whereas the rest is embedded in the bulk SnO2. For instance, at nominal 0.5 mol% Pd, only 30% of it is leached while at 3 mol% Pd it increased to 45%. Apparently, most Pd is embedded and thereby not exposed to the analytes during sensing.Figure 1c shows the sensor responses at 350 °C to 1 ppm of acetone at 50% RH of annealed Pd-containing SnO2 as a function of the nominal Pd content. Before leaching (triangles), the addition of small amounts of Pd (up to 0.2 mol%) slightly increases the responses to acetone (within the error bar of reproducibility). At higher Pd contents, the responses continuously deteriorate until they are hardly detectable anymore at 3 mol% Pd. The circles in Figure 1c show the analyte responses after leaching the surface Pd as a function of the nominal Pd content. While the responses of pristine SnO2 were hardly affected by leaching, surprisingly, adding only 0.2 mol% Pd almost doubled the acetone response from 4 to 7. Overall, SnO2 containing both surface & embedded Pd (i.e. prior to leaching, triangles) results in lower responses than after leaching (circles).We reveal that flame-made Pd-containing SnO2 contains a significant fraction of Pd embedded in the bulk of (and/or strongly surface-bonded to) SnO2. Furthermore, small amounts of embedded Pd nearly double the responses of SnO2 to acetone at 350 °C. In contrast, the presence of surface Pd deteriorates the sensor performance below that of pure SnO2. This might point out, that small amounts of noble metals embedded in metal oxides can be more effective than on their surface.

Indirect fuel cell based on a redox-flow battery with a new structure to avoid cross-contamination toward the non-use of noble metals

An indirect fuel cell system is constructed. The system is composed of a redox flow battery (RFB) to extract electrical energy and two chemical reactors (anolyte and catholyte regenerators). A quinone as a redox mediator is reduced by a mixture of hydrogen and carbon monoxide in the anolyte regenerator, whereas a polyoxometalate as another redox mediator is oxidized in the catholyte regenerator, followed by a steady-state power generation at the RFB using the two redox mediators as active materials. This system demonstrates how to reduce the amount of platinum required in a proton-exchange membrane fuel cell (PEMFC), especially when using a fuel other than pure hydrogen. The RFB in our system contains two gas-diffusion electrodes (GDEs) with a platinum electrocatalyst to insert a “pure hydrogen gas phase” between the anolyte and catholyte to avoid cross-contamination. These two GDEs participate in the hydrogen evolution reaction and hydrogen oxidation reaction, respectively, and require only a small amount of platinum. In addition, the catalysts used in the anolyte regenerator are rhodium complexes. However, these catalysts are in a dissolved state (molecular catalysts) with micromolar-order concentrations, and very little noble metal is used. A carbonaceous catalyst without platinum is used in the catholyte regenerator. This eliminates the need for a noble metal for the oxygen reduction reaction, which is the main reason why platinum is used in a large amount in a conventional PEMFC. Steady-state operations of the anode side, the cathode side, and the total system are demonstrated in this work. Although a small amount of noble metal is still required at this stage, this work may contribute to the complete elimination of noble metals from a PEMFC.

A Process for the Separation of Noble Metals from HCl Liquor Containing Gold(III), Palladium(II), Platinum(IV), Rhodium(III), and Iridium(IV) by Solvent Extraction

The demand for noble metals is increasing, owing to their excellent chemical and physical properties. In order to meet the demand, the recovery of noble metals with high purity from diverse secondary resources, which contain small amounts of noble metals, is of immense value. In this work, the possibility of the separation of Au(III), Pd(II), Pt(IV), Rh(III), and Ir(IV) by solvent extraction from a synthetic HCl solution is investigated. Only Au(III) was selectively extracted by Cyanex 272 in the HCl concentration range from 0.5 M to 9 M, leaving the other metal ions in the raffinate. The loaded Au(III) in Cyanex 272 was efficiently stripped by (NH2)2CS. The other four noble metals were sequentially separated on the basis of the procedures reported in the previous work. The mass balance showed that about 98% of each metal, except Pt(IV), was recovered by the proposed process. An efficient process for the recovery of the five noble metal ions from the HCl leaching solution of secondary resources containing these metals can be developed.

Differences in the Catalytic Behavior of Au-Metalized TiO2 Systems During Phenol Photo-Degradation and CO Oxidation

For this present work, a series of Au-metallized TiO2 catalysts were synthesized and characterized in order to compare their performance in two different catalytic environments: the phenol degradation that occurs during the liquid phase and in the CO oxidation phase, which proceeds the gas phase. The obtained materials were analyzed by different techniques such as XRF, SBET, XRD, TEM, XPS, and UV-Vis DRS. Although the metallization was not totally efficient in all cases, the amount of noble metal loaded depended strongly on the deposition time. Furthermore, the differences in the amount of loaded gold were important factors influencing the physicochemical properties of the catalysts, and consequently, their performances in the studied reactors. The addition of gold represented a considerable increase in the phenol conversion when compared with that of the TiO2, despite the small amount of noble metal loaded. However, this was not the case in the CO oxidation reaction. Beyond the differences in the phase where the reaction occurred, the loss of catalytic activity during the CO oxidation reaction was directly related to the sintering of the gold nanoparticles.

Oxidation Resistance of Modified Aluminide Coatings

The application of protective aluminide coatings is an effective way to increase the oxidation resistance of the treated parts and prolongs their lifetime. The addition of small amount of noble metals (platinum or palladium) or reactive elements such as: hafnium, zirconium, yttrium and cerium has a beneficial effect on oxidation behavior. This beneficial effect includes an improvement of adhesion of alumina scales and reduction of oxide scale growth rate. Platinum and hafnium or zirconium modified aluminide coating were deposited on pure nickel using the electroplating and CVD methods. The coatings consisted of two layers: an outer, β-NiAl phase and the interdiffusion γ’-Ni3Al phase. Palladium dissolved in the whole coating, whereas hafnium and zirconium formed inclusions on the border of the layers. Samples were subjected to cyclic oxidation test at 1100 °C for 200h. Oxidation resistance of the palladium, Hf+Pd and Zr+Pd modified coatings deposited on pure nickel does not differ significantly, but is better than the oxidation resistance of the non-modified one.

Chlorine Influence on Palladium Doped Nickel Catalysts in Levulinic Acid Hydrogenation with Formic Acid as Hydrogen Source

Levulinic acid (LA) is a platform molecule, and its valorization toward biofuel additives like γ-valerolactone or tetrahydrofuran is considered as an important step in planning future biorefinery schemes. In this study, various Ni based catalysts were studied for the LA hydrogenation with formic acid (FA) used as a hydrogen source. Two different ways of catalytic activity improvement are discussed (nickel loading vs addition of dopants). The influence of Ni doping by small amount of noble metals (Pt, Pd, Ru, Rh) showed that Ni–Pd is the most active catalyst. Its high catalytic performance is attributed to the synergic effect between two metals and interaction with chlorine. The effect of chlorine on catalytic performance and properties of the catalysts was evaluated by variety of surface and bulk-sensitive characterization methods. It was shown that addition of chlorine is one of the key factors required for high catalytic performance. Chlorine influences distribution of metals on the surface of the catal...

Preparation of bimetallic Ni@Ru nanoparticles supported on SiO2 and their catalytic performance for CO methanation

Bimetallic Ni@Ru nanoparticles with Ni core and Ru shell supported on SiO2 were prepared by impregnation method using a perovskite-type oxide of LaRuxNi1−xO3 as the precursor and used as catalysts for CO methanation. The catalysts were characterized by using BET, XRD, H2-TPR, HRTEM + EDX, ICP, H2 chemisorption, XPS and TGA techniques. By reducing the catalysts with hydrogen, bimetallic nanoparticles with the structure of nickel shell and ruthenium core of Ru@Ni supported on SiO2 doped with La2O3 were made, and the Ru would migrate to the surface of the Ni-Ru cluster forming the ruthenium shell and nickel core of Ni@Ru under CO atmosphere. The supported bimetal catalysts with core–shell structure by doping small amount of noble metal exhibited very good catalytic performance for CO methanation, especially showed excellent resistance to carbon deposition and metal sintering, while the monometallic catalyst of nickel showed inferior catalytic performance.

Carbon nanofiber-supported PdNi alloy nanoparticles as highly efficient bifunctional catalysts for hydrogen and oxygen evolution reactions

Efficient bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) must be developed to realize an inexpensive water-splitting system for large-scale applications. Herein, a novel PdNi carbon nanofiber (PdNi/CNF) catalyst was synthesized by facile electrospinning and carbonization processes. The size and homogeneity of the Pd−Ni alloy nanoparticles (NPs) could be effectively tuned by controlling the molar feed ratio of metal precursors .The morphology and structure of the PdNi/CNFs were characterized, and the working electrodes fabricated from the prepared catalyst mats were directly employed in the HER and OER. The PdNi/CNFs-1:2 catalyst exhibits high catalytic activity in the HER with a low overpotential of 55mV at a current density of 10mAcm−2 in an acidic solution. Moreover, under 1M KOH electrolyte, an overpotential of 187mV is required in the HER over the catalyst to arrive 10mAcm−2 and an overpotential of 289mV is achieved in the OER at the same current density. The superior HER and OER activities of the PdNi/CNFs are attributed to the synergistic effects of the PdNi alloy nanoparticles (NPs) assembled on the CNFs. This work provides a simple route for synthesizing highly efficient bifunctional electrocatalysts from 3d transition metals and a small amount of noble metals for hydrogen and oxygen evolution reactions.