Gold Support Research Articles

Reduction Reaction by Porphyrin-Based Catalysts for Fuel Cells

In 2007, the field of oxygen reduction reaction (ORR) by porphyrins was partially reviewed by Y. Kiros. The new development reported under the current review is the effect of surface state (composition) on porphyrin’s activity toward oxygen reduction in fuel cells, and the highlight of the analogue of fuel cell cathode activity and the oxygen reduction activity in nature. This field also needs a fresh look vs. its overall importance. The porphyrins themselves are moderate oxygen reduction catalysts, and their activity needs to be enhanced. In perspectives of fuel cells, the methods that are practiced and reviewed here are the use of carbon and gold support, pyrolysis and co-deposition with transition metal oxides. Reasons for the porphyrin enhancements and catalysis have been scrutinized. Although great progress has been achieved, there are still some challenges ahead (concerning the ORR mechanism on porphyrins and the activity and stability enhancement for porphyrins to meet practical applications). Therefore, exploring ORR mechanisms on porphyrin, the continuation of the characterization efforts and enhancing porphyrins catalytic performance (a paper in preparation from this group), as well achieving better catalyst durability, are major focuses for fuel cell research in the future.

Gold supported cryptomelane-type manganese dioxide OMS-2 nanomaterials deposited on AISI 304 stainless steels monoliths for CO oxidation

Gold supported on cryptomelane-type OMS-2 catalysts deposited on AISI 304 stainless steels monoliths have been prepared for the first time, characterised and tested in the CO oxidation reaction. An easy and non-conventional method of incorporation of gold to the cryptomelane solid is used. This method allows the preparation of the monolithic catalysts without altering the structural and textural characteristics of the parent OMS-2 material. Although these catalysts do not show an optimal performance for the oxidation of CO, the presence of small gold particles enhances the catalytic performances of the cryptomelane producing promissory CO oxidation catalysts. The non-conventional gold deposition favours a partial loss of K+ into the channels, resulting in an increment of the average oxidation state of manganese which favours the catalytic behaviour of these kinds of materials. This study can be taken as a starting point to obtain very active gold catalysts supported on OMS-2 materials through the optimisation of the gold–support interaction and the decrease in the gold particle size.

Gold, palladium and gold–palladium supported nanoparticles for the synthesis of glycerol carbonate from glycerol and urea

Supported Au–Pd nanoparticles are shown to be effective catalysts for the transformation of glycerol into glycerol carbonate. The reaction of glycerol with urea to form glycerol carbonate is a very attractive reaction that utilises two inexpensive and readily available raw materials in a chemical cycle that, overall, results in the chemical fixation of carbon dioxide. Previous reports are largely based on the utilisation of high concentrations of metal sulphates or oxides, which suffer from low intrinsic activity and selectivity and limited recoverability due to the dissolution of the catalyst in the reaction media. We now report that magnesium oxide is an excellent support for gold and bimetallic gold–palladium nanoparticles for this reaction. The preparation method and pre-treatment affect the catalytic performance and a colloidal preparation route produces the most active catalysts.

Structural Characterization and Redox Catalytic Properties of Cerium(IV) Pyrochlore Oxides

Ce(IV) pyrochlore oxides have been prepared by hydrothermal synthesis, and the parent material, a sodium cerium titanate, has been studied using total neutron scattering. While analysis of Bragg diffraction is consistent with an average cubic pyroclore structure, the profile is broadened because of the crystal size of <10 nm. Analysis of the pair distribution function (PDF) produced by Fourier transformation of the total scattering yields a structural model consistent with formulation of the parent material as (Na0.33Ce0.53Ti0.14)2Ti2O7. This contains a proportion of A-site titanium, consistent with the measured bulk density of the material. The PDF also contains evidence that the short-range order of the pyrochlore structure is disordered, with oxide anions displaced from the positions of the ideal Fd3m pyrochlore structure to give local symmetry F43m. These observations are supported by static (broadline) solid state 49Ti NMR measurements on a 49Ti isotopically enriched sample, which showed a dominant, narrow resonance at an apparent shift of δ – 912 ppm and a second minor resonance consistent with A-site titanium. Sn(IV) doping of the pyrochlore phase is possible by one-step hydrothermal synthesis: this gives a series of materials with a maximum tin content of Sn:Ti = 0.4:0.6, for which 119Sn solid-state NMR confirms the presence of octahedral, B-site Sn(IV), and powder X-ray diffraction shows an associated expansion of the pyrochlore lattice. Temperature programmed reduction/oxidation studies of the materials reveal that after an activation cycle the parent pyrochlore shows a reversible low temperature reduction at <200 °C, more facile than ceria itself. The Sn-doped analogues also show a low temperature reduction, but on continued heating collapse irreversibly to yield a mixture of products that includes SnO. The parent pyrochlore has been tested as a support for gold in the water gas shift reaction and shows a lower temperature conversion of H2O and CO to H2 and CO2 than a ceria sample of similar surface area.

CuxCryOz mixed oxide as a promising support for gold – The effect of Au loading method on the effectiveness in oxidation reactions

CuxCryOz containing copper–chromium oxide spinel and CuO was used as a support for gold loaded by different methods: deposition–precipitation using KOH, deposition–precipitation using urea and gold–sol method with tetrakis(hydroxymethyl)phosphonium chloride. The technique of modification with gold determined not only the Au particle size (the smallest if gold–sol method was used) but also the number of oxygen vacancies and copper concentration on the surface. All these parameters were considered in the study of CO, glycerol and methanol oxidation. The size of gold particles is a key feature determining the activity in the oxidation of CO. Glycerol oxidation is also sensitive to this parameter but less than CO oxidation. The oxidation of methanol is not influenced by the presence of gold and it occurs on the CuxCryOz support.

Gold versus platinum on ceria–zirconia mixed oxides in oxidation of ethanol and toluene

The Ce–Zr mixed oxides have been examined as supports for platinum and gold in oxidation of ethanol and toluene. A weight ratio of Ce/Zr in the synthesized supports was 1/1. Two supported noble metals with a different loading (2.5 and 0.3 wt.%) were compared to each other as well as to selected industrial catalysts (HHC-5557 and VOC-1544). Whatever the metal content was, Pt catalysts were always more active in oxidation of ethanol and toluene than Au catalysts. Better reductive capability of platinum was confirmed by H 2-TPR profiles and a higher activity of platinum may also be linked to changes in surface basic properties (a higher amount of basic centers) illustrated by CO 2-TPD profiles. Deposition of gold on Ce–Zr mixed oxide resulted in a formation of certain amounts of crystalline Au phase detected by X-ray diffraction while the deposition of platinum did not produce any crystalline Pt phase. As observed by FE-SEM, part of Au was well dispersed but significant amount of Au was present as inactive crystals. Platinum catalysts were comparable or even more active than industrial catalysts (50% conversion of ethanol was achieved with 2.5Pt/CeZr(1) at 99 °C). On the other hand, gold catalysts proved the best selectivity in oxidation of ethanol.

Enhanced electrocatalytic activity of cubic Pd nanoparticles towards the oxygen reduction reaction in acid media

The electrochemical reduction of oxygen on cubic Pd nanoparticles (PdNPs) was studied in acid solution using the rotating disk electrode (RDE) method. The electrocatalytic properties of Pd nanocubes were compared with those of spherical PdNPs and bulk Pd. The morphology of PdNPs was examined by transmission electron microscopy (TEM). For electrochemical experiments, PdNPs were deposited on a gold support and oxidation of pre-adsorbed CO on Pd was employed for cleaning the surface of the nanoparticles. The Pd nanocubes displayed superior electrocatalytic activity towards the oxygen reduction reaction (ORR), exhibiting a threefold increase in the specific activity in comparison with spherical PdNPs and bulk palladium. Four-electron reduction of oxygen to water was observed on the Pd catalysts studied.

Label-Free Detection of DNA-Binding Proteins Based on Microfluidic Solid-State Molecular Beacon Sensor

A solid-state molecular beacon using a gold support as a fluorescence quencher is combined with a polydimethylsiloxane (PDMS) microfluidic channel to construct an optical sensor for detecting single-stranded DNA binding protein (SSBP) and histone protein. The single-stranded DNA-Cy3 probe or double-stranded DNA-Cy3 probe immobilized on the gold surface is prepared for the detection of SSBP or histone, respectively. Due to the different quenching ability of gold to the immobilized single-stranded DNA-Cy3 probe and the immobilized double-stranded DNA-Cy3 probe, low fluorescence intensity of the attached single-stranded DNA-Cy3 is obtained in SSBP detection, whereas high fluorescence intensity of the attached double-stranded DNA-Cy3 is obtained in histone detection. The amounts of SSBP in sample solutions are determined from the degree of fluorescence recovery of the immobilized single-stranded DNA-Cy3 probe, whereas that of histone in sample solutions is determined from the degree of fluorescence quenching of the immobilized double-stranded DNA-Cy3 probe. Using this approach, label-free detection of target proteins at nanomolar concentrations is achieved in a convenient, general, continuous flow format. Our approach has high potential for the highly sensitive label-free detection of various proteins based on binding-induced conformation changes of immobilized DNA probes.

Spectrochemical Characterization of Thin Layers of Lipoprotein Self-Assembled Films on Solid Supports Under Oxidation Process

Low density lipoprotein self-assembled layers on gold support, proposed as model for oxidation studies, were subjected to oxidation processes using different oxidative agents: 2,2′-Azobis(2methylpropionamidine)dihydrochloride, atmospheric oxygen, and metal-induced oxidation. The freshly prepared and the oxidized layers were characterized by X ray photoelectron spectroscopy (XPS), Fourier-Transformed infrared spectroscopy, and Matrix-Assisted Laser Desorption/Ionization-Time of Flight (MALDI-ToF) mass spectrometry to discriminate the effects of oxidative reagents. Data obtained from FTIR and MALDI spectra proved the lipoperoxide formation subsequent to reactive oxygen species attack and the opportunity to use the model to discriminate between oxidation toxicity.

Impact of the Gold Support on the Electrocatalytic Oxidation of Sugars at Enzyme‐Modified Electrodes

AbstractThe influence of gold support on the bioelectrocatalytic activity of glucose oxidase and cellobiose dehydrogenase immobilized on self‐assembled monolayer‐modified high surface area gold electrodes such as rough gold and gold nanoparticles has been studied. The two types of enzyme‐modified electrodes showed very high activity towards sugar oxidation. However, it has been shown that the largest part of this electrocatalytic activity comes from the underlying gold surface. These findings are of special importance for bioelectrochemical studies of enzymatic electrodes, where the immobilization support might show electrocatalytic properties toward the substrates of investigated enzymes.

Ion dynamics in the pseudocapacitive reaction of hydrous ruthenium oxide. Effect of the temperature pre-treatment

Pseudocapacitive redox reaction of hydrous ruthenium oxide was investigated by the combined electrochemical and quartz crystal nanobalance measurements on gold support in H2SO4 and Na2SO4 solutions. The results show that the pseudocapacitance arises from at least two different Faradaic reactions with significant influence of double layer capacitance. All three processes simultaneously take place during charging/discharging reaction, but their contribution vary depending on the electrolyte used, the temperature pre-treatment and on the potential range. One Faradaic reaction releases protons during oxidation reaction resulting in the electrode mass decrease, while another Faradaic reaction results in the chemical binding of water leading to the mass gain during the oxidation reaction. The former reaction is favoured in acidic electrolyte and at lower anodic potentials, and the latter reaction proceeds predominantly in neutral media and at higher anodic potentials. The influence of annealing temperatures on the characteristics of the redox reaction of hydrous ruthenium oxide, as well as on its capacitance, was confirmed. It was demonstrated that specific capacitances of hydrous ruthenium oxide could achieve values as high as 1500Fg−1, provided that conditions of good electronic conductivity among RuO2 particles, as well as good electrical contact between gold and RuO2, are met.

Electrosynthesis of thin sol–gel films at a three-phase junction

Thin, functionalised silica films of between 4 and 15 nm thickness were prepared by sol–gel processing at an electrode organic phase aqueous phase junction by slow withdrawal of a conducting support through the liquid–liquid interface. Protons were electrogenerated in the aqueous phase and catalysed the hydrolysis of the sol–gel precursor in the organic phase. The film was characterised using atomic force microscopy, scanning electron microscopy, ellipsometry, infrared spectroscopy, voltammetry and scanning electrochemical microscopy. The thickness, electrodeposited on gold, was determined to be less than 10 nm and the density of imidazolium functional groups was estimated to be 1.2 molecules nm −2. The film obtained on ITO is approximately twice thicker compared to the gold support.

NO and C 3H 6 adsorption and coadsorption in oxygen excess—A comparative study of different type zeolites modified with gold

Non-acidic NaY, and acidic H-Beta and H-ZSM-5 with various Si/Al ratios were used as supports for gold loaded by deposition-precipitation method. Acidity of the pristine supports and Au/zeolites was estimated from adsorption of pyridine followed by FTIR spectroscopy measurements. NO selective reduction with propene (SCR-HC) was studied by the use of FTIR technique. Adsorption and co-adsorption of the reagents of NO SCR-HC (NO, C 3H 6 and O 2) allowed a discussion of the reaction pathways. The catalytic behaviour of NaY referring to the intermediate formed was not significantly changed by gold modification and Au/NaY did not activate the partial oxidation of propene in the absence of NO. Au particles in Au/Na-Y play an important role in the total oxidation to CO 2. The role of Brønsted acidity in Au/H-Beta and Au/H-ZSM-5 is on the oxidation of NO towards various intermediates (NO 2 −/NO 3 −, N 2O 4, NO +) and their further interaction with propene, whereas gold species enhance this process by inducing formation of additional active complex (Au n+ -NO). Moreover, gold species are responsible for the second reaction pathway via primary partial oxidation of propene to oxygenates and further reaction with NO and R-CN and R-NCO active intermediates as observed on Au/H-Beta and Au/H-ZSM-5.

Catalytic Performance of SO&lt;sub&gt;2&lt;/sub&gt; by Colloidal Gold Supported on Nano γ-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;

A new catalyst of gold supported on nanometal oxide for oxidation of SO2 was developed. Deposition-precipitation method was used to prepare gold-based catalysts. The catalytic activity of the catalysts was evaluated by determining the concentration of SO2 with gas chromatography under reaction temperature from 100 to 700°C. The results showed that there was an enhancement of catalytic activity when gold nanoparticles were dispersed on the surface of nano-metal oxides, furthermore, γ-Fe2O3 showed the highest activity as the support of the colloidal gold supported catalysts among the nanometal oxides including γ-Fe2O3, Fe2O3, ZnO, and Al2O3. It was also found that water vapour in the reaction enhanced the catalytic activity of Au/γ-Fe2O3. The Au/γ-Fe2O3 was characterized by XRD and FTIR methods, which indicated that the gold nanoparticles were dispersed on the γ-Fe2O3 support and sulfate species were formed on the surface of catalysts.

Mesoporous Pt and Pt/Ru alloy electrocatalysts for methanol oxidation

Mesoporous Pt and Pt/Ru catalysts with 2D-hexagonal mesostructure were synthesized using a triblock poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) copolymer (Pluronic F127 ®) template, on a gold support. Large electrochemical surface areas were observed for the catalysts prepared at high overpotentials. Compared to the Pt catalyst, the Pt/Ru alloy containing 3 at% of Ru exhibited lower onset potential and more than three times the limit mass activity for methanol oxidation. This behavior is assigned to the larger pore size of the mesoporous Pt and Pt/Ru catalysts obtained with this template that seems to improve the methanol accessibility to the active sites compared to those obtained using lyotropic liquid crystals.

Nano-Jewels in Biology. Gold and Platinum on Diamond Nanoparticles as Antioxidant Systems Against Cellular Oxidative Stress

Diamond nanoparticles (DNPs) obtained by explosive detonation have become commercially available. These commercial DNPs can be treated under Fenton conditions (FeSO(4) and H(2)O(2) at acidic pH) to obtain purer DNP samples with a small average particle size (4 nm) and a large population of surface OH groups (HO-DNPs). These Fenton-treated HO-DNPs have been used as a support of gold and platinum nanoparticles (≤2 nm average size). The resulting materials (Au/HO-DNP and Pt/HO-DNP) exhibit a high antioxidant activity against reactive oxygen species induced in a hepatoma cell line. In addition to presenting good biocompatibility, Au/HO- and Pt/HO-DNP exhibit about a two-fold higher antioxidant activity than glutathione, one of the reference antioxidant systems. The most active material against cellular oxidative stress was Au/HO-DNP.

Electrocatalytic activity of supported gold nanoparticles toward CO oxidation: The perimeter effect of gold–support interface

The gold nanoparticles (AuNPs) sputtered on indium tin oxide (ITO) were used to investigate the origin of the high catalytic activity of AuNPs toward electrooxidation of CO in alkali media. We demonstrated that the catalytic activity is closely related to the gold–ITO perimeter, which represents only a very small percentage of the total surface area of AuNPs. Increasing the perimeter-to-surface ratio of the ITO-supported AuNPs leads to an increase of catalytic activity. This work provides a potential strategy to further promote the catalytic activity of AuNPs in the electrochemical system.

Some More Observations on the Unique Electrochemical Properties of Electrode–Monolayer–Nanoparticle Constructs

Physical and electrochemical properties of gold nanoparticle-based electrodes are highlighted. Polycrystalline gold electrodes are passivated by a self-assembled monolayer, then the immobilization of gold nanoparticles "switch on" the electrochemical reactivity of ruthenium. Herein, gap-mode Raman studies show that the location of the nanoparticles is on the top of the monolayer, meaning that the "switching on" cannot be attributed to a direct electrical contact between nanoparticles and the gold support. This "switching on" feature is also not affected by the size of the gold nanoparticles with a range of diameters between 4 and 67 nm. Further, the charge of the nanoparticles is investigated by grafting chemical groups onto the nanoparticles which is observed to alter the electron-transfer kinetics. The variation in rate constant however is insufficient to attribute the "switching on" phenomenon to a possible adsorption of the redox species onto the nanoparticles.

Effect of preparation method on the catalytic activity of Au/CeO 2 for VOCs oxidation

The Au/CeO 2 catalysts were synthesized by co-precipitation (CP), deposition-precipitation (DP) and metallic colloids deposition (MCD) method, and tested for oxidation of volatile organic compounds (VOCs). It was revealed that the Au/CeO 2 catalyst prepared by DP method was the most efficient catalyst towards the total oxidation of toluene. The Au/CeO 2 catalysts had obviously high catalytic activity, and the best results was obtained on 3 wt.% Au/CeO 2 catalyst prepared by DP method. These catalysts were characterized by means of specific surface area (BET), atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). XRD data showed that only metallic Au phase existed in the catalysts, and the size of gold particles played a crucial role in the catalytic conversion of toluene. The catalytic activity of Au/CeO 2 was related to the interaction between gold particles and supports, and the capability of gold particles to weaken the surface Ce-O bonds adjacent to Au atoms. This interaction enhanced the reactivity of the CeO 2 surface capping oxygen which was involved in volatile organic compounds oxidation.

Catalytic performance of niobium species in crystalline and amorphous solids—Gas and liquid phase oxidation

This paper is devoted to the role of niobium, located in crystalline and amorphous catalysts, in catalytic oxidation reactions. Bulk niobium(V) oxides (crystalline and amorphous), NbMCM-41, NbSBA-3, NbSBA-15 and NbY materials were used as catalysts in gas phase oxidation of methanol with oxygen, liquid phase oxidation of glycerol with oxygen and liquid phase oxidation of cyclohexene with hydrogen peroxide. When H 2O 2 was applied as an oxidation agent the amorphous materials containing niobium species were the most effective catalysts because Nb in such catalysts strongly interacts with H 2O 2 resulting in the formation of active O Nb(V)O 2 radicals. It was not the case for crystalline catalysts containing niobium. The results obtained for Nb-containing materials used as supports for copper, gold and binary Sb–V–O x oxides indicated that niobium species promotes stabilization of the active species loaded. Moreover, it was shown that gold loaded on crystalline niobia increases the catalytic activity in dehydrogenation of methanol and glycerol, which is the first step of their oxidation with oxygen.