Nanosized Composite Pt‐Ru Catalysts for Production of Modern Modified Fuels

A Pt‐Ru/2 % Ce/(θ+α)‐Al₂O₃ nanosized catalyst was developed for selective catalytic oxidation of CH₄ to synthesis gas. The process was carried out entirely with the formation of synthesis gas at high selectivity by H₂ and CO with H₂:CO = 2.0 ratio only at Pt:Ru = 2:1 or 1:1 atomic ratio and short contact time on Pt‐, Ru‐, and Pt‐Ru low‐percentage catalysts. Samples, which were reduced by H₂ at high temperature, presented a mixture of Pt‐, Ru‐, and Pt‐Ru nanosized particles, its alloy in the mixed catalysts. The correlation between experimental results and data of physicochemical research was established. The activity together with physicochemical properties and quantum chemical calculations for the developed low‐percentage Pt‐Ru catalysts was investigated.     

N2O Decomposition Catalysed by Transition Metal Ions

The ignition processes for the catalytic partial oxidation of methane (POM) to synthesis gas over oxidic nickel catalyst (NiO/Al₂O₃), reduced nickel catalyst (Ni⁰/Al₂O₃), and Pt-promoted oxidic nickel catalyst (Pt–NiO/Al₂O₃) were studied by the temperature-programmed surface reaction (TPSR) technique. The complete oxidation of methane usually took place on the NiO catalyst during the CH₄/O₂ reaction, even with a pre-reduced nickel catalyst, and Ni⁰ is inevitably first oxidized to NiO if the temperature is below the ignition temperature. It is above a certain temperature that Ni⁰ is formed again, which leads to the start of the POM. The POM can be initiated at a much lower temperature on a Pt–NiO catalyst because of Pt promotion of the reduction of NiO. The POM in a fluidized bed can be easily initiated due to the addition of Pt.     

Hydrogen production by partial oxidation of methanol over bimetallic Au–Ru/Fe2O3 catalysts

Hydrogen production by partial oxidation of methanol (POM) was investigated over Au–Ru/Fe₂O₃ catalyst, prepared by deposition–precipitation. The activity of Au–Ru/Fe₂O₃ catalyst was compared with bulk Fe₂O₃, Au/Fe₂O₃ and Ru/Fe₂O₃ catalysts. The reaction parameters, such as O₂/CH₃OH molar ratio, calcination temperature and reaction temperature were optimized. The catalysts were characterized by ICP, XRD, TEM and TPR analyses. The catalytic activity towards hydrogen formation is found to be higher over the bimetallic Au–Ru/Fe₂O₃ catalyst compared to the monometallic Au/Fe₂O₃ and Ru/Fe₂O₃ catalysts. Bulk Fe₂O₃ showed negligible activity towards hydrogen formation. The enhanced activity and stability of the bimetallic Au–Ru/Fe₂O₃ catalyst has been explained in terms of strong metal–metal and metal–support interactions. The catalytic activity was found to depend on the partial pressure of oxygen, which also plays an important role in determining the product distribution. The catalytic behavior at various calcination temperatures suggests that chemical state of the support and particle size of Au and Ru plays an important role. The optimum calcination temperature for hydrogen selectivity is 673 K. The catalytic performance at various reaction temperatures, between 433 and 553 K shows that complete consumption of oxygen is observed at 493 K. Methanol conversion increases with rise in temperature and attains 100% at 523 K; hydrogen selectivity also increases with rise in temperature and reaches 92% at 553 K. The overall reactions involved are suggested as consecutive methanol combustion, partial oxidation, steam reforming and decomposition. CO produced by methanol decomposition is subsequently transformed into CO₂ by the water gas shift and CO oxidation reactions.     

Electrochemical Reduction of Oxygen on Carbon Supported Pt and Pt/Ru Fuel Cell Electrodes in Alkaline Solutions

A study of O₂ reduction in 1 M NaOH solution at gas diffusion electrodes made from carbon supported Pt and Pt/Ru catalysts is reported. Two Tafel regions were observed for both the Pt and Pt/Ru electrodes. Although the same mechanism was suggested for oxygen reduction on both Pt and Pt/Ru catalysts, the O₂ reduction activity was lower on Ru. Electrochemical Impedance Spectroscopy (EIS) analysis was carried out at different potentials and showed the significant contribution of diffusion on the reaction process and kinetics. The effect of methanol on O₂ reduction was investigated in solutions containing various concentrations of methanol. The electrode performance deteriorated with increasing methanol concentration because of a mixed cathode potential. The methanol tolerance, i. e., the methanol concentration which polarises the O₂ reduction reaction for O₂ reduction, at the Pt/C electrode with a Pt loading of 1.2 mg cm^–2 is 0.2 M methanol in 1 M NaOH.     

Effect of Acid–Base Properties on the Catalytic Activity of Pt/Al2O3 Based Catalysts for Diesel NO Oxidation

The activity of Pt catalysts supported on Al₂O₃ modified with various acid–base additives has been investigated for oxidation of NO to NO₂. Although Pt dispersion was changed by the additives, there was no clear effect of Pt dispersion on the catalytic activity. The measurement of solid acid–base properties of the modified Pt/Al₂O₃ indicated that the NO oxidation activity increased by the increase of surface density of strong acid sites and decreased by the increase of basic sites. It was suggested that platinum on the acidic supports keeps its highly active metallic state for NO oxidation, while the formation of nitrate/nitrite on the basic supports inhibits the reaction on the Pt surface.     

Effect of Pt Dispersion on the Catalytic Activity of Supported Pt Catalysts for Diesel Hydrocarbon Oxidation

The catalytic activity of Pt/Al₂O₃ for the total oxidation of hydrocarbon mixture of n-decane and 1-methylnaphthalene was strongly dependent on the Pt dispersion. The maximum hydrocarbon oxidation activity was achieved for Pt/Al₂O₃ with Pt dispersion (D_Pt) of 0.39. On the other hand, the activity of Pt/ZrO₂ monotonously decreased with decreasing Pt dispersion from 1.00 to 0.09. In situ FT-IR spectroscopy suggested that the presence of plural Pt species in metallic state with slight different electric state, which well catalyze the formation of acrylate species as an intermediate, is responsible for the high catalytic activity of Pt/Al₂O₃ with D_Pt = 0.39.     

Effective Catalysts for Wet Oxidation Of Formic Acid by Oxygen and Ozone

The catalytic wet-air oxidation and catalytic ozonation of a formic acid solution have been studied at room temperature using more than 20 kinds of catalysts including Pt/C, Pt/Al₂O₃, Pd/Al₂O₃, etc. The most effective catalyst was Pt/Al₂O₃. The apparent activation energies for the catalytic wet-air oxidation and ozonation on Pt/Al₂O₃ were both about 5 kcal/mol. This fact suggests that these reactions on the catalyst were diffusion controlled, and thus, the potential of the catalyst is likely much higher.     

Improvement of thermal stability of NO oxidation Pt/Al2O3 catalyst by addition of Pd

The present work has been undertaken to tailor Pt/Al₂O₃ catalysts active for NO oxidation even after severe heat treatments in air. For this purpose, the addition of Pd has been attempted, which is less active for this reaction but can effectively suppress thermal sintering of the active metal Pt. Various Pd-modified Pt/Al₂O₃ catalysts were prepared, subjected to heat treatments in air at 800 and 830 °C, and then applied for NO oxidation at 300 °C. The total NO oxidation activity was shown to be significantly enhanced by the addition of Pd, depending on the amount of Pd added. The Pd-modified catalysts are active even after the severe heat treatment at 830 °C for a long time of 60 h. The optimized Pd-modified Pt/Al₂O₃ catalyst can show a maximum activity limited by chemical equilibrium under the conditions used. The bulk structures of supported noble metal particles were examined by XRD and their surface properties by CO chemisorption and EDX-TEM. From these characterization results as well as the reaction ones, the size of individual metal particles, the chemical composition of their surfaces, and the overall TOF value were determined for discussing possible reasons for the improvement of the thermal stability and the enhanced catalytic activity of Pt/Al₂O₃ catalysts by the Pd addition. The Pd-modified Pt/Al₂O₃ catalysts should be a promising one for NO oxidation of practical interest.     

The effects of Pt promotion on the oxi-reduction properties of alumina supported nickel catalysts for oxidative steam-reforming of methane: Temperature-resolved XAFS analysis

The effects of Pt trace addition on the oxi-reduction properties of the Ni/Al₂O₃ and Ni/La–Al₂O₃ catalysts during partial oxidation of methane (POM) and autothermal reforming of methane (ATR) were investigated. The xPt–Ni/yLa–Al₂O₃ catalysts containing 15 wt% of Ni, 0 or 12 wt% of La and 0 or 0.05 wt% of Pt were characterized by temperature-resolved X-ray absorption near edge structure (XANES) spectroscopy under various atmospheres.The in situ XANES analysis for Pt–Ni/Al₂O₃ under H₂ and CO revealed that the presence of Pt sites can initiate the NiO reduction process by rapid dissociation of H₂ and migration of atomic H to the NiO surface by hydrogen spillover. On the other hand, in situ XANES analysis under CH₄ showed that the presence of Pt sites induces the activation of the methane, probably by initial dissociation of methane (CH₄ → CH₃ + H) followed by migration of atomic H to the NiO surface. In situ XANES experiments under a POM mixture demonstrate that Pt has an important role keeping Ni in the metallic state. The catalytic test results for POM and ATR demonstrate that Pt is an important promoter to maintain Ni in the metallic state at the inlet region of the catalytic bed, where CH₄ and O₂ coexist.     

Co/Al2O3 catalysts promoted with noble metals for production of hydrogen by methane steam reforming

The effect of noble metal addition on the catalytic properties of Co/Al₂O₃ was evaluated for the steam reforming of methane. Co/Al₂O₃ catalysts were prepared with addition of different noble metals (Pt, Pd, Ru and Ir 0.3 wt.%) by a wetness impregnation method and characterized by UV–vis spectroscopy, temperature programmed reduction (TPR) and temperature programmed oxidation (TPO) of the reduced catalysts. The UV–vis spectra of the samples indicate that, most likely, large amounts of the supported cobalt form Co species in which cobalt is in octahedral and tetrahedral symmetries. No peaks assigned to cobalt species from aluminate were found for the promoted and unpromoted cobalt catalysts. TPO analyses showed that the addition of the noble metals on the Co/Al₂O₃ catalyst leads to a more stable metallic state and less susceptible to the deactivation process during the reforming reaction. The Co/Al₂O₃ promoted with Pt showed higher stability and selectivity for H₂production during the methane steam reforming.     

Complete Oxidation of Methane at Low Temperature over Pt Catalysts Supported on High Surface Area SnO2

The catalytic activity of Pt catalysts supported on high surface area tin(IV) oxide in the complete oxidation of CH₄ traces under lean conditions at low temperature was studied in the absence and in the presence of water (10 vol.%) or H₂S (100 vol.ppm). Their catalytic properties were compared to those of Pd/Al₂O₃ and Pt/Al₂O₃. In the absence of H₂S in the feed, Pt/SnO₂appears as a very promising catalyst for CH₄ oxidation, being even significantly more active under wet conditions than the best reference catalyst, Pd/Al₂O₃. Catalysts steamed-aged at 873 K were also studied in order to simulate long term ageing in real lean-burn NGV exhaust conditions. To this respect, Pt/SnO₂ is slightly less resistant than Pd/Al₂O₃. In the presence of H₂S, Pt/SnO₂catalysts are rapidly and almost completely poisoned, comparably to Pd/Al₂O₃and the catalytic activity is hardly restored upon oxidising treatment below 773 K. A synergetic effect between Pt and specific surface SnO₂sites active in CH₄oxidation is proposed to explain the superior catalytic behaviour of Pt/SnO₂.     

Graphite Electrodes Modified with Platinum‐Nickel Nano‐Particles for Methanol Oxidation

Methanol electro‐oxidation is investigated at graphite electrodes modified with various platinum and nickel nano‐particle deposits using cyclic voltammetry. The modified electrodes are prepared by the simultaneous electrodeposition of metals from their salt solutions using potentiostatic and galvanostatic techniques. They show enhanced catalytic activity towards methanol oxidation in KOH solution. The catalytic activity of platinum nano‐particles is found to be significantly affected by the presence of relatively small amounts of nickel deposits. A comparison is made between the electrocatalytic activity of Pt/C and (Pt‐Ni)/C electrodes. The results show that the methanol electro‐oxidation current increases with an increase in the nickel content. In particular, the highest catalytic activity is achieved for platinum to nickel deposits of 95%:5% (wt.‐%), in other cases the catalytic activity decreases. It is found that Ni enhances the catalytic activity of Pt by increasing the number of active sites, as well as through an electron donation process from Ni to Pt. This process takes place once the nickel hydroxide (Ni(OH)₂)/nickel oxy‐hydroxide (NiOOH) transformation begins. The effect of the methanol concentration on the methanol oxidation reaction is investigated. The order of reaction, with respect to methanol, at the modified (Pt‐Ni)/C electrode is found to be 0.5.     

Amplification of Periodic Temperature Disturbances in a Packed‐Bed Reactor: CO Oxidation over a CuO/Al2O3 Catalyst

Amplification of periodic variations of input temperature in a product‐inhibited reaction — CO oxidation over CuO‐γ‐Al₂O₃ — was investigated experimentally in an insulated packed‐bed reactor. At steady state the temperature profile was elongated compared with that of a reactant‐inhibited CO oxidation over Pt/Al₂O₃, studied elsewhere. Under periodic operation, amplitudes of the resulting travelling temperature waves, monitored downstream from the reaction front, were amplified to a greater extent than those in the reactant‐inhibited CO oxidation over Pt/Al₂O₃. The magnitude of the amplification depended on the perturbation frequency and showed resonance behaviour. The magnitude decreased monotonically with increasing perturbation amplitude.     

Characterisation and microstructure of Pd and bimetallic Pd–Pt catalysts during methane oxidation

The catalytic oxidation of methane was studied over Pd/Al₂O₃ and Pd–Pt/Al₂O₃. It was found that the activity of Pd/Al₂O₃ gradually decreases with time at temperatures well below that of PdO decomposition. The opposite was observed for Pd–Pt/Al₂O₃, of which the activity decreases slightly with time. Morphological studies of the two catalysts showed major changes during operation. The palladium particles in Pd/Al₂O₃ are initially composed of smaller, randomly oriented crystals of both PdO and Pd. In oxidising atmospheres, the crystals become more oxidised and form larger crystals. The activity increase of Pd–Pt/Al₂O₃ is probably related to more PdO being formed during operation. The particles in Pd–Pt/Al₂O₃ are split into two different domains: one with PdO and the other likely consisting of an alloy between Pd and Pt. The alloy is initially rich in palladium, but the composition changes to a more equalmolar Pd–Pt structure during operation. The ejected Pd is oxidised into PdO, which is more active than its metallic phase. The amount of PdO formed depends on the oxidation time and temperature.     

Electrochemical effect of gold nanoparticles on Pt/α-Fe2O3/C for use in methanol oxidation in alkaline solution

A catalyst containing gold nanoparticles with Pt/α-Fe₂O₃/C was prepared by a co-precipitation method and its catalytic activity for the oxidation of methanol, formaldehyde, and formic acid in alkaline solutions was evaluated by an electrochemical method and high-performance liquid chromatography (HPLC). The addition of gold nanoparticles improved catalytic activity only for the oxidation of methanol and formaldehyde, and not for the oxidation of formic acid. HPLC analysis was performed for methanol oxidation to detect the oxidative products. In HPLC analysis, only formate anion could be detected in the electrolyte solution and the ratio of formate anion obtained to the total passed charge in Pt/nano-Au/α-Fe₂O₃/C was less than that in Pt/C, indicating that formic acid is not the final product of methanol oxidation. These results show that gold nanoparticles promoted methanol oxidation up to CO₂.     

Catalytic oxidation for carbon-black simulating diesel particulate matter over promoted Pt/Al2O3 catalysts

Catalytic oxidation activity of carbon-black (CB) simulating the soot of diesel particulate matters to CO₂ over 3Pt/Al₂O₃, 3Pt5Mn/Al₂O₃ and 3Pt/30Ba–Al₂O₃ catalysts is investigated with model gases of diesel emission. In case of the large amount of CB compared to the amount of catalyst (3/1, w/w) in the mixture sample, insufficient oxygen at the point of sudden increase in the amount of CO₂ is leaded to the partial oxidation using the lattice oxygen of the catalyst. And the peaks of CO₂ after the first peak were attributed to the regional combustion of the CB, which was not in contact with catalyst particles. The fresh 3Pt5Mn was estimated to the oxidation states on the catalyst surface by XPS. For used sample at 700 °C, the BEs of Pt 4d5 was revealed to metallic state Pt(0) (314.4 eV) in a predominant levels compared with Pt(II) (317.3 eV). While BEs of Mn 2p were similar to that obtained from the fresh 3Pt5Mn. It is suggested that Pt is in charge of the roles in CB-oxidation, using the lattice oxygen of the catalyst. Two-stage catalytic system with the strategies of promoting the soot oxidation and NO_x reduction, simultaneously, were composed of the CB oxidation catalyst and the diesel oxidation catalyst. The catalytic oxidation of CB was accelerated by activated oxidants and exothermic reaction resulted from the diesel oxidation catalyst, which lies in upstream of two-stage. But the system with the CB oxidation catalyst sited in the upstream showed the initiation of CB oxidation at a lower temperature than the other case. Two-stage catalytic system composed of 3Pt5Mn with CB in the upstream and DOC in the downstream showed high oxidation activity with 95% consumption rate of CB to the total loaded CB in the range of 100–500 °C during the TPR process.     

Catalytic hydrogenation of linoleic acid over platinum-group metals supported on alumina

Catalytic activity and selectivity for hydrogenation of linoleic acid (cis-9,cis-12 18:2) were studied on Pt, Pd, Ru, and Ir supported on Al₂O₃. Stearic acid (18:0) and 10 different octadecenoic isomers (18:1) in the products could be separated completely by using a new capillary column coated by isocyanopropyl trisilphenylene siloxane for gas-liquid chromatography. The monoenoic acid isomers and dienoic acid isomers in the products on the various catalysts showed different distributions. The catalysts exhibited nearly equal selectivity for stearic acid formation. The 12-position double bond in linoleic acid has higher reactivity than the 9-position double bond in catalytic hydrogenation on platinum-group metal catalysts. In addition to hydrogenation products of linoleic acid, geometrical and positional dienoic acid isomers (trans-9,trans-12; trans-8,cis-12; cis-9,trans-13; trans-9,cis-13; cis-9,trans-12 18:2), due to isomerization of linoleic acid during hydrogenation, were contained in the reaction products. Ru/Al₂O₃ exhibited the highest activity for isomerization of linoleic acid with the noble metal catalysts. Conjugated octadecadienoic acid isomers have been observed in products of the reaction on Pt/Al₂O₃, Ru/Al₂O₃, and Ir/Al₂O₃. Catalytic activities of noble metals for positional and geometric isomerization of linoleic acid during hydrogenation decreased in the sequence of Ru ≥ Pt > Ir » Pd.     

Electrooxidation of methanol on platinum bonded to the solid polymer electrolyte,Nafion

The electrooxidation of methanol was enhanced on PtSn-SPE, PtRu-SPE and PtIr-SPE in sulfuric acid solution, when compared with the activity of Pt-SPE, which has already been shown to have a higher activity than a Pt electrode. SPE is an abbreviation for Nafion, a solid polymer electrolyte. It is suggested that this dual enhancement of the oxidation rate for PtSn-SPE and PtRu-SPE catalysts is due to the modification of the oxidation state of Pt by Sn and Ru and to the presence of H₂O and CH₃OH, both modified by the SPE matrix. This modification appears to weaken their hydrogen bonds in solution. Both Pt and Ir have catalytic properties for methanol oxidation, but a PtIr-SPE catalyst showed a more enhanced catalytic activity than either of them. This will be discussed in terms of Ir, oxidized at relatively low positive potentials, assisting the redox process of Pt⁰/Pt²⁺ or Pt²⁺/Pt⁴⁺ in the SPE matrix, where CH₃OH and H₂O are present in modified forms. For comparison, IrPd-SPE was also used as an electrode and showed a higher activity than Ir alone, although Pd did not have any activity toward methanol oxidation in sulfuric acid solution. Irrespective of the kind of Pt-SPEs, the Tafel slope was approximately 120 mV; the CH₃OH concentration dependence was of the order of 0.2–0.6. The pH dependence was nearly 0.5 against NHE. The activation energy of the Pt-SPEs for the reaction ranged between 20 and 33 kJ mol^–1.     

Low Temperature Steam Reforming of Ethanol Over Supported Noble Metal Catalysts

The catalytic activity of M/Al₂O₃ catalysts for the reaction of steam reforming of ethanol has been investigated in the temperature range of 300–450 °C. It has been found that the catalytic performance varies in the order of Pt > Pd > Rh > Ru, with Pt exhibiting high activity and selectivity toward hydrogen production, as well as long term stability at low temperatures. It is shown that the reaction occurs in a bifunctional manner, with the participation of both the dispersed metallic phase and the support. Ethanol interacts strongly with the Al₂O₃ carrier, promoting mainly ethanol dehydration, while in the presence of Pt, catalytic activity is shifted toward lower temperatures. Ethanol decomposition and dehydrogenation reactions dominate at low temperatures, while reforming, water-gas shift and methanation contribute significantly to product distribution.     

Catalytic degradation of aqueous Fischer–Tropsch effluents to fuel gas over oxide‐supported Ru catalysts and hydrothermal stability of catalysts

BACKGROUND: The catalytic degradation of aqueous Fischer–Tropsch (FT) effluents to fuel gas over Ru/AC has been investigated. In order to understand the catalytic performance and stability of oxide‐supported Ru catalysts, several oxide supports (titania, zirconia, γ‐alumina and silica) were selected for study, with a focus on the hydrothermal stability of catalysts. RESULTS: The catalytic efficiency for transforming the oxygenates in aqueous FT effluents to C₁–C₆ alkanes decreased in the order: Ru/ZrO₂～ Ru/TiO₂ > Ru/SiO₂ > Ru/Al₂O₃. The conversion of alcohols was greatly suppressed over Ru/γ‐Al₂O₃. The former two catalysts (Ru/ZrO₂ and Ru/TiO₂) exhibited enhanced efficiency and long‐term stability (400 h) relative to Ru/SiO₂ and Ru/Al₂O₃. N₂‐physisorption, XRD and SEM showed that titania and zirconia exhibited high structural stability in an aqueous environment. However, the structures of γ‐alumina and silica were unstable due to significant drop in surface area and adverse changes in surface morphology. Especially for the case of the Ru/γ‐Al₂O₃ catalyst, the γ‐alumina was transformed into boehmite structure after reaction, and metal leaching and carbon deposition were extensive. CONCLUSION: Ru/ZrO₂ or Ru/TiO₂ may be a promising alternative for degrading aqueous FT effluents due to their long‐term stability. Copyright © 2012 Society of Chemical Industry