Catalytic Activity Of Pt Catalysts Research Articles

Improved catalytic stability of Pt/TiO2 catalysts for methylcyclohexane dehydrogenation via selenium addition

To improve the catalytic activity of Pt catalysts for methylcyclohexane (MCH) dehydrogenation, which is utilized for hydrogen transportation, the effects of the addition of Se on the performance of Pt/TiO2 catalysts were investigated. In Se/Pt/TiO2 catalysts, even a small amount of Se addition (Se/Pt = 0.01) improved the catalyst stability. Se was highly dispersed on the Pt/TiO2 surface, without volatilizing in a reducing atmosphere at temperatures below 450 °C, and did not form an alloy with Pt. The analysis of adsorption-desorption characteristics revealed that the addition of Se promoted the desorption of products, including the main product, toluene. Moreover, an electron donation effect from Se to Pt was observed by FT-IR measurement after the reduction. The desorption characteristic caused by the electron donation effect suppressed the deterioration of the catalyst and allowed stable catalytic activity toward the MCH dehydrogenation reaction.

Influence of Carbon Support on Electronic Structure and Catalytic Activity of Pt Catalysts: Binding to the CO Molecule

Single-atom catalysts, especially with single Pt atoms, exhibit potentially improved catalytic activity as compared to metal clusters and metal surfaces. Here, the atop and bridged bondings of the CO molecule on the Pt/C system are studied. Vibrational frequencies, Mulliken populations, charge transfer, charge density differences, and density of states are examined to determine the influence of the carbon support on electronic properties and catalytic activity of the Pt adatom and dimer. Comparing orbital populations and the amount of electron transfer to/from the CO molecule shows that the net amount of electron transfer to the antibonding 2π* orbitals of the CO molecule is higher for the supported Pt dimer than for the substrate-free Pt dimer, which leads to a lower vibrational frequency and a larger C–O bond distance. The hybridization between the π orbitals of the polycyclic aromatic hydrocarbons surface and the d orbitals of the Pt adatoms is responsible for enhancing the back-donation of electrons t...

The Effect of Platinum Loading and Surface Morphology on Oxygen Reduction Activity

The catalytic activity of Pt catalysts towards the oxygen reduction reaction (ORR) was investigated on a catalyst system developed by thermally induced chemical deposition of Pt on carbon. The use of this deposition method made it possible to prepare a practical catalyst system with various Pt loadings on the support. Increasing the Pt loading caused a change in the Pt surface morphology which was confirmed by transmission electron microscopy (TEM) and CO stripping voltammetry measurements. The occurrence of a low and high-potential CO oxidation peak suggested the presence of Pt agglomerates and Pt nanoparticles, respectively. An increase in Pt loading lead to a subsequent decrease in the electrochemical surface area (ECSA, m2 Pt/gPt) as the platinum surface transitioned from isolated platinum nanoparticles to platinum agglomerates. The specific activity was found to increase with increasing Pt loadings, while the mass activity decreased with loading. The mass and specific activity data from this study was found to follow a ‘master curve’ obtained by the comparison of normalised activities from various different studies in the literature. Pt selectivity was also affected by Pt loading and hence Pt surface morphology. At low Pt loadings, i.e. large interparticle distances, the amount of H2O2 produced was significantly higher than for high Pt loadings. This confirms the presence of a ‘series reaction pathway’ and highlights the importance of the H2O2 desorption-readsorption mechanism on Pt nanoparticles and the ultimate role of Pt interparticle distance on the ORR mechanism.

One-pot Synthesis of PtSn Bimetallic Composites and Their Application as Highly Active Catalysts for Ethanol Electrooxidation.

PtSn nanoparticles with different molar ratio are fabricated by chemical reduction to form a relatively efficient catalyst for ethanol electrooxidation in an alkaline solution of KOH (1.0 m) containing C2 H5 OH (1.0 m). The surface composition and structure of the as-prepared catalysts are characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDX). Cyclic voltammogram (CV) and chronoamperometric (CA) measurements are used to evaluate the electrochemical activity and stability of the as-prepared catalysts. As the content of Sn in the catalysts changed, the catalysts showed different catalytic activity. The results indicate that the moderate addition of Sn can enhance the catalytic activity of Pt catalyst, and Pt3 Sn1 displays the highest catalytic activity and stability among the as-synthesized PtSn nanoparticles during the electrooxidation of ethanol.

Tailoring carbon xerogels' properties to enhance catalytic activity of Pt catalysts towards methanol oxidation

The work presented herein deals with the study of the influence of the synthesis conditions on the properties of carbon xerogels (CXGs). The study analyzes the effect of the composition of the mixture of carbon gel precursors and the pH on the porous structure, the arrangement of carbon, the surface chemistry and the electrical conductivity. Certain conditions allow obtaining CXGs with a high porosity, high ordering and polymerization degree. CXGs are used as Pt catalyst supports for the electro-oxidation of methanol. CXGs with the higher ordering and polymerization degree result in catalysts with low crystal sizes and good metallic distribution. Such catalysts show the highest activities towards methanol oxidation. CXG-supported Pt catalysts outperform a Vulcan-supported Pt catalyst prepared in the same conditions.

Carbon Support Modification for Improving Platinum Performance in PEMFC

With high activities for anodic electro-oxidation reaction and cathodic electro-reduction reactions, Platinum (Pt) has been the general choice of catalyst for low-temperature fuel cells. However, the insufficient durability and catalytic activity remain major obstacles to the widespread commercialization of fuel cell technology.1The catalytic activity and stability of Pt catalysts depend on many factors, among which the carbon supports play a crucial role. On Pt electrodes, since the electrocatalytic reactions are confined to the three phase boundary (TPB) regions, it is essential to build an efficient TPB. An efficient TPB, which ensures a good contact between reactants and catalysts and an easy transport of electron, ion, gas, and liquid, can simultaneously meet the requirements both of activity and utilization of Pt catalysts.2 Recently, we have devoted our research to synthesize carbon nanostructure supported platinum electrode to build an efficient TPB.3,4 Carbon nanostructure supports directly grown on the gas diffusion layer (GDL) ensures a fast electron, mass transport and low internal resistance creating an efficient TPB.3 Moreover, all the preparation processes were conducted in dry plasma atmosphere which could effectively avoid the cohesion of nanostructures induced by capillary force in the liquid-air interface of drying process.This integrated structure electrode which possesses ultra-low Pt loading, high Pt utilization and efficient TPB structure, is desirable for application in low-temperature fuel cells. In order to further improve the catalytic activities of the Pt catalysts, one of the strategies is creating strong catalyst-support interactions by functionalizing carbon support materials. Nitrogen (N) modification of carbon nanomaterial, which plays a critical role in improving Pt performance, has shown fascinating applications. We synthesized N-doped carbon nanofiber (CNF) supported platinum catalysts using an approach combined of plasma enhanced chemical vapor deposition and in situ plasma activation. This approach can successfully introduce nitrogen functionalities into carbon network, and at the same time, preserve the graphitic structure of carbon support. XPS results indicate that NH3 plasma modification mainly creates pyridinic nitrogen functionalities, while N2 plasma modification mainly increases the percentage of pyrrolic nitrogen in carbon network, suggesting a modification of certain nitrogen functionalities on carbon support. The oxidative CO-stripping peak potentials for Pt/CNF, Pt/CNF-N2 and Pt/CNF-NH3 are 0.67 V, 0.64 V and 0.62 V vs. SCE, respectively (Fig. 1). The negative shifts for peak potential suggest that the adsorbed CO can be more easily removed from Pt/CNF-NH3 and Pt/CNF-N2 electrodes than from Pt/CNF. The measurements of chronoamperometry were carried out and the results were in good agreement with the CO-stripping. The decay of the oxidation current densities on Pt/CNF-N2 and Pt/CNF-NH3 electrodes are slower than that of Pt/CNF, and the oxidation current densities at the end of the test on the Pt/CNF-NH3 are larger than that on the Pt/CNF-N2and Pt/CNF electrodes. N-modified Pt/CNF electrodes exhibit a better poisoning-resistance/durability ability than pristine Pt/CNF electrode, suggesting that the nitrogen functionalities in the carbon network may play an important role for anti-poisoning from intermediates. Fig.1. CO-stripping voltammetry in 1 M H2SO4 solution for Pt/CNF, Pt/CNF-N2, and Pt/CNF-NH3 at a scan rate of 50 mV s–1. Acknowledgements This research is financially supported by the National Nature Science Foundation of Anhui province (No. 1308085QA09) and National Nature Science Foundation of China (Nos. 11205202, 21203204, 11175214).

Bimetallic alloy Pt/Ag nanoparticles with enhanced catalytic activity for formic acid oxidation

Here, we report the synthesis of Pt/Ag bimetallic alloy catalyst through combining the ion implantation and electrodeposition method. Ag nanoparticles are employed as the seeds for the growth of Pt nanoparticles. Pt/Ag alloy catalyst demonstrates much higher catalytic activity than pure Pt catalyst, which is about three times more active on the basis of equivalent Pt electrochemically active surface area than that of the pure Pt catalyst. The ion implantation of Ag efficiently enhances the catalytic activity of Pt catalyst for formic acid oxidation.

Pt nanoparticles supported on mesoporous carbon nanocomposites incorporated with Ni or Co nanoparticles for fuel cells

We report the preparation and characterization of mesoporous carbon nanocomposites with Ni and Co nanoparticles incorporated into the pore walls, which are synthesized via template strategy by sucrose-impregnation and benzene chemical vapor deposition (CVD) routes separately. Pt nanoparticles supported on the nanocomposites for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in fuel cells are fabricated via hydrogen reduction method. It is found that the introduction of metal nanoparticles into the pore walls of carbon materials via both synthesis routes had negligible change in pore structure. Highly dispersed Pt nanoparticles supported on nanocomposites synthesized by sucrose-impregnation method shows better catalytic activities for both ORR and MOR than that on those by CVD method and greatly improve the limiting current densities for ORR. The promotional effect of Ni on the catalytic activity of Pt catalysts for both ORR and MOR is evidenced in nanocomposites obtained with sucrose-impregnation method, but not with CVD method. Interesting results revealed that Ni performed as a better promoter in MOR while Co is a better promoter in ORR. Our investigation not only provides further insight on the roles of Ni and Co in ORR and MOR, but also can assist the design and synthesis of the new nanostructured electrocatalyst supports.

Catalytic activity of Pt catalysts promoted by MnOx for n-hexane oxidation

The deep oxidation of n-hexane was studied over Pt catalysts with small and large Pt crystallites, promoted by MnOx. The Mn was deposited on the Pt/Al2O3 by deposition-precipitation method using two alkalis, ammonia and dimethylamine. The strength of the base influenced morphology and performances of Mn-Pt catalysts. Ammonia formed mostly spherical structure of manganese oxide, while dimethylamine created fibrous needle-like shape of MnOx, typical for cryptomelane phase of manganese oxide. This was confirmed by XPS results that show an oxidation state of Mn close to that for cryptomelane. The Pt-Mn catalysts were more active than catalysts containing Pt only. Promoting effect of MnOx is more pronounced for larger Pt crystallites. Among Pt-Mn samples, catalysts synthesized with dimethylamine exhibited the highest activities. Mobility and reactivity of oxygen from Pt–O–Mn sites associated with cryptomelane phase may be responsible for increased activity.

Novel methanol electro-oxidation catalyst assisting with functional phthalocyanine supports

Novel electro-catalyst based on phthalocyanine stabilized Pt colloids has been developed for methanol electro-oxidation. Water soluble Cu 2+ phthalocyanine functioned with sulfonic groups were selected as catalyst supports because of the relatively high catalytic activity of Pt catalyst and nearly the same catalytic selectivity complex with Cu-phthalocyanine, compared to others that chelated with Fe, Co and Ni ions. The as-resulting Pt–CuTsPc catalysts have average particle size of 2 nm and narrow size distribution. With the assistance of CuTsPc supports, the methanol electro-oxidation activity and poison tolerance of Pt catalyst have a significant increase. I f/ I b ratio (anodic peak current density, forward to backward) of the Pt–CuTsPc/C catalysts also has obvious increase to 2.5, from value of 0.8 for pure Pt/C catalyst. The reaction Tafel slope of Pt-CuTsPc/C catalysts is 56.6 mV dec −1, much smaller than that of the Pt/C catalyst. The transient current density on Pt–CuTsPc/C at 0.60 V is enhanced to 650% of that on the Pt/C catalyst while the enhancement factor R for comparison of steady-state current obtained on Pt–CuTsPc/C and Pt/C catalyst varies between 111% and 534% in the potential region of 0.3–0.75 V.

Characterization of a Pt/TiO 2 (rutile) catalyst for water gas shift reaction at low-temperature

Recently, we have reported that the Pt/TiO 2 (R: rutile) catalyst has relatively high activity for the water gas shift reaction at low-temperature (LT-WGS). In this study, Pt catalysts supported on TiO 2 (R), TiO 2 (A: anatase), ZrO 2 and Al 2O 3, were characterized by TEM, XPS, TPD, and FT-IR measurements. These results suggested detailed reasons for the high catalytic activity of the Pt/TiO 2 (R) catalyst. TEM micrographs showed that the Pt dispersion of the Pt/TiO 2 (R) catalyst was lower than those of the Pt/ZrO 2 and Pt/Al 2O 3 catalysts, although Pt/TiO 2 (R) had superior catalytic activity. Furthermore, the Pt/TiO 2 (R) catalyst had larger Pt dispersion than Pt/TiO 2 (A), although Pt/TiO 2 (R) had lower BET surface area than Pt/TiO 2 (A). XPS spectra indicated that the TiO 2 (R and A) supports had a stronger electronic effect with Pt than ZrO 2 and Al 2O 3. In addition, CO-TPD profiles revealed that the strength of Pt–CO bonding on Pt/TiO 2 (R) and Pt/TiO 2 (A) catalysts was weakened due to the interaction between the support and Pt. These results indicated that the catalytic activity of Pt catalysts for LT-WGS is greatly affected by the interaction between the support and Pt, rather than by Pt dispersion, although the difference in catalytic activity between the Pt/TiO 2 (R) and Pt/TiO 2 (A) catalysts can mainly be explained by the degree of Pt dispersion. Finally, IR spectra of CO–H 2O and –D 2O reactions on the Pt catalysts indicated that the high catalytic activity of Pt/TiO 2 (R) could be attributed to the fast formation and decomposition of formate as a reaction intermediate.

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/SnO2 appears 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/SnO2 catalysts are rapidly and almost completely poisoned, comparably to Pd/Al2O3, and the catalytic activity is hardly restored upon oxidising treatment below 773 K. A synergetic effect between Pt and specific surface SnO2 sites active in CH4 oxidation is proposed to explain the superior catalytic behaviour of Pt/SnO2.

Effects of support and additive on oxidation state and activity of Pt catalyst in propane combustion

The effects of support and additive on the oxidation state and catalytic activity of Pt catalyst in the low temperature propane combustion were systematically investigated on Pt/MgO, Pt/Al 2O 3 and Pt/SiO 2–Al 2O 3. The catalytic activity varied much with both support materials and additives. The catalyst on the more acidic support showed higher activity, and the catalytic activity on every support materials increased as the electronegativity of additives increased, while some additives decreased the activity. The oxidation state of platinum, estimated by white line intensity of Pt L III-edge XANES spectrum, also varied with the support and additives, and additives with higher electronegativity greatly prevented the platinum from its oxidation under oxidising atmosphere. Among almost all the catalysts with various supports and various additives, a clear relationship was observed between the oxidation state of platinum and the catalytic activity; the more metallic platinum showed higher activity. Thus, it was concluded that the total electrophilic/electrophobic property derived from those of the support and additive controls the oxidation state of platinum, which intensively affects the catalytic activity; i.e. higher electrophilic property provides less oxidised platinum, resulting in high catalytic activity. The mechanism of this effect was also discussed on the basis of thermochemical data, and it was proposed that the electrophobic materials promote the noble metal oxidation since the noble metal oxo-anion such as PtO α δ− is more stabilised with electrophobic cation.

Improvement of Pt catalyst for soot oxidation using mixed oxide as a support

Catalytic activity of Pt catalysts for soot oxidation was studied using temperature programmed reactions. The activity of Pt loaded over TiO2–SiO2 (Pt/TiO2–SiO2) showed higher activity than other Pt/MOx systems (MOx=TiO2, ZrO2, SiO2, Al2O3, TiO2–ZrO2, TiO2–Al2O3, ZrO2–SiO2, ZrO2–Al2O3, SiO2–Al2O3). The activity was highest when the molar ratio of TiO2/(TiO2+SiO2) ranged from 0.4 to 0.7. The effect of pretreatment with a gas containing low SO2 concentrations on the activity was compared for Pt/SiO2, Pt/TiO2 and Pt/TiO2–SiO2. In the case of Pt/TiO2–SiO2, the activity was markedly promoted by the pretreatment whereas no variation in the activity was observed for Pt/SiO2. The difference in the behavior towards the SO2 pretreatment was attributed to property difference in the supports for sulfate accumulation. The high activity of Pt/TiO2–SiO2 was also confirmed under practical conditions with a diesel engine exhaust using a catalyst-supported diesel particulate filter (DPF).

Effect of Ba Addition on Catalytic Activity of Pt and Rh Catalysts Loaded on γ-Alumina

The catalytic activity of Pt catalyst loaded on γ-alumina was improved by Ba addition in simulated automotive exhaust gases. On the other hand, the result of Rh catalyst was the opposite. From the results of the partial reaction orders in C3H6–O2 reaction and TPR, it was concluded that the Ba addition to Pt catalyst suppressed the hydrocarbon chemisorption on the Pt catalyst and therefore allowed the catalytic reaction to proceed smoothly. On the other hand, Ba addition to Rh catalyst caused such a strong oxygen adsorption on Rh that rejected the hydrocarbon adsorption and suppressed the reaction.