Oxide Supported Platinum Catalysts Research Articles

The practical utility of ternary nickel-cobalt-manganese oxide-supported platinum catalysts for room-temperature oxidative removal of formaldehyde from the air

Formaldehyde (FA), a carcinogenic oxygenated volatile organic compound, is present ubiquitously in indoor air. As such, it is generally regarded as a critical target for air quality management. The oxidative removal of FA under dark and room-temperature (RT) conditions is of practical significance. A series of ternary nickel–cobalt-manganese oxide–supported platinum catalysts (Pt/NiCoMnO4) have been synthesized for FA oxidative removal at RT in the dark. Their RT conversion values for 50 ppm FA (XFA) at 5,964 h−1 gas hourly space velocity (GHSV) decrease in the following order: 1 wt% Pt/NiCoMnO4 (100 %) > 0.5 wt% Pt/NiCoMnO4 (25 %) > 0.05 wt% Pt/NiCoMnO4 (14 %) > NiCoMnO4 (6 %). The catalytic performance of 1 wt% Pt/NiCoMnO4 has been examined further under the control of various process variables (e.g., catalyst mass, flow rate, relative humidity, FA concentration, time on stream, and molecular oxygen content). The catalytic oxidation of FA at low temperatures (e.g., RT and 60 °C) is accounted for by Langmuir–Hinshelwood mechanism (single-site competitive-adsorption), while Mars van Krevelen kinetics is prevalent at higher temperatures. In situ diffuse-reflectance infrared Fourier-transform spectroscopy reveals that FA oxidation proceeds through a series of reaction intermediates such as DOM, HCOO–, and CO32–. Based on the density functional theory simulations, the unique electronic structures of the nearest surface atoms (platinum and nickel) are suggested to be responsible for the superior catalytic activity of Pt/NiCoMnO4.

Design composite oxide supported Pt catalyst for catalytic wet air oxidation of ammonia with a high concentration in chloride system

Massive discharge of ammonia nitrogen wastewater not only causes eutrophication of the water body but also has a toxic effect on humans and living things. How to deal with ammonia nitrogen wastewater is a crucial topic for researchers. Here, a novel catalyst of Pt@Ti–Si where platinum was supported on a composite oxide of titanium oxide (TiO2) and silicon oxide (SiO2) via a one-pot method was successfully synthesized for catalytic wet air oxidation (CWAO) of ammonia with a high concentration (more than 2000 ppm). Due to the improved specific surface area of SiO2 and the excellent acid-base resistance of TiO2, the prepared composite oxide-supported platinum catalyst has excellent catalytic performance and good stability for CWAO with a high concentration of ammonia. At 200 °C and the O2 pressure of 2 MPa for 2 h, the 1%Pt@Ti10–Si1 catalyst has a 96.32% conversion of 2470 ppm ammonia and 97.15% selectivity to N2 and has good catalytic performance even after five cycles. Under the same reaction conditions, when the chloride concentration in the system is 3000–10000 ppm, the CWAO reaction can be inhibited at an early stage and promote conversion and selectivity at a later stage. The results show that the catalyst has good tolerance to chloride ions, and the treated ammonia nitrogen wastewater can be used for subsequent biochemical processes. Therefore, the developed novel catalyst in this study is effective for the CWAO of highly concentrated ammonia and has potential industrial application value.

Effect of Chemical and Physical Properties of Titanium Oxide Support Surface during Nitrogen Monoxide Reduction by Carbon Monoxide in Presence Water over Titanium Oxide Supported Platinum Catalyst

With the goal of developing a method for utilizing reactive nitrogen species emitted from combustion processes as raw materials for the synthesis of useful compounds, we investigated the selective conversion of NOx to NH3 by means of the NO–CO–H2O reaction over Pt/TiO2 catalysts. High NH3 selectivity was obtained for high-specific-surface-area catalysts. Catalytic activity tests revealed that the activities of catalysts depended on the crystal structure of the support. Comparing CO conversion between NO–CO–H2O reaction and CO–H2O reaction, which could play a role of H-supply reaction, Pt/TiO2 exhibited higher CO conversion for the NO–CO–H2O reaction than that for CO–H2O reaction except for high-surface-area anatase TiO2-supported catalyst around 200 °C. We focused on how the chemical and physical properties of the catalyst surface. Specifically, we carried out temperature-programmed desorption of CO2, which revealed that the CO2 formed during the NO–CO–H2O reaction had no effect on the difference in activity. Carbonaceous surface species and NHx species were observed on the surface of Pt/TiO2 catalyst during NO–CO–H2O reaction by diffused reflectance infrared Fourier transform spectroscopy, and difference in formate formation on anatase-TiO2 supported Pt catalyst was confirmed compared to rutile-TiO2 supported Pt catalyst. We supposed that the difference in activity between anatase and rutile TiO2 was caused by behavior of formate formation.

A One‐Pot Synthesis of Platinum Nanoparticles on Electrochemically Exfoliated Graphite

AbstractGraphite rods were electrochemically exfoliated in an aqueous solution of H2PtCl6 at potentials ranging from 2.5 V to 10 V. The solution was then directly reduced in the same pot with hydrazine hydrate. Scanning Electron Microscopy (SEM) confirmed the platinum deposition onto the exfoliated graphene while Raman spectroscopy and X‐Ray Diffraction (XRD) displayed varying degrees of disorder and oxidation in the graphitic lattices exfoliated at the various potentials. Half‐cell electrochemical tests showed the reduced graphene oxide supported platinum catalysts exfoliated at 5 V displayed the highest electrochemical activity for oxygen reduction in the acidic media while the catalyst exfoliated at 8 V displayed the lowest activity.

In situ molten salt derived iron oxide supported platinum catalyst with high catalytic performance for o-xylene elimination

Supported noble metal catalysts are highly effective for eliminating volatile organic compounds (VOCs). A catalyst with less noble metal loading is always desirable. Using a mixture of NaNO3 and NaF as molten salt, Fe(NO3)3 and Pt(NH3)4(NO3)2 as metal precursors, xPt/Fe2O3 catalysts (x = 0–0.3 wt%) were fabricated after calcination at 350 °C for 3 h. At space velocity of 40,000 mL/(g h), 0.22 wt% Pt/Fe2O3 showed the best catalytic activity, and o-xylene could be completely oxidized into CO2 and H2O at 225 °C. Furthermore, 0.22 wt% Pt/Fe2O3 exhibited good stability, and high resistance to water vapor, CO2, and SO2. We deduce that the excellent catalytic performance of 0.22 wt% Pt/Fe2O3 was associated with the high dispersion of the Pt species and good low-temperature reducibility. The possible reaction mechanism of o-xylene oxidation over 0.22 wt% Pt/Fe2O3 involved the adsorption of o-xylene molecules, partial decomposition into small organic intermediates (e.g. maleic anhydride and aliphatic carboxylate species), and total oxidation into CO2 and H2O. Due to the high efficiency, good stability, low cost, and convenient preparation, the present catalysts are promising for the practical removal of VOCs.

Effects of hierarchical structure on the performance of tin oxide-supported platinum catalyst for room-temperature formaldehyde oxidation

Flower-like tin oxide-supported platinum (Pt/SnOx) with a hierarchical structure was synthesized by a hydrothermal method and characterized by XRD, SEM, TEM, high resolution TEM, XPS and nitrogen adsorption. The flower-like Pt/SnOx microspheres of 1 μm in diameter were composed of staggered petal-like nanosheets with a thickness of 20 nm. Pt nanoparticles (NPs) of 2–3 nm were well dispersed on the SnOx nanosheets. The catalyst was tested in the catalytic oxidation of gaseous formaldehyde (HCHO) at room temperature, and exhibited enhanced activity compared to Pt NPs supported on commercial SnO and ground SnOx. HCHO removal of 87% was achieved over the hierarchical Pt/SnOx after 1 h of reaction, which was 1.5 times that over the ground SnOx-supported Pt (Pt/g-SnOx), and the high activity was maintained after six recycles, showing the high stability of this catalyst. HCHO decomposition kinetics was modeled as a second order reaction. The reaction rate constant for Pt/SnOx was 5.6 times higher than Pt/g-SnOx. The hierarchical pore structure was beneficial for the diffusion and adsorption of HCHO molecules, and the highly dispersed Pt NPs on the SnOx nanosheets were the active sites for the oxidative decomposition of HCHO into CO2 and H2O. This study provided a promising approach for designing efficient catalysts for indoor HCHO removal at ambient temperature.

Interaction of SO2 with Pt Model Supported Catalysts Studied by XPS

Sulfur dioxide that exists in gaseous reaction media as a reagent or impurity can have various effects, both poisoning and promoting, on oxide-supported platinum catalysts. In this work, the interaction of Al2O3, Pt/Al2O3, CeO2, and Pt/CeO2 thin film model catalysts with SO2 (2.5 mbar) or a SO2 + O2 mixture (5 mbar) was studied by X-ray photoelectron spectroscopy (XPS). SO2 reacts with the bare supports to form mainly sulfite species at 200 °C and mainly sulfate species at 400 °C. For Pt/Al2O3 and Pt/CeO2, the reaction with SO2 produces additionally sulfide species on the platinum surface. Pt/Al2O3 reacts with the SO2 + O2 mixture to yield the sulfide and sulfate species in comparable amounts at ≤200 °C, whereas sulfates become the main product at higher temperatures (300–400 °C). The addition of oxygen to the Pt/CeO2 + SO2 system almost completely suppresses the formation of sulfide species and increases the yield of sulfate. The reduction of ceria accompanies the formation of sulfate; both processes pro...

Catalytic oxidation of formaldehyde over Pt/Fe2O3 catalysts prepared by different method

Iron oxide supported platinum catalysts were prepared by different methods, including co-precipitation, impregnation and colloid deposition methods. The catalytic properties of these catalysts were investigated for the complete oxidation of formaldehyde. It is found that the catalyst prepared by colloid deposition method (Pt/Fe2O3-CD) exhibited relatively high catalytic activity, which could completely oxidize HCHO even at room temperature. Based on a variety of physical–chemical characterization results, it is proposed that the presence of suitable interaction between Pt particles and iron oxide supports (i.e., PtOFe), which would influence the structure and properties of iron oxide supports, should play a positive role in determining the catalytic activity of Pt/Fe2O3-CD catalyst.

Iridium-Titanium Oxide as Support for Pt Catalyst in PEFC Cathodes

Platinum supported on iridium-titanium oxide was investigated as cathode catalyst under polymer electrolyte fuel cell relevant conditions. Degradation of the cathode catalyst layer during automotive fuel cell operation was simulated by performing 1000 cyclic voltammetry scans between 0.5 V vs. RHE and 1.5 V vs. RHE in 0.1 M perchloric acid at room temperature. The electrochemically active platinum surface area was determined by CO stripping voltammetry with a novel method of baseline subtraction, and was found to reduce by 42% under these conditions. The activity of the metal oxide supported platinum catalyst towards oxygen reduction reaction was determined before and after the degradation test by rotating disk electrode measurements. The absolute kinetic current suffered a loss of 36% during the start / stop cycling. In contrast, the specific kinetic current was found to increase, which could be explained with a particle size effect due to platinum nanoparticle growth during potential cycling.

Aerobic oxidation of primary aliphatic alcohols over bismuth oxide supported platinum catalysts in water

Catalytic oxidation of non-activated aliphatic alcohols with molecular oxygen is rather challenging, especially in an aqueous medium in the absence of an additional base. Bismuth is usually used as a promoter of platinum-based catalysts. In this work, bismuth oxide was explored as a support, and Pt0 nanoparticles supported on bismuth oxide (Pt/Bi2O3) exhibited high activity for aerobic oxidation of n-butanol using water as a solvent in the absence of an additional base under optimized conditions. Besides n-butanol, liquid primary aliphatic alcohols with low solubility in water could also be smoothly oxidized into the corresponding carbonyl compounds with molecular oxygen. Pt/Bi2O3 reduced by H2 at about 200 °C showed the highest activity for aerobic oxidation of n-butanol. At this temperature, platinum oxide was reduced to Pt0 and bismuth oxide could be reduced partially which might change the surface property of bismuth oxide.

An alternative cobalt oxide-supported platinum catalyst for efficient hydrolysis of sodium borohydride

This study presents an alternative cobalt (II, III) oxide-supported platinum (Pt/Co3O4) catalyst for hydrogen generation in a sodium borohydride (NaBH4) system for the first time. The Pt/Co3O4 exhibits approximately a 410% increase in the hydrogen generation rate compared with pristine Co3O4, indicating that the Pt/Co3O4 is an efficient catalyst to generate hydrogen for NaBH4 hydrolysis. Both the Co K-edge and the Pt LIII-edge results delivered from X-ray absorption near edge structure (XANES) analysis reveal that stable features, including the local structure and the electronic state, are observed after a fifth cycle, suggesting that the Pt/Co3O4 has a potential application in NaBH4 hydrolysis. The catalytic mechanism of the Pt/Co3O4 for NaBH4 hydrolysis is proposed based on the XANES results, which involves catalysis of the NaBH4 and simultaneous reduction of Pt and Co ions during hydrolysis.

Complete oxidation of formaldehyde at ambient temperature over supported Pt/Fe2O3 catalysts prepared by colloid-deposition method

The catalytic properties of iron oxide supported platinum catalysts (Pt/Fe2O3), prepared by a colloid deposition route, were investigated for the complete oxidation of formaldehyde. It is found that all the Pt/Fe2O3 catalysts calcined at different temperatures (200–500°C) were active for the oxidation of formaldehyde. Among them, the catalysts calcined at lower temperatures (i.e., 200 and 300°C) exhibited relatively high catalytic activity and stability, which could completely oxidize HCHO even at room temperature. Based on a variety of physical–chemical characterization results, it is proposed that the presence of suitable interaction between Pt particles and iron oxide supports, which is mainly in the form of Pt–O–Fe bonds, should play a positive role in determining the catalytic activity and stability of the supported Pt/Fe2O3 catalysts.

Electrocatalytic activity and stability of niobium-doped titanium oxide supported platinum catalyst for polymer electrolyte membrane fuel cells

Rutile phase niobium-doped titanium oxide [NbxTi(1−x)O2, x=0.25] with a high electrical conductivity (1.11Scm−1) was synthesized and investigated as a cathode catalyst support material for polymer electrolyte membrane fuel cells (PEMFCs). The TEM image of the Pt/NbxTi(1−x)O2 catalyst revealed that Pt particles (dPt=3–4nm) were deposited on the NbxTi(1−x)O2 support using a borohydride reduction method. The Pt/NbxTi(1−x)O2 catalyst showed comparable oxygen reduction reaction (ORR) activity to that of a commercial Pt/C catalyst (E-TEK) when tested in rotating ring-disk electrode (RRDE). The results of an accelerated durability test (ADT, continuous cycling between 0.6 and 1.4V) in RRDE indicated high stability for the Pt/NbxTi(1−x)O2 electrocatalysts at high potentials in terms of minimum loss in Pt electrochemical surface area (ECSA). Furthermore, the Pt/NbxTi(1−x)O2 showed nearly 10-fold higher ORR activity after potential cycling tests when compared to the Pt/C catalyst (1.19 and 0.13mAcm−2 for Pt/NbxTi(1−x)O2 and Pt/C, respectively). The Pt/C catalyst showed no activity in fuel cell testing after 1000 cycles due to severe carbon corrosion and subsequent disintegration of the catalyst layer. Conversely, the Pt/NbxTi(1−x)O2 catalyst showed only a small voltage loss (0.11V at 0.6Acm−2) even after 3000 cycles. Based on the ADT results, the Pt/NbxTi(1−x)O2 electrocatalyst synthesized in this investigation offers a new approach to improve the reliability and durability of PEM-based fuel cell cathode catalysts.

Ethanol oxidation on metal oxide-supported platinum catalysts

Ethanol is a renewable fuel that can be used as an additive to gasoline (or its substitute) with the advantage of octane enhancement and reduced carbon monoxide exhaust emissions. However, on the standard three-way catalysts, the conversion of unburned ethanol is low because both ethanol and some of its partially oxidized derivatives are highly resistant to oxidation. A combination of first-principles density-functional theory (DFT)-based calculations and in situ diffuse reflectance infrared spectroscopy (DRIFTS) analysis was applied to uncover some of the fundamental phenomena associated with ethanol oxidation on Pt-containing catalysts. In particular, the objective was to analyze the role of the oxide (i.e., γ-Al 2O 3 or SiO 2) substrate on the ethanol oxidation activity. The results suggest that Pt nanoparticles trap and accumulate oxygen at their surface and perimeter sites and play the role of sites that burn ethanol molecules and their partially oxidized derivatives to the final products. The γ-Al 2O 3 surfaces provided higher mobility of the fragments of ethanol molecules than the SiO 2 surface and hence increased the supply rate of these species to the Pt particles. This in turn produces a higher conversion rate of unburned ethanol.

Interaction of Cinchonidine and 1-Phenyl-1,2-Propanedione on the Surface of a Chirally Modified Pt/Al2O3 Hydrogenation Catalyst

Enantioselective hydrogenation of 1-phenyl-1,2-propanedione (PPD) over cinchona-modified oxide-supported platinum catalysts represents an extension to the well-known Orito reaction with methyl and ethyl pyruvates (EtPy) as typical substrates for the asymmetric reduction. In this paper, the adsorption of PPD and cinchonidine on a Pt catalyst was studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The catalyst preparation and the adsorption of the reactant and modifier were carried out according to the procedure generally used in catalysis under actual reaction conditions. The catalysts with adsorbed species were analyzed ex situ. The selective deposition of cinchonidine and PPD on the metal surface was confirmed by parallel experiments with alumina samples and by analyzing the platinum adsorption sites with carbon monoxide as a probe molecule. Among the IR visible adsorbed species, η1(O2)-configuration of PPD was found as the most populated on Pt surface under the conditions of ex situ measurements. New data on the mutual interactions among cinchonidine, PPD, and the Pt catalyst are presented. Tilted π-bonded cinchonidine was detected on the surface under the modifier concentration profile used for obtaining high enantioselectivity in the hydrogenation of PPD. Hydrogen bonding between adsorbed cinchonidine and PPD was also detected.

Effect of Reduction‐Oxidation Treatment on the Catalytic Activity over Tin Oxide Supported Platinum Catalysts

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Fabrication and characterization of a PTFE-reinforced integral composite membrane for self-humidifying PEMFC

A novel PTFE-reinforced self-humidifying membrane based on low-cost sulfonated poly (ether ether ketone) (SPEEK) resin was fabricated. In the membrane a base layer and a thin protective layer were bonded by porous polytetrafluoroethylene (PTFE) film. The base layer, which is composed of silicon oxide supported platinum catalyst (abbreviated as Pt-SiO2) dispersed in SPEEK resin, can suppress reactant crossover and achieve good membrane hydration due to the imbedded hygroscopic Pt-SiO2 catalysts. The thin protective layer, which constitutes of H2O2 decomposition catalyst Pt-SiO2 and high H2O2-tolerant Nafion resin, aims to prevent the SPEEK resin degradation by H2O2 produced at the cathode side by incomplete reduction of oxygen. The porous PTFE film tightly bonds with the SPEEK and the Nafion resins to form an integral membrane and accordingly to avoid delamination of the two different resins. The self-humidifying membrane was characterized by TEM, SEM and EDS, etc. The self-humidifying membrane exhibits higher open circuit voltage (OCV) of 0.98 V and maximum power density value of 0.8 W cm −2 than 0.94 V, 0.33 W cm −2 of SPEEK/PTFE membrane under dry condition, respectively. The primary 250 h fuel cell durability experiment was conducted and suggested that this low-cost self-humidifying membrane was durable both on fuel cell performance and the membrane structure under fuel cell operation condition with dry H2/O2. © 2007 Elsevier B.V. All rights reserved.

Stability of supported platinum sulfuric acid decomposition catalysts for use in thermochemical water splitting cycles

The activity and stability of several metal oxide supported platinum catalysts were explored for the sulfuric acid decomposition reaction. The acid decomposition reaction is common to several sulfur based thermochemical water splitting cycles. Reactions were carried out using a feed of concentrated liquid sulfuric acid (96 wt%) at atmospheric pressure at temperatures between 800 and 850 ∘ C and a weight hour space velocity of 52 g acid/g catalyst/h. Reactions were run at high space velocities such that variations in kinetics were not masked by surplus catalyst. The influence of exposure to reaction conditions was explored for three catalysts; 0.1–0.2 wt% Pt supported on alumina, zirconia and titania. The higher surface area Pt / Al 2 O 3 and Pt / ZrO 2 catalysts had the highest activity but deactivated rapidly. A low surface area Pt / TiO 2 catalyst had good stability in short term tests, but slowly lost activity for over 200 h of continuous operation.

FTIR and mass spectrometric study of the interaction of ethanol and ethanol–water with oxide-supported platinum catalysts

The formation and stability of surface species formed in the interaction of ethanol and ethanol–water mixture with Al 2O 3-, TiO 2- and CeO 2-supported Pt catalysts were studied by FTIR. The changes of the gas phase composition during the above processes were monitored by mass spectrometer. It was found that water enhanced the stability of ethoxide surface species formed in the dissociation of ethanol on Pt catalysts and suppressed the formation of CO. Dehydrogenation of molecularly adsorbed ethanol was proposed as a key reaction step. On the temperature programmed desorption (TPD) spectra of adsorbed ethanol in the case of supported Pt there is a high temperature desorption stage, which was explained by the formation and decomposition of surface acetate species. A possible mechanism of the reaction is discussed.

Electrochemical oxidation of CO over tin oxide supported platinum catalysts

Tin oxide supported platinum catalysts (Pt/SnO x ) for use in polymer electrolyte fuel cells were prepared, and their electrochemical oxidation of CO was investigated. From the XPS measurements of Pt/SnO x catalysts, it was found that the binding energy of Pt showed no change compared to bulk Pt, regardless of tin oxide addition. In accordance with this result, CO-stripping voltammograms for Pt/SnO x catalysts revealed that the peak potential for the pre-adsorbed CO oxidation was almost the same value of Pt/C catalyst. However, the onset potential of CO oxidation shifted negatively compared to PtRu/C catalyst, indicating an enhancement of CO tolerance of Pt/SnO x catalysts.