Water-gas shift reaction over magnesia-modified Pt/CeO2 catalysts

Fuel cells have risen as a clean technology for power generation and much effort has been done for converting renewable feedstock in hydrogen. The water-gas shift reaction (WGS) can be applied aiming at reducing the CO concentration in the reformate. As Pt/CeO₂ catalysts have been pointed out as an alternative to the industrial WGS catalysts, the modification of such systems with magnesium was investigated in this work. It was shown that the addition of MgO to Pt/CeO₂ increased the activity and stability of the catalyst irrespective of the preparation method used, either impregnation or co-precipitation. Based on TPR and IR spectroscopy experiments, it was seen that the presence of magnesium improved ceria reduction favoring the creation of OH groups, which are considered the active sites for the WGS reaction. The evolution of the surface species formed under reaction conditions (CO, H₂O, H₂) observed by DRIFTS evidenced that the formation of formate species and the generation of CO₂ is closely attached to each other; under a reaction stream containing hydrogen the presence of formate species showed to be more relevant while the CO₂ formation was hindered. It is suggested that the addition of MgO favors the formate decomposition and lower the carbonate concentration on the catalyst surface during WGS reaction.     

Mechanistic aspects of the low temperature steam reforming of ethanol over supported Pt catalysts

The influence of the support of Pt catalysts for the reaction of steam reforming of ethanol at low temperatures has been investigated on Al₂O₃, ZrO₂ and CeO₂. It was found that the conversion of ethanol is significantly higher when Pt is dispersed on Al₂O₃ or ZrO₂, compared to CeO₂. Selectivity toward H₂ is higher over ZrO₂-supported catalyst, which is also able to decrease CO production via the water-gas shift reaction. Depending on catalyst employed, interaction of the reaction mixture with the catalyst surface results in the development of a variety of bands attributed to ethoxy, acetate and formate/carbonate species associated with the support, as well as by bands attributed to carbonyl species adsorbed on platinum sites. The oxidation state of Pt seems to affect catalytic activity, which was found to decrease with increasing the population of adsorbed CO species on partially oxidized (Pt^δ+) sites. Evidence is provided that the main reaction pathway ethanol dehydrogenation, through the formation of surface ethoxy species and subsequently acetaldehyde, which is decomposed toward methane, hydrogen and carbon oxides. The population of adsorbed surface species, as well as product distribution in the gas phase varies significantly depending on catalyst reactivity towards the WGS reaction.     

Catalytic and DRIFTS study of the WGS reaction on Pt-based catalysts

The water–gas shift (WGS) activity of Pt/SiO₂, Pt/CeO₂ and Pt/TiO₂ catalysts was studied by in-situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). Samples contained a similar amount of Pt, between 0.34 and 0.50%, and were characterized by employing a variety of physical and spectroscopic techniques. The catalyst activities were evaluated through both CO conversion versus temperature and CO conversion versus time tests. The DRIFTS spectra were obtained on stream during the WGS reaction at increasing temperatures, from 303 to 573 K. Reduced ceria was the only active support and promoted the WGS reaction on surface bridging OH groups that react with CO to form formate intermediates. Pt/SiO₂ was more active than CeO₂ and catalyzed the WGS reaction through a monofunctional redox mechanism on metallic Pt sites. The CO conversion turnover rate was more than one order of magnitude greater on Pt/CeO₂ than on Pt/SiO₂ showing that the reaction proceeds faster via a bifunctional metal-support mechanism. Platinum on Pt/CeO₂ increased the concentration of OH groups by increasing the ceria reduction extent and also provided a faster pathway for the formation of formate intermediates in comparison to CeO₂ support. Pt/TiO₂ catalysts were clearly more active than Pt/CeO₂. The WGS reaction on Pt/TiO₂ was catalyzed via a bifunctional metal-support mechanism, probably involving the activation of CO and water on the metal and the support, respectively. The role of platinum on Pt/TiO₂ was critical for promoting the reduction of Ti⁴⁺ ions to Ti³⁺ which creates oxygen vacancies in the support to efficiently activate water.     

H2-induced thermal treatment significantly influences the development of a high performance low-platinum core-shell PtNi/C alloyed oxygen reduction catalyst

In the purpose of maximizing the utilization of noble metal Pt in oxygen reduction catalysts, we illustrate a synthesis method of preparing the low-platinum PtNi/C alloyed oxygen reduction reaction (ORR) catalyst, which is developed through the H₂-induced treatment to a glucose reduced PtNi/C alloy. After post-treatment with H₂/N₂ mixture gases, this catalyst displays excellent ORR catalytic activity and durability for the synergetic influences of electronic and geometry effects on catalysts during the alloying. Specifically, the as-prepared PtNi/C (350°C-6 h) sample delivers preponderant ORR activity with only 53.5% Pt usage than the commercial Pt/C. The specific activity and mass activity are corresponding 7.49 times and 3.5 times to the commercial Pt/C. This catalyst exhibits excellent ORR catalytic activity after 10 000 potential cycles in acid, which benefits from the well alloyed core-shell structure of PtNi/C. H₂-induced thermal treatment has significant effects on the development of high performance low-platinum PtNi/C alloy catalyst, and plays the significant role in the formation of well-alloyed core-shell structures. The lowered d-band center is believed to facilitate ORR catalysis through weakening the adsorption of intermediate oxygen species on the alloyed Pt surface. Therefore, PtNi/C(350°C-6 h) alloyed catalyst possesses outstanding ORR catalytic activity with much lower Pt loading.     

Pt-CeO2/TiN NTs derived from metal organic frameworks as high-performance electrocatalyst for methanol electrooxidation

Metal organic frameworks (MOFs) have attracted tremendous attention in recent years owing to their high-specific surface area (SSA) and variable porous structures. Owing to the strong interaction between Pt and CeO₂, Pt combined steadily with CeO₂. Furthermore, the surface of CeO₂ can activate water to produce hydroxyl groups, which can accelerate the removal of catalytic intermediate CO. But the bad conductivity of metal oxide is still a huge obstacle. More importantly, utilizing TiN with excellent conductivity as support can strengthen conductivity of catalyst and improve catalytic activity. Herein, a novel Pt-CeO₂/TiN Nanotubes (TiN NTs) catalysts derived from Ce-MOF was fabricated for the first time. In the synthesis process of the targeted catalyst, the compounds of Ce-MOF and TiN NTs was prepared via the hydrothermal method and post-nitriding treatment, and implemented as the Pt support. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption/desorption and electrochemical measurements were carried out to characterize the catalyst. Notably, the peak current density of Pt-CeO₂/TiN NTs (0.67 A mg⁻¹Pt) was approximately 3 times higher than Pt/C (0.28 A mg⁻¹Pt) during methanol oxidation test, showing the exceptional properties toward methanol oxidation reaction (MOR). Remarkably, electrochemical testing data verified the superior tolerance to CO and enhanced catalytical activity of Pt-CeO₂/TiN NTs and it could be attributed to the porous structures and the interaction between TiN NTs and CeO₂.     

The effect of copper oxide on the CuO–NiO/CeO2 structure and its influence on the CO-PROX reaction

The effect of copper oxide species on the CuO–NiO/CeO₂ structure and the influence on the preferential CO oxidation in H₂ excess (CO-PROX) reaction at low and high temperatures were investigated. Temperature-programmed surface reaction (TPSR), In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS) results allowed determining the surface species. The maximum temperature of CO₂ formation or selectivity decreased about 40 °C for the CuO–NiO/CeO₂ catalyst compared to the NiO/CeO₂, which suggests that the addition of Cu⁺ species increases the active sites due to interaction with the Ni–Ce structure. Therefore, the activity of the catalyst was closely related to the oxygen in vacancies and the formation of Cu⁺-carbonyl species of the redox mechanism. Besides, the superior selectivity towards CO₂ below 150 °C depends on the carbonyl stabilization at the surface, inhibiting the adsorption and subsequent oxidation of H₂. Using TPSR and spectroscopic analyzes by DRIFTS and XPS allowed us to propose the reaction mechanisms for low and high temperatures.     

Methanol electro-oxidation reaction at the interface of (bi)-metallic (PtNi) synthesized nanoparticles supported on carbon Vulcan

Ni-rich PtNi bi-metallic catalyst and its counterpart free of nickel supported on carbon Vulcan have been synthesized by the impregnation methodology from Na₂PtCl₆ and Ni(C₅H₇O₂)₂ as precursors. The obtained materials Pt/C and PtNi/C were used as electrocatalysts for the methanol oxidation reaction (MOR) in acid conditions. Electrochemical evaluations demonstrated that the addition of Ni in the Pt-Vulcan matrix promotes an important increment in the faradic current during MOR of one order of magnitude, even though the platinum load is lower in the bi-metallic catalyst. These results suggest that the incorporation of nickel promotes some structural and electronic modifications that enhance a better reaction performance at the electrode interface. Morphological characterization using scanning electron microscopy and transmission electron microscopy with energy dispersive spectroscopy (SEM-TEM-EDS) showed Pt/C and PtNi/C catalysts have a particle size of 5.7 nm and 4.4 nm, respectively. X-ray diffraction (XRD) reveals the formation of Ni₃Pt from the synthesis of PtNi catalysts. Additionally, X-ray photoelectron spectroscopy (XPS) confirmed the presence of Pt and Ni in their metallic-oxidation states on the carbon surface.     

Frustrated Lewis pair engineering on ceria to improve methanol oxidation activity of Pt for direct methanol fuel cell applications

Practical application of direct methanol fuel cell (DMFC) technology is greatly hindered by the strong dependence of anodic methanol oxidation reaction (MOR) on precious Pt based catalyst and the unsatisfying performance of Pt. Therefore, increasing the utilization and the catalytic performance of Pt toward MOR in DMFC is urgent. Here in this work, CeO₂ is modified via a plasma-phosphating combing strategy and is invited as Frustrated Lewis Pair to assist the catalytic MOR process on Pt sites. Simultaneously, the plasma-phosphating combing strategy leads to negatively charged sites on CeO₂ surface, which can be functioned as host for Pt anchoring, facilitating the even dispersion of Pt nanocrystals. Besides, this strategy also has an effect on the Ce³⁺/Ce⁴⁺ ratio and vacancy oxygen ratio on CeO₂ surface, which are critical to the adsorbed OH generation and anti-CO poisoning ability, thus boosting the MOR catalytic activity of Pt. DMFC device therefore exhibits ca. 30% maximum power density enhancement compared with the commercial Pt/C based DMFC.     

Pt/C catalyst impregnated with tungsten-oxide – Hydrogen oxidation reaction vs. CO tolerance

Hydrogen Oxidation Reaction (HOR) is anode reaction in Proton exchange membrane fuel cells (PEMFCs) and it has very fast kinetics. However, the purity of fuel (H₂) is very important and can slow down HOR kinetics, affecting the overall PEMFC performance. The performance of commercial Pt/C catalyst impregnated with WO_x, as a catalyst for HOR, was investigated using a set of electrochemical methods (cyclic voltammetry, linear scan voltammetry and rotating disk electrode voltammetry). In order to deepen the understanding how WO_x species can contribute CO tolerance of Pt/C, a particular attention was paid to CO poisoning. In the absence of CO, HOR is under diffusion limitations and HOR kinetics is not affected by WO_x species. Appreciable HOR current on the electrodes pre-saturated with CO_ads at potentials above 0.3 V vs. RHE, which is not observed for pure Pt/C, was discussed in details. HOR liming diffusion currents for higher concentrations of W are reached at high anodic potentials. The obtained results were explained by donation of OH_ads by WO_x phase for CO_ads removal in the mid potential region and reduced reactivity of Pt surface sites in the vicinity of the Pt|WO_x interface. The obtained results can provide guidelines for development of novel CO tolerant PEMFC anode catalysts.     

Hydrogen production over highly active Pt based catalyst coatings by steam reforming of methanol: Effect of support and co-support

The effect of metal oxide (CeO₂, Al₂O₃ and ZrO₂) support and In₂O₃ co-supported Pt catalysts has been investigated on steam reforming of methanol in microreactors. CeO₂, Al₂O₃ and ZrO₂ were prepared by the sol-gel method and they were used as a support, which was impregnated with In₂O₃ as co-support followed by the introduction of Pt species via the wet impregnation method. The size and dispersion of the Pt nanoparticles on In₂O₃/support have been examined by transmission electron microscopy. From these TEM and XPS results, it was found that the addition of In₂O₃ supports the formation of a high concentration of metallic Pt nanoparticles with enhanced dispersion and controlled particle size on the surface. The activity and stability of all the developed catalysts were tested for the steam reforming of methanol in microreactors at different temperatures. Under reforming conditions without prior reduction, a Pt/CeO₂ catalyst containing 15 wt % of Pt exhibited complete methanol conversion and high selectivity towards hydrogen at 350 °C. However, the CO formation was found to be very high (7.0 vol %) for this catalyst. Upon addition of In₂O₃ as a co-support to this formulation the formation of CO decreased considerably. Pt/In₂O₃/CeO₂ catalyst containing 15 wt % of Pt and 15 wt % of In₂O₃ showed excellent catalytic performance at much lower concentration of CO. This change could be closely associated with the formation of metallic Pt nanoparticles with smaller size, higher dispersion with strong interaction between Pt, In₂O₃ and support, which creates more oxygen vacancies to activate the water molecule which then react with methanol to produce H₂ and CO₂ suppressing the CO formation. Moreover, CeO₂ supported Pt/In₂O₃ catalyst displayed higher stability with lowest CO formation under continuous steam reforming operation of 100 h. The superior performance of this catalyst is thought to be due to the relative abundance of redox sites on the CeO₂ surface, which is able to create an oxygen vacancy as it possesses higher oxygen storage capacity and oxygen exchange capacity. This work demonstrates that the nature of support plays a crucial role for the continuous activation of reactants and determines the catalytic stability during methanol steam reforming.     

Core-shell structured tungsten–tungsten carbide as a Pt catalyst support and its activity for methanol electrooxidation

Tungsten carbide was synthesized by calcination of carbon cryogel containing tungsten in a form of metatungstate. Characterization by X-ray diffraction and transmission electron microscopy indicated core-shell structure of the particles with tungsten core and tungsten carbide shell, attached to graphitized carbon. Pt nanoparticles were deposited on this material and most of them were nucleated on tungsten carbide. Cyclic voltammetry of W-C support and Pt/W-C catalyst indicated hydrogen intercalation in surface hydrous tungsten oxide. Oxidation of CO_ads on Pt/W-C commences earlier than on Pt/C for about 100 mV. The onset potentials of MOR on Pt/W-C and Pt/C are the same, but at more positive potentials Pt/W-C catalyst is more active. It was proposed that promotion of MOR is based on bifunctional mechanism that facilitates CO_ads removal. Stability test was performed by potential cycling of Pt/W-C and Pt/C in the supporting electrolyte and in the presence of methanol. Pt surface area loss observed in the supporting electrolyte of both catalysts after 250 cycles was about 20%. Decrease in the activity for methanol oxidation was 30% for Pt/W-C, but even 48% for Pt/C. The difference was explained by the presence of hydrous tungsten oxide on Pt in Pt/W-C catalyst, which reduces accumulation of poisoning CO_ads.     

Ultra-low Au decorated PtNi alloy nanoparticles on carbon for high-efficiency electro-oxidation of methanol and formic acid

We provide a simple method to design and prepare a highly efficient Pt_10.9Au_0.2Ni_88.9/C trimetallic nanocatalyst with a novel nanostructure of ultra-low (0.075 wt%) Au decorated PtNi alloy nanoparticles for methanol oxidation (MOR) and formic acid oxidation (FAOR). The electro-catalytic properties of Pt_10.9Au_0.2Ni_88.9/C toward the MOR and FAOR are much more excellent than Pt_11.1Ni_88.9/C, Au_11.1Ni_88.9/C and commercial Pt/C, which is attributable to the synergy effect among Pt, Au, and Ni (electron charge donor effect of Au and Ni to Pt). It has transformed the surface electronic structure of Pt atoms. Moreover, Ni triggers the rearrange towards Pt and Au atoms, it could maximize the use of noble metals. The gold atoms decorated on the surface are conducive to the formation of OH_ads as well as to weaken the adsorption of CO_ads at platinum active sites. The Pt_10.9Au_0.2Ni_88.9/C catalyst also exhibits outstanding stability during the MOR and FAOR. A series of characterization techniques are adopted to reveal the nanostructures, electronic, and surficial active sites properties of Pt_10.9Au_0.2Ni_88.9/C.     

CeO2 nanoparticles improved Pt-based catalysts for direct alcohol fuel cells

We developed an ultrasonic co-deposition technique to enhance the activity of Pt/C catalyst (and Pt/CNT, PtRu/C catalysts) for direct alcohol fuel cells (DAFCs) by CeO₂ nanoparticles. The composite catalyst architecture is obtained by an ultrasonically mixing commercial Pt/C catalyst and CeO₂ nanoparticles. Both Pt and CeO₂ are dispersed uniformly in the electrodes resulting in a great deal of CeO₂–Pt–C triple junction interfaces. Unlike traditional preparation of metal oxide supported Pt catalysts, CeO₂ will not cut the connection between Pt and C in this composite catalyst structure. Electrochemical measurements confirm that CeO₂ can improve almost all Pt based catalysts (Pt/C, Pt/CNT, and PtRu/C) for almost all small molecular alcohols (methanol, ethanol, ethylene glycol, and glycerol) electro-oxidation. EIS measurement shows that reaction resistance between Pt and alcohols is decreased much by adding small CeO₂ nanoparticles. Besides, these composite catalysts have high stability. It proves CeO₂ a very promising co-catalyst of Pt based catalysts for DAFCs.     

Supported mesoporous Cu/CeO2-δ catalyst for CO2 reverse water–gas shift reaction to syngas

The design and development of a high performance hydrogenation catalyst is an important challenge in the utilization of CO₂ as resources. The catalytic performances of the supported catalyst can be effectively improved through the interaction between the active components and the support materials. The obtained results demonstrated that the oxygen vacancies and active Cu⁰ species as active sites can be formed in the Cu/CeO_2-δ catalysts by the H₂ reduction at 400 °C. The synergistic effect of the surface oxygen vacancies and active Cu⁰ species, and Cu⁰–CeO_2-δ interface structure enhanced catalytic activity of the supported xCu/CeO_2-δ catalysts. The electronic effect between Cu and Ce species boosted the adsorption and activation performances of the reactant CO₂ and H₂ molecules on the corresponding Cu/CeO_2-δ catalyst. The Cu/CeO_2-δ catalyst with the Cu loading of 8.0 wt% exhibited the highest CO₂ conversion rate in the RWGS reaction, reaching 1.38 mmol·g_cat⁻¹ min⁻¹ at 400 °C. Its excellent catalytic performance in the RWGS reaction was related to the complete synergistic interaction between the active species via Ce³⁺-□-Cu⁰ (□: oxygen vacancy). The Cu/CeO_2-δ composite material is a superior catalyst for the RWGS reaction because of its high CO₂ conversion and 100% CO selectivity.     

A comparative study of electrochemical methods on Pt–Ru DMFC anode catalysts: The effect of Ru addition

In the present study comparative electrochemical study of methanol electro-oxidation reaction, the effect of ruthenium addition and experimental parameters on methanol electro-oxidation reaction at high performance carbon supported Pt and Pt–Ru catalysts have been studied by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) in H₂SO₄ (0.05–2.00 M) + CH₃OH (0.01–4.00 M) at 20–70 °C. Tafel plots for the methanol oxidation reaction on Pt and Pt–Ru catalysts show reasonably well-defined linear region with the slopes of 128–174 mV dec⁻¹(α = 0.34–0.46). The activation energies from Arrhenius plots have been found as 39.06–50.65 kJ mol⁻¹. As a result, methanol oxidation is enhanced by the addition of ruthenium. Furthermore, Pt–Ru (25:1) catalyst shows best electro–catalytic activity, higher resistance to CO, and better long term stability compared to Pt–Ru (3:1), Pt–Ru (1:1), and Pt. Finally, the EIS measurements on Pt–Ru (25:1) catalyst reveals that methanol electro-oxidation reaction consists of two process: methanol dehydrogenation step at low potentials (<700 mV) and the oxidation removal of CO_ads by OH_ads at higher potentials (>700 mV).     

nPt (Hx−2nMoO3) as a promising catalyst for the oxidation of methanol. Synthesis and electrocatalytic properties

A new method for the synthesis of the catalyst systems Pt–Mo was suggested. nPt⁰(H_x−2nMoO₃)/GC electrodes were prepared by a redox reaction between the hydrogen-containing molybdenum bronzes and potassium tetrachloroplatinate (II) in acid solutions at open circuit potential. The electrodes were characterized by CVA, SEM, X-ray microanalysis, XRD, XPS and ICP-AES. Pt⁰conglomerates formation with nonuniform distribution over the molybdenum bronzes surface has been revealed. nPt⁰(H_x−2nMoO₃)/GC electrodes showed high catalytic activity (not inferior to Pt–Ru-catalyst) in the oxidation of carbon monoxide and methanol as compared with Pt/GC-electrodes. Catalytic effect is apparently achieved by effective oxidation of strongly chemisorbed species (CO_ads, HCO_ads), which occurs at boundaries platinum – molybdenum oxide. Therefore nPt⁰(H_x−2nMoO₃) can be considered as one of perspective catalysts for DMFC.     

Influence of metal oxides on Pt catalysts for methanol electrooxidation using electrochemical impedance spectroscopy

Carbon nanotubes used as supports for platinum catalysts deposited with metal oxides (CeO₂, TiO₂, and SnO₂) were prepared for their application as anode catalysts in a direct methanol fuel cell. Cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy measurements were carried out in a solution of 0.5 M CH₃OH and 0.5 M H₂SO₄. Catalysts with the addition of CeO₂, TiO₂, and SnO₂ presented higher catalytic activity than pure platinum catalysts, and the catalysts with CeO₂ were the best among them. Electrochemical impedance spectra indicated that methanol electrooxidation on these catalysts had different impedance behaviors at different potential regions. The mechanism of methanol electrooxidation changed with increases of the potential. The promotion effect of the metal oxides lies in the oxidation of intermediate CO_ads on Pt at low potential regions.     

Cooperative effect of Pt and Cu on CeO2 for the CO-PROX reaction under CO2–H2O feed stream

Catalyst improvement for the preferential oxidation of CO (CO-PROX) is essential in developing efficient fuel cell technologies. Here, we investigate the promotion of the Cu/CeO₂ system with Pt, prepared by impregnation and alcohol-reduction methods, in the CO-PROX reaction under ideal and realistic feed compositions. The high Pt dispersion in PtCu/CeO₂ prepared by impregnation led to a CO conversion of 62% and CO₂ selectivity of 83% at 50 °C under a feed stream composed of H₂/CO/O₂, while monometallic Cu/CeO₂ and Pt/CeO₂ showed negligible activity at these conditions. By adding CO₂–H₂O to the feed stream, PtCu/CeO₂ catalysts prepared by both methods presented similar activity. The maximum CO conversion temperature was shifted to 100 °C. Under these conditions, Cu/CeO₂ was inactive, and Pt/CeO₂ showed identical conversion but lower CO₂ selectivity. In-situ XANES revealed that fast oxidation of Cu species at low temperatures is responsible for Cu/CeO₂ deactivation, while preferential adsorption of CO on Pt⁰ sites in PtCu/CeO₂ avoided deactivation. The use of deactivation-resistant Pt sites as complimentary sites for CO activation associated with improved oxygen mobility over Cu–CeO₂ surface proved to be an effective strategy for CO-PROX under H₂O/CO₂ feed stream at low temperatures.     

Structure-dependent activity and stability of Al2O3 supported Rh catalysts for the steam reforming of n-dodecane

Steam reforming of liquid hydrocarbon fuels is an appealing way for the production of hydrogen. In this work, the Rh/Al₂O₃ catalysts with nanorod (NR), nanofiber (NF) and sponge-shaped (SP) alumina supports were successfully designed for the steam reforming of n-dodecane as a surrogate compound for diesel/jet fuels. The catalysts before and after reaction were well characterized by using ICP, XRD, N₂ adsorption, TEM, HAADF-STEM, H₂-TPR, CO chemisorption, NH₃-TPD, CO₂-TPD, XPS, Al²⁷ NMR and TG. The results confirmed that the dispersion and surface structure of Rh species is quite dependent on the enclosed various morphologies. Rh/Al₂O₃-NR possesses highly dispersed, uniform and accessible Rh particles with the highest percentage of surface electron deficient Rh⁰ active species, which due to the unique properties of Al₂O₃ nanorod including high crystallinity, relatively large alumina particle size, thermal stability, and large pore volume and size. As a consequent, Rh/Al₂O₃-NR catalyst exhibited superior catalytic activity towards steam reforming reactions and hydrogen production rate over other two catalysts. Especially, Rh/Al₂O₃-NR catalyst showed the highest hydrogen production rate of 87,600 mmol g_fuel^?1 g_Rh^?1min^?1 among any Rh-based catalysts and other noble metal-based catalysts to date. After long-term reaction, a significant deactivation occurred on Rh/Al₂O₃–NF and Rh/Al₂O₃-SP catalysts, due to aggregation and sintering of Rh metal particles, coke deposition and poor hydrothermal stability of nanofibrous structure. In contrast, the Rh/Al₂O₃-NR catalyst shows excellent reforming stability with negligible coke formation. No significantly sintering and aggregation of the Rh particles is observed after long-term reaction. Such great catalyst stability can be explained by the role of hydrothermal stable nanorod alumina support, which not only provides a unique environment for the stabilization of uniform and small-size Rh particles but also affords strong surface basic sites.     

Carbon supported PtRh catalysts for ethanol oxidation in alkaline direct ethanol fuel cell

Owing to the formation of an oxametallacyclic conformation, the C–C bond cleavage is the preferential channel for the ethanol dissociation on the Rh surface, the addition of Rh to Pt can increase the CO₂ yield during the ethanol oxidation. However, in acidic media the slow oxidation kinetics of CO_ads to CO₂ limits the overall reaction rate. In this work, we prepare carbon supported PtRh catalysts and compare their catalytic activities with that of Pt/C in alkaline media. Cyclic voltammetry tests demonstrate that the Pt₂Rh/C catalyst exhibits a higher activity for the ethanol oxidation than Pt/C does. Linear sweep voltammetry tests show that the peak current density on Pt₂Rh/C is about 2.4 times of that on Pt/C. The enhanced electro-activity can be ascribed not only to the improved C–C bond cleavage in the presence of Rh, but also to the accelerated oxidation kinetics of CO_ads to CO₂ in alkaline media.