High Metal Dispersion Research Articles

Embedded Ru@ZrO2 Catalysts for H2 Production by Ammonia Decomposition

AbstractAmmonia can be used as fuel in internal combustion engines (ICEs). In this case, a flame accelerator, such as hydrogen, is needed. H2 can be produced on‐board by partial decomposition of ammonia. In this work, ruthenium nanoparticles were embedded into a lanthanum‐stabilized zirconia (LSZ) support to obtain active and stable heterogeneous catalysts for NH3 decomposition. The effects of the preparation of both Ru nanoparticles and LSZ support were investigated. The embedded catalysts present high metal dispersion and good metal accessibility. Despite the relatively low metal loading (3 wt %), activity was very high in the temperature range 400–600 °C. The activity of the reference catalysts prepared by using classical impregnation was significantly lower under the same working conditions. Although many factors contribute to the final catalyst performances, the data reported confirm that the embedding strategy minimizes the undesirable sintering of the Ru nanoparticles, leading to promising and stable catalytic activity.

Surface modification of solution combustion synthesized Ni/Al 2O 3 catalyst for aqueous-phase reforming of ethanol

The effect of surface modification of an alumina powder supported nano-scale nickel catalyst used in aqueous-phase reforming of ethanol has been explored in this paper. The Al 2O 3 powder was prepared by a solution combustion synthesis (SCS) route and the surface of the powder was modified by a non-thermal RF plasma treatment using nitrogen gas. Catalysts were coated by an impregnation method. The performances of the unmodified and modified Ni/Al 2O 3 catalysts have been compared from a catalytic activity, selectivity, and microstructural point of view. The catalytic activity results showed that while nature, relative ratio and selectivity of the products both in gas and liquid effluents did not change, catalytic activity (in terms of EtOH conversion and H 2 yield per g) of the sample increased after plasma modification. Microstructural (XRD, surface area) analysis showed that phase content and surface area of unmodified and modified catalysts are similar, while TEM and H 2-chemisorption showed higher metal surface area, higher metal dispersion and lower active metal particle size for the modified sample compared to the unmodified sample. The temperature programmed reduction (TPR) analysis demonstrated stronger support-metal interaction and smaller NiO particles for the modified catalyst at lower heat treatment temperature. The temperature programmed desorption (TPD) of ammonia analysis showed stronger acidity for the modified support, which can explain better dispersion of the metal particles on the modified catalyst compared to the unmodified sample.

Synthesis of SWNTs over nanoporous Co-Mo/MgO and using as a catalyst support for selective hydrogenation of syngas to hydrocarbon

Single-wall carbon nanotubes (SWNTs) with high surface area were synthesized over nanoporous Co-Mo/MgO by a chemical vapor deposition (CVD) method. The SWNTs were used as catalyst support for selective hydrogenation of syngas to hydrocarbons. Here an extensive study of Fischer-Tropsch synthesis (FTS) on CNT-supported cobalt catalysts with different amounts of cobalt loading up to 40 wt% is reported. The catalysts were characterized by different methods including N 2 adsorption-desorption, X-ray diffraction, hydrogen chemisorption, inductively coupled plasma (ICP) and temperature-programmed reduction. Enhancement of the reducibility of Co 3O 4 to CoO, CoO to Co o and small cobalt oxide particles, dispersion of the cobalt, and activity and selectivity of FTS were investigated and compared with a conventional support. The CNT supported catalysts achieve a high dispersion and high loading of the active metal, cobalt in particular, so that the bulk formation of cobalt metal, which tends to occur in conventional support, can be avoided. The results showed that the specific activity of CNT supported catalysts increase significantly (there is a two fold increase in CO Conversion per gram of the active metal) with respect to the conventional supported catalyst.

Contributions of Electron Microscopy to Understanding CO Adsorption on Powder Au/Ceria–Zirconia Catalysts

The influence of the highly dispersed gold phase on the CO-support interaction occurring in two 2.5 wt % Au/Ce(0.62)Zr(0.38)O(2) catalysts with medium (Au/CZ-MD) and high (Au/CZ-HD) metal dispersion is quantitatively assessed. For this purpose, we have followed an approach in which high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), computer modelling, volumetric adsorption and FTIR spectroscopy studies are combined. This approach has already been fruitfully applied to the investigation of the specific CO-metal adsorption in Au/ceria-zirconia catalysts. As deduced from the experimental studies reported herein, the presence of gold dramatically increases the amount of CO strongly chemisorbed on the support. Moreover, this amount is sensitive to the metal dispersion, thus suggesting the occurrence of a mechanism in which the CO molecules that are initially adsorbed on the gold nanoparticles are further transferred to the support by means of a spillover process. An annular model is proposed for the growth of the CO phase adsorbed on the ceria-zirconia mixed oxide in the presence of Au. By assuming this model, we have estimated the width of the annulus, Delta r, of the adsorbed CO grown around the Au nanoparticles in Au/CZ-MD and Au/CZ-HD catalysts. This value is found to be very close to Delta r approximately 2 nm in both cases, the coincidence lending some additional support to the model. To further confirm this proposal, we have investigated the influence of CO pre-adsorption on the D(2)-Au/CZ-MD interaction, at 298 K. As revealed by FTIR spectroscopy, the kinetics of the deuterium spillover is significantly disturbed by the pre-adsorbed CO, which is fully consistent with an annular model for the CO adsorption. We conclude from the global analysis of the results reported here and those already available on CO-Au adsorption that the appropriate combination of nanostructural, computer modelling and chemical techniques is a powerful tool allowing us to gain a comprehensive picture of the complex series of processes involved in the CO adsorption on this relevant family of gold catalysts.

Hydrogen purification for fuel cell using CuO/CeO 2–Al 2O 3 catalyst

CuO/CeO 2, CuO/Al 2O 3 and CuO/CeO 2–Al 2O 3 catalysts, with CuO loading varying from 1 to 5 wt.%, were prepared by the citrate method and applied to the preferential oxidation of carbon monoxide in a reaction medium containing large amounts of hydrogen (PROX-CO). The compounds were characterized ex situ by X-ray diffraction, specific surface area measurements, temperature-programmed reduction and temperature-programmed reduction of oxidized surfaces; XANES-PROX in situ experiments were also carried out to study the copper oxidation state under PROX-CO conditions. These analyses showed that in the reaction medium the Cu 0 is present as dispersed particles. On the ceria, these metallic particles are smaller and more finely dispersed, resulting in a stronger metal–support interaction than in CuO/Al 2O 3 or CuO/CeO 2–Al 2O 3 catalysts, providing higher PROX-CO activity and better selectivity in the conversion of CO to CO 2 despite the greater BET area presented by samples supported on alumina. It is also shown that the lower CuO content, the higher metal dispersion and consequently the catalytic activity. The redox properties of the ceria support also contributed to catalytic performance.

Mesoporous silica as supports for Pd-catalyzed H 2O 2 direct synthesis: Effect of the textural properties of the support on the activity and selectivity

Pd-based catalysts supported on commercial silica, SBA-15 and MCM-41 were tested for the direct synthesis of hydrogen peroxide under very mild conditions of temperature and pressure and outside the explosion range. Silica and SBA-15 impart good catalytic activity, selectivity, mechanical stability and reusability. Best results were obtained with SBA-15 samples that show higher productivity than plain silica. Further catalytic tests were performed at higher pressures, still outside the explosive region. Even under these reaction conditions, the SBA-15 catalysts are the most selective. Characterization data indicate a close correlation between the textural properties of the support and the catalytic activity of the examined samples. The mean Pd particle size observed on the SBA-15 is a good compromise between a high metal dispersion necessary for high catalytic activity and the presence of less energetic sites, on which O 2 can chemisorb without dissociation.

Hydrotreating activities of alumina-supported bimetallic catalysts derived from noble metal containing molecular sulfide clusters Mo 3S 4M′ (M′ = Ru, Rh, Ir, Pd, Pt)

Molecular sulfide clusters with bimetallic Mo 3S 4M′ cluster cores (M′ = Ru, Rh, Ir, Pd, Pt) were impregnated on γ-alumina as the compounds [(Cp′) 3Mo 3S 4M′(L) x ][pts] y (Cp′ = methylcyclopentadienyl; L = ligand; pts = para-toluenesulfonate). These catalyst precursors were sulfided at 350 °C leading to decomposition of the molecular clusters and the formation of MoS 2-like phases with optimal chances for noble metal atoms to be in close contact with MoS 2. The hydrotreating activities of the catalysts obtained were measured by using a feed containing dibenzothiophene, indole and naphthalene. The HDS, HDN and HYD activities followed the order Mo 3Ir > Mo 3Rh > Mo 3Ru > Mo 3Pt > Mo 3Pd. Comparison with the sum of activities of a monometallic Mo and a monometallic noble metal reference catalyst revealed strong synergies for the Mo 3Ir and Mo 3Rh catalysts, whose HDS and HDN activities had increased by factors of 2.7–3.9 and 1.8–4.3, respectively. A comparison with the hydrotreating activities of a Mo 3Ni catalyst prepared from [(Cp′) 3Mo 3S 4NiL][pts] showed, however, that the performances of the Mo 3Rh and Mo 3Ir catalysts generally were inferior by a factor of 2 to a Mo 3Ni catalyst. An inhibiting effect on the catalyst activity was observed for the Mo 3Pd catalyst. The sulfided Mo 3Rh, Mo 3Ir and Mo 3Pd catalysts were studied by TEM. The Mo 3Rh and Mo 3Ir catalysts showed a homogeneous and very high dispersion of both metals, the MoS 2 dispersion being higher than in the monometallic Mo reference catalyst. The Mo 3Pd catalyst showed a strong inhomogeneity due to the presence of 10 nm large Pd 4S particles fully encapsulated by layers of MoS 2.

Tuning of nitrogen-doped carbon nanotubes as catalyst support for liquid-phase reaction

This work reports the synthesis of nitrogen-doped carbon nanotubes (N-CNTs) using a Chemical Vapor Deposition (CVD) process at temperature ranging from 600 °C to 850 °C and ethane/ammonia concentration (defined as a volume percentage of C 2H 6/(C 2H 6 + NH 3)) of 20–100%. Several characterizations, i.e. XPS, SEM and TEM were done on the as-synthesized nitrogen-doped carbon nanotubes in order to get more insight about the influence of the synthesis conditions on the characteristics and properties of these N-CNTs. Depending on the synthesis conditions, the atomic percentage of nitrogen in carbon nanotubes varied from 0 at.% to about 5.5 at.%. The undoped carbon nanotubes (N-free CNTs) and two kinds of N-CNTs with different types of nitrogen incorporated species have been used as the supports for palladium in the liquid-phase hydrogenation of cinnamaldehyde. The introduction of nitrogen atoms into the carbon matrix significantly modified the chemical properties of the support compared to the N-free carbon nanotube resulting in a higher metal dispersion. N-CNTs exhibit much higher activity in the hydrogenation reaction compare to the undoped ones. Nitrogen incorporation also strongly improved the selectivity towards the C C bond hydrogenation. The results show that the type of nitrogen species incorporated in CNTs structure can also influence the catalytic activity. Recycling test confirms the high stability of the catalyst as neither palladium leaching nor deactivation has been observed.

Effects of nanotubes pore size on the catalytic performances of iron catalysts supported on carbon nanotubes for Fischer–Tropsch synthesis

In this report, the effects of pore diameter and structure of iron catalysts supported on carbon nanotubes (CNTs) on the reaction rates and product selectivities of Fischer–Tropsch (FT) reactions are presented. In order to study the effects of pore diameter, two types of CNTs with different average pore sizes (12 and 63 nm), however, with similar surface areas were prepared. The iron catalysts were prepared using incipient wetness impregnation method and characterized by ICP, BET, XRD, TPR, SEM and TEM analyses. According to the TEM images of iron catalysts supported on narrow pore CNTs (Fe/np-CNT) and wide pore CNTs (Fe/wp-CNT), a vast majority (∼80%) of the iron oxide particles were deposited inside the nanotubes’ pores. The TEM and XRD analysis showed that the iron oxide particles on the Fe/wp-CNT (17 nm) were larger than those on Fe/np-CNT sample (11 nm). Temperature programmed reduction analyses of the catalysts showed that the extent of reduction of the Fe/np-CNT catalyst was 17% higher compared to that of the Fe/wp-CNT catalyst. Finally, catalytic performances of both catalysts were evaluated in a fixed-bed reactor for FT reactions at 2 MPa and 275 °C. At these conditions, the activity of the np-CNT catalyst (%CO conversion of 30) was 2.5 times that of the wp-CNT catalyst (%CO conversion of 12). In addition, the Fe/wp-CNT was more selective toward lighter hydrocarbons with a methane selectivity of 41% compared to that of the np-CNT catalyst with methane selectivity of 14.5%. Deposition of metal particle on the CNT with narrow pore size resulted in more active and selective catalyst due to higher degree of reduction and higher metal dispersion.

Hidrogenación de Metil Oleato con Catalizadores de Ru-Sn/Al2O3: Método Sol-gel vs. Impregnación

In this work, the effect of the preparation method (sol-gel vs. impregnation) over conversion and selectivity to oleyl alcohol in the hydrogenation of methyl oleate over Ru-Sn/Al2O3 catalysts at 270oC and 5 MPa was evaluated. The catalysts were characterized by SEM-EDS, TPR, XRD and surface area by nitrogen adsorption. The sol-gel method produced high dispersion of metals in the support, however catalysts prepared by sol-gel method were less reducible. For both methods an optimum Sn/Ru atomic ratio that allowed higher percentage of unsaturated alcohol was found. For the impregnation method this atomic ratio was 2 and for sol-gel method was 1. However, higher conversions and higher selectivity toward the oleyl alcohol were obtained with the impregnation method, using the optimum atomic ratio,

Solvothermal synthesis and characterization of nanosized zinc aluminate spinel used in iso-butane combustion

Abstract Nanocrystalline (average crystallite size 3 nm), single-phase zinc aluminate with spinel structure (ZnAl 2 O 4 ) was prepared under solvothermal conditions at medium temperature and pressure (200 °C, 2.5 MPa), and heating time (0.5 h), using zinc acetate and aluminium isopropoxide as precursors, 1,4-butanediol as solvent, and by using two different heating methods: microwaves (MW) and conventional. Structural and physicochemical properties of ZnAl 2 O 4 samples and Pt catalysts supported on them, were investigated using X-ray diffraction (XRD), electron microscopy (HRTEM), infrared spectroscopy (FTIR), H 2 chemisorption and N 2 adsorption–desorption measurements. Catalytic performances of 0.5 and 1% Pt/ZnAl 2 O 4 samples were evaluated in the total oxidation of iso -butane reaction. Solvothermally obtained ZnAl 2 O 4 is characterized by a high specific surface area (above 400 m 2 /g) with narrow pore size distributions centered below 5 nm. Additionally, ZnAl 2 O 4 prepared using MW heating presented superior thermal stability (>900 °C). Pt catalysts supported on such prepared ZnAl 2 O 4 were found to exhibit good activity in iso -butane combustion, which could be correlated with a high metallic dispersion and low particle sizes.

A pretreatment method of Ni/γ-Al2O3 catalyst for naphthalene hydrogenation

Abstract A pretreatment method of Ni/γ-Al 2 O 3 catalysts was proposed, which is that the catalyst precursor without calcination was reduced directly at the reduction temperature for a shorter time and cooled quickly. The catalysts pretreated in proper reduction conditions show high activities for naphthalene hydrogenation. When the reduction temperature is lower than 700 °C, the decomposition and the reduction will complete gradually with increasing the reduction temperature, which leads to the improvement of the metal dispersion and activity; while when the reduction temperature is higher than 700 °C, higher metal dispersion and activity can also be attained under appropriate conditions.

A structured catalyst: Noble metal supported on a plate-type zirconia substrate prepared by anodic oxidation for steam reforming of hydrocarbon

A structured catalyst: noble metal supported on a plate-type zirconia substrate was prepared by subjecting a zirconium plate to a process consisting of anodic oxidation in an oxalic acid bath and calcination in the air, followed by rhodium or ruthenium component deposition by the dipping treatment. The catalytic performances of the prepared catalysts were evaluated for steam reforming of n-butane and propane. The substrate surface was significantly corroded by the anodic oxidation and calcination, and a rugged zirconia layer about 100 μm thick was formed. The crystalline state of zirconia was mainly monoclinic and tetragonal. In steam reforming of n-butane, the structured ruthenium catalyst had some activity, while the activity of the rhodium catalyst exceeded that of the commercial catalyst. For the rhodium catalyst, its reforming activity was improved by changing the temperature of dipping bath and the number of dips for adjustment of the rhodium deposition state. The rhodium catalyst prepared by dipping twice at a bath temperature of 25 °C has the largest metal surface area and a higher metal dispersion, which were thought to be the causes for the high performance. In steam reforming of propane, the rhodium catalyst showed a significantly higher activity than the commercial catalyst. The rhodium catalyst was less prone to deterioration of activity due to n-butane and propane reforming.

Biogas reforming for hydrogen production over nickel and cobalt bimetallic catalysts

Abstract Ni/Co bimetallic catalysts supported by commercial γ-Al2O3 modified with La2O3 for biogas reforming were prepared by conventional incipient wetness impregnation. The catalysts were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET surface area and porosity analysis (BET), H2 temperature-programmed reduction (H2-TPR), transmission electron microscopy (TEM) and thermogravimetry coupled to differential scanning calorimetry (TG–DSC). XRD and XPS analysis revealed that a Ni/Co alloy was formed in the bimetallic catalysts. The Ni/Co ratio could be adjusted to improve pore textural properties, which enhanced the metal particle dispersion and resulted in smaller metal particle size, and thus increased the catalytic activity and resistance to carbon deposition. The activity and stability of the catalysts for biogas reforming was tested at 800 °C, ambient pressure, GHSV of 6000 ml gcat−1 h−1 and a CH4/CO2 molar ratio of 1 without dilute gas. Experimental results showed that the catalytic activity could be closely related to the Ni/Co ratio. The bimetallic catalyst 7Ni3Co/LaAl exhibited better catalytic and anti-coking performance due to smaller metal particles, higher metal dispersion, uniform pore distribution, surface enrichment of Co, as well as the synergetic effect between Ni and Co. During a 290 h stability test over the catalyst 7Ni3Co/LaAl, the average conversion of CH4 and CO2, selectivity to H2 and CO, and ratio of H2/CO were 93.7%, 94.0%, 94.9%, 97.8%, and 0.97, respectively. The average coking rate was 0.0946 mg gcat−1 h−1.

Hydrogenation of 2-pentyne over Pd/Al 2O 3 catalysts: Effect of operating variables and solvent selection

Hydrogenation of 2-pentyne over 1 wt.% Pd/Al 2O 3 was studied in a 2.65 L baffled stirred vessel. The effects of stirring speed, hydrogen pressure, concentration of substrate, catalyst loading, solvent selection and catalyst preparation method upon the rate and selectivity were investigated. It was shown that increasing the stirring speed from 445 to 1100 rpm and crushing the particles from >150 to 45–75 μm led to increases in the reaction rate, confirming the existence of mass transfer resistances. Catalyst preparation method (Type A: crushing followed by impregnation or Type B: impregnation followed by crushing) had a strong effect on reaction behaviour, with Type B particles showing a much higher metal dispersion and consequently faster reaction rate than Type A. Solvent selection was found to have a very strong effect upon reaction rate and selectivity and in heptane the reaction rate was faster than isopropanol. In a 50/50 mixture of heptane and isopropanol the rate of alkyne hydrogenation was intermediate to that observed in the solvents individually while selectivities were up to 5 times greater. The most favourable conditions in terms of selectivity were 2 bar of hydrogen, a stirring speed of 445 rpm and a solvent mixture of 1:1 heptane/isopropanol, where the highest cis/trans pentene ratio was 25.39, and the highest pentene/pentane ratio was 49.41.

Nanofibrous γ-Al 2O 3 as support for Co-based Fischer–Tropsch catalysts: Pondering the relevance of diffusional and dispersion effects on catalytic performance

Hierarchical macro-mesoporous nanofibrous γ-alumina (Al 2O 3_nf) synthesized by a surfactant-templated route has been applied for the first time as support for preparing RuCo catalysts at two different loading levels (20 wt% Co–0.5 wt% Ru and 30 wt% Co–1.0 wt% Ru). Equivalent catalysts involving four commercial aluminas (Sasol, mean pore size ranging from 6.0 to 32.4 nm) have also been prepared for comparison purposes. The materials have been exhaustively characterized (XRD, elemental analysis, ICP-OES, N 2 physisorption, Hg intrusion porosimetry, TEM-HRTEM, FE-SEM, H 2 chemisorption, and H 2-TPR) and evaluated for Fischer–Tropsch synthesis (FTS) in a fixed-bed reactor under realistic conditions. Nanofibrous alumina displayed simultaneously the highest specific surface area (321 m 2/g) and the largest macroporosity. The introduction of the original nanofibrous morphology allowed us to conclude that Co dispersion is mainly driven by support surface area rather than by pore size. By taking advantage of these properties, RuCo/Al 2O 3_nf catalysts bearing both the highest metal dispersion and macroporosity have been used in this work to ponder the relevance of dispersion and intrapellet diffusion on FTS catalyst performance, which is of paramount importance for designing improved Co-based FTS catalysts. While initial ( TOS → 0 ) FTS rates were related to cobalt dispersion through the recently reported particle size–TOF dependence, pseudo-steady-state FTS activity and selectivity were dictated by both dispersion and support porosity, evidencing the kinetic relevance of CO and α-olefin intrapellet diffusion through the liquid phase filling the catalyst pores under working conditions. At high metal loadings, where the relative population of intrinsically less active and C 5+ selective Co 0 nanoparticles is decreased, RuCo/Al 2O 3_nf catalyst displayed the highest cobalt-time-yield and diesel productivity.

Characterization of ZnAl2O4 Obtained by Different Methods and Used as Catalytic Support of Pt

In this work the synthesis of a ZnAl2O4 spinel to be used as a support of metals and its characterization were studied. The methods used for the ZnAl2O4 preparation were: ceramic method (CM), mechanochemical synthesis in humid medium (HMS) and coprecipitation (COPR). ZnAl2O4 CM and ZnAl2O4 HMS showed negligible acidity, but the ZnAl2O4 COPR displayed a low acidity. The spinels obtained by COPR and HMS showed higher specific surface area and pore volumes than that prepared by the ceramic method. In addition the catalytic performance of Pt supported on the prepared spinel was evaluated in the n-butane dehydrogenation reaction. The Pt catalysts prepared with ZnAl2O4 COPR presented better activity and selectivity to olefins than the ones prepared with ZnAl2O4 HMS and ZnAl2O4 CM, which could be correlated with a higher metallic dispersion and lower particle sizes, detected by TEM. The acidity of ZnAl2O4 COPR, observed by isopropanol dehydration and TPD of pyridine, and the sequence of specific surface areas of the different spinels (ZnAl2O4 COPR > ZnAl2O4 HMS > ZnAl2O4 CM) are other important factors to define the final dispersion of the catalysts.

Synthesising Fe-Mo catalysts supported on silica for the selective oxidation of methane to formaldehyde

The selective oxidation of methane to formaldehyde was analysed using iron-molybdenum catalysts supported on silica prepared by the sol-gel method which leads to obtaining a greater surface area and high iron and molybdenum metal dispersion on the silica’s amorphous surface. Seven catalysts were prepared, one of them as silica support, another as 0.5% wt iron load without molybdenum and the remaining five having 0.1%-1.0% weight molybdenum and 0.5% wt iron loads. The highest BET areas were 830 and 879 m2.g-1 for catalysts 2 (0.5% Fe - 0% Mo) and 4 (0.5% Fe - 0.3% Mo) respectively, having 28% average microporosity and 47% average mesoporosity. X-ray diffraction confirmed the catalysts’ amorphous structure. The TPR spectrum showed low hydrogen consumption attributed to the absence of isolated Fe and Mo species. ESCA analysis revealed the same Fe/Mo atomic ratio on the catalyst surface as in the bulk preparation. Catalytic activity was carried out at atmospheric pressure, CH4/ O2/N2 = 7.5/1/4 reaction mixture, 400-800°C temperature interval. Catalysts 4 (0.5% Fe - 0.3% Mo), 5 (0.5% Fe - 0.5% Mo) and 7 (0.5% Fe - 1.0% Mo) displayed greater methane conversion, whereas catalysts 5 (0.5% Fe - 0.5% Mo), 4 (0.5% Fe - 0.3% Mo), 2 (0.5% Fe - 0% Mo) and 7 (0.5% Fe - 1.0% Mo) gave better formaldehyde product results. The highest conversion per-centage (4.07% mol) was presented at 700°C for catalyst 4 (0.5% Fe-0.3% Mo). Formaldehyde yield was 202,0 gHCHO.kg-1cata.h-1 at this temperature.

Ordered micro-porous carbon molecular sieves containing well-dispersed platinum nanoparticles for hydrogen storage

Ordered micro-porous carbon molecular sieves containing highly dispersed platinum nanoparticles with tunable sizes from 1 to 6 nm are synthesized in this work. The synthesis is simply realized by nanocasting of furfuryl alcohol precursor on Pt-impregnated NaY zeolite hard templates and complemented by chemical vapor deposition by propylene gas. During the carbonization, Pt ions can be reduced to form highly dispersed Pt nanoparticles on the carbon matrixes. This method allows a very high Pt-loading up to 40 wt % while maintaining a high metal dispersion. X-ray diffraction and transmission electron microscopy measurements reveal the existence of uniformly dispersed Pt nanoparticles and microstructural regularity. Nitrogen adsorption isotherms show that the ordered micro-porous carbon molecular sieves possess a high surface area around 2750 m 2/g, large micro-pore volume 1.38 cm 3/g, and narrow pore size distribution (∼1 nm) in the micropore-range. A high hydrogen uptake up to 2.8 wt% at 77 K and 1 bar is observed. A high and relatively homogeneous value of hydrogen adsorption heat 11 kJ/mol in 1% Pt contained carbon was obtained, which exceeds the literature reported values for other carbon based adsorbents or metal organic framework compounds and is very close to the optimal value, 15 kJ/mol, recommended in the literature, suggesting a great potential for hydrogen storage or fuel cell applications.

Effect of the preparation conditions of carbon-supported Pt catalyst on PEMFC performance

Carbon-supported Pt catalysts were prepared using NaBH4 as a reducing agent in either ethylene glycol or water for use as a cathode catalyst in PEMFCs (polymer electrolyte membrane fuel cells). Aqueous NaBH4 solution was used to reduce Pt precursor and to produce the Pt-W catalyst, while Pt-E and Pt-E-base catalysts were synthesized using NaBH4 in ethylene glycol for the reduction of Pt. Compared to Pt-W catalyst, Pt-E and Pt-E-base catalysts have higher Pt dispersion and larger EAS (electrochemically active surface area) due to the stabilizing effect of ethylene glycolic NaBH4 solution on Pt particles. In addition, increasing pH of the preparation solution improved the Pt dispersion (Pt-E-base). In unit cell tests the performance of Pt catalysts decreased in the following order: Pt-E-base > Pt-E > Pt-commercial > Pt-W. Higher metal dispersion and larger EAS are believed to be responsible for the superior performance of Pt-E catalysts, particularly Pt-E-base, compared to other catalysts.