Ammonia is a well known hydrogen carrier which can be effectively utilized as a fuel in internal combustion engines (ICEs) when a small percentage of other fuels are added as combustion promoters. Among them, hydrogen is certainly the most valuable since it is carbon free and has opposed and complementary characteristics to those of ammonia.In this work, a Hydrogen Generation System (HGS) capable of supplying up to 1.4 Nm(3)h(-1) of H-2 from ammonia was successfully developed and coupled to an ICE fuelled with ammonia. The main component of the HGS is a cracking reactor housing a ruthenium based catalyst. This system is capable of working both in a stand-alone mode (as required in vehicular applications for the cold start) and in combination with a spark ignited (SI) ICE (i.e. using the combusted gases exhausted by the engine). Beside the cracking reactor, an integrated system was designed and realized in order to allow system cold start and increase overall efficiency during steady state operations.The engine experimental activity confirmed the reactor performance, which was previously verified on a dedicated test bench. Although a lower hydrogen flow rate could be used to achieve satisfactory engine operation, a greater value was used during engine experimentation with benefits for fuel economy and engine cyclic variability. On the other hand, this choice led to higher NOx emissions. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Iron phthalocyanine‐based materials have been used herein as efficient catalysts for the ammonia decomposition reaction. These materials showed high activity, even superior to that showed by the commercial nickel‐based catalyst and iron‐doped carbon nanotubes, which were used as benchmarks in this study. Catalyst stability under reaction conditions appeared satisfactory, because no deactivation phenomena were observed. The type of the phthalocyanine precursor did not affect the catalytic performance; however, the preparation method had a strong effect. If the resulting material was exposed to the reaction conditions, some structural modification occurred. No clear correlation between phase composition and activity could be established because similar nitrogen content and similar crystalline domains in the sample led to different behaviors. However, the results of extensive characterization suggested that catalytic activities and conversion profiles were most likely dependent on material textural properties and thus on the preparation method used. The accessibility of iron species seems to be limited for catalysts prepared under vacuum. These phenomena are most likely responsible for the activation profile and for the low catalytic activity typical of these materials. In contrast, higher accessibility of iron species, typical of materials prepared under argon, would lead to improved and stable catalytic performance.

AbstractLow‐temperature electricity‐driven water splitting is an established technology for hydrogen production. However, the two main types, namely proton exchange membrane (PEM) and liquid alkaline electrolysis, have limitations. For instance, PEM electrolysis requires a high amount of costly platinum‐group‐metal (PGM) catalysts, and liquid alkaline electrolysis is not well suited for intermittent operation. Herein we report a highly efficient alkaline polymer electrolysis design, which uses a membrane‐electrode assembly (MEA) based on low‐cost transition‐metal catalysts and an anion exchange membrane (AEM). This system exhibited similar performance to the one achievable with PGM catalysts. Moreover, it is very suitable for intermittent power operation, durable, and able to efficiently operate at differential pressure up to 3 MPa. This system combines the benefits of PEM and liquid alkaline technologies allowing the scalable production of low‐cost hydrogen from renewable sources.

In the prospective to reduce greenhouse gas emission from vehicles, the use of hydrogen as fuel represents a possible solution. However, if proper engine running with hydrogen has been widely demonstrated, hydrogen storage onboard of the vehicle is a major problem. A promising solution is storing hydrogen in the form of ammonia that is liquid at roughly 9 bar at environmental temperature and therefore involves relatively small volumes and requires light and low-cost tanks. Moreover, liquid ammonia contains 1.7 times by volume as much hydrogen as liquid hydrogen itself. It is well known that ammonia can be burned directly in I.C. engines, however a combustion promoter is necessary to support combustion especially in the case of high-speed S.I. engines. As a matter of fact, the best (and carbon-free!) promoter is hydrogen, which has very high combustion velocity and wide flammability range, whereas ammonia combustion is characterised by low flame speed, low flame temperature, narrow flammability range (combustion is impossible if mixture is just slightly lean), high ignition energy and high self-ignition temperature. The experimental activity shown in the paper was aimed at determining proper air-ammonia-hydrogen mixture compositions for the actual operating conditions of a twin-cylinder 505 cm3 S.I. engine. Hydrogen and ammonia are separately injected in the gaseous phase. The experimental results confirm that it is necessary to add hydrogen to air-ammonia mixture to improve ignition and to speed up combustion, with ratios that depend mainly on load and less on engine speed. This activity is correlated with a larger-scale project, founded by Tuscany Region, in which a partnership of research and industry entities has developed a fully-working plug-in hybrid electric vehicle equipped with a range-extending 15 kW IC engine fuelled with hydrogen and ammonia. Hydrogen is obtained from ammonia by means of on-board catalytic reforming.

Ammonia can be used as fuel in internal combustion engines (ICEs). In this case, a flame accelerator, such as hydrogen, is needed. H-2 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 degrees 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.

Uniform and highly dispersed γ-Fe(2)O(3) nanoparticles with a diameter of ∼6 nm supported on CMK-5 carbons and C/SBA-15 composites were prepared via simple impregnation and thermal treatment. The nanostructures of these materials were characterized by XRD, Mössbauer spectroscopy, XPS, SEM, TEM, and nitrogen sorption. Due to the confinement effect of the mesoporous ordered matrices, γ-Fe(2)O(3) nanoparticles were fully immobilized within the channels of the supports. Even at high Fe-loadings (up to about 12 wt %) on CMK-5 carbon no iron species were detected on the external surface of the carbon support by XPS analysis and electron microscopy. Fe(2)O(3)/CMK-5 showed the highest ammonia decomposition activity of all previously described Fe-based catalysts in this reaction. Complete ammonia decomposition was achieved at 700 °C and space velocities as high as 60,000 cm(3) g(cat)(-1) h(-1). At a space velocity of 7500 cm(3) g(cat)(-1) h(-1), complete ammonia conversion was maintained at 600 °C for 20 h. After the reaction, the immobilized γ-Fe(2)O(3) nanoparticles were found to be converted to much smaller nanoparticles (γ-Fe(2)O(3) and a small fraction of nitride), which were still embedded within the carbon matrix. The Fe(2)O(3)/CMK-5 catalyst is much more active than the benchmark NiO/Al(2)O(3) catalyst at high space velocity, due to its highly developed mesoporosity. γ-Fe(2)O(3) nanoparticles supported on carbon-silica composites are structurally much more stable over extended periods of time but less active than those supported on carbon. TEM observation reveals that iron-based nanoparticles penetrate through the carbon layer and then are anchored on the silica walls, thus preventing them from moving and sintering. In this way, the stability of the carbon-silica catalyst is improved. Comparison with the silica supported iron oxide catalyst reveals that the presence of a thin layer of carbon is essential for increased catalytic activity.

We use a colloidal deposition method to prepare gold nanoparticles with similar size distributions centered at 3 nm over various anatase titania supports. All UV100, PC500 and AK350 titanias are loaded with similar amount of gold (1.0 ± 0.2 wt.%) which is in similar electronic and optical environments, as shown by X-ray photoelectron spectroscopy (XPS) and UV–vis. This allows us to assess the effect of the titania crystallization, morphology and chemical composition on the catalytic properties of gold in the aerobic epoxidation of trans-stilbene. We find that Au/UV100 is more active than Au/PC500 and Au/AK350 but that selectivities are similar on all materials. Epoxide yields on the other hand critically depend on the support functionalization and surface composition. TG–DTA characterization of the bare titania powders reveals indeed that AK350, which leads to the least active catalyst, is slightly less hydroxylated than PC500 and UV100. This indicates that surface titanol groups might be involved in the epoxidation of trans-stilbene. The presence of boron oxide on Au/UV100 (XPS), due to reaction of UV100 with the NaBH4 reductant during the synthesis, is also thought to promote the epoxide-forming mechanism. This chemical promotion effect appears to compensate for the specific and beneficial gold–P25 interaction. As a result, Au/UV100 is more efficient than the reference Au/P25 catalyst for this reaction.

The interaction of carbon monoxide and oxygen with gold particles supported on zinc oxide, alumina, and titania was investigated by microcalorimetry. Multiple processes were detected during CO adsorption, including adsorption of CO on the gold particles and support, oxidation of CO, and formation of carbonates. The rate of O2 adsorption was much slower than that of CO adsorption. The heats and entropies of CO adsorption on the Au sites indicated that the interaction between CO and Au supported on TiO2 is much stronger than that between CO and Au supported on ZnO. The Au/ZnO sample had the largest amount of lattice oxygen (7.6 μmol/g), which reacted with CO to give CO2.

Gold catalysts supported on zinc oxide with Au loadings of 1, 2, and 3 wt% were prepared by the colloidal deposition method and applied in methanol synthesis in CO2-free (CO + H-2) and in CO2-containing (CO + CO2 + H-2) synthesis gas. The characterization by transmission electron microscopy and X-ray diffraction before and after the catalytic high-pressure tests demonstrated a very narrow and uniform Au particle size distribution and a high stability against sintering. Reactive frontal chromatography (RFC) experiments with N2O were performed aiming at the titration of oxygen vacancies. With increasing Au loading, the amount of consumed N2O increased in good correlation with the number of Au perimeter atoms present in the Au/ZnO catalysts suggesting an enhanced formation of oxygen vacancies at the Au/ZnO interface. In both synthesis gas mixtures the presence of the Au particles led to an increased activity compared with pure ZnO. All Au/ZnO samples exhibited higher catalytic activity in the absence of CO2, as had been observed for pure ZnO with similar apparent activation energy. It is concluded that oxygen vacancies in ZnO are also the active sites in methanol synthesis over Au/ZnO, and that the presence of the Au particles enhances the number of exposed oxygen vacancies in ZnO, presumably located at the interface region. (C) 2009 Elsevier B.V. All rights reserved.

Since the introduction of the nanocasting (hard templating) pathway, increasing efforts have been devoted to the preparation of ordered mesoporous metal oxides such as Co3O4, 2–4 Cr2O3, 5,6 CeO2, 7 MgO, Fe3O4 9 and ferrihydrite. These materials have high surface area compared to bulk materials, and therefore can be used as efficient catalyst supports and as catalysts themselves. Low temperature CO oxidation is very important in many applications including air purification and pollution control devices, automotive emission control, gas purification of the hydrogen to feed PEM fuel cells, closedcycle CO2 lasers and CO gas sensors. 11 Although the most often studied materials for low temperature CO oxidation are gold based catalysts several studies have also used Co3O4 (bulk or supported) which shows a very high activity for this reaction as well. Depending on the preparation method for the materials and the reaction conditions, Co3O4 shows different activity in CO oxidation. Recently Wang et al. reported catalytic activity of a series of Co3O4 samples, 20 and they showed that CO conversion of the samples can reach 100% at ambient temperature and even below, using a gas mixture consisting of 0.5 vol% CO, 14.4 vol% O2, and 85.1 vol% N2 with a total flow rate of 20 mL min , corresponding to a space velocity of 4000 mL gcat 1 h . Deactivation was observed to be severe, and reliable activities of the catalysts could not be extracted from the data, since the experiments were carried out at full conversion, and the deactivation patterns did not show consistent trends. Haruta’s group has reported light-off temperatures (temperature of 50% conversion, T50) as low as 54 1C under conditions close to the ones used in our study, but only if the reaction gas was meticulously dried. At normal operation, the T50 was around 40 1C. Since the nanocasting pathway allows the synthesis of highly defined pore systems and the generation of high surface areas, we studied the catalytic activity of nanocast Co3O4 in CO-oxidation and the dependence of the catalytic activity on the porosity of the samples. Ordered mesoporous Co3O4 with different textural parameters was prepared via the nanocasting pathway. The catalytic performance of these materials was in the same range as that of the best reported materials with respect to conversion at room temperature, but a more precise comparison is difficult due to the different conditions used in previous publications. Cubic ordered mesoporous silica (KIT-6) was synthesized according to the literature. The pore size of the KIT-6 was varied by changing the aging temperature (40, 100 and 135 1C). With increasing aging temperature during the hydrothermal process, pore size and pore volume of the synthesized KIT-6 increase while silica wall thickness decreases. KIT-6 was used as a hard template to fabricate ordered mesoporous Co3O4. Briefly, 0.5 g of KIT-6 was dispersed in 5 ml of 0.8 M Co(NO3)2 6H2O in ethanol and stirred for 1 h at room temperature, followed by evaporation of the ethanol at 50 1C. The composite was calcined at 200 1C for 6 h. The material was re-impregnated again, followed by calcination at 450 1C for 6 h. The silica template was then removed by leaching with 2 M NaOH aqueous solution. Finally, the resulting Co3O4 was washed several times with water and then dried at 50 1C. All samples were characterized by nitrogensorption, X-ray diffraction, (XRD), transmission electron microscopy (TEM) and high resolution scanning electron microscopy (HR-SEM). The activities of the catalysts for CO oxidation were measured in a plug flow reactor using 200 mg of catalyst (250–500 mm size fraction) in a gas mixture of 1 vol% CO in air (Air Liquide, 99.997% purity) at a flow rate of 60 mL min , corresponding to a space velocity of 18 000 mL gcat 1 h . Temperatures during these tests were ramped at 2 1C min 1 while CO conversion was recorded. Control experiments proved that this transient operation gives the same activity as a steady state measurement of activity. For clarification, the samples were labelled as Co3O4-T, with T representing the aging temperature of the hard template. The structure and porosity of nanocast Co3O4 strongly depend on the parameters of the nanocasting process, and the results of a detailed study will be reported elsewhere, since this would exceed the scope of this contribution. In summary, Co3O4-40 which had been fabricated from KIT-6 aged at low temperature has uncoupled sub-frameworks while Co3O4-100 and Co3O4-135 have a coupled framework. The parent material aged at higher temperature contains a high fraction of micropores connecting the two mesopore systems. Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, Mülheim an der Ruhr, 45470, Germany. E-mail: schueth@mpimuelheim.mpg.de; Fax: +49 208 306 2995; Tel: +49 208 306 2373 w Electronic supplementary information (ESI) available: Fig. S1. Deactivation plot for Co3O4-40 catalyst. Fig. S2, XPS spectrum for Co3O4-100 before and after catalytic test. See DOI: 10.1039/b808815b

Cubic ordered mesoporous Co3O4, prepared via the nanocasting pathway using KIT-6 as hard template, was found to be an excellent catalyst for low temperature CO oxidation, with the activity clearly depending on surface area and pore systems of the catalysts.

Introduction Several models for methanol synthesis on ZnO are under discussion, assuming oxygen vacancies on polar ZnO surfaces as active sites for the hydrogenation of CO [1] or CO2 [2] to methanol. It has been shown that Au can be an active catalyst in CH3OH synthesis, when it is well dispersed in small nanoparticles on oxidic supports, and ZnO was shown to be essential to obtain high selectivity towards CH3OH [3]. In situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) was applied to identify adsorbed surface intermediates, steady state kinetic experiments gave insight in reactivities and transient kinetic experiments were used to monitor single elementary steps and to investigate reaction pathways.

Fresh commercial carbon nanotubes (CNTs) containing residual Co or Fe nanoparticles are highly active for NH3 decomposition while the microstructure of CNTs remains unchanged. The catalysts are promising for elimination of NH3 from coal gasification stream and for production of H-2 from NH3.

Gold catalysts were prepared on different allotropic phases of TiO2 using the colloidal deposition method. The supports were chosen in order to study the influence of the support structure on the catalytic activity of the final material. Furthermore, for the same allotropic modification of titania, materials with a different particle size distributions have been used to study the influence of the grain size of the support on the deposition of the colloid. Our results indicate that the activity of the final catalyst is not much affected by the variation of the titania structure, though the situation becomes different when the catalyst is calcined at different temperatures. In this case, pure anatase and rutile supported catalysts showed a lower thermostability than the one prepared using P25 titanium oxide (Degussa). Concerning the colloid immobilization on the support it was found that the most important parameter is the grain size of the support. In particular, the deposition of the colloidal gold particles is greatly enhanced in the case of supports composed of particles of few nanometers in size.

Nanocarbons (graphite, tube, diamond) were used as highly efficient catalyst for styrene synthesis from oxidative dehydrogenation of ethylbenzene. Long-time stability and outstanding performance suggested a much more promising future for industrialization of nanocarbon. Metal-free nanocarbons are not highly active for NH3 decomposition while residual metal nanoparticles in commercial CNTs could efficiently catalyze this reaction. Its catalytic performance is comparably high to those of typical industrial catalysts.

Mesoporous MgAl2O4 spinel monolith was synthesized by the nanocasting pathway; high activity in CO oxidation was observed over gold catalysts based on such monoliths as support.