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A series of the mixed oxides of iron and cerium, with an iron(III) oxide content ranging from 0 wt% to 100 wt% were tested as oxygen carriers in the chemical looping dry reforming of methane (CL-DRM). The reactivity during the CL-DRM significantly increased when iron and cerium are forming a mixed oxide. By careful control of the Fe2O3/CeO2 mass ratio, initial oxidation state and reaction time the activity of the oxygen carrier material can be adjusted so as to substantially favour oxidation of methane to syngas and discourage both total oxidation of methane and carbon deposition via decomposition of methane.

This work studies the feasibility of a pioneer technology for on-board hydrogen production: the Ammonia Cracking Hollow Fibre Converter. The catalytic activity of a series of ruthenium-based catalysts supported on carbon xerogel, during the ammonia cracking reaction, was studied in a catalytic packed bed reactor. To improve their physical-chemical properties, carbon xerogels were activated in either carbon dioxide or ammonia atmosphere. The most active catalyst (i.e. Ru-NCX) was then deposited inside the micro-structured hollow fibre support by a combination of sol-gel and incipient wetness impregnation methods. At 450 °C and 1 atm the hollow fibre reactor was 4.6 times more efficient than the packed bed reactor (i.e. rNH3 = 6.5 × 104 molNH3/m3·h·gcat and rNH3 = 3.0 × 105 molNH3/m3·h·gcat, respectively), due to its narrower residence time distribution and reduced mass transfer limitations. Furthermore, the use of the hollow fibre converter entailed significantly lower pressure drop (i.e. >99% less), volume (i.e. 80% less) and catalyst loading (i.e. 80% less) compared to the packed bed reactor. Therefore, the potential of this new technology is enormous, as it will push the incorporation of green ammonia in the present-day fuel scenario.

Piezocatalysis is a promising area of research that would enable new advances in environmental catalytic processes independent of energy sources such as light or electricity. To shed more light on this field, theoretical and experimental studies were conducted using poled and unpoled BF-KBT-PT ceramics as catalysts in order to investigate the effect that piezocatalyst size, piezocatalyst poling/unpoling and agitation mode have on the degradation of a dye, Rhodamine B (RhB), in water. While an apparently contradictory trend in the theoretical and experimental results was observed in relation to piezocatalyst size, poling indeed had a significant effect on the degradation of RhB, indicating that a complex combination of different phenomena such as ‘top-to-bottom’ electric potential difference due to ‘bulk’ piezoelectric polarisation, nanoscale piezoelectric response and sonocatalysis may result in the overall catalytic degradation of RhB. However, the greatest contribution to the degradation of the dye would come from sonochemistry, as ultrasound in absence of a catalyst already achieved a remarkable degradation of RhB. This study therefore demonstrates the complexity of piezocatalysis, and why other phenomena besides bulk piezoelectric polarisation of catalysts must be taken into account in piezocatalysis research.

Hollow fibre-based after-treatments impregnated with iron and chromium-based oxides (non-PGM) have been tested for residual methane catalytic oxidation under extreme conditions (sulfur concentration 100-times larger than in real conditions), real timeframes (1000 h) and real operating cycles (thermal shocks). The results from this study have proven, for the first time reported in the literature, that hollow fibre reactors can be scaled up and that non-PGM impregnated hollow fibre after-treatments are the ideal candidate for the development of commercial residual methane after-treatments.

The presence of traces of sulfur dioxide (i.e. 1–10 ppmV) alongside residual methane emissions induces the rapid deactivation of typical methane abatement catalysts. As a result, sulfur-induced poisoning is the main challenge faced by after-treatment technologies for residual methane abatement. The aim of this study was to synthesise a series of cobalt and molybdenum catalysts and assess their performance under realistic after-treatment conditions. The series of catalysts was characterised by BET, XRD, XPS, TPR, TGA under air flow, SEM, EDX and in situ DRIFTS. In addition, the performance of Co100 supported on an alumina hollow fibre was assessed under similar reaction conditions and characterised by SEM and EDX. It was found that the catalytic activity of the series of cobalt and molybdenum catalysts decreased in the following order: Co100 > Co80Mo20 > Co60Mo40. In addition, it was discovered that the other two catalysts (i.e. Co25Mo75 and Mo100) were inactive at 450 °C due to the lack of highly active Co3+ species. Among the active catalysts, Co100 and Co80Mo20 experienced an initial activation followed by a gradual deactivation whereas Co60Mo40 experienced a 1 h interval with stable methane conversion levels in between the activation and deactivation. The delay in poisoning of the active cobalt (II,III) oxide phase of Co60Mo40 was attributed to the sulfur sink-properties of the cobalt molybdenum oxide present in this catalyst (i.e. 44 wt%). Finally, Co100 supported on an alumina hollow fibre achieved the highest methane conversion per unit mass of catalyst and its performance was stable for a duration of 2.5 h. The high activity was attributed to the large surface area provided by the geometry of the support while the higher resistance to sulfur poisoning was credited to the sulfur sink-properties of the alumina, which delayed the poisoning of the active phase.

The aim of this work is to understand the role of oxygen surface groups during the preparation, activation and reaction of heterogeneous ruthenium catalysts supported on activated carbon materials. Hence, non-promoted and sodium promoted ruthenium catalysts supported on two different activated carbon materials, with and without oxygen surface groups, were prepared by successive incipient wetness impregnation and tested in the ammonia decomposition reaction. The catalysts were characterised with a multi-technique approach that involves; nitrogen adsorption isotherms at −196 °C (BET and BJH methods), temperature programed oxidation (TPO), scanning electron microscope (SEM), temperature programed desorption (TPD), transmission electron microscopy (TEM), in-situ X-ray absorption near edge structure (XANES), temperature programed reduction (TPR) and microcalorimetry of hydrogen chemisorption. The performance of the different ruthenium supported catalysts during the ammonia decomposition reaction was determined in a constant flow fixed-bed reactor at 1 atm, in the temperature range from 350 °C to 450 °C. This work shows how the oxygen surface groups of the activated carbon can be used to control/influence (i) the final oxidation state of ruthenium particles, (ii) ruthenium particles size, (iii) selective deposition of the sodium promotor. We believe that such use of the presence of surface groups on the activated carbon surface could potentially be employed to improve the catalytic performance of next generation heterogeneous catalysts.

International audience; Hydrogen interaction with ruthenium surfaces is a complex phenomenon that can play an important role in catalytic reactions such as ammonia synthesis. In this study, H-2/D-2 isotopic homomolecular exchange has been used to characterize four different catalytic surfaces, namely Ru/AC(0), Ru/AC(1), Ru-Na/AC(0) and Ru-Na/AC(1). They are composed of 2%Ru or 2%Ru-4.5%Na supported on an active carbon with (AC(0)) and without surface groups (AC(1)). The AC(1) carbon (1162 m(2) g(-1)) is obtained by treatment of AC(0) (960 m(2) g(-1)) in N-2 at 900 degrees C. Ru/AC(0) and Ru/AC(1) catalysts are prepared by impregnation of the supports with aqueous solutions of Ru(NO)( NO3)(3). Na-promoted catalysts are then prepared by impregnation of Ru catalysts with NaOH solutions. An overall picture of the surface mobility phenomena on the four different catalytic surfaces has been described. It has been demonstrated that the presence of Na promoter in Ru-Na/AC0 and Ru-Na/AC(1) catalysts inhibits the spillover of H atoms from the Ru particles to the AC surface. However, for non Na promoted catalysts, the extension of the H spillover phenomenon depends on the amount of oxygen groups present on the AC surface. Likewise, the formation of a ruthenium hydride during the reduction treatment is suggested for catalysts promoted or not by Na. Finally, this work shows how the kinetics of the H-2/D-2 isotopic exchange reaction may be related to the surface electron density of the catalyst, which allows us to better understand the effect that both promoter and support have on the metal particles.

A series of iron and chromium-based oxides were used as catalysts for the total oxidation of residual methane under realistic after-treatment conditions. This study operated with sulfur dioxide, steam and methane concentrations similar to those typically found in natural gas turbines and natural gas-powered vehicle exhausts (around 4.6 ppmV of sulfur dioxide and 10%vol of steam alongside 312 ppmV of methane balanced in air). The catalysts were synthesised using the citrate sol-gel method and characterised by BET, XRD, TPR, in situ UV–vis, in situ DRIFTS, SEM, EDX, TEM and TGA under flowing air. The performance of the catalysts was tested at atmospheric pressure and operating temperatures between 450 °C and 550 °C using three different reactant mixtures: i) 366 ppmV of methane balanced in air, ii) 347 ppmV of methane and 5.1 ppmV of sulfur dioxide balanced in air, iii) 312 ppmV of methane, 4.6 ppmV of sulfur dioxide and 10%vol steam balanced in air. This study revealed that the iron:chromium ratio has a profound impact on the performance of the catalysts. The XRD characterisation revealed that the iron and chromium-based oxides are solid solutions of hematite and eskolaite. Furthermore, the iron oxide-rich catalysts (60%mol to 80%mol iron content) contain an additional phase, which was identified as a metastable FeCr2O4 mixed oxide with spinel structure. In terms of catalytic activity, resistance to sulfur poisoning and sensitivity towards steam inhibition, these two catalysts were superior to pure iron oxide and comparable to pure chromium oxide. Under dry conditions, these two catalysts achieved higher methane conversion levels than pure chromium oxide, suggesting that the metastable FeCr2O4 spinel gives rise to improved catalytic performance. Finally, this study has proven that the sulfur resistance characteristic of chromium oxide is maintained in iron and chromium-based oxides with a chromium oxide loading as low as 20%mol, resulting in similarly effective catalysts with a lower cost, a reduced environmental impact and a considerable reduction in the health hazards associated with the exposure to chromium.

The micro-structured catalytic converter, which has proven to be 5-times more efficient than packed bed reactors for the total oxidation of residual methane, opens the door for a new line of catalytic converters that will be smaller (larger S/V ratio of the support), cheaper (non-precious metal-based catalysts) and more durable (sulfur and steam-resistant catalyst) than traditional catalytic converters.

All real processes, be they chemical, mechanical or electrical, are thermodynamically irreversible and therefore suffer from thermodynamic losses. Here, we report the design and operation of a chemical reactor capable of approaching thermodynamically reversible operation. The reactor was employed for hydrogen production via the water–gas shift reaction, an important route to ‘green’ hydrogen. The reactor avoids mixing reactant gases by transferring oxygen from the (oxidizing) water stream to the (reducing) carbon monoxide stream via a solid-state oxygen reservoir consisting of a perovskite phase (La0.6Sr0.4FeO3-δ). This reservoir is able to remain close to equilibrium with the reacting gas streams because of its variable degree of non-stoichiometry and thus develops a ‘chemical memory’ that we employ to approach reversibility. We demonstrate this memory using operando, spatially resolved, real-time, high-resolution X-ray powder diffraction on a working reactor. The design leads to a reactor unconstrained by overall chemical equilibrium limitations, which can produce essentially pure hydrogen and carbon dioxide as separate product streams. Conventional chemical reactors are subject to the equilibrium limitations imposed by the overall reaction. It has now been shown that this limitation can be overcome if reactants are fed separately to a reactor and a non-stoichiometric oxygen carrier is used to transfer both oxygen and key chemical information across a reaction cycle.

11th International Conference on Catalysis in Membrane Reactors, The authors gratefully acknowledge the research funding provided by EPSRC in the United Kingdom (grant no.EP/I010947/1)

Direct conversion of methane to methanol (DMTM) has become a particularly attractive route for the functionalisation of natural gas. Here the proven capability of copper-exchanged ZSM-5 zeolites to carry out DMTM at mild conditions has been extended by also demonstrating its capability to perform repeated reactions in a concept known as cycling. A series of five copper-exchanged ZSM-5 zeolites with different Si:Al ratio were prepared via aqueous ion exchange. The materials characterisation was carried out using a combination of transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption isotherms at −196 °C (BET and BJH methods), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and in-situ ultraviolet-visible spectroscopy (UV–vis) techniques. Under mild isothermal conditions (air activation; T = 200 °C; P = 1 atm), methanol productions of 2.8 ± 0.1 μmol·gcat−1, 26.6 ± 0.1 μmol·gcat−1, 12.5 ± 0.1 μmol·gcat−1, 10.8 ± 0.1 μmol·gcat−1 and 3.2 ± 0.1 μmol·gcat−1 were achieved for copper-exchanged ZSM-5 containing 20:1, 30:1, 50:1, 80:1, and 200-400:1 Si:Al ratio, respectively. Comparing the results of cycling Cu-ZSM-5 (Si:Al = 200-400:1) with those obtained for Cu-ZSM-5 (Si:Al = 30:1) has led to the conclusion that hydrophobicity plays a decisive role in the capability to cycle, with materials containing a higher Si:Al being better suited to cycling. A total of five repeated cycles were achieved using Cu-ZSM-5 (Si:Al = 200-400:1). The methanol production was higher, the lower the Si:Al ratio with an optimal Si:Al = 30:1. However, TEM analysis suggests that precipitation of copper nanoparticles on the catalyst support structure could account for the reduced activity found within the material containing the lowest Si:Al. in situ UV-vis spectroscopy characterisation of the copper-exchanged ZSM-5 zeolite materials under similar DMTM reaction conditions suggested that active copper complexes were being created and then destroyed during the DMTM reaction. A speculative discussion of the copper complexes present within these materials has also been provided.

In this study, asymmetric and symmetric Al 2 O 3 hollow fibres were employed as a support of a 10% CuO/CeO 2 catalyst in the development of an asymmetric hollow fibre reactor (AHFR) and a symmetric hollow fibre reactor (SHFR), respectively. The 10% CuO/CeO 2 catalyst was successfully deposited in both Al 2 O 3 hollow fibre substrates by the sol–gel Pechini method. The impregnated fibres were characterized by Ar permeability, Hg porosimetry, X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution optical microscopy. The water gas shift (WGS) reaction was chosen as a sample reaction to compare the performances of both AHFR and SHFR with a traditional fixed bed reactor (FBR). The catalytic activity tests in the FBR were carried out using the powder ground from either the asymmetric or symmetric Al 2 O 3 hollow fibre impregnated with 10% CuO/CeO 2 . Two different configurations, “dead-end” and “open-end”, were studied in the AHFR and SHFR. The experimental results show that, despite the differences observed between the AHFR and SHFR, both reactors offer important advantages over conventional FBRs including high catalytic activity along with a better selectivity.

Catalytic propane dehydrogenation has been tested on different reactor configurations employing Pt–Sn/MgAl2O4 as a catalyst. Hollow fiber palladium membranes coupled to the two-zone fluidized bed reactor (TZFBR) combine the possibility of improving propane conversion by hydrogen removal from the reaction bed through the membrane with in situ catalyst regeneration in the lower section of the TZFBR. Experiments have been carried out at different reaction temperatures and time on stream. In addition, the optimum regenerative agent flow fraction (diluted oxygen) to be fed into the TZFBR has been determined at the reaction temperatures between 500 °C and 600 °C to get a constant catalytic activity without net deactivation. Moreover, the TZFBR with palladium membranes has been successfully tested, displacing the reaction equilibrium towards the production of propylene, and still keeping steady state in the catalytic propane dehydrogenation. These results were better than those reported in the literature for con...

The use of non-renewable resources together with the high-energy consumption and low selectivity makes current reforming processes unsustainable solutions for syngas and/or hydrogen production. New reforming technology is needed in order to control and manage CO2 emissions, circumvent the current high-energy consumption and enhance the selectivity of the reforming process. The UK Catalysis Hub has proposed three different approaches to reforming which are envisaged to overcome the above-mentioned issues. The aim of this chapter is to present a critical review of recent approaches in reforming processes for hydrogen and/or syngas production, with particular focus on catalytic reforming of alcohols, chemical looping reforming (CLR) technology, and novel photocatalytic reforming routes. Likewise, the last section of the chapter summaries the challenges and current achievements of the UK Catalysis Hub projects in this area. Read More: http://www.worldscientific.com/doi/abs/10.1142/9781786341228_0001

The present work provides a summary of the state of the art of using asymmetric ceramic hollow fibres as substrates for inorganic dense membranes and/or catalysts, in the development of new hollow fibre reactors for heterogeneous catalytic gas phase reactions. Three different hollow fibre reactor designs were studied; a hollow fibre membrane reactor (HFMR), a catalytic hollow fibre micro-reactor (CHFMR) and a catalytic hollow fibre membrane micro-reactor (CHFMMR). The performance of the HFMR, CHFMR and CHFMMR in different reactions such as methanol steam reforming (MSR), dry reforming of methane (DRM) and water gas shift (WGS) was compared with that of a traditional fixed-bed reactor configuration. A Pd-based membrane (thickness of approximately 5 μm) was deposited on the outer surface of the asymmetric ceramic hollow fibres using an electroless plating technique, in the development of both the HFMR and CHFMMR. The Pd-based membranes showed high H2 permeability ( 10.7 ≤ P H 2 ≤ 14.1 L m − 2 s − 1 atm − 1 / 2 at T = 450 °C and ΔP = 1 bar) and infinite H2 selectivity under the different reaction conditions studied. The catalyst was deposited on the walls of finger-like region of the asymmetric ceramic hollow fibres by the sol–gel Pechini method, in the development of the CHFMR and CHFMMR. The CHFMMR, which showed a performance 2.5 times higher than that in a traditional fixed-bed reactor, is proposed as a key step in the intensification of heterogeneous catalytic gas phase processes by integration of membrane-reactor and micro-reactor technologies.

A novel catalytic hollow fiber membrane microreactor (CHFMMR) generates hydrogen suitable for vehicular applications. Ethanol is converted to hydrogen through the ethanol steam reforming (ESR) with 5 mole of water per mole of ethanol. Yttria stabilised zirconia (YSZ) hollow fibres have been used as substrate for the deposition of Pd/Ag membrane on the outer shell of the hollow fiber and for 10 wt%NiO/MgO–CeO2 ESR catalyst inside the hollow fiber. The ESR has been carried out in a fixed-bed reactor, the catalytic hollow fibre microreactor (CHFMR) and the CHFMMR at temperatures ranging from 350 to 550 °C. At 510 °C, and the flow rate of hydrogen produced in the CHFMMR is three fold higher than that in the fixed-bed reactor and two fold higher than that in the CHFMR despite less amount of the catalyst is used in the CHFMMR. During the operation of the CHFMMR, high purity hydrogen is obtained outside of the shell, and the yield of this high purity hydrogen is more than 53% of the total hydrogen produced in the ESR.

A novel catalytic hollow fibre microreactor (CHFMR) that uses an asymmetric YSZ hollow fibre has been developed for on-board H 2 generation to be used in portable device applications. In the development of CHFMR, the 10 wt.%Ni/MgO–CeO 2 catalyst that was selected as a catalyst for the ethanol steam reforming (ESR) was impregnated into the inner surface of YSZ hollow fibres using the sol–gel Pechini technique. The catalytic activity tests were performed in the YSZ hollow fibres and the results were compared with fixed-bed reactors. An excellent catalyst utilisation in the CHFMR enables a small quantity of catalyst to be used for the ESR. The result shows that 8 units of CHFMR that only has an 18 mg catalyst produced a relatively similar amount of H 2 compared to a fixed-bed reactor that used 100 mg.

In this study, CuO/CeO2 catalysts with a Cu content ranging from 5% to 40% were synthesized by sol–gel Pechini method and were tested in a fixed-bed reactor for water gas shift (WGS) reaction. The catalysts were characterized by XRD, N2 adsorption isotherms at 77 K (SBET) and H2-TPR. Based on the catalytic activity results, 10% CuO/CeO2, identified to be the most active catalyst, was deposited inside finger-like regions of an Al2O3 hollow fibre support for the further development of both catalytic hollow fibre micro-reactor (CHFMR) and catalytic hollow fibre membrane micro-reactor (CHFMMR) where Pd or Pd/Ag membrane was coated on the outer layer of the Al2O3 hollow fibre using a single or multilayer electroless plating (ELP) technique. The prepared catalytic membranes were characterized by SEM, EDX, and pure H2 and Ar permeation. Also, a comparative study of the CO conversion obtained in the WGS reaction as a function of the reaction temperature (from 200 °C to 500 °C) in a fixed-bed reactor, a CHFMR, a Pd-CHFMMR and a Pd/Ag-CHFMMR, was performed showing that the conversion was highest in the Pd/Ag-CHFMMR.

Al 2 O 3 hollow fibres fabricated by phase-inversion, followed by sintering at different temperatures (1350, 1400 and 1450 °C) have been employed for the further development of a novel catalytic hollow fibre micro-reactor (CHFMR). After depositing with a 10%CuO/CeO 2 catalyst, the catalytic activity of the CHFMR has been compared with that of a conventional fixed-bed reactor using water gas shift (WGS) as a sample reaction. The deposition of catalyst into the finger-like voids was carried out using the sol–gel Pechini method. The Al 2 O 3 hollow fibres were characterized before and after catalyst deposition by BET surface area analysis, Hg porosimetry and SEM–EDS. The catalytic activity tests were performed at P = 1 atm and between T = 200 and 400 °C. It has been observed that the dispersion of the 10%CuO/CeO 2 catalyst within the Al 2 O 3 hollow fibres is strongly dependent on the physical and chemical properties of the fibre surface, which are determined by the sintering temperature. Finally, an increase of 20% in the CO conversion of the WGS reaction was observed for the CHFMR when compared with a conventional fixed-bed reactor, since the finger like structure of Al 2 O 3 hollow fibres ( D p = 10 μm) acts as a micro-reactor and improves the heat and mass transfer, and the mixing of gases during the reaction.

This article describes development of a catalytic hollow fibre membrane micro-reactor (CHFMMR) for high purity H2 production. Asymmetric Al2O3 hollow fibres produced by a phase-inversion and sintering technique were employed as a single substrate for both coating of the Pd membrane and impregnation of the 30%CuO/CeO2 catalyst. The Pd membrane was first deposited onto the outer layer of Al2O3 hollow fibre using the electroless plating (ELP) technique, followed by impregnation of the 30%CuO/CeO2 catalyst into the inner finger-like structure of the substrate using the sol–gel Pechini method. Performance of the proposed reactor was carried out using water gas shift (WGS) reaction as a sample reaction. A comparative study of conversion obtained in the WGS reaction as a function of the reaction temperature (from 200 °C to 500 °C) in a fixed-bed reactor, a catalytic hollow fibre micro-reactor (CHFMR) and the CHFMMR using different flow rates of a sweep gas (from 45 to 70 ml/min) was performed, concluding that the conversion is the highest in the CHFMMR. It is important to highlight that, at 500 °C and a sweep gas flow rate of 75 ml/min, a conversion of 17% higher than the corresponding thermodynamic equilibrium conversion was achieved in the CHFMMR. In the operation of the CHFMMR, high purity H2 has been obtained in the shell side, which was 78% of the total H2 produced in the WGS reaction.

A novel catalytic hollow fibre membrane microreactor (CHFMMR), consisting of a thin Pd layer and a 30%CuO/CeO2 catalyst supported on an asymmetric Al2O3 hollow fibre has been developed. In the preparation of the CHFMMR, the Pd layer was deposited on outer surface of the hollow fibre substrate by electroless plating first, followed by impregnation of 30%CuO/CeO2 catalyst in the finger pores located in the inner surface of the hollow fibre lumen by sol–gel coating. The catalytic activity of the CHFMMR was tested using water–gas shift (WGS) reaction and compared to that of a catalytic hollow fibre microreactor (CHFMR) and a conventional fixed-bed reactor. The catalytic activity tests were performed at 1 atm and from 200 °C to 500 °C using different flow rates of sweep gas (from 50 to 75 ml/min). The ratio between CO and H2O in the feed was 1 to 0.5 with a space velocity of 80 l g−1 h−1. The conversion obtained in the CHFMMR is 35% higher than that in the conventional fixed-bed reactor. Furthermore, a conversion which was 17% higher than the corresponding thermodynamic equilibrium conversion was achieved in the CHFMMR, at 500 °C with a sweep gas flow rate of 75 ml/min.

Ru catalysts were supported on two different carbon materials, multiwall carbon nanotubes and bamboo-like carbon nanotubes doped with nitrogen, which were synthesized by catalytic chemical vapour deposition of C 2 H 2 /H 2 /N 2 or C 2 H 2 /NH 3 /H 2 /N 2 , respectively, over Fe/SiO 2 catalyst. All the carbon supports and/or the prepared Ru catalysts were characterized by several techniques including transmission electron microscopy, X-ray photoelectron spectroscopy, N 2 adsorption isotherms and CO chemisorption. The Ru catalysts were tested in the catalytic ammonia decomposition reaction. High yields towards hydrogen production were achieved. Carbon nanotubes were heated in an inert atmosphere at temperatures up to 1773 K in order to study the effects of such support treatments on the ammonia decomposition reaction. The elimination of acidic groups from the surfaces, prior to catalyst preparation, and/or the surface graphitization of the materials produced a higher catalytic activity during the reaction. The catalytic activity of Ru particles was significantly improved when supported on carbon nanotubes doped with nitrogen.

A series of activated carbon supported Ru catalysts have been reduced at different temperatures under hydrogen flow, and in some cases under ammonia flow, in order to modify the morphology and the particle size of the metallic active sites. CO chemisorption and transmission electron microscopy have been applied to follow the variations of these particles. The samples have been tested in the ammonia decomposition reaction, where systematic differences in catalytic activities as consequence of the support modification as well as due to the changes in the Ru particle sizes have been detected. Furthermore when potassium is added as catalyst promoter the sintering of Ru particles is significantly diminished and thus the changes in catalytic activities are inhibited. The electronic states of the Ru particles have been evaluated by determination of the chemisorption heats of the CO probe molecule. A part of other promoter or support effects it seems to exit a critical mean size for Ru particles on where maximum of catalytic activity is achieved. This behavior can be rationalized by the presence of surface highly active B5 sites, which consist of an arrangement of three Ru atoms in one layer and two further Ru atoms in an internal layer. These especial surface sites are expected to be in a higher proportion over Ru crystallites of those critical sizes, namely for Ru diameter sizes in the rage of 3–5 nm.

Ru catalysts supported on three types of graphite nanofiber materials, stacked-cup (PR24-HHT), platelet (CNF-P) and bamboo-like (CNF-B), have been synthesized and characterized by HRTEM and calorimetry of CO adsorption. The influence of the support nanostructure on their catalytic performance in the selective hydrogenation of paracetamol was also studied. An inverse correlation between the heats of CO adsorption and the activity and stereoselectivity to the trans-4-acetamidocyclohexanol was found. The results have been rationalized in terms of the morphology and electronic properties of the metal particles. These features are controlled by the different location of the crystallites and the metal-support interactions induced that eventually depend on the nanostructure of the support. As a consequence the supports seem to modify the Ru nanoparticles surface structures, and the shift in selectivities can be related with variations of the reactant chemisorption over such Ru surfaces.

Acetylene CVD carbon replication of a hierarchical pore silica-based material, Fe-UVM-7, is reported. The original template organization, which is based on the aggregation of mesoporous nanoparticles, is accurately replicated in the final carbon material: a bimodal porous carbon combining mesoporous nanoparticles and inter-particle textural-like pores which provide high surface area, a highly accessible pore system and semi-crystalline pore walls in the form of graphitic-like nanodomains is presented.

Carbon nanotubes have been synthesized by catalytic chemical vapour deposition (CVD) of acetylene, over several iron–silica catalysts, in a fluidized bed reactor at 973 K. High yield and selective syntheses of carbon nanotubes was achieved with this reactor. The carbonaceous samples were submitted to acidic treatments (HF and/or HNO 3 ), which clearly produced structural changes in the nanotubes structure, as observed by transmission electron microscopy (TEM). Moreover, the formation of oxidic groups on the surface of carbon nanotubes was followed by means of temperature desorption experiments and thermo-gravimetric analyses. Adsorption of hydrogen at 300 K and relative high pressures (up to 70 bar) has been also investigated on these purified carbon nanotubes, besides on different carbon materials.

Catalytic ammonia decomposition for the generation of high purity CO x free hydrogen has been performed in a multifunctional membrane reactor with Pd membrane walls for the hydrogen separation and a high performance Ru-carbon catalyst. By adjusting the experimental conditions an enhancement of the efficiency of the system for the hydrogen production has been achieved. The chemical thermodynamic equilibrium conversion has been exceeded using an improved catalyst, at temperatures lower than those reported in the literature. In addition, both the membrane and the catalyst components were very stable. The system showed no loss of performance after having been operated for several cycles.

In this study, asymmetric Al 2 O 3 hollow fibres have been used as a support for either a Cu/Zn/GaO X based catalyst or a Pd/Ag membrane in the development of a catalytic hollow fibre micro-reactor (CHFMR) and hollow fibre membrane reactor (HFMR), respectively. The Cu/Zn/GaO X based catalyst was successfully deposited inside the finger-like region of the Al 2 O 3 hollow fibres by the co-precipitation technique. The impregnated fibres were characterised by X-ray diffraction (XRD), high resolution optical microscopy, scanning electron microscopy (SEM) and energy-disperse X-ray spectroscopy (EDS). The Pd/Ag membrane was deposited on the outer surface of the Al 2 O 3 hollow fibres by the electroless plating technique and was characterized by SEM, and Ar and H 2 permeability. The performance of both the CHFMR and HFMR was compared with that of a conventional fixed-bed reactor (FBR) during the methanol steam reforming (MSR) reaction. The CHFMR offers important advantages over conventional FBRs such as high catalytic activity along with a maximum selectivity. It has been observed that at 300 °C the CH 3 OH conversion in the CHFMR was 6 times larger and the CO produced 4 times smaller than that obtained in a conventional FBR. Likewise, the results obtained using the HFMR during the MSR showed that at 250 °C the CH 3 OH conversion was 75%, which is 34% higher than that obtained in the conventional FBR. Moreover, at 250 °C and using a sweep gas of 100 ml/min in the HFMR, the H 2 recovery index of the Pd/Ag membranes was 50%, which showed the feasibility of a large production of high purity H 2 (5.5 ml/mg h). The Pd/Ag membrane was stable under the reaction conditions, showing high H 2 permeance (1.2×10 −3 mol m −2 s −1 Pa −1/2 at 300 °C) and permeability (7.6×10 −9 mol m −1 s −1 Pa −1/2 at 300 °C) and infinite selectivity to H 2 .

In this study, NiO/MgO/CeO2 catalysts with Ni content from 5% to 30% were synthetized by sol–gel method and tested in a fixed-bed reactor (FBR) in the glycerol steam reforming (GSR) reaction. The catalysts were characterized by N2 adsorption isotherms at −196 °C (SBET), X-ray diffraction (XRD), H2 temperature programmed reduction (H2-TPR), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). The 20% NiO/MgO/CeO2 catalyst, which showed the highest catalytic activity in GSR reaction, was selected to be deposited in the finger-like region of the asymmetric Al2O3 hollow fibre and the sponge-like region of the symmetric Al2O3 hollow fibre in the development of the asymmetric hollow fibre reactor (AHFR) and symmetric hollow fibre reactor (SHFR), respectively. The impregnated ceramic substrates were characterized by scanning electron microscopy (SEM), EDX and TEM. The performances of the AHFR and SHFR were compared with that in a conventional FBR during the GSR reaction. Both AHFR and SHFR were operating at “dead-end” configuration at a temperature range from 250 °C to 550 °C, atmospheric pressure and in a reactant mixture of steam and glycerol (16:1 molar ratio). At 550 °C the glycerol conversion in the AHFR and SHFR was 70% and 46%, respectively, which are 5 and 2 times higher than that obtained in the FBR. The different performances of the AHFR and SHFR could be explained due to the unlike catalyst particle size deposited in the asymmetric and symmetric substrates, 8 nm and 3 nm, respectively., The authors gratefully acknowledge the research funding provided by EPSRC in the United Kingdom (grant no. EP/G01244X/1) and by MINECO at Spain (projects CTQ2011-29272-C04-01 and -03).

In this study, performance and feasibility of a hollow fibre membrane reactor (HFMR), consisting of a packed catalyst bed around a Pd coated Al2O3 hollow fibre membrane, has been studied and compared with both conventional Pd based tubular membrane reactor (TMR) fabricated from a stainless steel substrate and traditional fixed-bed reactor (FBR). The ceramic based HFMR presents several advantages over MRs such as the deposition of ultra thin Pd membranes and the possibility to scale up the whole multifunctional process by module configuration. The results obtained at 450 °C during the methane dry reforming (MDR) reaction showed that, although CH4 conversion using the HFMR was almost the same as that of a catalytic TMR, the amount of Pd employed for the Pd layer deposition in the HFMR was fifteen times less than that in TMR. Moreover, the CH4 conversion using the HFMR was 72% higher than that in a traditional FBR and 34% higher than thermodynamic equilibrium. Also, a high purity COX-free H2 production (10.5 ml/mg h) was achieved at 525 °C using a sweep gas of 100 ml/min in the lumen side of the HFMR., The authors gratefully acknowledge the research funding provided by EPSRC in the United Kingdom (grant No. EP/G012679/1), MINECO in Spain (projects CTQ2011-29272-C04-01 and 03).

Oxygen surface groups, which are typically present on the surface of activated carbon, have a decisive effect on the achieved dispersion of active phases, which affects the electronic properties of the surface sites and stabilizes the materials against sintering phenomena. Therefore, the desorption of oxygen surface groups during the decomposition–reduction of the metal salt precursors of the fresh carbon‐based catalysts can lead to surface reconstruction of the metal nanoparticles, which can significantly affect their catalytic activity. In this work, the oxidation states of Ru atoms supported on both an activated carbon thermally treated to remove all oxygen groups and the untreated material were studied during the reduction process. The precursor to prepare these catalysts is Ru(NO)(NO3)3. The main results were obtained by using in situ X‐ray absorption near‐edge structure analysis of the Ru K‐edge under conditions comparable to the temperature‐programmed reduction experiments. The different reduction mechanism observed in each of the catalysts, of a multistep nature if oxygen surface groups are present and single‐step in the case of clean graphitic surfaces, can be regarded as a typical metal–support interaction. Moreover, differences in both the final Ru oxidation state and the subsequent interaction of the active phase with the support are the main cause of the five‐times higher catalytic activity observed in the presence of the catalyst without surface oxygen groups for the NH3 decomposition reaction., This work was supported by the Spanish Government (project CTQ2011‐29272‐C04‐01 and 03). F.R.G.‐G. gratefully acknowledges financial support from the Spanish Ministry of Science and Technology, JdC postdoc programme.

The Temporal Analysis of Products (TAP) technique has been used to investigate the mechanism involved in the catalytic decomposition of NH(3) over a series of catalysts consisting of activated carbon supported Ru (promoted and non-promoted with Na) and over an activated carbon supported Ir. An extensive study of the role played by both the support and the promoter in the "side reactions" and in the stability and surface lifetime of the NH(x) species has been performed. It was suggested that the N(2) produced during the first steps of the reaction over the activated carbon supported Ru catalysts promoted with Na forms a Na-N-Ru complex at the promoter-transition metal crystallite interface. This study also suggests that the Na promoter prevents the diffusion of hydrogen from the metal to the support via spill-over. A similar effect was observed after the thermal treatment at high temperature of the carbon catalyst support. Finally large differences in multi-pulse TAP results have been detected between Ru and Ir catalysts implying that the NH(3) decomposition reaction mechanism must be different on both metals.

El aumento en el consumo de propileno ha favorecido el desarrollo de nuevos procesos para su producción, siendo la deshidrogenación catalítica de propano una alternativa muy interesante. Sin embargo, este proceso lleva asociadas varias limitaciones: reacción endotérmica y limitada por el equilibrio termodinámico, existencia de reacciones secundarias que disminuyen la selectividad a propileno, y desactivación del catalizador por formación de coque. El reactor de lecho fluidizado de dos zonas con membrana permeable al hidrógeno se presenta como un dispositivo capaz de solventarlas todas en un único espacio físico, complementándolo con un catalizador (Pt-Sn/MgAl2O4) que reduce la formación de reacciones secundarias. En este sistema existen dos puntos de alimentación, generánose dos zonas de diferente atmósfera: una zona superior de reacción, y una inferior de regeneración con atmósfera oxidativa. Así, en la zona superior se produce el propileno y se desactiva el catalizador, el cual desciende (por el fenómeno de fluidización) a la zona de regeneración donde se reactiva por combustión del coque depositado, aportando un calor directo al sistema endotérmico. Por ello se consigue un sistema cícliclo de reacción-regeneración que permite mantener un estado estacionario del proceso, logro inviable en los reactores tradicionales. Además el hidrógeno formado en reacción se separa a través de una membrana de paladio, modificando y solventando la limitación del equilibrio termodinámico hacia una mayor formación de productos y aumentando el rendimiento del proceso. Así, este sistema supone un claro ejemplo de intensificación de procesos.