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Abstract: As a clean energy carrier, hydrogen has attracted global attention in recent years, because it could address issues that are related to reducing global climate change. It has to be stipulated that to date''s processes for hydrogen production using fossil fuels need to be coupled with CO2 separation and storage. Thermally and hydrothermally stable microporous membranes with intrinsic high H2/CO2 selectivity are highly demanded in steam-reforming and water gas-shift processes for H2 gas separation. In this study a composite alumina–titania membrane was synthesized by the combination of atomic layer deposition (ALD) and sol–gel processes. By adjusting the number of ALD cycles (280 cycles), a thin TiO2 layer corresponding to a thickness of ∼10nm was deposited on the surface of γ-Al2O3 membranes. The gas permeation was tested to assess the membranes’ gas separation performance. The membranes exhibited a good balance between H2 permeance and separation properties. At 450K, the H2 permeance is approximately 12.5×10−8 molm−2 s−1 Pa−1 and the separation factor is 5.8 for a H2/CO2 mixture. The results clearly demonstrate that the studied deposition method ALD is a promising route to prepare ceramic microporous membranes for hydrogen separation. [Copyright &y& Elsevier]

Structural, thermodynamic and phase properties in the Na2S–H2O system for application in a chemical heat pump have been investigated using XRD, TG/DTA and melting point and vapour pressure determinations. Apart from the known crystalline phases Na2S·9H2O, Na2S·5H2O and Na2S a new phase Na2S·2H2O has been proven to exist. Na2S·SHAPE="CASE" ALIGN="C" STYLE="S">12H2O is not a phase but a 3:1 mixture of Na2S and Na2S·2H2O, presumably stabilised by very slow dehydration kinetics. The vapour pressure–temperature equilibria of the sodium sulphide hydrates have been determined and a consistent set of thermodynamic functions for these compounds has been derived. XRD measurements indicate the topotactic character of the transitions between the hydration states. [Copyright &y& Elsevier]

Pd–Cu is a well-known alloy for H 2 separation membranes. Using a new optical combinatorial method we determined the H 2 permeability of Pd–Cu alloys at room temperature in relation to their crystal structure and microstructure. Compositional gradient samples allow us to determine the intrinsic permeability as a function of the alloy composition. From a detailed XRD, TEM and AFM analysis we find that the pure fcc and bcc phases have a very low permeability, whereas the mixed bcc/fcc phases show the highest permeability for thin film alloys prepared at higher temperatures. Therefore interstitial-bulk hydrogen diffusion is most probably not the main transport mechanism. Instead we argue that the hydrogen transport occurs mainly along the heterogeneous grain boundaries. As compared to the bulk phase diagram we find that the mixed bcc/fcc region in our Pd–Cu thin films is larger than reported in literature (ranging from 43 at% – 65 at% Pd at 483 K). [ABSTRACT FROM AUTHOR]

Abstract: In this study, alumina, silica and alumina-silica binary (36% mol silica) thin films are synthesized using the sol-gel technique. These form the basis for future gas separation membranes. The characterization of the synthesized oxides was performed using nitrogen physisorption, X-ray diffraction (XRD), Doppler-broadening measurements on the 511keV annihilation photon peak, together with 3γ/2γ analysis, and Fourier transform infrared spectroscopy (FTIR) of adsorbed CO. It is found that silica is microporous, γ-alumina is mesoporous, and the binary material shows fingerprints of both the meso- and microporous nature of its constituents as well as of the respective crystal structures. These results open the possibility to also investigate thin supported porous films (a few microns thick), and especially the setting and drying aspects on porous supports for membrane production, using the positron annihilation technique. [Copyright &y& Elsevier]

Abstract: Apart from H2 production, hydrogen membrane reforming is also an attractive process for CO2 capture when integrated in a natural gas fired power plant. In this study, a bench-scale multi-tubular Pd membrane reactor which has a capacity of 8.5Nm3/h H2 product, was used to carry out the methane steam reforming reaction at near-practical working conditions: 823K and up to 35bar(a). The maximum CH4 conversion and H2 production rate were respectively achieved as 73.4% and 1.3Nm3/h at a feed/permeate pressure of 35/5bar(a). A typical pre-reformed mixture (PR) was used as feed gas in this work, and was found to be more efficient than CH4/H2O mixture that is normally adopted in the literature. The steam sweep exhibited a similar effect as N2 sweep except at very low space velocity that revealed steam outperforming N2. Stable performance was found both for the membranes and the membrane reactor under the challenging conditions for over 30 days, showing a great potential of hydrogen membrane reforming for H2 production. However, membrane reforming is found to be less attractive for CO2 capture due to the low CH4 conversion and consequent low driving force for transmembrane hydrogen transport at the high permeate pressure typical for NGCC operation. [Copyright &y& Elsevier]

Abstract: The search for and development of stable Pd-based membranes for hydrogen separation applications with resistance to hydrogen embrittlement and cracking is a challenging and time-consuming task. Membrane failure is most often caused by the occurrence of the α–β phase transition during hydrogen absorption and desorption by the Pd-alloy below the critical temperature. By finding a suitable alloy with a critical temperature below room temperature, the membrane lifetime can be extended tremendously. Here we present a combinatorial approach that enables the fast screening of phase transitions in multi-component Pd-alloys for hydrogen separation membranes by experiments and thermodynamic calculations. The method is applied to the well-documented Pd–Cu alloy compositions. Hydrogenography, a compositional gradient thin film technique, is used to experimentally investigate the alloy compositions. Using a new phenomenological method to determine the critical temperature from hydrogenography measurements, we show that the experimental results and the calculations, using the Cluster Variation Method (CVM), agree well with the phase boundaries and critical temperatures reported in literature. Our results show that the combined capabilities of hydrogenography and CVM enable an efficient screening of promising multi-component alloys for which thermodynamic data are scarce or absent. [Copyright &y& Elsevier]

Abstract: Neutron diffraction and thermal desorption spectroscopy are used to determine the details in the crystallographic structure and the deuterium desorption characteristics of deuterated Pd–Au alloys. Compositions under investigation include alloys corresponding to both subcritical and supercritical conditions with respect to the α–β phase transitions. The effect of the Au-content on deuterium desorption properties is discussed in relation to the degree of deuterium loading and the phase diagram. Furthermore, the distribution of deuterium over the octahedral and tetrahedral interstitial sites is determined. The tetrahedral site occupancy increases with increasing Au content and is significant for both supercritical and subcritical phases. [Copyright &y& Elsevier]