Selective deposition of Pd nanoparticles in porous PET membrane for hydrogen separation

Hydrogen purification based on Pd deposition in porous polymeric membranes show promising results for hydrogen permeability and selectivity. It is due to high absorption property of Pd nanoparticles. In this work, gas permeability of carboxylic group functionalized Polyethylene terephthalate (PET) membranes with different time of functionalization have been examined. It has been found that PET membrane having more –COOH group shows higher selectivity for Hydrogen (H₂). Further to improve the selectivity, these carboxylated PET membranes dipped in Pd nanoparticles solution for 6 h and found more selective for H₂ in comparison to Carbon dioxide (CO₂) and Nitrogen (N₂). As the carboxylation increases selectivity of H₂ improves drastically in the beginning and nearly get saturated after 24 h. Similar trend has been observed for these membranes after Pd nanoparticles deposition. Fourier transform infrared spectroscopy (FTIR) spectra of these membranes revealed that intensity of peaks related to –COOH group at 2968 cm^?1 & 1716 cm^?1 increases with functionalization time. Field Emission Scanning Electron Microscopy (FESEM) was used to study the surface morphology of membranes.     

Palladium nanoparticle binding in functionalized track etched PET membrane for hydrogen gas separation

In this work, track-etched poly (ethylene terephthalate) (PET) membranes having different pore sizes were functionalized by the carboxylic groups and the amino groups. Palladium (Pd) nanoparticles of average diameter 5 nm were synthesized chemically and deposited onto pore walls as well as on the surface of these pristine and functionalized membranes. Effect of Pd nanoparticles binding on these membranes were explored and aminated membrane were found to bind more Pd nanoparticles due to its affinity. The morphology of these composite membranes is characterized by Scanning Electron Microscope (SEM) for confirmation of Pd nanoparticle deposition on pore wall as well as on the surface. Gas permeability of functionalized and non-functionalized membranes for hydrogen and carbon dioxide has been examined. From the gas permeability data of hydrogen (H₂) and carbon dioxide (CO₂) gases, it was observed that these membranes have higher permeability for H₂ as compared with CO₂. Due to absorption of hydrogen by Pd nanoparticles selectivity of H₂ over CO₂ was found higher as compared to without Pd embedded membranes. Such type of membranes can be used to develop hydrogen selective nanofilters for purification/separation technology.     

High performance composite hollow fiber membranes for CO2/H2 and CO2/N2 separation

The search for a clean energy source as well as the reduction of CO₂ emissions to the atmosphere are important strategies to resolve the current energy shortage and global warming issues. We have demonstrated, for the first time, a Pebax/poly(dimethylsiloxane)/polyacrylonitrile (Pebax/PDMS/PAN) composite hollow fiber membrane not only can be used for flue gas treatment but also for hydrogen purification. The composite membranes display attractive gas separation performance with a CO₂ permeance of 481.5 GPU, CO₂/H₂ and CO₂/N₂ selectivity of 8.1 and 42.0, respectively. Minimizing the solution intrusion using the PDMS gutter layer is the key to achieving the high gas permeance while the interaction between poly(ethylene oxide) (PEO) and CO₂ accounts for the high selectivity. Effects of coating solution concentration and coating time on gas separation performance have been investigated and the results have been optimized. To the best of our knowledge, this is the first polymeric composite hollow fiber membrane for hydrogen purification. The attractive gas separation performance of the newly developed membranes may indicate good potential for industrial applications.     

Hydrogen permeation through a Pd-based membrane and RWGS conversion in H2/CO2, H2/N2/CO2 and H2/H2O/CO2 mixtures

This study investigated the effect of gases such as CO₂, N₂, H₂O on hydrogen permeation through a Pd-based membrane −0.012 m² – in a bench-scale reactor. Different mixtures were chosen of H₂/CO₂, H₂/N₂/CO₂ and H₂/H₂O/CO₂ at temperatures of 593–723 K and a hydrogen partial pressure of 150 kPa. Operating conditions were determined to minimize H₂ loss due to the reverse water gas shift (RWGS) reaction. It was found that the feed flow rate had an important effect on hydrogen recovery (HR). Furthermore, an identification of the inhibition factors to permeability was determined. Additionally, under the selected conditions, the maximum hydrogen permeation was determined in pure H₂ and the H₂/CO₂ mixtures. The best operating conditions to separate hydrogen from the mixtures were identified.     

Effect of Pd overlayer and mixed gases on hydrogen permeation of Pd/Nb30Hf35Co35/Pd composite membranes

Effect of Pd overlayer and mixed gases on hydrogen permeation of Pd/Nb₃₀Hf₃₅Co₃₅/Pd composite membranes was investigated. The diameter of Pd particle increases with increasing sputtering power. With this change, the membrane shows a signification reduction in hydrogen permeability/or flux, but its durability and stability increases significantly, which can be mainly attributed to a decrease in hydrogen solubility coefficient. In addition, H₂S impurity in mixed gases can greatly degrade membrane performance, especially the hydrogen permeability, whereas the Ar impurity content has less effect in the temperature range of 523–673 K. Lowering of permeability caused by the change of gas purity can be attributed to a decrease in hydrogen solubility, which is closely related to the stronger adsorption of H₂S molecules to the Pd overlayer of the membrane. Thus, it is concluded that aside from the optimum design for composition of Nb-based hydrogen permeable alloy to improve their permeability, the control of Pd overlayer film on membrane surface and gas purity in the feed gas is important.     

CO2 methanation combined with NH3 decomposition by in situ H2 separation using a Pd membrane reactor

Combination of the reactions by means of membrane separation techniques are of interest. The CO₂ methanation was combined with NH₃ decomposition by in situ H₂ separation through a Pd membrane. The CO₂ methanation reaction in the permeate side was found to significantly enhance the H₂ removal rate of Pd membrane compared to the use of sweep gas. The reaction rate of CO₂ methanation was not influenced by H₂ supply through the Pd membrane in contrast to NH₃ decomposition in the retentate side. However, the CH₄ selectivity could be improved by using a membrane separation technique. This would be caused by the active dissociated H species which might immediately react with adsorbed CO species on the catalysts to CH₄ before those CO species desorbed. From the reactor configuration tests, the countercurrent mode showed higher H₂ removal rate in the combined reaction at 673 K compared to the cocurrent mode but the reaction rate in CO₂ methanation should be improved to maximize the perfomance of membrane reactor.     

H2 production via water gas shift in a composite Pd membrane reactor prepared by the pore-plating method

In this work, H₂ production via catalytic water gas shift reaction in a composite Pd membrane reactor prepared by the ELP “pore-plating” method has been carried out. A completely dense membrane with a Pd thickness of about 10.2 μm over oxidized porous stainless steel support has been prepared. Firstly, permeation measurements with pure gases (H₂ and N₂) and mixtures (H₂ with N_2, CO or CO₂) at four different temperatures (ranging from 350 to 450 °C) and trans-membrane pressure differences up to 2.5 bar have been carried out. The hydrogen permeance when feeding pure hydrogen is within the range 2.68–3.96·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5, while it decreases until 0.66–1.35·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5 for gas mixtures. Furthermore, the membrane has been also tested in a WGS membrane reactor packed with a commercial oxide Fe–Cr catalyst by using a typical methane reformer outlet (dry basis: 70%H₂–18%CO–12%CO₂) and a stoichiometric H₂O/CO ratio. The performance of the reactor was evaluated in terms of CO conversion at different temperatures (ranging from 350 °C to 400 °C) and trans-membrane pressures (from 2.0 to 3.0 bar), at fixed gas hourly space velocity (GHSV) of 5000 h⁻¹. At these conditions, the membrane maintained its integrity and the membrane reactor was able to achieve up to the 59% of CO conversion as compared with 32% of CO conversion reached with conventional packed-bed reactor at the same operating conditions.     

Graphene decorated Pd-Ag nanoparticles for H2 sensing

Hydrogen sensor based on graphene nano-composite with Pd-Ag nanoparticles was fabricated by MEMS process. Structural and morphological properties of the sensing film were studied by an energy dispersive spectroscopy (EDS) and field emission scanning electron microscopy (FESEM), respectively. The H₂ sensing properties of as-formed sensor were investigated by measuring the resistance changes at different H₂ concentrations. The maximum gas response was 16.2% at 1000 ppm of H₂ gas. The gas sensitivity of the as-formed H₂ sensor showed linear behavior with the hydrogen concentration. Experimental results showed that the coupling of graphene with Pd/Ag alloy enhanced significantly hydrogen sensing performance.     

Bench-scale WGS membrane reactor for CO2 capture with co-production of H2

This study investigated the water-gas shift reaction in a bench-scale membrane reactor (M-WGS), where three supported Pd membranes of 44 cm in length and ca. 6 μm in thickness were used, reaching a total membrane surface area of 580.6 cm². The WGS reaction was studied with the syngas mixture: 4.0% CO, 19.2% CO₂, 15.4% H₂O, 1.2% CH₄ and 60.1% H₂, under high temperature/pressure conditions: T = 673 K, p_feed = 20–35 bar(a), p_perm = 15 bar(a), mimicking CO₂ capture with co-production of H₂ in a natural gas fired power plant. High reaction pressure and high permeation of Pd membranes allowed for near complete CO conversion and H₂ recovery. Both the membranes and the membrane reactor demonstrated a long-term stability under the investigated conditions, indicating the potential of M-WGS to substitute conventional systems.     

Determination of laminar burning velocities for lean low calorific H2/N2 and H2/CO/N2 gas mixtures

Combustion of lean and ultra-lean synthetic H₂/CO mixtures that are highly diluted in inert gases is of great importance in several fields of technology, particularly in the field of post combustion for combined heat and power (CHP) systems based on fuel cell technology. In this case H₂/CO mixtures occur via hydrocarbon reforming and their complete conversion requires efficient, compact and low emission combustion systems. In order to design such systems, knowledge of global flame properties like the laminar burning velocity, is essential. Using the heat flux burner method, laminar burning velocities were experimentally determined for highly N₂ diluted synthetic H₂ and H₂/CO mixtures with low calorific value, burning with air, at ambient temperature and atmospheric pressure. Furthermore, numerical 1-D simulations were performed, using a series of different chemical reaction mechanisms. These numerical predictions are analysed and compared with the experimental data.     

Photocatalytic H2 production from acetic acid solution over CuO/SnO2 nanocomposites under UV irradiation

The CuO/SnO₂ composites have been prepared by the simple co-precipitation method and further characterized by the XRD, FESEM and Raman spectroscopy. The photocatalytic H₂ production from acetic acid (HAc) solution over CuO/SnO₂ photocatalyst has been investigated at room temperature under UV irradiation. Effects of CuO loading, photocatalyst concentration, acetic acid concentration and pH on H₂ production have been systematically studied. Compared with pure SnO₂, the 33.3 mol%CuO/SnO₂ composite exhibited approximately twentyfold enhancement of H₂ production. The H₂ yield is about 0.66 mol-H₂/mol-HAc obtained under irradiation for prolonged time. The Langmuir-type model is applied to study the dependence of hydrogen production rate on HAc concentration. A possible mechanism for photocatalytic degradation of acetic acid over CuO/SnO₂ photocatalyst is proposed as well. Our results provide a method for pollutants removal with simultaneous hydrogen generation. Due to simple preparation, high H₂ production activity and low cost, the CuO/SnO₂ photocatalyst will find wide application in the coming future of hydrogen economy.     

Combustion characteristics of H2/N2 and H2/CO syngas nonpremixed flames

Turbulent nonpremixed H₂/N₂ and H₂/CO syngas flames were simulated using 3D large eddy simulations coupled with a laminar flamelet combustion model. Four different syngas fuel mixtures varying from H₂-rich to CO-rich including N₂ have been modelled. The computations solved the Large Eddy Simulation governing equations on a structured non-uniform Cartesian grid using the finite volume method, where the Smagorinsky eddy viscosity model with the localised dynamic procedure is used to model the sub-grid scale turbulence. Non-premixed combustion has been incorporated using the steady laminar flamelet model. Both instantaneous and time-averaged quantities are analysed and data were also compared to experimental data for one of the four H₂-rich flames. Results show significant differences in both unsteady and steady flame temperature and major combustion products depending on the ratio of H₂/N₂ and H₂/CO in syngas fuel mixture.     

Effect of dry/wet-phase inversion method on fabricating polyetherimide-derived CMS membrane for H2/N2 separation

The research investigated carbon molecular sieve (CMS) membranes through the dry/wet-phase inversion method from the casting polyetherimide (PEI) on alumina support for hydrogen separation. Different coating techniques such as dry method (slide casting followed by drying under vacuum; and spin coating followed by drying under vacuum); and wet method (spin coating and then later kept in an isopropyl alcohol (IPA)/water coagulating bath) at different pyrolysis temperatures of 550, 600, 650 °C min⁻¹ were also investigated.     

Thermal stability and effect of typical water gas shift reactant composition on H2 permeability through a Pd-YSZ-PSS composite membrane

This work comprises a study of hydrogen separation with a composite Pd-YSZ-PSS membrane from mixtures of H₂, N₂, CO and CO₂, typical of a water gas shift reactor. The Pd layer is extended over a tubular porous stainless steel support (PSS) with an intermediate layer of yttria-stabilized-zirconia (YSZ). YSZ and Pd layers were incorporated over the PSS using Atmospheric Plasma Spraying and Electroless Plating techniques, respectively. The Pd and YSZ thickness values are 13.8 and 100 μm, respectively, and the Pd layer is fully dense. Permeation measurements with pure, binary and ternary gases at different temperatures (350–450 °C), trans-membrane pressures (0–2.5 bar) and gas composition have been carried out. Moreover, thermal stability of the membrane was also checked by repeating permeation measurements after several cycles of heating and cooling the system. Membrane hydrogen permeances were calculated using Sieverts' law, obtaining values in the range of 4·10⁻⁵–4·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5. The activation energy of the permeance was also calculated using Arrhenius' equation, obtaining a value of 16.4 kJ/mol. In spite of hydrogen selectivity being 100% for all experiments, the hydrogen permeability was affected by the composition of feed gas. Thus, a significant depletion in H₂ permeate flux was observed when other gases were in the mixture, especially CO, being also more or less significant depending on gas composition.     

MoS2/Mo2TiC2Tx supported Pd nanoparticles as an efficient electrocatalyst for hydrogen evolution reaction in both acidic and alkaline media

Development of electrocatalytic hydrogen production technology is the key to solving environmental and energy problems. Two-dimensional material Mo₂TiC₂T_x (T_x = –OH, –F) has shown great potential in electrocatalytic hydrogen evolution because of its excellent conductivity and hydrophilicity. However, due to the lack of sufficient active sites of Mo₂TiC₂T_x itself, its practical applications in electrocatalytic hydrogen evolution are limited. In this work, a highly-efficient hydrogen evolution electrocatalyst, namely Pd@MoS₂/Mo₂TiC₂T_x, is prepared through a simple pyrolysis method. In such a composite, the MoS₂ nanoflowers hybridized with the ammonia-treated Mo₂TiC₂T_x (MoS₂/Mo₂TiC₂T_x) are used as a substrate for loading a small number of Pd nanoparticles (4.27 at.%). Notably, the introduction of Pd nanoparticles into MoS₂/Mo₂TiC₂T_x provides abundant active sites for the hydrogen evolution reaction, improves the conductivity of the electrocatalyst, speeds up the adsorption and desorption of hydrogen, and induces a synergistic effect with the MoS₂. As a result, the Pd@MoS₂/Mo₂TiC₂T_x catalyst exhibits excellent electrocatalytic performance and remarkable stability in both acidic and alkaline media. In a 0.5 mol/L H₂SO₄ electrolyte, the overpotential of Pd@MoS₂/Mo₂TiC₂T_x was 92 mV with a Tafel slope of 60 mV/dec at a current density of 10 mA/cm². Meanwhile, the catalyst displayed an overpotential of 100 mV associated with a Tafel slope of 80 mV/dec at the current density of 10 mA/cm² in a 1 mol/L KOH electrolyte. This work shows the great potential of using Mo₂TiC₂T_x-based material in the field of electrocatalysis.     

Autothermal steam reforming of glycerol for hydrogen production over packed-bed and Pd/Ag alloy membrane reactors

In this study, glycerol, with its high H/C ratio feature, was steam reformed with oxygen to produce hydrogen in packed-bed and Pd/Ag membrane reactors. The addition of oxygen, which causes the partial oxidation, was to achieve thermal neutral for the energy saving purposes.     

The property of hydrogen separation from CO2 mixture using Pd-based membranes for carbon capture and storage (CCS)

This study investigates the module configuration for upscaling CO₂ capture capacity to a bench-scale in hydrogen selective Pd-based composite membranes. In order to confirm effective upscaling, four plate-type membranes of two inch diameter were stacked in a newly designed plate-and-frame type module, reaching a total membrane surface area of 6.64 × 10⁻³ m² (66.4 cm²). A pure gas test carried out using H₂ and He confirmed that there were no effects of module configuration in gas permeation behavior, indicating that the upscale of the separation capacity by numbering-up of membranes using our module design was successful. The CO₂ enrichment test was conducted using a 40%CO₂ + 60%H₂ mixture (i.e. a similar composition for the coal gasifier after both the shift reaction and H₂O removal), under high feed pressure and flow rate, i.e. 600–2100 kPa and 0.48–0.72 N m³ h⁻¹. The mixture gas test confirmed that the bench-scale membrane module could enrich 40% of the CO₂ at a feed flow rate of 0.48 N m³ h⁻¹ up to 93% with a hydrogen recovery ratio of >90% at 673 K and a total feed pressure of 2100 kPa, i.e. ∼4 times CO₂ enrichment capacity of one membrane.     

The promoted effect of UV irradiation on preferential oxidation of CO in an H2-rich stream over Au/TiO2

The catalytic oxidation of CO over Au/TiO₂ in an H₂-rich stream was performed under UV irradiation. It is found that UV irradiation over Au/TiO₂ promotes the preferential oxidation of CO in the H₂-rich stream. The respective chemisorption of CO, H₂ and O₂ at Au/TiO₂ can be described as a process of forming –OH or H₂O species. UV irradiation over Au/TiO₂ enhances the chemisorption of CO but suppresses the chemisorption of H₂ both at TiO₂ and Au surface. It is proposed that the photogenerated electrons from TiO₂ will cause the change of the chemisorption of CO, H₂ and O₂ at Au/TiO₂, which promotes the preferential oxidation of CO in an H₂-rich stream.     

Explosion behavior of CH4/O2/N2/CO2 and H2/O2/N2/CO2 mixtures

In this work, the explosion behavior of stoichiometric CH₄/O₂/N₂/CO₂ and H₂/O₂/N₂/CO₂ mixtures has been studied both experimentally and theoretically at different CO₂ contents and oxygen air enrichment factors. Peak pressure, maximum rate of pressure rise and laminar burning velocity were measured from pressure time records of explosions occurring in a closed cylindrical vessel. The laminar burning velocity was also computed through CHEMKIN–PREMIX simulations.     

Effect of H2S on carbon-catalyzed methane decomposition and CO2 reforming reactions

The effect of H₂S on catalytic processing of methane is of a great practical importance. In this work, the effect of small quantities (0.5–1.0 vol.%) of H₂S present in the feedstock on the methane decomposition and CO₂ reforming reactions over carbon and metal based catalysts was investigated. Activated carbon (FY5), an in-house prepared alumina-supported Ni catalyst (NiA) and the mixture of both (FY5 + NiA) were used as catalysts in this study. It was found that CH₄ and CO₂ conversions were noticeably increased when H₂S was added to the reacting mixture, which points to (i) the tolerance of carbon catalyst to H₂S and (ii) the catalytic effect of H₂S on carbon-catalyzed decomposition and dry reforming of methane. In contrast, NiA catalyst and the mixture FY5 + NiA were deactivated in the presence of H₂S in both reactions. The effect of the heating system (i.e., conventional electric resistance vs microwave heating) on the products yield of the dry reforming reaction in the presence of H₂S is also discussed in this paper.