Hydrogen isotope absorption amount and rate of Pd–Al2O3 pellets

A special type of Pd–Al₂O₃ pellet, which included Pd in high weight percent as a hydrogen isotope separation material was prepared by a compression molding method. The pressure–composition isotherm and the plateau pressure of the Pd–Al₂O₃ hydrogen isotope system were determined by a volumetric method. The pellet has high hydrogen absorption ability even at 196 K, and the reaction rate is controlled by surface reaction. The hydrogen absorption capacity and the rate of the Pd–hydrogen system were unchanged by the addition of Al₂O₃. It was found that the Pd–Al₂O₃ pellet has high durability against repeated absorption–desorption cycles. There is no change in the absorption amount and the rate up to 1000 times of absorption–desorption cycles.     

Improved hydrogen permeation through thin Pd/Al2O3 composite membranes with graphene oxide as intermediate layer

Here we proposed the decreasing in the roughness of asymmetric alumina (Al₂O₃) hollow fibers by the deposition of a thin graphene oxide (GO) layer. GO coated substrates were then used for palladium (Pd) depositions and the composite membranes were evaluated for hydrogen permeation and hydrogen/nitrogen selectivity. Dip coating of alumina substrates for 45, 75 and 120 s under vacuum reduced the surface mean roughness from 112.6 to 94.0, 87.1 and 62.9 nm, respectively. However, the thicker GO layer (deposited for 120 s) caused membrane peel off from the substrate after Pd deposition. A single Pd layer was properly deposited on the GO coated substrates for 45 s with superior hydrogen permeance of 24 × 10⁻⁷ mol s⁻¹m⁻² Pa⁻¹ at 450 °C and infinite hydrogen/nitrogen selectivity. Activation energy for hydrogen permeation through the Al₂O₃/GO/Pd composite membrane was of 43 kJ mol⁻¹, evidencing predominance of surface rate-limiting mechanisms in hydrogen transport through the submicron-thick Pd membrane.     

A YH3 promoted palladium catalyst for reversible hydrogen storage of N-ethylcarbazole

N-ethylcarbazole (NEC) is a promising liquid organic hydrogen carrier, while sluggish kinetics of hydrogen absorption and desorption restrict its application. To overcome that, a YH₃ promoted palladium catalyst Pd/Al₂O₃-YH₃ is developed in this work by taking advantage of the fast reversible hydrogenation and dehydrogenation kinetics of YH₃. With the Pd/Al₂O₃-YH₃, NEC can reversibly store 5.5 wt% hydrogen in 4 h below 473 K. The performance is the best compared to that of all the reported catalysts for both hydrogen absorption and desorption. Moreover, there are no gaseous impurities produced and no performance decay during three hydrogen storage cycles. The excellent performance derives from the intrinsic high catalytic activity of Pd/Al₂O₃ and the promoting effect of YH₃ by providing a new hydrogen transfer path, making NEC more attractive for practical application.     

Hydrogen isotopes separation using frontal displacement chromatography with Pd–Al2O3 packed column

Separation or purification of tritium isotopes is one of the key technologies in ITER. A set of frontal displacement chromatography (FDC) device was designed and constructed for hydrogen isotopes separation using palladium loading on/in alumina (Pd–Al₂O₃) as the separation material. The hydrogen isotopes separation experiments were carried out. It was found that deuterium abundance of the product was up to 98.5% and the average separation factor was as high as 64, under the condition of 273 K column temperature and 15 mL(NTP)/min flow rate, for a feed gas of 5%H₂-5%D₂-90%Ar. The deuterium recovery ratio was 42% in this separation test. The results showed that the separation performance of our FDC device was good by using Pd–Al₂O₃ as separation materials, and it suggested considerable potential for the applicability of FDC in hydrogen isotopes separation.     

An improvement of the hydrogen permeability of C/Al2O3 membranes by palladium deposition into the pores

The development of compact hydrogen separator based on membrane technology is of key importance for hydrogen energy utilization, and the Pd-modified carbon membranes with enhanced hydrogen permeability were investigated in this work. The C/Al₂O₃ membranes were prepared by coating and carbonization of polyfurfuryl alcohol, then the palladium was introduced through impregnation–precipitation and colloid impregnation methods with a PdCl₂/HCl solution and a Pd(OH)₂ colloid as the palladium resources, and the reduction was carried out with a N₂H₄ solution. The resulting Pd/C/Al₂O₃ membranes were characterized by means of SEM, EDX, XRD, XPS and TEM, and their permeation performances were tested with H₂, CO₂, N₂ and CH₄ at 25 °C. Compared with the colloid impregnation method, the impregnation–precipitation is more effective in deposition of palladium clusters inside of the carbon layer, and this kind of Pd/C/Al₂O₃ membranes exhibits excellent hydrogen permeability and permselectivity. Best hydrogen permeance, 1.9 × 10⁻⁷ mol/m² s Pa, is observed at Pd/C = 0.1 wt/wt, and the corresponding H₂/N₂, H₂/CO₂ and H₂/CH₄ permselectivities are 275, 15 and 317, respectively.     

Hydrogen absorption–desorption cycle experiment of Pd–Al2O3 pellets

A series of hydrogen absorption–desorption processes using a pellet form of Pd–Al₂O₃ was repeated up to 1010 cycles. Variations in the amounts and rates of hydrogen absorption and desorption with cycles were determined by means of a constant-volume method. The amounts and rates of absorption and desorption were almost unchanged up to 1010 cycles. The Scanning Electron Microscope pictures and Energy Dispersive Spectroscopy showed no microscopic change on the pellet surface after 1010 cycles. The experimental results assured a high tolerance of the Pd–Al₂O₃ pellet to repetitive absorption–desorption cycles.     

Superhydrophobic Pd@CeO2/Al2O3 catalyst coating for hydrogen mitigation systems in nuclear power plants

Passive autocatalytic recombination (PAR) was employed as an effective hydrogen mitigation system for nuclear power plants. Despite the great progress achieved in catalysts for PAR, few reports could be found on PAR catalysts, which exhibit strong resistance to poisoning by iodine compounds and the detrimental effect of water, as well as good anti-sintering properties. In this study, a superhydrophobic Pd@CeO₂/Al₂O₃ catalyst coating was prepared through a self-assembly method and the grafting of 1H,1H,2H,2H-perfluorooctyltriethoxysilane. The superhydrophobicity of the catalyst coating effectively alleviated water poisoning. The ceria shell of Pd@CeO₂/Al₂O₃ served as a protective layer against poisoning by iodine compounds because it was difficult for iodine vapor to access the catalyst core of the Pd nanoparticles when the shell pore diameter was below 1.2 nm. Given the interface effect between palladium and ceria, the CeO₂ shells also served as an effective barrier to prevent the Pd nanoparticles from aggregating at high temperatures. The superhydrophobic Pd@CeO₂/Al₂O₃ coating showed excellent potential for the mitigation of hydrogen containing various poisons during a nuclear accident.     

Influence of the method of synthesis on hydrogen adsorption properties of mesoporous binary B2O3/Al2O3 gel systems

Three series of binary oxide systems B₂O₃/Al₂O₃ were prepared and the effect of alumina on dispersion of boron (B₂O₃) component was investigated. The aim of the study was to achieve a maximum dispersion of B₂O₃ in the Al₂O₃ a gel matrix that would lead to increased sorption capacity on boron oxide. Many attempts were made to establish the preparation conditions that would lead to a maximum dispersion of B₂O₃ in the Al₂O₃ gel matrix needed to increase the hydrogen sorption capacity on boron oxide. The systems were characterized by X-ray diffraction, SEM, TEM and low temperature nitrogen adsorption. Hydrogen adsorption was tested in the volumetric system.Results of the study showed that the amount of hydrogen adsorbed on B₂O₃ depended not only on the surface area of the system but also on the separation of B₂O₃ domains in Al₂O₃ gel network. Irrespective of the method of synthesis of the binary oxide system, the dispersion of B₂O₃ phase reflected in the amount of hydrogen adsorbed was the highest for the systems of the lowest B/Al molar ratios studied, i.e. for B/Al = 0.25.     

Toward low-cost Pd/ceramic composite membranes for hydrogen separation: A case study on reuse of the recycled porous Al2O3 substrates in membrane fabrication

The development of hydrogen energy systems has placed a high demand on hydrogen-permeable membranes as compact hydrogen separators and purifiers. Although Pd/Ceramic composite membranes are particularly effective in this role, the high cost of these membranes has greatly limited their applications; this high cost stems largely from the use of expensive substrate material. This problem may be solved by substrate recycling and the use of lower cost substrates. As a case study, we employed expensive asymmetric microporous Al₂O₃ and low-cost macroporous symmetric Al₂O₃ as membrane substrates (average pore sizes are 0.2 and 3.3 μm, respectively). The palladium membranes were fabricated by electroless plating, and substrate recycling was carried out by palladium dissolution with a hot HNO₃ solution. The functional surface layer of the microporous Al₂O₃ was damaged during substrate recycling, and the reuse of the substrate led to poor membrane selectivity. With the assistance of pencil coating as a facile and environmentally benign surface treatment, the macroporous Al₂O₃ can be successfully utilized. Furthermore, the macroporous Al₂O₃ can be also recycled and reused as membrane substrate, yielding highly permeable, selective and stable palladium membranes. Consequently, the substrate cost can be further decreased, and the applications of this kind of membranes would expand.     

Synergistic tuning of the phase structure of alumina and ceria-zirconia in supported palladium catalysts for enhanced methane combustion

CeO₂–ZrO₂–Al₂O₃ composite oxides supported palladium catalysts (Pd/CZA) are promising candidates for catalytic oxidation reactions. However, the efficient and stable oxidation of methane over Pd-based catalysts remains a longstanding challenge. Herein, we present a facile strategy to boost the catalytic performance of Pd/CZA through elaborately tuning the phase structure of supports. Calcining supports at relatively high temperatures (1200, 1300 °C) induced the phase transition of alumina (from γ-to α-) and the development of CeO₂–ZrO₂ solid solution (CZ). The weak interaction between α-Al₂O₃ and PdO resulted in an improved reducibility of catalysts. Meanwhile, the higher oxygen mobility originated from well-crystallized CZ phase contributed to the reoxidation of Pd to PdO, giving rise to abundant surface active Pd²⁺ species. Coupled with the hydrophobicity of α-Al₂O₃, the catalyst prepared with CZA supports calcined at 1300 °C demonstrated an excellent low-temperature activity, astounding stability and greatly enhanced water resistance towards methane combustion.     

Effects of different Al2O3 support on HDPE gasification for enhanced hydrogen generation using Ni-based catalysts

This study examined the effects of Ni loading on different types of alumina (γ-Al₂O₃, mesoporous Al₂O₃, 13 nm-sized Al₂O₃, and <50 nm-sized Al₂O₃) for high-density polyethylene gasification for enhanced hydrogen generation. The catalytic activity of Ni loaded alumina was observed in the order of 13 nm-sized Al₂O₃> mesoporous Al₂O₃> (<50 nm-sized Al₂O₃) > γ-Al₂O₃ for the gas yield and γ-Al₂O₃> (<50 nm Al₂O₃) > mesoporous Al₂O₃ > 13 nm Al₂O₃ for the oil yield, respectively. In addition, the production of hydrogen from Ni loaded alumina showed an increasing trend in the order of (<50 nm-sized Al₂O₃) > γ-Al₂O₃> 13 nm-sized Al₂O₃.> mesoporous Al₂O₃. In contrast, CO showed the trend as Ni/mesoporous Al₂O₃> Ni/13 nm-sized Al₂O₃> Ni/γ-Al₂O₃> (Ni/<50 nm Al₂O₃). The highest level of hydrogen production from the Ni/<50 nm-sized Al₂O₃ catalyst might be because of its highest Ni dispersion and surface area. The use of Ni-loaded nm-sized alumina could be an excellent method for increased hydrogen production compared to other types of alumina available.     

Remarkable activity of Pd catalyst supported on alumina synthesized via a hydrothermal route for hydrogen release of perhydro-N-propylcarbazole

The investigation of dehydrogenation catalysts to achieve rapidly hydrogen release of Liquid Organic Hydrogen Carriers (LOHCs) are of crucial importance for large-scale applications. The catalyst supports with bulk surface area and decent acid-base nature is a key parameter for catalyst to improve its catalytic performance as well as reduce precious metal dosage. Herein, alumina was chosen as a support for Pd loading and prepared through hydrothermal route at different temperatures. The morphology and surface acid property of the alumina supports were investigated in detail. The results revealed that the hydrothermal temperature had a closely effect on the morphology, surface acidity and specific surface area of alumina, resulting in a further impact on Pd dispersion and particle size associated tightly with catalytic activity of Pd/Al₂O₃. The catalyst with 1 wt% Pd loaded on alumina carrier prepared via hydrothermal treatment at 120 °C showed the best catalytic performance for dehydrogenation of perhydro-N-propylcarbazole (12H-NPCZ). Full dehydrogenation with 100% conversion to N-propylcarbazole (NPCZ) could be achieved after 360 min at 180 °C and 101 kPa, which is higher than that of commercial 5 wt% Pd/Al₂O₃ catalyst. The catalyst has potential commercial application value in large-scale application of LOHC technology.     

Superhydrophobic Pt–Pd/Al2O3 catalyst coating for hydrogen mitigation system of nuclear power plant

Passive auto-catalytic recombiner (PAR) system is an important hydrogen mitigation method which has been applied in most modern light water nuclear reactors. The two challenges for the highly efficient PAR are the detrimental effect of water and poisoning by fission products. In this study, to address the two challenges, superhydrophobic Pt–Pd/Al₂O₃ catalyst coatings were prepared by wet impregnation method and the grafting of 1H,1H,2H,2H-perfluorooctyltriethoxysilane.The formation of a Pt–Pd intermetallic compound was confirmed by in situ diffuse reflectance infrared Fourier transform infrared spectroscopy for the Pt–Pd/Al₂O₃ catalyst. The Pt–Pd/Al₂O₃ catalyst exhibited a superior resistance of water poisoning to the monometallic catalysts. In addition, compared with the monometallic catalysts, the least influence by the iodine poisoning was observed for the Pt–Pd/Al₂O₃ catalyst, which is attributed to the smallest influence on the bindings of H₂ and O₂ on the Pt–Pd intermetallic compound by the iodine addition. For the reactor with the superhydrophobic Pt–Pd/Al₂O₃ catalyst coating, under the conditions simulating the nuclear accident, the reaction was ignited immediately as soon as the hydrogen was introduced at 298 K and the hydrogen conversion kept 100% when the reaction temperature exceeded 398 K. The superhydrophobic Pt–Pd/Al₂O₃ catalyst coating showed great potential for the mitigation of hydrogen containing various poisons during the nuclear accident.     

Hydrogen production from acetic acid decomposition as bio-oil model molecule over supported metal catalysts

Acetic acid decomposition to produce hydrogen was studied over Pd/Al₂O₃, Pt/Al₂O₃, Ni/Al₂O_3, and Co/Al₂O₃ catalysts. Pd/Al₂O₃ and Pt/Al₂O₃ systems exhibited high levels of conversion and hydrogen selectivity, with Pt/Al₂O₃ showing a hydrogen selectivity of 51.3% at 973 K. This behavior was influenced by the high dispersion and small particle size of Pt as well as the dissociative adsorption of acetic acid (acetate species) as exhibited by Pt/Al₂O₃ and Pd/Al₂O₃ systems. Additionally, Ni/Al₂O₃ and Co/Al₂O₃ were less active and presented low selectivity to hydrogen. These catalysts exhibited low dissociation of acetic acid on their surfaces, therefore hindering acetic acid transformation and hydrogen generation. However, when Ni/Al₂O₃ and Co/Al₂O₃ were reduced at 973 K, the conversion of acetic acid and hydrogen formation increased favorably. Co/Al₂O₃ showed less deactivation during time on stream. Deposited carbon on catalysts corresponded to the formation of carbon filaments for Pd/Al₂O₃ and Co/Al₂O₃ and of carbon nanotubes in the case of Ni/Al₂O_3.     

Pd/In2O3-based bilayer H2 sensor with high resistance to silicone toxicity and ultra-fast response

Hydrogen sensors are easily deactivated by hexamethyldisiloxane (HMDSO) poisoning. Moreover, the existing anti-poisoning strategies can also damage the overall sensing performance of these hydrogen sensors. Therefore, a new bilayer design with a Pd/In₂O₃ sensitive layer and an In₂O₃/Al₂O₃ catalytic filter layer is proposed to avoid the deactivation of hydrogen sensors. The In₂O₃/Al₂O₃ layer helps in hindering HMDSO and its decomposition products from reaching the Pd/In₂O₃ layer. The H₂ response of the sensors is enhanced due to the small size of In₂O₃ and the electronic sensitization of Pd. As a result, the bilayer sensors exhibit high response (Ra/Rg = 53) and ultra-fast response time (1 s) towards 3000 ppm H₂ at 365 °C. The resistance and the H₂ response of the bilayer sensors are almost unchanged after 40 min of 10 ppm HDMSO poisoning. In this paper, the mechanism of resistance against silicone poisoning and the H₂ response of the bilayer sensors are discussed from the separation of sensing and catalytic filtration reactions to the behavior of adsorbed oxygen.     

Fabrication of Pd/ceramic membranes for hydrogen separation based on low-cost macroporous ceramics with pencil coating

Increasing hydrogen energy utilization has greatly stimulated the development of the hydrogen-permeable palladium membrane, which is comprised of a thin layer of palladium or palladium alloy on a porous substrate. This work chose the low-cost macroporous Al₂O₃ as the substrate material, and the surface modification was carried out with a conventional 2B pencil, the lead of which is composed of graphite and clay. Based on the modified substrate, a highly permeable and selective Pd/pencil/Al₂O₃ composite membrane was successfully fabricated via electroless plating. The membrane was characterized by SEM (scanning electron microscopy), field-emission SEM and metallographic microscopy. The hydrogen flux and H₂/N₂ selectivity of the membrane (with a palladium thickness of 5 μm) under 1 bar at 723 K were 25 m³/(m² h) and 3700, respectively; the membrane was found to be stable during a time-on-stream of 330 h at 723 K.     

Wet-impregnated bimetallic Pd-Ni catalysts with enhanced activity for dehydrogenation of perhydro-N-propylcarbazole

Palladium/platinum-based catalysts are widely used in the dehydrogenation process of Liquid Organic Hydrogen Carriers (LOHCs). The cost of noble metal has become a main drawback for LOHCs large-scale application. Partial replacement of Pd/Pt by other transition metals can be an effective solution. In this paper, we synthesize the bimetallic Pd–Ni catalyst by incipient wet impregnation and the catalytic dehydrogenation performance of perhydro-N-propylcarbazole (12H-NPCZ) as a LOHC candidate. Ni and Pd were impregnated on mesoporous alumina to obtain both monometallic and bimetallic catalysts, i.e. Pd/Al₂O₃, Ni/Al₂O₃ and Pd–Ni/Al₂O₃ (Pd:Ni = 1:1) with total metal loading of 5 wt%, respectively. The above catalysts were characterized by N₂-adsorption/desorption, H₂-temperature programmed reduction, X-Ray diffraction, X-Ray photoelectron spectroscopy, Inductively coupled plasma - optical emission spectrometer, CO pulse adsorption and Transmission electron microscopy. The catalytic dehydrogenation results indicated that the bimetallic Pd–Ni/Al₂O₃ showed best catalytic activity, followed by Pd/Al₂O₃, commercial Pd/Al₂O₃ and Ni/Al₂O₃. Notably, the catalytic activity of bimetallic was well maintained after 5 cycles at 200 °C with no degradation, indicating this bimetallic catalyst has potential prospect for large-scale application.     

Evaluation of catalyst activity for release of hydrogen from liquid organic hydrogen carriers

This contribution investigate the effect of parameters for production of hydrogen by catalytic dehydrogenation of perhydrodibenzyltoluene (H18-DBT). The sensitivity of the dehydrogenation reaction to temperature (290–320 °C) is justified by an increase in degree of dehydrogenation (DoD) from 40 to 90% when using 1 wt % Pt/Al₂O₃ catalyst. However, the increase in temperature increases the hydrogen production rate and decreases the hydrogen purity by increasing the formation of by-products. In addition, the DoD of 96% is obtained when 2 wt % Pt/Al₂O₃ is used at 320 °C. The DoD obtained for Pd, Pt, and Pt–Pd catalysts is 11, 82 and 6%, respectively. Therefore, Pd is not a metal of choice for dehydrogenation of H18-DBT, in both monometallic and bimetallic system. The ab-initio density functional theory (DFT) calculations are consistent with this observation. Furthermore, dehydrogenation of H18-DBT followed 1st order reaction kinetics and the activation energies for 1 wt % Pt/Al₂O₃, 1 wt % Pd/Al₂O₃ and 1:1 wt % Pt–Pd/Al₂O₃ catalysts are: 205, 84 and 66 kJ/mol, respectively.     

Pellet size dependent steam reforming of polyethylene terephthalate waste for hydrogen production over Ni/La promoted Al2O3 catalyst

The effect of different pellet sizes of nickel (Ni) and lanthanum (La) promoted Al₂O₃ support on the catalytic performance for selective hydrogen production from polyethylene terephthalate (PET) plastic waste via steam reforming process has been investigated. The catalysts were prepared by impregnation method and were characterized using XRD, BET, TPD-CO₂, TPR, SEM, EDX, TEM and TGA. The results showed that NiLa-co-impregnated Al₂O₃ catalyst has excellent activity for the production of hydrogen. Feed conversion of 88.53% was achieved over 10% Ni/Al₂O₃ catalyst which increased to 95.83% in the case of 10% Ni-5% La/Al₂O₃ catalysts with a H₂ selectivity of 70.44%. The catalyst performance in term of gas production and feed conversion was further investigated under various operating parameters, e.g., feed flow-rate, and catalyst pellet size. It was found that at 0.4 ml/min feed flow rate, highest feed conversion and H₂ selectivity were achieved. The Ni particles, which are the noble-based active species are highly effective, thus offered good hydrogen production in the phenol-PET steam reforming process. Incorporation of La as a promoter in Ni/Al₂O₃ catalyst has significantly increased the catalyst reusability with prolonged stability. The NiLa/Al₂O₃ catalyst with larger size showed remarkable activity due to the presence of significant temperature gradients inside the pellet compared to smaller size. Additionally, the catalyst showed only slight decrease in H₂ selectivity and feed conversion even after 24 h, although production of carbon nanotubes was evidenced on its surface.     

Ni/Pd-promoted Al2O3–La2O3 catalyst for hydrogen production from polyethylene terephthalate waste via steam reforming

Ni/Pd-co-promoted Al₂O₃–La₂O₃ catalysts for selective hydrogen production from polyethylene terephthalate (PET) plastic waste via steam reforming process has been investigated. The catalysts were prepared by impregnation method and were characterized using XRD, BET, TPD-CO₂, TPR-H₂, SEM, TGA and DTA. The results showed that Ni-Pd-co-impregnated Al₂O₃–La₂O₃ catalyst has excellent activity for the production of hydrogen with a prolong stability. The feed conversion of 87% was achieved over 10% Ni/Al₂O₃ catalyst which increased to 93.87% in the case of 10% Ni-1% Pd/Al₂O₃–La₂O₃ catalysts with an H₂ fraction of 0.60. The catalyst performance in term of H₂ selectivity and feed conversion was further investigated under various operating parameters, e.g., temperatures, feed flow rates, feed ratios and PET concentrations. It was found that the temperature has positive effects on H₂ selectivity and conversion, yet feed flow rate has the adverse effects. In addition, PET concentrations showed improved in H₂ selectivity in comparison to when only phenol as a solvent was involved. The Ni particles, which are the noble-based active species are more effective, thus offered good hydrogen production in the PET steam reforming process. Incorporation of La₂O₃ as support and Pd as a promoter to the Ni/Al₂O₃ catalyst significantly increased catalyst stability. The Ni–Pd/Al₂O₃–Al₂O₃ catalyst showed remarkable activity even after 36 h along with the production of carbon nanotubes, while H₂ selectivity and feed conversion was only slightly decreased.