Intermetallide catalysts for hydrogen storage on the basis of reversible aromatics hydrogenation/dehydrogenation reactions

New efficient intermetallide catalysts for hydrogen storage in reversible processes of aromatics hydrogenation and naphthene dehydrogenation were studied. These catalysts provide an enhanced activity in the dehydrogenation of saturated organic molecules, with no side reactions like cracking, hydrogenolysis, ring opening, or coke formation occurring on these catalysts. The use of intermetallides provides some hydrogen storage capacity in the low-temperature region, while their catalytic activity in the dehydrogenation affords the hydrogen supply in the high-temperature range.     

Hydrogen storage in nickel catalysts supported on activated carbon

We have studied hydrogen storage in a commercial activated carbon impregnated with nickel. High-pressure (20–30 bars) hydrogen uptake at room temperature was assessed using a high-pressure volumetric adsorption–desorption system. The properties of the prepared materials were studied by means of _N2${\mathrm{N}}_2$ physisorption, X-ray diffraction, transmission electron microscopy, metal surface area, hydrogen temperature programmed reduction and hydrogen temperature programmed desorption. Various factors influencing the level of hydrogen uptake (metal precursor, metal content, method of preparation) were examined and discussed. It is concluded that the hydrogen stored is loosely chemisorbed on the carbonaceous material surface as spilt-over species through _H2${\mathrm{H}}_2$ dissociation on the metal phase then migration onto the support. This hydrogen would also be directly adsorbed on carbon acceptor sites induced by _H2${\mathrm{H}}_2$-pretreatment at 623 K. In both cases, the stored hydrogen directly desorbs from the active carbon support.     

Hydrogen storage in liquid organic hydride: Selectivity of MCH dehydrogenation over monometallic and bimetallic Pt catalysts

Hydrogen storage for mobile and stationary applications is an expanding research topic. One of the more promising storage techniques relies on the reversibility, high selectivity, and high hydrogen density of liquid organic hydrides, in particular methylcyclohexane (MCH). Catalyst evaluation for MCH dehydrogenation to toluene is based on three catalytic parameters: activity, selectivity, and stability. Current catalysts, optimized for catalytic reforming, do not meet the targeted aromatic selectivity (+99%) for MCH dehydrogenation. Therefore, a range of Pt catalysts was prepared and compared with commercially available catalysts in a fixed-bed reactor under operating conditions suitable for mobile and stationary applications. The best overall performance was realized by a particular monometallic Pt catalyst. This catalyst showed superior activity, selectivity, and stability compared with other prepared and commercial catalysts. As an effort to further enhance the aromatic selectivity, this study identified the main side-reactions associated with MCH dehydrogenation, the effect of operating parameters on by-product yields, and the effect of catalyst deactivation on long-term selectivity.     

Hydrogen production by catalytic dehydrogenation of methylcyclohexane over Pt catalysts supported on pyrolytic waste tire char

Pyrolytic waste tire char was modified to be used as support and a series of catalysts supported with 0.1-1.0 wt% Pt were prepared by conventional wetness impregnation method. TEM images show that the Pt nanoparticles are well-dispersed in any microregions in the sample view on the TEM grid. The results of methylcyclohexane dehydrogenation reaction show the Pt loadings and the reaction temperature have a significant impact on the catalytic activity.     

Hydrogen production by aqueous-phase biomass reforming over carbon textile supported Pt-Ru bimetallic catalysts

The objective of this study is to develop highly efficient and low cost Pt-Ru bimetallic catalyst to convert biomass to bio-hydrogen fuel and chemicals by utilizing an aqueous-phase reforming (APR) reactor. The Pt-Ru bimetallic nanocatalysts on activated carbon supports were uniformly coated on the carbon textile as functionalized mesoporous media by electrophoretic deposition (EPD) method or dip-coating process. The carbon textile containing Pt-Ru nanoparticles was then rolled up and fastened to form pillar-like catalysts, which were placed in the reactor for the APR process. New catalytic processing techniques, which allow the design of catalyst at the atomistic level with controlled adsorption properties, are used to develop highly active catalysts for aqueous-phase process. The microstructure of the catalysts and activity/selectivity were optimized. This study provided a viable option for bio-hydrogen generation and reduced sugar production at the same time via a one-pot process to deal with low-cost energy crops or agriculture wastes as the substrate.     

Nano-Pd/CeO2 catalysts for hydrogen storage by reversible benzene hydrogenation/dehydrogenation reactions

Nano-CeO₂ supports, which have different structure from different preparation methods, were used to prepare nano-Pd/CeO₂ catalysts. The hydrogen storage capacity of prepared nano-Pd/CeO₂ catalysts were studied via vapor phase benzene hydrogenation and cyclohexane dehydrogenation reactions. Results show that the prepared Pd/CeO₂ catalysts exhibit excellent benzene hydrogenation and cyclohexane dehydrogenation performances. The catalytic performance of the Pd/CeO₂ catalysts is related to the dispersion of metallic Pd, hydrogen adsorption-desorption ability and structure of Pd/CeO₂ catalysts and so on. And those properties are also directly affected by the morphology and mesoporous structure of the prepared nano-Pd/CeO₂ catalysts that can be regulated by CeO₂ support preparation methods. The synergistic effect between metal Pd, CeO₂ support and their structures can effectively promote benzene hydrogenation and cyclohexane dehydrogenation, thus promoting hydrogen storage capacity. The prepared Pd/CeO₂-HT catalyst, which has high specific surface area, developed pore structure and highly dispersed metal Pd species, exhibits superior catalytic performances. And, the Pd/CeO₂-HT catalyst exhibits superior catalytic hydrogen storage performances. The benzene conversion over it at 200 °C reaches 99.5%. Whereas the cyclohexane conversion at 450 °C is 65.3%, and the H₂ production capacity is 73.77 g/h.     

Effect of platinum doping of activated carbon on hydrogen storage behaviors of metal-organic frameworks-5

In this work, we prepared platinum doped on activated carbons/metal-organic frameworks-5 hybrid composites (Pt-ACs-MOF-5) to obtain a high hydrogen storage capacity. The surface functional groups and surface charges were confirmed by Fourier transfer infrared spectroscopy (FT-IR) and zeta-potential measurement, respectively. The microstructures were characterized by X-ray diffraction (XRD). The sizes and morphological structures were also evaluated using a scanning electron microscopy (SEM). The pore structure and specific surface area were analyzed by N₂/77 K adsorption/desorption isotherms. The hydrogen storage capacity was studied by BEL-HP at 298 K and 100 bar. The results revealed that the hydrogen storage capacity of the Pt-ACs-MOF-5 was 2.3 wt.% at 298 K and 100 bar, which is remarkably enhanced by a factor of above five times and above three times compared with raw ACs and MOF-5, respectively. In conclusion, it was confirmed that Pt particles played a major role in improving the hydrogen storage capacity; MOF-5 would be a significantly encouraging material for a hydrogen storage medium as a receptor.     

Hydrogen adsorption on modified activated carbon

The aim of this work is to investigate hydrogen adsorption on prepared super activated carbon (AC). Litchi trunk was activated by potassium hydroxide under N₂ or CO₂ atmosphere. Nanoparticles of palladium were impregnated in the prepared-AC. Hydrogen adsorption was accurately measured by a volumetric adsorption apparatus at 77, 87, 90 and 303 K, up to 5 MPa. Experimental results revealed that specific surface area of the prepared-AC increased according to KOH/char ratio. The maximum specific surface area reached up to 3400 m²/g and total pore volume of 1.79 cm³/g. The maximum hydrogen adsorption capacity of 2.89 wt.% at 77 K and under 0.1 MPa, was obtained on these materials. The hydrogen adsorption capacity of the 10 wt.% Pd-AC was determined as 0.53 wt.% at 303 K and under 6 MPa. This amount is higher than that on the pristine AC (0.41 wt.%) under the same conditions.     

Hydrogen storage behaviors of platinum-supported multi-walled carbon nanotubes

In this work, the hydrogen storage behaviors of multi-walled carbon nanotubes (MWNTs) loaded by crystalline platinum (Pt) particles were studied. The microstructure of the Pt/MWNTs was characterized by X-ray diffraction and transmission electron microscopy. The pore structure and total pore volumes of the Pt/MWNTs were analyzed by N₂/77 K adsorption isotherms. The hydrogen storage capacity of the Pt/MWNTs was evaluated at 298 K and 100 bar. From the experimental results, it was found that Pt particles were homogeneously distributed on the MWNT surfaces. The amount of hydrogen storage capacity increased in proportion to the Pt content, with Pt-5/MWNTs exhibiting the largest hydrogen storage capacity. The superior amount of hydrogen storage was linked to an increase in the number of active sites and the optimum-controlled micropore volume for hydrogen adsorption due to the well-dispersed Pt particles. Therefore, it can be concluded that Pt particles play an important role in hydrogen storage characteristics due to the hydrogen spillover effect.     

Automotive hydrogen storage system using cryo-adsorption on activated carbon

An integrated model of a sorbent-based cryogenic compressed hydrogen system is used to assess the prospect of meeting the near-term targets of 36 kg-H₂/m³ volumetric and 4.5 wt% gravimetric capacity for hydrogen-fueled vehicles. The model includes the thermodynamics of H₂ sorption, heat transfer during adsorption and desorption, sorption dynamics, energetics of cryogenic tank cooling, and containment of H₂ in geodesically wound carbon fiber tanks. The results from the model show that recoverable hydrogen, rather than excess or absolute adsorption, is a determining measure of whether a sorbent is a good candidate material for on-board storage of H₂. A temperature swing is needed to recover >80% of the sorption capacity of the superactivated carbon sorbent at 100 K and 100 bar as the tank is depressurized to 3–8 bar. The storage pressure at which the system needs to operate in order to approach the system capacity targets has been determined and compared with the breakeven pressure above which the storage tank is more compact if H₂ is stored only as a cryo-compressed gas. The amount of liquid N₂ needed to cool the hydrogen dispensed to the vehicle to 100 K and to remove the heat of adsorption during refueling has been estimated. The electrical energy needed to produce the requisite liquid N₂ by air liquefaction is compared with the electrical energy needed to liquefy the same amount of H₂ at a central plant. The alternate option of adiabatically refueling the sorbent tank with liquid H₂ has been evaluated to determine the relationship between the storage temperature and the sustainable temperature swing. Finally, simulations have been run to estimate the increase in specific surface area and bulk density of medium needed to satisfy the system capacity targets with H₂ storage at 100 bar.     

Production of hydrogen and carbon nanofibers through the decomposition of methane over activated carbon supported Pd catalysts

Hydrogen has been produced by decomposing methane thermocatalytically at 1123 K in the presence of activated carbon supported Pd catalysts (Samples coded as Pd5 and Pd10 respectively) procured from SRL Chemicals, India. The studies indicated that the Pd10 catalyst has higher catalytic activity and life for methane decomposition reaction at 1123 K and volume hourly space velocity (VHSV) of 1.62 L/hr?g. An average methane conversion of 50 mol % has been obtained for Pd10 catalyst at the above reaction conditions. SEM and TEM-EDXA images of Pd10 catalyst after methane decomposition showed formation of carbon nanofibers. XRD of the above catalyst revealed, moderately crystalline peaks of Pd which may be responsible for the increase in the catalytic life and the formation of carbon nanofibers.     

A new hydrogen storage system based on efficient reversible catalytic hydrogenation/dehydrogenation of terphenyl

Noble metal catalysts on mesoporous SiO₂ and modified carbon supports were found to enhance the activities of terphenyl (TPh) hydrogenation and tercyclohexane (TCH) dehydrogenation without side reactions, such as cracking, hydrogenolysis, ring opening and/or coke formation. The noble metal catalysts could be used for a reversible hydrogen storage system. Five percent Pt/SiO₂ catalyst was highly active in TCH dehydrogenation without stirring, due to an easier diffusion of organic molecules to the small catalyst particles during dehydrogenation.     

Transition metal-decorated activated carbon catalysts for dehydrogenation of NaAlH4

Dehydrogenation of NaAlH₄ can be greatly facilitated by activated carbon catalysts. The catalytic function can be further enhanced by decorating the carbon with Co, Ni, or Cu nanoparticles. The decomposition temperature was lowered by as much as 100 °C using a 3 wt.% Co or Ni-decorated activated carbon, comparable to a Ti-based catalyst, which were the most effective among the metals tested. The catalytic effect is likely due to a combination of hydrogen spillover effect, high contact area between carbon and the hydride, and confinement of the hydride as nano-sized domains in the pores of the carbon matrix. The catalysts were also effective in facilitating rehydrogenation of NaAlH₄ under moderate pressure (75.8 bar H₂) and low temperature (120 °C), when no rehydrogenation would occur without the catalyst. The fact that this new catalyst system is not specific to any hydride offers many potential applications.     

Production of hydrogen and carbon nanofibers through the decomposition of methane over activated carbon supported Ni catalysts

Hydrogen has been produced by decomposing methane thermocatalytically at 1123 K and volume hourly space velocity (VHSV) of 1.62 L/h g in the presence of activated carbon supported Ni catalysts of different compositions (Samples coded as Ni10, Ni20, Ni30 and Ni40 respectively). The studies indicated that the sample coded Ni30 catalyst (with Ni content of 23.33 wt.%) has the highest catalytic activity among all the catalysts tested. The initial methane decomposition rate, accumulated carbon in 4 h and sustainability factor (SF) of Ni30 catalyst are 0.89 mmol/min.g, 7.92 g C/g Ni and 0.7 respectively. SEM image of Ni30 catalyst after methane decomposition reaction showed formation of degenerated carbon fibers. XRD of the above catalyst revealed, moderately crystalline peaks of Ni which may be responsible for the increase in the catalytic life and the formation of carbon fibers.     

Hydrogen production via the aqueous phase reforming of polyols over three dimensionally mesoporous carbon supported catalysts

In order to investigate the relationship between the type of polyol feed and three-dimensionally mesoporous carbon supports with different mesopore structures and sizes, aqueous phase reforming (APR) reactions of xylitol and glycerol were carried out in a continuous fixed bed reactor. The effect of reaction conditions such as the reaction temperature and pressure on the APR performance were studied in the range of 215–250 °C and 28–45 bar. Three-dimensionally bimodal mesoporous carbon (3D-BMC) with the larger secondary mesopores showed the best catalytic performance in terms of carbon conversion to gas, hydrogen yield, selectivity, and hydrogen production rate due to its unique mesoporous structure, regardless of the kind of polyol feed. In addition, the reaction temperature and pressure significantly affected catalytic performance in the APR of polyols. The product selectivity was dependent on the reaction conditions and the type of polyol feed. The hydrogen selectivity of glycerol was higher than that of xylitol, whereas alkane selectivity was higher for xylitol, and the selectivity increased significantly by promoting the reactions favorable for alkane formation with increased reaction temperature and pressure.     

Hydrogen production by propylene-assisted decomposition of methane over activated carbon catalysts

Catalytic decomposition of methane (CDM) permits obtaining hydrogen in high yields and – what is essential – it does not lead to release of CO₂. Unfortunately, most of the catalysts used in this process undergo fast deactivation. Their possible regeneration, consisting in the removal of pore blocking carbonaceous deposit of low catalytic activity, leads to generation of undesirable carbon dioxide. An alternative solution for maintaining high catalyst activity in the CDM reaction can be generation of the catalytically active carbonaceous deposit on its surface. Such a deposit can be obtained by decomposition of different organic substances. This paper reports on methane decomposition carried out in the presence of propylene (used in the concentration of 10 or 20%). The reaction was performed at three temperatures of 750 °C, 850 °C or 950 °C. Three types of activated carbon were tested as catalysts: the first one was obtained by activation of pine wood biomass with Na₂CO₃, whereas the second and third ones were commercial carbons (WG-12 and Norit RX3 Extra). According to the results, the addition of propylene to the CDM system effectively reduces deactivation of the activated carbon catalysts and permits fast stabilisation of their catalytic activity at a high level.     

Hydrogen storage performance of platinum supported carbon nanohorns: A DFT study of reaction mechanisms,thermodynamics, and kinetics

Platinum (Pt) is one of a robust hydrogen dissociative catalyst. However, the migration of dissociated hydrogens from Pt nanoparticles to carbon supports such as graphene and carbon nanotube are energetically unfavorable reactions. To enhance the hydrogen storage via migration mechanism, carbon nanohorn is applied as a support for Pt nanoparticles (Pt and Pt₄). The H₂ storage performance of Pt and Pt₄ supported on the mono-vacancy carbon nanohorn (vNH) has been investigated by using density functional theory calculations. The Pt and Pt₄ firmly deposit at the vacancy site through the three strong Pt–C bonds with binding energies about ?7.0 eV, which can prevent the metal desorption and migration. The mechanism of H₂ storage starts with H₂ adsorption followed by H₂ spillover reaction. The calculation results reveal that the supported Pt nanoparticles are the active sites for H₂ dissociative adsorption while the high curvature surface of carbon nanohorn is the active area for accommodating the migrated H atoms from the spillover reaction. Remarkably, the hydrogen spillover reactions over Pt– and Pt₄-supported on vNHs in this study are spontaneous at room temperature with highly exothermic reaction energy. The fundamental understanding obtained from this study is beneficial for further design and synthesis of high-performance materials for H₂ storage applications.     

Hydrogen storage properties of various carbon supported NaBH4 prepared via metathesis

Sodium borohydride nanoparticles prepared via the metathesis reaction between LiBH₄ and NaCl were successfully deposited on various carbon supporting materials such as graphite, graphene oxide and carbon nanotubes. The X-ray diffraction analyses were conducted to identify the phase of NaBH₄ deposited on various carbon supporting materials. The transmittance electron micrograph analyses were also conducted to investigate the particle size and dispersion of NaBH₄ within carbon supporting materials. The particle size and size distribution of NaBH₄ on graphite were observed to be larger and broader than of other two supporting materials, graphene oxide and CNT due to the lower surface energy as compared to GO and CNT. The bonding state of NaBH₄ was confirmed by the Fourier-transformed infrared spectroscopy analysis. The TG and PCT results show that the hydrogen desorption of the NaBH₄ deposited on carbon supports takes place at temperature (130 °C～) significantly lower than that of pure NaBH₄ (above 500 °C) and the amount of desorption was in the order of graphene oxide (12.3 mass %) > CNT (9.8 mass %) > graphite (5.7 mass %). The reversibility of hydrogen adsorption after five cycles of adsorption-desorption showed that NaBH₄/GO and NaBH₄/CNT were much better than that of pure NaBH₄ due to excellent structural stability.     

Hydrogen storage properties of activated carbon confined LiBH4 doped with CeF3 as catalyst

CeF₃ as a catalyst is first added to activated carbon (AC) by ball milling under low rotation speed. Then the treated AC was used as the scaffold to confine LiBH₄ by melt infiltration process. The combined effects of confinement and CeF₃ doping on the hydrogen storage properties of LiBH₄ are studied. The experimental results show that LiBH₄ and CeF₃ are well dispersed in the AC scaffold and occupy up to 90% of the pores of AC. Compared with pristine LiBH₄, the onset dehydrogenation temperature for LiBH₄-AC and LiBH₄-AC-CeF₃ decreases by 150 and 190 °C, respectively. And the corresponding dehydrogenation capacity increases from 8.2 wt% to 13.1 wt% for LiBH₄-AC and 12.8 wt% for LiBH₄-AC-CeF₃, respectively. The maximum dehydrogenation speed of LiBH₄-AC and LiBH₄-AC-CeF₃ is 80 and 288 times higher than that of pristine LiBH₄ at 350 °C. And LiBH₄-AC andLiBH₄-AC-CeF₃ show good reversible hydrogen storage properties. On the during 4th dehydrogenation cycle, the hydrogen release capacity of LiBH₄-AC and LiBH₄-AC-5 wt% CeF₃ reaches 8.1 and 9.3 wt%, respectively.     

Hydrogen storage properties of multi-walled carbon nanotubes and carbon nano-onions grown on single and bi-catalysts including Fe,Mo, Co and Ni supported by MgO

The effects of various catalysts including Fe, Mo, Ni, Co and their dual compounds supported by MgO, on production yield, diameter, quality and hydrogen storage properties of carbon nanostructures (CNSs) containing multi-walled carbon nanotubes and carbon nano-onions are studied. It is shown that the production yield of CNSs depends on applied catalyst. The production yields of CNSs are in descending order by using the following catalyst as: Co/Mo, Fe/Mo, Ni/Mo, Mo, Fe/Co, Fe/Ni, Fe, Ni, Co and Ni/Co. Moreover, the CNSs grown on Fe/Co@MgO catalyst have the highest quality, and those grown on Mo@MgO catalyst have the highest surface area, micro-pore distribution and dangling bands, compared to the others. The results of Raman spectroscopy and N₂ adsorption confirm the relation between D′ peak area and pores volume less than 10 nm. The hydrogen storage capacities of CNSs grown on the catalysts with production yield more than 45% are in the ascending order as: Mo, Ni/Mo, Fe/Mo, Co/Mo and Fe/Co. It inferred that the CNSs grown on catalysts including Mo are more suitable for hydrogen storage applications, due to high micro-pores (vacancy-like defects) and likely presence of molybdenum carbide structures for enhancing hydrogen uptake. The findings elucidate that specific surface area, micro and meso-pore (certainly less than 10 nm), and vacancy-like defects of the CNSs affect hydrogen uptake and desorption temperature of the stored hydrogen.