GNs/MOF-based mixed matrix membranes for gas separations

NU-1000 and graphene nanosheet (GNs) with different loadings have been used as fillers to prepare mixed matrix membranes (MMMs) with polyethersulfone (PES). The high performance of the MMMs has been successfully fabricated for the evaluation of gas separation at 1 bar and various temperatures (20, 40, 60 °C). The successful fabrication of the MMMs were confirmed by using SEM, FTIR, AFM, and XRD. The crystalline nature of GNs and NU-1000 in the MMMs are evidenced by XRD, which confirms the successful fabrication of the MMMs. In addition, the thermal stability of the MMMs was enhanced with the increase of the GNs. Separation performance of H₂ was superior to CO₂, N₂ and CH₄ separation on the MMMs which is a critical for producing energy. The best gas separation results in terms of both permeability and selectivity were obtained with 0.03% GNs and 10% NU-1000. PG3N membrane presented maximum H₂/CO₂, H₂/N₂ and H₂/CH₄ selectivity of 5, 4.2, 3.3 at 20 C, respectively. With an increase in temperature, the permeability increased, while the selectivity of all the MMMs decreased. The MMMs exhibited excellent gas separation capability, which offers unique opportunities for potential large-scale practical applications.     

Sonochemical synthesis of novel decorated graphene nanosheets with amine functional Cu-terephthalate MOF for hydrogen adsorption: Effect of ultrasound and graphene content

A novel graphene oxide nanosheet (GO) decorated with functional Cu-terephthalate (Cu-BDC-NH₂) metal-organic framework (MOF) designed for hydrogen adsorption and storage. The composite framework was produced under low-frequency high-power ultrasound (20 kHz) waves to improve reaction time and yield. The obtained green powder was then characterized by SEM, XRD, FTIR, BET, and TGA analysis. Box-Behnken Design (BBD) was applied to optimize the reaction condition and GO content. Compared to pure MOF, our results revealed that the coupled effects of sonochemical synthesis and GO content improved both the production yield and hydrogen adsorption capacity of the composite framework. Also, it was observed that ultrasound waves improve the solvent exchange process for framework activation. Besides, the incorporation of GO enhances the chemical and thermal stability of the Cu-BDC-NH₂ framework. The ultrasound wave and GO content increased the hydrogen adsorption capacity by improving the BET surface area, more active sites population and decreasing gas diffusion resistance by creating more defects.     

Preparation of PPO-silica mixed matrix membranes by in-situ sol–gel method for H2/CO2 separation

Poly(2,6-dimethyl-1,4-phenylene oxide)(PPO)-silica mixed matrix membranes (MMMs) were synthesized through the in-situ sol–gel method. The effects of the acid–base catalysis conditions and silica loading weight on the gas separation performance of the membranes were investigated. The functional groups, crystalline structure, thermal stability, and morphology of the MMMs were examined using Fourier transform-infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and thermogravimetric analysis (TGA), respectively. The results indicate that using the in-situ sol–gel method to synthesize PPO-silica MMMs is beneficial for improving the adhesion between the silica and polymer and for the dispersion of the silica. The additives significantly enhanced the thermal stability of the membranes. Compared with pure PPO membranes, the PPO-silica MMMs prepared with 10 wt.% acid-silica loading exhibited the best H₂/CO₂ separation properties: H₂ permeability was enhanced from 82.1 to 548.7 Barrer, and an H₂/CO₂ separation ratio of approximately 3.56 was observed.     

Fabrication and characterization of poly(phenylene oxide)/SBA-15/carbon molecule sieve multilayer mixed matrix membrane for gas separation

A novel multilayer mixed matrix membrane (MMM), consisting of poly(phenylene oxide) (PPO), large-pore mesoporous silica molecular sieve zeolite SBA-15, and a carbon molecular sieve (CMS)/Al₂O₃ substrate, was successfully fabricated using the procedure outlined in this paper. The membranes were cast by spin coating and exposed to different gases for the purpose of determining and comparing the permeability and selectivity of PPO/SBA-15 membranes to H₂, CO₂, N₂, and CH₄. PPO/SBA-15/CMS/Al₂O₃ MMMs with different loading weights of zeolite SBA-15 were also studied. This new class of PPO/SBA-15/CMS/Al₂O₃ multilayer MMMs showed higher levels of gas permeability compared to PPO/SBA-15 membranes. The permselectivity of H₂/N₂ and H₂/CH₄ combinations increased remarkably, with values at 38.9 and 50.9, respectively, at 10 wt% zeolite loading. Field emission scanning electron microscopy results showed that the interface between the polymer and the zeolite in MMMs was better at a 10 wt% loading than other loading levels. The increments of the glass transition temperature of MMMs with zeolite confirm that zeolite causes polymer chains to become rigid.     

Preparation of functional copolymer based composite membranes containing graphene oxide showing improved electrochemical properties and fuel cell performance

The objective of this work is to prepare a functional copolymer of poly(acrylonitrile)-co-poly(2-Acrylamido-2-methyl-1-propanesulfonic acid) (PAN-co-PAMPS) and impregnation of graphene oxide (GO) into the copolymer followed by crosslinking to prepare conetwork composite membranes by simple and cost effective solution casting method and evaluating their structural, morphological, thermal, and mechanical properties. The successful incorporation of different amounts of GO content (0.1–1 wt%) within the polymer matrix was confirmed by FT-IR spectroscopy, X-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The mechanical properties of the prepared crosslinked composite membranes are found to be greatly enhanced by the addition of GO in the copolymer matrix. The thermogravimetric analysis (TGA) demonstrated considerable improvements in thermal stability for the composite membrane with low GO content. The effect of loading of GO in the copolymer matrix on proton conductivity and fuel cell performance has been studied systematically. The membranes prepared by mixing with 0.5 wt% GO in the copolymer followed by crosslinking exhibited maximum ionic conductivity (K^m), lower methanol permeability (P_M), and higher relative selectivity. This observed P_M value is much lower range from 3.02 × 10^?7 to 11.9 × 10^?7 cm²/s compared to the Nafion® 117 membrane (22 × 10^?7 cm²/s). The fuel cell performance in terms of maximum power density and current density and the durability of the crosslinked composite membranes have also been evaluated here. Low P_M, high K^m, and high selectivity values show that functional co-polymer/GO crosslinked co-network composite membrane is a promising alternative membrane separator to replace the expensive Nafion® 117 for proton exchange membrane fuel cells (PEMFCs) application.     

Hydrogen separation and purification using crosslinkable PDMS/zeolite A nanoparticles mixed matrix membranes

The transport properties of gases in polydimethylsiloxane (PDMS)/zeolite A mixed matrix membranes (MMMs) were determined based on pure gas permeation experiments. MMMs were prepared by incorporating zeolite 4A nanoparticles into a PDMS matrix using a new procedure. The permeation rates of C₃H₈, CH₄, CO₂, and H₂ were evaluated through a dense homogeneous pure PDMS membrane and PDMS/4A MMMs to assess the viability of these membranes for natural gas sweetening and hydrogen purification. SEM investigations showed good adhesion of the polymer to the zeolite in MMMs. Permeation performance of the membranes was also investigated using a laboratory-scale gas separation apparatus and effects of feed pressure, zeolite loading and pore size of zeolite on the gas separation performance of the MMMs were evaluated. The MMMs exhibited both higher selectivity of H₂/CH₄ and H₂ permeability as compared with the neat PDMS membrane, suggesting that these membranes are very promising for gas separations such as H₂/CH₄ separation.     

Chemical modification of polysulfone: Composite anionic exchange membrane with TiO2 nano-particles

Synthesis of quaternary polysulfone/Titanium dioxide (QPSf/TiO₂) nanocomposite membranes by the recasting procedure as suitable electrolyte in alkaline fuel cells is described. The composite membranes were characterized by ionic conductivity measurements, TGA, SEM, XRD, and AFM. Thermal analysis results showed that the composite membranes have good thermal properties. The introduction of the inorganic filler supplies the composite membrane with a good thermal resistance. The physico-chemical properties studied by means of SEM and XRD techniques suggested the uniform and homogeneous distribution of TiO₂ at 2.5 wt.% loading, and negligible agglomeration at 10 wt.% loading, also indicated enhancement of crystalline character of these membranes. The energy dispersive X-ray spectra (EDS) analysis gave proportional percentages that the distribution of Titania element on the surface of the composite membrane was uniform. Observations from the results suggest that QPSf/TiO₂ nanocomposite membranes have good prospects for possible use in AFC.     

Structural effect of Ni/SBA-15 by Zr promoter for H2 production via methane dry reforming

5 wt% of Ni/SBA-15 supported with numerous Zr loading (1–7 wt%) were produced using sol-gel technique at 60 °C. The influence of Zr promoter on the physiochemical properties of Ni/SBA-15 catalysts for methane dry reforming were examined in a fixed-bed reactor at 800 °C. Analytical characterizations including XRD, BET, FTIR, N₂ adsorption desorption, TEM and TGA were conducted to study the physiochemical properties of Zr/Ni/SBA-15 catalysts for the sake of identification of the amount of coke deposition formed on the spent catalyst. Increasing the amount of Zr loading from 1 to 7 wt% supported on Ni/SBA-15 reduced the catalyst's surface area as was proven from the physiochemical properties of Zr/Ni/SBA-15 catalyst. The catalytic activity test revealed that the optimum Zr loading was 1 wt% at which CH₄ and CO₂ conversions were 87.07% and 4.01%, meanwhile H₂:CO ratios was 0.42. This result was owing to the existence of the Zr species in promoting a good dispersion of Nickel (Ni) active sites on the catalyst surface as affirmed from XRD and FTIR results. The latest discovery indicates that promotion of 1 wt% Zr onto Ni/SBA-15 can prompt excellent catalytic performance in CRM.     

Composite membrane by incorporating sulfonated graphene oxide in polybenzimidazole for high temperature proton exchange membrane fuel cells

The objective of this work is to examine the polybenzimidazole (PBI)/sulfonated graphene oxide (sGO) membranes as alternative materials for high-temperature proton exchange membrane fuel cell (HT-PEMFC). PBI/sGO composite membranes were characterized by TGA, FTIR, SEM analysis, acid doping&acid leaching tests, mechanical analysis, and proton conductivity measurements. The proton conductivity of composite membranes was considerably enhanced by the existence of sGO filler. The enhancement of these properties is related to the increased content of –SO₃H groups in the PBI/sGO composite membrane, increasing the channel availability required for the proton transport. The PBI/sGO membranes were tested in a single HT-PEMFC to evaluate high-temperature fuel cell performance. Amongst the PBI/sGO composite membranes, the membrane containing 5 wt. % GO (PBI/sGO-2) showed the highest HT-PEMFC performance. The maximum power density of 364 mW/cm² was yielded by PBI/sGO-2 membrane when operating the cell at 160 °C under non humidified conditions. In comparison, a maximum power density of 235 mW/cm² was determined by the PBI membrane under the same operating conditions. To investigate the HT-PEMFC stability, long-term stability tests were performed in comparison with the PBI membrane. After a long-term performance test for 200 h, the HT-PEMFC performance loss was obtained as 9% and 13% for PBI/sGO-2 and PBI membranes, respectively. The improved HT-PEMFC performance of PBI/sGO composite membranes suggests that PBI/sGO composites are feasible candidates for HT-PEMFC applications.     

Micro-cogeneration application of a high-temperature PEM fuel cell stack operated with polybenzimidazole based membranes

High temperature Proton Exchange Membrane Fuel Cells (HT-PEMFC) have attracted the attention of researchers in recent years due to their advantages such as working with reformed gases, easy heat management and compatibility with micro-cogeneration systems. In this study, it is aimed to designed, manufactured and tested of the HT-PEMFC stack based on Polybenzimidazole/Graphene Oxide (PBI/GO) composite membranes. The micro-cogeneration application of the PBI/GO composite membrane based stack was investigated using a reformat gas mixture containing Hydrogen/Carbon Dioxide/Carbon Monoxide (H₂/CO₂/CO). The prepared HT-PEMFC stack comprises 12 cells with 150 cm² active cell area. Thermo-oil based liquid cooling was used in the HT-PEMFC stack and cooling plates were used to prevent coolant leakage between the cells. As a result of HT-PEMFC performance studies, maximum 546 W and 468 W power were obtained from PBI/GO and PBI membranes based HT-PEMFC stacks respectively. The results demonstrate that introducing GO into the PBI membranes enhances the performance of HT-PEMFC technology and demonstrated the potential of the HT-PEMFC stack for use in micro-cogeneration applications. It is also underlined that the developed PBI/GO composite membranes have the potential as an alternative to commercially available PBI membranes in the future.     

Fabrication and characterization of poly(vinyl alcohol)/montmorillonite/poly(styrene sulfonic acid) proton-conducting composite membranes for direct methanol fuel cells

A high performance poly(vinyl alcohol)/montmorillonite/poly(styrene sulfonic acid) (PVA/MMT/PSSA) proton-conducting composite membrane was fabricated by a solution casting method. The characteristic properties of these blend composite membranes were investigated by using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, methanol permeability measurement, and the AC impedance method. The ionic conductivities for the composite membranes are in the order of 10⁻³ S cm⁻¹ at ambient temperature. There are two proton sources used on this novel composite membrane: the modified MMT fillers and PSSA polymer, both materials all contain the -SO₃H group. Therefore, the ionic conductivity was greatly enhanced. The methanol permeabilities of PVA/MMT/PSSA composite membranes is of the order of 10⁻⁷ cm² s⁻¹. It is due to the excellent methanol barrier properties of the PVA polymer. The peak power densities of the air-breathing direct methanol fuel cells (DMFCs) with 1M, 2M, 4M CH₃OH fuels were 14.22, 20.00, and 13.09 mW cm⁻², respectively, at ambient conditions. The direct methanol fuel cell with this composite polymer membrane exhibited good electrochemical performance. The proposed PVA/MMT/PSSA composite membrane is therefore a potential candidate for future applications in DMFC.     

Experimental investigation of natural polysaccharide-based mixed matrix membrane modified with graphene oxide and Pd-nanoparticles for enhanced gas separation performance

In this work, we proposed a mixed matrix membrane prepared by using a glycerol modified guar gum (GGP) polymer matrix incorporated with graphene oxide (GO). The influence of varying GO concentration on the gas separation performance was investigated and 2 wt% was found to be the optimum concentration for high performance. The 2 wt% GO mixed matrix membranes were further modified with Pd nanoparticles. When GO, and Pd nanoparticles were mixed, CO₂ permeability increased by 49.94%, while the permeability of H₂ gas molecules decreased by 98.11%, respectively, compared to the pristine GGP membrane. The selectivity of CO₂/H₂ was obtained as 18.27. The glass transition temperature of the membrane increased from 85 to 95.2 °C, tensile strength and elongation of the break were significantly improved by 29.09% and 84.37% through the addition of Pd and GO into the membrane. The scanning electron microscopy revealed a dense top surface after GO nanosheets incorporation. Further, the thermogravimetric analysis proposes that the modified membrane is thermally stable than GGP. Henceforth, the study suggests GO incorporation and Pd nanoparticles modification of guar gum membrane is a promising gas separation membrane with potentially high selectivity for CO₂ gas.     

Thermal stability study of La0.9Sr0.1Ga0.8Mg0.2O2.85–(Li/Na)2CO3 composite electrolytes for low-temperature solid oxide fuel cells

Novel composite materials based on La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM) and a binary eutectic carbonates (52 mol% Li₂CO₃:48 mol% Na₂CO₃) are potential electrolytes for low-temperature solid oxide fuel cells (LTSOFCs) operating at 400–600 °C. However, thermal stability of the LSGM–(Li/Na)₂CO₃ composites remains in doubt due to the molten state of the carbonates at elevated temperature. In this paper, XRD, SEM, TGA and EIS were employed for thermal ageing and cycling studies of the LSGM–(Li/Na)₂CO₃ composites. XRD and SEM results showed that ageing induced a slight effect on the structure and morphology of the composites. TGA and EIS results indicated that the composites had a good stability during cycling. The LSGM–20 wt% (Li/Na)₂CO₃ sample showed a relatively stable conductivity (7–9 × 10⁻² S cm⁻¹) during a 650 h measurement under air at 600 °C. Single cell based on the composite electrolytes was reported for the first time, a maximum power density of 617 W cm⁻² and the open circuit voltage (OCV) of 1.01 V were achieved at 600 °C for the composite containing 20 wt% carbonates. The notable thermal stability together with fairly high performance emphasize the promise of LSGM–(Li/Na)₂CO₃ composite electrolytes for long-term LTSOFCs.     

Room-temperature hydrogen storage performance of metal-organic framework/graphene oxide composites by molecular simulations

Metal-organic framework/graphene oxide (MOF/GO) composites have been regarded as potential room-temperature hydrogen storage materials recently. In this work, the influence of MOF structural properties, GO functional group contents and different amounts of doped lithium (Li⁺) on hydrogen storage performance of different MOF/GO composites were investigated by grand canonical Monte Carlo (GCMC) simulations. It is found that MOF/GO composites based on small-pore MOFs exhibit enhanced hydrogen storage capacity, whereas MOF/GO based on large-pore MOFs show decreased hydrogen storage capacity, which can be ascribed to the novel pores at MOF/GO interface that favors the enhanced hydrogen storage performance due to the increased pore volume/surface area. By integrating the small-pore MOF-1 with GO, the hydrogen storage capacity was enhanced from 9.88 mg/go up to 11.48 mg/g. However, the interfacial pores are smaller compared with those in large-pore MOFs, resulting in significantly reduced pore volume/surface area as well as hydrogen storage capacities of large-pore MOF/GO composite. Moreover, with the increased contents of hydroxyl, epoxy groups as well as carboxyl group modification, the pore volumes and specific surface areas of MOF/GO are decreased, resulting in reduced hydrogen storage performance. Furthermore, the room-temperature hydrogen storage capacities of Li⁺ doped MOF/GO was improved with increased Li⁺ at low loading and decrease with the increased Li⁺ amounts at high loading. This is due to that the introduced Li⁺ effectively increases the accessible hydrogen adsorption sites at low Li⁺ loading, which eventually favors the hydrogen adsorption capacity. However, high Li⁺ loading causes ion aggregation that reduces the accessible hydrogen adsorption sites, leading to decreased hydrogen storage capacities. MOF-5/GO composites with moderate Li⁺ doping achieved the optimum hydrogen storage capacities of approximately 29 mg/g.     

Phosphorylated chitosan/poly(vinyl alcohol) based proton exchange membranes modified with propylammonium nitrate ionic liquid and silica filler for fuel cell applications

In our previous work, phosphorylated chitosan was modified through polymer blending with poly(vinyl alcohol) (PVA) polymer to produce N-methylene phosphonic chitosan/poly(vinyl alcohol) (NMPC/PVA) composite membranes. The aim of this work is to further investigate the effects of a propylammonium nitrate (PAN) ionic liquid and/or silicon dioxide (SiO₂) filler on the morphology and physical properties of NMPC/PVA composite membranes. The temperature-dependent ionic conductivity of the composite membranes with various ionic liquid and filler compositions was studied by varying the loading of PAN ionic liquid and SiO₂-PAN filler in the range of 5–20 wt%. As the loading of PAN ionic liquid increased in the NMPC/PVA membrane matrix, the ionic conductivity value also increased with the highest value of 0.53 × 10^?3 S cm^?1 at 25 °C and increased to 1.54 × 10^?3 S cm^?1 at 100 °C with 20 wt% PAN. The NMPC/PVA-PAN (20 wt%) composite membrane also exhibited the highest water uptake and ion exchange capacity, with values of 60.5% and 0.60 mequiv g^?1, respectively. In addition, in the single-cell performance test, the NMPC/PVA-PAN (20 wt%) composite membrane displayed a maximum power density, which was increased by approximately 14% compared to the NMPC/PVA composite membrane with 5 wt% SiO₂-PAN. This work demonstrated that modified NMPC/PVA composite membranes with ionic liquid PAN and/or SiO₂ filler showed enhanced performance compared with unmodified NMPC/PVA composite membranes for proton exchange membrane fuel cells.     

Effective encapsulation of Ni nanoparticles in metal-organic frameworks and their application for CO2 methanation

Ni(10 wt%)@UiO-66 and Ni(10 wt%)@MIL-101 composites were prepared by the classical impregnation method (IMP) and the “double solvent method” (DS), followed by the rapid and simple reduction of Ni²⁺ to Ni⁰ by aqueous solution of NaBH₄. Structural characterization by BET, XRD, TGA, SEM/EDX, EELS, XPS showed that Ni nanoparticles of maximum 4 nm are uniformly dispersed on the microporous UiO-66 or the mesoporous MIL-101 support, regardless of the deposition method, without any significant difference in crystallinity and morphology of the MOF support. Functional characterization through temperature programmed desorption of CO₂ (CO₂-TPD) reveals an important contribution of the Ni-MOF interaction in the CO₂ adsorption capacity. The best catalytic performance in CO₂ hydrogenation reaction was obtained in case of the Ni@MIL-101 (IMP) sample: X_CO2 of 56.4%, and S_CH4 of 91.6% at 320 °C, 4650 h⁻¹ and CO₂:H₂ = 1:8. All catalyst samples show stable catalytic performance parameters over a 10 h time on stream.     

Development of high performance amine functionalized zeolitic imidazolate framework (ZIF-8)/cellulose triacetate mixed matrix membranes for CO2/CH4 separation

High cost and complex fabrication process of inorganic membranes and lower position of pristine polymeric membranes in the Robeson upper bound curve urged the researchers to develop mixed matrix membranes (MMMs). Cellulose acetate being most commercially used polymer, dominates the market of CO₂ separation mainly because of low cost and environmental friendly resource. In the present study, MMMs consists of amine functionalized zeolitic imidazolate framework (NH₂-ZIF-8) and cellulose triacetate were fabricated for the first time. NH₂-ZIF-8 was used as a filler because the pore size of ZIF-8 is between the kinetic diameter of separating gases (CO₂ and CH₄). Moreover,  NH₂ group attached on the surface of ZIF-8 has affinity with condensable gases like CO₂. Morphology, crystallinity, tensile strength and functional groups of fabricated membranes were investigated using different analytical techniques. Results revealed that the increase of feed pressure has increased CO₂ permeability and decreased permselectivity. However, improvements in gas separation performance were observed with the addition of nanofiller. Best position in Robeson's upper bound curve at 4 bar was obtained with 10 wt% loading with CO₂ permeability and CO₂/CH₄ permselectivity of 218 barrer and 13.84, respectively. The improvement in the gas separation performance with loading is attributed to the increased diffusion coefficients as well as solubility coefficients, which was increased to 33% and 3.8%, respectively.     

Nonoxidative methane activation,coupling, and conversion to ethane,ethylene, and hydrogen over Fe/HZSM‐5, Mo/HZSM‐5, and Fe–Mo/HZSM‐5 catalysts in packed bed reactor

A high abundance of methane and its relatively low price make it an attractive raw feedstock for the production of ethylene, which is in the consumer demand in recent years. Direct catalytic nonoxidative conversion is interesting, because it could be utilized on natural gas well sites. Monometallic and bimetallic Fe and Mo catalysts were prepared for the purpose of the coupling to ethane and ethene. Three supported materials were synthesized with the following loading of metal: 2.5‐wt% Fe, 5.0‐wt% Fe, and 2.5‐wt% Mo on HZSM‐5. Process' chemical reactions were also catalyzed with a constant 2.5‐wt% Mo/HZSM‐5, which had different amounts of Fe, namely, 0.5, 1.0, and 2.5 wt%. Fourier transform infrared (FTIR), N₂ adsorption/desorption, NH₃ temperature‐programmed desorption (TPD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) were applied for characterization. Coke, accumulated on spent solids, was determined by thermogravimetric analysis (TGA). Activity was evaluated in quartz‐packed bed reactor. All surfaces suffered from deactivation due to carbon formation. The addition of Fe to Mo increased CH₄ reacted. The highest selectivity for alkenes was achieved over 1.0‐wt% Fe to 2.5‐wt% Mo/HZSM‐5. At the peak of performance, the C‐based reactivity was 52% for olefins and 2% for alkanes. Stability was accomplished over 2.5‐wt% Fe/HZSM‐5, where the rate of C₂ synthesis was comparatively stable for 20 hours of the time on stream. The selective C‐basis yield for C₂H₄ and C₂H₆ was 36% and 23%, respectively. The lowest measured quantity of (carbonaceous) by‐products was deposited on 2.5‐wt% Fe/HZSM‐5 after 26 hours. Propylene was detected very limitedly.     

Synthesis,characterization and catalytic performance of MgO-coated Ni/SBA-15 catalysts for methane dry reforming to syngas and hydrogen

A series of MgO-coated SBA-15 mesoporous silica with MgO contents ranging from 2 wt% to 15 wt% have been successfully synthesized by a simple one-pot synthesis method and further impregnated with 10 wt% Ni. Ni/SBA-15 modified with 8 wt% MgO was also prepared by conventional impregnation method. The materials were characterized by means of XRD, N₂ physisorption, TEM by applying high-angle annular dark field (HAADF), XPS, CO₂-TPD, TGA and temperature-programmed hydrogenation (TPH) techniques, and their catalytic performance was tested for methane reforming with CO₂. The results showed that MgO was successfully coated on the walls of mesoporous silica and the mesoporous structure of SBA-15 was well maintained after MgO modification. Compared to MgO-impregnated material, MgO-coated counterpart showed a better order in the mesostructure and more medium basic sites. The addition of MgO enhanced initial catalytic activity of Ni/SBA-15, and the catalyst with 8 wt% MgO coating showed the most excellent catalytic activity. The MgO coating induced an improved dispersion of Ni species and larger medium basic sites than that of MgO impregnation, which led to an enhanced long-term stability and resistance to carbon formation. The deposition of graphitic carbon species during the reaction was the main reason for the deactivation of Ni/SBA-15 catalyst.     

Hydrogenation properties of MgH2- x wt% AC (x=0, 5, 10, 15) nanocomposites

Magnesium is considered as a promising candidate for hydrogen storage due to its high storage capacity (theoretical value ~ 7.6 wt%). Nanocomposites of Magnesium hydride and activated charcoal (AC) were prepared using ball milling method. These nanocomposites were characterized by XRD, TGA, DSC and SEM techniques. The TGA analysis show that the MgH₂-5 wt% AC nanocomposite exhibits dehydrogenation capacity of 7.45 wt% (which is very close to the storage capacity of MgH₂) and starts release of hydrogen at 140 °C temperature. The results from the Kissinger plot from DSC result showed that the activation energy for hydrogen desorption of MgH₂ with 5 wt% AC was reduced compared to those of as-received.