High BET Area Research Articles

Recovery of Fe and Al from red mud by a novel fractional precipitation process.

The development of cheap and effective approach for utilizing red mud (RM) waste is a long and arduous task. This work provided a technically and economically feasible route to utilize RM waste for the production of high valuable chemicals by use of the industrial wastes as cheap raw materials. The Fe and Al elements were first leached from RM through hydrothermal reaction and then were separated by precipitation after the Fe(III) in leachate was reduced to Fe(II) by iron powder. Above 90% Fe and Al were extracted from RM with the Fe and Al purity of about 95% and 45%, respectively. The control test revealed that the main impurity of Al product was caused by the adsorbed SO42- during the precipitation of the Al3+. The structural characterization demonstrated that the obtained Fe products were in nanoscale, and the Ti-Si residue has high BET area of 203.7m2/g. Four products of nano-Fe3O4/nano-Fe, aluminum oxide, Ti-Si residue, and (NH4)2SO4 were obtained as valuable chemical materials for industry. This demonstrated utilization of industrial waste to produce high added-value products with high efficiency and low cost will possess promising application prospect for the resource utilization of RM in industry.

Preparation and characterization of Ni catalysts supported on pillared nanoporous bentonite powders for dry reforming reaction

The Ni/pillared-bentonite catalysts with high BET area were synthesized and used in dry reforming reaction. The effects of different parameters such as calcination temperature, OH−/Al3+ ratio, temperature and time of pillaring process and the content of nickel on the textural and catalytic properties of the synthesized catalysts were studied. The results indicated that the 15 wt% Ni catalyst supported on pillared bentonite prepared under specified conditions (OH−/Al3+ = 2.2, pillaring temperature of 40 °C and pillaring time of 3 h) possessed the highest BET area (90.80 m2/g). Also, this catalyst possessed higher catalytic activity and stability with lower amount of deposited carbon in comparison to other prepared catalysts in methane reforming with CO2.

SBA-15 as a Support for Effective Olefin Metathesis Catalysts

Olefin metathesis is the catalytic transformation of olefinic substrates, finding a wide range of applications in organic synthesis. The mesoporous molecular sieve Santa Barbara Amorphous (SBA-15) has proven to be an excellent support for metathesis catalysts thanks to its regular mesoporous structure, high BET area, and large pore volume. A survey of catalysts consisting of (i) molybdenum and tungsten oxides on SBA-15, and (ii) molybdenum and ruthenium organometallic complexes (Schrock and Grubbs-type carbenes) on SBA-15 is provided together with their characterization and catalytic performance in various metathesis reactions. The comparison with catalysts based on other supports demonstrates the high quality of the mesoporous molecular sieve SBA-15 as an advanced catalyst support.

Formation of the Solid Electrolyte Interphase on the Graphite Anode in Lithium-Ion Batteries – an Operando Neutron Depth Profiling Study

To date, commercial LIB cells are mostly based on graphite as anode material. During the first inter­calation of lithium into graphite, the electrolyte gets reduced at the anode, forming a nm-thick surface layer, the so-called solid electrolyte interphase (SEI). The SEI stops further electrolyte reduction, but as it consumes lithium during its formation, there is a loss of active lithium inventory, which causes the irreversible capacity loss during the first cycle of an LIB.[1] Neutron depth profiling (NDP) is a non-destructive technique and a suitable tool to measure lithium concentrations as a function of depth.[2,3] When irradiating the sample with a cold neutron beam, 6Li nuclides emit charged particles after neutron capture. The residual energy and the signal rate of the emitted 3H particles are correlated to depth and amount of lithium, respectively. Thus, SEI growth and lithium (de-)intercalation in graphite anodes can be studied up to a depth of ca. 30 µm. So far, in-situ NDP measurements in LIBs have been limited to thin solid-state cells or to cells with sub-mm thick anodes.[4,5] Here, we present operando NDP data for the first charge/discharge cycle of a 14 mm thick graphite anode (4 mm particles) vs. a capacitively over­sized LiFePO4 cathode, using a custom-designed coin-cell casing with 0.5 mm diameter holes which are sealed with a 7.5 µm-thick Kapton® window. Fig. 1 shows the voltage profile during cycling, demonstrating that the operando cell yields the expected first-cycle discharge capacity of 350 mAh/ggraphite. The higher irreversible capacity of ca. 98 mAh/g (ca. 22%) compared to conventional graphite used in commercial cells (ca. 10%) is due to the very high BET area of ca. 14 m2/g of the 4 µm sized graphite particles. Fig. 2 shows the NDP signals at three different states-of-charge (SOC): i) for the pristine graphite anode (0 h, black line), reflecting the lithium-containing electrolyte (1 M LiPF6 in EC/EMC 3:7 v:v) within the electrode pores; ii) for 100% SOC at the end of the first charge (16 h, red line); and, iii) at the end of the first discharge at again 0% SOC (32 h, blue line). The difference between the red and the blue line indicates that ca. ¼ of the active lithium has been consumed irreversibly for the SEI formation, in good agreement with the electrochemical data.

Hydrothermal pre-treatment, an efficient tool to improve activated carbon performances

In this study, the successful preparation of activated carbons from Corn Stigmata, either through direct pyrolysis and activation or through a preliminary additional hydrothermal carbonisation (HTC) step, was reported. It was shown that the latter allowed producing higher carbon yield, higher carbon content and higher BET area (ABET) after 2 h of activation with CO2 than what was observed for activated carbons (ACs) prepared in the same conditions but without HTC. The AC having the most developed porous texture, ABET = 1111 m2/g, was further investigated by FTIR, SEM and potentiometric titration, and its pH at point of zero charge was determined. Its performances in terms of methylene blue (MB) adsorption were studied and discussed in relation to its textural and chemical characteristics. Due to its very heterogeneous surface, the fractal Brouers–Sotolongo model was the most relevant for describing both kinetic and equilibrium adsorption data. The calculated thermodynamic parameters also showed that MB adsorption was spontaneous on this material. The high MB uptake at room temperature, compared to many other results published in the literature, further confirmed the interest of Corn Stigmata-derived hydrochars as precursors of activated carbons.

Dry reforming over mesoporous nanocrystalline 5% Ni/M-MgAl2O4 (M: CeO2, ZrO2, La2O3) catalysts

In this article mesoporous nanocrystalline 5 wt%M-95 wt%MgAl2O4 (M: CeO2, ZrO2, La2O3) powders were prepared by a novel on-step sol-gel process and employed as a support for the synthesis of 5 wt%Ni catalysts for synthesis gas production via dry reforming. The magnesium aluminate spinel prepared with this sol-gel method possessed a high BET area of 264 m2 g−1 with a high pore volume of 0.436 cm3 g−1. The results indicated that the addition of promoters (CeO2, ZrO2, La2O3) to magnesium aluminate improved the BET area and pore volume and also decreased the crystallite size. Among the prepared powders and catalysts, 5 wt%La2O3-95 wt%MgAl2O4 and 5 wt%Ni/5 wt%CeO2-95 wt%MgAl2O4 exhibited the highest BET area of 306 m2 g−1 and 263 m2 g−1, respectively. The catalytic results indicated that the 5 wt%Ni/5 wt%CeO2-95 wt%MgAl2O4 catalyst exhibited the highest activity and the lowest carbon formation among the prepared catalysts with the same content of the promoter. The influence of the CeO2 content on the textural and catalytic performance was also investigated and the results illustrated that the increment in CeO2 content improved the methane conversion and reduced the amount of deposited carbon, which could be related to the redox properties of the catalyst support.

Ultrasound-assisted hydrothermal method for the preparation of the M-Fe2O3-CuO (M: Mn, Ag, Co) mixed oxides nanocatalysts for low-temperature CO oxidation.

In this article, M-Fe2O3-CuO (M: Mn, Ag and Co) mixed oxides nanocatalysts were synthesized by a novel ultrasound-assisted hydrothermal method and the effect of irradiation power and time on the physicochemical and catalytic properties in oxidation of carbon monoxide at low temperature was investigated. The synthesized samples were studied using XRD, BET, TPR and SEM techniques. The results indicated that the incorporation of Mn into Cu-Fe catalyst had a significant influence on the catalytic properties and the catalyst promoted with 10 wt% Mn exhibited the full conversion of CO at 100 °C. This catalyst possessed a high BET area (145.1 m2 g-1) and a mesoporous texture with a relatively narrow pore size distribution with a mean crystal size of 13 nm.

Synthesis of novel hard mesoporous carbons and their applications as anodes for Li and Na ion batteries

Mesoporous-microporous carbons, were obtained from the pyrolysis of resol polymerized in the presence of tetraethoxysilane (TEOS) and the triblock copolymer PEO140-PPO39-PEO140 (F108). Carbons Cx-y (x = TEOS/F108 M ratio; y = synthesis temperature) exhibit interconnected porosity measured by N2 adsorption with high BET area and micro-mesoporous volume. According to this information and that obtained by Raman, XRD and CO2 adsorption, the carbons are described as hard carbons.As conductive additive-free anodes for Li- ion coin cells (LIBs), the carbons Cx-y present high initial specific capacity, being the highest for C70-100 (670 mAh/g) with high capacity retention: 500 mAh/g at 27 mA/g, 68 cycles and rate capability: 100 mAh/g at 1365 mA/g, 56 cycles. The C70-100 improved efficiency is attributed to the highest mesoporosity and lowest non-graphitizing hard carbon nature and surface activity.As anodes for Na-ion batteries (NIBs), these carbons present higher first discharge capacities ∼ 780-420 mAh/g and initial capacity, ∼192-109 mAh/g, than graphite. C90-150 with the lowest irreversible capacity is promising anode for NIBs. This result is due to its higher hard carbon nature and surface activity than C70-100 and lower porosity than C70-100 and C90-100, allowing more stability in carbon-sodium intercalation and less electrolyte decomposition, respectively.

Promotional effect of Mg in trimetallic nickel-manganese-magnesium nanocrystalline catalysts in CO2 reforming of methane

In the present paper, the dry reforming reaction was studied over the 10 wt%Ni-3wt.%Mn-x wt.% Mg (x = 2, 4 and 6 wt%) catalysts supported on γ-Al2O3 with mesoporous structure. The physicochemical characteristics of the samples were determined by XRD, BET, TPO, and SEM techniques. Mesoporous γ-Al2O3 carrier with the high BET area (186 m2/g) was synthesized by a simple sol–gel method and the Ni, NiMn and Mg promoted catalysts possessed nanocrystalline mesoporous structure with the BET area in the range of 127–176 m2/g. The average pore radius of the prepared catalysts were smaller than 11 nm. All the synthesized samples exhibited a CH4 conversion in the range of 60–65% at 700 °C. The small differences in methane conversion in all catalysts could be related to the same nickel loading. According to the TPR results, the Mg addition caused an increase in the reducibility of the nickel catalyst and the Mg-promoted sample exhibited a higher conversion compared to the monometallic catalyst, due to its higher reducibility. The results showed that the textural characteristics of the catalysts were affected by the content of Mg. The results indicated that the NiMn/Al2O3 catalyst promoted by 4 wt% Mg showed the highest CH4 conversion in all studied reaction temperatures (550–700 °C). Furthermore, only one oxidation peak was detected for all catalysts in TPO analysis, which was related to the filamentous form carbon. The 10Ni/Al2O3 and 10Ni3Mn4Mg/Al2O3 catalysts exhibited the highest and the lowest amount of deposited filamentous carbon, respectively. The 10Ni3Mn4Mg/Al2O3 catalyst was stable during the 20 h time on stream without any decline in CH4 conversion.

Controllable growth of MoS2 nanosheets on novel Cu2S snowflakes with high photocatalytic activity

Herein, we, for the first time, report the controllable syntheses of the snowflake-like Cu2S architectures by using a template free, facile hydrothermal route, in which thiourea as the precursor of sulfur and EDA as the solvent. It is surprising that the Cu2S snowflakes show a higher photocatalytic activity than the other samples (Cu2S dendrites and sheets), has been mainly ascribed to its high light absorbance and BET area. Then the MoS2 nanosheets (NSs) are uniformly distributed on the Cu2S snowflake (SF) substrate, the obtained MoS2 NS/Cu2S SF composite manifests high specific surface area (60.512 m2 g−1) and large pore volume (0.148 cm3 g−1), which are favorable for the efficient light capturing together with the rapid transfer of charge carriers. In comparison with the pure Cu2S, the MoS2 NS/Cu2S SF composite exhibits much enhanced activity and long-term stability towards the photocatalytic degradation of organic dye pollutants and hydrogen production. The improved photocatalytic activity could be owed to two aspects, namely the enhanced light trapping and scattering ability benefited from large specific area of unique snowflake-like structural features and improved charge separation activity of heterojunction between MoS2 and Cu2S.

Synthesis and photocatalytic properties of Bi2SiO5 and Bi12SiO20

Abstract Herein, the photochemical properties of layered Bi2SiO5 and body-centered Bi12SiO20 are investigated mainly. Under visible light irradiation (>420 nm), Bi12SiO20 shows a high photoactivity for the degradation of rhodamine B (RhB), but Bi2SiO5 does not nearly show photoactivity due to its wide band gap. Under UV light irradiation (shorter than 420 nm), however, Bi2SiO5shows 2.1 times activity higherthan Bi12SiO20. Compared with Bi12SiO20 (1.6 m2 g−1), the obviously higherBET area (28.3 m2 g−1) of Bi2SiO5can provide more active sites. Moreover, the layer structure and the interlayer Bi-O-Si bonds of Bi2SiO5have improved the electron transfer efficiency.

Preparation of high surface area Ni/MgAl2O4 nanocatalysts for CO selective methanation

Methanation of carbon monoxide in the H2-rich gas stream was performed on a series of the Ni/MgAl2O4 catalysts in a fixed bed micro-reactor. The catalysts were synthesized using wetness impregnation method and the prepared samples were characterized by XRD, BET, SEM, TEM, H2-TPR, CO chemisorption and CO-TPD techniques. The catalyst carrier was prepared by a novel sol-gel method using nitrate salts precursors and propylene oxide as a gelation agent. MgAl2O4 as catalyst carrier possessed a high BET area of 340 m2 g−1 with high pore volume (0.563 cc g−1) and small pore size (6.56 nm). The catalysts also showed high BET area, which decreased with the increase in Ni content. These catalysts exhibited mesoporous structure with average nickel crystal size smaller than 20 nm. The catalyst with Ni content of 25 wt% exhibited the maximum CO conversion and CH4 selectivity and can be considered as a catalyst with high catalytic potential for the selective methanation of carbon monoxide.

Single cobalt sites in mesoporous N-doped carbon matrix for selective catalytic hydrogenation of nitroarenes

A supported cobalt catalyst with atomically dispersed Co-Nx sites (3.5 wt% Co) in a mesoporous N-doped carbon matrix (named Co@mesoNC) is synthesized by hydrolysis of tetramethyl orthosilicate (TMOS) in a Zn/Co bimetallic zeolitic imidazolate framework (BIMZIF(Co,Zn)), followed by high-temperature pyrolysis and SiO2 leaching. A combination of TEM, XRD XPS and X-ray absorption spectroscopy studies confirm the absence of cobalt nanoparticles and indicate that these highly dispersed cobalt species are present in the form of Co-Nx. The exclusive formation of Co-Nx sites in the carbon matrix is attributed to the presence of a large amount of Zn and N in the BIMZIF precursor together with the presence of SiO2 in the pore space of this framework, extending the initial spatial distance between cobalt atoms and thereby impeding their agglomeration. The presence of SiO2 during high-temperature pyrolysis is proven crucial to create mesoporosity and a high BET area and pore volume in the N-doped carbon support (1780 m2 g−1, 1.54 cm3 g−1). This heterogeneous Co@mesoNC catalyst displays high activity and selectivity (>99%) for the selective hydrogenation of nitrobenzene to aniline at mild conditions (0.5–3 MPa, 343–383 K). When more challenging substrates (functionalized nitroarenes) are hydrogenated, the catalyst Co@mesoNC displays an excellent chemoselectivity to the corresponding substituted anilines.The presence of mesoporosity improves mass transport of reactants and/or products and the accessibility of the active Co-Nx sites, and greatly reduces deactivation due to fouling.

Synthesis and Application of Noble Metal Nanocatalysts Supported on MgAl2O4 in Glycerol Dry Reforming Reaction

Noble metal catalysts (Rh, Ru, Ir, Pd, Pt) supported on alumina-stabilized magnesia (MgAl2O4) were prepared and employed in order to convert glycerol to syngas in the presence of carbon dioxide. The physiochemical properties of the fresh and spent catalysts were determined using BET, TPR, TPO, TEM and H2S chemisorption techniques. The BET analysis showed higher surface area for the Rh, Ru and Pd catalysts compared to other samples. The TEM images of the prepared catalysts exhibited that the sizes of the active metals are smaller than 5 nm with high dispersion on the surface of the catalyst carrier. The H2S chemisorption results showed that the crystallite sizes of the noble metals were in the range of 1.28–4.2 nm. The catalytic results showed that the Rh catalyst exhibited the highest activity and stability in this reaction. The high activity of Rh catalyst could be attributed to its high BET and active metal areas. The catalytic activity of Rh catalyst declined with time on stream due to the carbon formation. It was seen that increasing the CO2 to glycerol ratio (CGR) from 0 to 3 improved the catalytic activity and decreased the amount of deposited carbon on the catalyst surface. The noble metal nanocatalysts were prepared and employed for the production of synthesis gas via glycerol dry reforming. Rh nanocatalyst exhibited the highest catalytic activity in this reaction.

Effect of substitution by Ni in MgAl2O4 spinel for biogas dry reforming

Mesoporous nanocrystalline Mg1-xNixAl2O4 (x = 0.10, 0.13, 0.17 and 0.20) with large surface area were synthesized via a simple one-step sol-gel method using nonprecious metals. The prepared Mg1-xNixAl2O4 catalysts exhibit good catalytic performance towards methane and carbon dioxide dry reforming reaction. The catalysts were evaluated by various techniques, including XRD, BET, TPR, TPO, EPR, Chemisorption, SEM and TEM. All the Ni incorporated MgAl2O4 samples possessed high BET area (296–305 m2 g−1) and pore volume (0.47–0.56 cm3 g−1) with small pore size (6.4–7.4 nm) in meso region after calcination at 700 °C. The TPR results suggested strong interaction effect in NiMg and the reducibility property of the catalysts improved with the increase of nickel doping. Mg0.8Ni0.2Al2O4 exhibited the highest activity for biogas dry reforming with 72.6% CH4 and 80.7% CO2 conversion at 700 °C. Electron paramagnetic resonance (EPR) results indicated that the incorporation of Ni in MgAl2O4 spinel lattice led to the lattice distortion and formed oxygen vacancies which are a benefit for the dry reforming reaction.

COx-free hydrogen and carbon nanofibers production by thermocatalytic decomposition of methane over mesoporous MgO·Al2O3 nanopowder-supported nickel catalysts

The catalytic performance of nickel catalysts with various nickel loadings supported on mesoporous nanocrystalline MgO·Al2O3 powders with different MgO/Al2O3 molar ratios (0.5, 1, 1.5, and 2) was investigated in the thermocatalytic decomposition of methane. The catalysts carriers were prepared by a simple and fast sol–gel method. This procedure led to the synthesis of the supports with high BET area and mesoporous structure. The samples were characterized by XRD, BET, SEM, H2-TPR and TPO methods. The catalysts with various nickel contents (10, 25, 40, and 55wt%) exhibited high catalytic potential in this proves. The sample with the highest amount of Ni (55wt% Ni/2MgO·Al2O3) possessed an acceptable catalytic performance.

Efficient Mechanochemical Synthesis of MOF-5 for Linear Alkanes Adsorption

An efficient mechanochemical method was proposed to synthesize MOF-5 with high BET area within minutes. The effects of parameters such as solvents activation, the metal/ligand ratio, grinding speed and time were carefully studied and the optimized MOF-5-B was used to investigate its adsorption properties of linear alkanes (C1–nC7). The results showed that solvents activation played an important role in the formation of MOF-5. Besides, the Zn2+/BDC ratio had a great impact on the formation of crystalline MOF-5, and the appropriate Zn2+/BDC ratio was 3:1 for mechanochemical synthesis of MOF-5. Grinding for 60 min could lead to a better crystallinity and the highest surface area of MOF-5-B. The resulting MOF-5-B possessed BET area of 3465.9 m2·g–1. More importantly, MOF-5-B showed a preferential adsorption for long alkanes over short alkanes at low pressures. The saturated adsorption capacities of nC4–nC7 decreased with the increase of hydrocarbon chain length. The isosteric heats of C1–nC7 increased with th...

Thermocatalytic decomposition of methane over mesoporous nanocrystalline promoted Ni/MgO·Al2O3 catalysts

Thermocatalytic decomposition of CH4 is an interesting method for the production of hydrogen. In this article, the catalytic and structural properties of the La, Ce, Co, Fe, and Cu-promoted Ni/MgO·Al2O3 catalysts were investigated in the thermal decomposition of CH4. Mesoporous MgO·Al2O3 powder with the high BET area (>250 m2/g) was synthesized by a novel and simple sol–gel method. The different instrumental methods (XRD, BET, SEM, H2-TPR and TPO) were used for evaluating the physicochemical characteristics of the samples. The addition of Cu to Ni/MgO·Al2O3 dramatically improved the catalytic performance and the Cu-promoted catalysts exhibited the highest CH4 conversion and H2 yields among the promoted and unpromoted catalysts. The Cu-promoted catalyst possessed the highest stability in CH4 conversion during 10 h of reaction. The results also indicated that the Ni–Cu/MgO·Al2O3 catalyst with 15 wt.% Cu showed the highest catalytic activity and stability at higher temperatures (>80% CH4 conversion).

Enhanced activity of CO2 methanation over mesoporous nanocrystalline Ni–Al2O3 catalysts prepared by ultrasound-assisted co-precipitation method

The ultrasound-assisted co-precipitation method was employed for the synthesis of the Ni–Al2O3 catalysts with different metal loadings for the CO2 methanation reaction. This study indicated that increasing the Ni loading up to 25 wt.% enhanced the surface area, decreased the crystallinity and improved the reducibility of the catalysts, while further raise in Ni loading adversely influenced the surface area. Improvements in catalytic performance were obtained with the raise in Ni content because of enhancing the BET area. The results confirmed that the 25Ni–Al2O3 catalyst with the highest BET area (188 m2 g−1) and dispersion of Ni has the highest catalytic activity in CO2 methanation and reached to 74% CO2 conversion and 99% CH4 selectivity at 350 °C. In addition, this catalyst exhibited a great stability after 10 h time-on-stream.

Investigation on surface metal vacancy electrochemistry

In this work, BiOCl nanosheets with and without surface bismuth vacancy (VBi-BiOCl and BiOCl) are prepared by a simple hydrothermal method. The formation of surface bismuth vacancy is confirmed mainly by XPS, EPR, PL, and UV-DRS. It is found that although BiOCl has a higher BET area (16m2g−1) and a lower electrical resistance (2.62Ω) than VBi-BiOCl (4m2g−1, 6.33Ω), the specific capacitance (23.6 mF cm−2) of VBi-BiOCl is 3.4 times higher than that (6.9 mF cm−2) of BiOCl at 0.5mAcm−2. However, the improved capacitance has been mainly attributed to the formation of surface bismuth vacancies, which could provide excess electrochemically adsorption sites for Na (I) ions. This finding is obviously different from conventional viewpoint that the available electrochemically active surface and electrical conductance are usually regarded as the crucial factors for the electrochemical performance. Hence, this work provides a new idea to develop excellent electrode materials.