Alumina Xerogel Research Articles

Comparative catalytic performance of PGM-nanoparticle-doped alumina Xerogels and aerogels for potential application in automotive pollution mitigation

The structural (low density, high porosity), thermal (low thermal conductivity, high temperature stability), and chemical (high degree of tailorability) properties of aerogels make them attractive in a range of applications, including catalysis. The automotive industry relies on three-way-catalysts (TWCs) for automotive pollution mitigation, and TWCs in turn depend heavily on the use of platinum group metals (PGMs). Reduction of the use of PGMs in TWCs would be advantageous. To investigate the effect of aerogel structure and processing on three-way catalytic performance we prepared alumina wet gels doped with ca. 15 nm rhodium and palladium nanoparticles and dried them (1) supercritically to form aerogels and (2) under ambient conditions to form xerogels. Nanoparticle concentration was adjusted to ensure that both forms of the catalyst (aerogel and xerogel) had the same volumetric concentration of PGM after calcination to 800°C. Powder x-ray diffraction and transmission electron microscopy (TEM) confirmed the presence of PGMs. TEM images showed PGM particle agglomeration on the order of 40 to 200 nm in both the aerogel and xerogel materials. Gas adsorption analysis indicated that the aerogels have a surface area of 460 m2/g with most pores in the 2- to 100-nm range, whereas the xerogel surface area was 170 m2/g with a narrow pore distribution around 10 nm. Catalytic performance tests under a range of simulated automotive operating conditions show that, in all cases, the aerogels outperformed the xerogels. The aerogel light-off temperatures (the temperature at which a 50 % conversion is achieved) were 45 to 120 °C lower for the conversion of HCs, 25 to 55 °C lower for the conversion of CO and 40 to 145 °C lower for the conversion of NO. This study provides direct evidence that aerogel processing of catalysts provides catalytic performance benefits separate from the underlying chemistry of the catalysts.

Developing a novel Ti-doped ɣAl2O3 xerogel with high photocatalytic chemical and microbial removal performance: Characterization and mechanistic insights

In this work, a Ti-doped alumina (Ti-γAl2O3) xerogel (TAX) was synthesized from Al powder as a cost-effective precursor. Full physical, chemical, structural, and electrochemical characterization of the prepared materials were performed. It was shown that as-made Ti-γAl2O3 is a mesoporous nanomaterial with high specific surface area, uniform morphology, the existence of polyhedral coordinated Al3+ ions, many acidity active sites, high light absorption efficiency, and effective bandgap energy. These features made it an efficient photocatalyst for water photocatalytic treatment. In the photocatalytic process with the TAX as the catalyst irradiated by the ultraviolet A photons, around 97% of 10 mg/L Remdesivir (RDV) was degraded within 30 min (pH = 7, TAX = 100 mg/L), and elucidation of the degradation pathway was achieved; low adsorption and minimal O2·- contribution was found in the otherwise HO•-dominated photocatalytic process, as suggested by the scavenger tests. The Electron Paramagnetic Resonance spectroscopy validated the proposed species (but not 1O2), while the RDV degradation pathway towards mineralization was proposed by Liquid Chromatography–Mass Spectrometry analysis. Besides, concerning its applicability, the effect of operational parameters (pH, [TAX], [RDV], water matrix) was scrutinized and validated a notable performance over several consecutive reused cycles. Finally, almost 6.5 log E. coli inactivation was attained (in mild conditions), all indicating the high photocatalytic potential of this material.

Sol-gel derived boehmite nanostructures is a versatile nanoplatform for biomedical applications

Alumina is one of the most promising carriers for drug delivery due to the long history of its usage as a vaccine adjuvant. Sol-gel synthesis provides excellent conditions for entrapment of biomolecules within an inorganic cage providing stabilization of proteins under the extremal conditions. In this paper, we show in vitro investigation of monodisperse alumina xerogel nanocontainers (AXNCs) using bovine serum albumin as a model protein entrapped in sol-gel alumina building blocks. Particularly, dose and cell-type dependent cytotoxicity in HeLa and A549 cancer cell lines were employed as well as investigation of antibacterial effect and stability of AXNCs in different biological media. It was shown, that the release of entrapped protein could be provided only in low pH buffer (as in cancer cell cytoplasm). This property could be applied for anticancer drug development. We also discovered boehmite nanoparticles effect on horizontal gene transfer and observed the appearance of antibiotic resistance by means of exchanging of the corresponding plasmid between two different E. coli strains. The present work may help to understand better the influence of AXNCs on various biological systems, such as prokaryotic and eukaryotic cells, and the activity of AXNCs in different biological media.

Biobased process intensification in selective synthesis of γ-butyrolactone from succinic acid via synergistic palladium–copper bimetallic catalyst supported on alumina xerogel

Biomass-based processes are gaining importance for sustainable chemical industry. The economic aspects of products from valorization of succinic acid are important. Selective synthesis of γ-butyrolactone is challenging, and catalyst development is a stumbling block. The synergistic effect of palladium–copper supported on alumina xerogel is demonstrated to obtain higher yield of γ-butyrolactone during successive dehydration and hydrogenation of succinic acid. The catalytic performance studies were carried out in slurry batch reactor, and 2.5% Pd–2.5% Cu on alumina xerogel was found to be active, selective and reusable catalyst. The catalyst was characterized by FTIR, XRD, TPD-NH3, BET nitrogen analysis, XPS and TEM at various stages of synthesis to understand the structure activity relationship. A kinetic model was developed for selective synthesis of γ-butyrolactone and validated. The activation energy for the reaction was found to be 11 kcal/mol.

Steam reforming of liquefied natural gas (LNG) for hydrogen production over nickel–boron–alumina xerogel catalyst

A series of mesoporous nickel–boron–alumina xerogel (x-NBA) catalysts with different boron/nickel molar ratio (x = 0–1) were prepared by an epoxide-driven sol–gel method. The effect of boron/nickel molar ratio on the catalytic activities and physicochemical properties of nickel–boron–alumina xerogel catalysts was investigated in the steam reforming of liquefied natural gas (LNG). All the mesoporous x-NBA catalysts showed similar surface area. Introduction of boron increased interaction between nickel and support. In addition, introduction of boron into x-NBA catalysts reduced methane activation energy and increased nickel surface area. Promotion of boron had a positive effect on the catalytic activity due to the increase of adsorbed methane and nickel surface area. The amount of adsorbed methane and nickel surface area exhibited volcano-shaped trends with respect to boron/nickel molar ratio. LNG conversion and hydrogen yield increased with increasing the amount of adsorbed methane and with increasing nickel surface area. Among the catalysts, 0.3-NBA, which retained the largest amount of adsorbed methane and the highest nickel surface area, showed the best catalytic performance. It was also revealed that x-NBA catalysts showed strong coke resistance during the steam reforming reaction.

Performance enhanced UV/vis spectroscopic microfluidic sensor for ascorbic acid quantification in human blood

Quantitative analysis of antioxidants in a fast, simple and accurate manner is of great importance in the view of real-time monitoring the health of individuals. Recently, we have developed a UV/vis spectroscopic microfluidic sensor to specifically quantify ascorbic acid based on the immobilization of ascorbate oxidase, a relatively unstable enzyme. In this work, three different strategies for the immobilization of the unstable enzyme, including alumina sol-gel encapsulation, physisorption to PDMS channels with, and without alumina xerogel modification, were compared to build a microsensor. We found that the loading amount of the enzyme is not the determinative factor for the performance of the microfluidic biosensor but the retained activity of the enzyme and diffusion in the microfluidic channel. Taking into account of the two factors, the protocol of adsorbing enzymes to alumina (Al2O3) xerogel modified PDMS surface was demonstrated to be the best for preparing the microfluidic sensor among the utilized protocols. The microsensor prepared under the optimized protocol was further used to quantify ascorbic acid in human blood, where only dozens of microliters of blood (few drops) was required, demonstrating its potential application in clinical diagnosis. The developed strategy is featured with optimized enzymatic activity, simple process of microfluidic platform, low sample consumption, and straightforward spectrophotometry based detection.

Hydrogen production by tri-reforming of methane over nickel–alumina aerogel catalyst

A mesoporous nickel–alumina aerogel catalyst (NAA) was prepared by an epoxide-initiated gelation method and a subsequent supercritical carbon dioxide drying method. For comparison, a mesoporous nickel–alumina xerogel catalyst (NAX) was also prepared by an epoxide-initiated gelation method without supercritical carbon dioxide drying. Both catalysts were applied to the hydrogen production by tri-reforming of methane. The effect of preparation method on the physicochemical properties and catalytic activities of the catalysts was investigated. Although both catalysts exhibited a well-developed mesoporous structure, NAA catalyst retained higher surface area and larger pore volume than NAX catalyst. It was also revealed that NAA catalyst retained higher nickel dispersion and larger methane adsorption capacity than NAX catalyst. In the hydrogen production by tri-reforming of methane, both catalysts exhibited a stable catalytic performance. However, NAA catalyst showed higher hydrogen yield and higher CH4 conversion than NAX catalyst. High nickel dispersion and strong affinity with methane of NAA catalyst was responsible for its high catalytic performance.

Hydrogen production by steam reforming of liquefied natural gas (LNG) over mesoporous nickel–iron–alumina catalyst

A set of mesoporous nickel–iron-alumina xerogel catalysts (denoted as 20NixFeAl) with different iron loading (x = 0–10) were prepared by an epoxide-driven sol–gel method. The effect of iron loading on the physicochemical properties and catalytic activities of mesoporous nickel–iron–alumina xerogel catalysts in the steam reforming of liquefied natural gas (LNG) was investigated. It was found that all the calcined 20NixFeAl catalysts showed a well-developed mesoporous structure and retained finely dispersed nickel and iron species. Reducibility of calcined 20NixFeAl catalysts was enhanced by iron addition due to the increased amount of octa-coordinated nickel species. From H2-TPD and XPS results, it was revealed that nickel surface area of reduced 20NixFeAl catalysts showed a volcano-shaped trend with respect to iron loading. This result indicates that an optimal iron addition was required for fine dispersion of nickel species in the reduced 20NixFeAl catalysts. In the steam reforming of LNG, 20Ni4FeAl catalyst with the highest nickel surface area showed the best catalytic performance in terms of LNG conversion and hydrogen yield. Thus, nickel surface area of 20NixFeAl catalysts played a key role in determining the catalytic performance in the steam reforming of LNG.

Hydrogen production by steam reforming of liquefied natural gas (LNG) over mesoporous nickel–phosphorus–alumina aerogel catalyst

A mesoporous nickel–phosphorus–alumina aerogel catalyst (NPAA) was prepared by a single-step epoxide-driven sol–gel method and a subsequent supercritical CO2 drying method for use in the hydrogen production by steam reforming of liquefied natural gas (LNG). In order to investigate the effect of drying method of nickel–phosphorus–alumina catalysts on their physicochemical properties and catalytic activities, a mesoporous nickel–phosphorus–alumina xerogel catalyst (NPAX) was also prepared by a single-step epoxide-driven sol–gel method and a subsequent evaporative drying method for comparison purpose. It was found that supercritical CO2 drying method was effective for enhancing textural properties of NPAA catalyst. Although both NPAX and NPAA catalysts retained surface nickel aluminate phase, NPAA catalyst showed stronger metal-support interaction than NPAX catalyst. XRD patterns of reduced NPAX and NPAA catalysts revealed that NPAA catalyst retained smaller metallic nickel crystallite than NPAX catalysts. It was also observed that the reduced NPAA catalyst exhibited high nickel dispersion, large amount of strong hydrogen-binding sites, and large amount of methane adsorption compared to the reduced NPAX catalyst. In the steam reforming of LNG, NPAA catalyst with high affinity toward methane showed a better catalytic performance than NPAX catalyst.

Laser absorption spectroscopy of oxygen confined in highly porous hollow sphere xerogel

An Al2O3 xerogel with a distinctive microstructure is studied for the application of laser absorption spectroscopy of oxygen. The xerogel has an exceptionally high porosity (up to 88%) and a large pore size (up to 3.6 µm). Using the method of gas-in-scattering media absorption spectroscopy (GASMAS), a long optical path length (about 3.5m) and high enhancement factor (over 300 times) are achieved as the result of extremely strong multiple-scattering when the light is transmitted through the air-filled, hollow-sphere alumina xerogel. We investigate how the micro-physical feature influences the optical property. As part of the optical sensing system, the material's gas exchange dynamics are also experimentally studied.

Hydrogen production by steam reforming of simulated liquefied natural gas (LNG) over nickel catalyst supported on mesoporous phosphorus-modified alumina xerogel

A series of nickel catalysts supported on mesoporous phosphorus-modified alumina xerogel (Ni/XPA, X=P/Al molar ratio) were prepared by an epoxide-driven sol–gel method and a subsequent incipient impregnation method, and they were applied to the hydrogen production by steam reforming of simulated liquefied natural gas (LNG). All the calcined phosphorus-modified alumina xerogel supports (XPA, X=P/Al molar ratio) retained a mesoporous structure with amorphous crystalline phase. The amount of penta-coordinated aluminum species increased with increasing X (P/Al molar ratio) of XPA supports. Although the calcined Ni/XPA catalysts retained both nickel oxide phase and nickel aluminate phase, relative distribution of nickel species of the catalysts was different depending on X (P/Al molar ratio). Among the catalysts, Ni/0.05PA catalyst showed the highest binding energy of nickel species. Crystallite size of metallic nickel increased with increasing X (P/Al molar ratio) in the reduced Ni/XPA catalysts. However, Ni/0.05PA catalyst showed the largest amount of strong hydrogen-binding sites and exhibited the largest amount of adsorbed methane in the H2-TPD and CH4-TPD measurements, respectively. Catalytic performance in the steam reforming of LNG over Ni/XPA catalysts showed a volcano-shaped trend with respect to X (P/Al molar ratio). This result was well correlated with the amount of adsorbed methane calculated from CH4-TPD measurements. Among the catalysts tested, Ni/0.05PA catalyst with the highest affinity toward methane showed the best catalytic performance in hydrogen production by steam reforming of LNG.

Methanation of carbon dioxide over mesoporous Ni–Fe–Ru–Al2O3 xerogel catalysts: Effect of ruthenium content

Mesoporous nickel (35wt%)–iron (5wt%)–ruthenium (x wt%)–alumina xerogel (denoted as 35Ni5FexRuAX) catalysts with different ruthenium contents (x=0, 0.2, 0.4, 0.6, 0.8, and 1.0) were prepared by a single-step sol–gel method for use in the methane production from CO2 and H2. Conversion of CO2, yield for CH4, metal surface area, and the amount of desorbed carbon dioxide of the catalysts showed volcano-shaped trends with respect to ruthenium content. Experimental results revealed that metal surface area and the amount of desorbed carbon dioxide of 35Ni5FexRu catalysts were well correlated with conversion of CO2 and yield for CH4.

Structure characterisation and mechanical properties of crystalline alumina coatings on stainless steel fabricated via sol–gel technology and fibre laser processing

Abstract The surface modification of stainless steel by coating with alumina (Al 2 O 3 ) was carried out using sol–gel coating technology in combination with laser processing. Alumina coatings have been synthesised via a sol–gel route and deposited on stainless steel substrates by dip coating. The coated substrates were then treated with pulsed ytterbium fibre laser radiation ( λ = 1064 nm) in continuous wave mode with different specific energies. The composition and structure of the coated surfaces after laser processing were characterised by ATR-FTIR, XRD, SEM and contact angle measurements, whilst the mechanical properties of modified surfaces were determined using nano-indentation. The results showed that the alumina xerogel films coated on the substrates are successfully converted into crystalline alumina ceramic coatings by the laser irradiation, the structure of resulting coatings being dependent on the irradiation conditions, with increase of laser specific energy leading to the formation of initially γ-Al 2 O 3 with increasing amounts of α-Al 2 O 3 at higher energy. Nano-indentation results reveal that the laser processing results in significant improvement in hardness and Young's modulus of the alumina-coated surface and, at optimum, can achieve the mechanical properties at the same level as pure α-alumina ceramic, much higher than those of the as-dried xerogel coating.

Hydrogenation of CO to Methane Over Mesoporous Nickel–Iron–Alumina Xerogel Nano-Catalysts

Mesoporous nickel-iron-alumina xerogel ((40-x)Ni(x)FeAX) nano-catalysts with different iron content (x = 0, 2.5, 5, 7.5, and 10) were prepared by a single-step sol-gel method for use in the methane production from carbon monoxide and hydrogen. The effect of iron content on the catalytic performance of (40-x)Ni(x)FeAX catalysts was investigated. In the methanation reaction, yield for CH4 decreased in the order of 35Ni5FeAX > 32.5Ni7.5FeAX > 30Ni10FeAX > 37.5Ni2.5FeAX > 40Ni0FeAX. This indicated that optimal iron content of mesoporous nickel-iron-alumina xerogel nano-catalyst was required for maximum production of CH4 in the methanation reaction. Experimental results revealed that optimal CO dissociation energy and large H2 adsorption ability of the catalyst were favorable for methane production. Among the catalysts tested, 35Ni5FeAX catalyst, which retained the most optimal CO dissociation energy and the largest H2 adsorption ability, exhibited the best catalytic performance in terms of conversion of CO and yield for CH4 in the methanation reaction. CO dissociation energy and H2 adsorption ability of the catalyst played a key role in determining the catalytic performance of (40-x)Ni(x)FeAX in the methanation reaction.

Hydrogen production by steam reforming of liquefied natural gas (LNG) over mesoporous nickel–alumina xerogel catalysts prepared by a single-step carbon-templating sol–gel method

A series of mesoporous nickel–alumina xerogel catalysts (denoted as CNAX) were prepared by a single-step carbon-templating sol–gel method using different amount of carbon template (X), and they were applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). Textural properties of CNAX catalysts were improved with increasing the amount of carbon template. CNAX catalysts exhibited diffraction peaks corresponding to nickel aluminate phase, while CNA18 and CNA24 catalysts showed additional bulk nickel oxide phase. From TPR measurements, it was revealed that the interaction between nickel species and alumina in the CNAX catalysts became weakened with increasing the amount of carbon template. Crystallite size of metallic nickel in the reduced CNAX catalysts showed a volcano-shaped trend with respect to the amount of carbon template. In the steam reforming of LNG, CNAX (X = 0, 6, 12, and 18) catalysts exhibited a stable catalytic performance during the reaction, while CNA24 catalyst showed a significant catalyst deactivation. Crystallite size of metallic nickel served as an important factor determining the catalytic performance in the steam reforming of LNG. Initial LNG conversion and initial hydrogen yield increased with decreasing crystallite size of metallic nickel of the catalysts. Among the catalysts tested, CNA12 catalyst with the smallest crystallite size of metallic nickel showed the best catalytic performance.

A study on the properties of Zr-doped γ-Al2O3 xerogels hybridized with α-Al2O3 whiskers synthesized by solvothermal drying

Hydrophobic zirconium doped alumina xerogels and zirconium doped alumina xerogels hybridized with α-Al2O3 whisker were fabricated by Si(CH3)3 (trimethylsilyl substituent) modification of alcogels via ambient pressure solvothermal drying procedure. One-step solvent exchange and surface modification were simultaneously progressed by immersing alumina alcogels in hexamethyldisilazane/hexane solution. The synthesized Zr doped Al2O3 xerogels have shown increased phase transition temperature from γ-phase to α-phase over 200°C. Although phase transition temperature was increased, the porous structure of Zr-doped Al2O3 xerogel was collapsed over 1200°C losing its specific surface area. To maintain their porous structures at the elevated temperatures, the Zr-doped Al2O3 xerogels were hybridized with α-Al2O3 whiskers. The α-Al2O3 whiskers were grown at 1400°C and thus sustained its phase and structure over 1400°C. The α-Al2O3 whiskers in xerogels act as a pillar at elevated temperatures. As a result, Zr doped Al2O3 xerogels hybridized with α-Al2O3 whiskers maintained their porous structure over 1400°C even though there was a phase transition from γ-Al2O3 to α-Al2O3.

Methanation of Carbon Dioxide Over Mesoporous Nickel–M–Alumina (M = Fe, Zr, Ni, Y, and Mg) Xerogel Catalysts: Effect of Second Metal

Mesoporous nickel (35 wt%)–M (5 wt%)–alumina xerogel (denoted as 35Ni5MAX) catalysts with different second metal (M = Fe, Zr, Ni, Y, and Mg) were prepared by a single-step sol–gel method for use in the methane production from carbon dioxide and hydrogen. In the carbon dioxide methanation reaction, yield for CH4 decreased in the order of 35Ni5FeAX > 35Ni5ZrAX > 35Ni5NiAX > 35Ni5YAX > 35Ni5MgAX. This indicated that the catalytic performance was greatly influenced by the identity of second metal in the carbon dioxide methanation reaction. Experimental results revealed that CO dissociation energy and metal-support interaction of the catalyst played key roles in determining the catalytic performance of 35Ni5MAX catalysts in the reaction. Among the catalysts tested, 35Ni5FeAX catalyst, which retained the most optimal CO dissociation energy and the weakest metal-support interaction, exhibited the best catalytic performance in terms of conversion of CO2 and yield for CH4. In the carbon dioxide methanation over mesoporous nickel–M–alumina xerogel catalysts with different second metal (M = Fe, Zr, Ni, Y, and Mg), yield for CH4 increased with decreasing TPSR peak temperature and with decreasing metal-support interaction of the catalyst.

Steam Reforming of Glycerol over Ni Supported Alumina Xerogel for Hydrogen Production

Momentous amount of glycerol is produced as a by-product during bio-diesel production by the transesterification of vegetable oils, which are available at low cost in large supply from renewable raw materials. As hydrogen is a clean energy carrier, conversion of glycerol to hydrogen is one among the most attractive ways to make use of glycerol. In this study, the catalytic production of hydrogen by steam reforming of glycerol has been experimentally performed in a fixed-bed reactor. The performance of this process was evaluated over 10wt% Ni supported alumina xerogel catalysts. Ni is impregnated over alumina xerogel which was pretreated at different temperatures of 700°C, 800°C, 900°C and 1000°C. For a comparative purpose, the steam reforming experiments were conducted under same operating conditions, i.e., reaction temperature of 600°C, atmospheric pressure and 1:6 glycerol to water molar ratio where we are getting 100% glycerol conversion in all the runs. The results showed that the hydrogen production increased with the increase in the treatment temperature of the support. The highest amount of hydrogen produced was attained over 10wt% Ni doped alumina xerogel pretreated at 1000°C. The catalytic enhancement over the best catalyst system is due to the thermal stability of the support which is treated at highest temperature. Sol gel method of preparation is implemented in the support development and different catalyst systems used in the reforming process were characterized using X-ray powder diffraction, BET surface area and SEM analysis.

Hydrogenation of carbon monoxide to methane over mesoporous nickel-M-alumina (M = Fe, Ni, Co, Ce, and La) xerogel catalysts

Mesoporous nickel(30 wt%)-M(10 wt%)-alumina xerogel (30Ni10MAX) catalysts with different second metal (M = Fe, Ni, Co, Ce, and La) were prepared by a single-step sol–gel method for use in the methane production from carbon monoxide and hydrogen. In the methanation reaction, yield for CH 4 decreased in the order of 30Ni10FeAX > 30Ni10NiAX > 30Ni10CoAX > 30Ni10CeAX > 30Ni10LaAX. Experimental results revealed that CO dissociation energy of the catalyst and H 2 adsorption ability of the catalyst played a key role in determining the catalytic performance of 30Ni10MAX catalyst in the methanation reaction. Optimal CO dissociation energy of the catalyst and large H 2 adsorption ability of the catalyst were favorable for methane production. Among the catalysts tested, 30Ni10FeAX catalyst with the most optimal CO dissociation energy and the largest H 2 adsorption ability exhibited the best catalytic performance in terms of conversion of CO and yield for CH 4 in the methanation reaction. The enhanced catalytic performance of 30Ni10FeAX was also due to a formation of nickel–iron alloy and a facile reduction.

Terbium luminescence in alumina xerogel fabricated in porous anodic alumina matrix under various excitation conditions

Terbium-doped alumina xerogel layers are synthesized by the sol-gel method in pores of a porous anodic alumina film 1 μm thick with a pore diameter of 150–180 nm; the film is grown on a silicon substrate. The fabricated structures exhibit terbium photoluminescence with bands typical of trivalent terbium terms. Terbium X-ray luminescence with the most intense band at 542 nm is observed for the first time for such a structure. Morphological analysis of the structure by scanning electron microscopy shows the presence of xerogel clusters in pore channels, while the main pore volume remains unfilled and pore mouths remain open. The data obtained confirm the promising applications of fabricated structures for developing matrix converters of X-rays and other ionizing radiations into visible light. The possibilities of increasing luminescence intensity in the matrix converter are discussed.