Alumina Catalysts Research Articles

Aluminium Oxide Catalysts and Supports Synthesized by Thermal Activation Technology

Aluminium Oxide Catalysts and Supports Synthesized by Thermal Activation Technology

Bifunctional metal doping engineering of Ni-supported alumina catalyst for dry methane reforming

Increasing the basicity of catalysts using basic promoters is known to be effective in retarding rapid coke deposition on catalysts, which is the biggest obstacle to the commercialization of dry methane reforming (DRM). In this study, we investigated the doping of various basic metals (Mg, Ca, Sr, Ba, and La) in nickel-supported alumina catalysts and found that Sr, an element that has drawn less attention than others, has the greatest effect on coke formation resistance. The highest coke resistance attributes more to the small nickel particle size, high reducibility, and strong interaction between the active metal and support, than to the basicity of the catalysts. Furthermore, except for Mg, metal doping was efficient for improving the thermal stability of the catalysts, which is beneficial for maintaining the nickel particle size and mesoporous structure, leading to long-term reaction stability. Under the reaction conditions of accelerated coke formation, the catalytic activity of Ni/Sr-MA was maintained for 50 h without performance decline and coke formation-mediated reactor blockage. This discovery offers new opportunities to develop effective nickel-based DRM catalysts with coke resistance by comprehensively considering the nickel particle size, acidity/basicity, reducibility, and strong interaction between the active metal and the support.

Synthesis of Silico-Phospho-Aluminum Nanosheets by Adding Amino Acid and its Catalysis in the Conversion of Furfuryl Alcohol to Fuel Additives.

Self-assembled spheres of silico-phospho-aluminum nanosheets were synthesized with the addition of l-arginine and evaluated as catalysts for the valorization of furfuryl alcohol to fuel additives. Adding the amino acid, a bio-derived additive, contributed to higher external specific surface area and more active sites, featuring a simple, environmentally friendly, and feasible strategy to regulate the growth of nanosheets. Herein, in the reaction of furfuryl alcohol with ethanol, the performance of silico-phospho-aluminum nanosheets was significantly improved compared with typical silicon phosphorus aluminum catalyst SAPO-34. The yield of ethyl levulinate with the use of silico-phospho-aluminum nanosheets was 7.8 times higher than for SAPO-34, and meanwhile the amount of undesirable byproduct diethyl ether was decreased by two orders of magnitude and negligibly produced compared with SAPO-34. Moreover, replacing part of aluminum isopropoxide with aluminum sulfate as aluminum source could introduce sulfate in situ in the process of catalyst synthesis and increase the amount of acid sites on the catalyst.

Alumina catalyst with high density of medium acid sites for N-arylpyrrolidines synthesis

The N-alkylation of amines with tetrahydrofuran (THF) to synthesize pyrrolidine compounds is an economic and environmental benign route. However, current catalytic system often suffered from harsh reaction condition and hazardous reagents. In this work, we developed an alumina nanosheet catalyst with a large amount of medium acid sites for synthesis of N-arylpyrrolidines. Nearly 100% target product yield could be obtained at 190 °C, and this catalyst could be reused at least 5 times without obvious deactivation. NH3-temperature programmed desorption (TPD) and pyridine-infrared (py-IR) revealed that the catalytic performance is positively correlated with the content of medium acid sites. In-situ IR spectrum proved that the reaction follows the carbocation mechanism. This work affords a competitive system for green sustainable chemistry.

Synthesis and Investigation of Nickel–Aluminum Oxide Catalysts on a Carbon Support

Synthesis and Investigation of Nickel–Aluminum Oxide Catalysts on a Carbon Support

Cerium-Promoted Nickel / Alumina Catalyst for Producer Gas Reforming and Tar Conversion

Cerium-Promoted Nickel / Alumina Catalyst for Producer Gas Reforming and Tar Conversion

Selectivity-induced conversion model explaining the coke-catalysed O2-mediated styrene synthesis over wide-pore aluminas

Explaining the conversion and selectivity of a heterogeneous catalyst is often done separately. The general rule is that with high temperatures conversion increases but the catalyst becomes less selective to the desired product, as other pathways to side products are activated. However, this study shows that conversion and selectivity can be correlated. Ethylbenzene (EB) can be converted into styrene under oxidative dehydrogenation conditions. This process is catalysed by the coke formed on an acidic solid material (alumina in this study) at the beginning of the reaction. The process also produces unwanted CO and CO2 (denoted as COx). In a previous study, the alumina calcination temperature influenced the coke selectivity; it increased the styrene selectivity. The EB conversion was also enhanced and it was explained in qualitative terms. In this work, we developed a quantitative model explaining the changes in EB conversion related to the selectivity. The model was obtained by setting an O2 mass balance and showed to explain the experimental reaction data well. The enhanced EB conversion, observed in the alumina series, was explained by the fact that the coke becomes less selective to the unwanted COx, and more to styrene. The COx-forming reactions consume more O2 than the styrene reaction, and have a highly negative impact on the EB conversion. The study provides evidence for the difficulty in achieving a high EB conversion under ODH conditions when COx is formed. For instance, to achieve an EB conversion above 80%, the selectivity to COx should be below 4% at O2/EB of 0.6 (mole) for a typical alumina catalyst. The model proves the link between conversion and selectivity and, secondly, the demanding conditions to achieve a high EB conversion for this reaction. To the best of our knowledge, this is the first example showing a quantitative model relating selectivity and conversion for a heterogeneously catalysed reaction.

Hydrolytic vs. Nonhydrolytic Sol-Gel in Preparation of Mixed Oxide Silica–Alumina Catalysts for Esterification

The development of green and sustainable materials for use as heterogeneous catalysts is a growing area of research in chemistry. In this paper, mesoporous SiO2-Al2O3 mixed oxide catalysts with different Si/Al ratios were prepared via hydrolytic (HSG) and nonhydrolytic sol-gel (NHSG) processes. The HSG route was explored in acidic and basic media, while NHSG was investigated in the presence of diisopropylether as an oxygen donor. The obtained materials were characterized using EDX, N2-physisorption, powder XRD, 29Si, 27Al MAS-NMR, and NH3-TPD. This approach offered good control of composition and the Si/Al ratio was found to influence both the texture and the acidity of the mesoporous materials. According to 27Al and 29Si MAS NMR analyses, silicon and aluminum were more regularly distributed in NHSG samples that were also more acidic. Silica–alumina catalysts prepared via NHSG were more active in esterification of acetic acid with n-BuOH.

Alumina catalyst waste utilization for aluminum-based composites using the friction stir process

Abstract A significant amount of environmental pollution is caused by oil refinery industries in the form of spent alumina catalyst (SAC) waste generated during the process. This waste causes various detrimental effects on human health. In this study, an effort has been made to consume the SAC in the fabrication of aluminum-based composite materials via the friction stir process (FSP). An X-ray diffraction image of the SAC powder used in this work confirms the occurrence of Al2O3, Fe2O3, SiO2, and CaO phases. These hard-phase materials form the basis for SAC to be used as reinforcement content with the aluminum alloy. The FSP is used to create the composite material. It is evident from the scanning electron microscopy image of the Al/SAC composite developed by the FSP technique that fair distribution of constituent ingredients is attained during the process. The incorporation of SAC contents in the aluminum alloy results in remarkable enlargement in tensile strength and hardness of the composite material. The Al2O3, Fe2O3, SiO2, and CaO phases of SAC showed a considerable effect on thermal expansion and corrosion weight loss of the composite.

Surfactant Production of Methyl Ester Sulfonate from Virgin Coconut Oil using Aluminum Oxide with Microwave Assistance

As a surfactant, methyl ester sulfonate (MES) can be produced from virgin coconut oil (VCO) raw materials through the following stages: transesterification, sulfonation, and purification. The transesterification process was carried out to produce methyl esters by reacting VCO with methanol in a mole ratio of 1:41 using a 1% KOH catalyst at a microwave power of 300 W for 60 min. The effects of microwave power and mole ratios between methyl esters and sodium bisulfite in the sulfonation process were investigated. The sulfonation process was carried out using a 1% aluminum oxide catalyst. The purification process was carried out by reacting MES with 35% v/v methanol at 150 W of microwave power for 10 min. The resulting MES was analyzed using gas chromatography and Fourier transform-infrared (FT-IR) spectroscopy. The optimum conditions for surfactant production included a microwave power of 450 W and reactant mole ratio of 1:1, which resulted in a surface tension of 37.9 dyne/cm, pH of 4.21, density of 0.8

Carbonylation of o-phenylenediamines with CO2 to 2-benzimidazolones catalyzed by alumina

Biological carbon fixation can convert carbon dioxide (CO2) into chemicals with a variety of uses, and has thus attracted considerable attention, as CO2 is nonhazardous, inflammable and plentiful in the environment. We report here that alumina (Al2O3) can by itself catalyze the carbonylation of o-phenylenediamines with CO2 to produce 2-benzimidazolones. Such alumina-catalyzed carbonylation with CO2 is applicable to various diamine derivatives to provide the corresponding cyclic ureas. Following the reaction, the alumina catalyst is also advantageous in that it can be filtered, accumulated, and reused.

Ni/Al2O3 spherical catalysts produced by magnetron sputtering

This paper discusses the development of Ni-covered alumina catalysts by the magnetron sputtering. Thin films of magnetron sputter Ni were deposited on alumina spherical substrates as a function of the deposition time with and without the substrate previously coated by washcoating. For comparison purposes, samples were prepared by washcoating alumina spherical substrates with an alumina porous layer impregnated with Ni. Catalysts were characterized by scanning electron microscopy with field emission gun, X-ray diffraction, Raman spectroscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. The catalytic activity was evaluated from the decomposition of methylene blue solution and characterized by optical spectrophotometry. Results show that the catalyst produced by the impregnation route presents a high concentration of Ni oxides, irregular Ni layer, and lower catalytic activity when compared to catalysts produced through magnetron sputtering. Thin Ni films deposited by magnetron sputtering without the washcoating layer present a high concentration of metallic Ni, more uniform film distribution, high catalytic activity, and ferromagnetic behavior. This latter property associated with the small mass of the alumina sphere allows controlling the motion of the spheres in aqueous solutions by applying external magnetic fields.

Promotion of Ru or Ni on Alumina Catalysts with a Basic Metal for CO2 Hydrogenation: Effect of the Type of Metal (Na, K, Ba).

Ru and Ni on alumina catalysts have been promoted with a 10 wt% of alkali metal (K or Na) or alkaline earth metal (Ba) and tested in CO2 methanation. For the catalyst consisting of Ni and Ba, the variation of Ba loading while keeping Ni loading constant was studied. The promotion in terms of enhanced CH4 yield was found only for the addition of barium to 15 wt% Ni/Al2O3. In contrast, K and Na addition increased the selectivity to CO while decreasing conversion. For the Ru-based catalyst series, no enhancement in conversion or CH4 yield was attained by any of the alkaline metals. CO2 temperature-programed desorption (CO2-TPD) revealed that the amount of chemisorbed CO2 increased significantly after the addition of the base metal. The reactivity of COx ad-species for each catalyst was assessed by temperature-programed surface reaction (TPSR). The characterization revealed that the performance in the Sabatier reaction was a result of the interplay between the amount of chemisorbed CO2 and the reactivity of the COx ad-species, which was maximized for the (10%Ba)15%Ni/Al2O3 catalyst.

Ce-doped cobalt aluminate catalysts for the glycerol hydrodeoxygenation (HDO) with in-situ produced hydrogen

In this study, the hydrodeoxygenation (HDO) of glycerol with in-situ produced H2, via aqueous-phase reforming, was investigated over Ce-doped CoAl2O4 catalysts synthesized by coprecipitation. The catalytic runs were performed at 50 bar/260 ºC for 3 h TOS in a fixed bed reactor. The synthesized catalysts were extensively characterized to better understand the effect of physicochemical and surface characteristics on the catalytic performance. The results revealed that doping with Ce increases the population and strength of acid centers, which results in a higher selectivity towards deoxygenated liquid products. Ce-doped catalysts exhibited higher yield to hydroxyacetone and 1,2-propanediol. Post-reaction characterization revealed a decrease of the metallic surface area, mainly due to alumina coating, and to a lesser extent, due to the oxidation and leaching of the cobalt.

Mass fractal dimension from 2D microscopy images via an aggregation model with variable compactness.

Microscopy-image analysis provides precious information on size and structure of colloidal aggregates and agglomerates. The structure of colloids is often characterized using the mass fractal dimension , which is different from the two-dimensional (2D) fractal dimension that can be computed from microscopy images. In this work, we propose to use a recent morphological aggregation model to find a relationship between 2D image fractal dimension and 3D mass fractal dimension of aggregates and agglomerates. Our case study is represented by scanning transmission electron microscopy images of boehmite colloidal suspensions. The behaviour of the computed at different acid and base concentration shows a fair agreement with the results of small angle x-ray scattering and with the literature, enabling to use the versus relationship to study the impact of the composition of the colloidal suspension on the density of colloidal aggregates andagglomerates.

Preparation of Pt/Ce–Zr–Y mixed oxide/anodized aluminium oxide catalysts for hydrogen passive autocatalytic recombination

The use of a Pt-based catalyst was evaluated for autocatalytic hydrogen recombination. The Pt was supported on a mixture of Ce-, Zr- and Y-oxides (CZY) to yield nanosized Pt particles. The Pt/CZY/AAO catalyst was then prepared by the spray-deposition of the Pt/CZY intermediate onto an anodized aluminium oxide (AAO) layer on a metallic aluminum core. The Pt/CZY/AAO catalyst (3 × 1 cm) was evaluated for hydrogen combustion (1–8 vol% hydrogen in the air) in a recombiner section testing station. The thermal distribution throughout the catalyst surface was investigated using an infrared camera. The maximum temperature gradient (ΔT) for the examined hydrogen concentrations did not exceed 36 °C. The Pt/CZY/AAO catalyst was also evaluated for prolonged hydrogen combustion duration to assess its durability. An average combustion temperature of 239.0 ± 10.0 °C was maintained for 53 days of catalytic hydrogen combustion, suggesting that there was limited, or no, catalyst deactivation. Finally, a Pt/CZY/AAO catalytic plate (14.0 × 4.5 cm) was prepared to investigate the thermal distribution. An average surface temperature of 212.5 °C and a maximum ΔT of 5.4 °C was obtained throughout the catalyst surface at a 3 vol% hydrogen concentration. • Reactive Pt/CZY/AAO catalysts were prepared for catalytic hydrogen combustion. • Catalysts contained an aluminum core to rapidly dissipate reaction heat. • Thermal conductivity ensured temperature gradients of <36 °C at 1–8 vol% hydrogen. • No decrease in catalytic activity after 53 days of hydrogen combustion at 239 °C. • Catalysts suitable for safe PAR applications.

Recent Advances in Aluminum Compounds for Catalysis

AbstractThis review highlights recent advances in the research of organoaluminum complexes in catalysis. Many fundamental transformations can be carried out by aluminum catalysts, such as hydroboration, hydroamination, copolymerization and CO2 insertion reactions, hydrosilylation, and hydroacetylenation of carbodiimides, which make use of the abundant reserves of aluminum in the earth‘s crust to accomplish the transformation. Recent research in the field has shown that these systems have extraordinary catalytic activity and are inexpensive, abundant, and environmentally friendly.

Control of textural property in spherical alumina ball for enhanced catalytic activity of Ni-supported Al2O3 catalyst in steam–methane reforming

Designing Ni-based catalyst with high performance is one of the most important challenges for operation of practical steam-methane reforming (SMR) processes. We report control of the textural properties of commercial alumina ball for Ni-supported catalysts in SMR. The textural properties of the commercial Al2O3 sphere are successfully controlled by aqueous HCl treatment for elongated periods. The pore diameters and pore volumes of the controlled alumina supports are finely tuned by varying the HCl treatment period. The catalytic activity of the corresponding Ni-supported alumina is significantly enhanced with increasing HCl treatment period on alumina ball. The alumina supports with longer HCl treatment period have larger pore size and bigger pore volume, and the corresponding Ni-Alumina catalysts exhibited higher catalytic activity at even higher space velocity, due to the increased intraparticle diffusion of reactant molecules inside the catalyst. Ni-supported alumina catalyst prepared by using alumina support treated with HCl for 18 h showed the largest pore size and pore volume, revealing enhanced catalytic activity in terms of CH4 conversion and H2 yield. It showed the well-maintained activity without any further deactivation in both continuous operation for 24 h and cyclic operation at different WHSV conditions.

Influence of tin(II), aluminum(III) and titanium(IV) catalysts on the transesterification of poly(L-lactic acid)

Influence of tin(II), aluminum(III) and titanium(IV) catalysts on the transesterification of poly(L-lactic acid)

Evolution of Hierarchically Porous Nickel Alumina Catalysts Studied by X-Ray Ptychography.

The synthesis of hierarchically porous materials usually requires complex experimental procedures, often based around extensive trial and error approaches. One common synthesis strategy is the sol–gel method, although the relation between synthesis parameters, material structure and function has not been widely explored. Here, in situ 2D hard X‐ray ptychography (XRP) and 3D ptychographic X‐ray computed tomography (PXCT) are applied to monitor the development of hierarchical porosity in Ni/Al2O3 and Al2O3 catalysts with connected meso‐ and macropore networks. In situ XRP allows to follow textural changes of a dried gel Ni/Al2O3 sample as a function of temperature during calcination, activation and CO2 methanation reaction. Complementary PXCT studies on dried gel particles of Ni/Al2O3 and Al2O3 provide quantitative information on pore structure, size distribution, and shape with 3D spatial resolution approaching 50 nm, while identical particles are imaged ex situ before and after calcination. The X‐ray imaging results are correlated with N2‐sorption, Hg porosimetry and He pycnometry pore characterization. Hard X‐ray nanotomography is highlighted to derive fine structural details including tortuosity, branching nodes, and closed pores, which are relevant in understanding transport phenomena during chemical reactions. XRP and PXCT are enabling technologies to understand complex synthesis pathways of porous materials.