Calcination Step Research Articles

Gas-Phase Hydrogenation of Furfural to Furfuryl Alcohol over Cu-ZnO-Al2O3 Catalysts Prepared from Layered Double Hydroxides

Several layered double hydroxides (LDHs) with general chemical composition (Cu,Zn)1−xAlx(OH)2(CO3)x/2·mH2O have been synthesized by the co-precipitation method, maintaining a (M2+/M3+) molar ratio of 3, and varying the Cu2+/Zn2+ molar ratio between 0.2 and 6.0. After calcination and reduction steps, Cu/ZnO/Al2O3 catalysts were synthesized. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), H2 thermoprogrammed reduction (H2-TPR), N2 adsorption-desorption at −196 °C, N2O titration, X-ray photoelectron miscroscopy (XPS), NH3-thermoprogramed desorption (NH3-TPD) and CO2- thermoprogrammed desorption (CO2-TPD). The characterization data revealed that these catalysts are mainly meso-and macroporous, where Cu, ZnO and Al2O3 are well dispersed. The catalytic results show that these catalysts are active in the gas-phase hydrogenation of furfural, being highly selective to furfuryl alcohol (FOL) and reaching the highest FOL yield for the catalyst with a Cu2+/Zn2+ molar ratio of 1. In an additional study, the influence of the aging time on the synthesis of the LDHs was also evaluated. The catalytic data revealed that the use of shorter aging time in the formation of the LDH has a beneficial effect on the catalytic behavior, since more disordered structures with a higher amount of available Cu sites is obtained, leading to a higher yield towards FOL (71% after 5 h of time-on-stream at 210 °C).

Acid and Acid-Alkali Treatment Methods of Al-Chloride Solution Obtained by the Leaching of Coal Fly Ash to Produce Sandy Grade Alumina

Sandy grade alumina is a valuable intermediate material that is mainly produced by the Bayer process and used for manufacturing primary metallic aluminum. Coal fly ash is generated in coal-fired power plants as a by-product of coal combustion that consists of submicron ash particles and is considered to be a potentially hazardous technogenic waste. The present paper demonstrates that the Al-chloride solution obtained by leaching coal fly ash can be further processed to obtain sandy grade alumina, which is essentially suitable for metallic aluminum production. The novel process developed in the present study involves the production of amorphous alumina via the calcination of aluminium chloride hexahydrate obtained by salting-out from acid Al-Cl liquor. Following this, alkaline treatment with further Al2O3 dissolution and recrystallization as Al(OH)3 particles is applied, and a final calcination step is employed to obtain sandy grade alumina with minimum impurities. The process does not require high-pressure equipment and reutilizes the alkaline liquor and gibbsite particles from the Bayer process, which allows the sandy grade alumina production costs to be to significantly reduced. The present article also discusses the main technological parameters of the acid treatment and the amounts of major impurities in the sandy grade alumina obtained by the different (acid and acid-alkali) methods.

Direct synthesis of b-axis oriented H-form ZSM-5 zeolites with an enhanced performance in the methanol to propylene reaction

A b-axis oriented microsized H-form ZSM-5 zeolite with a thinness of approximately 300–500 nm along the b-axis direction was prepared for the methanol to propylene (MTP) reaction by a two stage hydrothermal crystallization method with ammonium hydroxide as the base source and glucose as an additive. Ammonium hydroxide contributed to the direct synthesis of H-form ZSM-5 zeolite after calcination to remove the template and decompose the NH 4 + -form zeolite, thus removing the need for further ion-exchange and calcination steps. Glucose was beneficial to the formation of the thin hierarchical b-axis oriented ZSM-5 zeolites. The b-axis oriented H-form ZSM-5 catalyst exhibited a longer catalyst lifetime and a higher propylene selectivity in the MTP reaction compared to that of ZSM-5 made by a conventional method. The better catalytic performance was ascribed to the relatively low content of strong acid sites especially those on the external surface of the b-axis oriented microsized ZSM-5 catalyst. • B-axis oriented H-form ZSM-5 zeolite was directly prepared by a two-stage crystallization method. • The ion-exchange and further calcination steps for the preparation of H-form ZSM-5 were omitted. • Newly prepared ZSM-5 catalyst exhibited longer catalyst lifetime and higher propylene selectivity.

High-performance ZnTiNb2O8 microwave dielectric ceramics produced from ZnNb2O6–TiO2 nano powders

Abstract Ixiolite-structured ZnTiNb2O8 (ZTN) ceramics were prepared by the simple but effective route of reaction sintering ZnNb2O6 and TiO2 nano powders. The effect of sintering temperature and soaking time on the densification behavior, microstructure evolution and microwave dielectric properties of the synthesized ZTN ceramics were systematically studied. Nano ZnNb2O6 and TiO2 raw materials were mixed, pressed and sintered directly into ceramic bodies without any calcination step involved. The sintered samples were characterized by Field-Emission Scanning Electron Microscopy (FESEM), X-ray Diffraction (XRD), and microwave dielectric measurements. Single-phase ZnTiNb2O8 ceramics with relative densities up to 97% theoretical density were achieved by sintering at 975–1075 °C. The ixiolite ZTN ceramics reaction sintered at 1050 °C for 3 h exhibited excellent microwave dielectric properties with a dielectric constant ( e r ) = 35.5, quality factor (Q × f0) = 52,500 GHz and a temperature coefficient of resonant frequency ( τ f ) = −60 ppm/°C. These results demonstrate that high-performance ZTN microwave dielectric ceramics can be successfully produced by the simple and efficient reaction-sintering method.

A new synthesis approach for upconverting nanoparticles based on rare earth ternary vanadates

According to our knowledge, rare earth based upconverting ternary vanadates are synthesized by the hydrothermal method for the first time. This facile procedure offers an alternative approach to obtain nanomaterials with the desired crystal structure, while omitting calcination step as to prevent from particle size growth and their agglomeration. The systems discussed exhibit visible luminescence under 980 nm laser irradiation, as a result of Yb3+/Ln3+ ion pairs (Ln = Er, Ho, Tm) doping. Detailed structural analysis revealed small amounts of additional vanadate phases with no major host structure changes while dopants are introduced. The emission colour was dependent on both the selected concentrations of the dopant ions and the excitation source. The most noticeable colour tunability was observed for Yb3+/Ho3+ activated materials, ranging from yellow to orange. The presence of a strong 800 nm hypersensitive emission in Yb3+/Tm3+ doped material may be used in biological studies after cytotoxicity testing.

Fabrication of Hollow and Porous Tin-Doped Indium Oxide Nanofibers and Microtubes via a Gas Jet Fiber Spinning Process.

We report the morphologies of tin-doped indium oxide (ITO) hollow microtubes and porous nanofibers produced from precursor solutions of polyvinylpyrrolidone (PVP), indium chloride (InCl3), and stannic chloride (SnCl4). The polymer precursor fibers are produced via a facile gas jet fiber (GJF) spinning process and subsequently calcined to produce ITO materials. The morphology shows strong dependence on heating rate in calcination step. Solid porous ITO nanofibers result from slow heating rates while hollow tubular ITO microfibers with porous shells are produced at high heating rates when calcined at a peak temperature of 700 °C. The mechanisms of formation of different morphological forms are proposed. The ITO fibers are characterized using several microscopy tools and thermogravimetric analysis. The concentration of inorganic salts in precursor solution is identified as a key factor in determining the porosity of the shell in hollow fibers. The data presented in this paper show that GJF method may be suitable for fabrication of hollow and multi-tubular metal oxide nanofibers from other inorganic precursor materials.

Efficient production of biodiesel by using a highly active calcium oxide prepared in presence of pectin as heterogeneous catalyst

The cation binding ability of pectin was explored for the preparation of a highly active CaO catalyst for soybean oil transesterification. The catalyst was prepared by the precipitation method using Na2CO3 and Ca(NO3)2 in the presence of pectin followed by calcination. The best catalyst, CaP-600, was prepared at 600 °C and was characterized by FTIR, TGA, BET, CO2-TPD and powder X-ray diffraction (PXRD). CaP-600 was characterized as CaO containing carbonaceous materials left from pectin combustion. At only 1 wt% CaP-600 loading, biodiesel conversion reaches 99% after 4 h with a methanol:oil = 7:1 M ratio. Importantly, the calcium content in the produced biodiesel was only 0.7 ppm, which implies a satisfactory compliance with the ASTM D6751 and EN 14,214 standards. To the best of our knowledge, this is the best CaO catalyst reported for biodiesel production in terms of efficiency and amount of calcium leached. For comparison, CaO prepared in the absence of pectin showed poor catalytic activity in the optimized reaction conditions, demonstrating that the presence of the biopolymer prior to the calcination step is crucial for the catalytic performance of the CaO particles. Possible rationales for the biopolymer role are discussed.

Effect of coating with silica on acidic and catalytic properties of SAPO-18 in MTO conversion

Abstract Silicoaluminophosphate with AEI structure has been modified by silica coating using polydimethylsiloxane (PDMS) and tetraethoxysilane (TEOS) as silica sources. The single step procedure including deposition of 0.5, 1.0, 1.5 and 2.0 wt% of silicon in one step and the multistep procedure including stepwise deposition of silica source by small portions corresponding to 0.5 wt% of silicon with intermediate calcination steps have been applied. The modified materials have been characterized by X-ray fluorescence spectroscopy, X-ray diffraction analysis, low temperature nitrogen adsorption, 29Si MAS NMR, thermoprogrammed desorption of ammonia and FTIR spectroscopy of adsorbed 2,6-ditertbutylpyridine (2,6-DTBPy). The results show that multistep procedure leads to the gradual increase of silicon content and results in the deposition of 2 wt% of Si in 4 steps, whereas single step procedure does not lead to the desired result. Coating with silicon leads to poisoning of Bronsted acid sites located on the external surface of SAPO-18 crystal. This effect is more pronounced in the case of PDMS due to more uniform silica deposition in this case. Coated materials show higher stability of catalytic activity with time on stream in methanol to olefins conversion (MTO) and higher selectivity to light olefins. The mechanism of silica coating with PDMS and TEOS is discussed.

Pengaruh Penambahan Template Polietilen Glikol Terhadap Karakter -Al2O3 dari Kaolin

Synthesis of g-Al 2 O 3 from Tatakan, South Kalimantan kaolin using simple methods: metakaolinization, dealumination, precipitation process using polyethylene glycol (PEG-6000) as a structure directing agent, calcination steps, and characterization of its products have been presented. The purified kaolin was metakaolinized and dealuminated to get amorphous aluminum hydroxide. After that, the sample was precipitated using the various concentration of PEG and NH 4 OH as the precipitating agent. Calcination process was carried out at calcined at a temperature of 700°C for 3 hours. Based on the FTIR spectra and X-ray diffraction of the g-Al 2 O 3 obtained was similar to that of commercial g-Al 2 O 3 . The highest crystallinity of g-Al 2 O 3 was formed when using twice of critical micelle concentration of PEG (10 -3 mol/L). This simple process is an industrially practicable substitute to the Bayer process

Selective Catalytic Oxidation of Benzyl Alcohol by MoO2 Nanoparticles

Selective oxidation of benzyl alcohol to benzaldehyde was carried out with MoO2 nanoparticles (MoO2 NPs). MoO2 NPs were synthesized by two different approaches and characterized by several techniques. The synthesis was done by a hydrothermal procedure using ethylenediamine and either Fe2O3 or hydroquinone. In the latter case, an additional calcination step under N2 was performed to eliminate passivating agents at the surface of the nanoparticles. The synthesized nanocatalysts showed similar catalytic properties, being efficient catalysts in the oxidation of benzyl alcohol. High substrate conversion and product selectivity were achieved under all tested conditions. Studies were conducted using two different oxidants: tert-butyl hydroperoxide and hydrogen peroxide, in our continuous effort to obtain more efficient catalysts for more sustainable catalytic processes. When H2O2 was used as the oxidant, 94% yield was achieved with 100% selectivity for benzaldehyde, which was a very promising result to undergo other studies with this system. Moreover, to elucidate some aspects of the reaction mechanism, a study was conducted, and it was possible to conclude that the reaction undergoes, to some extent, through a radical mechanism with both oxidants.

Innovation in Fischer\u2013Tropsch: Developing Fundamental Understanding to Support Commercial Opportunities

In this contribution we provide details of the BP-Johnson Matthey proprietary Fischer–Tropsch technology and the advanced CANS reactor and catalyst system. The advanced CANS catalyst carrier reactor provides superior heat transfer, reduced pressure drop and higher productivity that lead to major economic savings. Fundamental understanding of catalyst behaviour is also key to obtaining a catalyst that is stable over the lifetime of its use. Synthesis, calcination and reduction steps introduce changes in the catalyst properties prior to syngas introduction. In particular, the presence of water can affect the final catalyst performance. The activity of a good catalyst can be significantly reduced by a sub-optimal activation or start-up. Similarly, stable operation and minimising deactivation are vital for long and stable catalyst life, with years of operation without requiring regeneration. In this report we also share a fundamental study on the catalyst activation across different catalyst supports. This combines advanced in situ techniques with reactor testing to explore the role of the support on catalyst performance. The results illustrate the critical need for a logical and systematic catalyst development programme to explore these effects to optimise the whole FT process. The combination of a joint approach in development plays a key role in a long term success in a process. The fundamental catalyst understanding, optimisation and improvements in combination with the novel CANS reactor design maximise their potential and offer the potential for a world leading technology.

Effect of surface properties of ZnO rods on the formation of anatase-phase TiO2 tubes prepared by liquid deposition method

The effects of the surface properties of ZnO rods on the formation of anatase-phase TiO2 tubes prepared by liquid deposition method is reported. A template made of ZnO rods was prepared on FTO-coated glass by chemical bath deposition and this was then treated under different experimental conditions in an aqueous solution of ammonium hexafluorotitanate and boric acid to investigate the role of the neutral and polar (zinc/oxygen terminated) surfaces of ZnO rods on the formation of TiO2. A calcination step at 550 °C in air was applied to convert the developed Ti-based complexes on the ZnO rods into anatase-phase TiO2 nanostructures. It was observed that a 10-min deposition process led to the development of a mixture of end-capped, open-ended and perforated TiO2 tubes with dimensions resembling those of the ZnO template. Further chemical modification of the surfaces of ZnO rod templates led to the development of anatase-phase TiO2 tubes with open-ends. The surfaces of ZnO rods act as reaction sites for the synthesis of Ti-based complexes. The production of these complexes on the ZnO surface takes place on the neutral side facets of the ZnO rods, while etching of the ZnO rods occurs preferentially along the c-axis (i.e. on the Zn-(O) terminated faces. Consequently, the deposition of TiO2 is considered to happen in two stages: an early and a late stage. The early stage is characterised by the development of Ti-based complexes (Ti hydroxide monomers) on the ZnO surfaces, while the late stage is characterised by polymerisation of these monomers into Ti hydroxide polymers. At the early stage, the deposition process starts on lateral surfaces constituting a foundation for more Ti hydroxide development. Upon calcination at 550 °C in air, these tubular amorphous structures are converted into end-capped anatase-phase TiO2 tubes.

New aluminum mesh from recyclable material for immobilization of TiO2 in heterogeneous photocatalysis

AbstractThis study presents a new aluminium mesh made out of soda can rings as a support for titanium dioxide (TiO2) in the degradation of the synthetic dyes Bordeaux Red (BR) and Tartrazine (TT). Three pre‐treatments including calcination and acidification steps were investigated in order to select the most efficient immobilization procedure for photocatalysis application. Raw and titania‐aluminum meshes were characterized by scanning electron microscopy, x‐ray diffraction, diffuse reflectance, and Fourier transform infrared spectroscopy. The material presented itself as a suitable alternative in the immobilization of titania for wastewater treatment. Preliminary tests selected H2O2/TiO2(suspension) oxidation systems under natural sunlight and germicidal lamps (UVC) exhibiting 97.2% and 99.5% of degradation in 180 minutes, respectively. Immobilized TiO2 systems reached high degradation rates (>99%) after 180 minutes in both UVC and solar light‐based processes. An experimental planning study was carried out for the processes in order to find the best operational conditions and pseudo‐first‐order model fit well the removal data (discolouration rates of in the order of 0.0274 and 0.0145 min−1 for UVC and solar light systems, respectively). Parameters such as TOC, COD, and turbidity, revealed a great improvement in the environmental quality of the water after the treatment and acute toxicity bioassays demonstrated a significant decrease in toxicity for both systems after the treatments. The TiO2‐meshes demonstrated high performance in the removal after five cycles of operation. Therefore, the new immobilization procedure demonstrated that the TiO2‐aluminum mesh is a feasible option for wastewater treatment and photocatalysis.

Porous microspheres consisting of carbon-modified LiFePO4 grains prepared by a spray-drying assisted approach using cellulose as carbon source

Porous microspheres composing of carbon-modified LiFePO4 (C/LFP) nanoparticles have been prepared successfully by a spray-drying process combined with a calcination step using cellulose as carbon source. LiOH plays duple roles as agency for dissolving cellulose with aqueous solution and source of lithium for LiFePO4. The synthesized C/LFP composite microspheres are rich in porosity, and all the C/LFP microspheres consist of numerous LiFePO4 grains with a diameter of about 200 nm. In addition, the individual LiFePO4 grains are encapsulated by the carbon matrix derived from cellulose. The carbon cladding enhances the electronic conductivity of LiFePO4, while the porous structure shortens the Li+ diffusion distance and facilitates the penetration of electrolyte when the C/LFP composites are used as cathode material for the battery. Hence, the unique composites delivered an initial specific discharge capacity of 165 mAh g−1 and showed good rate performance.

Porous MgO-stabilized CaO-based powders/pellets via a citric acid-based carbon template for thermochemical energy storage in concentrated solar power plants

The reversible CaO/CaCO3 carbonation reaction (CaL) is one of the most promising candidates for high-temperature thermochemical energy storage (TCES) in concentrated solar power plants (CSP). Here, a sacrificial citric acid-based carbon template was developed to produce high-performance CaO-based sorbents to mitigate the progressive deactivation with sequential carbonation-calcination cycling. The carbon template was formed through in situ pyrolysis of citric acid in a simple heating process under nitrogen. After a secondary calcination step in air, a stable porous MgO-stabilized nano-CaO powder was generated and achieved high long-term effective conversion due to its resistance to pore plugging and sintering. By dry mixing citric acid with limestone-dolomite mixtures, this procedure can also be applied to synthesize MgO-stabilized CaO pellets via an extrusion–spheronization route, which resulted in comparably stable and effective conversion as the optimized CaO powder. Additionally, the considerable mechanical strength of MgO-stabilized CaO pellets should enable their realistic application in fluidized bed reactors. Thus, this simple, cost-effective and easily-scalable synthesis technique appears to have great potential for CSP-TCES under high temperature operation.

Hybrid Electrochemical Deposition Route for the Facile Nanofabrication of a Cr-Poisoning-Tolerant La(Ni,Fe)O3-δ Cathode for Solid Oxide Fuel Cells.

Cr poisoning of cathode materials is one of the main degradation issues hampering the operation of solid oxide fuel cells (SOFCs). To overcome this shortcoming, LaNi0.6Fe0.4O3-δ (LNF) has been developed as an alternative cathode material owing to its superior chemical stability in Cr environments. In this study, we develop a hybrid electrochemical deposition technique to fabricate a nanostructured LNF-gadolinium-doped ceria (GDC) (n-LNF-GDC) cathode with enhanced active reaction sites for the oxygen reduction reaction. For this purpose, Fe and Ni cations are co-deposited onto an electrically conductive carbon nanotube-modified GDC backbone by electroplating, whereas La cations are successively deposited through a chemically assisted electrodeposition method. The proposed method involves a low-temperature (900 °C) calcination step of electrodeposited cations, which avoids the need of fabricating a GDC diffusion barrier layer which is otherwise needed to avoid the formation of insulating phases (e.g., La2Zr2O7) when fabricating by conventional high-temperature (≥1000 °C) sintering. Scanning electron microscopy images reveal a unique nanofibrous structure of n-LNF-GDC, which is believed to play an instrumental role in enhancing the electrochemical characteristics by increasing the active triple-phase boundaries. An anode-supported SOFC with the n-LNF-GDC cathode showed the superior performance of 0.984 W cm-2 at an intermediate temperature of 750 °C as compared to the power densities of 0.495 and 0.874 W cm-2 produced by LNF-GDC and state-of-the-art La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)-GDC composite cathodes fabricated by conventional sintering. A short-term accelerated Cr-poisoning durability test indicated good electrochemical stability of n-LNF-GDC, whereas LSCF exhibited severe degradation. The electrochemically engineered nanostructured n-LNF-GDC can serve as an effective cathode for SOFCs to achieve high performance and long-term durability.

Highly efficient catalysts for oxygen reduction using well-dispersed iron carbide nanoparticles embedded in multichannel hollow nanofibers

Well-dispersed and highly active iron carbide nanoparticles encapsulated in multichannel hollow nanofibers (Fe3C@MHNFs) were synthesizedviasimple electrospinning and calcination steps, exhibiting highly efficient activity and robust durability for oxygen reduction.

Electrical properties of KTa0.65Nb0.35O3 lead-free ceramics

In the present study, lead-free KTa0.65Nb0.35O3 ceramics were prepared by solid state reaction method using successive calcination steps in order to ensure the complete reaction of the system. The X-ray diffraction analyses of the prepared ceramics have shown the formation of a perovskite structure without any secondary phases. The increase of sintering temperature from 1150 to 1200?C leads to a better densification and decreasing of the Curie temperature (associated with tetragonal-cubic phase transition) closer to the room temperature, i.e. to 290K. The ceramics sintered at 1200?C exhibits a high tunability (n = 1.6) and a reduced hysteretic behaviour. Due to its moderate permittivity, low losses and field dependence permittivity, the KTa0.65Nb0.35O3 ceramics is suitable candidate for application as tunable capacitors.

Conductive Electrospun Nanofiber Mats.

Conductive nanofiber mats can be used in a broad variety of applications, such as electromagnetic shielding, sensors, multifunctional textile surfaces, organic photovoltaics, or biomedicine. While nanofibers or nanofiber from pure or blended polymers can in many cases unambiguously be prepared by electrospinning, creating conductive nanofibers is often more challenging. Integration of conductive nano-fillers often needs a calcination step to evaporate the non-conductive polymer matrix which is necessary for the electrospinning process, while conductive polymers have often relatively low molecular weights and are hard to dissolve in common solvents, both factors impeding spinning them solely and making a spinning agent necessary. On the other hand, conductive coatings may disturb the desired porous structure and possibly cause problems with biocompatibility or other necessary properties of the original nanofiber mats. Here we give an overview of the most recent developments in the growing field of conductive electrospun nanofiber mats, based on electrospinning blends of spinning agents with conductive polymers or nanoparticles, alternatively applying conductive coatings, and the possible applications of such conductive electrospun nanofiber mats.

Investigation and Improvement of Scalable Oxygen Reducing Cathodes for Microbial Fuel Cells by Spray Coating

This contribution describes the effect of the quality of the catalyst coating of cathodes for wastewater treatment by microbial fuel cells (MFC). The increase in coating quality led to a strong increase in MFC performance in terms of peak power density and long-term stability. This more uniform coating was realized by an airbrush coating method for applying a self-developed polymeric solution containing different catalysts (MnO2, MoS2, Co3O4). In addition to the possible automation of the presented coating, this method did not require a calcination step. A cathode coated with catalysts, for instance, MnO2/MoS2 (weight ratio 2:1), by airbrush method reached a peak and long-term power density of 320 and 200–240 mW/m2, respectively, in a two-chamber MFC. The long-term performance was approximately three times higher than a cathode with the same catalyst system but coated with the former paintbrush method on a smaller cathode surface area. This extraordinary increase in MFC performance confirmed the high impact of catalyst coating quality, which could be stronger than variations in catalyst concentration and composition, as well as in cathode surface area.