Influence Of Calcination Conditions Research Articles

N-alkylation of amines with alcohols over hydrothermally prepared Nb-W mixed oxides

Hydrothermally synthesized Nb-W mixed oxides (Nb-W-O) have been employed as a cost-effective and recyclable alternative to noble metals and homogeneous catalysts for the N-alkylation of amines with alcohols, with the model reaction of aniline and benzyl alcohol. The synergistic roles of Nb and W and the influence of calcination conditions were explored. Nb-W-O exhibited a linear packing of corner-sharing octahedra, analogous to the hexagonal tungsten bronze (HTB) structure, but without the long-range order of the HTB in the ab plane, characteristic of pseudo-crystalline materials. Calcination at 773 K in an N2 flow preserved the pseudo-crystalline phase and generated additional Brønsted acid sites, associated with reduced tungsten oxide species stabilized by Nb. The primary reaction pathway involved the activation of the benzyl alcohol by Brønsted acid sites, followed by a nucleophilic attack of the formed carbocation by the aniline. Nb-W-O demonstrated superior activity to other solid acids including metal oxides, silica-alumina, and zeolites in the N-alkylation reaction.

Hydrogen production by ammonia decomposition over ruthenium supported on SiC catalyst

A series of ruthenium catalysts using β-SiC as a support was synthesized with different metal loading (1−5wt.% of Ru). Catalysts were characterized and tested with hydrogen production by catalytic ammonia decomposition. Additionally, the influence of calcination conditions as well as reduction temperatures (673K and 873K) was studied. Ru dispersion and metallic particle size were found to greatly influence catalytic activity. Moreover, calcination in a nitrogen atmosphere could remove a higher proportion of chlorine species derived from the precursor, thereby enhancing catalytic activity. Furthermore, a lower reduction temperature resulted in smaller particle sizes of ruthenium, which were more active in ammonia decomposition. Maximum intrinsic activity was obtained for a Ru size of around 5nm. The catalyst containing 2.5wt.% Ru, calcined in a N2 atmosphere and reduced at 673K resulted in excellent H2 production from ammonia decomposition, with ammonia conversion close to 100% at 623K was obtained. Porous SiC proved to be a suitable support for the nanosized Ru catalyst and was highly active in hydrogen production from ammonia decomposition. Moreover, this support provided good performance stability after one day of reaction.

Structurally improved MgO adsorbents derived from magnesium oxalate precursor for enhanced CO2 capture

Facile, green and solvent-free fabrication of efficient MgO-based adsorbents is highly necessary for their intermediate-temperature CO2 capture applications. In this work, MgO adsorbents were prepared by calcining magnesium oxalate precursor under different calcination atmospheres and temperatures. N2 adsorption-desorption, X-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy and CO2 temperature programmed desorption were employed to study their physicochemical properties. CO2 adsorption performance was evaluated by testing the adsorbents in a dry stream containing 10%CO2 at a mild temperature of 200 °C. The influence of calcination conditions on their structure-performance relationships was investigated. Calcination atmosphere and temperature will significantly affect the microstructure and CO2 adsorption performance. Calcination in a flowing CO2 stream will endow the adsorbent with minimized MgO crystal size, and this will offer more O2− active sites at the edges and corners for enhanced CO2 adsorption capacity. The precursor can hardly be completely decomposed at a lower calcination temperature to form porous structure, and the basic active sites available for CO2 adsorption are limited. A higher calcination temperature will result in sintering of MgO crystals, pore structure blockage and loss of the O2− basic active sites, and CO2 adsorption capacity will therefore be reduced. The desired MgO-C-500 adsorbent calcined in a flowing CO2 stream at 500 °C exhibits the highest CO2 adsorption capacity of 5.09 mmol CO2/g. The results will pave the way for developing highly efficient MgO adsorbents for separating CO2 from industrial exhaust gas.

Influence of Calcination Conditions on Structural and Solid-State Kinetic Properties of Iron Oxidic Species Supported on SBA-15.

Iron oxidic species supported on silica SBA‐15 were synthesized with various iron loadings using two different FeIII precursors. The effect of varying powder layer thickness during calcination on structural and solid‐state kinetic properties of FexOy/SBA‐15 samples was investigated. Calcination was conducted in thin (0.3 cm) or thick (1.3 cm) powder layer. Structural characterization of resulting FexOy/SBA‐15 samples was performed by nitrogen physisorption, X‐ray diffraction, and DR‐UV/Vis spectroscopy. Thick powder layer during calcination induced an increased species size independent of the precursor. However, a significantly more pronounced influence of calcination mode on species size was observed for the FeIII nitrate precursor compared to the FeIII citrate precursor. Temperature‐programmed reduction (TPR) experiments revealed distinct differences in reducibility and reduction mechanism dependent on calcination mode. Thick layer calcination of the samples obtained from FeIII nitrate precursor resulted in more pronounced changes in TPR profiles compared to samples obtained from FeIII citrate precursor. TPR traces were analyzed by model‐dependent Coats‐Redfern method and model‐independent Kissinger method. Differences in solid‐state kinetic properties of FexOy/SBA‐15 samples dependent on powder layer thickness during calcination correlated with differences in iron oxidic species size.

Activated Carbon‐Supported Mo‐Co‐K Sulfide Catalysts for Synthesizing Higher Alcohols from CO2

AbstractActivated carbon‐supported Mo‐Co‐K sulfide catalysts, prepared by stepwise impregnation, were used in the synthesis of higher alcohols via CO2 hydrogenation. The catalysts with varying Mo contents and defined K/Mo and Co/Mo molar ratios exhibited relatively high CO2 conversions and high selectivity to total alcohols and C2+ alcohols. Moreover, the influence of calcination conditions on the sulfidation states and catalytic performance was studied. The surface sulfur runoff of the supported catalysts can be effectively suppressed by online calcination. As a result, the selectivity to total alcohols and C2+ alcohols can be improved.

Influence of the calcination procedure on the thermoelectric properties of calcium cobaltite Ca3Co4O9

Calcium cobaltite is one of the most promising oxide p-type thermoelectric materials. The solid-state reaction (or calcination, respectively), which is well known for large-scale powder synthesis of functional materials, can also be used for the synthesis of thermoelectric oxides. There are various calcination routines in literature for Ca3Co4O9 powder synthesis, but no systematic study has been done on the influence of calcination procedure on thermoelectric properties. Therefore, the influence of calcination conditions on the Seebeck coefficient and the electrical conductivity was studied by modifying calcination temperature, dwell time, particle size of raw materials and number of calcination cycles. This study shows that elevated temperatures, longer dwell times, or repeated calcinations during powder synthesis do not improve but deteriorate the thermoelectric properties of calcium cobaltite. Diffusion during calcination leads to idiomorphic grain growth, which lowers the driving force for sintering of the calcined powder. A lower driving force for sintering reduces the densification. The electrical conductivity increases linearly with densification. The calcination procedure barely influences the Seebeck coefficient. The calcination procedure has no influence on the phase formation of the sintered specimens.

THE USE OF A HIGH LIMESTONE CONTENT MINING WASTE AS A SORBENT FOR CO2 CAPTURE

In this work, a high limestone content waste was evaluated as a potential material for CO2 capture. The influence of calcination conditions on the CO2 capture capacity was evaluated using 5 cycles of calcination-hydration-carbonation reactions. A Central Composite Design of Experiments was set using calcination temperatures and time as variables. The response evaluated was the CO2 capture measured by thermogravimetric analysis. The results indicate that both calcination temperature and time influence the CO2 capture capacities in the initial cycles but, after a large number of cycles, the effect becomes less relevant. The optimum calcination temperature did not change significantly between cycles - about 893 °C in the first and 850 °C in the fourth cycle. However, the optimum calcination time decreased from 40.1 min in the first to 22.5 min in the fourth cycle. The maximum CO2 capture capacity declines over the reaction cycles due to the sorbent sintering, which becomes more noticeable. Moreover, the waste used in this work is suitable for separating CO2 from flue gas, achieving more than 0.2 g/g of capture capacity after five cycles.

CHARACTERIZATION OF OIL SHALE PROCESSING RESIDUES AND SEPARATED PRODUCTS

Different residues of Huadian oil shale processing were investigated. Their inorganic chemical composition and phase structural characteristics were identified by X-ray fluorescence spectrometry (XRF) and X-ray diffractometry (XRD). The influence of calcination conditions on processing residues at different ash activation degrees and impurities' leaching rates as well as the quality of obtained SiO 2 concentrate were investigated by a single-factor method. The results showed that only circular crossflow-type retortingderived semicoke has different phase-structural characteristics at different calcination temperatures. In the range of 700–800 °C , the leaching rate of aluminum and iron reaches the maximum. To prepare SiO 2 concentrate, starting material should be calcined for 1.5 h at 700–800 °C. As a result, SiO2 concentrate which meets the national standard of silica white will be obtained; the content of SiO 2 is 92.34% and its specific surface area 104 m 2 /g. Phase structures of Fushun-type retorting residue and cogeneration power plant ash did not change dramatically at different calcination temperatures. The leaching rate of Al and Fe reached the maximum. Further calcination is unnecessary in reutilization, only removal of impurities by means of acid soaker is relevant. Fushun-type retorting residue can also be used to make SiO2 concentrate which meets the national standard; the content of SiO2 is 90.38%, its specific surface area is 91 m 2 /g. The leaching rate of aluminum from cogeneration power plant ash is lower, and this ash cannot be used to prepare silica white meeting the national standard. It can be applied as an ingredient of cement, at brick preparation, etc. Separation and purification products are a mixture of crystalline SiO 2 and amorphous SiO2, while the content of crystalline SiO 2 is 32.2%.

Influence of calcination conditions on phase formation and particle size of indium niobate powders synthesized by the solid-state reaction

A wolframite-type phase of indium niobate, InNbO4, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. The formation of the InNbO4 phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. Single-phase InNbO4 powders have been obtained successfully for calcination condition of 900 °C for 4 h or 950 °C for 2 h with heating/cooling rates of 30 °C/min. Higher temperatures and longer dwell times clearly favoured particle growth and the formation of large and hard agglomerates.

Influence of calcination conditions on superconducting properties of YBCO coated conductors by advanced TFA-MOD process

We have investigated influences of the H2O gas inlet temperature in the calcination process on both microstructures and superconducting properties of YBCO films fabricated by the advanced TFA-MOD process, from the viewpoint of the process control in the reel-to-reel system. Low Ic values were recognized in the films which were prepared by introducing the H2O gas from the lower temperature than 200°C. XRD measurements and cross-sectional TEM observations suggest that the YBCO films calcined with the H2O inlet temperature below 200°C revealed a random orientation without epitaxial growth. Consequently, it has been understood that control to keep low partial pressure of the H2O gas in a lower temperature region is important for fabrication of long-length YBCO tapes with high performance by the reel-to-reel system.

Synthesis of LiCoO 2 starting from carbonate precursors II. Influence of calcination conditions and leaching

The effect of initial Li:Co ratio, calcination atmosphere, temperature, leaching in H 2O or acetic acid solution on reaction completeness, final Li:Co ratio, primary particle size, conductivity and its sensitivity to different atmospheres has been investigated. The calcination gas composition was found to be very important. A powder with a primary particle size of 100–300 nm and with less than 3 wt.% of unreacted Li 2CO 3 was obtained.

Properties of aluminium oxides obtained by calcination of the products of reductive roasting of basic aluminium-potassium sulfate

The influence of calcination conditions on changes in phase composition and porous structure was studied for hydrous aluminium oxide, obtained by leaching out potassium salts from the products of roasting basic aluminium-potassium sulfate in hydrogen atmosphere at 600°C. The product of calcination at 350°C in vacuum has the most developed porous structure with most pores of internal radius within 10–60 Å. Calcination in air atmosphere at temperatures 700, 800, 900, or 1000°C resulted in decrease of specific surface of aluminium oxide and increase of the share of pores with internal radius above 60 Å in the overall porosity of the samples. The reconstruction of the porous structure proceeds mainly as a result of coalescent sintering.

Influence of calcination conditions on the phase composition of vanadium-phosphorus oxide catalysts

The influence of calcination time and temperature on the formation of phases related to VPO catalysts with P/V ratios in the range 0.90 to 1.10 has been studied. In the preparation, lactic acid was used for the reduction of V 2O 5 and the reduced vanadium complex thus formed was reacted with o-H 3PO 4. The evolution of phases was followed by XRD. For calcinations at 773 K, low P/V ratios favour the formation of βVPO 5; high ratios (>1) favour the formation of a reduced phase labelled β * (d = 4.67, 4.07, 3.14 and 2.59Å). For all P/V ratios studied, this phase was not stable in air at 773 K but transformed slowly into βVPO 5. The β */βVPO 5 ratio did not influence the surface area. The β * phase was not observed after calcination above 873 K. For calcination of catalysts with a P/V ratio of 1.10, carried out at 923 K, a reduced phase with principal d spacings at 3.90, 3.13 and 2.99Åand variously labelled B, β and (VO) 2P 2O 7 in the literature, was observed.