Influence of thermal, hydrothermal, and acid-base treatments on structural stability and surface and catalytic properties of AlPO45$minus (original) (raw)
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Advanced porous materials with tailored porosity (extremely high development of microporosity together with a narrow micropore size distribution (MPSD)) are required in energy and environmental related applications. Lignocellulosic biomass derived HTC carbons are good precursors for the synthesis of activated carbons (ACs) via KOH chemical activation. However, more research is needed in order to tailor the microporosity for those specific applications. In the present work, the influence of the precursor and HTC temperature on the porous properties of the resulting ACs is analyzed, remarking that, regardless of the precursor, highly microporous ACs could be generated. The HTC temperature was found to be an extremely influential parameter affecting the porosity development and the MPSD of the ACs. Tuning of the MPSD of the ACs was achived by modification of the HTC temperature. Promising preliminary results in gas storage (i.e. CO 2 capture and high pressure CH 4 storage) were obtained with these materials, showing the effectiveness of this synthesis strategy in converting a low value lignocellulosic biomass into a functional carbon material with high performance in gas storage applications.
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The Effect of Thermal Treatment on Porous Structure of Carbon Materials
The article investigates the effect of thermal modification of porous carbon material (PCM), obtained by method of hydrothermal carbonization of plant products at a temperature of 750°С, on its porous structure. The implication of the low-temperature porosimetry method has shown that increase of modification temperature (from 300 to 600°С) and time (from 0.25 to 3 h) leads to substantial development of the porous structure of the initial material, accompanied by the doubling of the specific surface area, total volume growth of pores, micro-and mesopores – 2.5, 1.8 and 4.6 times respectively and doubling of the relative proportion of mesopores by the total volume of pores. The pore size distribution (PSD) analysis by means of DFT (Density Functional Theory) allowed to determine that thermal modification most efficiently promotes the development of pores 1.4 and 4 nm in diameter.
Journal of Analytical and Applied Pyrolysis, 2001
This paper discusses the pore structure of chars and activated carbons prepared at different temperatures from rockrose (Cistus ladaniferus L.), extracted previously into petroleum ether. The isothermal temperature of carbonization in nitrogen ranged from 600 to 1000°C. The starting char for activated carbons was prepared by treating a larger amount of precursor in the atmosphere formed as temperature increased from 30 -600°C, at 10°C min − 1 , being the total heating time 120 min. This char was heated in nitrogen before activation, which was carried out using carbon dioxide at 700 -950°C to 40% burn-off. Pycnometry (Hg, He), adsorption (N 2 , 77 K), mercury porosimetry and scanning electron microscopy techniques have been applied to the characterization. In the chars prepared in nitrogen, a shrinkage of the carbon structure is responsible for the pore narrowing in all the pore ranges, including a micropore closing above 800°C, which is attributed to the disappearance of ether groups. This shrinkage is less important in comparison with that occuring in chars prepared from rockrose without extraction. The starting char of the activated carbons presents a rudimentary pore structure due to the different conditions of its preparation. In the activated carbons, the pore volumes (micro, meso and macro) increase up to 750°C. At higher temperatures, the mesopore volume increases, whereas the micro-and macropore volumes decrease. These structural changes are discussed considering the starting char as a Ca-supported catalyst. A shrinkage of the carbon structure also occurs at high temperatures, without causing micropore closing.
Microporous and Mesoporous Materials, 2005
Two complementary wearing off cycling methods based on an initial wet oxidation in a sodium hypochlorite solution or an initial dry oxidation under air, both followed by a thermal pyrolysis under nitrogen, have been applied to a same carbon molecular sieve to study its gradual pore structure modifications. The changes in microporous properties resulting from these cycles were studied by N 2 physisorption at 77 K and analyzed by using the Dubinin-Radushkevich equation. The observed textural behaviour is different from those usually observed using conventional activation processes. The surface complexes created on the surface of carbon by each NaOCl oxidation were characterized by temperature-programmed desorption (TG-TPD-MS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Corresponding surface functional species have been identified and quantified.
Adsorption Science & Technology, 2002
AlPO4 and Al2O3–AlPO4 mixed catalysts of different composition (Al/P > 1) were prepared and calcined in the temperature range 350–650°C. Such catalysts were characterized by DTA and X-ray diffraction methods, and by nitrogen adsorption studies at −196°C. Their acidity was determined using a calorimetric titration method while their catalytic activity towards the dehydration of isopropanol was determined using a pulse microcatalytic technique. The data obtained from XRD studies showed that pure AlPO4 when calcined at 650°C had a rather low crystallinity with its crystalline structure (which is of the α-cristobalite type) being characterized by poorly developed peaks. However, significant changes in the texture, surface acidity and catalytic activity were observed as a result of changing the chemical composition of the solid, with the surface area, total pore volume and surface acidity generally increasing with increasing alumina content. Sintering commenced above 550°C leading to ...
Carbon, 2013
Six nanoporous carbons were prepared by a hard-template method using furfuryl alcohol (FA), 4,4'-bismaleimidediphenyl methane (BM), its copolymer with divinylbenzene (BM-DVB), and sucrose as carbon precursors, and two silica gels as templates. The influence of the templates and precursors on the properties of the synthesized porous carbons was studied. Other factors affecting the porous structure of the final products, such as surface activators and the final carbonization temperature, were also investigated. Results indicated that the specific surface areas and total pore volumes of the samples with micropores were in the range of 836-1785 m 2 ·g -1 and 0.9-2.0 cm 3 ·g -1 , respectively. The highest surface area was obtained for the systems when sulphosalicylic or/and phosphoric acids were used as surface activators. The porous carbons were mesoporous when benzene vapor was present during carbonization under argon atmosphere. An increase in final carbonization temperature resulted in an increase in total pore volume. The influence of carbon precursors on the properties of nanoporous carbons was not that obvious. The presence of nitrogen atoms in the precursors (BM and BM-DVB) improved the thermal stability of the product.
There is significantly abundant portion of waste agricultural materials in the world serving as environmental challenge, however, they could be converted into useful value added products like activated carbon. Coconut shell based carbons were synthesized using physical activation by CO 2 and chemical activation with potassium hydroxide and potassium acetate. The BET surface areas and pore volumes are 361m 2 /g and 0.19cm 3 /g for physical activation, 1353m 2 /g and 0.61cm 3 /g for activation with KOH and 622m 2 /g and 0.31cm 3 /g for potassium acetate activated carbon. From the Fourier Transform Infrared Spectroscopy analysis, hydroxyls, alkenes and carbonyl functional groups were identified with more prominence on the chemically activated porous carbons. Thermogravimetric analysis (TGA) results showed occurrence of moisture pyrolysis at 105 o C, the pyrolysis of hemicellulose and cellulose occurred at 160-390 o C and lignin at (390-650 o C). Carbonization at 700 o C and 2hrs had highest yield of 32%. Physical activation yielded lower surface area with approximately 88% micropores. On the other hand, chemically activation yielded higher surface area with elevated mesopores. The porous carbons can be applied to salvage pollution challenges.