Effect Of Steam Activation Research Articles

A-site deficient La1-xCr0.95Ru0.05O3-δ perovskites for N-hexadecane steam reforming: Effect of steam activation and active oxygen

Liquid fuels like diesel, biodiesel, and alcohols can be utilized for onboard hydrogen production in auxiliary power systems by steam reforming, in which hydrogen productivity and carbon deposition are key issues. A-site deficient La1-xCr0.95Ru0.05O3 catalysts are prepared using the Glycine-nitrate method and characterized by multiple techniques. The catalyst with 20 % A-site deficiency exhibits about 95 % fuel conversion and stable performance over a 100 h continuous test at 750 °C and a steam/carbon ratio of 3.0 using n-hexadecane. However, the catalyst with a 10 % deficiency shows fluctuating fuel conversion with higher ethylene and ethane contents. Catalyst performance is mainly determined by active oxygen. The activation of steam on oxygen vacancies and Cr ions with variable valences could produce surface-free oxygen and freely migrating lattice oxygen respectively, which can react with CHx intermediates to form CO and H2.

Catalytic effect of rice straw‐derived chars on the decomposition of naphthalene: The influence of steam activation and solvent treatment during char preparation

AbstractRice straw char (RSC) was prepared as the catalyst for naphthalene decomposition in this work. The effects of steam activation and solvent treatment on the catalytic naphthalene decomposition during the char preparation were investigated. Four chars were prepared: RSC, steam‐activated RSC at 500°C (SRS500), steam‐activated RSC at 800°C (SRS800), and solvent‐treated RSC (ResC). The catalytic activity of each catalyst was discussed, and the catalytic mechanisms were also proposed. The results revealed that the SRS catalysts gave a higher catalytic activity than the RSC, due to the enhancement of the surface area after steam activation. The SRS800 gave the highest naphthalene conversion and net gas yield: approximately 76.9% and 45%, respectively. However, its catalytic activity was more rapidly decreased by coke deposition than the other chars. Compared with the RSC, the ResC showed a slightly lower naphthalene conversion, but the net gas yield was slightly higher, especially that of H2 and CH4, due to the existence of K in silicate form.

Synthesis of PAN/PVDF nanofiber composites-based carbon adsorbents for CO2 capture

In this work, we have prepared PAN/PVDF hybrid composites via electrospinning. And, the carbonization and activation process were performed to obtain the porous carbons for CO2 capture. The features and morphologies were observed by HR-SEM, and the surface properties were investigated by XPS. The textural properties were analyzed by N2 adsorption/desorption isotherms at 77 K. The CO2 adsorption/desorption isotherms were measured at 298 K and practical use on CO2 capture processes of the samples were performed under 15% CO2 in N2 as flue gas in fossil fuel power plants through temperature swing adsorption process. The effect of steam activation in electrospun PVDF/PAN nanofibers was investigated in relation to textural properties and CO2 capture. The A-PAN/PVDF nanofibers attained a high CO2 uptake of 2.21 wt%, and exhibited reversible CO2 capturing performances under flue gas condition. These results indicate that the effects of hybridization and steam activation on the CO2 adsorption were confirmed, and the capture performances of the adsorbents were maximized under practical conditions.

Effects of steam activation on the pore structure and surface chemistry of activated carbon derived from bamboo waste

Abstract The effects of steam activation on the pore structure evolution and surface chemistry of activated carbon (AC) obtained from bamboo waste were investigated. Nitrogen adsorption–desorption isotherms revealed that higher steam activation temperatures and/or times promoted the creation of new micropores and widened the existing micropores, consequently decreasing the surface area and total pore volume. Optimum conditions included an activation temperature of 850 °C, activation time of 120 min, and steam flush generated from deionized water of 0.2 cm 3 min −1 . Under these conditions, AC with a BET surface area of 1210 m 2 g −1 and total pore volume of 0.542 cm −3 g −1 was obtained. Changes in surface chemistry were determined through Boehm titration, pH measurement, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Results revealed the presence of a large number of basic groups on the surface of the pyrolyzed char and AC. Steam activation did not affect the species of oxygen-containing groups but changed the contents of these species when compared with pyrolyzed char. Scanning electron microscopy was used to observe the surface morphology of the products. AC obtained under optimum conditions showed a monolayer adsorption capacity of 330 mg g −1 for methylene blue (MB), which demonstrates its excellent potential for MB adsorption applications.

Effect of Steam Activation on Development of Light Weight Biomorphic Porous SiC from Pine Wood Precursor

Biomorphic SiC materials with tailor-made microstructure and properties similar to ceramic materials manufactured by conventional method are a new class of materials derived from natural biopolymeric cellulose templates (wood). Porous silicon carbide (SiC) ceramics with wood-like microstructure have been prepared by carbothermal reduction of charcoal/silica composites at 1300-1600 °C in inert Ar atmosphere. The C/SiO2 composites were fabricated by infiltrating silica sol into porous activated biocarbon template. Silica in the charcoal/silica composite, preferentially in the cellular pores, was found to get transformed in forms of fibers and rods due to shrinkage during drying. The changes in the morphology of resulting porous SiC ceramics after heat treatment to 1600 °C, as well as the conversion mechanism of wood to activated carbon and then to porous SiC ceramic have been investigated using scanning electron microscope, x-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. Activation of carbon prior to silica infiltration has been found to enhance conversion of charcoal to SiC. The pore structure is found to be uniform in these materials than in those made from as-such charcoal/silica composites. This provides a low-cost and eco-friendly route to advanced ceramic materials, with near-net shape potential.

Effect of steam activation on the electric conductivity of nanodispersed carbon

The effect of steam activation at 1150°C on the electric conductivity of nanodispersed carbon prepared by the thermooxidative pyrolysis of hydrocarbons was studied. It was found that the changes detected in the structure-morphological and surface characteristics of the nanodispersed carbon were accompanied by an increase in the electric conductivity of the test system.

Surface Functional Characteristics (C, O, S) of Waste Tire-Derived Carbon Black before and after Steam Activation

The effects of steam activation on the surface functional characteristics of waste tire-derived carbon black were investigated. Two carbon-based materials, powdered carbon black (PCB) and PCB-derived powdered activated carbon (PCB-PAC), were selected for this study. A stainless steel tubular oven was used to activate the PCB at an activation temperature of 900 °C and 1 atm using steam as an activating reagent. X-ray photoelectron spectroscopy (XPS) was adopted to measure the surface composition and chemical structure of carbon surface. Various elemental spectra (C, O, and S) of each carbon sample were further deconvoluted by peak synthesis. Results showed that the surfaces of PCB and PCB-PAC consisted mainly of COC and C—O. The PCB-PAC surface had a higher percentage of oxygenated functional groups (C═O and O—C═O) than PCB. The O1s spectra show that the oxygen detected on the PCB surface was mainly bonded to carbon (C—O), whereas the oxygen on the PCB-PAC surface could be bonded to hydrogen (O—H) and carbon (C—O). Sulfur on the surface of PCB consisted of 58.9 wt% zinc sulfide (ZnS) and 41.1 wt% S═C═S, whereas that on the surfaces of PCB-PAC consisted mainly of S═C═S. Furthermore, the increase of oxygen content from 9.6% (PCB) to 11.9% (PCB-PAC) resulted in the increase of the pH values of PCB-PAC after steam activation.

Influence of Steam Activation on Pore Structure and Acidity of Zeolite Beta: An Al K Edge XANES Study of Aluminum Coordination

The effect of steam activation on the aluminum coordination in zeolite NH4-beta was investigated by means of quantitative analysis of Al K edge XANES spectra. Framework tetrahedral aluminum is converted to octahedral aluminum after calcination and steaming, a process that, at the same time, removes NH3 and brings about Lewis acidity. After mild activation, this octahedral aluminum can revert to the tetrahedral state by NH3 treatment while preserving long-range ordering. This implies that structural changes are fully reversible. Intense steaming causes irreversible changes in the structure of the zeolite: some of the tetrahedrally coordinated aluminum is distorted and octahedrally coordinated aluminum is present in the zeolite. NH3 treatment of intensely steamed zeolite beta results in the reversal of all octahedrally coordinated aluminum to the tetrahedrally coordinated structure, while medium range ordering around some of the tetrahedral aluminum is lost. N2 physisorption experiments indicate that intense steaming creates clefts or mesopores in the zeolite crystallites, resulting in a decrease in the length of the diffusion pathways of the reactants. This explains, at least in part, the enhanced activity of zeolite beta in the Lewis acid (Al-)-catalyzed Meerwein–Ponndorf–Verley (MPV) reaction after intense steaming.

Influence of Steam Activation on Pore Structure and Acidity of Zeolite Beta: An Al K Edge XANES Study of Aluminum Coordination

The effect of steam activation on the aluminum coordination in zeolite NH 4-beta was investigated by means of quantitative analysis of Al K edge XANES spectra. Framework tetrahedral aluminum is converted to octahedral aluminum after calcination and steaming, a process that, at the same time, removes NH 3 and brings about Lewis acidity. After mild activation, this octahedral aluminum can revert to the tetrahedral state by NH 3 treatment while preserving long-range ordering. This implies that structural changes are fully reversible. Intense steaming causes irreversible changes in the structure of the zeolite: some of the tetrahedrally coordinated aluminum is distorted and octahedrally coordinated aluminum is present in the zeolite. NH 3 treatment of intensely steamed zeolite beta results in the reversal of all octahedrally coordinated aluminum to the tetrahedrally coordinated structure, while medium range ordering around some of the tetrahedral aluminum is lost. N 2 physisorption experiments indicate that intense steaming creates clefts or mesopores in the zeolite crystallites, resulting in a decrease in the length of the diffusion pathways of the reactants. This explains, at least in part, the enhanced activity of zeolite beta in the Lewis acid (Al-)-catalyzed Meerwein–Ponndorf–Verley (MPV) reaction after intense steaming.

Effect of binder addition on the mechanical and physicochemical properties of low rank coal char briquettes

A series of chars obtained from a low rank coal by N2 pyrolysis at different temperatures was blended in different proportions with a commercial binder pitch and pressed at 125 MPa in a mould-and-plunger press. The briquettes obtained (1.5 cm long, 1 cm diameter) were subjected to a heat treatment consisting of a curing stage at 200°C in air followed by a carbonization stage in N2, at 500°C or 700°C depending on the starting char. A further stage of activation in steam was performed on the briquettes as well as on the chars. The mechanical properties of the briquettes were assessed by means of their impact resistance index and compressive strength, and their surface properties were determined by N2 B.E.T. surface area and pore volume measurements, as well as by acidic–basic titration. An increase in pitch content within the range tested (10–25% by weight) improves significantly the impact and compressive resistance of the briquettes. Whatever the amount of pitch used, the mechanical resistance of the briquettes decreases after activation. In both cases (before and after activation) the mechanical resistance of the briquettes depends on the starting char and the pitch content used. The changes, with respect to parent chars, found in surface properties of the briquettes were explained in relation to textural and acidic–basic properties of the pitch added, as well as to the changes undergone by the char itself during heat treatment. The effect of steam activation on these properties of the briquettes depends on the parent char, pitch content and the temperature of activation.

The Effect of Steam Activation on Multilayer Adsorption from Solution by Carbon

The Effect of Steam Activation on Multilayer Adsorption from Solution by Carbon