Combustion synthesized crystalline La-Mn perovskite catalysts: Role of fuel molecule on thermal and chemical events

Solution combustion synthesis (SCS) technique was applied to produce LaMnO_3+δ with the aim to investigate the effect of the chemical nature of a series of six fuel molecules (glycine, maleic acid, succinic acid, citric acid, acetic acid, urea) on the combustion reaction mechanism and physicochemical properties of the as-prepared powders. The whole SCS process was found to involve two types of combustion reactions depending on the used sacrificial molecules. Type I (with glycine, maleic acid and succinic acid) was characterized by a one-step exothermic reaction implying a semi-decomposed mixed nitrate-fuel complex and NO₂ arising from manganese nitrate decomposition. The heat emission allows reaching the temperature suitable for well crystallized as-prepared perovskite powders. Type II (with citric acid, acetic acid and urea) was typified by a multi stage process in which intermediate decomposition reactions occurred before the formation of a mixed nitrate-fuel complex. In this case, the heat emission became lower than that expected from stoichiometric reaction, thus limiting the completion of the direct reaction for perovskite production. Consequently, part (with citric acid and acetic acid) or totally (with urea) of lanthanum and manganese remained distinctly combined in two amorphous phases (La(OH)₂NO₃, MnO_x) that were intimately mixed. With respect to other fuels, combustion synthesis, using glycine, produced better crystallized, more defective and performant catalytic perovskite phase toward deep ethanol oxidation.     

Removal of sulfur from commercial kerosene using nanocrystalline NiFe2O4 based sorbents

This paper deals with the simultaneous removal of sulfur from commercial kerosene at room temperature using sorbents containing NiFe₂O₄ nanoparticles. The nanocrystalline NiFe₂O₄ based sorbents were prepared using the combustion route. The effect of fuel content on the surface properties and desulferization activity of Ni/Fe mixed oxide sorbents has been studied.It was observed that incorporation of metal cations (Ni²⁺) into the hematite (α-Fe₂O₃) crystal structure alters the surface properties and desulferization activity of the investigated oxides, which in turn depends on the nature and concentration of the incorporated metal cation and the released heat during the combustion process. The effect of fuel content in modifying the resultant surface area could be directly related to the variations in the rate of crystal growth of the solids studied depending upon preparation temperature. Interestingly, all the prepared ferrites exhibit a narrow pore size distribution in the range of 0.9–2 nm. The capacity of NiFe₂O₄ to adsorb sulfur from commercial kerosene was evaluated in terms of their textural and chemical characteristics.     

Preparation of γ-Al2O3 sorbents loaded with metal components and removal of thiophene from coking benzene

Series sorbents of Cu, Zn, Ni, Ce and Ag metal components supported on γ-Al₂O₃ carrier for removing thiophene from benzene were prepared by conventional and ultrasound-assisted incipient-wetness impregnation method. The static adsorption experiments were carried out in the thiophene-benzene solution with thiophene concentration of 500?mg/L. The results show that the desulfurization activity of all γ-Al₂O₃ sorbents modified by different metal components obviously increase, among which the sorbent modified by silver nitrate has the best performance. The active components of sorbents from Cu, Zn, Ni, Ce nitrates loaded on γ-Al₂O₃ carrier are their oxides. Besides Ag₂O, the products of silver nitrate thermal decomposition in sorbent prepared still have Ag⁰ and Ag–O–Al species. The assistant ultrasound in the process of sorbent preparation can not only shorten the impregnation time, but also enrich the pore structure of sorbent and improve the size and distribution of the Ag species, which is favorable to the removal of thiophene from benzene. The desulfurization capacity of sorbent changes with the Ag content loaded. The sorbent with 15?% quality content of Ag prepared by ultrasound-assisted impregnation method has the highest desulfurization efficiency. It could reduce the thiophene concentration to 1.7?mg/L from 500?mg/L at room temperature and ambient pressure, with the desulfurization efficiency of more than 99?%, when the ratio of sorbent to solution was 1:4?(g/mL).     

Adsorption of colloidal trivalent iron on alumina

The adsorption of colloidal trivalent iron on neutral, acid and basic Al₂O₃ from aqueous solution as a function of pH has been studied. The dependence of sorption of pH is characterized by a maximum, whose position depends on the nature of colloidal particles and surface properties of the sorbents. Adsorption isotherms for the given range of sorbent loading can be expressed by the Langmuir adsorption equation.     

Regenerable Fe-Mn-ZnO/SiO2 sorbents for room temperature removal of H2S from fuel reformates: performance, active sites, Operando studies

Fe- and Mn-promoted H(2)S sorbents Fe(x)-Mn(y)-Zn(1-x-y)O/SiO(2) (x, y = 0, 0.025) for desulfurization of model fuel reformates at room temperature were prepared, tested and characterized. Sulfur uptake capacity at 25 °C significantly exceeds that of both commercial unsupported ZnO sorbents and un-promoted supported ZnO/SiO(2) sorbents. Sulfur capacity and breakthrough characteristics remain satisfactory after multiple (～10) cycles of adsorption/regeneration, with regeneration performed by a simple and robust heating in air. XRD shows that both "calcined" and "spent" sorbents contain nano-dispersed ZnO, and XPS confirms conversion of ZnO to ZnS. "Calcined" sorbent contains Fe(3+) and Mn(3+) that are reduced to Mn(2+) upon reaction with H(2)S, but not with H(2). Operando ESR is used for the first time to study dynamics of reduction of Mn(3+) promoter sites simultaneously with measuring sulfidation dynamics of the Fe(x)-Mn(y)-Zn(1-x-y)O/SiO(2) sorbent. Fe cations are believed to occupy the surface of supported ZnO nanocrystallites, while Mn cations are distributed within ZnO.     

FT-IR study on CO<Subscript>2</Subscript> adsorbed species of CO<Subscript>2</Subscript> sorbents

The stability of amine-functionalized silica sorbents prepared through the incipient wetness technique with primary, secondary, and tertiary amino organosilanes was investigated. The prepared sorbents were exposed to different gaseous streams including CO₂/N₂, dry CO₂/air with varying concentration, and humid CO₂/air mixtures to demonstrate the effect of the gas conditions on the CO₂ adsorption capacity and the stability of the different amine structures. The primary and secondary amine-functionalized adsorbents exhibited CO₂ sorption capacity, while tertiary amine adsorbent hardly adsorbed any CO₂. The secondary amine adsorbent showed better stability than the primary amine sorbent in all the gas conditions, especially dry conditions. Deactivation species were evaluated using FT-IR spectra, and the presence of urea was confirmed to be the main deactivation product of the primary amine adsorbent under dry condition. Furthermore, it was found that the CO₂ concentration can affect the CO₂ sorption capacity as well as the extent of degradation of sorbents.     

Photoinduced redox reactions between colloidal manganese dioxide and some organic compounds of environmental importance

Numerous organic compounds of environmental importance, i.e., phenol, citric, tartaric, and oxalic acids, proved to promote or accelerate reductive dissolution of colloidal manganese dioxide upon irradiation. This is accounted for the formation of surface-located charge-transfer complexes between the MnO₂ particulates and the organic electron donors. From the dependences of the rate of the photoassisted and thermal dissolution on the concentration of the organic compounds, the equilibrium constants for the formation of these complexes have been determined in the case of phenol, resorcinol, citrate, and tartaric acid. The quantum yields for these photoinduced reactions (at λ _ir = 365 nm), however, do not show any correlation with the values of the corresponding equilibrium constants, although adsorption is prerequisite for the efficient reductive dissolution of MnO₂. The changes in pH markedly affect the rate of this process, indicating that protonation of both the electron donors and the surface of the MnO₂ particulates may play significant roles in these systems. The results of experiments carried out in manganese dioxide excess suggest that total mineralization of organic electron donors is strongly hindered by the disadvantageous adsorption properties of the primary redox products. Dedicated to Professor Janos H. Fendler on the occasion of his 70th birthday.     

Reactive adsorption of hydrogen sulfide by promoted sorbents Cu‐ZnO/SiO2: active sites by experiment and simulation

In the Cu_x‐Zn_(1‐x)O/SiO₂ sorbents for ultradeep adsorptive removal of H₂S from gaseous fuel reformates for fuel cells at room temperature, Cu promoter sites significantly increase sulfur uptake capacity of the sorbents. We report characterization of the family of Cu_x‐Zn_(1‐x)O/SiO₂ sorbents for reactive adsorption of H₂S using X‐ray diffraction (XRD), Brunauer‐Emmett‐Teller (BET) surface area analysis, electron spin resonance (ESR), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS) and calculations by the density functional theory (DFT). Both the supported ZnO phase and Cu promoter sites in the Cu_x‐Zn_(1‐x)O/SiO₂ sorbents are nano‐dispersed, as shown by XRD. The Cu_x‐Zn_(1‐x)O/SiO₂ sorbents contain Cu promoter as the Cu²⁺ site of octahedral geometry, as found by the complementary ESR and UV–vis DRS. Mechanism of the promoter effect of the Cu²⁺ site in the Cu_x‐Zn_(1‐x)O/SiO₂ sorbents in reaction with H₂S is proposed based on DFT calculations. Copyright © 2012 John Wiley & Sons, Ltd.     

高温燃煤钙基纳米金属氧化物复合吸附剂同时除砷脱硫研究

将纳米MgO、Al2O3和ZnO分别添加于超细CaCO3中制备出钙基纳米金属氧化物复合吸附剂,并进行燃煤过程中除砷脱硫的试验研究。结果表明,在Ca/S摩尔比为1.8,燃烧温度为1200℃,纳米金属氧化物的添加量为超细CaCO3质量的8%时,添加了纳米MgO的复合吸附剂除砷脱硫性能最好,比单一的超细CaCO3除砷率和脱硫率分别高出了28.73%和37.21%,表现出同时除砷脱硫的良好性能。     

MgO/CaO-loaded porous carbons for carbon dioxide capture

Nanoporous carbons loaded with both MgO and CaO were prepared by a simple heating of mixtures consisting of poly(ethylene terephthalate) and natural dolomite. Preparations were carried out at temperatures ranging from 850 to 1,000 °C that ensured complete thermal decomposition of the dolomite contained in the mixtures to the oxides. An influence of the PET/dolomite weight ratio and temperature of the preparation process on the porosity of the obtained composite products and on CaO and MgO crystallite sizes are discussed using the results of nitrogen adsorption/desorption at 77 K and X-ray diffraction analyses, respectively. Performances of the hybrid materials as sorbents for carbon dioxide were examined using thermogravimetric analyses. Finally, possibility of regeneration of the spent sorbent materials together with a side—effect accompanying this process are discussed on the basis of thermogravimetric measurements. As found, a part of CO₂ captured by the hybrid sorbents gets adsorbed weakly and another portion is fixed strongly. During thermal regeneration, the strongly fixed CO₂ reacts with carbon material. In this way small fraction of a sorbent is lost.     

可控粒径纳米Fe_3O_4的制备及其磁性研究

本文用空气氧化法,在可见光作用下,添加配合剂(EDTA、柠檬酸、酒石酸、谷氨酸)在室温进行了不同粒径纳米Fe3O4的制备及其磁性能研究。结果表明:在可见光作用下,随EDTA、柠檬酸、酒石酸、谷氨酸等配合剂的添加,得到纳米Fe3O4的粒径有所减小、分散性有所提高;配合剂及可见光共存时,体系反应速率得到提高,高的反应速率使纳米Fe3O4晶粒减小;控制适当的光照度和添加剂的量,室温可得到11.8~29.6nm的Fe3O4颗粒。不同粒径纳米Fe3O4分别呈现出超顺磁性、铁磁性特征。     

A study on Zn-based catal-sorbents for the simultaneous removal of hydrogen sulfide and ammonia at high temperature

To simultaneously remove hydrogen sulfide and ammonia from hot coal gases, the ammonia decomposition abilities of various metal oxide catalysts were tested in the absence/presence of hydrogen sulfide, at 650 °C. Cobalt oxide, molybdenum oxide, and nickel oxide have high ammonia decomposition abilities (>95%) in the absence of hydrogen sulfide, but such abilities rapidly decreased during the reaction in the presence of hydrogen sulfide. To improve the simultaneous removal abilities of metal oxides, Zn-based catal sorbents were prepared via impregnation with various metals, such as cobalt, nickel, and molybdenum, on zinc oxide. The CZ-30 (promoted with 30 wt% cobalt oxide on zinc oxide) and NZ-30 (promoted with 30 wt% nickel oxide on zinc oxide) catal sorbents showed excellent sulfur removal capacities, which, calculated until the breakthrough point, were 0.35 and 0.39 g S/g catal sorbent, respectively, while MZ-30 promoted with molybdenum showed a low sulfur removal capacity of 0.08 g S/g catal sorbent. The ammonia decomposition ability of CZ-30, however, increased more than 18 times compared with Co₃O₄, whose ammonia decomposition ability was more than 95% until 465 min, even though the ammonia decomposition ability of NZ-30 sharply decreased after 30 min. The CZ catal sorbent is a good candidate for the simultaneous removal of ammonia and hydrogen sulfide.     

Influence of combustion reagent and microwave drying method on the characteristics of nano-sized Nd<Superscript>3+</Superscript>:YAG powders synthesized by the gel combustion method

Nanosized Nd³⁺ doped Y₃Al₅O₁₂ (Nd³⁺:YAG) powders have been synthesized by the gel combustion method using different combustion reagent such as citric acid, ethylene diamine tetraacetic acid (EDTA), glycine, glycol and the combination of citric acid and EDTA with different ratio. The pure YAG phase was obtained at relatively low temperature around 950 °C for citric acid or EDTA and 1,050 °C for glycine or glycol as combustion reagent, respectively by the gel combustion method. It was found that citric acid and EDTA are the better combustion reagents and yield rather homogeneous and well dispersed club-shape Nd³⁺:YAG samples, and the particle size synthesized by EDTA is larger than that by citric acid. Moreover, the particle size of Nd:YAG was enlarged when the ratio of EDTA was increased in the combination reagent, and the better dispersion of YAG was obtained when the ratio of citric acid to EDTA was 1:1 compared to that of other ratios and pure one as combustion reagent. On the other hand, the results showed that the microwave assisted in drying process of gel to xerogel produced more smaller Nd³⁺:YAG particles in size, and more homogeneous dispersion of the Nd³⁺:YAG particles than that of the traditional dry method.     

Separation of C60 and C70 fullerenes on silica modified by polyaromatic and π-acid aromatic compounds

Separation of C₆₀ and C₇₀ fullerenes by HPLC was studied using sorbents synthesized by reaction of perylenedicarboxylic anhydride, dimethoxyviolanthrene, the tetramer of chromotropic acid with formaldehyde (TCA), trinitrobenzoyl chloride, or chlorotrinitrobenzene with γ-aminopropyl silica. These sorbents possess satisfactory chromatographic properties. The sorbent based on TCA is effective for separation of preparative amounts of fullerenes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1544–1546, August, 1997.     

Cr(VI)在Mg-Al型类水滑石上的吸附-脱附性研究I. 吸附性

研究了Cr(VI)在带结构正电荷的Mg-Al型类水滑石(HTlc)上的吸附性能, 考察了pH、无机电解质添加剂NaCl, NaNO₃, Na₂SO₄和Na₃PO₄及有机添加剂EDTA和柠檬酸等因素的影响, 并结合红外光谱和XRD实验结果探讨了吸附机理. 研究表明, Mg-Al型HTlc对Cr(VI)有很强的吸附能力, 其吸附动力学和吸附等温线分别符合准二级速率方程和Langmuir方程, 饱和吸附量达105 mg/g, 有望成为一种优良的含Cr(VI)污水处理剂和Cr(VI)污染土壤修复剂. 初始pH增大, 吸附量降低. 无机电解质和有机添加剂均能明显抑制Cr(VI)在HTlc上的吸附, 其抑制吸附作用的强弱顺序分别为Na₃PO₄≥Na₂SO₄≥NaCl>>NaNO₃和柠檬酸＞EDTA. Cr(VI)在HTlc上的吸附可分为层间的离子交换吸附和外表面的吸附, 其中外表面的吸附层在微观上又可分为因化学键合作用而形成的内络合层和因静电作用而形成的外络合层.     

Effect of amine double-functionalization on CO<Subscript>2</Subscript> adsorption behaviors of silica gel-supported adsorbents

Amine double-functionalized adsorbents were fabricated using silica gel as supports and their capabilities for CO₂ capture were examined. Aminopropyltrimethoxysilane (1N-APS), and N¹-(3-trimethoxysilylpropyl)diethylenetriamine (3N-APS) were used as grafted amine compounds, and tetraethylenepentamine and polyethyleneimine were used as impregnated species. The influence of double-functionalization method on the CO₂ adsorption performance and textural properties of adsorbents was investigated. The adsorption capacity, the amine efficiency, and the thermal stability of double-functionalized sorbents depend strongly upon molecular variables associated with two different functional states (i.e., chemically grafted and physically impregnated amines). The temperature dependence of adsorption isotherms reveals that the CO₂ adsorption behavior in the double-functionalized adsorbents follow the diffusion limitation model proposed by Xu et al. (Energy Fuels 16:1463–1469, 2002) where the CO₂ adsorption is helped by the diffusion of impregnated amines. It is also found that the adsorption isotherm in the double-functionalized sorbent system with a proper choice for grafted and impregnated amines is nearly independent of temperature, which may offer a novel means to fabricate practically useful sorbents that can be used in a wide range of temperature without loss of CO₂ adsorption capacity.     

Removal of phenol from aqueous solution by adsorption onto hematite (α-Fe2O3): Mechanism exploration from both experimental and theoretical studies

Iron oxides in general and especially hematite, α-Fe₂O₃ have been proved promising materials for efficient removal of various organic pollutants. Herein, we report a successful preparation of hematite (α-Fe₂O₃) by a facile precipitation method and its potential application in the removal of phenol from wastewater. The prepared material was subjected to extensive characterization using a variety of techniques such as scanning electron microscope coupled with energy-dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction (XRD), and the Brunauer Emmett Teller (BET) method. The operating conditions were optimized to improve the adsorption process efficiently. The adsorption analysis showed an adsorption capacity of 16.17 mg g⁻¹ towards phenol at 30 °C. The reaction kinetics and potential rate-limiting steps were studied by Lagergren's pseudo-first-order and pseudo-second-order models, and it was found that the pseudo-second-order accurately described the adsorption kinetics. Freundlich and Langmuir adsorption isotherms models were applied, and the quality of the fittings clearly shows that the Langmuir model well describes the phenol adsorption on the hematite. The interaction mechanism between phenol and α-Fe₂O₃(0 0 1) surface was further addressed by Density Functional Theory (DFT) calculations and molecular dynamics (MD) simulations. Experimental and theoretical results indicate that there is strong evidence for the decisive effect of π–π interactions and H-bonds on the adsorption capacity.     

Study on the fluoride adsorption of various apatite materials in aqueous solution

The aim of this study was to evaluate the defluoridation efficiencies of various sorbents in aqueous solution. These sorbents include synthetic nano-hydroxyapatite (n-HAp), biogenic apatite (bone meal), treated biogenic apatite (bone meal prepared by H₂O₂ oxidation) and geogenic apatite (rock phosphate), which were characterized by XRD, FTIR, TEM and SEM. It has been observed that the defluoridation capacities follow the order: n-HAp > BH₂O₂ > B > rock phosphate. The controlling factors, sorbent dose, initial fluoride concentration, pH, contact time and temperature were investigated. The defluoridation capacities increased with the increase in the initial fluoride concentration and contact time, decreased with the increase in the sorbent dose. The optimum pH range for removal of fluoride on various apatite sorbents was considered to be 5.0-6.0. The fluoride adsorption can be explained by Langmuir, Freundlich isotherms, and the adsorption kinetic data follow the pseudo-second-order model. Thermodynamic parameters such as ΔH⁰, ΔS⁰ and ΔG⁰ indicated that the adsorption on various apatite sorbents was spontaneous and endothermic. These results showed that bone meal is a promising material for fluoride adsorption.     

Preparation and characterization of double metal-silica sorbent for gas filtration

This paper presents the preparation of a porous (Mg, Ca) silicate structure, which could be employed as sorbent filter media. The sorbents have been prepared using sodium silicate precipitated with various ratios of magnesium and calcium salts. The sorbents obtained were characterized using scanning electron microscope (SEM), X-ray diffraction (XRD) and nitrogen physisorption isotherm. Further, the applicability and performance of the sorbent impregnate with potassium hydroxide for removal of sulphur dioxide (SO₂) has been demonstrated. From the isotherms, specific surface area, pore diameter and volume of pores were estimated. Results show that the chemical composition and textural properties of the resultant sorbents were highly dependent on Mg/Ca molar ratio. It was found that sorbents made with 68 mol% Mg and 32 mol% Ca (PSS-MgCa-68/32); and 75 mol% Mg and 25 mol% Ca (PSS-MgCa-75/25) exhibited even higher specific surface area and pore volume than the sorbents containing a single metal. The Mg/Ca-silica sorbents obtained contains interconnected bimodal porosity with large portions being mesopores of varied sizes. The pore size distribution (PSD) results further indicate that PSS-MgCa-68/32 sorbent exhibits wide PSD of interconnected pores in the size range of 1 to 32 nm while PSS-MgCa-50/50 and PSS-MgCa-75/25 exhibits narrow PSD of 1 to 5 nm. Using SO₂ as model contaminate gas, it was shown that the dynamic adsorption performance of the PSS-MgCa-sorbents impregnated with 8 wt% KOH exhibits SO₂ uptake, with impregnated PSS-MgCa-68/32 showing better performance. This shows that the materials prepared can be used as adsorbent for gas filtration.     

Preparation and performance of potassium-based sorbent using SnO<Subscript>2</Subscript> for post-combustion CO<Subscript>2</Subscript> capture

Potassium-based sorbents using γ-Al₂O₃ or TiO₂ as a support or an additive material have disadvantages in terms of their thermal stability and cyclic CO₂ capture. To overcome the shortcomings of these sorbents, a novel potassium-based sorbent (KSnI30) using SnO₂ was developed in this study. The KSnI30 sorbent formed only K₂CO₃ and SnO₂ phases without any inactive alloy species even after calcination at high temperatures (500–700 °C), indicating the good thermal stability of the KSnI30 sorbent regardless of the calcination temperature. Furthermore, the KSnI30 sorbent has an excellent regeneration property (above 98 %), as well as high CO₂ capture capacities (89–94 mg CO₂/g sorbent). Its excellent regeneration property is due to the formation of a KHCO₃ phase without by-products during CO₂ sorption. These results of the present study demonstrate that the SnO₂ shows promise as a new support or an additive material to replace TiO₂ and γ-Al₂O₃ in the preparation of a regenerable potassium-based sorbent for post-combustion CO₂ capture with good thermal stability and excellent regeneration property.