Showing papers on "Oxalic acid published in 2015"

Multifunctionality of Cu–ZnO–ZrO2/H-ZSM5 catalysts for the one-step CO2-to-DME hydrogenation reaction

Abstract: A series of Cu–ZnO–ZrO 2 /H-ZSM5 multifunctional catalysts for the one-step CO 2 -to-DME hydrogenation reaction was prepared via coprecipitation of methanol catalyst precursors by means of different precipitating agents ( i.e. , sodium bicarbonate, ammonium carbonate, oxalic acid and urea) in a slurry containing dispersed zeolite particles. The samples were characterized by XRF, XRD, N 2 adsorption/desorption isotherms, SEM, N 2 O-titration, TPR and NH 3 /CO 2 TPD techniques, while the catalytic testing was carried out in a fixed-bed reactor operating at 3.0 MPa, in the T R range 473–513 K and space velocity of 10,000 h −1 (CO 2 /H 2 /N 2 , 3/9/1). The experiments revealed that the preparation methodology significantly affects catalyst properties and hence catalyst activity. The multifunctional catalyst prepared via ammonium carbonate precipitation resulted to be the most active in CO 2 conversion, also accomplishing high DME selectivity, with a maximum space-time yield of 0.225 kg DME /kg cat /h. Catalyst characterization disclosed that the strength of basic sites, the ratio between acid and basic sites along with the Cu particle sizes are crucial to achieve maximum catalytic performance, keeping CO selectivity to a minimum value.

A UiO-66 analogue with uncoordinated carboxylic acids for the broad-spectrum removal of toxic chemicals

Abstract: Zirconium-based metal–organic frameworks (MOFs) are of great importance as sorbents due to their increased chemical and thermal stability when compared to other MOF families. Here we report a novel analogue of UiO-66 modified with oxalic acid via solvent-assisted ligand incorporation. This analogue has the ability to remove ammonia, cyanogen chloride, sulphur dioxide, nitrogen dioxide and octane at levels greater than or equal to the base UiO-66. We report here the highest known capacities exhibited by a MOF for SO2 and NO2, at pressures less than 0.10 bar and at room temperature, by UiO-66-ox. Furthermore, we show here the importance of the secondary building unit of the MOF in the removal of ammonia and cyanogen chloride.

Deep Eutectic Solvents: Fractionation of Wheat Straw

Abstract: Deep eutectic solvents (DESs) are a relatively new topic in science. Their usage is not yet clearly defined, and the areas in which DESs may be applied are constantly growing. A simple and clean fractionation of the main components of biomass represents a very important step in creating a clean, renewable carbon economy. A major challenge is the use of DESs for fractionation of biomass components at lower temperatures, without the use of expensive raw materials. In this work, wheat straw was pretreated with six different DES systems composed of choline chloride with urea (1:2), malonic acid (1:1), lactic (1:9; 1:10), malic (1:1), and oxalic acid (1:1). The pretreated biomass was characterized in terms of lignin content, ash, and holocellulose. A deep eutectic solvent, composed of choline chloride and oxalic acid, was found to produce the best delignification results. The solvents are not selective in the process of delignification.

Tuning mechanical properties of pharmaceutical crystals with multicomponent crystals: voriconazole as a case study.

Abstract: Crystals of voriconazole, an antifungal drug, are soft in nature, and this is disadvantageous during compaction studies where pressure is applied on the solid. Crystal engineering is used to make cocrystals and salts with modified mechanical properties (e.g., hardness). Cocrystals with biologically safe coformers such as fumaric acid, 4-hydroxybenzoic acid, and 4-aminobenzoic acid and salts with hydrochloric acid and oxalic acid are prepared through solvent assisted grinding. The presence (salt) or absence (cocrystal) of proton transfer in these multicomponent crystals is unambiguously confirmed with single crystal X-ray diffraction. All the cocrystals have 1:1 stoichiometry, whereas salts exhibit variable stoichiometries such as HCl salt (1:2) and oxalate salts (1:1.5 and 1:1). The nanoindentation technique was applied on single crystals of the salts and cocrystals. The salts exhibit better hardness than the drug and cocrystals in the order salts ≫ drug > cocrystals. The molecular origin of this mechanic...

Catalytic ozonation with γ-Al2O3 to enhance the degradation of refractory organics in water

Abstract: Nowadays, heterogeneous catalytic ozonation appears as a promising way to treat industrial wastewaters containing refractory pollutants, which resist to biological treatments. Several oxides and minerals have been used and their behavior is subject to controversy with particularly the role of Lewis acid sites and/or basic sites and the effect of salts. In this study, millimetric mesoporous γ-Al2O3 particles suitable for industrial processes were used for enhancing the ozonation efficiency of petrochemical effluents without pH adjustment. A phenol (2,4-dimethylphenol (2,4-DMP)) was first chosen as petrochemical refractory molecule to evaluate the influence of alumina in ozonation. Single ozonation and ozonation in presence of γ-Al2O3 led to the disappearance of 2,4-DMP in 25 min and a decrease in pH from 4.5 to 2.5. No adsorption of 2,4-DMP occurred on γ-Al2O3. Adding γ-Al2O3 in the process resulted in an increase of the 2,4–DMP oxidation level. Indeed, the total organic carbon (TOC) removal was 14% for a single ozonation and 46% for ozonation with γ-Al2O3. Similarly, chemical oxygen demand (COD) removal increases from 35 to 75%, respectively. Various oxidized by-products were produced during the degradation of 2,4-DMP, but after 5 h ozonation 90% of organic by-products were acetic acid > formic acid ≫ oxalic acid. Some of the carboxylic acids were adsorbed on γ-Al2O3. The use of radical scavengers (tert-butanol) highlighted the involvement of hydroxyl radicals during catalytic ozonation with γ-Al2O3 in contrary to single ozonation, which mainly involved direct ozone reaction. γ-Al2O3 is an amphoteric solid with Lewis acid AlOH(H+) sites and basicAl-OH sites. After ozonation the amount of basic sites decreased due to carboxylates adsorption, while the Lewis acid sites remained constant as evidenced by FTIR. Several ozonation runs with γ-Al2O3 reported a progressive decrease of its catalytic activity due to the cumulative sorption of carboxylates on the basic sites. After 80 h of ozonation, a calcination at 550 °C allowed to recover allAl-OH basic sites and the initial activity of γ-Al2O3. A synthetic petrochemical effluent containing various petrochemicals (phenol, acetic acid, naphtenic acid, pyrene, naphtalene) was then treated with γ-Al2O3 with and without NaCl. Sodium ions prevented carboxylates adsorption on γ-Al2O3 leading to a higher efficiency of γ-Al2O3 in presence of NaCl and allowed to decrease the toxicity of the petrochemical effluent.

NiAl 2 O 4 nanoparticles: synthesis and characterization through modify sol–gel method and its photocatalyst application

Abstract: In this work, modify sol–gel method was used to synthesize nickel aluminate (NiAl2O4) nanoparticles with aid of nickel nitrate hexahydrate and aluminium nitrate nonahydrate as the starting reagents in the presence of ethanol as the solvent. Besides, to examine the effect of different chelate agent such as citric acid monohydrate, oxalic acid, salicylic acid, and malic acid on the morphology and particle size of final products several tests were performed. The structural, morphological, and optical properties of as-obtained products were characterized by techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, energy dispersive X-ray microanalysis, scanning electron microscopy and ultraviolet–visible. The photocatalytic degradation was investigated using methyl orange under visible light irradiation (λ > 400 nm). The resulting degradation rates of the methyl orange were measured to be as high as 90 % in 270 min.

Kinetics of inorganic and organic phosphorus release influenced by low molecular weight organic acids in calcareous, neutral and acidic soils

Abstract: Low molecular weight organic acids exuded by plants roots enhance inorganic P i release into soil solution and thereby increases plant-available Pi in soils. Low molecular weight organic acids may also induce organic P (P o ) release into soil solution, but kinetics of both Pi and Po displacement from the soil matrix into soil solution of agricultural soils is poorly understood, and the mechanism for P o release is not well explained. This study used kinetic experiments to determine the concentrations and release rates of P i and P o induced by oxalic acid, citric acid, and malic acid in calcareous, neutral and acidic soils. Kinetic data were well described by Elovich (r 2 = 0.801–0.993, P citric acid (0.61–2.82 mg kg –1 ) > malic acid (0.52–1.76 mg kg –1 ) and mainly resulted from the release of labile P o (NaHCO 3 -P o ) regardless of soil type. By contrast, oxalic acid was most effective in enhancing P i release from the HCl-P i (Ca-P i ) fraction of the calcareous soil, and citric acid was most effective in releasing Pi from the NaOH-Pi (Fe/Al-Pi) fraction of the neutral and acidic soils. Therefore, the mechanism for the kinetics of P o release induced by low molecular weight organic acids is ascribed to their ability to mobilize the labile P o (NaHCO 3 -P o ) rather than their ability to chelate cations (i.e. ,F e 3+ ,A l 3+ ) bound to P o in soil.

Synthesis of flower-like MoS 2 nanosheets microspheres by hydrothermal method

Abstract: In this paper, flower-like MoS2 nanosheets microspheres were successfully synthesized by low temperature hydrothermal process using the precursors of sodium molybdate (Na2MoO4·2H2O), thiourea (SC(NH2)2), oxalic acid (C2H2O4·2H2O) and de-ionized water. The effects of oxalic acid concentrations and growth time on the morphology and crystallographic structure of MoS2 nanosheets microspheres were investigated. The morphology, crystallographic structure, chemical composition of the flower-like MoS2 nanosheets microspheres were investigated by using scanning electron microscope, X-ray diffraction, Raman spectrum, high resolution transmission electron-microscopy, and X-ray photoelectron spectroscopy, respectively. It is revealed that MoS2 powders are composed of large, uniform flower-like microspheres, which are formed by several nanosheets gathering together perpendicular to the spherical surface. And the nanosheets are poly-crystallized hexagonal phase. The experiment results also show that the oxalic acid concentration in the precursors plays a key role on the diameter and crystalline of MoS2 nanosheets microspheres. The formation mechanism of flower-like MoS2 nanosheets microspheres was discussed.

Reduced graphene oxide–bismuth oxide composite as electrode material for supercapacitors

Abstract: We have reported a new reduced graphene oxide–bismuth oxide composite that can be used as a supercapacitor electrode Bi2O3 was synthesized from bismuth nitrate pentahydrate and oxalic acid as a precipitating agent using a hydrothermal process in an aqueous graphene oxide suspension Instead of mixing graphene oxide with bismuth oxide, we have developed a bismuth oxalate precipitation between the layers As prepared, composite of hydrated bismuth oxalate and graphene oxide was converted to bismuth oxide and reduced graphene oxide by thermal decomposition in a muffle stove The material exhibited the specific capacitance of 94 F/g at current density 02 A/g Using the cyclic voltammetry, the specific capacitance was as high as 55 F/g at scan rate 5 mV/s over the potential range 0–1 V The material exhibited long-term cycle stability retaining 90 % specific capacitance after 3,000 cycles Except Bi3+ ions present in Bi2O3, some amount of higher energy Bi5+ was confirmed