Homogeneous Route Research Articles

A green and moderate approach for the synthesis of methyl formate via dimethoxymethane disproportionation over H-zeolites

Methyl formate (MF) is an important building block in the modern chemical industry, primarily produced through homogeneous carbonylation of methanol under harsh reaction conditions. It is of great interest but remains challenges to develop new heterogeneous catalytic system under mild reaction conditions to replace the homogeneous route. Herein, we report an efficient and green strategy for MF production by dimethoxymethane (DMM) disproportionation over acidic zeolites. Up to nearly100 % DMM conversion and 0.76 g gcat−1 h−1 of MF space time yield (STY) is achieved over H-SSZ-13 under moderate conditions of 0.1 MPa and 393 K. Moreover, H-SSZ-13 shows superior stability during a 100 h continuous test. Combined with multiple characterizations, formaldehyde (FA) has been proved to be a crucial precursor for the formation of MF and the complete mechanism is proposed. This strategy provides a new and feasible approach for continuous large-scale MF production using acidic zeolite as catalyst by heterogeneous catalytic systems.

Efficient heterogeneous synthesis of nucleophilic carboxymethyl hydrazides of polysaccharides.

Nucleophilic moieties in polysaccharides (PS) with distinct higher reactivity compared with the hydroxy group are interesting for sustainable applications in chemistry, medicine, and pharmacy. An efficient heterogeneous method for the formation of such nucleophilic PS is described. Employing alcohols as slurry medium, protonated carboxymethyl (CM) PS and hydrazine hydrate are allowed to react at elevated temperatures. The CM derivatives of starch and pullulan can be transformed almost quantitatively to the corresponding hydrazides. The reaction is less efficient for CM dextrans and CM xylans. As slurry media, 2-propanol and ethanol were probed, and the results are compared with a homogeneous procedure performed in water. Overall, the heterogeneous procedure is superior compared with the homogeneous route. 2-Propanol is the best slurry medium investigated yielding PS hydrazides with the highest nitrogen content.

LIQUEFACTION OF COFFEE BIOMASS WITH RESIDUAL GLYCERIN: A STUDY OF RENEWABLE FUEL PRODUCTION

The present study analyzes the hydrothermal liquefaction of residual coffee biomass using glycerin from the production of biodiesel through the homogeneous route. The reactions occurred by varying the glycerol/water ratio (1:0, 1:1, and 1:2) and the solvent/biomass ratio (70 and 90%) with heating at 180°C for 30 minutes (mixing phase) and at 250°C for 15 minutes. The products obtained were identified as light bio-oil (BOL), heavy bio-oil (BOP), gaseous fraction (FG), and solids (SOL). These products were submitted to characterization through density, thermogravimetry, and viscosity analyses. The condition that generated the highest oil yields was the one where 70% solvent and a glycerin/water ratio of 1:2 were used, producing approximately 83% of bio-oils. In this perspective, coffee biomass and residual glycerin were suitable for use in the hydrothermal liquefaction process.

A comparison study of applying natural iron minerals and zero-valent metals as Fenton-like catalysts for the removal of imidacloprid.

Natural iron minerals and zero-valent metals have been widely tested as catalysts for the Fenton-like process, but the systematical comparison study about their catalytic performance was rarely conducted, and the risk of the secondary pollution of toxic heavy metals was still not uncertain. In this paper, a comparison study of applying pyrite, ilmenite, vanadium titano-magnetite (VTM), zero-valent iron (ZVI), and zero-valent copper (ZVC) as Fenton-like catalysts for the removal of imidacloprid was performed. The results showed that ZVI exhibited the highest activity among the recyclable solid catalysts with a removal rate of 96.8% at initial pH 3 using 10.78 mmol/L H2O2, due to iron corrosive dissolution. Vanadium titano-magnetite (VTM) exhibited the best activity at first use among tested minerals but with low reusability. Pyrite with stable morphology showed a medium but sustainable ability to degrade imidacloprid, achieving a removal rate of 10.5% in the fifth use. The reaction much favored the acidic condition of initial pH around 2 or 3. Meanwhile, there was a significant positive correlation between removal efficiency and dissolved Fe or Cu concentration. Pyrite was considered to be a promising catalyst in Fenton-like reaction. It was suggested that the system proceeded predominantly through a homogeneous route via dissolved Fe or Cu ions. Except ZVC and VTM, other tested catalysts showed the low possibility of causing secondary pollution of toxic metals in the application of Fenton-like process.

Biodiesel production from non-edible forage turnip oil by extruded catalyst

Oil from forage turnip (Raphanus sativus L) was investigated as a potential non-edible feedstock for ethanolic biodiesel production via transesterification using extrudate pellets of K2CO3/Sepiolite. The mechanical, structural and textural properties of the catalyst were measured using dynamometry, TGA, B.E.T and CO2-TPD. Catalytic performance during biodiesel synthesis in a volumetric glass reactor was evaluated after 2 and 4 h, for different catalyst mass (2, 3 and 5 wt%), oil/ethanol molar ratios (1:6, 1:9 and 1:12) and reaction temperatures (50 and 70 °C). A 99.9% biodiesel yield was obtained after 4 h at 70 °C, with a 1:12 oil/ethanol molar ratio and 2 wt% catalyst. Thus, the use of forage turnip oil for ethanolic biodiesel production using a heterogeneous catalyst (instead of the conventional homogeneous route) is viable.

Investigation on synergistic oxidation behavior of NO and Hg0 during the newly designed fast SCR process

In the present study, elemental mercury (Hg0) oxidation behavior in the NO oxidation step of fast SCR process was investigated. The Mn doped CeO2-ZrO2 (CZM0.3) was selected as the catalyst, due to its superior oxygen storage capacity. The results showed that NO could be oxidized efficiently over the catalyst at around 250 °C under the atmosphere of NO/O2/N2. In the Hg0/NO/O2/N2 reaction system, NO oxidation reaction remarkably improved Hg0 oxidation efficiency. Two domination reaction pathways were proposed to interpret the influence of NO oxidation reaction on Hg0 oxidation: one through a heterogeneous oxidation process, and the other through a homogeneous reaction. In the heterogeneous oxidation process, NO was adsorbed on the active sites and activated by the surface oxygen to form more active intermediates for Hg0 oxidation. Hg0 was probably oxidized in its gaseous state, since the affinity between NO and the catalyst was stronger than that between Hg0 and the catalyst. The other reaction pathway was a homogeneous route, during which the gaseous NO2 generated by NO oxidation could oxidize the gaseous Hg0 within the designed reaction conditions. According to the present research, synergistic oxidation of NO and Hg0 in the first step of fast SCR appears to be a promising way to remove Hg0 and NOx in coal-fired power plants.

First-principles theoretical assessment of catalysis by confinement: NO-O2 reactions within voids of molecular dimensions in siliceous crystalline frameworks.

Density functional theory methods that include dispersive forces are used to show how voids of molecular dimensions enhance reaction rates by the mere confinement of transition states analogous to those involved in homogeneous routes and without requiring specific binding sites or structural defects within confining voids. These van der Waals interactions account for the observed large rate enhancements for NO oxidation in the presence of purely siliceous crystalline frameworks. The minimum free energy paths for NO oxidation within chabazite (CHA) and silicalite (SIL) frameworks involve intermediates similar in stoichiometry, geometry, and kinetic relevance to those involved in the homogeneous route. The termolecular transition state for the kinetically-relevant cis-NOO2NO isomerization to trans-NOO2NO is strongly stabilized by confinement within CHA (by 36.3 kJ mol-1 in enthalpy) and SIL (by 39.2 kJ mol-1); such enthalpic stabilization is compensated, in part, by concomitant entropy losses brought forth by confinement (CHA: 44.9; SIL: 45.3, J mol-1 K-1 at 298 K). These enthalpy and entropy changes upon confinement agree well with those measured and combine to significantly decrease activation free energies and are consistent with the rate enhancements that become larger as temperature decreases because of the more negative apparent activation energies in confined systems compared with homogeneous routes. Calculated free energies of confinement are in quantitative agreement with measured rate enhancements and with their temperature sensitivity. Such quantitative agreements reflect preeminent effects of geometry in determining the van der Waals contributions from contacts between the transition states (TS) and the confining walls and the weak effects of the level of theory on TS geometries. NO oxidation reactions are chosen here to illustrate these remarkable effects of confinement because detailed kinetic analysis of rate data are available, but also because of their critical role in the treatment of combustion effluents and in the synthesis of nitric acid and nitrates. Similar effects are evident from rate enhancements by confinement observed for Diels-Alder and alkyne oligomerization reactions. These reactions also occur in gaseous media at near ambient temperatures, for which enthalpic stabilization upon confinement of their homogeneous transition states becomes the preeminent component of activation free energies.

Electrochemical performance of Ag–CuO nanocomposites towards glucose sensing

An effective and sensitive non-enzymatic electrochemical glucose sensor was fabricated by the use of Ag–CuO nanocomposites, which was synthesised by a simple one step homogeneous co-precipitation route using silver nitrate and copper sulphate as precursor materials. The crystalline nature, optical properties, morphology and chemical composition of the prepared sample was determined using X-ray diffraction, diffuse reflectance ultraviolet spectroscopy, scanning electron microscope and X-ray energy dispersive spectroscopy techniques. Further the prepared composites were tested for its glucose sensing property using electrochemical technique. The electrocatalytic and electrochemical properties of the modified electrode was investigated by cyclic voltammetry. Chronoamperometric behaviour shows that the step-wise increment in current as the concentration of glucose increases from 100 to 1000 μM at a constant oxidation potential of 0.6 V(Ag/AgCl). The results indicated that the sensing properties of developed non-enzymatic biosensor shows excellent sensitivity, fast response (5 s) and good selectivity because the prepared Ag–CuO nanocomposites exhibits enhanced electrocatalytic property, fast electron transfer towards the oxidation of glucose.

New immobilisation protocol for the template used in solid-phase synthesis of MIP nanoparticles

As a novel imprinting method, solid-phase synthesis has proven to be a promising approach to prepare polymer nanoparticles with specific recognition sites for a template molecule. In this method, imprinted polymer nanoparticles were synthesized using template immobilized on a solid support. Herein, preparation of immobilized templates on quartz chips through homogeneous route was reported as an efficient alternative strategy to heterogeneous one. The template molecule indole-3-butyric acid (IBA) was reacted with 3-aminopropyltriethoxysilane (APTES) to produce silylated template (IBA-APTES), and it was characterized by IR, 1H NMR and GC–MS. Then, the silylated template molecule was grafted onto the activated surfaces of quartz chip to prepare immobilized template (SiO2@IBA-APTES). The immobilization was confirmed by contact angle, XPS, UV and fluorescence measurement. Immobilization protocol has shown good reproducibility and stability of the immobilized template. MIP nanoparticles were prepared with high selectivity toward the molecule immobilized onto the solid surface. This provides a new approach for the development of molecularly imprinted nanoparticles.

Cationic palladium(II) catalysts on O-carboxymethyl chitosan Schiff base for Suzuki coupling reactions

ABSTRACTIn this study, catalytic activity of two different cationic O-Carboxymethyl chitosan Schiff base palladium (II) complexes in Suzuki coupling reactions and synthesis of biarlys having different functional groups, and reusability of the catalysts were tested. Chemical structures of the synthesized biaryls were elucidated by GC-MS and 1H-NMR; and no by-products were observed in the spectra. Cationic palladium (II) catalysts high turnover numbers and selectivity were recorded for the reactions. Mercury test demonstrated that the reaction mechanism proceed a homogeneous route. Reusability tests of cationic biocatalysts showed that their catalytic activity were still highly efficient even after six cycles.

Fenton-Like Oxidation of 4-Chlorophenol: Homogeneous or Heterogeneous?

Heterogeneous Fenton-like catalysts have received considerable research attention because they could potentially be attractive for oxidative removal of organic contaminants from tertiary wastewater. However, process design is still hampered by insufficient understanding of the chemical pathways involved, and especially whether oxidation activity stems from heterogeneous surface chemistry or minute concentrations of dissolved metal ions in the homogeneous phase. Using inductively coupled plasma-optical emission spectroscopy (ICP-OES) in combination with pH monitoring and ultraviolet–visible spectroscopy (UV–vis) we have monitored the degradation of 4-chlorophenol (4-CP) over two Fenton-like heterogeneous systems, namely FeOx supported on TiO2 and CuFe2O4. We show conclusively that these systems proceed predominantly through a homogeneous route via dissolved metal ions from the solid phase catalysts. Control experiments with homogeneous Fe3+ or Cu2+ systems reveal that even minute concentrations (μM/subppm) of dissolved metal ions leached from the solid phases account for the observed 4-CP degradation rates in the heterogeneous systems. ICP-OES revealed that metal leaching was time-dependent and variable because of pH variations associated with changing acid release rates. Buffering solutions at pH 7.4 suppressed metal leaching (and hence 4-CP degradation) in the FeOx/TiO2 system, but not in others. For example, pH buffering did not entirely suppress metal leaching from CuFe2O4, for which 4-CP degradation was retained through small concentrations of Fe and Cu ions in solution. Our results highlight the importance of careful monitoring of metal content in the aqueous phase, certainly with analytical sensitivity below ppm concentrations of the dissolved metals, and also the crucial influence of time-dependent pH variations on the reaction process. Recyclability of catalysts, pH buffering of solutions or monitoring of metal content in the solid phase by less sensitive analytical methods, for example, chemical analysis, gravimetry, X-ray fluorescence, or energy dispersive X-ray analysis in electron microscopes, cannot exclude the homogeneous Fenton route in the presence of solid catalysts.

Homogeneous preparation of polyamidoamine grafted silica gels and their adsorption properties as Au3+ adsorbents

A series of low generation dendrimer polyamidoamine grafted silica gels (named SiO2-G1.0, SiO2-G2.0, SiO2-G3.0) were synthesized via the homogeneous route. The new materials were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermal analysis, pore and surface area analysis, X-ray diffraction analysis (XRD) and elemental analysis. The adsorption properties of the three products for Au3+ were studied by batch methods. The adsorbents prepared via the homogeneous route showed higher adsorption capacities than those via the heterogeneous route. The maximum adsorption capacities for the three could reach up to 1.48, 2.45, and 2.21mmolg−1, respectively.

New Amine-Modified Silicas: Synthesis, Characterization and Its Use in the Cu(II)-Removal from Aqueous Solutions

Porous silica has been chemically modified with conjugated phenylamine and phenyldiamine moieties using the homogeneous route. This synthetic route involved the reaction of carbaldehyde derivatives with 3-aminopropyltrimethoxysilane prior to immobilization on the support. The resulting materials have been characterized by elemental analysis, FT-IR, 13 C NMR of the solid state, nitrogen adsorption-desorption isotherm, BET surface area, B.J.H. Pore sizes, thermogravimetry analyser (TGA) curves, X-ray diffraction (XRD) and scanning electron microscope (SEM). The new chelating surfaces exhibit good chemical and thermal stability. The solids were employed as Cu(II) adsorbents from aqueous solutions at room temperature. The effects of pH and adsorption kinetics have been studied using the batch technique. Flame atomic absorption spectrometry was used to determine the Cu(II) concentration in the filtrate after the adsorption process. The results indicate that under the optimum conditions, the maximum adsorption value for Cu(II) was 24.5 mg Cu(II) g −1 modified silica, whereas the adsorption capacity of the unmodified silica was only 1 mg Cu(II) g −1 silica. On the basis of these results, it can be concluded that it is possible to modify chemically silica with amine derivatives and to use the resulting modified porous silica as an effective adsorbent for Cu(II) in aqueous media.

An Experimental and Theoretical Investigation of the Inversion of Pd@Pt Core@Shell Dendrimer-Encapsulated Nanoparticles

Bimetallic PdPt dendrimer-encapsulated nanoparticles (DENs) having sizes of about 2 nm were synthesized by a homogeneous route that involved (1) formation of a Pd core, (2) deposition of a Cu shell onto the Pd core in the presence of H2 gas, and (3) galvanic exchange of Pt for the Cu shell. Under these conditions, a Pd@Pt core@shell DEN is anticipated, but detailed characterization by in-situ extended X-ray absorption fine structure (EXAFS) spectroscopy and other analytical methods indicate that the metals invert to yield a Pt-rich core with primarily Pd in the shell. The experimental findings correlate well with density functional theoretical (DFT) calculations. Theory suggests that the increased disorder associated with <~2 nm diameter nanoparticles, along with the relatively large number of edge and corner sites, drives the structural rearrangement. This type of rearrangement is not observed on larger nanoparticles or in bulk metals.

Homogeneous and heterogeneous catalysis production and evaluation of bio-diesel from Jatropha, neem and rubber seeds

Optimization of process parameters for producing biodiesel from Jatropha carcus, Azadirachta indica and hevea brasiliensis seed oils using homogeneous and heterogeneous catalyst were investigated. Temperature and methanol characteristics (oil molar ratio; catalyst type, concentration and agitation) controlled the ester convers-ion. A single-step and two-step trans-esterification were used to produce biodiesel from free fatty acid rubber, jatropha and neem seed oils. The maximum yields of ester from jatropha, neem and rubber oils were respective-ly 98.4, 94.6 and 92.8 % by homogeneous catalysis, and 79.0, 72.0 and 70.2 % by heterogeneous catalysis. While the homogeneous catalysis route produced higher biodiesel yields, the heterogeneous catalyst method produced biodiesel of lower ester content. The fuel properties of biodiesels and blends were analysed quantitati-vely, and the biodiesel produced by homogeneous catalysis compared favourably with conventional diesel fuel.

A Novel Route to Prepare ZnO-SnO&lt;sub&gt;2&lt;/sub&gt; Nanocomposite with High Photocatalytic Activity

A nanometer coupled oxide ZnO-SnO2 was prepared by the fractional homogeneous co-precipitation route using urea as the latent precipitant under boiling reflux condition. The samples prepared from different initial concentrations of urea or at different calcination temperatures were characterized by X-ray diffration (XRD) or transmission electron microscopy (TEM). It was found that the coupled oxides ZnO-SnO2 mainly consist of nanosized ZnO and SnO2, the calcination temperature had obvious effect on the phase composition and the crystal size of the samples obtained, and the precipitant concentration also had obvious effect on the oxide particles size and the production rate of ZnO. Moreover, their photocatalytic activity was investigated for the liquids-phase photocatalytic degradation of methyl orange (MO) in water under UV light irradiation.The coupled oxides showed better photocatalytic activity for the degradation of MO than the pure ZnO or SnO2.

Near surface carbon dioxide within the urban area of Essen, Germany

The aim of this investigation was to determine the allocation between carbon dioxide concentrations, by mobile measurements at 1.5 m a.g.l., within the urban canopy layer regarding different conditions: anticyclonic and cyclonic weather situations, on weekdays, at different times of the day and in different seasons. During winter 2002/2003 (December–February) and summer 2003 (June–August) 20 high frequency spatial and temporal mobile measurements of carbon dioxide were taken in the city of Essen (51° 28′N, 7° 0′E, North Rhine-Westphalia, Germany). The route of the taken measurements started in the southern part of the city and ended after 63 km in the north of Essen, considering all different kinds of its land utilization. The contribution of motor vehicles to the carbon dioxide concentration was being determined by calculating the relation of carbon dioxide to other atmospheric substances, such as CO, NO, NO 2 and O 3. All atmospheric substances were captured at the same time and height with a measurement frequency of 1 Hz and a maximum travel speed of 30 km h −1 (8 m s −1). The results of each mobile measurement were condensed to average values for homogeneous route sections. This facilitated a comparison of the urban CO 2 concentration between the CO 2-data of a rural station and the results of a base line station maintained by the Federal Environmental Agency (UBA). With assistance of different statistical methods it was possible to testify that the determined CO 2-data are representative for the situation of the air quality in the city of Essen. The results of this investigation have shown that it is neither generally possible to describe the urban area as a permanent anthropogenic source for CO 2 nor to call it an urban CO 2 dome as it is often mentioned in literature (e.g. Idso et al., 1998, 2001). A comparison of the carbon dioxide mixing ratio of the city of Essen and the rural station, maintained by the Dept. of Applied Climatology and Landscape Ecology, demonstrated that the city exceeds the rural station for less than 30% per season.

Kinetic and thermodynamic uranyl (II) adsorption process into modified Na-Magadiite and Na-Kanemite

The compound 2-mercaptopyrimidine (MPY) was attached onto synthetic Na-Magadiite (M) and Na-Kanemite (K) samples by homogeneous route. The final matrices named M MPY and K MPY have been characterized through X-ray powder diffraction and scanning electron microscopy (SEM). The resulted materials were submitted to process of adsorption with uranyl solution at pH 2.0 and 298 ± 1 K. The kinetic parameters were analyzed by the Lagergren and Elovich models of adsorption and demonstrated to be good fit for all experiments. From calorimetric determinations the quantitative thermal effects for uranyl(II)/basic center interactions gave exothermic enthalpy, negative Gibbs free energy, and positive entropy. These thermodynamic data confirmed the energetically favorable condition of such interactions at the solid/liquid interface for all systems.

Synthesis and electrochemical properties of monoclinic Li3V2(PO4)3/C composite cathode material prepared from a sucrose-containing precursor

Monoclinic structure Li3V2(PO4)3/C composite powders are synthesized via a novel homogeneous mixing route followed by a one-step heat treatment. The composites were characterized by X-ray diffraction (XRD) and galvanostatic charge/discharge, CV measurements. The influence of the heat treatment on the electrochemical properties of Li3V2(PO4)3/C composites was investigated. To examine the effect of residual carbon content on the properties of the composites, six samples with 1.2, 2.3, 3.4, 4.4, 5.8, and 7.0 wt% carbon were prepared. The sample with 4.4 wt% carbon exhibited good cycling performance and rate capability in the range of 3.0–4.8 V.

Síntese de poliestireno sulfonado para aplicações no tratamento de água produzido a partir de copos e bandejas descartadas de poliestireno

In the present paper, the use of poly(styrene sulfonate) (PSS), produced from discarded polystyrene materials through heterogeneous and homogeneous processes, was investigated. The use of PSS for water treatment, using a kaolin suspension as wastewater model, reduced water turbidity for all the employed materials when compared to the blank analysis, without PSS. The most efficient polyelectrolyte was PSS cups obtained by homogeneous route. The same behavior was observed for real system. The homogeneous PSS cups showed a balance between a moderate molecular weight and high anionic character that improved flocks formation and water removal turbidity.