Nano-sulfated titania (TiO ) as a new solid acid catalyst for Friedel–Crafts acylation and Beckman rearrangement in solvent-free conditions

A novel protocol for the highly selective N-monoalkylation of the sulfamate ester moiety has been developed. This reaction proceeded efficiently using alkyl halides, benzyl halides and α-halo ketones as the electrophile in the presence of KF-Al₂O₃ as a cost-effective and robust catalyst. This approach provides new access to N-monoalkylated Topiramate (anticonvulsant drug) derivatives which are potentially of great importance in medicinal chemistry.     

Influence of pseudo-boehmite binder modified dealuminated mordenite on Friedel–Crafts alkylation

The influence of pseudo-boehmite binder on the catalytic properties of dealuminated mordenite (MOR) catalyst for Friedel–Crafts alkylation was investigated. Solid-state ²⁷Al MAS NMR spectroscopy, temperature-programmed desorption of ammonia (NH₃-TPD), BET surface area measurement and catalyst particle mechanical strength were used to characterize the catalysts. It was observed that the addition of pseudo-boehmite binder results in improvement in terms of pore size distribution and its mechanical strength. Furthermore, the dredged pore path of MOR was not destroyed although the acid amount and acid type were adjusted properly when the modified MOR was calcinated. Among these catalysts studied, the catalyst bound with 10 wt% pseudo-boehmite binder showed the best catalytic performance in terms of yield and stability, which can be attributed to its maximum medium strong acid amount and its structural properties which is favorable for fast diffusion of products.     

Diels–Alder reactions of carbonyl-containing dienophiles catalyzed by tungstophosphoric acid supported on silica gel

Tungstophosphoric acid (H₃PW₁₂O₄₀) supported on silica gel proved to be an active heterogeneous catalyst for Diels–Alder reactions of enones with various dienes. The Diels–Alder adducts were formed in high regio- and/or stereoselectivity. In some cases the Diels–Alder reactions were accompanied by competing polymerization of the starting compounds. We also found that trifluoromethanesulfonic acid (triflic acid) is an effective homogeneous catalyst for the reaction of unprotected but-3-en-2-one (methyl vinyl ketone) with 1,3-cyclohexadiene, albeit with a lower activity than tungstophosphoric acid. This revised version was published online in July 2006 with corrections to the Cover Date.     

Friedel–Crafts catalysis using supported reagents. Synthesis, characterization and catalytic application of ZnCl2 supported on fluoride‐modified sol–gel‐derived aluminosilicates

ZnCl₂–aluminosilicate catalysts were prepared via a sol–gel route involving fluoride‐catalyzed hydrolysis of aluminum and silicon alkoxides in the presence of NaF, KF, NH₄F and ZnF₂. The catalysts were characterized by employing ²⁹Si, ²⁷Al and ¹⁹F solid‐state MAS NMR. The dependence of the activities of the catalysts on the nature and amount of fluoride present in the catalysts were investigated using Friedel–Crafts alkylation reaction of benzene with benzyl chloride. This revised version was published online in July 2006 with corrections to the Cover Date.     

Friedel–Crafts type benzylation and benzoylation of aromatic compounds over Hβ zeolite modified by oxides or chlorides of gallium and indium

Liquid phase benzylation (by benzyl chloride) and benzoylation (by benzoyl chloride) of benzene and other aromatic compounds over different Ga- and In-modified Hβ zeolite catalysts at 80 °C have been investigated. An impregnation of the zeolite by oxides or chlorides of Ga and In makes the zeolite highly active in the benzylation process but it results in a decrease in the acidity, particularly the strong acid sites (measured in terms of the ammonia chemisorbed at 250 °C) of the zeolite. Both the redox function, created due to the modification of the Hβ zeolite by Ga or In, and the zeolitic acidity seem to play important role in the benzylation or benzoylation process. Among the different Ga- and In-modified Hβ zeolite catalysts, the In₂O₃/Hβ showed highest activity for the benzene benzylation. This catalyst also showed high activity for both the benzylation and benzoylation of other aromatic compounds, even in the presence of moisture in the reaction mixture; in case of the benzoylation, the moisture has beneficial effect. The In₂O₃/Hβ catalyst can be reused in the benzylation for several times. Kinetics of benzene benzylation (using excess of benzene) over the different Ga- and In-modified Hβ zeolite catalysts has also been investigated. A plausible mechanism for the activation of both the reactants (aromatic substrate and benzyl or benzoyl chloride, forming corresponding carbocation) over the catalyst and also for the reaction between the carbocation and the activated and/or non-activated aromatic substrate is proposed.     

A kinetic study on the electrophoretic deposition of hydroxyapatite–titania nanocomposite based on a statistical approach

In the present study, the electrophoretic deposition (EPD) process of hydroxyapatite–titania nanocomposite was kinetically described by the use of response surface methodology (RSM). The electrostatic interaction between particles in ethanol based suspensions was determined by Zeta potential and particle size analyses. After successful electrophoretic deposition from hydroxyapatite–titania suspensions with 0, 10 and 20 wt% of titania nanoparticles, it was shown that Baldisserri model can well reproduce the experimental data among the other semi-empirical kinetic equations. The as-deposited hydroxyapatite–titania nanocomposites were characterized employing SEM, AFM, XRD, and FT-IR analyses. Then, the effects of deposition voltage, deposition time and wt% TiO₂ on the kinetic of EPD at two time intervals (10–60 s and 60–300 s) were identified and quantified via RSM based on a central composite design (CCD). According to the results obtained from the statistical analysis, it was found that the deposition rate decreases by an increase in wt% TiO₂ and time. Also, a transition in deposition mechanism from linear to parabolic mode was observed and two second order polynomial equations were fitted to the response (deposit weight) at each time intervals.     

Influence of quinone grafting via Friedel–Crafts reaction on carbon porous structure and supercapacitor performance

High specific surface area carbon has been modified with para-benzoquinone (p-BQ) via Friedel–Crafts reaction catalyzed by Iron(III) chloride followed by oxidation, in order to explore alternative strategies for obtaining high energy density supercapacitor materials by the combination of the double layer capacitance of carbons with the redox pseudocapacitance of the organic redox couple added on the carbon surface.Suitable structural and physicochemical characterization proved the formation of covalent bonds between carbon and p-BQ, and the electrochemical characterization showed a significant increase in gravimetric capacitance values after the addition of p-BQ which is maintained even after many cycles.This gravimetric capacitance increase was not only due to the redox reactions of p-BQ, but also to an increased double layer capacitance after p-BQ modification even when the BET surface area decreases after modification. A correlation with the pore structure of carbons showed that the increased double layer capacitance can be attributed to a better matching of carbon pore size with the size of electrolyte ions after p-BQ addition. Thus, this new addition strategy opens the way for the development of carbon-based materials for supercapacitors with higher energy densities coming from both increased pseudocapacitive reactions and increased double layer capacitance.     

A preliminary study of the n‐heptane conversion over supported platinum acid–base ZrPON catalysts

The catalytic behaviour of zirconium phosphate oxynitrides ZrPON and Pt supported ZrPON catalysts in n‐heptane conversion is examined. The results show that the distribution of the products depends on the reaction temperature. In addition, it has been established that the acid–base properties of ZrPON supports greatly influence the n‐heptane reforming reactions since the increase of ZrPON basicity enhances both n‐heptane conversion and aromatics selectivity. This revised version was published online in July 2006 with corrections to the Cover Date.     

A comparative study on selective properties of Kraft lignin–natural rubber composites containing different plasticizers

Effect of plasticizer type on the kraft lignin–natural rubber composite microstructure and selected properties was determined. The composites were prepared with addition of a commonly used naphthenic oil plasticizer to study the decomposition product of polyurethane (glycerolysate) and its characteristics. Kraft lignin powder was incorporated into the natural rubber matrix in amounts of 10 and 40 parts per 100 parts of natural rubber (phr). The reference samples were prepared without any lignin present. The chemical interaction between the filler particles and natural rubber macromolecules was analyzed by Fourier transform infrared spectroscopy (FTIR) and the adhesion was characterized by scanning electron microscopy (SEM). The results of the adhesion measurements confirmed poor distribution of lignin particles into the natural rubber matrix with increasing filler content. Optimal lignin content in the composites was 10 phr in the case of both plasticizers. Moreover, the results of FTIR verified the formation of non-covalent bonds and the need for modification of the filler to enhance the reinforcing effect in the natural rubber matrix. Dynamic mechanical analysis (DMA) and mechanical measurements proved that the specimen containing 10 phr of lignin with the use of glycerolysate as plasticizer displayed the highest mechanical performance. It was demonstrated that glycerolysate and naphthenic oil as plasticizing agents showed similar effect on the thermal properties of the prepared composites. Also, the measured mechanical properties, such as tensile strength, hardness, resilience, and abrasiveness confirmed these findings.     

Synthesis of carbon nanotubes over nickel–iron catalysts supported on alumina under controlled conditions

Carbon nanotubes (CNTs) were synthesized by catalytic decomposition of acetylene over Fe, Ni and Fe–Ni catalysts supported on alumina. The growth of CNTs was carried out at various reaction conditions. The growth density and diameter of CNTs could be controlled by varying the catalyst composition and the growth parameters. The growth density of CNTs increased with increasing the activation time of catalysts in H₂ atmosphere and/or decreasing acetylene concentration. At 600°C, higher density of CNTs was observed at 60 min for higher Fe containing catalyst, whereas at 90 min for higher Ni containing catalyst. The growth density of CNTs highly increased with increasing reaction time from 30 to 60 min. For all the catalysts, the diameter of CNTs decreased with increasing growth time further mainly due to hydrogen etching. Bimetallic catalysts produced narrower diameter CNTs than single metal catalysts. The growth of CNTs followed the tip growth mode and the CNTs were multi-walled CNTs.     

Synthesis of secondary amine-based fluorescent porous organic polymers via Friedel–Crafts polymerization reaction for adsorbing and fluorescent sensing iodine

We present the preparation and characterization of a novel class of secondary amine-based porous organic polymers (POPs: TDPA and TTPBTA), and their iodine adsorption, fluorescence sensing properties for the first time. Two secondary amine-based POPs were synthetized by Friedel−Crafts polymerization reaction catalyzed via methylsulfonic acid with yields of 22.51 and 54.44%. The thermal stability of resulting POPs run up to above 268 and 568°C, and their BET specific surface areas are 56.5 and 2.49 m² g⁻¹, respectively. Their iodine adsorption and fluorescent sensing properties are comparable to that of triphenylamine (TPA)-based (tertiary amine) POPs. The resulting POPs display excellent sorption abilities to iodine molecules with the iodine adsorption capacity of about 3.93 and 1.64 g g⁻¹. Adsorbed iodine is easily desorbed by heating or washing with organic solvents, which make them reusable. They can also adsorb iodine from cyclohexane solution. Moreover, the POPs possess excellent fluorescent sensing property for I₂ with Ksv of 1.85 × 10⁴ and 6.56 × 10⁴ L mol⁻¹, as well as the limits of detection (LODs) of 1.62 × 10⁻¹¹ and 6.86 × 10⁻¹² mol L⁻¹. The performance of adsorbing and fluorescence sensing iodine can be explained by electron transfer mechanism.     

A study on periodic boundary condition in direct numerical simulation for gas–solid flow

Direct numerical simulation(DNS) of gas–solid flow at high resolution has been carried out by coupling the lattice Boltzmann method(LBM) for gas flow and the discrete element method(DEM) for solid particles. However,the body force periodic boundary condition(FPBC) commonly used to cut down the huge computational cost of such simulation has faced accuracy concerns. In this study, a novel two-region periodic boundary condition(TPBC) is presented to remedy this problem, with the flow driven in the region with body force and freely evolving in the other region. With simulation cases for simple circulating fluidized bed risers, the validity and advantages of TPBC are demonstrated with more reasonable heterogeneity of the particle distribution as compared to the corresponding case with FPBC.     

A kinetic study on hydrochloric acid leaching of nickel from Ni–Al2O3 spent catalyst

Hydrochloric acid leaching of nickel from spent Ni–Al₂O₃ catalyst (12.7% Ni, 39.2% Al and 0.68% Fe) has been investigated at a range of conditions by varying particle size (50–180 μm), acid concentration (0.025–2 M), pulp density (0.2–0.4%, w/v) and temperature (293–353 K). Nickel was selectively leached from the catalyst, irrespective of the different conditions. Under the most suitable conditions (1 M HCl, 323 K, stirring at 500 rpm, 50–71 μm particle size), the extent of leaching of Ni and Al after 2 h was 99.9% and 1%, respectively. The XRD pattern of the spent catalyst corresponded to crystalline α-Al₂O₃ along with elemental Ni. The peak due to elemental Ni was absent in the residue sample produced at the optimum leaching conditions, confirming the complete dissolution of Ni from the spent catalyst. The leaching results were well fitted with the shrinking core model with apparent activation energy of 17 kJ/mol in the temperature range of 293–353 K indicating a diffusion controlled reaction.     

A systematic study on the interactions between carnosic acid and ethylpyrrolidine methacrylate–methyl methacrylate copolymer in supercritical media

In the present work, a systematic study on the interactions between carnosic acid (potent natural antioxidant from rosemary) and ethylpyrrolidine methacrylate–methyl methacrylate (EPyM/MMA) copolymer (synthesized in our laboratory) has been performed using different spectroscopic and thermogravimetric techniques. By comparing data obtained for the reference sample (carnosic acid + copolymer) with data of carnosic acid and copolymer alone, a polar interaction could be observed between the carboxylic acid group of carnosic acid with the tertiary amine of the EPyM/MMA copolymer, thus suggesting a charge-transfer complex of the carnosic acid molecules with the pyrrolidine nitrogen (conclusion supported by NMR, FT-IR and TGA data). In order to evaluate the possibility of using, in the near future, the copolymer as a selective stationary phase for preparative-SFC (supercritical fluid chromatography), the work has been completed by studying the remaining interactions, in the reference sample, once treated under several supercritical conditions. After the supercritical treatment (using CO₂ at different pressures and temperatures), depressurization takes place in the extraction cell and the samples remaining were characterized by ¹H NMR, TGA and FT-IR. From the results obtained, it can be inferred that interactions remain after supercritical treatment, thus allowing the design of selective polymers to be used in the purification of carnosic acid.     

A novel catalyst of Ni–Mn complex oxides supported on cordierite for catalytic oxidation of toluene at low temperature

The catalytic combustion of toluene over Ni–Mn mixed complex supported on industrial cordierite was investigated. The catalysts were prepared by the wet impregnation method and characterized by using the Brunauer Emmett Teller (BET), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Transmission Electron Microscope (TEM) and X-ray fluorescence (XRF). The catalytic activity toward the complete oxidation of toluene to CO₂ and H₂O strongly depended on the molar ratio of Ni/Mn, loading amount of Ni–Mn oxides, and calcination temperature. All the results above indicated that the Ni–Mn complex oxide catalyst calcined at 400 °C with 0.5 mol ratio of Ni/Mn, 10 wt.% loading amounts, and showed the highest activity as complete oxidation of toluene.     

Dynamic mechanical study on multilayer core–shell latex for damping applications

Multilayer core–shell poly (styrene-butyl acrylate) latex particles were synthesized via semi-continuous emulsion polymerization, and the process was monitored by a dynamic laser scattering (DLS). The layers of the latex particles were designed to have progressively decreasing glass transition temperatures (T_g) from the core (layer 1) to the outmost shell (layer 4), which was achieved by varying the mass ratio of butyl acrylate (BA) to styrene (St) in the synthesis of each layer. Divinylbenzene (DVB) was added as the crosslinking agent in each layer except for the outmost layer in order to ensure that a continuous film can be formed at room temperature. The damping properties of the formed films as well as the influences of synthesis variables, including the content of DVB added in the internal layers (i.e., layers 1, 2, and 3), the total mass ratio and sequence between layers 3 and 4, and the T_g of each layer were studied by dynamic mechanical analysis (DMA). The results showed that four-layer core–shell latex particles with proper DVB content in each layer exhibited the best damping properties, with a broad effective damping range (tan δ > 0.3) ranging from −12.0 °C to 97.2 °C. The widening of the damping peak can be explained by the formation of a gradient IPN structure in latex particles. Furthermore, the morphology of the formed films was studied by AFM in tapping mode.     

Structured hierarchical Mn–Co mixed oxides supported on silicalite-1 foam catalyst for catalytic combustion

Silicalite-1 (S1) foam was functionalized by supporting manganese–cobalt (Mn–Co) mixed oxides to develop the structured hierarchical catalyst (Mn–Co@S1F) for catalytic combustion for the first time. The self-supporting S1 foam with hierarchical porosity was prepared via hydrothermal synthesis with polyurethane (PU) foam as the template. Subsequently, Mn–Co oxide nano sheets were uniformly grown on the surface of S1 foams under hydrothermal conditions to prepare the structured hierarchical catalyst with specific surface area of 354 m²·g⁻¹, micropore volume of 0.141 cm³·g⁻¹ and total pore volume of 0.217 cm³·g⁻¹, as well as a good capacity to adsorb toluene (1.7 mmol·g⁻¹ at p/p₀ = 0.99). Comparative catalytic combustion of toluene of over developed structured catalyst Mn–Co@S1F was performed against the control catalysts of bulk Mn–Co@S1 (i.e., the crushed Mn–Co@S1F) and unsupported Mn–Co oxides (i.e., Mn–Co). Mn–Co@S1F exhibited comparatively the best catalytic performance, that is, complete and stable toluene conversion at 248 °C over 65 h due to the synergy between Mn–Co oxides and S1 foam, which provided a large number of oxygen vacancies, high redox capacity. In addition, the hierarchical porous structure also improved the accessibility of active sites and facilitated the global mass transfer across the catalyst bed, being beneficial to the catalysis and catalyst longevity.     

A comparative quality study and energy saving on intermittent heat pump drying of Malaysian edible bird’s nest

This paper aims to study the influence of temperature and relative humidity (RH) during intermittent heat pump drying at 28.6–40.6°C, 16.2–26.7% RH, α?=?0.2–1.0, and the comparison was made against fan drying (27°C, 39.7% RH, α?=?1.00). It was observed that the effects of temperature and RH on drying rate were significant when moisture content was high. Experimental results showed that intermittent heat pump drying at 28.6°C, 26.7% RH, α?=?0.2 of edible bird’s nest greatly reduced effective drying time by 84.2% and color change compared to fan drying, and retained the good energy efficiency.     

Assessment of ζ-potential in TiO2 aqueous suspensions: A comparative study based on thermodynamic and rheological methods

It is widely demonstrated that the distinct electrokinetic techniques lead to different values of ζ-potential despite what should be expected from the classical theory. Electrophoresis and conductivity measurements were used to estimate the ζ-potential and the electrical double layer parameters of TiO₂ aqueous suspensions. An assessment of the results was made following thermodynamic and rheological methods. In the first case, the Gibbs free energy increment was compared. In the second one, the yield stress/ζ-potential plots were used. In spite of the ζ-potentials obtained from conductivity, electrophoresis and electrophoresis-conductivity combined techniques are different, the Gibbs free energy increment values do not discriminate the best ζ-potential value. Moreover, the correlation between the yield stress and the square of the ζ-potential has shown that all the ζ-potentials can physically be acceptable. Therefore, the only reasonably conclusion from this study is that the use of combined techniques, like electrophoresis-conductivity, should always be taken as the more cautious approach of evaluating ζ-potentials.