A preliminary investigation of PAN based carbon fibre surfaces by flow microcalorimetry

The adsorption of n-butylamine, n-butyric acid, n-butanol and 1.2 epoxy propane from n-heptane solutions onto carbon fibres (PAN) has been investigated by flow microcalorimetry. No adsorption of n-butyric acid could be detected, but the adsorption of n-butanol and 1.2 epoxy propane was reversible and relatively unaffected by surface treatments. In contrast, the adsorption of n-butylamine was very strong, partially irreversible in character and was increased markedly by surface treatment. The areas of the exothermic peaks of irreversibly and reversibly adsorbed n-butylamine were measured, and the former is considered to be a semi-quantitative estimate of the surface acidity. The surface acidity, estimated in this way, is increased by the manufacturer's surface treatment, but the external area of the fibres is relatively unchanged suggesting an increase in the fraction of acid groups at the surface. HM fibres oxidised in nitric acid show an increase in both peak areas and in the external area. When the peak areas are related to the active surface areas of the fibres, however, it is clear that the fraction of the active, or edge, surface occupied by acid groups is greater on fibres oxidised in nitric acid than on those surface treated by the supplier.     

Influence of surfactant addition sequence on the suspension properties and electrophoretic deposition behaviour of alumina and zirconia

A well-known polyelectrolyte salt, ammonium polymethacrylate (Darvan-C) is used to stabilise ethanol-based Al₂O₃ and Ce-ZrO₂ suspensions with butylamine addition. The sequence in which n-butylamine and Darvan-C are added to the suspension greatly affects the properties of the wet deposit obtained by electrophoretic deposition. To investigate this effect, electrical conductivity of the suspension and the shear rate dependence of its viscosity are investigated. When n-butylamine is added first, the equilibrium in the suspension is almost immediately reached and a plastically deformable wet deposit is obtained over a large n-butylamine/Darvan-C ratio. The suspension has a shear-thinning viscosity and the deformable deposit is characterised by a high solvent content, which allows the rearrangement of particles during drying. When Darvan-C is added before the n-butylamine, the wet deposit is smooth and rigid. The suspension has a lower viscosity and a near-Newtonian behaviour is observed. A similar behaviour is observed for Al₂O₃ and Ce-ZrO₂ suspensions. The green density of the dried deposits is not influenced by the addition sequence and higher green densities are obtained for Al₂O₃ when compared to Ce-ZrO₂.     

Catalytic activity of mineral matter from western Kentucky coals for hydro-desulphurization and hydrodenitrogenation

A pulse reactor was used to study the catalytic activity and selectivity of mineral matter from Kentucky No.9 and No.11 seam coals and a low calorific value gasifier ash in the hydrodesulphurization (HDS) of thiophene and hydrodenitrogenation (HDN) of pyrrole, pyrrolidene and n-butylamine. Mineral matter in its least altered state was obtained by low temperature ashing. Thiophene conversion correlated well with the iron and zirconium contents (R > 0.95) of the catalysts, and at 450 °C all catalysts including a commercial Fe₂O₃/AI₂O₃ gave similar distributions of the butenes and <5% butane. Reactivities of N-compounds catalysed by mineral matter from Kentucky Nos.9 and 11 coals were in the order: n-butylamine > pyrrolidine > pyrrole ≈0. Nickel was found to be the important element n-butylamine conversion and 1-butene was the predominant product species for all the catalysts. Mineral acid treatment of the mineral matter from No.11 coal decreased its HDN activity but increased its HDS activity. Results of this study indicate that hydrogen consumption for removal of sulphur and nitrogen can be reduced by using dehydrogenation-type catalysts.     

Synthesis and characterisation of xTiO2·(1−x)SiO2-carbon composites

A series of xTiO₂·(1−x)SiO₂-carbon xerogels (0.0≤x≤1.0) was obtained by co-polymerisation of resorcinol, formaldehyde, tetrabutyl orthotitanate and tetraethoxysilane. A blank without inorganic phase was also synthesized. The xerogels were pyrolysed at 1000 °C in nitrogen to obtain the composites. The samples were characterised by thermal analysis, gas physisorption, mercury porosimetry, X-ray diffraction, and titration with n-butylamine. The heat treatment of the xerogels caused the removal of moisture and organic precursors and the carbonisation of material. The presence of inorganic phase affected the thermal behaviour of the xerogel. The xerogels and composites were essentially macroporous solids. The pyrolysis of the xerogels gave rise to the creation of microporosity. Mesoporosity was usually little developed in the xerogels and composites. No crystalline phase was detected for the composites with 0.0≤x≤0.4, this indicating a good dispersion of the inorganic phase into the carbonaceous matrix. For x>0.4, however, anatase was observed. The surface acidity increased for the composites as compared to the blank. The acid strength was higher and the distribution of surface acidity was wider for the composites with a high titania content, whereas surface acid sites were weaker for the sample containing only this metal oxide as inorganic phase.     

Esterification of stearic acid with p-cresol over modified Indian bentonite clay catalysts

The esterification of stearic acid with p-cresol using modified Indian bentonite clay catalysts has been reported. The reaction was studied over exchanged clays, acid activated clays, exchanged acid activated clays, aluminium pillared clay, aluminium pillared acid activated clay, molecular sieve Al-MCM-41, zeolite Hβ, ZrO₂, S-ZrO₂, p-TSA, montmorillonite K10, and montmorillonite KSF in o-xylene for 6 h. The catalysts were characterized by X-ray diffraction and surface area measurements. The acidity was determined by n-butylamine back-titration method and DRIFTS after pyridine adsorption. Acid activated Indian bentonite (AAIB) was found to be a better catalyst compared to other catalysts in the esterification of stearic acid with p-cresol.     

Electrical conduction of chalcogenide CuI-AgI-As2Se3 and PbI2-AgI-As2Se3 films obtained by the chemical deposition method

The electrical conduction of chalcogenide semiconductor CuI-AgI-As₂Se₃ and PbI₂-AgI-As₂Se₃ films obtained by the chemical deposition from n-butylamine, depending on the composition of films, has been studied. It has been shown that the electrical properties of chalcogenide glass and films based on them within the experimental error are characterized by the same values. This is explained by the model of the dissolution of glasslike semiconductors in amines.     

Characterization of Pd catalysts supported on USY zeolites with different SiO2/Al2O3 ratios for the hydrogenation of naphthalene in the presence of benzothiophene

A series of ultra-stable Y-type (USY) zeolites with different SiO₂/Al₂O₃ ratios in the range of 10–80 were used as supports for preparing Pd/USY at 2 wt% Pd loading. The FT-IR of hydroxyl groups of USY zeolites, the n-butylamine chemisorption and the temperature-programmed desorption were used in combination to characterize the zeolite acidity. TPR, H₂-TPD and chemisorption using H₂ were used to characterize the Pd reduction and dispersion. The hydrogenation of naphthalene was conducted at 200 °C in the presence of benzothiophene at different sulfur/metal ratios. The hydrogenation activity, selectivity, and the sulfur tolerance strongly depended on the SiO₂/Al₂O₃ ratio (thus the acidity) of the zeolites. The activity decreased with increasing SiO₂/Al₂O₃ in this range. The IR and n-butylamine TPD showed that both the amount and strength of Brönsted acidity decreased with the increase of the SiO₂/Al₂O₃ ratio. The good relationship between the acidity modification and catalytic performance suggests that the sulfur tolerance of Pd/USY zeolite might be due to the desired metal-support interaction, which resulted in larger amount of electron-deficient Pd. However, as shown in TGA and TPO-IR studies, the higher hydrogenation performance on more acidic zeolite also caused higher amount of carbonaceous species on the catalyst.     

Structure and catalytic activity correlation of CoAlPO4 in the synthesis of N,N-biphenyl urea via alkylation of aniline using dimethyl carbonate

Two sets of cobalt aluminophosphate materials, one at different pH (4.5, 7, 10, and 11.5) and the other containing different percentage of cobalt (0.5–20) were prepared by co-precipitation method. All the materials were characterized by XRD, SEM, ²⁷Al MASS NMR, TGA and DSC, FTIR, for their textural and structural properties. The surface area of the samples was determined by BET method and total surface acidity by n-butylamine titration method. The CoAlPO₄ obtained under acidic pH were found to be crystalline AlPO₄ with nonmicroporous tridymit structure associated with cobalt phosphate, whereas the one obtained under alkaline pH were amorphous aluminophosphate and also associated with cobalt phosphate. Tridymit-AlPO₄ crystals exhibited Al atom in a tetrahedral environment of phosphate groups. In the amorphous material the Al atoms were in a mixed tetrahedral and octahedral environment. The concentration of acid sites were found to be higher in the sample obtained under alkaline pH. This has been attributed due to the partial coordination of hydroxyl groups in the octahedral aluminum sites. The amorphous materials obtained under alkaline pH were found to be thermally stable up to 900 °C.The catalytic activity of all the materials was investigated in aniline alkylation using dimethyl/ethyl carbonates (DMC/DEC) under refluxing conditions. N-methyl/ethyl aniline (NMA/NEA) and biphenyl urea (BPU) were formed as the major products with the catalysts prepared at acidic and alkaline pH, respectively. A good correlation has been observed between the catalytic activity of CoAlPO₄ materials towards their selectivity for NMA/NEA and/or BPU and their textural and structural properties. Reaction conditions such as the amount of the catalyst, duration of the reaction, reusability and efficiency of the catalyst have also been evaluated. CoAlPO₄ prepared under alkaline pH with 5% of cobalt has been found to be the best catalyst for BPU synthesis from aniline and DMC/DEC under refluxing conditions.     

Examination and standardisation of amine titration in surface acidity measurements of silicas,aluminas and synthetic zeolites

The amine titration method using Hammett and arylmethanol indicators has been examined on selected samples of porous silica, active alumina and synthetic zeolites. On the basis of the successive approximation technique the evaluation of surface acid strength distribution has been standardised. A new method has been developed to assess the total acidity without employing indicators. The distinction between Bronsted and Lewis acidity through measuring the Ho and H_R acidity distribution function on aluminas and zeolites is shown to be erroneous. The acidity is strongly affected by the size of amine and by the density of surface acid centres—as demonstrated on a series of silicas and on synthetic zeolites. The size dependence can be utilised to detect the acidity of distinct pore size ranges within a given porous solid. Under certain conditions the acidity measurements can be correlated with those obtained from other techniques such as heterogeneous exchange and infrared spectroscopy.     

Tailoring Raney-catalysts for the selective hydrogenation of butyronitrile to n-butylamine

The influence of LiOH promotion on Co-based Raney-catalysts for the selective hydrogenation of butyronitrile to n-butylamine was explored. Doping with LiOH led to an increase in the fraction of metallic surface area and reduced concentration of Lewis acid sites resulting from alumina particles decorating the metal surface. Two factors were found to be crucial to achieving high selectivity to primary amines. These factors include a low adsorption constant of n-butylamine relative to butyronitrile (because adsorbed butylamine is necessary for byproduct formation) and a low concentration of Lewis acid sites catalyzing condensation reactions.     

New method for the study of surface acidity of zeolites by NH3-TPD, using a pH-meter equipped with an ion selective electrode

Desorbed ammonia is captured by an acetic acid solution whose concentration of ammonium ions formed by neutralization, is continuously recorded by a pH-meter equipped with an ion-selective electrode (ISE). This technique allows the study of both the acidity density and the distribution of acid site strengths. Such “strength profile” was obtained by plotting the relative rate of desorbed NH₃ versus the temperature. Results obtained can be fairly well correlated with those already published. It is shown that by investigating several H-ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios, the data of acid density obtained by the ISE method are very close to those calculated from the Al content. The slight shift of the desorption peaks towards higher temperature suggests a slightly higher strength for more isolated acid sites. Zeolite structures, which are richer in Al, contain weaker acid sites, as evidenced by the H-Y when compared to the H-mordenite, while the acid sites density of the former is much higher. The ultra-stabilized Y zeolite (H-USY) shows a lower acidity density than the parent H-Y owing to the removal of some of the tetrahedral Al atoms from the framework during the preparation. The strength profile of the H-USY is also quite different from that of the H-Y. The new technique appears to be much simpler, more rapid, more informative and quite accurate when compared to the technique using a gas chromatograph equipped with a thermal conductivity detector (GC-TCD).     

A suitable synthesis of azlactones (4-benzylidene-2-phenyloxazolin-5-ones and 4-alkylidene-2-phenyloxazolin-5-ones) catalyzed by silica–alumina supported heteropolyacids

Eleven examples of azlactones (4-benzylidene-2-phenyloxazolin-5-ones and 4-alkylidene-2-phenyloxazolin-5-ones) were prepared via an Erlenmeyer-type synthesis from aromatic aldehydes, hippuric acid and acetic anhydride was added to the hot solution as a dehydrating agent. Molybdophosphoric or tungstophosphoric acids supported on silica–alumina, obtained by the sol–gel method, catalyze the reaction. The prepared catalysts were characterized by X-ray diffraction and diffuse reflectance spectroscopy. The specific surface area of the catalysts was determined by the nitrogen adsorption/desorption at 196 °C technique, and the catalyst acidity was measured by potentiometric titration with n-butylamine. The heteropolyacid amount removed from the catalysts during the leaching with toluene was lower than 1%. The products were obtained with high conversion and selectivity. The yields were in the 87–96% range for the majority of the selected samples, with the exception of the azlactones synthesized from 2-nitrobenzaldehyde and cyclohexanone, which gave yields in the 70–80% range. The same catalysts were used several times without appreciable loss of their catalytic activity. A rational mechanism for the azlactone formation catalyzed by the supported heteropolyacid is proposed.     

Enhanced performance of Zn and Co co-doped MoO3 nanosheets as gas sensor for n-butylamine

High operating temperature of metal oxide sensor devices hinders their practical applications. In order to reduce operating temperature, molybdenum trioxide (MoO₃) nanosheets co-doped with zinc (Zn) and cobalt (Co) were successfully prepared by simple one-step hydrothermal method and characterized by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, and by using WS-30A gas sensor measurement system. The sensor exhibited high response to n-butylamine gas at low temperature. In particular, the response of Zn and Co co-doped MoO₃ sensor was higher than that of pure MoO₃ and retained excellent selectivity of MoO₃ to n-butylamine. Optimum operating temperature gradually decreased with increasing Co and Zn doping amount. Multi-doping system shows great potential for the development and application of sensors,and provides feasible method for reducing their operating temperature of the sensor.     

Water-dispersible TiO2 nanoparticles via a biphasic solvothermal reaction method

A biphasic solvothermal reaction method has been used for the synthesis of TiO₂ nanoparticles (NPs). In this method, hydrolysis and nucleation occur at the interface of organic phase (titanium (IV) n-propoxide and stearic acid dissolved in toluene) and water phase (tert-butylamine dissolved in water) resulting in the nucleation of the stearic acid-capped TiO₂ NPs. These NPs are hydrophilic due to hydrophobic stearic acid ligands and could be dispersed in toluene, but not in water. These stearic acid-capped TiO₂ NPs were surface-modified with 2,3-dimercaptosuccinic acid (DMSA) in order to make them water soluble. The resultant TiO₂ NPs were easily redispersed in water without any noticeable aggregation. The Rietveld profile fitting of X-ray diffraction (XRD) pattern of the TiO₂ NPs revealed highly crystalline anatase structure. The average crystallite size of TiO₂ NPs was calculated to be 6.89 nm, which agrees with TEM results. These results have important implications for the use of TiO₂ in biomedical, environmental, and industrial applications.     

Determination potentiometrique des constantes de stabilite des complexes entre l'argent(I) et quelques heterocycles azotes en milieu neutre et acide dans le carbonate de propylene

The formation of AgL⁺_n (n = 1–4) (L = pyridine), AgL′⁺ and AgL′₂⁺ [L′ = 2,2′ bipyridine, 2,2′ biquinoline, 2-(2-pyridyl)benzimidazole] complexes has been studied using potentiometry with a silver electrode. The acidity constants of the ligands have been measured potentiometrically with the hydrogen electrode. The silver distribution between the Ag⁺ and AgL_n⁺ species has been computed by means of the so obtained β_n. In acidic medium, the metallic complexes are destroyed by the ligand protonation.     

Multilayer single-solute adsorption from dilute solutions on energetically heterogeneous solids

The isotherm equations for multilayer single-solute adsorption from dilute solutions on energetically heterogeneous solids are derived by solving the integral equation for different energy distributions and local adsorption isotherm of BET-type. This procedure is analogous to that used in multilayer gas adsorption on heterogeneous solid surfaces. The equations, obtained for quasi-gaussian energy distribution, are examined using the adsorption data of n-valeric acid, n-amyl alcohol, aniline and cyclohexanol from dilute aqueous solutions on different types of carbon adsorbents of specific surface areas from 18.4m₂/g to 124m₂/g. The best equation for describing the above data is the modified Langmuir-Freundlich one, denoted in the paper by k-LF equation.     

Electrochemical determination of acidity level and dissociation of formic acid/water mixtures as solvent

The autoprotolysis constant K_HS of formic acid/water mixtures as solvent has been calculated from acid-base potentiometric titration curves. A correlation of the acidity scale pK_HS of each medium versus pure water has been implemented owing to the Strehlow R⁰(H⁺) electrochemical redox function. The results show that formic acid/water mixtures are much more dissociated than pure water; such media are sufficiently dissociated to allow electrochemical measures without addition of an electrolyte. It has also been shown that for a same H⁺ concentration the activity of protons increases with formic acid concentration. For more than 80 wt.% of formic acid the acidity is sufficiently increased to locate the whole acidity scale pK_HS in the super acid medium of the generalized acidity scale pHH₂O.     

Unraveling the spatial distribution of the acidity of HZSM-5 zeolite on the level of crystal grains

Here we developed a new method to quantitatively characterize the spatial distribution of the Brønsted acidity of HZSM-5 zeolite on the crystal grains level indirectly. The Brønsted acid sites of HZSM-5 zeolite completely covered or blocked by previous coke deposition were released gradually from the outer surface to the center of the crystal grains via shrinking core mode isothermal oxidation with high temperature and low oxygen concentration. The spatial distribution of the coke was obtained based on the one-dimensional position coordinate L_rp through building and solving an enhanced shrinking core model. Then the released acidity characterized by n-propylamine temperature-programmed decomposition was correlated to the specific position of L_rp. The results show that the acid density is roughly homogenous while the acid strength is heterogeneous within the crystal grains. From the outer surface to the center of the crystal grains, the strength of the Brønsted acid sites increase gradually.     

Synthesis and properties of multicomponent copper-containing chalcogenide films prepared by the method of deposition from solution

Multicomponent copper-containing chalcogenide CuI-AsI₃-As₂Se₃ and CuI-SbI₃-As₂Se₃ films have been prepared by the method of deposition from solutions of chalcogenide glasses in n-butylamine and electrical conductivity of films has been studied. The local environment of atoms in multicomponent copper-containing CuI-PbI₂-As₂Se₃ and CuI-SbI₃-PbI₂-As₂Se₃ films has been studied by the method of Mössbauer spectroscopy (NGR) on ¹²¹Sb and ¹²⁹I isotopes.     

Hydroisomerization of n-hexadecane over Brønsted acid site tailored Pt/ZSM-12

Hydroisomerization of n-hexadecane is performed over ZSM-12 framework having tailored Brønsted acidity to investigate the effect in terms of product selectivity and yield. For this purpose, pure phase of ZSM-12 (bulk molar ratio Si/Al ~ 60) has been synthesized using TEABr as a structure directing agent. The framework Brønsted acidity is tailored with group II elements (M) viz. Ca, Ba and Mg, by means of ion-exchange method. The samples so prepared have been characterized for phase purity, textural parameters, morphology by employing powder X-ray diffraction, nitrogen adsorption–desorption isotherm measurement at 77 K, and scanning electron microscopy technique, respectively. Similarly, % metal exchange is estimated using inductively coupled plasma technique. The quantification of Brønsted acidity for H⁺–M⁺⁺–ZSM-12 samples has been estimated by means of ammonia temperature programmed desorption (NH₃-TPD) and Fourier transform infrared spectroscopy of ammonia (NH₃-FTIR). The well characterized H⁺–M⁺⁺–ZSM-12 samples were loaded with Platinum (Pt, 0.5 wt%) and subjected to hydroisomerization of n-hexadecane using an up-flow fixed bed reactor to verify the effect of process parameters like temperature and WHSV. Pt/H⁺–Ba²⁺–ZSM-12 with tailored Brønsted acidity in the range of about 25 % demonstrated the optimum performance among all the catalysts with an increased isomer selectivity and yield (89.2 and 80.3 %, respectively) by about 4 wt% at a conversion level of about 90 % compared to Pt/H⁺–ZSM-12 framework at 568 K. Such enhancement in isomer selectivity and yield is found to be significant from commercial application point of view. Based on the obtained trend, the potential benefits of implementation of Pt/H⁺–Ba²⁺–ZSM-12 (bulk molar ratio Si/Al ~ 60) framework for cold flow property improvement of ‘bio-ATF’ have been envisaged.