Beyhan Erdem

Synthesis, characterization and catalytic behavior of functionalized mesoporous SBA-15 with various organo-silanes

Mesoporous silica SBA-15 has been synthesized and functionalized by one-step synthesis method to widen their various application possibilities. In this study, phenyltrimethoxysilane (PTMS), 3-mercaptopropyltrimethoxysilane (MPTMS) and trimethoxypropylsilane (TMPS) were used as silane precursors for the functionalization, and after treated with HCl solution, their catalytic activities were evaluated in the lactic acid-methanol esterification. The presence of anchoring of functional groups on SBA-15 was proved by XRD, FT-IR, BET surface area and pore size distributions. Good catalytic activity was observed especially for SBA-15-SO(3)H-MPTMS, and the catalytic activity order was determined as follows: SBA-15-SO(3)H-MPTMS>SBA-15-TMPS>SBA-15-PTMS, which is directly associated with the surface area, pore size and pore volume. As compared with homogeneous catalyst, SBA-15-SO(3)H-MPTMS heterogeneous catalyst shows remarkable performance, such as separation, recovery and reusability.

High-surface-area SBA-15–SO3H with enhanced catalytic activity by the addition of poly(ethylene glycol)

The influence of poly(ethylene glycol) (PEG) and synthesis temperature in the synthesis of SBA-15–SO3H was investigated to evaluate the catalytic activity in the esterification of propionic acid with methanol. The catalysts were characterized by means of surface and structure analyses; X-ray diffraction, FT-IR, scanning electron microscopy, Thermo-gravimetric and N2 adsorption/desorption techniques. It was found that, by the addition of PEG, the surface area and porosity of SBA-15–SO3H increased, while the structure and size of mesopores remained unchanged. Nitrogen sorption measurements indicate that PEG introduces additional pores into the pore walls of SBA-15–SO3H. Thus, a simple way of improving the porosity of mesoporous SBA-15–SO3H was presented that could enhance transport of substrates through the porous system and allow the generation of stable mesoporous replicas, important for catalytic applications and also beneficial for replication and nanocasting purposes.

Effect of calcination temperature on the structural and magnetic properties of Ni/SBA-15 nanocomposite

The effect of calcination temperature on the structural and magnetic properties of Ni/SBA-15 nanocomposite prepared by reductant-impregnation method was studied using SBA-15 mesoporous silica as support. The structure, morphology and magnetic properties of the samples were characterized using X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectrometry, N2 adsorption/desorption (BET and BJH), vibrating sample magnetometer, and FT-IR. Characterization results showed the presence of crystalline phases characteristics of the Ni and/or NiO, and that the structural characteristics of the support were maintained after the impregnation of nickel ions followed by calcinations. Calcination process helps in crystallization and formation of the desired phase such as well crystalline NiO and Ni nano-particles. Moreover, this heat resulted in significant effects on different properties of the products such as the crystallite size, homogeneity, particle distribution, porosity, surface area and the sintering process. Magnetic measurements suggested that the magnetic properties in nanocomposites is probably the sum of two contributions: superparamagnetic and ferromagnetic one depending on the calcination temperature. Calcination at high temperatures affects both of the structural and magnetic properties of Ni/SBA-15. Because the location of the Ni particles depends on the pore size of the support, the uniformity of particle size was related to the interaction between the Ni particles and support.

Determination of Steric Effect on the Esterification of Different Alcohols with Propanoic Acid over Cation-exchange Resin Catalyst Dowex 50Wx4

Abstract This paper describes the application of LFER in the form of Taft correlation to understand the mechanism of the esterification of propanoic acid with different alcohols over heterogeneous catalyst, Dowex 50Wx4. The rate constant (k1) in the rate equation decreases with change of alcohols in the order methanol, ethanol, n-propyl, n-butyl, n-pentyl, iso-butyl, iso-propyl and sec-butyl (2-buthanol). The reaction of propanoic acid with alcohols fits the Taft equation, log k1/kCH3 = 1.0061 Es - 0.0012, which implies that the steric effect of the substituent governs that reaction and the mechanism is similar between the different alcohols. The experimental results were modelled according to a simple second-order model. It was found that the equilibrium constant of this reaction does not depend on the structure of the organic alcohols, and has for 333 K the value 4.04.

Heterogeneous Catalysed Esterification of Propionic Acid with n-Amyl Alcohol over a Microporous Cation-exchange Resin Dowex 50Wx4

Abstract Kinetics of heterogeneous catalysed esterification of propionic acid with n-amyl alcohol was studied with a microporous cation-exchange resin catalyst, Dowex 50Wx4, in a stirred batch reactor to synthesise amyl propionate. Effects of various parameters such as speed of agitation, catalyst loading, and reaction temperature on reaction rate were investigated. The equilibrium conversion of propionic acid increased with in catalyst loading and reaction temperature. Stirrer speed had virtually no effect on the reaction rate under the experimental conditions. The apparent activation energy was found to be 43.167 kJmol−1 for the formation of amyl propionate and the equilibrium constant, which is independent of temperature ranging from 318 to 348 K, was found to be 4.05. It was also observed that the initial reaction rate decreased with water concentrations and increased with that of acid and increased with that of alcohol linearly. The reaction was found to occur between an adsorbed acid molecule and a molecule of alcohol in the bulk and it was concluded that the reaction mechanism can be represented by Eley-Rideal model.

B–SBA-15–SO3H: a versatile mesoporous catalyst

Novel approach was developed towards the synthesis of heterogeneous mesoporous B–SBA-15–SO3H acid catalysts. That is: B–SBA-15 materials were hydrothermally synthesized by using three different boron sources (boric acid, trisiopropylborate and potassium borohydride) and then post-synthetically functionalized with sulfonic acid to test their catalytic activity for the esterification of propionic acid with methanol. Mesoporous and amorphous character of the materials as well as the incorporation of the boron into the framework were verified by XRD, N2-adsorption/desorption, ICP–OES, SEM and FT-IR techniques. All of the boron incorporated acid catalysts showed better activity than pure SBA-15–SO3H for methyl propionate synthesis. Combining the advantageous of hydrothermal synthesis and post functionalization, the obtained B–SBA-15–SO3H catalysts should present versatile catalytic properties in terms of both catalytic activity and reusability. Boron incorporation and post functionalization encourage the structural configuration, since the grafted catalytically active groups may experience similar environments and be isolated from each other.

Sulfonic acid functionalized poly(ethylene glycol dimethacrylate-1-vinyl-1,2,4-triazole) as a high-performance solid acid catalyst for the esterification of lactic acid with methanol

Sulfonic acid functionalized poly(ethylene glycol dimethacrylate-1-vinyl-1,2,4-triazole), poly(EGDMA-VTAZ-SO(3)H), is evaluated in the esterification of lactic acid with methanol. From nitrogen physisorption data, high surface area (220 m(2)/g) and type IV isotherm are obtained. Conversion measurements indicate a stronger interaction of poly(EGDMA-VTAZ-20%SO(3)H) with water molecules than that occurring in poly(EGDMA-VTAZ-10%SO(3)H). Hence, the higher catalytic activity of poly(EGDMA-VTAZ-10%SO(3)H) is related to the more hydrophobic microenvironment of -SO(3)H sites, which reduces the acid site deactivation associated with adsorption of water generated during the reaction. Moreover, apparent activation energy is found to be 48.02 kJ mol(-1), which can be comparable with the literature values.

Volumetric, Chromatographic, Refractometric Studies on the Esterification of Methanol with Acetic Acid in the Presence of Cation-Exchange Resins

Summary Esterification of methyl alcohol with acetic acid catalysed by commercially available polymeric ion-exchange resins Amberlyst-15, Dowex 50W and Amberlite IR-120 was carried out in the temperature ranging between 323–338K. Mesh sizes and divinylbenzene contents had virtually no effect on the rate the data of which were correlated with a second-order homogeneous reaction. The samples were analysed with gas chromatography, refractometry and volumetry. The reproducibilities were the order of ±2.89%, ±5.07% and the order of ±6.58% respectively for the volumetric, chromatographic and refractometric methods.

MAGNETIC MESOPOROUS SILICA NANOCOMPOSITES PREPARED WITH DIFFERENT SIZED Fe3O4: STRUCTURAL AND MAGNETIC PROPERTIES, CATALYTIC EFFECTS

The magnetically separable mesoporous silica nanocomposites were successfully prepared through a one-pot method including the co-condensation of tetraethoxysilane (TEOS) as silica precursor and 3-mercaptopropyl trimethoxysilane (MPTMS) as functionalizing agent accompanied with hydrogen peroxide for oxidation of mercapto groups and triblock copolymers as structure directing agent in the presence of ferromagnetic and superparamagnetic Fe 3 O 4 nanoparticles. By incorporating the superparamagnetic (near zero coercivity) Fe 3 O 4 nanoparticles to the mesoporous silica (SBA-15) and functionalizing with sulfonic acid groups instead of ferromagnetic Fe 3 O 4 nanoparticles, we developed versatile nanocomposite having superior properties with respect to magnetism, catalysis and porosity. Reducing the particle size of Fe 3 O 4 from the ferromagnetic regime to the superparamagnetic regime, the pore closure could be eliminated because of the more open pore as well as saving magnetic properties.

Magnetic Vinylphenyl Boronic Acid Microparticles for Surface Catalytic Performance in Esterification of Propionic Acid with Methanol

Magnetic vinylphenyl boronic acid microparticles, poly(ethylene glycol dimethacrylate-vinylphenyl boronic acid) [m-poly(EGDMA-VPBA)], produced by suspension polymerization, was found to be efficient solid acid catalyst for the esterification of methanol and propionic acid. Characterization techniques such as FT-IR, Elemental analyses, ICP-AES, ESR, SEM and N 2 sorption showed that both of Fe 3 O 4 and H 2 SO 4 are bonded to the polymer successfully. Esterification was studied for different molar percentages of H 2 SO 4 at temperature range of 50-70 o C. The apparent activation energy was found to be 27.7 kj.mol -1 for 10% H 2 SO 4 doped m-poly(EGDMA-VPBA). Combining of strong acid H 2 SO 4 with m-poly(EGDMA-VPBA), leads to materials with different functional properties. In addition, H 2 SO 4 species could be introduced into the structure as acid centers, therefore this micro-dimensional catalyst has potential candidate for applications in the catalytic esterifications such as propionic acid with methanol.