Cr- and Ga-Modified ZSM-5 Catalyst for the Production of Renewable BTX from Bioethanol.

Light aromatics (benzene, toluene, and xylene, collectively known as BTX) are essential commodity chemicals in the petrochemical industry. The present study examines the aromatization of bioethanol with Cr- and Ga-modified ZSM-5. Both Cr and Ga were incorporated by the ion-exchange method. Cr-modified ZSM-5 outperforms the Ga-modified ZSM-5 and H-ZSM-5 catalysts. Cr-H-ZSM-5 almost doubled the carbon yield of aromatics compared to H-ZSM-5 at an optimum reaction temperature of 450 °C. Cr-H-ZSM-5 produced aromatics with a yield of ~40 %. The effect of dilution in feed on BTX production is also studied. Cr-H-ZSM-5 was found to be more active than H-ZSM-5. Complete ethanol conversion was obtained with both pure and dilute bioethanol. The Bronsted-Lewis acid (BLA) pair formed after metal incorporation is responsible for dehydrogenation followed by aromatization, leading to increased aromatic production.

DFT Study on the Stability and the Acid Strength of Brønsted Acid Sites in Zeolite ß.

Acid sites are studied computationally for zeolite ß. Different deprotonated and protonated models are used. The issue of difference in the stability of acid sites is addressed. Separate and paired acid sites are created, and their stability and acidity are estimated. The sites in the 6-membered rings have a favorable position; however, the study does not exclude the diversity of sites in other positions. The zeolite module and model chemistry have an influence on the computational results. The influence of the mutual arrangement of two acid sites in a single model is studied. Hydrogen bonding influences the stability and acidity in this case. Four and six acid sites are created that possess hydrogen bonding in the same model. The distance and mutual orientation of the sites affect their stability. Thus, the dipole-dipole interactions, structure deformations, and inductive effect all play their roles in the chemistry of the acid sites. Both thermodynamics and chemical kinetics of the zeolite can influence Al locations in zeolites, and their influence should be concerted according to the linear relation of the free energies.

Benchmarking semiempirical and DFT methods for the interaction of thiophene and diethyl sulfide molecules with a Ti(OH)4(H2O) cluster.

Semiempirical methods pm6 and pm7 as well as density functional theory functionals exchange LSDA, exchange-correlation PW91 and PBE, hybrid B3LYP1 and PBE0 were compared for energy and geometry of thiophene, diethyl sulfide (DES) molecules and their binding to a frozen Ti(OH)4(H2O) complex having one coordinatively unsaturated Ti5C site representing small fragment of TiO2 anatase (001) surface. PBE0/6-31G(d) with DFT-D3 dispersion correction was the best method for description of thiophene and DES molecules geometries as comparison with experimental data demonstrated. Semiempirical methods pm6 and pm7 resulted in only three of four possible binding configurations of thiophene with the Ti(OH)4(H2O) complex while pm7 described correctly the enthalpy and all configurations of DES binding with the Ti(OH)4(H2O) complex. SBKJC pseudopotential and LSDA with and without dispersion correction produced flawed results for many configurations. PBE0 and PBE with and without dispersion correction and PW91 with 6-31G(d) basis set systematically produced dependable results for thiophene and DES binding to the Ti(OH)4(H2O) complex. PBE0-D3/6-31G(d), B3LYP1-D3/6-31G(d), and PBE-D3/6-31G(d) gave best match of binding energy for thiophene while PBE0/6-31G(d) gave best match of DES binding energy as comparison with CCSD(T) energy demonstrated. On the basis of the superior results obtained with PBE0/6-31G(d), it is the recommended method for modeling of adsorption over TiO2 surfaces. Such a conclusion is in agreement with recent literature.

Parametric studies of diethyl phosphoramidate photocatalytic decomposition over TiO2.

The present study is focused on influences of parameters including pH, temperature, TiO(2) catalyst concentration, and reactant concentration on the rate of photocatalytic diethyl phosphoramidate (DEPA) decomposition with Hombikat UV 100 (HK) and Degussa P25 (P25) TiO(2). Total mineralization of DEPA is observed. Two regimes of pH, namely in acid and near-neutral environments were found where maximum total carbon (TC) decomposition was observed. The electrostatic effects on adsorption over the TiO(2) surface explain the above phenomena. The maximum rate is observed for P25 at DEPA concentration 1.3 mM whereas the rate grows continuously with DEPA concentration rise for HK. The temperature dependence of TC decomposition rate in the range of 15-63°C with both HK and P25 follows the Arrhenius equation. The activation energy for total carbon decomposition with HK and P25 are 29.5±1.0 and 24.3±3.1 kJ/mol, respectively. The decomposition rate of DEPA is larger over P25 than over HK. The rate over P25 increases faster than that with HK for each unit of the titania added when the TiO(2) concentration is less than 375 mg/l. The higher light absorption and particles aggregation of P25 are responsible for the decrease of reaction rate we observed at catalyst concentration above a certain level. In contrast, the rate over HK increases monotonically with the concentration of the photocatalyst used.

Synthesis of ordered large pore SBA-15 spherical particles for adsorption of biomolecules.

The synthesis of spherical particles of mesoporous silicates (SBA-15) with mesopore diameter upto 127A, and particle diameter of 4-10 microm has been achieved. The SBA-15 spheres were obtained using pluronics P123 (EO20PO70EO20) as a surfactant coupled with cetyltrimethylammonium bromide (CTAB) as a co-surfactant. Ethanol played a very important role in the formation of silica spheres, as it delays the reaction rate of the SBA-15 synthesis. A wide range of pore diameters (28-127 A) of these spherical SBA-15 materials with large surface area >700 m2/g has been synthesized. The effects of temperature, ethanol, CTAB and swelling agent have also been studied. The SBA-15 samples were characterized using small angle X-ray scattering (SAXS), N2 adsorption-desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The spherical SBA-15 after mechanical grinding was used for protein adsorption, and adsorption capacity was compared with that of conventional fibrous SBA-15. The spherical SBA-15 particles with pore diameter of 127 A have a very high capacity of 700 mg/g for lysozyme at pH 7.

Visible light photocatalysis with platinized rutile TiO2 for aqueous organic oxidation.

Platinized rutile TiO2 samples containing varying concentrations of Pt were synthesized using Kemira (KE, BET surface area 50 m2/g, from Finland), and Toto HT0270 (HT, BET surface area 2.9 m2/g, from Japan) as the starting materials by solution mixing followed by sintering the precursors. Photocatalytic activities were established for phenol oxidation under visible light (wavelength >400 nm). Our results show optimal performance for 8 wt % platinized KE (8 wt % Pt/KE) and (1/2) wt % platinized HT rutile samples. The specific roles of O2 and visible light were examined using the 8 wt % Pt/KE sample in either N2 gas ambient or no illumination. Separately, 8 wt % platinized SiO2 was tested to compare its performance with that of platinized rutile TiO2. Several other chemicals containing different functional groups (formic acid, salicylic acid, 4-chlorophenol, 2,4,6-trichlorophenol, diethyl phosphoramidate) were selected for photooxidation tests with (1/2) wt % platinized HT rutile. X-ray diffraction reveals Pt metal clusters segregating on the surface of rutile TiO2 particles with increasing Pt weight percent. The Pt cluster surface area broadly increases, while the effective optical band gap steadily decreases with platinization of the rutile samples. These results suggest that Pt clusters on the surface of rutile TiO2 particles serve to mediate electron transfer from rutile to O2, thus facilitating photooxidation of organic chemicals.

Visible light Cr(VI) reduction and organic chemical oxidation by TiO2 photocatalysis.

Here we report the simultaneous Cr(VI) reduction and 4-chlorophenol (4-CP) oxidation in water under visible light (wavelength > 400 nm) using commercial Degussa P25 TiO2. This remarkable observation was attributed to a synergistic effect among TiO2, Cr(VI), and 4-CP. It is well known that TiO2 alone cannot remove either 4-CP or Cr(VI) efficiently under visible light. Moreover, the interaction between Cr(VI) and 4-CP is minimal if not negligible. However, we found that the combination of TiO2, Cr(VI), and 4-CP together can enable efficient Cr(VI) reduction and 4-CP oxidation under visible light. The specific roles of the three ingredients in the synergistic system were studied parametrically. It was found that optimal concentrations of Cr(VI) and TiO2 exist for the Cr(VI) reduction and 4-CP oxidation. Cr(VI) was compared experimentally with other metals such as Cu(ll), Fe(lll), Mn(IV), Ce(IV), and V(V). Among all these metal ions, only Cr(VI) promotes the photocatalytic oxidation of 4-CP. The amount of 4-CP removed was directly related to the initial concentration of Cr(VI). The system was also tested with four other chemicals (aniline, salicylic acid, formic acid, and diethyl phosphoramidate). We found that the same phenomenon occurred for organics containing acid and/or phenolic groups. Cr(VI) was reduced at the same time as the organic chemicals being oxidized during photoreaction under visible light. The synergistic effect was also found with pure anatase TiO2 and rutile TiO2. This study demonstrates a possible economical way for environmental cleanup under visible light.

Photocatalytic oxidation of VX simulant 2-(butylamino)ethanethiol.

Photocatalytic oxidation of 2-(butylamino)ethanethiol (BAET) was undertaken in aqueous suspension of TiO2 Hombikat UV 100 and Degussa P25 under different initial reaction conditions in order to determine the best parameters for the fastest mineralization of the substrate. BAET is considered to be a simulant for the VX chemical warfare agent. The application of ultrasound had only a small positive effect on the BAET photocatalytic degradation. The highest mineralization rate of 0.433 mg/(l min) was found in unbuffered TiO2 Degussa P25 suspension with initial pH value of about 9.4, TiO2 concentration 500 mg/l and the initial BAET concentration 1000 mg/l. Decreasing of the initial solution pH to 6.1 or below stops the mineralization of BAET while increasing of pH to about 11 drastically changed the degradation profile. At this initial pH, the first 100 min of reaction led to only oxidation of sulfur moiety and organic intermediates accumulated in the solution. Thereafter, mineralization of the products started. The main detected volatile product was butyl aldehyde and the main polar one was 2-(butylamino) acetic acid. In the case of TiO2 Hombikat UV 100, conversion of TOC at initial pH 11 exceeded that at initial pH 9.1. For Degussa P25, the starting pH 9.4 was the best for TOC conversion. The results can be used for treatment of water from pollutants with aliphatic nitrogen and sulfur atoms.

Enhanced photocatalytic degradation of dimethyl methylphosphonate in the presence of low-frequency ultrasound.

Mechanistic aspects of the role of 20 kHz ultrasonication in photocatalytic oxidation of dimethyl methylphosphonate (DMMP), a simulant for nerve chemical warfare agents, were studied in a batch reactor. We found that DMMP did not undergo mineralization under low frequency (20 kHz) ultrasonic irradiation. The increase of the rate of DMMP photocatalytic mineralization in the presence of ultrasound was not due to deagglomeration of TiO2, but was associated with enhanced mass transport of reagents. The same intermediate non-volatile products were detected in photocatalytic and sonophotocatalytic degradation. A kinetic model involving all stable intermediate species detected was introduced. Apparent rate constants of all stages of DMMP mineralization increase under sonication. A reaction route of DMMP mineralization without the formation of intermediate products appeared under ultrasonication. Such behaviour was attributed to enabling mass transport of DMMP into micropores and to the surface of TiO2.

Photocatalytic degradation of 2-phenethyl-2-chloroethyl sulfide in liquid and gas phases.

This work explores the ability of photocatalysis to decontaminate water and air from chemical warfare agent mustard using its simulant 2-phenethyl 2-chloroethyl sulfide (PECES). PECES like mustard slowly dissolves in water with hydrolysis, forming 2-phenethyl 2-hydroxyethyl sulfide (PEHES). Irradiation of TiO2 suspension containing PECES with the unfiltered light of a mercury lamp (lambda > or = 254 nm) decomposed all PECES mostly via photolysis. Reaction under filtered light (lambda > 300 nm) proceeds mainly photocatalytically and requires longer time. Sulfur from starting PECES is completely transformed into sulfuric acid at the end of the reaction. Detected volatile, nonvolatile, surface products, and the suggested scheme of degradation are reported. The main volatile products are styrene and benzaldehyde, nonvolatile--hydroxylated PEHES, surface--2-phenethyl disulfide. Photolysis of PECES produced the same set of volatile products as photocatalysis. Photocatalytic degradation of gaseous PECES in air results in its mineralization but is accompanied by TiO2 deactivation. The highest rate of mineralization with minimum deactivation was observed at about room temperature and a water concentration of 27,500 ppm. No gaseous products except CO2 were detected. The main extracted surface product was styrene. It was concluded that PECES photocatalytic degradation proceeds mainly via C-S bond cleavage and further oxidation of the products. Hydrolysis of the C-S bond was detected only in gas-phase photocatalytic degradation. The quantum efficiency of gas-phase degradation (0.28%) was much higher than that of liquid-phase degradation (0.008%). The results demonstrate the ability of photocatalysis to decontaminate an aqueous and especially an air environment

Low-Temperature Selective Catalytic Reduction (SCR) of NO with NH3 by Using Mn, Cr, and Cu Oxides Supported on Hombikat TiO2.

A Highly active, time stable, and water resistant, Hombikat TiO2 supported Mn catalyst has been developed for the selective reduction of NO by NH3 [Eq. (1)]. The analogous Cu and Cr supported catalysts also provide 100 % N2 selectivity at ≤120°C. Lewis acidity, redox properties, and a high surface metal oxide concentration are essential for good catalytic performance.