Showing papers in "Journal of Molecular Catalysis A-chemical in 2011"

Efficient decomposition of organic compounds and reaction mechanism with BiOI photocatalyst under visible light irradiation

Abstract: BiOI photocatalyst was synthesized by a precipitation–filtration process and consequent hydrothermal treatment. The as-prepared BiOI exhibits efficient photocatalytic activity on the decomposition of widely used model pollutants, methyl orange (MO) and phenol, under visible light irradiation. Even under the illumination of a compact fluorescent lamp, the obtained BiOI also exhibits high photocatalytic activity. The possible photodegradation mechanism was studied by the examination of active species HO , h vb + , or O 2 − anions through adding scavengers such as tert -butanol ( t -BuOH), I − anion, bromate anion and benzoquinone (BQ). The results show that photodegradation of MO molecules is attributed to the action of h vb + via direct hole oxidation process and the oxidation action of the generated O 2 − radicals. Dissolved oxygen play an important role in photocatalytic reaction, which could trap the photogenerated electrons to reduce the recombination of h vb + and e cb − and also function as a precursor of main oxidant O 2 − . Hydroxyl radical was verified to be inappreciable for the decomposition of MO.

p-Nitrophenol degradation by a heterogeneous Fenton-like reaction on nano-magnetite: Process optimization, kinetics, and degradation pathways

Abstract: Heterogeneous Fenton-like reactions on nano-magnetite (Fe 3 O 4 ) were investigated for the degradation of p-Nitrophenol (p-NP). A four factor central composite design (CCD) coupled with response surface methodology (RSM) was applied to evaluate and optimize the important variables. A significant quadratic model ( P -value R 2 = 0.9442) was derived using analysis of variance (ANOVA), which was adequate to perform the process variables optimization. Optimum conditions were determined to be 1.5 g L −1 Fe 3 O 4 , 620 mM H 2 O 2 , pH 7.0 and 25–45 mg L −1 p-NP. More than 90% of p-NP was experimentally degraded after 10 h of reaction time under the optimum conditions, which agreed well with the model predictions. The results demonstrated that the degradation of p-NP was due to the attack of hydroxyl radicals ( OH) generated by the surface-catalyzed decomposition of hydrogen peroxide on the nano-Fe 3 O 4 , i.e. heterogeneous Fenton-like reactions. Possible mechanisms of p-NP degradation in this system were proposed, based on intermediates identified by LC–MS and GC–MS and included benzoquinone, hydroquinone, 1,2,4-trihydroxybenzene and p-nitrocatechol. The kinetic analysis implied that the generation rate of OH ( V OH ) was increased along with the degradation of p-NP. This was attributed to the formation of acidic products, which decreased the solution pH and enhanced the decomposition of absorbed hydrogen peroxide via a radical producing pathway on the nano-Fe 3 O 4 surface.

Metal nanoparticles with high catalytic activity in degradation of methyl orange: An electron relay effect

Abstract: Gold, silver and platinum nanoparticles have been synthesized following a green approach by reducing the corresponding salt using tannic acid as reducing agent at room temperature in aqueous medium. The reaction is instantaneous and the average diameter of the particles formed is around 10 nm in all the three cases as measured by TEM. These nanoparticles have been used as a catalyst for the degradation of methyl orange in the presence of sodium borohydride (NaBH4). Silver nanoparticles have a drastic catalytic effect as compared to gold or platinum nanoparticles on the degradation of methyl orange in the presence of sodium borohydride. From the kinetic data it is concluded that the rate constant follows the order: kAg nanoparticles ≫ kAu nanoparticles > kPt nanoparticles ≫ kuncatalyzed reaction. The high catalytic effect of silver nanoparticles has been attributed to its low value of work function as compared to Au and Pt. The uncatalyzed reaction does not show any decrease in the absorbance value within the given experimental time due to the large kinetic barrier, i.e. high activation energy. Decrease in absorbance value for uncatalyzed reaction is observed after nearly 48 h that too at a very high concentration of reducing agent, thereby indicating that reaction is extremely slow and reduction of methyl orange is thermodynamically feasible.

Reduced graphene oxide–TiO2 nanocomposite with high photocatalystic activity for the degradation of rhodamine B

Abstract: Reduced graphene oxide–TiO 2 (RGO–TiO 2 ) nanocomposites have been successfully synthesized through a facile hydrothermal reaction with minor modification using graphene oxide (GO) and commercial P25 as starting materials in an ethanol–water solvent, followed by calcining temperature at 400 °C for 2 h in Ar. These nanocomposites prepared with different ratios of graphene oxide (GO) were characterized by BET surface area, X-ray diffraction (XRD), Raman spectroscopy, UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Transmission Electron Microscopy (TEM) and ultraviolet–visible (UV–vis) absorption spectroscopy. The RGO–TiO 2 nanocomposites exhibited much higher photocatalytic activity than bare P25 for the degradation of rhodamine B (Rh.B) in an aqueous solution. The improved photocatalytic activities may be attributed to increased adsorbability for Rh.B molecular, light absorption levels in visible region and charge transfer rate in the presence of a two-dimensional graphene network.

The influence of La doping on the catalytic behavior of Cu/ZrO2 for methanol synthesis from CO2 hydrogenation

Abstract: A series of Cu/ZrO2 catalysts with various La loadings for methanol synthesis from CO2 hydrogenation were prepared by a urea–nitrate combustion method. The catalysts were characterized with N2 adsorption, XRD, reactive N2O adsorption, XPS, TPR, H2-TPD and CO2-TPD techniques, and tested for methanol synthesis from CO2 hydrogenation. With increasing La loading, the Cu surface area increases first and then decreases, whereas the amount of basic site over catalysts increases continuously. The results of catalytic test reveal that a linear relationship exists between the conversion of CO2 and the Cu surface area. Moreover, it is found for the first time that the selectivity to methanol is related to the distribution of basic site on the catalyst surface. The presence of La favors the production of methanol, and the optimum catalytic activity is obtained when the amount of La doping is 5% of the total amount of Cu2+ and Zr4+.

Catalytic activity of first row transition metal oxides in the conversion of p-nitrophenol to p-aminophenol

Abstract: The catalytic activities of first row transition metal oxides in the conversion of p-nitrophenol to p-aminophenol were investigated The conversion was carried out at room temperature (30° C) using aqueous sodium borohydride The reduction process was accelerated by CuO, Co 3 O 4 , Fe 2 O 3 and NiO The oxides such as TiO 2 , V 2 O 5 , Cr 2 O 3 , MnO 2 and ZnO were found to be inactive towards the conversion of the nitrophenol The active catalysts were analyzed before and after the reaction by XRD and the reduction reaction was monitored and confirmed by UV–vis, HPLC, 1 H NMR and FT-IR techniques

Enhanced sunlight photocatalytic performance of Sn-doped ZnO for Methylene Blue degradation

Abstract: In the present study, nano-structured ZnO and Sn-doped ZnO photocatalysts with high sunlight photocatalytic activity were successfully synthesized through the decomposition of zinc acetate and glucose by microwave heating. The prepared ZnO and Sn-doped ZnO photocatalyst were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectrum (PL), UV–vis absorption spectrum (UV–vis), N 2 adsorption and UV–vis diffuse reflectance spectra (DRS). The results showed that the doping greatly changed the microstructure, morphology and optical properties of ZnO, which may contribute to the enhancement of photocatalytic activity. The sunlight photocatalytic activity of the prepared pure ZnO and Sn-doped ZnO photocatalyst was investigated by the degradation of Methylene Blue (MB) solution under sunlight irradiation. Compared with pure ZnO, 13% higher decolorization rate and 29–52% higher mineralization efficiency were obtained by the Sn-doped ZnO. The results indicated that Sn-doped ZnO had a higher photocatalytic activity and Sn dopant greatly increased the photocatalytic activity of ZnO.

Byproducts and pathways of toluene destruction via plasma-catalysis

Abstract: To improve toluene removal efficiency and reduce byproducts, a TiO2/γ-Al2O3/nickel foam catalyst was combined in and after the non-thermal plasma (NTP), leading to a plasma-driven catalysis (PDC) and plasma-assisted catalysis (PAC) process, respectively. The addition of catalysis could significantly enhance the toluene destruction with an increased CO2 selectivity and carbon balance while the byproducts, such as O3 and organic compounds, were dramatically reduced. The PAC exhibited the highest efficiency in toluene destruction due to the formation of more atomic oxygen and hydroxyl radicals from O3 catalytic decomposition. The pathways of toluene destruction by NTP and plasma-catalysis were proposed according to the identified intermediates.

Synthesis of highly stable CoFe2O4 nanoparticles and their use as magnetically separable catalyst for Knoevenagel reaction in aqueous medium

Abstract: Synthesis of spinel cobalt ferrite magnetic nanoparticles (MNPs) with average sizes in the range 40–50 nm has been achieved using a combined sonochemical and co-precipitation technique in aqueous medium without any surfactant or organic capping agent. The nanoparticules form stable dispersions in aqueous or alcoholic medium. The uncapped nanoparticles were utilized directly as a reusable catalyst for Knoevenagel reaction in aqueous ethanol (1:3). Compartmentation and recovery of the catalyst from reaction medium was done with the aid of an external magnet. High yield of corresponding Knoevenagel products were obtained within a very short time in presence of just 5 mol% of the catalyst at 50 °C.

Aqueous-phase hydrodeoxygenation of carboxylic acids to alcohols or alkanes over supported Ru catalysts

Abstract: For the aqueous-phase hydrodeoxygenation (APHDO) of carboxylic acids over the Ru/C, Ru/ZrO2 and Ru/Al2O3 catalysts, the C O hydrogenation and C–C bond cleavage reactions were studied by collecting reaction kinetics data and the measures of DRIFTS. The C–C bond cleavage was improved at high temperature and with high metal loadings. The acidic supports in combination with Ru metal can favor the C O hydrogenation of carboxyl. The C–C bond cleavage derived from the decarbonylation of acyl on the catalyst was studied by the measures of DRIFTS. The APHDO and DRIFTS results demonstrated that the C–C bond cleavage was favored in the order of Ru/C > Ru/ZrO2 > Ru/Al2O3. The catalysts were characterized by multiple methods (H2-TPR, NH3-TPD, CO-FTIR and DRIFTS of propanoic acid). It is concluded that the effect of support on the reaction routes may be attributed to these factors of catalysts, i.e., surface acidity, metal–support interaction and electronic state of Ru species.

A study of furfural decarbonylation on K-doped Pd/Al2O3 catalysts

Abstract: Vapor-phase decarbonylation of furfural to furan was performed on K-doped Pd/Al2O3 catalysts in a fixed-bed reactor. A series of K-doped catalysts were prepared by impregnation method with various potassium salt precursors and different potassium content. The catalyst evaluation results revealed that the doping of K not only promoted the furfural decarbonylation, but also suppressed the hydrogenation side reaction. Among the investigated catalysts, Pd–K2CO3/Al2O3 (K% = 8 wt.%) presented the best performance and achieved the furan yields up to 99.5% at 260 °C. The selectivity of 2-methylfuran would approach zero at high K content (K% > 4 wt.%). Furthermore, the catalysts were characterized by BET, SEM, ICP, H2-TPR, H2-TPD, H2-chemisorption, CO-FTIR, furfural-TPSR, and furfural-FTIR experiments. It was shown that the dopant phase had a remarkable effect on the precursor Pd2+ and the reduced Pd metal particles. Furfural-TPSR and furfural-FTIR exhibited that K-doped catalysts enhanced the furfural adsorption and promoted the decarbonylation reaction, which was due to the different adsorption mode and intensity of furfural on K-doped and undoped samples. Besides, the decrease of C–O adsorption of furfural (η2(C,O)-furfural) by K doping is the main reason for suppressing the furfural hydrogenation.

An efficient and one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles catalyzed via solid acid nano-catalyst

Abstract: A simple highly versatile and efficient synthesis of 2,4,5-trisubstituted imidazoles is achieved by three component cyclocondensation of 1,2-dicarbonyl compounds, aldehydes and NH4OAc, as ammonia source using clays, zeolite, nano-crystalline sulfated zirconia (SZ) as catalyst in ethanol at moderate temperature Moreover, the utility of this protocol was further explored conveniently for the one-pot, four component synthesis of 1,2,4,5-tetrasubstituted imidazoles in high yields, short reaction times and milder conditions, easy work-up and purification of products by non-chromatographic methods The catalysts can be recovered for the subsequent reactions and reused without any appreciable loss of their efficiency

Acetalization of carbonyl compounds catalyzed by acidic ionic liquid immobilized on silica gel

Abstract: Imidazolium-silica heterogeneous catalyst (SG-[(CH 2 ) 3 SO 3 H-HIM]HSO 4 ) was prepared by immobilization of acidic ionic liquid 1-(propyl-3-sulfonate) imidazolium hydrosulfate ([(CH 2 ) 3 SO 3 H-HIM]HSO 4 ) on silica–gel using tetraethoxysilane (TEOS) as silica source in this study. The properties of the samples were characterized by FT-IR, SEM and TG/DSC. The results suggested that [(CH 2 ) 3 SO 3 H-HIM]HSO 4 had been successfully immobilized on the surface of silica–gel and the immobilized ionic liquid catalyst SG-[(CH 2 ) 3 SO 3 H-HIM]HSO 4 had good thermal stability. The original smooth surface of silica–gel was covered with [(CH 2 ) 3 SO 3 H-HIM]HSO 4 and a rough surface of SG-[(CH 2 ) 3 SO 3 H-HIM]HSO 4 was formed, but the size of particles had no obvious change. Moreover, SG-[(CH 2 ) 3 SO 3 H-HIM]HSO 4 exhibited high catalytic activity for a series of acetalization and could be recovered easily. After reused for 10 times in the synthesis of benzaldehyde ethanediol acetal, the catalyst could still give satisfactory catalytic activity.

Direct conversion and NMR observation of cellulose to glucose and 5-hydroxymethylfurfural (HMF) catalyzed by the acidic ionic liquids

Abstract: Direct conversion and NMR observation of cellulose to glucose and 5-hydroxymethylfurfural (HMF) catalyzed by the acidic ionic liquids

Characterization of coupled NiO/TiO2 photocatalyst for the photocatalytic reduction of Cr(VI) in aqueous solution

Abstract: NiO/TiO 2 coupled photocatalysts were fabricated by sol–gel process in this study. The coupled catalyst exhibited higher response of surface photovoltage than pure TiO 2 indicating that the recombination of photogenerated electron–hole pairs was retarded by the inner electric field caused by p–n junction region. Photocatalytic reduction of hexavalent chromium in aqueous solution was studied using these NiO/TiO 2 coupled photocatalysts prepared with various NiO loadings and calcined temperatures. The coupling of NiO strongly affects the performance of coupled photocatalysts, including the retard of phase transformation of TiO 2 , the decrement of particle size and the enhancement of separation efficiency of photogenerated electron–hole pairs. The addition of ethanol as a sacrificial agent significantly increased the photocatalytic activity of hexavalent chromium reduction using these NiO/TiO 2 coupled photocatalysts.

Cellulose sulfuric acid catalyzed multicomponent reaction for efficient synthesis of 1,4-dihydropyridines via unsymmetrical Hantzsch reaction in aqueous media

Abstract: C5-unsubstituted 1,4-dihydropyridines were obtained in good to excellent yields by proceeding through a simple, mild and efficient procedure utilizing cellulose sulfuric acid (CSA) as a catalyst. The reaction work-up is very simple and catalyst can be easily separated from reaction mixture and reused several times in subsequent reactions. © 2010 Elsevier B.V. All rights reserved.

Experimental and kinetic modeling studies on the biphasic hydrogenation of levulinic acid to gamma-valerolactone using a homogeneous water-soluble Ru-(TPPTS) catalyst

Abstract: gamma-Valerolactone (GVL) is considered a very attractive biomass derived platform chemical. This paper describes the application of biphasic homogeneous catalysis for the hydrogenation of levulinic acid (LA) to GVL using molecular hydrogen. A water soluble Ru-catalyst made in situ from RuCl3 center dot 3H(2)O and sodium-tris(m-sulfonatophenyl)phosphine (Na3TPPTS) in dichloromethane/water biphasic mixtures was used. The hydrogenations were performed at mild conditions in a batch hydrogenation reactor and essentially quantitative GVL yields were obtained at 45 bar, 90 degrees C and 80 min reaction time (1 mol% catalyst). The effects of process variables like LA concentration, hydrogen pressure, temperature, pH and the catalyst to substrate ratio on the LA conversion and GVL yield were determined. The experimental data were quantified by kinetic modeling and it was shown that the reaction is first order in LA. Catalyst recycle experiments show that the recycled catalyst is still active, though the activity is lower than for the first run (81% LA conversion for first run versus 55% for recycle experiment). (C) 2011 Elsevier B.V. All rights reserved.

Sulfamic acid heterogenized on hydroxyapatite-encapsulated γ-Fe2O3 nanoparticles as a magnetic green interphase catalyst

Abstract: A highly efficient and green system is introduced to chemical synthesis. Magnetic nanoparticle-supported propylsulfamic acid deposited onto hydroxyapatite [γ-Fe2O3-HAp-(CH2)3-NHSO3H] synthesized as a unique heterogeneous acid catalyst of excellent activity and recyclable for at least 10 reaction runs without significant loss of activity. The facile recovery of the catalyst is carried out by applying an external magnet device. It is both “green” and efficient. The catalyst was fully characterized by spectroscopic, magnetic, adsorptive and thermal techniques (TEM, SEM, FTIR, TGA, XRD, BET, elemental analysis (CHNOS) and VSM).

Significant enhancement of the visible photocatalytic degradation performances of γ-Bi2MoO6 nanoplate by graphene hybridization

Abstract: After hybridized with graphene, the photocatalytic performances of γ-Bi 2 MoO 6 were increased about 2–4 times. The photocatalytic activity enhancements were dependent on the amount of graphene and it was found that the optimal hybridized amount of graphene was about 1.0 wt%, which was close to the monolayer disperse of graphene on γ-Bi 2 MoO 6 surface. The mechanism on the enhancement of photocatalytic activity is attributed to the higher separation efficiency of photo-induced electrons and holes, which come from the electronic interaction between γ-Bi 2 MoO 6 and graphene. The electronic interaction was verified by the photoelectrochemical measurements.

Activity of chromium oxide deposited on different silica supports in the dehydrogenation of propane with CO2 – A comparative study

Abstract: Four series of chromium oxide-based catalysts containing 0.7–7 wt.% of Cr were prepared by incipient wetness impregnation of conventional amorphous silicas (SiO2-p; SBET = 261 m2 g−1 and SiO2-a; SBET = 477 m2 g−1) and mesoporous siliceous sieves with cubic (SBA-1; SBET = 1181 m2 g−1) and hexagonal (SBA-15; SBET = 750 m2 g−1) pore structure. The combination of different techniques (chemical analysis with Bunsen–Rupp method, ICP, XRD, UV–vis DRS and quantitative/qualitative H2-TPR) in the characterization of the calcined catalysts revealed that the chromium species anchored on the surface of mesoporous supports show structural properties similar to those on the conventional silicas, but a higher dispersion of chromium species could be achieved using mesoporous supports due to their much higher SBET. This reflects in higher content of Cr6+ species stabilized in comparison with conventional silicas. The Cr6+ species was found to be crucial for high activity in the dehydrogenation of propane with CO2 (DHP–CO2). The rate of propene formation increases almost proportionally to the concentration of Cr6+ species in the calcined catalysts. In situ UV–vis DRS measurements during DHP–CO2 process evidences that the Cr6+ species are reduced rapidly (in a stream of CO2 + propane) to Cr3+ and Cr2+ species indicating that the Cr6+ species are rather precursor than active sites, similar as in nonoxidative dehydrogenation of propane (DHP). The reduction of Cr6+ species generates dispersed Cr3+ and Cr2+ sites at the beginning of the DHP–CO2 that participate in nonoxidative pathway of propene formation. In the presence of CO2, Cr3+ and Cr2+ sites, may participate additionally in an alternative oxidative pathway of propene formation and in a consumption of hydrogen produced in the DHP by reverse water-gas shift reaction.

Synthesis and applications of novel imidazole and benzimidazole based sulfonic acid group functionalized Brönsted acidic ionic liquid catalysts

Abstract: In this study, a variety of imidazole/benzimidazole based sulfonic acid group functionalized Bronsted acidic ionic liquids (BAILs) were synthesized. Catalytic activities of BAILs were assessed using multi-component coupling reactions. Catalytic activities of BAILs were high when compared with those of solid acid catalysts such as H-ZSM-5, H-BETA, and sulfonic acid functionalized SBA-15 catalysts. The Hammett acidity order determined from UV–visible spectroscopy of BAILs is consistent with their activity order observed in acid-catalyzed reactions. Theoretical studies demonstrate that the hydrogen bonding plays a key role in tuning the acidity of BAILs. Recycling experiments suggest that these novel BAILs can be reused without significant loss in catalytic activity. Novel BAILs offer several attractive features such as low cost, high catalytic activity, and recyclability.

Highly efficient mesoporous base catalyzed Knoevenagel condensation of different aromatic aldehydes with malononitrile and subsequent noncatalytic Diels–Alder reactions

Abstract: Knoevenagel condensation and [4 + 2] cycloaddition reactions are very important class of reactions in synthetic organic chemistry. We have prepared amino-functionalized mesoporous silica through co-condensation of 3-aminopropyltriethoxy-silane (APTES) along with tetraethylorthosilicate (TEOS) in presence of a cationic surfactant CTAB hydrothermally. Small angle powder XRD, HR TEM, FE SEM, N 2 sorption and FT IR spectroscopic tools are used to characterize the 2D-hexagonal mesostructure and to identify the presence of surface –NH 2 groups in amino-functionalized mesoporous silica material. Our experimental results reveal that amino-functionalized mesoporous silica is an efficient base catalyst for the Knoevenagel condensation of different aromatic aldehydes with malononitrile to α,β-unsaturated dicyanides under very mild reaction condition and in the presence of ethanol solvent. The isolated α,β-unsaturated dicyanides obtained through the condensation reaction further react very efficiently with cyclopentadiene to form a series of Diels–Alder cycloaddition products in excellent yields in the absence of any catalyst.

Oxidative desulfurization of fuel catalyzed by metal-based surfactant-type ionic liquids

Abstract: a b s t r a c t Metal-based surfactant-type ionic liquids (MSILs) methyltri-n-octylammonium peroxomolybdate ((CH3)N(n-C8H17)3)2Mo2O11 and peroxotungstate ((CH3)N(n-C8H17)3)2W2O11 were synthesized and characterized, which have been extended to new families and generations of functionalized ILs. Here the MSILs were applied in removal of sulfur-containing compounds with H2O2 and possessed of the character of reaction-induced self-separation catalysis. The effects of H2O2/DBT (molar ratio), oil/MSIL (mass ratio) and the agitation rate were studied to estimate the optimal conditions for the desulfuriza- tion system catalyzed by ((CH3)N(n-C8H17)3)2Mo2O11. The quaternary ammonium cation could transfer the catalytic active species to the aromatic sulfur compounds under the reaction conditions and higher oxidative reaction rate was achieved. Kinetic experiments revealed that the oxidative desulfurization reaction was in accordance with pseudo-first-order kinetics and the reaction rate constant and half- life were calculated. Furthermore, the oxidation reactivity of different substrates was in the following order: DBT > 4,6-DMDBT > BT. The MSIL ((CH3)N(n-C8H17)3)2Mo2O11 could be recycled for 10-times with a slight decrease in activity. ((CH3)N(n-C8H17)3)2Mo2O11 was also an efficient catalyst to remove the sulfur- containing compound in different solvents. Multiple reactions of oxidation desulfurization process were feasible and effective for prehydrotreated gasoline.

Effect of acid treatment on the surface of multiwalled carbon nanotubes prepared from Fe–Co supported on CaCO3: Correlation with Fischer–Tropsch catalyst activity

Abstract: Carbon nanotubes (CNTs) were obtained through the catalytic decomposition of C 2 H 2 at 700 °C over Fe–Co supported on CaCO 3 and confirmed by TEM to be composed of multiwalled carbon nanotubes. The CNTs were refluxed in 30% and 55% HNO 3 for 2 and 6 h in order to remove impurities and introduce oxygen surface groups. This rendered the CNTs less hydrophobic. The morphology, microstructure, surface area, pore volume and surface chemical properties of the acid treated CNTs were analysed by TEM, N 2 physisorption, TGA, FTIR, Raman spectroscopy and zeta potential measurements. The surface roughness, together with the degree of surface functionalization correlated with the harshness (time and concentration) of the acid treatment. Fischer–Tropsch synthesis studies (275 °C, 8 bar) were performed on all the Fe loaded (10%)/CNT catalysts and activity studies revealed that the more severe the acid treatment the higher the activity of the catalysts.

Band gap and photocatalytic properties of Ti-substituted hydroxyapatite: Comparison with anatase-TiO2

Abstract: We experimentally and theoretically evaluated the effect of Ti substitution in hydroxyapatite (HAP) on the band gap. For samples, we used 10 mol% of Ti-substituted HAP (Ti-HAP) and normal HAP powder, synthesized by the co-precipitation method, with typical anatase-TiO 2 photocatalytic powder. The Ti-HAP and HAP powder showed a hexagonal apatite structure by X-ray diffraction. The experimentally obtained optical band gap energies of Ti-HAP, HAP and TiO 2 powder measured by diffuse reflectance spectroscopy were 3.65 eV, >6 eV, and 3.27 eV, respectively. Depending on total energy evaluation and structure optimization by the first principle density functional calculation, the Ti position in the apatite structure was predicted to be at columnar, Ca(I), site with a Ca(I) site deficiency. In Ti-HAP, Ti 3d orbital hybridized with O 2p orbital and formed an internal state in the HAP band gap. It caused absorption-edge lowering of Ti-HAP. Based on the band structure, we proposed a photocatalytic model of Ti-HAP as a two-step excitation model. Moreover, acetaldehyde gas decomposition of Ti-HAP by UV with VIS irradiation appeared to be enhanced compared with when UV irradiation alone was used. We confirmed the validity of the proposed model.

XPS studies on the Cu(I,II)–polyampholyte heterogeneous catalyst: An insight into its structure and mechanism

Abstract: A complex between Cu(II) and a polyampholyte synthesized from methacrylic acid, imidazole and ethyleneglycol diglycidyl ether was used as a heterogeneous catalyst for hydrogen peroxide activation and degradation of chlorophenols. The material was characterized by XPS and by measurements of the zeta potential. The isoelectric point determined experimentally was 8.0, differing from that obtained by titration (6.4), which indicated the presence of fixed positive charges in disubstituted imidazole units. The XPS N 1 s signal for pyridinic nitrogen in the imidazole units, and the O 1 s signals from the carbonyl, hydroxyl and carboxylate groups shifted to higher binding energies after copper uptake, proving the chemical nature of Cu(II) adsorption on the polyampholyte. The XPS spectrum of the complex showed a Cu 2 p 3/2 peak at 934.7 eV and the characteristic shake-up satellite of Cu(II). When the complex was used as a heterogeneous catalyst for H 2 O 2 activation, Cu(I) was proved to be a probable intermediate species and contributed to elucidate the mechanism. The Auger CuLMM spectrum supports the presence of Cu(I) with a kinetic energy value of 914.8 eV. The complex was applied in the oxidation of chlorinated phenols in aqueous solution at room temperature without any loss in efficiency.

Zn,Al hydrotalcites calcined at different temperatures: Preparation, characterization and photocatalytic activity in gas–solid regime

Abstract: Layered double hydroxides (LDH) containing zinc and aluminium within the brucite-like layers and carbonate as the interlayer anion have been used as precursors for the preparation of mixed metal oxides by calcination. Zinc oxide and the ZnAl 2 O 4 spinel were formed with different degree of crystallinity depending of two parameters, i.e., the Zn 2+ /Al 3+ molar ratio and the calcination temperature (500–800 °C) of the LDH precursor. A pure spinel phase was obtained to remove ZnO upon a basic post-treatment in NaOH solution of the samples calcined at 800 °C. All the samples were tested for the photodegradation of 2-propanol in gas–solid regime. All the samples resulted active as heterogeneous photocatalysts. The photocatalytic activity increased by increasing the Zn 2+ /Al 3+ molar ratio and the calcination temperature of the solids.

Synthesis, characterization and photocatalytic activity of AgBr/H2WO4 composite photocatalyst

Abstract: A new composite photocatalyst AgBr/H 2 WO 4 was prepared by loading H 2 WO 4 on AgBr substrate via deposition–precipitation method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy (DRS). Photocatalytic degradation of methyl orange (MO) and rhodamine B (RhB) was carried out to evaluate the photocatalytic activity of AgBr/H 2 WO 4 under visible-light irradiation ( λ > 420 nm). The photocatalytic results show that the AgBr/H 2 WO 4 composite could degrade MO and RhB efficiently and had much higher photocatalytic activity than AgBr or H 2 WO 4 . X-ray photoelectron spectroscopy (XPS) suggests that AgBr/H 2 WO 4 transformed to be Ag/AgBr/H 2 WO 4 system while remained good photocatalytic activity after 5 times of cycle experiments. In addition, the quenching effect was examined in the photocatalytic reaction process of MO and RhB, respectively. Active h + , Br 0 and the resulting O 2 − played the major roles for the dye degradation while OH was verified to be insignificant. The high photocatalytic activity and good stability are closely related to the efficient electron–hole pairs separation derived from the matching band potentials between AgBr and H 2 WO 4 , as well as the surface plasmon resonance of Ag nanoparticles formed on AgBr particles during the photocatalytic reaction process.

Kinetics and mechanism for oxidative desulfurization of fuels catalyzed by peroxo-molybdenum amino acid complexes in water-immiscible ionic liquids

Abstract: Three peroxo-molybdenum amino acid complexes (PMAACs) were synthesized and characterized. Their catalytic activities for oxidation of dibenzothiophene (DBT) in extraction and catalytic oxidative desulfurization system (ECODS) were evaluated using different ionic liquids. Comparing with simple catalyst Na 2 MoO 4 ·2H 2 O in ECODS, PMAACs were effective wide-ranging catalysts and exhibited high desulfurization efficiency not only in water-miscible IL [bmim]BF 4 but also in water-immiscible [bmim]PF 6 , [omim]BF 4 and [omim]PF 6 . Especially 4,6-dimethyldibenzothiophene (4,6-DMDBT), the most difficult refractory compound in HDS, could be completely removed under optimal conditions. The reaction mechanism and desulfurization differences between using Na 2 MoO 4 ·2H 2 O catalyst and PMAACs in water-miscible and water-immiscible ionic liquids have been investigated and explained by UV–vis. Kinetic parameters of the oxidation of DBT, BT and 4,6-DMDBT were studied.

Effect of operational key parameters on photocatalytic degradation of phenol using nano nickel oxide synthesized by sol–gel method

Abstract: Photocatalytic oxidation of phenol was studied using nickel oxide (NiO) nanoparticles synthesized by sol–gel method. The morphology of synthesized catalyst was studied by using field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The average particle size was 6.5 nm as estimated by Scherrer formula and was confirmed by HRTEM and FESEM analysis. The photocatalytic activity of NiO was evaluated by degradation of phenol under irradiation of unique source like UV laser. The influence of various key parameters such as amount of photocatalyst, initial solution pH and the initial concentration of phenol was investigated. The operational parameters show the expected influence regarding the efficiency of the photocatalytic degradation process. The photocatalytic degradation efficiency of NiO was found to decrease with the increase in the initial solution pH. The degradation of the phenol followed a pseudo first-order rate kinetics with k = 5.7 × 10 −2 min −1 .