Authors:Chunyan Liu, Zhengfeng Shao, Zihui Xiao and Changhai Liang
Activated carbon supported Pt, Pd, and Pt–Pd catalysts have been successfully prepared by incipient wet impregnation with a hydrochloric solution of PdCl2 and PtCl4. Hydrodeoxygenation of benzofuran was used as a probe reaction to investigate their catalytic properties. The activated carbon supported Pt–Pd catalyst was confirmed to form Pt–Pd alloy by X-ray diffraction. All the catalysts were active in the hydrodeoxygenation of benzofuran. Pd catalyst did not only give higher hydrogenation activity, but also showed faster deoxygenation rate than the Pt catalyst. The Pt–Pd catalyst with the mole ratio of Pd/Pt = 4 showed the highest catalytic activity among all of the catalysts. 2-Ethylcyclohexanone, which was not observed over the sulfide catalysts, was detected as a new oxygen-containing intermediate in the hydrodeoxygenation of benzofuran over the activated carbon supported Pt, Pd, and Pt–Pd catalysts. A ketone/enol isomerization reaction route is proposed to happen over the activated carbon supported noble metal Pt, Pd, and Pt–Pd catalysts.
The oxidation of thioanisole to its sulfone with hydrogen peroxide (H2O2) in the presence of acetic acid and Amberlyst 15 was investigated and found to be a simple and effective method. Oxidation experiments in the absence of acetic acid or Amberlyst 15 confirmed the essentiality of these components for the complete oxidation of thioanisole to its sulfone with H2O2. In the two-step oxidation process of sulfide, in the oxidation of sulfide to sulfoxide, H2O2 plays a major role, whereas in the oxidation of sulfoxide to sulfone, peracetic acid formed with H2O2 in the presence of acetic acid and Amberlyst 15 plays a major role. Sulfone formation increased with an increase in H2O2, temperature and Amberlyst 15 and decreased with acetic acid. However, with a very low amount of acetic acid, sulfone formation decreased due to water in H2O2 and released in the reaction. Reutilization of Amberlyst 15 for six cycles resulted in a 6.8 % decrease in sulfone yield and 3.4 % decrease in oxygenation. Dialkyl, dibenzyl, diphenyl, alkylaryl, arylbenzyl, alkylbenzyl sulfides are completely oxidized with this oxidation system to their corresponding sulfones. The reactivity of sulfides is in the order dialkyl > dibenzyl > diphenyl sulfides, which is in line with their order of nucleophilicity.
Authors:Prince Osei Bonsu, Xiaomeng Lü, Jimin Xie, Deli Jiang, Min Chen and Xiaojun Wei
Brookite titania nanomaterials modified with gold nanoparticles (NPs) Au–TiO2 were prepared in this research. The photocatalytic activity of the prepared composite was assessed by the photodegradation of organic pollutants. Rhodamine blue was used as a model organic pollutant. The study determined the optimum loading ratio of Au/Ti, which will result in the best photodegradation efficiency. Also, the photocatalytic activity of gold loaded brookite titania nanomaterials was ascertained under visible light. The hydrothermal method was used to prepare brookite titania whiles, gold NPs were loaded on its surface by consecutive ion adsorption and photoreduction. The results revealed that the sample Au–TiO2 (Au/Ti = 2 % molar ratio) had the best photocatalytic degradation efficiency of 100 % after 2 h of irradiation under visible light and was also higher than commercial P25.
Authors:Mohamed Triki, Anton Dafinov, Jordi Llorca and Francisco Medina
Continuous catalytic wet air oxidation was investigated as a suitable treatment of p-hydroxybenzoic acid chosen as a phenolic compound typically found in olive mill wastewater. The reaction was conducted in a continuous reactor at 140 or 150 °C and 50 bar of air using ruthenium catalysts supported by aerogel mixed oxides (Ru/CeO2–Al2O3, Ru/CeO2–TiO2). The influence of the Ru precursor and the nature of the support were studied. The results show that supported ruthenium catalysts were active to oxidize p-hydroxybenzoic acid and that the catalytic activity is very stable.
Authors:N. Batalha, L. Pinard, S. Morisset, J. L. Lemberton, Y. Pouilloux, M. Guisnet, F. Lemos and F. R. Ribeiro
n-Hexadecane hydroisomerization at 220 °C and 30 bar was used as a model reaction for comparing the catalytic performances of a Pt/HBEA sample whose zeolite crystals were germinated on an α alumina surface with those of 1Pt/HZM-22 catalyst well-known for its high isodewaxing selectivity. Similar values of selectivity to isomers were obtained with both catalysts even at high conversions. Moreover, despite its low zeolite content (13 wt%), the Pt/HBEA Al2O3 catalyst had the important advantage to be 4.6 times more active.
A silica-supported Pd nanoparticle catalyst was prepared by refluxing a Pd(II) precursor in alkaline 2-propanol; it consisted of metallic Pd nanoparticles (ca. 2–8 nm) dispersed in the silica-gel pores. This catalyst exhibited much more efficient dechlorination of p-chloroanisole and 1,1-bis(4-chlorophenyl)-2,2-dichloroethylene (DDE) in an alkaline 2-propanol/methanol (99:1 v/v) solution than a conventional Pd/C catalyst.
Authors:Bing Xue, Kai Jia, Jie Xu, Na Liu, Ping Liu, Chongfu Xu and Yongxin Li
An efficient and novel method to prepare KNO3/NaY solid base catalysts was developed. High selectivity for phenetole along with high conversion of phenol was obtained in the vapor phase O-alkylation of phenol with diethyl carbonate over KNO3 modified NaY zeolite. Experimental results showed that a large number of basic sites on KNO3/NaY were generated mainly during catalytic evaluation, which was responsible for the outstanding catalytic performance. Furthermore, the excess KNO3 loadings might lead to the blockage of the pores in the NaY zeolite and decrease the catalytic activity.
Authors:Andrés Pena, Santiago Veiga, Mariángeles Sapelli, Natalia Martínez, Victoria Márquez, Eduardo Dellacassa and Juan Bussi
Liquid-phase oxidation of limonene was performed with molecular oxygen as the sole oxidizing agent under non-solvent conditions. The oxidation took place under atmospheric pressure and temperatures between 70 and 90 °C in the presence of three different nickel–aluminium hydrotalcites. The final limonene conversion at 80 °C and 6 h of reaction time was comprised between 40 and 50 %. Several oxygenated limonene derivatives such as endo- and exo-epoxides, carveol and carvone represent 45–60 % of the whole amount of products. In the absence of a catalyst, a higher initial content of peroxides in limonene lead to a higher reaction rate with no significant changes in product selectivities. Thermal decomposition of limonene peroxides took place as the initiation path of an autooxidation mechanism leading to the different products. The catalyst played an important role in the initial paths involving activation of both reactants as well as in the decomposition of limonene peroxide to form radicals.
The effects of Ru precursor, Ru loading and calcination conditions on the properties and catalytic activities of ruthenium catalysts supported on activated carbon (Ru/AC) to remove bromate ion in water were investigated. A series of Ru/AC catalysts were prepared by the impregnation method and were characterized. From the examination of X-ray photoelectron spectra, RuO2 was deemed as the major active component on the Ru/AC catalysts to reduce bromate ion. The Ru precursors have significant effect on the activities of Ru/AC catalysts, due mainly to that (NH4)2RuCl6 was prone to generate metallic Ru, while RuCl3·3H2O could form RuO2. It was also found that calcination of Ru/AC in pure nitrogen gas favored the RuO2 formation compared with those calcined in vacuum and 1.5 vol.% H2/N2. The maximum bromate reduction efficiency around 95 % can be successfully achieved by Ru/AC prepared when the Ru loading, calcination temperature and time were 0.1 wt.%, 900 °C, and 3 h, in order, in a pure N2 atmosphere. From the characterization of catalysts, it was found that the excellent performance of Ru/AC would benefit from two aspects: one is that the structure and texture of the support carbon was strengthened during the calcination process, and the other is that an even distribution of RuO2 particles was obtained.
Carbothermally reduced and nitrided Ta2O5 powder at varying temperature (680–760 °C) in flowing NH3 facilitated both nitrogen doping and the formation of the traces of TaON and Ta3N5 to a greater degree than the simply NH3-heat-treated Ta2O5. It demonstrated an enhanced visible-light absorption, an enhanced surface adsorption of rhodamine B molecules in the dark, and subsequently an improved visible-light photocatalytic activity to decompose rhodamine B in aqueous solution (via mainly surface photosensitization), as compared to the simply nitrided counterpart in NH3 atmosphere. The carbothermal reduction followed by the NH3-treatment (nitridation) is proven to be an efficient way to improve the degree of nitridation at a given temperature. The product of such process can be an efficient visible light photocatalyst.
Cu(II) tetradentate Schiff base complexes of N,N′-(bis(pyridin-2-yl)formylidene)ethane-1,2-diamine (pfed), N,N′-(bis(pyridin-2-yl)formylidene)propane-1,3-diamine (pfpd), N,N′-(bis(pyridin-2-yl)formylidene)benzene-1,2-diamine (pfbd), N,N′-(bis(pyridin-2-yl)formylidene)cycohexane-1,2-diamine (pfcd) and N,N′-(bis(pyridin-2yl)formylidene)meso-stilben-1,2-diamine (pfmd) were synthesized, characterized and immobilized on sodium montmorillonite. These catalysts were characterized by X-ray diffraction, IR spectroscopy, diffuse reflectance spectra (DRS) and atomic absorption spectroscopy. The IR and DRS data of the heterogeneous catalysts show that copper(II) complexes were physically entrapped within sodium montmorillonite. The basal spacing (d001) of heterogeneous catalysts indicates that Cu(II) Schiff base complexes were fixed in the axial direction into the interlayer of montmorillonite. All new heterogeneous catalysts show excellent catalytic activity in the epoxidation of cyclooctene using tert-butylhydroperoxide in acetonitrile. The supported [Cu(pfed)] exhibited a moderate 74 % selectivity for epoxidation with 76 % conversion. The catalytic activity and selectivity of heterogeneous catalysts have not changed after three times of reusing.
Authors:Pingle Liu, Haike Zhang, Sihua Liu, Zhengjie Yao, Fang Hao, Kuiyi You and He'an Luo
A new composite catalytic system of Pd/C, 2,4,6-trichloro-[1,3,5]-triazine and N,N-dimethylformamide was investigated in nitrocyclohexane hydrogenation to ∊-caprolactam. The Pd/C catalyst was prepared by the incipient impregnation method and characterized by BET, N2 adsorption–desorption, XRD, TEM and H2 chemisorption. The results indicate that 2,4,6-trichloro-[1,3,5]-triazine plays a key role in one step synthesis of ∊-caprolactam from nitrocyclohexane hydrogenation. Besides ∊-caprolactam, the products include cyclohexanone oxime, cyclohexamine, cyclohexanone and cyclohexanol. A possible mechanism for nitrocyclohexane hydrogenation in 2,4,6-trichloro-[1,3,5]-triazine and N,N-dimethylformamide complex was proposed.
Authors:A. Martínez-de la Cruz, D. B. Hernández-Uresti, Leticia M. Torres-Martínez and S. W. Lee
PbMoO4 oxide with scheelite structure was obtained by hydrothermal synthesis in the absence of additives. The material was characterized by X-ray powder diffraction, scanning electron microscopy, diffuse reflectance spectroscopy, and adsorption–desorption N2 isotherms. The organic dyes rhodamine B (rhB), indigo carmine (IC), orange G (OG), and methyl orange (MO) were selected as molecules model to study its photocatalytic degradation over PbMoO4 oxide under UV irradiation. Total organic carbon analysis of samples irradiated revealed that mineralization of organic dyes by the action of PbMoO4 was feasible in 80 % (rhB), 69 % (IC), 71 % (MO), and 65 % (OG) after 96 h of UV irradiation.
Authors:Pathakaraimuthu Balakumar, Subramaniam Balakumar and Perumal Subramaniam
The electron transfer (ET) reaction between benzylthioacetic acid (BTAA) and tris(1,10-phenanthroline)iron(III) perchlorate resulted in the formation of benzylsulfinylacetic acid. The reaction is first order with respect to both BTAA and [Fe(phen)3]3+ and is retarded by hydrogen ion. The ET reaction is studied in 50 % aqueous methanol medium. The Marcus theory is successfully applied to the present redox system and this supports the operation of single electron transfer in the rate controlling step of the reaction.
Authors:Lida Hamidipour, Faezeh Farzaneh and Mehdi Ghandi
Fe3O4 nanoparticles were prepared and modified with (3-aminopropyl) trimethoxysilane (APTMS) followed by complexation with Co(acac)2. The prepared nanocatalyst, designated as Fe3O4@APTMS@Co(acac)2 was characterized by FTIR, XRD, SEM, and TEM techniques. It was found that Fe3O4@APTMS@Co(acac)2 successfully catalyzes the epoxidation of cyclooctene, styrene, cyxlohexene, trans-stilbene, and norbornene with O2 as an oxidant and isobutyraldehyde (RCHO) as a co-reductant with 48–100 % reactivity and 40–92 % selectivity.
Authors:Sachin Malwadkar, Parthasarathi Bera, M. S. Hegde and C. V. V. Satyanarayana
Preferential oxidation of CO (CO-PROX) was carried out over Ni supported on CeO2 prepared by the co-precipitation method. The influence of metal loadings (2.5, 5 and 10 wt.% Ni) and the reaction conditions such as reaction temperature and feed composition on CO oxidation and oxidation selectivity were evaluated by using dry reformate gas. No other reactions like CO or CO2 methanation, coking, reverse water gas shift (RWGS) reaction is observed in the temperature range of 100–200 °C on these catalysts. Hydrogen oxidation dominates over CO oxidation above the temperature of 200 °C. An increase in oxygen leads to an increase in CO conversion but a simultaneous decrease in the O2 selectivity. It has been noticed that 5 and 10 % Ni/CeO2 show better catalytic activity towards CO-PROX reaction. These catalysts were characterized by SBET, XRD, TEM, XPS and H2-TPR.
Authors:Susana Pinto-Castilla, Santiago Marrero, Yraida Díaz, Joaquín L. Brito, Pedro Silva and Paulino Betancourt
A novel synthesis route was designed to obtain highly active vanadium based catalysts. Three different activated carbons were used as supports (one of them being treated with ozone). The supported catalysts were characterized by XRD, TEM, XPS and EPR. These systems were tested in hydrotreating reactions (HDS, HDN and hydrogenation). The characterization results showed well dispersed vanadium nanoparticles. However, it was evidenced that during the synthesis process, a vanadium carbide phase was produced within vanadium oxides. Reactivity studies showed that the vanadium catalysts were slightly better for HDS and hydrogenation reactions than a commercial NiMoS catalyst, but that was not the case for HDN reactions. The reduction method proposed is potentially an excellent route to synthesize more active supported vanadium carbide catalysts than the conventional TPS method. Under reaction conditions, carbide and sulfide vanadium species coexist in the catalyst; vanadium carbide sites probably remain intimately mixed with the active vanadium sulfide sites.
In this work, a new approach was proposed to get glycerophosphocholine (GPC) from natural soybean lecithin catalyzed by the quaternary ammonium base resin made in our laboratory. The results showed that the resin has the potential for preparing GPC under mild conditions, and the catalyst could be easily separated and recycled with stable catalytic activity. The effects of different parameters on the rate of reaction verified that the transesterification was intrinsically kinetically controlled and there were no external and internal mass transfer resistance. The results showed that when the reaction was carried out with agitation speed of 675 rpm, reaction temperature of 50 °C, catalyst loading of 80 g L−1, the lecithin conversion was 98 % after 3.5 h. A kinetic model was developed and the experimental data fitted it well, and the mechanism of methanolysis of natural lecithin catalyzed by resin was proposed.
Authors:C. U. Aniz, P. P. Robinson, K. K. Abdul Rashid and T. D. Radhakrishnan Nair
The kinetics of the reduction of nickel, cobalt and copper ferrites was studied by the temperature programmed reduction method at different heating rates in hydrogen atmosphere. The activation energy values of the reduction processes were calculated using the non-isothermal isoconversional method according to the Kissinger-Akahira-Sunose equation and the dependence of apparent activation energy on the degree of conversion was determined. The carbon monoxide oxidation activities of all the three samples were determined at various temperatures up to 140 °C. An interesting correlation between the apparent activation energies for the reduction process was observed. The decreasing trend of activation energy on the ‘extent of conversion’ in all cases showed that the reduction is a multi-step process involving a reversible process followed by an irreversible step.
A fast, economic, and green synthesis of benzimidazole derivatives using iron oxide modified sepiolite (IMS) as a catalyst has been reported. IMS showed excellent catalytic properties and the reactions completed within 20–30 min to give products in high yield. The adsorption mechanism of formic acid on IMS was studied by infrared (IR) spectroscopy at temperature range 120–400 °C. Thermal desorption of pyridine was followed by IR and thermal analysis techniques to estimate the acidity of IMS. Lewis acid-bound pyridine bands at 1,618–1,631 and 1,443–1,445 cm−1 were observed even after IMS sample were heated above 400 °C.
Authors:C. Robert Dennis, Jannie C. Swarts and Dale W. Margerum
Protonation of copper(II)- and nickel(II) tetrapeptide complexes with bulky α-carbon substituents has been studied. The pKa-values for the second and terminal metal–N(peptide) bond formation have been determined spectrophotometrically. More than one deprotonated peptide nitrogen exists in a complex but the individual protonation steps for the different CuII–N(tetrapeptide) positions could not be accounted for by the variation of the hydrogen ion concentration in the same experiment, as the protonation of the different metal–N(tetrapeptide) positions takes place at different wavelengths. For the NiII-tetra-alanine complex, the proton transfer to the terminal and second deprotonated peptide nitrogens have been detected by varying the hydrogen ion at the same wavelength. The proton transfer to the terminal metal–N(tetrapeptide) of CuII- and NiII-tetrapeptide complexes show first order kinetics with respect to the hydrogen ion and the peptide complex concentration and proceed via an outside protonation pathway. The relatively high pKa values for the terminal deprotonated peptide nitrogen indicate the instability of this metal–N(peptide) bond due to strain in the chelate ring because of atom overcrowding of the bulky α-carbon substituents.
Authors:Oriana D'alessandro, Horacio J. Thomas and Jorge E. Sambeth
A series of Mn–Ce(M) solids (M = K or Na), with molar ratios 100–0, 50–50 and 0–100 were prepared by co-precipitation of manganese and cerium nitrate from NaOH or KOH solutions at pH = 11. In addition, part of the solids precipitated with NaOH were dried and impregnated with a Cu2+ salt. The solids were characterized by XRD, Specific Surface Area, XPS and EDS. The characterization analyses show the formation of Mn mixed oxides with different oxidation states (Mn3+, Mn4+), for samples without Ce or Mn–Ce(M) 50–50. In the latter solid and in the one where there is no Mn, the formation of CeO2 (fluorite type) was detected. The samples were tested in the phenol removal in water at 100 °C and at atmospheric pressure with the aim to analyze the adsorbed species in the first stage of the adsorption-oxidation mechanisms. The results indicate, on the one hand, that [MnOx] is the active species in the process and that the most active solids are those that present (i) a higher concentration of OI, (ii) a higher amount of Mn4+ ions. DRIFT spectroscopy showed a possible mechanism of phenol adsorption on two sites, in the first one by H interaction of OH (phenol) with an OH of the catalyst and in the second, by the formation of a phenolate species between an O (OH phenol) and Mnn+.
Authors:István Szalai, Krisztina Kurin-Csörgei and Miklós Orbán
The general model developed by Rábai for describing the dynamics of the two-substrate pH-oscillators was refined and shown that its appropriately formulated versions are suitable for the simulation of the dynamics both in the semi-batch and in the recently reported batch pH-oscillators as well.
Authors:Joanna Wiśniewska, Grzegorz Wrzeszcz, Stanisław Koter and Tomasz Ligor
The kinetics of the oxidation of imipramine and opipramol using peroxydisulfate salts in the presence of a large excess of dibenzoazepine derivative (TCA) in acidic sulfate media was studied using UV–vis spectroscopy. The reaction between imipramine and S2O82− proceeds via the formation of two intermediates: a free organic radical and a dimeric dication. Further reaction of the intermediate dimeric dication leads to a positively charged radical dimer as one final product. Simultaneously, two other substituent cleavage degradation processes occur, leading to two dimeric derivatives. The first product, the positively charged radical dimer, and the next main product, a radical dimer without one alkyl substituent, were identified by EPR measurements. The measured kinetic trace is not first order and revealed a sigmoid shape with a characteristic induction time. The rate constants were determined by numerical analysis based on ordinary differential equations (ODEs). The reaction between opipramol and S2O82− proceeds by a two consecutive reaction scheme. The kinetics of the first degradation step were studied independently of the slower degradation reactions. Linear dependences, with zero intercept, of the pseudo-first-order rate constants (kobs) on [TCA] were determined for the first degradation process of opipramol.
Authors:M. R. Granados-Uribe, F. J. Lona-Ramírez, C. Pérez-Pérez, J. Barajas-Fernández, V. Rico Ramírez and G. González-Alatorre
The nitrosation of 1,3-dialkylureas was carried out in the presence of carboxylic acids and halides in an aqueous perchloric medium. The aim of this work was to validate the proposed mechanism for the nitrosation of such substrates. In accordance with the rate limiting step of the proposed mechanism, the protonic transfer to the solvent, basic catalysis and an absence of catalysis by halides should be observed. The Br⊘nsted parameters were determined by basic general catalysis.
Authors:Xuan Tang, Yefei Nan, Fenglin Huang and Xunli Zhang
The oscillatory behavior of the reaction of partial oxidation of methane has been investigated over metallic nickel surfaces. It was found that the chemical compositions and the reaction temperature within the reactor exhibited regular oscillations over a range of reactor temperatures between 710 and 930 °C with different feed gas compositions at flow rate ratios (Ar/CH4/O2) ranging from 30:29:1 to 30:12:18 cm3 min−1. When the reactor temperature increased, the oscillation frequency increased showing indicative correlations, while the amplitude decreased with the rise in system temperature. Varying feed gas composition resulted in complex changes in oscillatory waveforms, frequencies, amplitudes, and product selectivities. The oscillation was attributed to the cyclic reduction and oxidation of the nickel surface under the reaction conditions.
Authors:María A. Sánchez, Vanina A. Mazzieri, Mario R. Sad and Carlos L. Pieck
The influence of the operating conditions and preparation methods of Ru–Sn–B/Al2O3 catalysts on the activity and selectivity for the hydrogenation of methyl oleate to oleyl alcohol was studied. It was found that catalysts prepared by incipient wetness (IW) are more active and selective than those prepared by co-impregnation. This better performance is possibly due to a lower level of residual chlorine. The experiences of hydrogenation of methyl oleate showed that activity increases as the reaction temperature increases while the selectivity to oleyl alcohol has a maximum value. This could be due to the higher activation energies for the hydrogenolysis of carboxymethyl groups than those found for C=C double bonds hydrogenation. The increase in operating pressure has a positive effect on the activity but it influences selectivity time patterns in a more complex way. Experiments carried out by varying methyl oleate/n-dodecane ratio show that the selectivity and conversion not depend on this parameter. A simple kinetic model is proposed.
Authors:Zhenwu Fu, Hui Wan, Xiaoshuang Hu, Qun Cui and Guofeng Guan
A carbon-based solid acid catalyst was prepared by incomplete carbonization of H3PO4-impregnated pulp fibers followed by sulfonation. XRD, FT-IR, BET, TGA, and acid density test were employed to characterize the structure and performance of the catalyst. Results showed that the catalyst was amorphous carbon composed of aromatic carbon sheets with –COOH, –OH and –SO3H groups. Previous impregnation with H3PO4 could promote porosity formation of the catalyst. The optimized carbonization temperature and time for the catalyst were 250 °C and 1.5 h. The –SO3H density and specific surface area for the catalyst prepared under the optimized conditions were 1.1 mmol g−1 and 118 m2 g−1, respectively. Compared to HZSM-5, Amberlyst-15 and previous reported carbon catalysts, the catalyst showed higher catalytic activity for transesterification of methyl acetate with n-butanol as hydrophobic reaction. The catalyst had good thermal stability, which could bear 200 °C without decomposition. The catalyst retained satisfactory catalytic activity for transesterification of methyl acetate after 8 reaction cycles.
Nanodimensional pores of metal-exchanged zeolite Y containing 5,10,15,20-tetra(4-methoxyphenyl)porphyrin have been prepared by the template “ship-in-a-bottle” method. This approach requires four pyrrole molecules and four 4-methoxy benzaldehyde molecules to diffuse into the pores of FeIII, MnIII and CoIII-exchanged zeolite Y. The host–guest nanocomposite materials have been applied to catalyze the epoxidation of (R)-(+)-limonene, using H2O2/ammonium acetate, at a defined temperature and atmospheric pressure. The encapsulated iron(III) complex is catalytically very efficient as compared to manganese(III) and cobalt(III) complexes for the partial epoxidation of (R)-(+)-limonene and is stable to be recycled without much deterioration. All catalytic systems have been characterized by UV/Vis diffuse reflectance spectroscopic, X-ray diffraction, BET, scanning electron microscopy and energy dispersive X-ray spectrometry analyses to confirm the immobilization of complexes.
Authors:Chun-Ni Fan, Cheng-Hua Xu, Chuan-Qi Liu, Zun-Yu Huang, Jian-Ying Liu and Zhi-Xiang Ye
TiO2–SiO2 catalysts for glycerol acetalization with acetone are synthesized by the sol–gel method and characterized by N2 adsorption–desorption, X-ray diffraction, NH3-temperature programmed desorption, Fourier transform infrared spectroscopy and ultraviolet–visible diffuse reflectance spectroscopy techniques in the present work. The effects of catalyst preparation and acetalization parameters such as reaction time, acetone/glycerol ratio, catalyst amount and reaction temperature on acetalization are investigated simultaneously. Pyridine adsorption results indicate that Ti–Si mixed oxides naturally only consist of Lewis acidic sites. The results of catalyst preparation and characterization show that Br⊘nsted acidic sites can be produced after Ti–Si mixed oxides adsorb water molecules, and TiO2–SiO2 (Si/Ti = 1) calcined at 550 °C exhibits the most total acidic density leading to the highest catalytic property in glycerol acetalization. The glycerol catalytic acetalization mainly occurs on the Br⊘nsted acidic sites. The effects of acetalization parameters indicate that the formation of the main product 5-membered ring ketal 2,2-dimethyl-1,3-dioxolane-4-yl methanol (about 90 %) is governed by kinetics. About 95 % glycerol conversion in acetalization is obtained under the optimum conditions.
Authors:Bijan Barghi, Moslem Fattahi and Farhad Khorasheh
The aim of this study was to develop an appropriate kinetic model for propane dehydrogenation (PDH) over an industrial Pt–Sn/γ-Al2O3 catalyst in the presence of small amounts of oxygenated compounds. Experimental data were obtained from a previous study where catalytic PDH was carried out in a laboratory scale reactor at atmospheric pressure in the temperature range of 575–620 °C in the presence of small amounts of water or methanol. The kinetics of the main dehydrogenation reaction was described and the effects of water and methanol on coke deposition and catalyst sintering were considered in a catalyst deactivation model to explain the observed optimum level in the amount of added oxygenated compounds. The model predictions were in good agreement with experimental data.
Authors:Shaoqin Peng, Ran An, Zhisheng Wu and Yuexiang Li
CdxZn1−xS and Ru3+ doped Ru(m)/Cd0.5Zn0.5S photocatalysts were prepared by a simple hydrothermal method, and characterized by X-ray diffraction, UV–Vis absorption spectroscopy and electrochemistry techniques. Their photoactivities were evaluated by hydrogen evolution from aqueous solution containing Na2S and Na2SO3 as a hole scavenger under visible light (λ ≥ 420 nm) irradiation. Ru3+ doping enhances the photocatalytic activity markedly. It was found that 0.10 mol% Ru3+ doped Cd0.5Zn0.5S photocatalyst showed the highest activity. The reason for the positive effects of Ru3+ was discussed.
Authors:M. Kompany-Zareh, H. Tavallali, N. Shakernasab, M. Khoshkam and E. Shamsdin
Digital image-based calibration was applied for the determination of iron(III), Fe3+, as a catalyst in the oxidation of indigo carmine (IC) using bromate ion (BrO3−). During the reaction, a colorless product was produced and there was an induction period (IP) before the color of the solution faded. The length of IP depended on the concentration of Fe3+. The color fading of reaction was recorded as a change of red, blue and green colors (%RBG). Kinetic profiles similar to what has been reported in a previous spectrophotometric study were obtained. Fe3+ was determined in the concentration range of 6–16 ppm at pH = 2 and 25 °C. The detection limit of Fe3+ was found to be 1.994 ppm, which is better in comparison with the previous work. Optimum concentrations of IC and BrO3− were obtained as 5.5 × 10−5 and 3 × 10−3 M, respectively, using a one-at-a-time optimization method. The optimum pH value was 2. The interference effect of various cations and anions on the determination of iron is reported. In addition, the application of the method to real samples of human serum was performed. The obtained results from real samples were in accordance with the obtained results using standard methods. The analysis of images (movies) recorded from an evolutionary chemical systems seems to open new, simple and low-cost analytical opportunities.
Authors:Yue Yao, Jianhong Wang, Yanyan Deng and Jun Wang
A bifunctional catalyst Pt/Hβ-n (Pt loading: 0.4 wt%) was prepared by the impregnation of an aqueous solution of chloroplatinic acid with β zeolite, wherein the β zeolite support has an unusual morphology of egg-like microspheres assembled by nanocrystallites. Other two control catalysts were also prepared using a β support with micro-sized crystals and a commercial one with varying crystal sizes. The catalysts were characterized by XRD, SEM, ICP, N2 sorption isotherms and mesopore size distribution, and evaluated in the hydroisomerization of n-heptane in an atmospheric fixed bed flow reactor. Though Pt/Hβ-n has similar acidity and Pt loading (0.4 wt%) to the two control catalysts, it exhibits remarkably higher conversion of n-heptane and selectivity to isomerization. According to the characterization data, the higher activity of Pt/Hβ-n is the result of the faster diffusion of reactants in shorter channels of nanocrystallines and the uniformly distributed mesopores within the microspheres.
Alumina/TiO2/Apatite interface nanostructure composite filters have been developed for air purification. It was shown that these filters can efficiently absorb and decompose organic species which are suspended in air. To prepare the filters, TiO2 nanopowder was dispersed in titanium sol in 30 and 70 g/L concentrations, and the prepared mixture was deposited on the porous alumina body by dip-coating. Then, the calcined nanostructure composite TiO2–TiO2 was soaked in a simulated physiological solution (SBF) at 37 °C. The surface morphology, surface area, crystalline structure and crystallite sizes of the films were investigated by SEM, EDS, BET, and XRD. The photocatalytic activity of the composite filters, as well as the effect of the TiO2 nanopowder concentration in the titania sol and soaking time in SBF were also evaluated through the degradation of nitrogen oxides (NOx) as one of the dominant causes of air pollution in the car exhaust gases. SEM and XRD results showed that immersion in SBF forms a layer of carbonate-containing apatite on the TiO2 layer. The results showed that increasing nanopowder TiO2 concentration increases the NOx oxidation rate. The prepared alumina/TiO2/HA filter can be used to remove CO gas with the absorption mechanism, as an interesting CO degradation performance (about 95 %) was observed in the alumina/TiO2/HA filter after soaking into SBF for 20 days. However, it could not significantly alter the concentrations of other car exhaust pollutants (SO2 and CxHy).
The properties of Co/Al2O3 catalysts prepared by the solid-state reaction between gibbsite and various cobalt salts such as cobalt acetate (CoAc), cobalt acetylacetonate, cobalt chloride, and cobalt nitrate (CoNT) were investigated in the hydrogenation of carbon dioxide at 270 °C and atmospheric pressure and characterized by N2 physisorption, X-ray diffraction, X-ray photoelectron spectroscopy, and H2-temperature programmed reduction. Compared to the catalyst prepared by conventional impregnation of aqueous solution of cobalt nitrate on alumina (CoNT-Imp), the solid-state catalysts (CoNT and CoAc) exhibited much higher activity in the CO2 hydrogenation with comparable CH4 and CO selectivity. Unlike the impregnation catalysts, in which most of the Co3O4 particles/clusters were located deep inside the pores of alumina, the solid-state reaction resulted in the dispersion of cobalt oxides mostly on the external surface of alumina. As a consequence, CO2 adsorption and dissociation to adsorbed CO and O (the initial steps in CO2 hydrogenation) were not limited by the slow diffusion of CO2 so high CO2 hydrogenation activity was obtained. As revealed by the XRD and H2-TPR results, the average crystallite size of Co3O4 and the metal-support interaction depended on the cobalt precursor used during the solid-state synthesis. Nevertheless, the solid-state reaction of gibbsite and cobalt chloride at 650 °C resulted in very poor CO2 hydrogenation activity due to the formation of inactive cobalt aluminate.
Authors:Wincenty Turek, Joanna Strzezik and Agnieszka Krowiak
The catalytic activity of nickel oxysalts NiCo2O4 NiFe2O4, NiTiO3, NiMoO4, Ni3(PO4)2, with different ionic character of the oxygen bond in the anionic ligand was investigated. The acid–base and redox properties of selected catalysts were studied on the basis of kinetics of isopropyl alcohol conversion. The kinetics of propene oxidation over the catalysts and the activation energy and selectivity of oxidation reactions were determined. Activities of the catalysts in the propene oxidation reaction were compared with their oxidation–reduction and acid–base properties. The influence of the amount and form of chemisorbed oxygen on the propene oxidation pathway was investigated. Over the most active catalysts, the non-destructive propene oxidation towards acrolein is the least selective. Oxysalt catalysts active in oxidation reactions exhibit strong redox properties but direct the process towards destructive oxidation products.
Ceria–alumina composite supports were prepared by the co-precipitation (cop), impregnation (imp) or deposition–precipitation (dp) methods. Co–Mo catalysts supported on these composite supports were prepared by the imp method and their catalytic activities for sulfur-resistant methanation of synthesis gas were investigated. The catalysts were characterized by nitrogen adsorption, X-ray diffraction (XRD), and hydrogen temperature-programmed reduction (TPR). It was found that the preparation method of ceria–alumina composite support had a marked influence on the surface area, the interaction between ceria and alumina, and the catalytic performance for sulfur-resistant methanation. Among them, the ceria–alumina composite support prepared by dp method achieves the best methanation activity due to its smaller ceria particle size, better ceria dispersion, weak interaction between ceria–alumina as suggested by XRD and TPR results.
Authors:Van-Khoa Nguyen, Jung-Hyun Park and Chae-Ho Shin
Binary CeO2–MgO oxides with various Ce/Mg mol ratios were prepared by the co-precipitation method and were tested in the dehydrogenation of ethylbenzene to styrene. The obtained materials were characterized by N2 adsorption, X-ray diffraction, and X-ray photoelectron spectroscopy. The N2 adsorption showed that CeO2–MgO oxides were mesoporous materials and the BET surface area increased with increasing magnesia content. The fluorite type structure of ceria was observed in samples with low magnesia content while the mixture of the ceria phase and the magnesia phase existed simultaneously in samples with high magnesia content. The results showed that the Ce4+–Mg2+–O2− couple in CeO2/MgO catalyst could be supposed to be an active site in the dehydrogenation of ethylbenzene.
Authors:Frederico A. D. Araújo, Sonia V. Pereira, Deivson C. S. Sales, A. R. Schuler and Cesar A. M. Abreu
The free fatty acids of cotton seed oil were processed with methanol and ethanol into the corresponding alkyl fatty esters in the presence of diluted sulfuric acid. The products characterized as biodiesels presented higher mass fraction levels (43.0 wt%) of the alkyl linoleates, and 17.0 and 13.0 wt% of the alkyl esters C16:0 and C18:1, respectively. A model based on the mechanism of the acid esterification, and representing the evolutions of the fatty ester concentrations, was fitted to the experimental evolution results where the orders of magnitude of the kinetic parameters were quantified. The selectivities of the methyl and ethyl fatty esters in the biodiesel mixtures were compared, where the C18:2 ethyl linoleate selectivity (92.3 %) in the ethyl biodiesel was almost twice the methyl linoleate selectivity (57.3 %) in the methyl biodiesel.
Authors:Shenghua Yuan, Hao Jin, Wensheng Xia, Xiaodong Yi and Weiping Fang
Hydrogen spillover on Ni–CsxH3−xPW12O40 (x = 0, 1, 2) double-function hydrocracking catalyst was studied by temperature-programmed desorption (H2-TPD and NH3/H2-TPD) and thermodynamic calculations. The results of H2-TPD show that the hydrogen adsorption amount on the two-component Ni–CsxH3−xPW12O40 (x = 0, 1, 2) catalysts is much greater than that on single-component catalysts, such as nickel, tungstophosphoric acid and its cesium salts. Moreover, the H+ content is related to the content of Ni–CsxH3−xPW12O40. The above phenomena can be explained by the spillover hydrogen H combining with H+ to form Hn+ (n = 2, 3). The results of NH3/H2-TPD can also indirectly prove the existence of Hn+. It is demonstrated by the theoretical calculation that the formation of Hn+ (n = 2, 3) from H and H+ is favorable in energy, and NH3 may combine with H3+ to form NH6+.
Authors:Zhiwei Wu, Fan Yang, Huabang Wang, Jianchao Ma, Ligong Chen and Yang Li
A general process for the cyclization of aminoalcohols to the corresponding amines over Cu–Cr–La/γ-Al2O3 is established in a continuous fixed-bed reactor. The catalyst was characterized by XRD, XPS and NH3-TPD. The doped Cr is found to improve the copper particle dispersion. The addition of La neutralized the strong acid sites and decreased the amount of the acid sites, which facilitated the desorption of amino compounds on the surface of catalysts and inhibited the carbon deposition. Under the optimum conditions, the yields of pyrrolidine, piperidine and piperazine were 99.5, 99.5 and 98.6 %, in order, while the yields of hexahydro-1H-azepine and homopiperazine were 46.5 and 32.7 % due to the unstable seven-membered ring by the cyclization of the corresponding aminoalcohols over Cu–Cr–La/γ-Al2O3.
Authors:Mojtaba Nasr-Esfahani and Abolghasem Nourmohammadi
We have produced zinc oxide (ZnO) photocatalyst nanostructure films by the deposition of ZnO onto indium tin oxide (ITO) glass substrates. A polyethylene glycol (PEG) aided sol–gel route using zinc acetate, 2-methoxyethanol and monoethanolamine, followed by spin coating and heat treatment, was utilized to form these photocatalyst films. The obtained interface nanostructure films were characterized with X-ray diffraction, scanning electron microscopy and UV–Vis spectroscopy. The photocatalytic activity of the films were also investigated using Direct Sky Blue 5B (C. I. Direct Blue 15) as a model organic compound under UV light irradiation. The influence of operating parameters, including the pH of the solution and the number of ZnO layers on Direct Sky Blue 5B degradation, were examined. An interesting decolorization performance was observed in the ZnO/ITO thin films produced using 2 % PEG.
Authors:Hugo Rojas, José J. Martínez, Sonia Mancípe, Gloria Borda and Patricio Reyes
The hydrogenation of citral over Au, Ir–Au and Ir catalysts prepared from colloids using as supports TiO2 and Nb2O5 has been studied. The samples were characterized by N2 adsorption at 77 K, transmission electron microscopy and temperature programmed reduction. The reactivity and selectivity differences between the prepared catalysts have been explained considering that the deposition of colloids prepared in basic media at high pressures of hydrogen occurs preferentially as iridium oxide or gold complexes, similarly to classical methods of preparation (wetness impregnation and deposition–precipitation). In this sense, the catalytic behavior of supported colloids is similar to these methods without the reduction process. This was corroborated when the solids were reduced at 773 K, which leads to catalysts active and highly selective to the hydrogenation of the carbonyl bond.
Authors:Heondo Jeong, Churl Hee Cho and Tae Hwan Kim
Methanol synthesis by carbon dioxide hydrogenation was investigated over a series of Cu/ZnO catalysts prepared by various pH conditions. These catalysts were confirmed by XRD, BET, N2O chemisorption and TPR measurements before and after the reaction. It was revealed that pH conditions on catalyst preparation played an important role in active metal formation on the catalysts surface and catalytic performance in the hydrogenation of carbon dioxide. Zr added to Cu/ZnO catalysts favorably served in enhancing copper dispersion on the catalyst surface and improving carbon dioxide conversion. Among the catalysts tested, Cu/ZnO/ZrO2/Al2O3 catalyst exhibited the highest carbon dioxide conversion, methanol yield and CO concentration in the outlet gas.
The gas phase selective hydrogenation of a series of nitroarenes (nitrobenzene, p-chloronitrobenzene, p-bromonitrobenzene, p-nitroaniline, p-nitrotoluene, p-nitrophenol and p-nitroanisole) has been examined over Au/TiO2 (0.3 % w/w Au, mean Au particle size = 3.9 nm). Compensation behavior is demonstrated with an associated isokinetic temperature (Tiso) of 558 ± 32 K. We account for this response in terms of the selective energy transfer (SET) model where the occurrence of resonance between catalyst and reactant vibrations generates the activated complex. An analysis of the stepwise variation of the activation energies has identified a critical vibrational frequency of 853 cm−1, which is close (±2 cm−1) to the reference value for nitro-group (in-plane symmetric O–N–O bending and stretching) vibrations. Application of SET suggests activation of weakly adsorbed nitroarene (at the support or metal/support interface) by excitation of the nitro-group via IR radiation from a strongly adsorbed surface nitroarene component. The excited nitroarene is then attacked by reactive hydrogen supplied by the Au sites to generate the respective aromatic amine with 100 % selectivity. Agreement of the SET predicted Tiso with the experimental value requires the incorporation of a term due to C–N torsional entropy resulting from distortion of the O–N–O plane.
The influence of the activation conditions on the catalytic performance and microstructure of supported V–Mo oxides used for benzene oxidation to maleic anhydride has been investigated. To activate the catalysts, two sets of activation conditions were tested. In condition I, the catalysts were activated in an atmosphere of air and benzene, which was similar to the industrial practice. In condition II, the catalysts were pre-activated in an atmosphere consisting of the gas products produced by the decomposition of the freshly prepared catalysts during activation process. The activity and selectivity of the catalysts were evaluated on a bench scale reactor as well as on a pilot reactor. The catalysts activated by condition II at the appropriate temperature showed a better performance: the selectivity and yield of MA were nearly 80 and 100 wt%, respectively. They are 5 % higher than those of the catalyst activated by condition I. The catalysts were characterized in terms of several techniques including isotherm adsorption, TG-DTG, XRD, SEM, EDX and XPS. The characterization results indicated that the microstructures of the catalysts were significantly influenced by the activation conditions. Based on the above information, the better performance exhibited by the catalyst activated by condition II are analyzed.
Authors:O. Machalický, L. Lichý, M. Tomica, R. Hrdina and O. Šolcová
The photocatalytic decomposition of indigo-5,5′-disulfonic acid (indigocarmine) and indigo-6,6′-dicarboxylic acid has been studied using TiO2 suspension and the polychromatic irradiation of a high-pressure Hg arc lamp. The dyestuffs were dissolved in aqueous medium at pH = 10 and photolyzed in a back-flow tubular photoreactor. The reaction products were determined by HPLC, NMR and MS spectroscopy. Two main photoproducts obtained from indigocarmine (2-amino-5-sulfobenzoic acid and isatine-5-sulfonic acid) were detected. The photocatalysis of indigo-6,6′-dicarboxylic acid gave aminoterephthalic acid and isatine-6-carboxylic acid as two main products. The quantitative analyses of reaction products were performed with UV/Vis and HPLC using chemical standards. A stoichiometric model and kinetic description of photocatalysis of sulfo and carboxy indigo dyes are suggested. The effect of hydroxide and carbonate anions on the rate of photocatalysis was also studied.
Nanosized Pd doped and supported on Mn2O3 catalysts were prepared and tested for CO oxidation. The introduction of Pd in Mn2O3 enhances the activity for CO oxidation due to a synergistic effect. The supported samples showed total CO conversion at lower temperature as compared to doped samples, whereas pristine Mn2O3 showed total CO conversion at a much higher temperature. The presence of Pd greatly improved the catalytic activity for CO oxidation. The presence of moisture in the feed gas does not deactivate the catalysts for CO oxidation. XRD pattern substantiates the formation of Mn2O3 phase, SEM images show that the particles are in the nanosized range and roughly spherical in appearance. From TEM images, the average particle size was found to be around 50 nm. Thermal analysis data indicates the phase change from Mn2O3 to Mn3O4 beyond 900 °C and also gives information regarding the thermal stability of Mn2O3 after the incorporation of Pd in the lattice.
Effects of KNO3, CeO2, Fe2O3, their mixture and their thermally treated mixture on the combustion reactivity of two coals, bituminous coal (BC) and high ash coal (HAC), were investigated by thermogravimetric analysis. The ignition performance, burnout performance and exothermic behavior were used to evaluate the catalytic effect. Moreover, the kinetic parameters were determined using the Coats–Redfern method. The results indicated that the activity sequence of the catalysts on BC relative to the ignition performance can be described as follows: the thermally treated mixture > the mixture > KNO3 > Fe2O3 > CeO2, and the activity sequence relative to the burnout performance is the same. The activity sequence of the catalysts on HAC relative to the ignition performance can be described as follows: the thermally treated mixture > the mixture > Fe2O3 > CeO2 > KNO3, and the activity sequence relative to the burnout performance is the same. The exothermic heats of catalyst-incorporating samples increased and the activation energies of the samples decreased.
Authors:Michal Baudys, Martin Zlámal, Josef Krýsa, Jaromír Jirkovský and Petr Kluson
Photocatalytic activities of a series of well available commercial TiO2 powders in both suspended and immobilized forms were determined by kinetic measurements of the degradation of acid orange 7 as model compound. Although the powders showed lower photoactivity in the immobilized than suspended form, the differences among particular materials considerably varied. The porosity of the photocatalysts and related adsorption/desorption phenomena strongly influence the photocatalytic degradations occurring in aqueous suspension. The adsorption of the azo dye has a significant effect on observed concentration changes during irradiation and must be taken in account in the evaluation of degradation rates in suspensions. No direct correlation between photocatalyst material properties and photoactivity was found. The paper brings a convincing discussion that, with only minor exceptions, it is not possible to form any general conclusions on the performance of a standard type photocatalyst, even if a model reactant is used.
Authors:V. Gnana Glory Kanmoni, Sheeba Daniel and G. Allen Gnana Raj
The photocatalytic degradation of an organophosphorus insecticide chlorpyrifos (O,O-diethyl O-3,5,6-trichloro-2 pyridyl phosphorothioate) in aqueous suspensions of nano ZnO and nano TiO2 under sunlight is reported in this study. Nanocrystals of ZnO (34.3 nm) were prepared by the wet chemical method and TiO2 nanocyrstals (7.5 nm) were synthesized from titanium tetraisopropoxide by hydrolysis and peptization. The synthesized nanocrystals were characterized by X-ray diffraction, FT-IR, SEM–EDS and UV–Visible analytical techniques. The degradation of the insecticide was studied by monitoring the change in substrate concentration employing UV–Visible spectroscopy. The influence of catalyst loading, substrate concentration and pH were studied. The intermediates of the degradation process were identified by GC–MS. The synthesized nano ZnO and nano TiO2 demonstrated high photocatalytic activity under solar light. The results show that nanocrystals of TiO2 exhibit a better photocatalytic activity on the degradation of Chlorpyrifos than nanocrystals of ZnO.
Authors:Sangeeta Vijay Jagtap and Raj Madhukar Deshpande
PdCl2(bipy) was found to be an efficient and stable catalyst in biphasic medium (organic-glycol) for the Heck reaction. The kinetics of the Heck coupling of styrene with iodobenzene using the same catalyst was studied in a biphasic medium in a temperature range of 393–413 K. The rate was found to have a first order dependence tending to a fractional order, on the iodobenzene as well as catalyst concentration. The rate was found to have a complex dependence on the styrene concentration and passes through a maximum, showing typical substrate inhibition kinetics. The rate had a first order dependence on the base (morpholine) concentration. The trends observed for the influence of the different parameters on the activity of the catalyst are in agreement with the established mechanism for Heck reaction. An empirical rate model has been proposed to fit the observed rate data. The activation energy was found to be 72.91 kJ/mol. This is the first time that kinetic modeling of Heck reaction in a biphasic medium (organic-glycol) has been attempted.
Authors:Ping Chen, Jiqing Lu, Guanqun Xie, Lin Zhu and Mengfei Luo
Vapor-phase selective hydrogenation of crotonaldehyde was carried out over Ir/TiO2 catalysts with different Ir contents prepared by an impregnation method. The catalysts were characterized by X-ray powder diffraction (XRD), temperature-programmed reduction (TPR), diffuse reflectance infrared Fourier transform spectra of CO adsorption (CO-DRIFTS), NH3 temperature-programmed desorption (NH3-TPD), Raman spectroscopy and temperature-programmed oxidation (TPO). It was found that with increasing Ir content in Ir/TiO2, both the activity (TOF) and selectivity to crotyl alcohol first increased and then slightly decreased. The 3 % Ir/TiO2 catalyst showed the highest activity, (with a TOF of 9.3 × 10−3 s−1) and the highest selectivity to crotyl alcohol (74.6 %) in the hydrogenation of crotonaldehyde. The results of CO-DRIFTS indicated that the reduced catalyst contains a mixture of Ir0 and Irδ+. It was concluded that the catalytic performance of the catalysts depended on the strength of surface acidity and the Ir particles size for the selective hydrogenation of crotonaldehyde to crotyl alcohol.
Authors:Yuelun Wang, Bo Hou, Debao Li, Jiangang Chen and Yuhan Sun
Sol–gel Co/SiO2 catalysts were prepared using Co–en (ethylenediamine) complex precursors with different cobalt introduction order. More highly reduced catalysts were obtained by gelling the silica support followed by depositing cobalt nanoparticles on silica surface, and then catalysts exhibited higher FT activity and concomitant higher C18+ selectivity. Meanwhile, both series of catalysts prepared with en/Co molar ratio of 2/1 exhibited higher activity due to their high cobalt reduction.
Authors:M. Jose John, K. Muraleedharan, V. M. Abdul Mujeeb, M. P. Kannan and T. Ganga Devi
Pure and doped samples of sodium oxalate (Na2C2O4) were subjected to pre-compression and their thermal decomposition kinetics was studied at five different temperatures in the range 783–803 K under isothermal conditions by thermogravimetry. The pre-compressed samples decomposed in two stages governed by different rate laws; the Prout–Tompkins model best describes the acceleratory stage of the decomposition while the decay region is best fitted with the contracting cylinder model as in the case of uncompressed sodium oxalate samples. The rate constants k1 and k2 of the acceleratory and deceleratory stages of the thermal decomposition were dramatically decreased on pre-compression. However, the activation energies, evaluated by model fitting kinetic method, E1 and E2 for the respective stages of decomposition remained unaltered by pre-compression. The results favor ionic diffusion mechanism proposed earlier on the basis of doping studies.
Authors:Haiying Wang, Yucheng Yang, Jianhong Wei, Ling Le, Yang Liu, Chunxu Pan, Pengfei Fang, Rui Xiong and Jing Shi
Nitrogen-doped titanium dioxide (TiO2) nanotube arrays were synthesized by anodization in ethylene glycol electrolyte and annealing in ammonia at 500 °C. Detailed analysis showed that the nitrogen-doped titania nanotubes were pure anatase of ordered structure, with a crystallite size of 8.5 nm. The doping nitrogen atoms were induced on the interstitial sites and substitutional sites and the ratio of oxygen vacancies increased to 27.15 %, resulting in an add-on peak in the absorption spectrum and extended the absorption from 387 to 618 nm. The photocatalytic activity of the nitrogen-doped TiO2 nanotubes was evaluated by photocatalytic degradation of methyl blue under visible light irradiation. Significant improvement of photocatalytic activity under visible light irradiation was observed. We assumed the nitrogen doping induced the effect produced by nitrogen atoms, Ti3+ cations and oxygen vacancies and the size effect of the TiO2 crystallite should be responsible for the effective photocatalytic activity.
Authors:Munevver Zeynep Selcuk, Mehtap Safak Boroglu and Ismail Boz
Nitrogen-doped titanium dioxide (N–TiO2) powders were synthesized by hydrolysis and used as a support for doping with various metals, such as, Fe, Cr, Ni, and Pt. Aqueous solutions of metal salts were used as a metal source and metals were deposited on N–TiO2 powders. Ni–N–TiO2 catalysts with various nickel concentrations were studied in detail. X-ray diffraction and diffuse reflectance spectrophotometry were used for the characterization of the photocatalysts. The Ni–N–TiO2 photocatalysts were then tested in photocatalytic water splitting under visible light. The optimum dopant concentration was found to be 10 μmol Ni/g N–TiO2 for Ni–N–TiO2. The photocatalyst, Ni–N–TiO2, has shown a stable and high activity, 490 μmol of H2 gcat−1 h−1 for the first 6 h of operation.
Authors:Magdalena Janus, Ewelina Kusiak-Nejman and Antoni Waldemar Morawski
In this study, it was shown that a possible explanation of increasing photocatalytic activity with temperature may be the fact that with increasing water temperature, the amount of hydroxyl radicals in water also increases, because the ionic product of water increases with an increase in temperature. For measurements of the amount of hydroxyl radicals, the fluorescence technique was used. Terephthalic acid was used as a hydroxyl radical scavenger. After inducing of TiO2, positive holes in the valance band may react with OH ions and produce •OH radicals, a strong oxidizing agent.