Applied Catalysis A, General (v.382, #2)
Editorial Board (CO2).
Pathways of light compounds formation during propane and isobutane dehydrogenation on Al-Cr catalysts by V.Z. Fridman (139-147).
This present study revealed that the majority of light compounds produced during propane and isobutane dehydrogenation on Al-Cr catalyst is formed via consecutive dehydrogenation hydrocracking of the newly produced main olefin with formation of the “one carbon shorter chain olefin” and methane. The “one carbon shorter chain olefin” can be further hydrogenated to the “one carbon shorter chain paraffin”; otherwise it can be further transformed into “two carbons shorter chain olefin” and methane by additional consecutive reaction of hydrocracking. This sequence of the pathway is presented using isobutane dehydrogenation as an example which also includes steps of the light compounds formation from C3 hydrocarbons.Reaction pathways of the light hydrocarbons formation during propane and isobutane dehydrogenation on Al-Cr catalyst have been studied. It was determined that the majority of light compounds are formed not directly from initial paraffin, but from the main product of the paraffin dehydrogenation; olefin. The sequence of the light compounds formation reactions includes: (1) dehydrogenation of the initial paraffin with formation of targeted olefin; (2) consecutive hydrocracking of the newly produced main olefin with formation of the one carbon shorter chain olefin and methane; (3) one carbon shorter chain olefin can be converted by two parallel reactions further. The first reaction is hydrogenation of the one carbon shorter chain olefin to the formation of the one carbon shorter chain paraffin. Another parallel reaction is hydrocracking of the one carbon shorter olefin to the two carbon shorter olefin and methane. If short olefin is ethylene the final product of the hydrocracking reaction is methane. This sequence can be presented by using isobutane dehydrogenation as an example which also includes steps of light compounds formation from C3 hydrocarbons: (1) C4H10 → C4H8 + H2 (2) C4H8 + H2 → C3H6 + CH4 (3a) C3H6 + H2 → C3H8 (3b) C3H6 + H2 → C2H4 + CH4 (4a) C2H4 + H2 → C2H6 (4b) C2H4 + 2H2 → 2CH4 Obtained reaction pathways of light compounds formation can be applied to optimize the concept of the dehydrogenation process and explain puzzling phenomena regarding the temperature profile in the fixed bed dehydrogenation process.
Keywords: Light compounds; Al-Cr catalyst; Dehydrogenation; Thermo-cracking; Hydrocracking; Propane; Isobutane;
Mesoporous MAl2O4 (M = Cu, Ni, Fe or Mg) spinels: Characterisation and application in the catalytic dehydrogenation of ethylbenzene in the presence of CO2 by Andressa H. de Morais Batista; Francisca S.O. Ramos; Tiago P. Braga; Cleanio L. Lima; Francisco F. de Sousa; Eduardo B.D. Barros; Josue M. Filho; Aldenor S. de Oliveira; Jackson R. de Sousa; Antoninho Valentini; Alcineia C. Oliveira (148-157).
TEM image of NiAl exhibits the void (indicated by an arrow) that is evidence that isolated nanoparticles are formed. The SAED pattern shows the lattice fringe distances that corresponds to the (1 1 1) and (2 2 0)-spacing of cubic spinel structures.The catalytic properties of nanostructured MAl2O4 (M = Cu, Ni, Fe or Mg) were investigated in the dehydrogenation of ethylbenzene with CO2. The catalysts were characterised by XRD, Raman spectroscopy, textural properties, acidity (TPD-NH3) and basicity (CO2-TPD) measurements, SEM and TEM analyses and TPR techniques. XRD revealed the spinel structure of MAl2O4, except for the NiO, CuO, Fe2O3 and MgO phases. All solids exhibited the nanostructured features of the SBA-15 template, including high values of textural properties and morphologies characteristic of the mesoporous silica. The acidic strength follows the electronegativity trends of the cations present on the spinel aluminates: CuAl > NiAl > FeAl and MgAl, which is the inverse order of the basicities. The selectivities in the dehydrogenation of ethylbenzene with CO2 showed that styrene was the predominant product for all catalysts except for those based on Ni, which was highly selective for the production of toluene. The FeAl2O4 catalyst provided the best catalytic performance among the solids studied due to the continuous oxidation of Fe3+ sites by the CO2 from the reaction. This solid has the additional advantage of being stable over the timescale of the reaction, as compared to the traditional Fe-based catalysts, due to its nanostructured features.
Keywords: Ethylbenzene; Spinels; Raman; Metals; CO2;
Highly effective MnCeO x catalysts for biodiesel production by transesterification of vegetable oils with methanol by C. Cannilla; G. Bonura; E. Rombi; F. Arena; F. Frusteri (158-166).
Novel MnCeO x catalysts characterized by both high surface area and Mn dispersion have shown a superior activity in the transesterification reaction of refined sunflower oil with methanol. The catalyst performance is the result of a synergic role played by both the acid/base surface character and textural porosity.This paper reports the results obtained using a novel MnCeO x system in the transesterification reaction of refined sunflower oil with methanol. The performance of such catalysts has been compared with that of common acid supported catalysts. Results obtained revealed that MnCeO x system possesses a superior activity especially by operating at low temperatures (≤120 °C). Independently of Mn loading, the redox-precipitation method for the preparation of Mn-based systems allowed to obtain always high dispersed catalysts and, as a consequence, a linear relationship between reaction rate and Mn loading was obtained. NH3-TPD and CO2-TPD measurements indicate that MnCeO x systems are characterized by a prevalent nature of basic sites. However, the catalyst performance is the result of a synergic role played by both the surface acid/base character and textural porosity.
Keywords: Biodiesel; Transesterification reaction; Heterogeneous (liquid–solid) catalysis; Ceria–manganese catalysts;
Synthesis and characterization of Pd/ZSM-5/MCM-48 biporous catalysts with superior activity for benzene oxidation by Chi He; Peng Li; Jie Cheng; Hailin Wang; Jinjun Li; Qin Li; Zhengping Hao (167-175).
ZSM-5/MCM-48 composite materials with various acidities and enhanced thermal stability have been synthesized via a simple and reliable in situ overgrowth approach. All Pd-loaded composite catalysts demonstrate superior activity, in particular, Pd/ZM-5% shows the best activity, reducing the 100% benzene conversion temperature from 328 °C (Pd/MCM-48) to 230 °C. These novel Pd-loaded composite catalysts are promising materials for eliminating VOCs in air.ZSM-5/MCM-48 composite materials with different acidities and enhanced thermal stability have been synthesized via a simple and reliable in situ overgrowth method. The as-prepared biporous materials and the Pd-impregnated catalysts were systematically investigated by various techniques, including XRD, ICP-OES, N2 adsorption/desorption, H2 chemisorption, SEM, TEM/HRTEM, FT-IR, 27Al MAS NMR, NH3-TPD, H2-TPR and XPS. The characterization results reveal that all composite catalysts exhibit high surface area, large pore volume and long pore diameter. The quantity of acid sites increases as the ZSM-5 additive amount increases, and Al atoms are in the tetrahedral coordination positions in composite materials. The activity tests demonstrate that all the Pd-loaded catalysts are active in the total elimination of benzene, while the catalytic activity values of Pd-loaded ZSM-5/MCM-48 composite catalysts are much higher than those of Pd/ZSM-5 or Pd/MCM-48 alone. Both Pd0 and Pd2+ are responsible for the oxidation reaction, and the catalytic activities are primarily related to the support acidity and the Pd dispersion. In addition, the stability of the composite catalysts also improves with an appropriate amount of ZSM-5 additives in MCM-48. This research shows that the novel Pd-loaded composite catalysts are promising materials in the elimination of VOCs.
Keywords: In situ overgrowth; ZSM-5/MCM-48; Acidity; Superior activity; VOCs;
Hydrodeoxygenation of oleic acid and canola oil over alumina-supported metal nitrides by Jacques Monnier; Hardi Sulimma; Ajay Dalai; Gianni Caravaggio (176-180).
Nitrides of molybdenum, tungsten and vanadium supported on γ-Al2O3 were prepared and tested for the hydrodeoxygenation of oleic acid and canola oil at 380–410 °C and 7.15 MPa H2. Molybdenum nitride was found to be a better HDO catalyst producing more normal alkanes (diesel fuel cetane enhancers). Results of a 450-h long hydrotreating test performed with Mo2N/Al2O3 and canola oil are also presented.Nitrides of molybdenum, tungsten and vanadium supported on γ-Al2O3 were prepared by temperature-programmed reaction with NH3 and tested as catalysts for hydrodeoxygenation of oleic acid and canola oil at 380–410 °C and 7.15 MPa H2. The molybdenum nitride catalyst was found superior to the vanadium and tungsten nitrides for catalytic hydrotreating of oleic acid in terms of fatty acid conversion, oxygen removal and production of normal alkanes (diesel fuel cetane enhancers). The supported molybdenum nitride favoured the hydrodeoxygenation of oleic acid to n-C18H38 three times out of four compared to decarbonylation and decarboxylation. A 450-h long hydrotreating test performed at 400 °C and 8.35 MPa H2 with Mo2N/Al2O3 and canola oil, indicated that oxygen removal exceeded 90% over the duration of the experiment and that the yield of middle distillate hydrocarbons (diesel fuel) ranged between 38 and 48 wt% (based on liquid feed).
Keywords: Hydrodeoxygenation; Metal nitrides; Molybdenum nitride; Vanadium nitride; Tungsten nitride; Canola oil; Oleic acid; Biomass hydrodeoxygenation; Renewable diesel fuel;
Telomerisation of 1,3-butadiene with glycerol under aqueous biphasic conditions: Influence of the reaction conditions on the products distribution by Sandra Bigot; Jonathan Lai; Isabelle Suisse; Mathieu Sauthier; André Mortreux; Yves Castanet (181-189).
The telomerisation of butadiene with glycerol catalyzed by palladium under aqueous biphasic conditions has been investigated in detail as well as under gaseous atmosphere of butadiene than in the presence of a liquid phase of butadiene. The influence of various experimental parameters such as the nature of the hydrosoluble ligand, the nature of the base and its amount, the amount of butadiene or water, …, has been checked with the aim to obtain high activities and selectivities either into mono-, di- or tritelomers.The palladium-catalyzed telomerisation of butadiene with glycerol has been studied under aqueous biphasic conditions both in the presence of a liquid phase of butadiene and under gaseous atmosphere of butadiene. In this last case, gaseous butadiene was continuously added during the whole reaction time keeping constant its pressure. Most of the products formed have been fully characterized. The influence of various experimental parameters has been checked with the aim to obtain high activities and selectivities either into mono-, di- or tritelomers.
Keywords: Telomerisation; Glycerol; Butadiene; Palladium catalysis; Octadienyl ethers;
Nanoscale calcium bismuth mixed oxide with enhanced photocatalytic performance under visible light by Renata Solarska; Andre Heel; Joanna Ropka; Artur Braun; Lorenz Holzer; Jinhua Ye; Thomas Graule (190-196).
A significant decrease in particle size of calcium bismuth mixed oxide, a promising photocatalyst has been achieved by a single-step flame spray synthesis. This provided high-quality functional nanoparticles nominally 15 nm in size, with a specific surface area of 41 m2/g. The preparation route afforded oxygen vacancies which enhanced the photocatalytic activity of calcium bismuth oxide and extended the absorption spectrum to the visible region.The objective of materials research is the development of economical, safe and efficient synthesis routes that lead to the formation of a photocatalyst which is able to overcome performance problems related to particle size, crystallinity, or low surface area. Here, we report high-quality functional nanoparticles of calcium bismuth mixed oxide with 15 nm nominal size corresponding to a specific surface area of 41 m2/g which were produced by single-step flame spray synthesis (FSS). The high temperature of the flame afforded creation of oxygen vacancies which were quantified by near edge X-ray absorption fine structure (NEXAFS) spectra. These two parameters, developed active surface area and created in the flame oxygen vacancies, allowed to enhance the photocatalytic activity of calcium bismuth oxide by a factor of 6, in comparison to previously reported calcium bismuth mixed oxide produced by conventional methods which required additional temperature treatment steps.
Keywords: Flame spray synthesis; Mixed oxide; Nanoparticles; Oxygen vacancies; Photocatalysis;
Biochar based solid acid catalyst for biodiesel production by Amir Mehdi Dehkhoda; Alex H. West; Naoko Ellis (197-204).
A promising catalyst based on a biomass pyrolysis by-product, biochar, has been developed for the production of biodiesel showing effective catalytic activity in transesterification and esterification reactions.A promising catalyst based on a biomass pyrolysis by-product, biochar, has been developed for the production of biodiesel. Two carbon-based solid acid catalysts were prepared by sulfonating pyrolysis char with concentrated or fuming sulfuric acids. Prepared catalysts were studied for their ability to catalyze transesterification of vegetable oils and esterification of free fatty acids. The catalyst sulfonated with the concentrated sulfuric acid demonstrated considerable conversion in free fatty acid esterification, while indicating limited transesterification activity. Using the stronger sulfonating reagent, fuming sulfuric acid, resulted in much higher transesterification activity. Further investigation of the latter catalyst was conducted to determine the effect of sulfonation time (5 and 15 h) and surface area on the transesterification reaction. The surface area of the biochar was increased by chemical treatment using 10 M potassium hydroxide through porosity development. The resulting four catalysts were compared for their catalytic activity. Results showed the catalyst with the highest surface area and acid density to have the highest catalytic activity for the production of biodiesel from canola oil in the presence of methanol as the reagent. Furthermore, the catalyst with the higher surface area indicated higher transesterification activity among the catalyst with similar acid densities. The effects of alcohol to oil (A:O) molar ratio, reaction time and catalyst loading on the esterification reaction catalyzed by the sulfonated biochar were also investigated. Free fatty acid (FFA) conversion increased with increasing A:O molar ratio, reaction time and catalyst loading. The catalyst has a tremendous potential to be used in a process converting a high FFA feedstock to biodiesel.
Keywords: Biodiesel; Heterogeneous acid catalyst; Biochar; Esterification; Transesterification;
Modeling the effect of pressure and temperature on the hydrocracking of heavy crude oil by the continuous kinetic lumping approach by Ignacio Elizalde; Miguel A. Rodríguez; Jorge Ancheyta (205-212).
The effect of LHSV, temperature and pressure on hydrocracking of heavy oil at moderate conditions was modeled by the continuous kinetic lumping approach. Experimental data at 1.5–0.33 h−1 LHSV, 380–420 °C and 6.9–9.8 MPa were used to obtain the optimal set of parameters. The correlations were used in the kinetic model to predict distillation curves of products at different conditions. Prediction of liquid distillation curves of (●) feedstock and products at 0.5 h−1: (□) 380 °C and 6.9 MPa; (○) 400 °C and 8.3 MPa; (▵) 420 °C and 9.8 MPa. Predicted (lines) and experimental (symbols) data.The effect of space velocity, temperature and pressure on hydrocracking of heavy crude oil at moderate reaction conditions was modeled by the continuous kinetic lumping approach. Experimental data obtained at space velocity of 1.5, 0.5 and 0.33 h−1, varying the temperature from 380 to 420 °C and pressure from 6.9 to 9.8 MPa were used to obtain the optimal set of model parameters. Different functionalities were proposed to correlate the values of the parameters with pressure and temperature. The developed correlations were used in the continuous kinetic lumping model to predict distillation curves of the hydrocracked products at different reaction conditions.
Keywords: Continuous kinetic lumping model; Hydrocracking; Pressure effect;
One-dimensional molecular sieves for hydrocarbon cold-start emission control: Influence of water and CO2 by A. Iliyas; H.M. Zahedi-Niaki; M. Eić (213-219).
We have demonstrated in previous studies that single-file diffusion concept (shown schematically in this figure) is a promising approach to control automotive cold-start emissions. This study was aimed to mimic practical conditions by presenting the influence of water and CO2 on the trapping behavior of selected one-dimensional molecular sieves for cold-start emission control application.Using temperature-programmed desorption (TPD) method, we have investigated the performance of one-dimensional molecular sieves to trap hydrocarbons (HCs), e.g., toluene and ethylene, after co-adsorption with 6 vol.% water vapor or 8 vol.% CO2, as well as 14 vol.% combined water–CO2 mixture. The HC trapping capacity of the non-hydrothermally treated samples was reduced by the presence of water, and this effect was much more pronounced for metalloauminophosphate (MeAPO) molecular sieves than Si–Al zeolites. CO2 was found to be a lesser inhibiting species than water in the MeAPO samples. ZSM-12, SAPO-5 and FAPO-36 were found to be hydrothermally stable up to the examined temperature of 800 °C, though with reduction in their trapping efficiency, whereas MAPO-5 sample collapsed under the hydrothermal conditions.
Keywords: Automotive cold-start emission control; One-dimensional zeolites; Temperature-programmed desorption; Multi-component mixtures with water and CO2;
In situ generation of Ni metal nanoparticles as catalyst for H2-rich syngas production from biomass gasification by Yohan Richardson; Joël Blin; Ghislaine Volle; Julius Motuzas; Anne Julbe (220-230).
During wood impregnation with nickel nitrate aqueous solution, specific adsorption of Ni2+ cations on oxygenated groups of wood surface occurs and leads to high metal dispersion inside the solid fuel matrix. During pyrolysis, nickel(II) species are reduced by carbon atoms yielding Ni0 nanoparticles which can act as the catalytic active phase for tar conversion and H2 production in biomass gasification process.The strategy of impregnating lignocellulosic biomass with aqueous metal salts solutions was efficiently applied in our group for producing H2-rich gas by pyrolysis of wood at 700 °C. The present work is a thorough study on the formation of nickel metal nanoparticles (NPs) during the pyrolysis of nickel(II) impregnated wood in the temperature range of 400–500 °C. During the wood impregnation step, the numerous oxygenated groups present in the bio-macromolecules act as adsorption sites for metal cations in aqueous medium yielding very high metal precursor dispersion into the wood matrix. During pyrolysis, an amorphous Ni x O y H z phase is formed which is reduced to metallic nickel (Ni0) by carbon atoms at temperatures below 500 °C, leading to the formation of Ni0 NPs, as demonstrated by XRD, XPS, STEM and temperature-programmed pyrolysis characterizations. These findings reveal that the in situ formed Ni0 nanocrystallites act as the catalytic active phase for enhancing both H2 production and tar conversion during biomass pyrolysis, i.e. during the initial stage of gasification. Potential interests of these in situ generated Ni nanocatalysts for biomass gasification applications are discussed.
Keywords: Ni0 nanoparticles; Biomass gasification; Pyrolysis; Wood; Tar; Hydrogen;
Synthesis of nanozeolites and nanozeolite-based FCC catalysts, and their catalytic activity in gas oil cracking reaction by Gia-Thanh Vuong; Vinh-Thang Hoang; Dinh-Tuyen Nguyen; Trong-On Do (231-239).
A new method for the synthesis of nanozeolite using organic medium allows the control of crystal sizes. Different crystal sizes such as 25, 40 and 100 nm were prepared in toluene or formamide solvents. The activity of these nanozeolite-based FCC catalysts was evaluated in the gas oil cracking reaction. It was found that the activity increased with the decrease in crystal size.A new method for the synthesis of nanosized zeolites in organic solvents, such as formamide and toluene as crystallization medium instead of water, in the presence of organosilane has been developed. Organic solvents have a great impact on the synthesis of nanozeolites. Formamide, which has similar properties to water, is a good candidate as the solvent for the synthesis of nanosized zeolites. This synthetic method allows easy manipulation with the control of crystal sizes. In this study, different crystal sizes such as 25, 40 and 100 nm were prepared in toluene and formamide solvents. To study the effect of crystal nanosizes on the catalytic performance of nanosized zeolites, nanozeolite-based FCC catalysts were also prepared using different nanozeolite sizes as active component and silica as inactive matrix. The activity of these catalysts was evaluated with FCC feedstock. The results revealed a good correlation between the crystal size of zeolites and the activity: smaller nanozeolite-based FCC catalyst exhibits higher catalytic activity.
Keywords: Nanozeolites; Formamide; Non-aqueous synthesis; FCC catalysts; FCC cracking;
Catalytic hydrogenation of ethylanthraquinone over highly dispersed eggshell Pd/SiO2–Al2O3 spherical catalysts by Jun-Ting Feng; Hai-Yan Wang; David G. Evans; Xue Duan; Dian-Qing Li (240-245).
Spherical SiO2–Al2O3 supports with different silica contents have been synthesized. After impregnation and calcination, PdO/SiO2–Al2O3 catalyst precursors were obtained. The addition of silica increased the thermal stability, surface acidity, specific surface area and total pore volume of the alumina. The activity and stability of ethylanthraquinone hydrogenation over the reduced Pd/SiO2–Al2O3 catalysts increased with increasing silica content.Spherical Al2O3 and SiO2–Al2O3 supports with different silica contents have been synthesized by the oil column method. After impregnation with Na2PdCl4 solution and subsequent calcination, PdO/Al2O3 and PdO/SiO2–Al2O3 catalyst precursors were obtained. X-ray powder diffraction and low temperature N2 adsorption–desorption measurements showed that the addition of silica increased the thermal stability, surface acidity, specific surface area and total pore volume of the spherical alumina. Temperature programmed reduction and H2–O2 titration indicated that Pd supported on the SiO2–Al2O3 spheres possessed higher dispersion and smaller particle size than that supported on pristine spherical Al2O3. Catalytic hydrogenation of ethylanthraquinone using molecular hydrogen was studied over the reduced Pd/Al2O3 and Pd/SiO2–Al2O3 catalysts with different silica contents. Under identical reaction conditions, the reaction activity and stability increased with increasing silica content.
Keywords: Hydrogen peroxide; Ethylanthraquinone; Eggshell palladium catalyst; High dispersion;
MOF-5 as an efficient heterogeneous catalyst for Friedel–Crafts alkylation reactions by Nam T.S. Phan; Ky K.A. Le; Tuan D. Phan (246-253).
MOF-5 was used as an efficient heterogeneous acid catalyst for the Friedel–Crafts alkylation reaction. Quantitative conversion was achieved under mild conditions without the need for an inert atmosphere.A highly porous metal-organic framework (MOF-5) was synthesized by a solvothermal method, and used as an efficient heterogeneous acid catalyst for Friedel–Crafts alkylation reactions. The solid acid catalyst was characterized using a variety of different techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), atomic absorption spectrophotometry (AAS), and nitrogen physisorption measurements. Quantitative conversion was achieved under mild conditions without the need for an inert atmosphere. The MOF-5 catalyst could be facilely separated from the reaction mixture, and could be reused several times without significant degradation in catalytic activity. Furthermore, no contribution from homogeneous catalysis of active acid species leaching into reaction solution was detected.
Keywords: Metal-organic framework; Friedel–Crafts alkylation; Solid acid catalyst;
Direct detection of coking and regeneration of single particles and fixed bed reactors by electrical sensors by N. Müller; C. Kern; R. Moos; A. Jess (254-262).
A new sensor concept which allows us to measure coking and regeneration process of a heterogeneous catalyst is discussed. It enables monitoring of the axial coke profile of a fixed bed by means of distributed sensors. The velocity of the reaction front and the length of the reaction zone are directly deduced from the local transient change of the sensor signal.The activity of solid catalysts is often reduced by the formation of coke. Thus, regeneration by coke burn-off is needed from time to time. A new method to monitor in situ the coke load during coking and decoking by electrical sensors is presented, which could be used as a controlling instrument of high value. Single particles of an Al2O3 catalyst were electrically contacted and characterised by impedance spectroscopy. A clear relationship between coke load and the impedance is observed. The sensor was tested by regeneration experiments both with single particles and in a coked fixed bed reactor. The results show that the coke burn-off within a single coked catalyst particle can be monitored and that it is possible to distinguish how strong the decoking of a single particle is influenced by pore diffusion. For a fixed bed, the axial coke profile can be monitored by means of axially distributed sensors, and the velocity of the reaction front and the length of the reaction zone are directly deduced by the local change of the coke profile with time.
Keywords: Regeneration; Coke burn-off; Sensor; Impedance spectroscopy;
Origin of the rate enhancement and enantiodifferentiation in the heterogeneous enantioselective hydrogenation of 2,2,2-trifluoroacetophenone over Pt/alumina studied in continuous-flow fixed-bed reactor system by György Szőllősi; Szabolcs Cserényi; Imre Bucsi; Tibor Bartók; Ferenc Fülöp; Mihály Bartók (263-271).
Based on the results of a study on the enantioselective hydrogenation of 2,2,2-trifluoroacetophenone over cinchona alkaloids modified Pt catalysts in the absence or in the presence of trifluoroacetic acid using continuous-flow fixed-bed reactor system and racemic – cinchona 1–cinchona 2–cinchona 1 hydrogenation series we propose reaction routes determined by the equilibrium between the electrophilic and nucleophilic intermediate complexes.A study on the origin of rate enhancement and enantiodifferentiation in the enantioselective hydrogenation of 2,2,2-trifluoroacetophenone (TFAP) over a Pt/alumina catalyst modified by cinchona alkaloids in toluene/acetic acid (AcOH) solvent mixture with and without trifluoroacetic acid (TFA) using continuous-flow fixed-bed reactor system is presented. The experimental data of the racemic – cinchona 1–cinchona 2–cinchona 1 hydrogenation series confirm the intrinsic nature of rate enhancement, namely the so-called “ligand acceleration” phenomenon. Hydrogenation in the presence of 0.1% (v/v) TFA follows the general rule of the Orito reaction, according to which the products formed in excess are (R)-alcohols on Pt-cinchonidine and Pt-quinine and (S)-alcohols on Pt-cinchonine and Pt-quinidine chiral catalysts. In toluene/AcOH mixture without TFA, unexpected inversion took place on the Pt-cinchonine and Pt-quinidine catalysts since the (R)-product formed in excess instead of the (S)-product. The observed unexpected inversion can be interpreted on the basis of the nucleophilic intermediate complex. Based on these observations we propose that in the hydrogenation of TFAP the reaction route involves the equilibrium of electrophilic and nucleophilic intermediate complexes, which was found to be dependent on the acid strength and concentration.
Keywords: Asymmetric hydrogenation; Platinum; Cinchona alkaloids; Trifluoroactophenone; Continuous-flow fixed-bed reactor; Origin of rate enhancement; Origin of enantiodifferentiation;
Highly basic catalysts obtained by intercalation of La-containing anionic complexes in layered double hydroxides by Iuliana Cota; Eliana Ramírez; Francisco Medina; Jesús E. Sueiras; Géraldine Layrac; Didier Tichit (272-276).
Preformed negatively charged guest La hydroxy citrate colloids were introduced into host Mg/Al LDHs to give nanocomposites precursors for La/Mg(Al)O(x) mixed oxides. The TPD of CO2 indicates the generation of strong basic sites. Accordingly the La/Mg(Al)O(x) mixed oxides were found highly active for the synthesis of unsymmetrical organic carbonates.Nanocomposites have been obtained by intercalation of preformed negatively charged guest La hydroxy citrate colloids into host Mg/Al layered double hydroxides (LDH). These compounds have been used as precursors for La/Mg(Al)O mixed oxides catalysts. The La loading has been controlled by the colloids exchange rate in order to achieve a better dispersion of the lanthanum cations and thus improve the basic properties of the new catalysts. The increase of the d 0 0 3 interlayer distance from 0.830 nm in the host LDH to 1.196 nm in the nanocomposites shows that the intercalation has taken place leading to 1.82–11.16 wt% of lanthanum cation loadings. The basic properties of the La/Mg(Al)O(x) mixed oxides were evaluated qualitatively using Hammett indicators and quantitatively by TPD of CO2. Both techniques indicated the presence of strong basic sites. The transesterification of 1-phenylethanol with diethylcarbonate (DEC), which is known to involve strong basic sites, was used to evaluate the catalytic activity of the La/Mg(Al)O(x) mixed oxides. Yields into carbonate product increase with the density of strong basic sites of the catalyst.
Keywords: Layered double hydroxides; Basic catalysts; Lanthanum; Nanocomposites; Unsymmetrical organic carbonates;
Enhanced electrocatalytic reduction of CO2/H2O to paraformaldehyde at Pt/metal oxide interfaces by Boxun Hu; Victor Stancovski; Martha Morton; Steven L. Suib (277-283).
The simultaneous activation of CO2 and H2O was performed by polarizing metal/metal oxide interfaces with a DC voltage or current. The selectivity of CO2 to paraformaldehyde was as high as 100% and CO2 conversion up to 8% with Pt/calcia stabilized zirconia (CSZ) catalysts at temperatures of 600–900 °C and at a pressure of 1 atm. The temperature was lowered to 350–450 °C when using Pt/MnO2 catalyst.A long-standing goal of chemistry is to synthesize organic compounds from CO2 and H2O to mimic natural photosynthetic processes. Achieving this goal requires catalysts and methods that activate CO2 and split water simultaneously. Here we report such catalysts and methods for the synthesis of paraformaldehyde from CO2 and H2O at atmospheric pressure. The activation was realized by polarizing metal/metal oxide interfaces with a DC voltage or current. The selectivity to paraformaldehyde was as high as 100% and CO2 conversion up to 8%. Both Pt/CSZ and Pt/MnO2 catalysts with ionic conductivity and mixed conductivity respectively produced paraformaldehyde. The former works at high temperatures of 600–900 °C; the latter works at low temperatures of 300–450 °C. This gas-phase electrocatalysis technique provides new insight into the utilization of CO2 as a carbon source in organic chemical syntheses and in the clean activation of CO2.
Keywords: Platinum; CO2 activation; Electrocatalysis; Formaldehyde;
Synthesis of TiO2-coated CoFe2O4 photocatalysts applied to the photodegradation of atrazine and rhodamine B in water by Henrique A.J.L. Mourão; Andréa R. Malagutti; Caue Ribeiro (284-292).
Nanocomposites of TiO2/CoFe2O4 were prepared by the polymeric precursor method. The materials showed photocatalytic activity due to the presence of TiO2 on their surface, associated with the magnetic activity of CoFe2O4 cores. In rhodamine photodegradation, pure TiO2 showed higher photocatalytic efficiency. However, in atrazine photodegradation, the nanocomposites were more effective than pure TiO2.Various strategies for the synthesis of anatase TiO2 nanoparticles and nanocomposites with particular morphologies and stability are currently generating a lot of interest and many research papers. In this study, composites of TiO2/CoFe2O4 in nanometric sizes were prepared by the polymeric precursor method. These materials were characterized by X-ray diffraction, Raman spectroscopy, surface area through N2 physisorption, Zeta potential, scanning and high-resolution transmission electron microscopy. The photocatalytic potential of the nanocomposites prepared was assessed by photodegradation of rhodamine B dye and atrazine pesticide under UV light. The materials showed photocatalytic activity due to the presence of TiO2 on their surface, associated with the magnetic activity of CoFe2O4 cores, which is useful for the separation and recovery of the photocatalysts after use in an oxidative process. In rhodamine photodegradation, pure TiO2 showed higher photocatalytic efficiency than the nanocomposites. However, in atrazine photodegradation, the nanocomposites were more effective, being this effect attributed to difference in charge at the surface of pure TiO2 and of nanocomposites, which enables adsorption processes of atrazine molecules on nanocomposites surface, and consequently, their higher photoactivity.
Keywords: Photocatalysis; Nanocomposites; Titanium dioxide;
Spinel-type zinc aluminate (ZnAl2O4) nanoparticles prepared by the co-precipitation method: A novel, green and recyclable heterogeneous catalyst for the acetylation of amines, alcohols and phenols under solvent-free conditions by Saeid Farhadi; Somayeh Panahandehjoo (293-302).
Zinc aluminate (ZnAl2O4) nanoparticles with an average particle size of 8 nm were easily prepared by the co-precipitation method and used as a novel and environmentally benign recyclable heterogeneous catalyst for the efficient and selective acetylation of various amines, alcohols and phenols with acetic anhydride and/or acetyl chloride as the acetylating agents at room temperature under solvent-free conditions.Zinc aluminate (ZnAl2O4) nanoparticles with an average particle size of about 8 nm were easily prepared by the co-precipitation method using aqueous ammonia solution as the precipitating agent. This nanosized spinel-type oxide was characterized by TGA, XRD, FT-IR, TEM, and surface area measurement and used as the heterogeneous catalyst for the acetylation reaction. Efficient acetylation of various amines, alcohols and phenols was carried out over ZnAl2O4 nanoparticles using acetic anhydride and/or acetyl chloride as the acetylating agents at room temperature without the use of a solvent. The method is highly selective, allowing the alcoholic hydroxyl group to be protected while the phenolic hydroxyl group remains intact, and the amine group can be acetylated in the presence of the hydroxyl group. This method is fast and has a high yield. It is also clean, safe, cost effective, compatible with substrates that have other functional groups and very suitable for practical organic synthesis. In addition, the catalyst can be reused without significant loss of activity. Indeed, the catalytic activity of the ZnAl2O4 nanoparticles is higher than that of bulk ZnAl2O4.
Keywords: Spinel-type oxide; Zinc aluminate; Nanoparticles; Acetylation; Solvent-free conditions;
Elucidating the role of Cu species in the oxidative carbonylation of methanol to dimethyl carbonate on CuY: An in situ spectroscopic and catalytic study by Jana Engeldinger; Christine Domke; Manfred Richter; Ursula Bentrup (303-311).
CuY catalysts with varied Cu content were examined by in situ FTIR investigations to characterize the Cu species and elucidate their specific role in the oxidative carbonylation of methanol. High Cu loadings favor oxidation and oxocarbonylation reactions of methanol and enhance the formation of dimethyl carbonate confirmed also by the catalytic tests.CuY catalysts with varied Cu content obtained by incipient-wetness-impregnation of commercial NH4-Y zeolite with copper nitrate solution and calcination at 400 °C in air were examined by in situ FTIR investigations to characterize the Cu species and elucidate their specific role in the oxidative carbonylation of methanol. The adsorption of CO was applied to check the state of Cu(I) species whereas the acidity was characterized by pyridine adsorption. Depending on the Cu content different intensity ratios of the characteristic Cu(I)–CO bands at 2160 and 2146 cm−1 were observed which give information about the distribution of Cu(I) cations at different positions near the supercage. Lewis sites of different strengths are created by introduction of Cu resulting from Cu(I)/Cu(II) cations positioned in the super cages.MeOH adsorbs dissociatively on preferable Cu(I) Lewis sites by formation of methoxy species without additional supply of oxygen. Methoxy species and CO adsorb at the same Cu sites. Oxygenated products (monomethyl carbonate, dimethyl carbonate, CO2) are formed during simultaneous adsorption of MeOH and CO with and without oxygen which indicates a participation of lattice oxygen of CuO x aggregates in the oxidation process and points to a Mars-van-Krevelen mechanism. Adsorbed formate species more pronounced at higher Cu loadings were additionally found. CO reacts with adsorbed methoxy species by formation of mainly monomethyl carbonate whereas the simultaneous presence of formate-like species promotes the formation of dimethyl carbonate. This implicates a specific role of adsorbed carbonate-like species for dimethyl carbonate formation. High Cu loadings were found to be beneficial because the additional formation of CuO x agglomerates in the super cages favors oxidation and oxocarbonylation reactions of methanol and enhances the formation of dimethyl carbonate which was also confirmed by the catalytic tests.
Keywords: CuY zeolite; Dimethyl carbonate; FTIR spectroscopy;
A periodic mesoporous hybrid material with a built-in palladium complex: An efficient catalyst for the Suzuki coupling and alcohol oxidation by Hengquan Yang; Zhancheng Ma; Yong Qing; Guangyong Xie; Jie Gao; Li zhang; Jinhua Gao; Lin du (312-321).
A new periodic mesoporous hybrid material with a built-in Pd–guanidine complex has been synthesized in the presence of a structure-directing agent. The synthesized solid material exhibited high activity and recyclability for the Suzuki coupling reactions of various aryl bromides in air and the aerobic oxidation of benzylic alcohols under ambient pressure of O2.A new periodic mesoporous hybrid material with a built-in Pd–guanidine complex was synthesized in the presence of a structure-directing agent. The N2 sorption, XRD and TEM characterizations revealed that this hybrid material had a large surface area (>700 m2 g−1), a narrow pore size distribution (centered at 2.7 nm), and a periodic 2D-hexagonal structure. FT-IR, solid state NMR and XPS investigations confirmed that palladium–guanidine complex was covalently integrated with the solid material. The solid material exhibited high activity for the Suzuki coupling reaction of various aryl bromides in an aqueous ethanol solution under air. Furthermore, it was found that the solid material worked well for the aerobic oxidation of benzylic alcohols under ambient pressure of O2, affording over 99% selectivity. This catalyst could be reused 9 times without a decrease in selectivity. This study supplies a new periodic mesoporous hybrid material with a built-in active palladium sites, which may be applied to other catalytic reactions.
Keywords: Mesoporous material; Metal complex; Guanidine; Suzuki coupling; Alcohol oxidation;
Visible photodecomposition of methylene blue over micro arc oxidized WO3–loaded TiO2 nano-porous layers by M.R. Bayati; F. Golestani-Fard; A.Z. Moshfegh (322-331).
(WO3) x -(TiO2)1-x layers were grown by microarc oxidation process under direct current, and a formation mechanism was proposed based on the electrochemical foundations. The layers were porous and rough and consisted of anatase, rutile, and tungsten oxide phases. The reaction rate constants of MB degradation on the layers were measured as k=2.2×10−2 and k=0.93×10−2 min−1 for UV and visible irradiations, respectively.WO3-TiO2 nano porous layers were synthesized by micro arc oxidation (MAO) process under different applied voltages in electrolytes containing sodium tungstate and phosphate salts with various concentrations. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDS) techniques were employed to study phase structure and chemical composition of the layers. According to our data analysis, the nano porous layers consisted of anatase, rutile, and tungsten oxide phases with a varying fraction depending on the voltage and electrolyte concentration. Moreover, it was found that WO3 not only dispersed in the TiO2 matrix, but also doped into the TiO2 lattice. Morphological and topographical investigations, carried out by scanning electron microscopy (SEM) and atomic force microscopy (AFM), revealed a porous structure with a rough surface. The pore size and the surface roughness of the layers increased with the applied voltage or the electrolyte concentration. The absorption edge of the layers, measured by a UV-Vis spectrophotometer, was observed to shift toward longer wavelengths when WO3 was introduced to the TiO2 layers. The band gap energy was determined as 3.21 eV and 2.88 eV for the MAO-grown TiO2 and WO3-TiO2 systems, respectively. Furthermore, photocatalytic activity of the layers was also examined by measuring the decomposition rate of methylene blue under both ultraviolet and visible photo irradiations. It was observed that the composite layers were more photoactive as compared to MAO-synthesized pure TiO2 layers. A possible growth mechanism was also proposed for the formation of WO3-TiO2 films via MAO process with emphasis on the electrochemical bases for the first time.
Keywords: Methelyne blue; Titanium oxide; Tungsten oxide; Porous materials; Photocatalysis;
Hydrogenation of sunflower oil over platinum supported on silica catalysts: Preparation, characterisation and catalytic activity by Shane McArdle; Teresa Curtin; J.J. Leahy (332-338).
The effect of varying the Pt content over a mesoporous SiO2 support was investigated for activity and selectivity to trans fatty acid formation during hydrogenation of sunflower oil. The amount of Pt supported on the silica was shown to influence the selectivity to trans C18:1.The effect of varying the Pt content (0.7 - 4.6 wt %) over a novel mesoporous SiO2 support was investigated for hydrogenation of sunflower oil. The reaction was carried out in a batch reactor at 170 °C, 400 rpm and 3 bar hydrogen pressure. The activity and selectivity of the different catalysts to trans fatty acid formation were compared. The choice of metal precursor affected the catalyst activity, H2PtCl6 showed a moderate increase of the Pt activity compared to Pt(AcAc)2. The presence of chlorine on a supported catalyst is believed to give rise to improved hydrogen spillover, which in turn may improve the hydrogenation activity. For the catalysts prepared using Pt(AcAc)2, the activity improved with increased Pt loading up to 1.5%Pt, above which no significant increase in activity was observed with additional Pt loading. Additionally, it was found that the activity per exposed metal was greater at lower Pt loadings. The amount of Pt supported on the silica was shown to influence the selectivity to trans C18:1. Increasing the Pt loading from 0.7% to 4.6% correspondingly decreased the metal dispersion and increased the metal particle size. The smaller particles on the 0.7%Pt/SiO2, 1.5%Pt/SiO2 and the 2.7%Pt/SiO2 catalysts presented a lower trans content compared to the 4.6%Pt/SiO2 catalyst that exhibited larger particles.
Keywords: Pt supported on silica; Hydrogenation of sunflower oil; Trans fatty acids;
Room temperature aerobic Suzuki cross-coupling reactions in DMF/water mixture using zeolite confined palladium(0) nanoclusters as efficient and recyclable catalyst by Feyyaz Durap; Murat Rakap; Murat Aydemir; Saim Özkar (339-344).
Zeolite confined palladium(0) nanoclusters are found to be efficient and recyclable catalysts for the Suzuki cross-coupling reactions of aryl bromides with phenylboronic acid under mild conditions (at room temperature and in air) in DMF/water (1:9) mixture, giving biaryl derivatives in high yield as determined by GC.Herein we report the use of zeolite confined palladium(0) nanoclusters as efficient and recyclable catalyst for Suzuki cross-coupling reactions of aryl bromides with phenylboronic acid. Zeolite confined palladium(0) nanoclusters are highly active catalyst for the Suzuki cross-coupling reactions under mild conditions (room temperature, in air) in DMF/water (1:9) mixture. A variety of aryl bromides undergo Suzuki cross-coupling with phenylboronic acid with quantitative GC yields of biaryl derivatives. Recycling experiments showed that zeolite confined palladium(0) nanoclusters can be used as recyclable catalyst in the Suzuki cross-coupling reactions.
Keywords: Zeolite; Palladium; Nanoclusters; Suzuki cross-coupling; Catalysis;