Applied Catalysis A, General (v.366, #1)
Editorial Board (CO2).
Retraction notice to “Catalytic applications of ordered mesoporous magnesium oxide synthesized by mesoporous carbon” [Appl. Catal. A: Gen. 338 (2008) 20–26] by Amit Dubey; Braj Gopal Mishra; Divya Sachdev (1).
The direct transformation of carbon dioxide to organic carbonates over heterogeneous catalysts by Wei-Li Dai; Sheng-Lian Luo; Shuang-Feng Yin; Chak-Tong Au (2-12).
The recent development of heterogeneous catalysts for the synthesis of valuable organic carbonates from CO2 through various synthetic routes has been reviewed. The supported ionic liquids are worthy of further research. The mechanisms of acid–base or electrophile–nucleophile catalysis proposed in the literature will be valuable for the design and fabrication of high-performance catalysts.In this review article, we report the recent developments of heterogeneous catalysts for the synthesis of cyclic and dimethyl carbonates from CO2 through various routes. The synthesis of cyclic carbonates via cycloaddition of CO2 to epoxides is one of the few processes that have been commercialized. Compared to the many effective homogeneous catalysts, the heterogeneous catalysts have the advantages of being superior in stability and reusability. However, of the reported catalysts including metal oxides, zeolites, smectite, supported organic bases, metal complexes, and ionic liquids, none can be considered as highly active and selective under mild conditions. Also, heterogeneous catalysts used in other routes do not perform satisfactorily. The supported ionic liquids have attracted much more attention and are worthy of further research for the cycloaddition reaction. We predict that the mechanisms of acid–base or electrophile–nucleophile catalysis proposed in the literature will be valuable for the design and fabrication of high-performance catalysts.
Keywords: Carbon dioxide utilization; Cyclic carbonate; Dimethyl carbonate; Heterogeneous catalysts;
Simulation of SCR equipped vehicles using iron-zeolite catalysts by Mona Lisa Moura de Oliveira; Carla Monteiro Silva; Ramon Moreno-Tost; Tiago Lopes Farias; Antonio Jiménez-López; Enrique Rodríguez-Castellón (13-21).
Three iron containing SCR catalysts were studied and a neural network-based approach to predict NO x conversion efficiency was proposed. The derived mathematical functions are integrated in a numerical model for diesel road vehicle simulation to simulate diesel vehicles equipped with such SCR catalysts. The simulation results on real cycles show lower levels of NO x for heavy-duty and light-duty diesel vehicles, compared with homologation load cycles.Iron-catalysts, based on ZSM-5 (FeZSM5) and Cuban natural Mordenite (FeMORD) zeolites have been prepared by a conventional ion-exchange method and their catalytic activity in the selective catalytic reduction (SCR) of NO with ammonia was studied in the presence of H2O and SO2. A commercial SCR catalyst (CATCO) based on V2O5–WO3–TiO2, was also studied as a reference. This paper presents the experimental results of using these catalysts without toxic vanadium and also exploits a neural network-based approach to predict NO x conversion efficiency of three SCR catalysts. The mathematical functions derived have been integrated into a numerical model to simulate diesel road vehicles equipped with SCR catalysts such as those studied here. The main results indicate that despite toxic vanadium and N2O formation, CATCO shows better NO x conversion efficiencies. However, FeMORD does not produce N2O and performs better than the FeZSM5. The simulation results on real cycles show lower level of NO x for heavy-duty and light-duty diesel vehicles compared with homologation load cycles.
Keywords: SCR; NO x ; Diesel road vehicle; Zeolites; Neural networks; Road vehicle simulator;
Supported hydrogensulfate ionic liquid catalysis in Baeyer–Villiger reaction by Anna Chrobok; Stefan Baj; Wojciech Pudło; Andrzej Jarzębski (22-28).
An efficient new procedure for the oxidation of cyclic ketones using macroporous silica supported hydrogensulfate ionic liquid as an active and low cost Brønsted acidic catalyst has been developed. The catalyst was easily separated from the reaction mixture and was recycled four times without any loss in activity.We report here the method of synthesis and characterisation of ionic liquid: 1-methyl-3-(triethoxysilylpropyl)imidazolium hydrogensulfate, anchored onto solid support via cation–anion stays unbounded to the surface. As a support, we used a silica material with the extensive system of meso- and macropores. The structure of the support was not destroyed after the immobilisation of the ionic liquid. The new material was tested as acidic catalyst with the Baeyer–Villiger reaction. Cyclic ketones were readily oxidised with 68% hydrogen peroxide in dry dichloromethane to their corresponding lactones in high yields (60–91%) at 50 °C within a short time (5–20 h). The use of hydrogen peroxide and a heterogeneous catalyst allows a clean oxidation and the possibility of easy catalyst removal by simple filtration and reuse three times in another oxidation process without lost of catalyst activity.
Keywords: Immobilisation of ionic liquids; Macroporous silica support; Baeyer–Villiger oxidation;
Effects of H2S and process conditions in the synthesis of mixed alcohols from syngas over alkali promoted cobalt-molybdenum sulfide by J.M. Christensen; P.M. Mortensen; R. Trane; P.A. Jensen; A.D. Jensen (29-43).
The work is an investigation of how the process conditions influence the synthesis of mixed alcohols from syngas over a K2CO3/Co/MoS2/C catalyst. The presence of more than 103 ppmv H2S in the feed stabilizes a high fraction of higher alcohols in the product (see figure), but the presence of H2S in the feed also leads to the incorporation of sulfur species into the alcohol product.The present work is an investigation of how the process conditions influence the synthesis of mixed alcohols from syngas over a K2CO3/Co/MoS2/C catalyst. The emphasis in the investigations is upon the effects of H2S in the syngas feed. However the effects of the temperature and of the partial pressures of H2 and CO are also investigated. With or without H2S in the feed the pre-sulfided catalyst requires an initiation period to reach a stabilized behavior, but the duration of this period depends upon the H2S level. Operation with a feed containing more than 103 ppmv H2S leads to a fairly rapid stabilization of the product distribution and ensures that higher alcohols are the dominant reaction products. With less than 57 ppmv H2S in the feed the stabilization of the product distribution is much slower, and methanol is the dominant product. An investigation of the reaction kinetics indicates a high CO coverage and low hydrogen coverage. Hydrogen sulfide in the syngas feed generally promotes chain growth for both alcohols and hydrocarbons, but lowers the alcohol selectivity by enhancing the hydrocarbon formation. The highest alcohol productivity reached in these investigations was 0.276 g/g cat./h, and this was achieved at 350 °C, 100 bar, GHSV = 5244 h−1, Feed: 49.9 vol% H2, 50.1 vol% CO. Finally it is found that sulfur fed to the reactor as H2S is incorporated into the condensed alcohol product, and the incorporation of sulfur species into the product continues for some time after H2S has been removed from the feed. When the catalyst is operated with an S-free syngas feed, the amount of sulfur in the condensed liquid product decreases over time, but after 35 h of operation with an S-free syngas the alcohol product still contains 340 ppmw of sulfur. Thiols appear to be the dominant sulfur compounds in the product.
Keywords: Syngas; MoS2; Higher alcohols; H2S; Synthetic fuels;
Heterogeneous hydrogenation of nitrobenzenes over recyclable Pd(0) nanoparticle catalysts stabilized by polyphenol-grafted collagen fibers by Hao Wu; Liangming Zhuo; Qiang He; Xuepin Liao; Bi Shi (44-56).
A novel heterogeneous palladium (Pd) nanoparticle catalyst stabilized by collagen fibers (CF) was synthesized. Epigallocatechin-3-gallate (EGCG), a typical natural polyphenol, was grafted onto the CF surface to improve the stabilization and immobilization of Pd(0) nanoparticles. These well-dispersed Pd(0) nanoparticles were found to be active, selective and recyclable catalysts for the hydrogenation of nitrobenzenes under mild reaction conditions.A novel heterogeneous palladium (Pd) nanoparticle catalyst stabilized by collagen fibers (CF) was synthesized. Epigallocatechin-3-gallate (EGCG), a typical natural polyphenol, was grafted onto the CF surface to improve the stabilization and immobilization of Pd(0) nanoparticles. The main physical and chemical properties of the catalyst were characterized by means of Scanning Electron Microscopy, Fourier Transform-Infrared Spectroscopy, X-ray Photoelectron Spectroscopy, X-ray Diffraction and Transmission Electron Microscopy. This catalyst is in an ordered fibrous state with high flexibility. The Pd(0) nanoparticles with diameters of 3–4 nm are homogeneously dispersed onto the outer surfaces of CF, and they are stabilized by the coordinative interactions between the surface Pd atoms of nanoparticle and the surrounding oxygen and nitrogen atoms of the EGCG-grafted CF. These stabilized Pd(0) nanoparticles were found to be active and selective catalysts for nitrobenzene and its derivatives, directly hydrogenating to the correspondingly reductive anilines under mild conditions. Both Pd particle size and activity of the catalyst showed a marked dependence on the grafting degree of EGCG on CF. These catalysts can be easily recovered, reused multiple times, and stored for two months in air while maintaining high catalytic efficiencies. All these facts suggest that the EGCG-grafted CF can be used as an effective stabilizer for the preparation of Pd(0) nanoparticle catalysts.
Keywords: Palladium nanoparticles; Collagen fiber; Epigallacatechin-3-gallate; Heterogeneous catalysis; Nitrobenzene; Hydrogenation;
A simple co-impregnation route to load highly dispersed Fe(III) centers into the pore structure of SBA-15 and the extraordinarily high catalytic performance by Yongsheng Li; Yong Chen; Liang Li; Jinlou Gu; Wenru Zhao; Lei Li; Jianlin Shi (57-64).
Highly dispersed iron centers supported on SBA-15 were successfully prepared via a simple incipient wetness co-impregnation route of carbon and iron sources into the pore structure of SBA-15. The catalyst demonstrates high reusability and stability, and the yield of diphenylmethane was still higher than 90% after 6 runs. The strategy is also verified to be applicable to prepare other well-dispersed metal oxides, i.e. Mn x O y loaded on mesoporous materials.Highly dispersed iron centers supported on SBA-15 were successfully prepared via a simple incipient wetness co-impregnation route by casting furfuryl alcohol (FA) solution of iron (III) acetylacetonate (Fe(acac)3), which were used as carbon and iron sources, respectively, into the pore structure of SBA-15, followed by the subsequent removal of carbonized FA. Various techniques such as XRD, TEM, N2 sorption, UV–vis, XPS and EPR, were employed to characterize the prepared catalysts. It was shown that both Fe2O3 nanoclusters and isolated iron species were present and highly dispersed onto the pore surface of SBA-15, due to the presence of abundant carbon source co-impregnated, with well-maintained, highly ordered and open mesoporous structure. A great number of acidities was introduced by the loading of Fe2O3, and the catalytic performance was tested on the Friedel–Crafts benzylation of benzene by benzyl chloride. Under the optimized reaction condition, the catalyst showed a superior catalytic performance with a 100% yield of monoalkylated product within 1.5 min at 60 °C. The catalyst demonstrated high reusability and stability, the yield of diphenylmethane was still higher than 90% after 6 runs. Moreover, the catalyst was still active at the temperature as low as 40 °C. Such a strategy is verified applicable to prepare other well-dispersed metal oxides, i.e. Mn x O y loaded into the pore structure of mesoporous materials.
Keywords: SBA-15; High dispersivity; Iron oxide; Incipient wetness impregnation; Catalytic activity;
Vapor phase alkylation of pyrrole with methanol and dimethylcarbonate over ferrospinels by Pawan Siwach; Surander Singh; R.K. Gupta (65-70).
The vapor phase alkylation of pyrrole was carried out over ferrospinels using methanol and dimethylcarbonate (DMC). The activity of the catalysts varied with the acidity of the ferrospinel systems tested. The yields of 2-methylpyrrole with respect to the conversion of pyrrole were 77.2% and 70.4% when methanol and DMC were used as alkylating agents, respectively, over CoFe2O4 under optimized conditions.The vapor phase alkylation of pyrrole was carried out over ferrospinels using methanol and dimethylcarbonate (DMC). The activity of the catalysts varied with the acidity of the ferrospinel systems tested. The yields of 2-methylpyrrole with respect to the conversion of pyrrole were 77.2% and 70.4% when methanol and DMC were used as alkylating agents, respectively, over CoFe2O4 under optimized conditions.
Keywords: Alkylation; Alkylating agent; Ferrospinels; Pyrrole; 2-Methylpyrrole;
An investigation of carbon-supported CuCl2/PdCl2 catalysts for diethyl carbonate synthesis by Daniel N. Briggs; Kenneth H. Lawrence; Alexis T. Bell (71-83).
The synthesis of diethyl carbonate by the oxidative carbonylation of ethanol was investigated using catalysts prepared by dispersing CuCl2 and PdCl2 on amorphous carbon. Evidence from XRD, XAFS, SEM and TEM indicated that copper is present as [CuCl2]− anions, whereas palladium exists as large PdCl2 particles. Together with catalysis data, these results suggest that DEC synthesis may occur on [PdCl2−x ][CuCl2] x species deposited on the surface of PdCl2 particles.The synthesis of diethyl carbonate (DEC) by the oxidative carbonylation of ethanol was investigated using catalysts prepared by the dispersion of CuCl2 and PdCl2 on amorphous carbon promoted with KCl and NaOH. Catalysts were characterized extensively by XRD, XAFS, SEM and TEM with the aim of establishing their composition and structure after preparation, pretreatment, and use. It was observed that after preparation and pretreatment in He at 423 K copper is present almost exclusively as Cu(I), most likely in the form of [CuCl2]− anions, whereas palladium is present as large PdCl2 particles. Catalysts prepared exclusively with copper or palladium chloride are inactive for DEC synthesis, indicating that both components must be present together. Evidence from XANES and EXAFS suggests that the DEC synthesis may occur on [PdCl2−x ][CuCl2] x species deposited on the surface of the PdCl2 particles. As-prepared catalysts exhibit an increase in DEC synthesis activity and selectivity with time on stream, but then reach a maximum activity and selectivity, followed by a slow decrease in DEC activity. The loss of DEC activity is accompanied by a loss in Cl from the catalyst and the appearance of paratacamite.
Keywords: Diethyl carbonate; Chlorocuprates; Copper chloride; Palladium chloride; Carbon-supported catalysis; X-ray absorption spectroscopy;
Transient reaction analysis and steady-state kinetic study of selective catalytic reduction of NO and NO + NO2 by NH3 over Fe/ZSM-5 by Masaoki Iwasaki; Kiyoshi Yamazaki; Hirofumi Shinjoh (84-92).
The reaction kinetics of SCRs by NH3 on NO (standard SCR) and NO + NO2 (fast SCR) over Fe/ZSM-5 were investigated. Although the standard SCR was transiently promoted in the absence of gaseous NH3, the fast SCR was not. The steady-state rate analysis combined with modeling suggested that competitive adsorption between NO2 and NH3 was occurring in the fast SCR.The reaction kinetics of selective catalytic reduction (SCR) by NH3 on NO (standard SCR) and on NO + NO2 (fast SCR) over Fe/ZSM-5 were investigated using transient and steady-state analyses. In the standard SCR, the N2 production rate was transiently promoted in the absence of gaseous NH3; this enhancement can be attributed to the negative reaction order of NH3 (between −0.21 and −0.11). The steady-state data for the standard SCR could be fit to a Langmuir–Hinshelwood-type reaction between NOad and Oad to form NO2. In the fast SCR, however, the promotion behavior in the absence of gaseous NH3 was not observed and the apparent NH3 order changed from positive to negative with NH3 concentration. The steady-state rate analysis combined with elementary reaction modeling suggested that competitive adsorption between NO2 and NH3 was occurring due to strong NO2 adsorption; this must be the main reason for the absence of the promotion effect.
Keywords: Selective catalytic reduction; Nitric oxide; Zeolite; Fe; Reaction mechanism;
Oxidative carbonylation of methanol to dimethyl carbonate over CuCl/SiO2–TiO2 catalysts prepared by microwave heating: The effect of support composition by Jun Ren; Shusen Liu; Zhong Li; Xinglu Lu; Kechang Xie (93-101).
Quantum-chemical calculations on cluster models indicated that the interactions between CuCl molecules and the Si–O–Ti bonds lead to the formation of the relatively strongly bound O-complexes, in which the bridging oxygen atoms at Si–O–Ti bonds serve as electron-donating ligands to Cu+ centers of CuCl.Copper(I) chloride catalysts with a loading of 20 wt%, supported on silica–titania mixed oxides with Si/Ti ratios of 1, 5, 10 and 50 were prepared by conventional and microwave heating methods and tested in the oxidative carbonylation of methanol to dimethyl carbonate (DMC). X-ray diffraction (XRD), nitrogen adsorption, X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis (TGA) were used to examine the bulk and surface properties of the CuCl/SiO2–TiO2 catalysts. Quantum-chemical calculations were performed to explore the interaction of CuCl with the silica–titania support. Microwave heating showed some significant advantages over the conventional heating method, with markedly reduced preparation temperature and time, and provided improved catalytic activity in the oxidative carbonylation of methanol. The catalytic behavior of CuCl/SiO2–TiO2 in the test reaction studied was strongly dependent on the support composition. Incorporation of tetrahedral Ti(IV) species into the silica matrix could enhance the interaction of copper species with the oxide support. The improved catalytic performance of CuCl/SiO2–TiO2 in the DMC synthesis can be understood by the existence of the strong coordination interactions between the Cu+ centers of CuCl and the bridging oxygen atoms at the Si–O–Ti bonds in the silica–titania support.
Keywords: Dimethyl carbonate (DMC); Microwave heating; CuCl/SiO2–TiO2 catalysts; Quantum-chemical calculations; Cu–O coordination;
Pervaporation membrane reactor study for the esterification of acetic acid and isobutanol using polydimethylsiloxane membrane by Sevinc Korkmaz; Yavuz Salt; Ayca Hasanoglu; Semra Ozkan; Inci Salt; Salih Dincer (102-107).
In this study, isobutyl acetate is produced by pervaporation–esterification equilibrium reaction in a batch pervaporation membrane reactor (PVMR) using homogeneous (sulphuric acid) and heterogeneous (Dowex 50W-X8) catalysts. The ester-permeable polydimethylsiloxane (PDMS) membrane was used in order to shift the equilibrium by removal of iBAc from the reaction mixture. In conclusion, PVMR experiments showed that the PDMS membrane can be used to remove the isobutyl acetate formed selectively with acceptable conversions and pervaporation fluxes.In this study, isobutyl acetate, a valuable solvent in cosmetics, aroma and paint industries, is produced by pervaporation–esterification equilibrium reaction in a batch pervaporation membrane reactor (PVMR) using homogeneous (sulphuric acid) and heterogeneous (Dowex 50W-X8) catalysts. The effects of catalyst loading, catalyst type, reaction time, membrane thickness, temperature and initial molar ratio of reactants were investigated. A cross-linked polydimethylsiloxane (PDMS) membrane selective to esters was prepared and used in PVMR. Batch reactions were carried out also in a simple batch reactor (SBR) without pervaporation under the same conditions to compare the conversions for the reactions with and without pervaporation. In conclusion, PVMR experiments showed that the PDMS membrane can be used to remove the isobutyl acetate formed selectively with acceptable conversions and pervaporation fluxes.
Keywords: Pervaporation membrane reactor; Esterification; Isobutyl acetate; Polydimethylsiloxane;
Polyaniline-supported acid as an efficient and reusable catalyst for a one-pot synthesis of β-acetamido ketones via a four-component condensation reaction by Mohammad Reza Nabid; Seyed Jamal Tabatabaei Rezaei (108-113).
Polyaniline-supported acid salts were used as catalyst for the preparation of β-acetamido ketones. Present methodology offers several advantages, such as cheaper process, easy synthesis of stable catalyst, and excellent activity with less amount of catalyst and in addition, the catalyst can be easily recovered after completion of the reaction and reusable without affecting its activity.Polyaniline-supported acid salts such as polyaniline-hydrochloride, polyaniline-sulfate and polyaniline-nitrate were prepared by oxidation of aniline using ammonium persulfate as oxidizing agents. Polyaniline salts were used as catalyst for the preparation of β-acetamido ketones. Polyaniline-sulfate salt was found to be the best catalyst for the preparation of β-acetamido ketones. Present methodology offers several advantages, such as cheaper process, easy synthesis of stable catalyst, simple work-up procedure, and excellent activity with less amount of catalyst and in addition, the catalyst can be easily recovered after completion of the reaction and reusable without affecting its activity.
Keywords: Polyaniline salts; Reusable catalyst; β-Acetamido ketones; Multi-component reactions;
Surface changes in Ru/KL supported catalysts induced by the preparation method and their effect on the selective hydrogenation of citral by Jesús Álvarez-Rodríguez; Inmaculada Rodríguez-Ramos; Antonio Guerrero-Ruiz; Adolfo Arcoya (114-121).
Steric hindrances produced by metal nanoparticles of adequate size and shape inside the Ru/KL catalyst, prepared by incipient wetness impregnation (IWI-Ru), inhibit its activity in the hydrogenation of citral in the liquid phase, but enhance its selectivity towards unsaturated alcohols (G + N). This effect is not observed for Ru/KL catalysts prepared by other procedures.Several 2 wt.% Ru/KL supported catalysts were prepared by various methods with different ruthenium precursors and characterized by CO and H2 chemisorption, N2 adsorption, TPD of NH3, TEM and XPS. Furthermore, CO chemisorbed species have been studied by FT-IR and microcalorimetry. Characterization measurements of catalyst IWI-Ru, prepared by incipient wetness impregnation from ruthenium acetylacetonate, evidence metal nanoparticles of 1 nm placed inside the zeolite channels, thus blocking the accessibility to part of ruthenium loading inside the micropores. Catalyst prepared by treating the KL zeolite with RuCl3·xH2O aqueous solution (I-Ru) exhibits nanoparticles in the range 6–8 nm at the external surface and clusters smaller that 1 nm, inside the micropores. These latter do not significantly affect the diffusion of probe molecules through the channels. Catalytic performances in the selective hydrogenation of citral in the liquid phase, at 323 K and 5 MPa, show that IWI-Ru is less active than I-Ru, but more selective towards unsaturated alcohols. Furthermore, for IWI-Ru, selectivity increases with the increasing conversion. On the other hand, removal of acid sites of the I-Ru catalyst enhances the hydrogenation activity and increases the selectivity towards citronellal. All these results are analyzed and discussed in terms of the size, shape and location of ruthenium particles in the catalysts, as well as of the metal–support interaction.
Keywords: KL-zeolite; Ru catalysts; Citral hydrogenation; FT-IR spectroscopy; TEM; CO chemisorption; Hydrogen chemisorption; Microcalorimetry;
The effects of Pt promotion on the oxi-reduction properties of alumina supported nickel catalysts for oxidative steam-reforming of methane: Temperature-resolved XAFS analysis by N.V. Parizotto; D. Zanchet; K.O. Rocha; C.M.P. Marques; J.M.C. Bueno (122-129).
The effects of Pt promotion on the oxi-reduction properties of Ni/Al2O3 catalysts used in methane reforming were investigated. The presence of Pt plays an important role to maintain Ni in the metallic state at the inlet region of the bed, where CH4 and O2 coexist.The effects of Pt trace addition on the oxi-reduction properties of the Ni/Al2O3 and Ni/La–Al2O3 catalysts during partial oxidation of methane (POM) and autothermal reforming of methane (ATR) were investigated. The xPt–Ni/yLa–Al2O3 catalysts containing 15 wt% of Ni, 0 or 12 wt% of La and 0 or 0.05 wt% of Pt were characterized by temperature-resolved X-ray absorption near edge structure (XANES) spectroscopy under various atmospheres.The in situ XANES analysis for Pt–Ni/Al2O3 under H2 and CO revealed that the presence of Pt sites can initiate the NiO reduction process by rapid dissociation of H2 and migration of atomic H to the NiO surface by hydrogen spillover. On the other hand, in situ XANES analysis under CH4 showed that the presence of Pt sites induces the activation of the methane, probably by initial dissociation of methane (CH4 → CH3 + H) followed by migration of atomic H to the NiO surface. In situ XANES experiments under a POM mixture demonstrate that Pt has an important role keeping Ni in the metallic state. The catalytic test results for POM and ATR demonstrate that Pt is an important promoter to maintain Ni in the metallic state at the inlet region of the catalytic bed, where CH4 and O2 coexist.
Keywords: Ni catalyst; FTIR of adsorbed CO; Natural gas; Autothermal reforming of methane; Partial oxidation of methane; In situ XANES;
Photocatalytic activity of Ag-substituted and impregnated nano-TiO2 by R. Vinu; Giridhar Madras (130-140).
The photocatalytic activities of Ag-substituted, Ag-impregnated and unsubstituted combustion-synthesized nano-TiO2 were evaluated for the degradation of dyes and the selective conversion of cyclohexane to cyclohexanone. The activities of these catalysts for the above reactions are correlated with the surface area, band gap, hydroxyl content, photoluminescence intensity and oxide ion vacancy.Ag-substituted (Ag sub) and Ag-impregnated (Ag imp), anatase phase nano-TiO2 have been synthesized by solution combustion technique and reduction technique, respectively. The catalysts were characterized extensively by powder XRD, TEM, XPS, FT-Raman, UV absorption, FT-IR, TGA, photoluminescence, BET surface area and isoelectric pH measurements. These catalysts were used for the photodegradation of dyes and for the selective photooxidation of cyclohexane to cyclohexanone. The photoactivities of the combustion-synthesized catalysts were compared with those of commercial Degussa P 25 (DP 25) TiO2, and Ag-impregnated DP 25 (Ag DP). For the photocatalytic degradation of dyes, unsubstituted combustion-synthesized TiO2 (CS TiO2) exhibited the highest activity, followed by 1% Ag imp and 1% Ag sub. For the photoconversion of cyclohexane, the total conversion of cyclohexane and the selectivity of cyclohexanone followed the order: 1% Ag sub > DP 25 > CS TiO2 > 1% Ag imp > 1% Ag DP. The kinetics of the photodegradation of dyes and of the photooxidation of cyclohexane were modeled using Langmuir–Hinshelwood rate equation and a free radical mechanism, respectively, and the rate coefficients were determined. The difference in activity values of the catalysts observed for these two reactions and the detailed characterization of these catalysts are described in this study.
Keywords: Ag substitution; Ag impregnation; Combustion synthesis; Cyclohexane; Photooxidation; Rate coefficients;
Magnetic hydroxyapatite-encapsulated γ-Fe2O3 nanoparticles functionalized with basic ionic liquids for aqueous Knoevenagel condensation by Yan Zhang; Chungu Xia (141-147).
The aqueous Knoevenagel condensation reaction was investigated over hydroxyapatite-encapsulated γ-Fe2O3 nanoparticles that had been modified by diethyl aliphatic amine basic ionic liquids. Recycle of the catalyst, through convenient magnetic decantation, shows non-significant loss in activity. The excellent performance of the magnetic catalyst was attributed to the cooperativity between the base sites generated by the framework HAP and the supported basic ionic liquids.Hydroxyapatite-encapsulated γ-Fe2O3 nanoparticles functionalized with diethyl aliphatic amine basic ionic liquids were synthesized and used as efficient magnetic catalysts for aqueous Knoevenagel condensation reactions. Quantitative conversion of the reactants was achieved under mild conditions; recycle of the catalyst, through convenient magnetic decantation, shows non-significant loss in activity. In comparison with the controlled experiments catalyzed by homogeneous basic ionic liquids and the basic ionic liquid-modified polystyrene resin, the excellent performance of the magnetic catalyst was attributed to the cooperativity between the base sites generated by framework HAP and the supported basic ionic liquids.
Keywords: Magnetic separation; Basic ionic liquids; Knoevenagel condensation; Cooperativity;
Preparation and photocatalytic activity of Keggin-ion tungstate and TiO2 hybrid layer-by-layer film composites by Sayaka Yanagida; Akira Nakajima; Takayoshi Sasaki; Toshihiro Isobe; Yoshikazu Kameshima; Kiyoshi Okada (148-153).
Keggin ions (PW12O40 3− (PW12), SiW12O40 4− (SiW12), H2W12O40 6− (H2W12)) and TiO2 hybrid thin films were prepared using the layer-by-layer method. Their photocatalytic activities were investigated using gaseous 2-propanol decomposition. All films were transparent in the visible wavelength range. For 2-propanol decomposition, H2W12 was the most effective for the combination with TiO2 despite having the smallest TiO2 deposition amount. The photocatalytic activity of the PW12–TiO2 hybrid film was increased 2.3 times by visible light with UV illumination. This increase was less remarkable for hybrid films of other Keggin ions, suggesting that the visible light excitation of reduced PW12 plays an important role in the enhancement of 2-propanol decomposition.Keggin ions (PW12O40 3− (PW12), SiW12O40 4− (SiW12), H2W12O40 6− (H2W12) and TiO2 hybrid thin films were prepared using the layer-by-layer method. All films were transparent in the visible wavelength range. The photocatalytic activity of the PW12–TiO2 hybrid film was increased 2.3 times by visible light with UV illumination. The visible light excitation of reduced PW12 is important in enhancement of photocatalytic activity.
Keywords: Photocatalyst; Heteropolyacid; TiO2; Layer-by-layer method; 2-Propanol;
Optimization of the activity of CaO/Al2O3 catalyst for biodiesel production using response surface methodology by Masoud Zabeti; Wan Mohd Ashri Wan Daud; Mohamed Kheireddine Aroua (154-159).
The catalytic activity of CaO/Al2O3 was optimized for transesterification of palm oil using response surface methodology. The results proved that both the loading amount of CaO on the support and the calcination temperature had significant effects on the biodiesel yield. The maximum basicity and methyl ester yields obtained were approximately 194 μmol/g and 94%, respectively.In this work the response surface methodology (RSM) in conjunction with the central composite design (CCD) were used to optimize the activity of CaO/Al2O3 solid catalysts for the production of biodiesel. In order to measure the catalyst activity, we used palm oil as a representative raw material for the conversion to biodiesel. The biodiesel production was carried out in a batch laboratory scale reactor. The results showed that both the calcination temperature and the amount of calcium oxide loaded on the support had significant positive effects on the biodiesel yield. The maximum basicity and biodiesel yield obtained were about 194 μmol/g and 94%, respectively. Overall, the catalyst showed high performance at moderate operating conditions and its activity was maintained after two cycles.
Keywords: Alumina; Calcium oxide; Optimization; Solid catalyst; Transesterification;
Quaternary ammonium salts ionic liquids for immobilization of chiral Ru-BINAP complexes in asymmetric hydrogenation of β-ketoesters by Tomas Floris; Petr Kluson; Lukas Bartek; Helena Pelantova (160-165).
Quatenary ammonium ionic liquids, namely n-alkyl-triethylammonium bis(trifluoromethane sulfonyl) imides (N R222Tf2N, R = 6,7,8,10,12,14), were used to accommodate the catalytic Ru-BINAP complex in the stereoselective hydrogenation of MAA. The role of the alkyl chain length in the N R222Tf2N ionic liquid was found essential.Chiral catalytic complex (R)—[RuCl(binap)(p-cymene)]Cl was used in asymmetric hydrogenation of methyl acetoacetate to methyl-3-hydroxybutyrate in the mixed methanol-ionic liquid phase. Quaternary ammonium salts ionic liquids, namely n-alkyl-triethylammonium bis(trifluoromethane sulfonyl) imides (N R222Tf2N, R = 6, 7, 8, 10, 12, 14), were prepared and employed in this transformation. Enough evidence was provided that only a small amount of this type of IL in a conventional solvent was necessary to accommodate the catalytic complex and that the reaction could be carried out with very high enantioselectivity. Similarly it was proved that under optimized conditions the catalytic complex immobilized in this manner could be used repeatedly. A part of the work was focused on the role of the alkyl chain length in the N R222Tf2N ionic liquid which was found as very essential. Role of the reaction impurities with origin in the synthesis of the employed ILs was also investigated.
Keywords: Asymmetric hydrogenation; Stereoselectivity; Ionic liquids; Ru-BINAP; Quaternary ammonium salts;
NOx adsorption and diesel soot combustion over La2O3 supported catalysts containing K, Rh and Pt by B.S. Sánchez; C.A. Querini; E.E. Miró (166-175).
In this work we report results of NOx adsorption and diesel soot combustion on a noble metal promoted K/La2O3 catalyst. K/La2O3 adsorbs NOx through the formation of La and K nitrate species when the solid is treated in NO + O2 between 70 and 490 °C. However, they become unstable at ca. 360 °C when either Rh and/or Pt are present, the effect of Rh being more pronounced. Regarding soot combustion, nitrates react with soot with a temperature of maximun reaction rate of c.a. 370 °C, under tight contact conditions.In this work we report results of NOx adsorption and diesel soot combustion on a noble metal promoted K/La2O3 catalyst. The fresh-unpromoted solid is a complex mixture of hydroxide and carbonate compounds, but the addition of Rh favors the preferential formation of lanthanum oxycarbonate during the calcination step. K/La2O3 adsorbs NOx through the formation of La and K nitrate species when the solid is treated in NO + O2 between 70 and 490 °C. Nitrates are stable in the same temperature range under helium flow. However, they become unstable at ca. 360 °C when either Rh and/or Pt are present, the effect of Rh being more pronounced. Nitrates decompose under different atmospheres: NO + O2, He and H2. The effect of Rh might be to form a thermally unstable complex (Rh–NO+) which takes part both in the formation of the nitrates when the catalyst is exposed to NOx and in the nitrates decomposition at higher temperatures. Regarding soot combustion, nitrates react with soot with a temperature of maximun reaction rate of ca. 370 °C, under tight contact conditions. This temperature is not affected by the presence of Rh, which indicates that the stability of nitrates has little effect on their reaction with soot.
Keywords: Diesel soot combustion; Nitric oxide adsorption; In situ FTIR characterization; Rh,K,Pt/La2O3 catalysts;
Rapid transesterification of soybean oil with phase transfer catalysts by Yi Zhang; Maria Stanciulescu; Michio Ikura (176-183).
Various PTCs (phase transfer catalysts) were investigated for base-catalyzed transesterification of soybean oil. Experimental results showed that the rates of base-catalyzed transesterification were enhanced with the use of PTCs, indicated by high methyl ester (ME) content within a relatively short time. Individual operating variables such as the molar ratios of methanol to oil, total OH− to oil, PTC to a base catalyst and agitation including ultrasound were investigated for transesterification with PTC.Biodiesel is a renewable, non-toxic and biodegradable alternative fuel for compression ignition engines. Biodiesel is produced mainly through base-catalyzed transesterification of animal fats or vegetable oils. However, the conventional base-catalyzed transesterification is characterized by slow reaction rates at both initial and final reaction stages limited by mass transfer between polar methanol/glycerol phase and non-polar oil phase.In our study we used phase transfer catalysts (PTCs) to facilitate anion transfer between polar methanol/glycerol phase and non-polar oil phase to speed up transesterification. The benefits of transesterification by PTCs include no need for expensive aprotic solvents, potentially simpler scaleup and higher activity (shorter reaction time). Various PTCs were investigated for base-catalyzed transesterification. Experimental results showed that base-catalyzed transesterification was enhanced with an effective PTC, indicated by the formation of high methyl ester (ME) content within a relatively short time. Individual operating variables such as molar ratios of methanol to oil, total OH− to oil, PTC to base catalyst and agitation including ultrasound were investigated for transesterification with PTC. Product analyses showed that ME content higher than 96.5 wt.% was achieved after only 15 min of rapid transesterification with PTC (tetrabutylammonium hydroxide or tetrabutylammonium acetate as PTC, MeOH/oil molar ratio of 6, total OH−/oil molar ratio of 0.22, PTC/KOH molar ratio of 1 and 60 °C). Free and total glycerol contents in the final product from 15 min rapid transesterification with PTC were lower than maximum allowable limits in the standard specification for biodiesel.
Keywords: Biodiesel; Transesterification; Base catalyst; Phase transfer catalyst; Methyl ester; Vegetable oils;
Phenol methylation over nanoparticulate CoFe2O4 inverse spinel catalysts: The effect of morphology on catalytic performance by Nicola Ballarini; Fabrizio Cavani; Sauro Passeri; Lucilla Pesaresi; Adam F. Lee; Karen Wilson (184-192).
Catalytic activity of CoFe2O4 nanoparticles in gas-phase methylation of phenol shows a pronounced dependence on particle size. Sub-20 nm particles exhibit low temperature activity in methylation with exceptional (>80%) regio and chemo selectivity towards o-cresol.A series of CoFe2O4 nanoparticles have been prepared via co-precipitation and controlled thermal sintering, with tunable diameters spanning 7–50 nm. XRD confirms that the inverse spinel structure is adopted by all samples, while XPS shows their surface compositions depend on calcination temperature and associated particle size. Small (<20 nm) particles expose Fe3+ enriched surfaces, whereas larger (∼50 nm) particles formed at higher temperatures possess Co:Fe surface compositions close to the expected 1:2 bulk ratio. A model is proposed in which smaller crystallites expose predominately (1 1 1) facets, preferentially terminated in tetrahedral Fe3+ surface sites, while sintering favours (1 1 0) and (1 0 0) facets and Co:Fe surface compositions closer to the bulk inverse spinel phase. All materials were active towards the gas-phase methylation of phenol to o-cresol at temperatures as low as 300 °C. Under these conditions, materials calcined at 450 and 750 °C exhibit o-cresol selectivities of ∼90% and 80%, respectively. Increasing either particle size or reaction temperature promotes methanol decomposition and the evolution of gaseous reductants (principally CO and H2), which may play a role in CoFe2O4 reduction and the concomitant respective dehydroxylation of phenol to benzene. The degree of methanol decomposition, and consequent H2 or CO evolution, appears to correlate with surface Co2+ content: larger CoFe2O4 nanoparticles have more Co rich surfaces and are more active towards methanol decomposition than their smaller counterparts. Reduction of the inverse spinel surface thus switches catalysis from the regio- and chemo-selective methylation of phenol to o-cresol, towards methanol decomposition and phenol dehydroxylation to benzene. At 300 °C sub-20 nm CoFe2O4 nanoparticles are less active for methanol decomposition and become less susceptible to reduction than their 50 nm counterparts, favouring a high selectivity towards methylation.
Keywords: Heterogeneous catalysis; Inverse spinel; Phenol methylation; Clean technology; XPS; Nanoparticles;
Dehydrogenation of ethylbenzene in the presence of CO2 using a catalyst synthesized by polymeric precursor method by Tiago Pinheiro Braga; Antônio Narcísio Pinheiro; Camila Vieira Teixeira; Antoninho Valentini (193-200).
Catalysts of iron oxide dispersed on Al or Si oxides were prepared via a polymeric precursor derived from the Pechini method and tested in the dehydrogenation of ethylbenzene in the presence of CO2, in order to contribute with the studies of this reaction. The catalysts were characterized by thermogravimetric analysis (TG), temperature-programmed reduction (TPR), X-ray diffraction (DRX) and temperature-programmed desorption of CO2 (TPD-CO2). Analysis of the spent catalysts by TG and Fourier transformed infrared spectroscopy (FT-IR) pointed to the contribution of CO2 to the coke deposition. The catalytic results suggest that the high initial ethylbenzene conversion is due to the contribution of basic sites, and the CO2 adsorption in the basic site (lattice oxygen) may compete with the oxidative dehydrogenation of ethylbenzene. Although CO2 provides the appropriate conditions to lower the consumption of the basic site, it is not able to promote the Fe2+ oxidation or to regenerate the basic site (lattice oxygen) in the iron oxide dispersed on Al or Si oxide catalysts.Is the CO2 able to promote the Fe2+ oxidation or to regenerate the basic site (lattice oxygen) in the iron oxide during the dehydrogenation of ethylbenzene? The experimental results presented herein, using catalysts synthesized by the polymeric precursor method, provide information to the studies of the role of CO2 in the reaction.
Keywords: Carbon dioxide; Dehydrogenation; Ethylbenzene; Styrene;
Hydrogenation of carbon monoxide under mechanical activation conditions by Francesco Delogu; Gabriele Mulas; Sebastiano Garroni (201-205).
Carbon monoxide was hydrogenated over different catalysts under mechanical activation conditions and the mechanochemical reaction rate compared to the one observed under thermal activation conditions. The mechanical processing remarkably enhances the activity of the catalysts employed. The figure below shows the conversion data of carbon monoxide over a Ni-based catalyst.The work focuses on the hydrogenation of carbon monoxide over solid catalysts undergoing mechanical activation by ball milling. The rate of carbon monoxide conversion at individual ball impacts was estimated by measuring the impact frequency, the mass of powders involved in individual impacts and their duration. The rate of the mechanochemical hydrogenation process was compared with the one of the corresponding thermal process. An enhancement of the catalyst activity under mechanical activation conditions is observed.
Keywords: Mechanochemistry; Carbon monoxide hydrogenation; Catalysis;
Structured cobalt oxide catalyst for VOC combustion. Part I: Catalytic and engineering correlations by J. Łojewska; A. Kołodziej; T. Łojewski; R. Kapica; J. Tyczkowski (206-211).
Structured reactors based on metallic catalyst carriers can be an interesting alternative to monolithic converters. The paper presents the results of cobalt catalyst deposition (non-equilibrium plasma, Langmuir–Blodgett film and wet impregnation), characterisation (Raman, XP spectroscopy) and catalytic tests of n-hexane oxidation. The carriers based on wire gauzes have been demonstrated to improve the efficiency of the VOC combustion decreasing the converter length.Structured reactors based on metallic carriers for catalysts of highly enhanced transport properties can be an interesting alternative to monolithic converters. In this study the carriers based on wire gauze have been shown to improve the efficiency of the VOC combustion simultaneously decreasing the converter length. A successful application of metallic microstructures needs proper methods of catalyst layering. This study focuses on non-equilibrium plasma (NEP) deposition technique which is referred to Langmuir–Blodgett (LB) film deposition and to wet impregnation. The cobalt oxide catalyst deposited on wire gauze and steel sheets were characterised by XPS and Raman microscopy and tested in n-hexane oxidation in tubular and gradientless (jet-stirred) reactors. The model cobalt catalysts showed sufficiently high activity in relation with Pt reference catalysts. The most important factor affecting the catalyst activity was the type of the carrier. The best performance was achieved for the catalysts deposited on wire gauzes.
Keywords: VOC combustion; Cobalt spinel; Structured reactor; Raman; XPS; Non-equillibrium plasma-deposition; Langmuir–Blodgett film deposition;
Oxidation of alcohols using RuMnCe catalysts by Marek Pawel Chęciński; Angelika Brückner; Jörg Radnik; Angela Köckritz (212-219).
The aerobic oxidation of 2-octanol and other alcohols to their corresponding ketones and aldehydes could successfully be achieved in the presence of Ru catalysts promoted with Mn and Ce oxides. The catalytic activity could significantly be improved by deposition of the ternary RuMnCe oxidic mixture on redox-active supports.The combination of ruthenium, manganese as well as cerium oxides formed an active catalytic system for the oxidation of 2-octanol and other alcohols. The addition of manganese species as promotors resulted in more active catalysts than comparable cobalt-doped oxidic materials. The application of RuMnCe oxides on redox-active supports, such as TiO2 or CeO2, by deposition–precipitation caused a further improvement of catalytic activity. A tolerance to nitrogen-containing substrates was observed.
Keywords: Alcohols; Aldehydes; Ketones; Catalytic oxidation; Molecular oxygen; Heterogeneous RuMnCe catalysts;
Preparation of sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)ester: A new and recyclable catalyst for the formylation and acetylation of alcohols under heterogeneous conditions by Khodabakhsh Niknam; Dariush Saberi (220-225).
We describe a simple and efficient procedure for the preparation of sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)ester (3) by the reaction of 3-(thio(propy-3-yl)silica)-propanol (2) and chlorosulfonic acid in chloroform. 3-(Thio(propy-3-yl)silica)-propanol was prepared by the reaction of 3-mercaptopropylsilica (MPS) with 3-chloropropanol in refluxing toluene. This solid sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)ester is employed as a new catalyst for the formylation of alcohols with ethyl formate under mild and heterogeneous conditions at room temperature with good to excellent yields. Also, 3 can catalyze the acetylation of various alcohols by the reaction of alcohols with ethyl acetate under reflux conditions or with acetic anhydride at room temperature.A simple procedure for the preparation of sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)ester is described. This solid is employed as a new catalyst for the formylation of alcohols with ethyl formate at room temperature. Also, this solid acid can catalyze the acetylation of alcohols with ethyl acetate under reflux conditions or acetic anhydride at room temperature.
Keywords: Formylation; Sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)ester; Ethyl formate; Alcohols; Acetylation; Ethyl acetate; Acetic anhydride;