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Applied Catalysis A, General (v.325, #1)
Recent developments in titanium oxide-based photocatalysts by Masaaki Kitano; Masaya Matsuoka; Michio Ueshima; Masakazu Anpo (pp. 1-14).
Recent development in titanium oxide-based photocatalysts was reviewed concerning the development in the highly dispersed titanium oxide photocatalysts prepared on or within zeolites and the visible light-responsive TiO2 photocatalysts prepared by ion-engineering techniques such as metal ion-implantation and an RF magnetron sputtering deposition method. ▪Recent development in titanium oxide-based photocatalysts was reviewed concerning the development in the highly dispersed titanium oxide photocatalysts prepared on or within zeolites and the visible light-responsive TiO2 photocatalysts. The unique and high reactivities of titanium oxide species anchored or incorporated in the zeolite for various photocatalytic reactions such as reduction of CO2 with H2O and direct decomposition of NO x into N2 and O2 were discussed focusing on the relationship between the reactivity and local structures of the catalysts. Moreover, the preparation of the visible light-responsive TiO2 photocatalysts by applying ion-engineering techniques such as an ion-implantation and an RF magnetron sputtering deposition method was discussed focusing on its unique reactivity for the decomposition of water into H2 and O2 with a separate evolution under sunlight irradiation.
Keywords: Highly dispersed titanium oxide photocatalysts; CO; 2; reduction; NO; x; decomposition; Visible light-responsive TiO; 2; Metal ion implantation; RF magnetron sputtering; Nitrogen substitution; Water splitting
One-pot synthesis of naturanol from α-pinene oxide on bifunctional Pt-Sn/SiO2 heterogeneous catalysts by G. Neri; G. Rizzo; A.S. Arico’; C. Crisafulli; L. De Luca; A. Donato; M.G. Musolino; R. Pietropaolo (pp. 15-24).
Bifunctional Pt-Sn/SiO2 catalysts with different Sn/Pt ratios have been prepared by co-impregnation, reduced in H2 and tested by means of the one-pot synthesis of α-campholenic alcohol (naturanol) from α-pinene oxide. All results are reported in two sections. In Part I, here presented, characterization of catalysts in terms of microstructure chemical and surface properties by X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and acid properties investigated by FT-IR of adsorbed pyridine are included.In the reduced Pt-Sn/SiO2 catalysts, oxidized and/or metallic species, having different microstructural and acid characteristics, strongly dependent on the Sn/Pt ratio have been identified. For Sn/Pt ratios <1, elemental Pt and the Pt-rich platinum-tin alloy Pt3Sn were found as main species. No ionic tin was detected by FT-IR analysis of adsorbed pyridine, further indicating that tin alloyed with platinum does not show acid properties. At Sn/Pt ratios higher than 1, the PtSn alloy was detected as the main species, whereas the excess of Sn was found in an oxidized state as suggested by the presence of strong IR bands at 1453 and 1608cm−1 attributed to pyridine bonded to Lewis acid sites associated with ionic tin species.A clear relationship between the intensity of FT-IR bands and the activity in α-pinene oxide isomerization was observed indicating that Lewis acid sites, associated with ionic tin species, present on the surface of bifunctional Pt-Sn/SiO2 catalysts, are active centres favouring the isomerization reaction. Sn addition also increases the selectivity to naturanol, in the subsequent consecutive hydrogenation of campholenic aldehyde intermediate. However, at high loading, the bifunctional effect is less significant because the excess of oxidized tin strongly decreases the catalytic activity. Our results indicate that the Sn/Pt ratio is the key factor in Pt-Sn/SiO2 bifunctional catalysts and influences both activity and selectivity in the one-pot synthesis of naturanol from α-pinene oxide.A detailed characterization of bifunctional Pt-Sn/SiO2 catalysts for the one-pot synthesis of naturanol from α-pinene oxide has been reported. Different metallic and oxidized species have been detected, depending on the Sn/Pt ratio. Oxidized Sn species, quantified by FT-IR of adsorbed pyridine, have been suggested to be the active centres for the isomerization step.▪
Keywords: α-Pinene oxide; Naturanol; Isomerization; Hydrogenation; One-pot synthesis; Pt-Sn catalysts
One-pot synthesis of naturanol from α-pinene oxide on bifunctional heterogeneous catalysts by G. Neri; G. Rizzo; A. Pistone; L. De Luca; A. Donato; M.G. Musolino; R. Pietropaolo (pp. 25-33).
Bifunctional Pt–Sn/SiO2 catalysts have been tested in the one-pot synthesis of α-campholenic alcohol (naturanol, NAT) from α-pinene oxide. The process involve the sequential isomerization of the substrate into α-campholenic aldehyde and its subsequent hydrogenation to naturanol. Optimizing the formulation of the Pt–Sn/SiO2 catalyst, a maximum naturanol yield of about 60% was obtained. ▪Bifunctional Pt–Sn/SiO2 catalysts described in the Part I, prepared by co-impregnation varying the Pt and Sn loading and the Sn/Pt ratio, have been tested in the one-pot synthesis of α-campholenic alcohol (naturanol) from α-pinene oxide. The process involves the sequential isomerization of the substrate into α-campholenic aldehyde and the subsequent hydrogenation of this intermediate to naturanol. In this Part II, a kinetic investigation of the catalytic process is reported.First, the isomerization and hydrogenation steps were studied separately. Results obtained indicate that the role of tin in the Pt–Sn/SiO2 catalysts formulation is crucial, affecting strongly the activity and/or selectivity in both steps. In the isomerization step, the catalytic activity increases linearly with tin loading whereas the selectivity to campholenic aldehyde remains essentially unchanged. In the second step, high tin loadings increase the selectivity to naturanol but a careful control on the Sn/Pt ratio is necessary to obtain a satisfactory hydrogenation rate, because for Sn/Pt>1 the catalytic activity falls out dramatically.The overall transformation of α-pinene oxide into naturanol was then investigated. It was found that the isomerization of α-pinene oxide to campholenic aldehyde is the step limiting the naturanol yield. Moreover, kinetic tests have shown that the ratio between the isomerization and hydrogenation rate is the other critical factor in order to synthesize naturanol in high yield. Optimizing the formulation of the Pt–Sn/SiO2 catalysts, a maximum naturanol yield of about 60% was obtained.
Keywords: α-Pinene oxide; Naturanol; Isomerization; Hydrogenation; One-pot synthesis; Pt–Sn catalysts
Selective maltose hydrogenation to maltitol on a ternary Co–P–B amorphous catalyst and the synergistic effects of alloying B and P by Hui Li; Pingfeng Yang; Dongsheng Chu; Hexing Li (pp. 34-40).
A ternary Co–P–B amorphous alloy catalyst was prepared by chemical reduction with the mixed KBH4 and NaH2PO2 in aqueous solution, and was characterized by ICP, XRD, SAED, TEM, SEM, XPS, H2-TPD and hydrogen chemisorption. During liquid phase hydrogenation of maltose, the as-prepared Co–P–B catalysts exhibited 100% selectivity to maltitol and much higher activity than the Co–B, Co–P and Raney Ni, apparently owing to the synergistic promotions of the alloying B and P. More specifically, the alloying B increased the number of active sites ( Sact) and donated partial electrons to the Co, which was favorable for the hydrogenation of the CO group in the maltose. Furthermore, the alloying P led to the enhancement of the intrinsic activity(RHS) by forming new Co clusters as active sites. The maximum activity was obtained on the Co72.2P5.9B21.9.A ternary Co–P–B amorphous alloy catalyst was prepared by chemical reduction with the mixed KBH4 and NaH2PO2 in aqueous solution. During liquid phase hydrogenation of maltose, the as-prepared Co–P–B catalysts exhibited 100% selectivity to maltitol and much higher activity than the Co–B, Co–P and Raney Ni, apparently owing to the synergistic promotions of the alloying B and P.▪
Keywords: Ternary Co–P–B amorphous alloy catalyst; Synergistic promotion; Hydrogenation; Maltose; Maltitol
Investigation of the structure and the redox behavior of gadolinium doped ceria to select a suitable composition for use as catalyst support in the steam reforming of natural gas by Ulrich Hennings; Rainer Reimert (pp. 41-49).
Gadolinium doped cerias in the range0
Keywords: Ceria; Gadolinium; Combustion synthesis; Structure; OSC; OEC; Redox behavior
Support effect on oxidation resistance of precious metal catalysts as examined by N2O decomposition by Hisao Yoshida; Tomohisa Tsuruta; Yoshiteru Yazawa; Tadashi Hattori (pp. 50-56).
Results from pulse reaction of N2O decomposition below 573K over Pt and Pd catalysts supported on a series of oxides and Pt LIII-edge XANES of Pt catalysts after the pulse reaction revealed that the acidic support depressed the oxidation step of precious metals and promoted the reduction step of them.▪The support effect on both steps of oxidation and reduction of precious metal catalysts was investigated by using pulse reaction of N2O decomposition below 573K over Pt and Pd catalysts supported on a series of oxides. Oxygen uptake was calculated from the amount of N2 formed and from white line intensity of Pt LIII-edge XANES after the pulse reaction. Although the oxygen uptake ratio to the surface metal atoms scarcely varied with the dispersion of precious metal, it varied with the support materials. At low temperature (≤373K), the oxygen uptake decreased as the acid strength of support materials enhanced, indicating that the acidic support materials depress the oxidation step of precious metal. On the other hand, at higher temperature (≥473K), the oxygen uptake calculated from N2 formed was larger on acidic support than those on the supports with moderate acid strength. However, the oxygen uptake calculated from white line intensity clearly decreased as the acid strength of support materials enhanced. This contradiction was interpreted by the desorption of oxygen, i.e., the reduction of metal oxide, during the period between the pulses. Thus, it was concluded that the acidic support affected the oxidation state of precious metal through not only the depression of oxidation step but also the promotion of the reduction step.
Keywords: Precious metal catalyst; Platinum; Palladium; Support effect; N; 2; O decomposition
Partial oxidation of methane over supported ruthenium catalysts by R. Lanza; S.G. Järås; P. Canu (pp. 57-67).
Partial oxidation of methane (POM) to synthesis gas was studied over Ru catalysts (1% (w/w)) supported on silica, alumina and ceria–zirconia. Catalyst samples were prepared by incipient wetness and characterized by BET area, XRD, ESEM–EDS, and TPR–TPO analyses. Ru on silica deactivated very fast, while Ru supported on alumina has good activity and selectivity. The mixture CeO2–ZrO2 led to low selectivity towards POM, with a higher selectivity towards complete combustion, common to all the catalysts at lower temperature. Both reduced and non-reduced catalysts were tested resulting in different behaviour in the same temperature range. We investigated the effect of different GHSVs, heating rates and also sequences of heating and cooling cycles. This allowed gaining insight into the sequence of reactions taking place in the reactor and revealed hysteresis for all reaction conditions. This can be explained through a cycling between Ru oxidation states on the surface. ▪Partial oxidation of methane (POM) to synthesis gas was studied over Ru catalysts (1% (w/w)) supported on silica, alumina and ceria–zirconia. Catalyst samples were prepared by incipient wetness and characterized by BET area, XRD, ESEM–EDS, and TPR–TPO analyses. Ru on silica deactivated very fast, while Ru supported on alumina has good activity and selectivity. The mixture CeO2–ZrO2 led to low selectivity towards POM, with a higher selectivity towards complete combustion, common to all the catalysts at lower temperature. Both reduced and non-reduced catalysts were tested resulting in different behaviour in the same temperature range. We investigated the effect of different GHSVs, heating rates and also sequences of heating and cooling cycles. This allowed gaining insight into the sequence of reactions taking place in the reactor and revealed hysteresis for all reaction conditions. This can be explained through a cycling between Ru oxidation states on the surface.
Keywords: Methane; Partial oxidation; Syngas; Ruthenium; Activity; Hysteresis
Influence of intermediate iron reduced species in Fischer-Tropsch synthesis using Fe/C catalysts by J.F. Bengoa; A.M. Alvarez; M.V. Cagnoli; N.G. Gallegos; S.G. Marchetti (pp. 68-75).
Two Fe/carbon catalysts were prepared to study the influence of the intermediate iron species on the activity and selectivity in the Fischer-Tropsch synthesis (FTS). The supports obtained showed different specific surface areas. The catalysts showed different iron species. The catalyst with lower reduction degree produces a non-stoichiometric iron carbide during FTS, which has a higher activity and light olefins selectivity.▪Two Fe/carbon catalysts were prepared to study the influence of the intermediate iron species on the activity and selectivity in the Fischer-Tropsch synthesis (FTS). The solids were characterized by XRD, CO chemisorption, Atomic Absorption, Nitrogen Adsorption and Mössbauer spectroscopy. Using two loading of consolidant agent, two supports with different specific surface areas were obtained. The resulting catalysts showed different iron species. The catalyst with lower reduction degree produces a non-stoichiometric iron carbide during FTS, which has a higher activity and light olefins selectivity.
Keywords: Fischer-Tropsch synthesis; Fe/C catalysts; Mössbauer spectroscopy; Iron carbides
Pd-leaching and Pd-removal in Pd/C-catalyzed Suzuki couplings by Jeng-Shiou Chen; Aleksey N. Vasiliev; Anthony P. Panarello; Johannes G. Khinast (pp. 76-86).
Pd-leaching in Pd/C-catalyzed Suzuki couplings was investigated using the model coupling reaction of biphenylacetic acid (Scheme 1). The filtration test proves that oxidative addition in the catalytic cycle is the main cause for Pd-leaching, which is independent of the reaction solvent and temperature. PVPy adsorption studies suggest that the activity of Pd/C is mainly due to leached Pd. Furthermore, PVPy was proven to be a good reagent to completely remove Pd-residuals from the reaction mixture. Excess PVPy (3equiv. to Pd) is sufficient to carry out the removal within 2h. Lastly, the kinetic studies suggest that exclusion of oxygen is not necessary.▪Pd-leaching in Pd/C-catalyzed Suzuki couplings was investigated using the model coupling reaction of biphenylacetic acid. The filtration test was used to prove that oxidative addition of aryl-bromides is the main cause for Pd-leaching, which is independent of the reaction solvent and temperature. In addition, the oxidative addition of aryl-borates is another cause for Pd-leaching. PVPy adsorption studies suggest that the activity of Pd/C is mainly due to leached Pd. Furthermore, PVPy was proven to be a good reagent for complete removal of Pd-residuals from the reaction mixture. Excess PVPy (3equiv. to Pd) is sufficient to carry out the removal within 2h. The influence of oxygen on reactions was also investigated. The kinetic results suggest that exclusion of oxygen is not necessary. The presence of water in the solvent is required to promote the reaction. Water may stabilize Pd-nanoparticles, which can act as a reservoir for active Pd species.
Keywords: Suzuki couplings; Palladium; Leaching; Oxidation addition; Biphenylacetic acid
Effect of alkylaluminum cocatalyst on ethylene polymerization with nickel-α-diimine complex by Caroline G. de Souza; Roberto F. de Souza; Katia Bernardo-Gusmão (pp. 87-90).
Ethylene polymerization was carried out with two nickel(II)(α-diimine) complexes: 1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine-dichloro-nickel(II) (1) and 1,4-bis(2,6-diisopropylphenyl)-ethanediimine-dichloronickel(II) (2) combined with alkylaluminum activators like methylalumoxane (MAO), trimethylaluminum (TMA), and ethylaluminum sesquichloride (EASC). The activity of these systems and the proprieties of the polymeric materials are strongly influenced by the choice of the ligand structure and, more dramatically, by the nature of the cocatalyst. EASC has been shown as giving higher productivities than TMA or MAO with both complexes, attaining 3966kgPE/(molNi·h). Complex2 gives lower productivities but produced polymers with higher polymer melting points ( Tm) and crystallinity than catalyst1.Ethylene polymerization with Ni(II)-α-diimine complexes in combination with alkylaluminum activators is described. The influence of ligand structure and nature of the cocatalyst on reaction activity as well as on the properties of the polymeric material is discussed. ▪
Keywords: Polymerization; Nickel; Diimine; Ethylene
Role of zinc chloride and complexing agents in highly active double metal cyanide catalysts for ring-opening polymerization of propylene oxide by Xing-Hong Zhang; Zheng-Jiang Hua; Shang Chen; Fei Liu; Xue-Ke Sun; Guo-Rong Qi (pp. 91-98).
Several double metal cyanide (DMC) catalysts based on Zn3[Co(CN)6]2 were prepared by an impregnation method. Infrared spectroscopy (IR), wide-angle X-ray diffraction (WAXD), and elemental analysis were used to characterize these DMC catalysts. The WAXD patterns showed that pure Zn3[Co(CN)6]2 had very high crystallinity (98.8%) with a typical cubic lattice structure, while DMC catalysts prepared with excess ZnCl2 and/or complexing agents had low crystallinity. Furthermore, no free ZnCl2 was found in DMC catalysts prepared with excess ZnCl2 (from WAXD characterization), although it seemed that free ZnCl2 existed in the catalyst (from elemental analysis). The characteristic absorptions ( νCN and νCo–C) in the IR spectra of DMC catalysts prepared with excess ZnCl2 were shifted to higher wave numbers than those in pure Zn3[Co(CN)6]2. These results showed that a new chemical linkage was produced between Co(CN)63− and ZnCl2 (or zinc center complexes) in the precipitation reaction. Excess ZnCl2 in DMC catalyst preparation was necessary to ensure its high catalytic activity for ring-opening polymerization (ROP) of propylene oxide (PO), while complexing agents were unnecessary in the composition. The role of the complexing agents was mainly to promote the formation of the amorphous DMC catalyst and thus increase the catalytic activity. A possible heterogeneous coordinative cationic polymerization mechanism is proposed for a reasonable interpretation of the ROP of PO.Double metal cyanide (DMC) catalysts with quantitative amounts of excess ZnCl2 were prepared by impregnation method for ring-opening polymerization (ROP) of propylene oxide (PO). Excess ZnCl2 in DMC catalyst was responsible for its high activity for ROP of PO, while complexing agents were not the necessary composition. They favored to form the amorphous DMC catalyst, and thus increase catalytic activity. ▪
Keywords: Double metal cyanide; Catalyst; Ring-opening polymerization; Propylene oxide; Mechanism; Zinc chloride; Complexing agent
ZrOCl2·8H2O: An efficient and reusable catalyst for the synthesis of imidazolines and bis-imidazolines under various reaction conditions by Valiollah Mirkhani; Iraj Mohammadpoor-Baltork; Majid Moghadam; Shahram Tangestaninejad; Mohammad Abdollahi-Alibeik; Hadi Kargar (pp. 99-104).
Efficient preparation of 2-imidazolines and bis-imidazolines by reaction of ethylenediamine with nitriles in the presence of catalytic amounts of zirconyl chloride (ZrOCl2·8H2O) as a reusable catalyst under reflux conditions is reported. Sonication of this system enhanced the catalytic activity of zirconyl chloride and this was led to higher product yields and shorter reaction times. When this catalytic system was exposed to microwave irradiation, the reaction times were reduced up to 10min and the yields increased to 96%. Another advantage of the systems, under ultrasonic and MW irradiation, is the ability to carry out large-scale reactions. In three cases, the catalyst was reused several times without loss of its activity.Efficient preparation of 2-imidazolines and bis-imidazolines by reaction of ethylenediamine with nitriles in the presence of catalytic amounts of ZrOCl2·8H2O as a reusable catalyst under reflux conditions, MW and under ultrasonic irradiation is reported. ▪
Keywords: Nitrile; Imidazoline; Ultrasonic irradiation; Microwave irradiation; Zirconyl chloride
Photocatalytic reactivity for O2− and OH radical formation in anatase and rutile TiO2 suspension as the effect of H2O2 addition by Tsutomu Hirakawa; Kenta Yawata; Yoshio Nosaka (pp. 105-111).
Effect of crystalline structure, anatase and rutile, on the production of OH and O2− by TiO2 photocatalytic reaction was investigated. The OH radical free from the TiO2 surface was monitored by the fluorescence intensity of 2-hydroxyl terephthalic acid produced by the reaction with terephthalic acid. Superoxide radical was detected by the chemiluminescence probe method with luminol. Formation rate of OH with rutile photocatalysts was significantly lower than that with anatase photocatalysts. By the addition of H2O2, the formation rate of OH was significantly increased for rutile and for anatase mixed with rutile by 10–20%, while pure anatase showed an opposite tendency. We suggest that the adsorption structure of H2O2 on the rutile TiO2 surface is preferable to produce OH. In photocatalytic production of O2−, rutile surpassed anatase in stabilizing the produced O2−. On H2O2 addition, anatase surpassed rutile in the photocatalytic activity to produce O2− from H2O2.Effect of crystalline structure, anatase and rutile, on production of OH and O2− by TiO2 photocatalysis was studied. Anatase surpassed rutile in the production of OH with water, while by addition of H2O2 the OH formation rate on rutile was significantly improved. Rutile surpassed anatase in stabilizing O2−, while by addition of H2O2 anatase shows higher activity to produce O2−. ▪
Keywords: TiO; 2; Photocatalytic reaction; Active oxygen species; Hydroxyl radical; Superoxide radical; Hydrogen peroxide; Luminol; Terephthalic acid
Supported palladium catalysts for the selective conversion of cis-2-butene-1,4-diol to 2-hydroxytetrahydrofuran: effect of metal particle size and support by Maria Grazia Musolino; Giuseppe Apa; Andrea Donato; Rosario Pietropaolo; F. Frusteri (pp. 112-120).
The selective conversion of cis-2-butene-1,4-diol to 2-hydroxytetrahydrofuran was studied at 303K and at 0.01 and 0.1MPa H2 pressure over palladium catalysts supported on different metal oxides. The acid–base characteristics of the carrier, determined by FT-IR of the adsorbed pyridine, have a significant impact on product selectivity. It has demonstrated that it is possible to tailor an active and selective palladium catalyst for the production of 2-hydroxytetrahydrofuran, by choosing an appropriate support and operating at low H2 pressure. ▪Palladium catalysts on different supports (SiO2, Al2O3, TiO2, ZrO2, MgO and ZnO) have been tested in selective liquid phase conversion of cis-2-butene-1,4-diol affording also, when hydrogenated, 2-hydroxytetrahydrofuran. The metal particle size was determined by TEM. The acidic properties of the catalysts were studied by FT-IR spectroscopy using pyridine as probe molecule. The influence of some preparative variables, such as the particle size, the support, the partial hydrogen pressure, on the catalytic behaviour of palladium catalysts has been investigated.TEM measurements indicated that Pd particles diameter observed was in the range 2.5–10nm. No significant variation of TOF and selectivity values with the metal particle size was observed in this range. Moreover, the activity and the selectivity towards reaction products were found to be strongly dependent on the acid–base characteristics of the support.The acid systems have been found more active and selective to isomerisation and hydrogenolysis products than the basic ones. No hydrogenolysis reaction was observed on basic supports. Among the examined catalysts, Pd/TiO2 resulted the most selective to 2-hydroxytetrahydrofuran. A maximum yield to this compound of about 74% was, in fact, obtained at 0.01MPa of H2 pressure.
Keywords: Supported palladium catalysts; cis; -2-Butene-1,4-diol hydrogenation; 2-Hydroxytetrahydrofuran; Isomerisation; Hydrogenolysis
Accelerated study of the citral–acetone condensation kinetics over activated Mg–Al hydrotalcite by Sònia Abelló; Saurabh Dhir; Gisela Colet; Javier Pérez-Ramírez (pp. 121-129).
The kinetics of the citral–acetone condensation over activated Mg–Al hydrotalcite has been systematically studied in an automated 16 parallel-batch reactor. Three days of experimentation generated 150 data points with high accuracy and reproducibility in a broad range of conditions. The acetone-to-citral ratio is a key reaction descriptor. The experiments have been adequately described by means of a Langmuir–Hinshelwood scheme. ▪The kinetics of the citral–acetone condensation to pseudoionone (PS) over activated Mg–Al hydrotalcite (meixnerite) was studied in a 16 parallel-batch reactor set-up varying the temperature, catalyst amount, and molar acetone-to-citral (A/C) ratio. Tests with different stirring speeds and particle sizes were conducted in order to exclude the presence of mass transport limitations. The A/C ratio is a key reaction descriptor. The initial rate of pseudoionone formation exhibits a maximum at A/C=3, leading to a PS selectivity of 100%. At higher or lower A/C ratios, diacetone alcohol is the main by-product and at A/C<2 the product of citral self-condensation is additionally formed. Due to this, the pseudoionone selectivity at extreme A/C ratios decreases to 70–80%. The amount of carbonaceous deposits was determined by thermogravimetry and increased as the A/C ratio decreased. A Langmuir–Hinshelwood model involving acidic Al3+ and basic OH− sites and the surface reaction as rate-determining step described well the experimental data. The position of the optimal A/C ratio is determined by the relative ratio of adsorption constants of the reactants on the catalyst, being one order of magnitude larger in citral than in acetone. This feature can be generalized to aldol reactions involving other substrates.
Keywords: Solid-base catalysis; Aldol condensation; Citral; Acetone; Activated hydrotalcite; High-throughput testing; Kinetics
Ag0 and Co0 nanocolloids as recyclable quasihomogeneous metal catalysts for the hydrogenation of α,β-unsaturated aldehydes to allylic alcohol fragrances by Pascal G.N. Mertens; Frederic Cuypers; Pieter Vandezande; Xingpu Ye; Francis Verpoort; Ivo F.J. Vankelecom; Dirk E. De Vos (pp. 130-139).
Polyvinylpyrrolidone-stabilized Ag0 and Co0 nanoclusters are successful quasihomogeneous catalysts for the chemoselective hydrogenation of α,β-unsaturated aldehydes to allylic alcohols. Particularly the Ag0 nanosols emerged as a worthwhile alternative for Pt and Ru based catalysts. Amides proved to be superior to the conventional alcohol solvents and emerged as excellent solvents for the synthesis and application of the colloidal metal catalysts. Finally, recycling of the colloidal catalysts by solvent-resistent nanofiltration (SRNF) with custom-made polyimide membranes proved practicable and a satisfactory preservation of the catalysts’ nanodispersion and performance was observed. ▪The hydrogenation of the α,β-unsaturated aldehydes cinnamaldehyde ( trans-3-phenyl-2-propenal), citral (3,7-dimethyl-2,6-octadienal) and leaf aldehyde ( trans-2-hexenal) was investigated with metal colloids as quasihomogeneous catalysts in organic solvents. Using polyvinylpyrrolidone-stabilized Ag0 and Co0 nanoclusters, the carbonyl compounds were chemoselectively hydrogenated to the desired allylic alcohol fragrances. Particularly the Ag0 nanosols emerged as a worthwhile alternative for Pt or Ru based catalysts. Amides proved to be excellent solvents for the synthesis as well as for the application of the metal nanocolloids in the hydrogenation of α,β-unsaturated aldehydes. In the challenging hydrogenation of citral, a selectivity exceeding 70% towards the doubly unsaturated alcohol isomers (geraniol and nerol) was attained at 90% conversion using Ag0 nanocolloids dispersed in N, N-dimethylacetamide. Reactions were performed under mild conditions (2.0MPa H2, 323K) at a molar citral/silver ratio of 200/1. The addition of Lewis acid cations, such as Fe3+ or Zn2+ resulted in a further improvement of the catalytic activity and chemoselectivity. Finally, by application of membrane filtrations, an efficient separation of the metallic nanocolloids from the reaction mixtures was realized. In the recycling of the metal nanosols, the metal catalysts’ nanodispersion and performance were satisfactorily preserved.
Keywords: Selective hydrogenation; Unsaturated aldehyde; Allylic alcohol; Quasihomogeneous catalyst; Colloidal catalyst; Silver; Cobalt; Cinnamaldehyde; Citral; Leaf aldehyde; Membrane; SRNF
The use of low-nuclearity oxoperoxo molybdenum species to achieve high dispersions on zirconia materials by I. Shupyk; J.-Y. Piquemal; E. Briot; M.-J. Vaulay; C. Connan; S. Truong; V. Zaitsev; F. Bozon-Verduraz (pp. 140-153).
Molybdenum(VI) species have been deposited on zirconia materials by adsorption equilibrium procedures using two precursors: (i) an isopolyanion salt: ammonium heptamolybdate and (ii) low-nuclearity oxoperoxo molybdenum complexes. Two zirconia supports have been considered: calcined zirconia (ZrO2) and the parent zirconium oxyhydroxide (ZrO x(OH)4−2 x). After drying, the catalysts have been calcined and characterized by chemical analysis, powder X-ray diffraction, thermogravimetry, Raman and UV–vis diffuse reflectance spectroscopies, X-ray photoelectron spectroscopy, nitrogen physisorption experiments, and TEM and EDX analysis. In contrast to ZrO2, quantitative grafting of molybdenum species can be obtained when zirconium oxyhydroxide is used. With this material, the anchoring of low-nuclearity oxoperoxo species leads to higher specific surface areas than with ammonium heptamolybdate, and hence to lower molybdenum surface densities.
Keywords: Zirconia; Hydrogen peroxide; Molybdenum; Oxoperoxo complexes
Catalytic performance and characterization of Pd/Ni0.2Mg0.8Al2O4 in oxidative steam reforming of methane under atmospheric and pressurized conditions by Mohammad Nurunnabi; Yuya Mukainakano; Shigeru Kado; Toshihiro Miyao; Shuichi Naito; Kazu Okumura; Kimio Kunimori; Keiichi Tomishige (pp. 154-162).
Addition of small amount of Pd to Ni0.2Mg0.8Al2O4 enhanced the catalytic activity and stability for the oxidative steam reforming of methane even under the high partial pressure of steam and pressurized conditions, where Ni0.2Mg0.8Al2O4 deactivated due to the oxidation of Ni and carbon deposition. Catalyst characterization results suggest that the formation of Pd–Ni alloy located preferentially on the surface improved the reducibility of Ni and the resistance to the carbon deposition. ▪Catalytic performance and characterization of Pd/Ni0.2Mg0.8Al2O4 were investigated in oxidative steam reforming of methane under atmospheric and pressurized conditions. Pd/Ni0.2Mg0.8Al2O4 showed much higher methane conversion under high partial pressure of steam, where Ni0.2Mg0.8Al2O4 lost the reforming activity because the Ni species was oxidized under atmospheric pressure. In addition, the addition of Pd on Ni0.2Mg0.8Al2O4 was effective to improve the stability and resistance to coke formation in oxidative steam reforming of methane under pressurized conditions. On the other hand, the formation of Pd–Ni alloy over Pd/Ni0.2Mg0.8Al2O4 was confirmed from the characterization results of TPR, TEM, EXAFS and FTIR, and this can contribute to high catalytic performance of Pd/Ni0.2Mg0.8Al2O4.
Keywords: Oxidative reforming; Steam reforming; Methane; Pd; Ni; Alloy; Deactivation; Carbon deposition
Application of polyol process to prepare AC-supported nanocatalyst for VOC oxidation by Chi-Yuan Lu; Ming-Yen Wey; Li-Ing Chen (pp. 163-174).
The purpose of this study was to prepare AC-supported nanocatalyst by the method “polyol process”, and evaluate the feasibility of the volatile organic compound (VOC) oxidation. The field emission scanning electron microscopy (FESEM) image showed that the polyol process involved very simple operations and the size and shape of the nanoparticles were easily controlled in this process with AC-support, owing high specific surface area and microporosity.▪The purposes of this study were to prepare a transition-metal catalyst by the polyol method, and subsequently to evaluate the feasibility of the catalytic incineration of volatile organic compounds (VOCs). Activated carbon (AC) was selected as the support material, and copper, cobalt, iron, and nickel were used as the catalytic active phases. The catalyst was characterized by UV–vis, Brunauer–Emmett–Teller (BET) surface area, X-ray powder diffractometer (XRPD), and field emission scanning electron microscopy (FESEM). The catalysts prepared by the polyol process exhibited well-dispersed nanoscale metal particles. Increases in the reduction time and in the particle size led to a lower toluene conversion. The activity of metal/AC with respect to metal was observed to follow a particular order: Cu>Co>Fe>Ni. Increasing the reaction temperature and decreasing the toluene concentration and space velocity resulted in better VOC conversion. The activity of Cu/AC with respect to the VOC molecule was observed to follow the following sequence: xylene>toluene>benzene. The results indicated that the polyol process could successfully be used to manufacture nanocatalysts that could be applied to eliminate VOCs by catalytic incineration.
Keywords: Polyol process; Catalyst; VOC oxidation; Activated carbon
Ring contraction and selective ring opening of naphthenic molecules for octane number improvement by Malee Santikunaporn; Walter E. Alvarez; Daniel E. Resasco (pp. 175-187).
Different catalytic strategies involving the use of Pt/HY and Ir/SiO2 catalysts have been evaluated to maximize the production of non-aromatic compounds with high octane number, starting from naphthenic molecules, which are typically obtained from the saturation of aromatics. The research octane number (RON), the motor octane number (MON), and the specific volume of the product mixtures were evaluated in each case.▪Different catalytic strategies have been evaluated to maximize the production of non-aromatic compounds with high octane number, starting from naphthenic molecules, which are typically obtained from the saturation of aromatics. The research octane number (RON), the motor octane number (MON), and the specific volume of the product mixtures were evaluated in each case. The product distribution obtained on acidic and Pt-containing zeolites was investigated in the temperature range 533–563K in the presence of hydrogen at a total pressure of 2MPa. It was found that skeletal isomerization (ring contraction) was the primary reaction in both HY and Pt/HY catalysts. The presence of Pt was found to enhance the stability of the catalyst, but also greatly altered the distribution of RC products, enhancing 1,1-dimethylcyclopentane. This enhancement can be explained in terms of a higher rate of hydride transfer caused by the presence of the metal. Evaluation of the octane numbers of the product indicated that a mixture of RC products results in rather high RON, but the MON and specific volume were about the same as that of the feed. To improve MON and specific volume an Ir/SiO2 catalyst with high hydrogenolysis activity was added to realize the ring opening (RO). The combination of RC and RO was tested on physical mixtures and segregated beds of Pt/HY and Ir/SiO2 catalysts in order to optimize the production of the iso-alkanes with highest octane number. It was found that with segregated catalyst beds, a better control of the selective breaking of CC bonds of RC isomers can be achieved, which optimizes octane number and specific volume.
Keywords: Methylcyclohexane; Ring opening; Ring contraction; Cracking; Gasoline; Octane number; RON; MON; Pt; HY zeolite; Ir/SiO; 2
Dowex-50W promoted synthesis of 14-aryl-14 H-dibenzo[ a, j]xanthene and 1,8-dioxo-octahydroxanthene derivatives under solvent-free conditions by Gazaleh Imani Shakibaei; Peiman Mirzaei; Ayoob Bazgir (pp. 188-192).
An efficient method for the synthesis of aryl-14- H-dibenzo[ a, j]xanthenes and 1,8-dioxo-octahydroxanthenes using Dowex-50W ion exchange resin as reusable eco-friendly catalyst under solvent-free conditions is described.▪An efficient method for the synthesis of aryl-14- H-dibenzo[ a, j]xanthenes and 1,8-dioxo-octahydroxanthenes using Dowex-50W ion exchange resin as reusable eco-friendly catalyst under solvent-free conditions is described.
Keywords: Dowex-50W; Xanthene; Solvent-free; Naphthol; Reusable catalyst