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Applied Catalysis A, General (v.406, #1-2)
Oxidative coupling of methane: Influence of the phase composition of silica-based catalysts by A.G. Dedov; G.D. Nipan; A.S. Loktev; A.A. Tyunyaev; V.A. Ketsko; K.V. Parkhomenko; I.I. Moiseev (pp. 1-12).
Display Omitted► A solid-phase technique was applied for alkali–W–Mn/SiO2 catalyst preparation. ► The new alkali–W–Mn/SiO2 catalysts are efficient in the OCM reaction. ► A thorough phase analysis of the alkali–W–Mn/SiO2 catalysts was performed. ► The T–x phase diagrams of Me2O–SiO2 (Me=alkali metal) systems were constructed. ► The catalytic results are interpreted in terms of the silica phase composition.A simple solid-phase synthesis technique was applied to prepare a series of silica-based composite materials. Each material contains tungsten, manganese and an alkali oxide. To determine the influence of the alkali nature on the catalytic properties of SiO2-based composites, a W–Mn/SiO2 material without any alkali was prepared. In addition, material containing tungsten, manganese and lithium without SiO2 was synthesized. The composites were studied by XRD, TPR, BET, XPS, SDB/SEM and EDS methods. A thorough analysis of the phase parameters, which were crystallized in alkali-doped W–Mn/SiO2 catalysts and determined by XRD, was performed for the first time. Most synthesized materials demonstrated higher catalytic activity in the oxidative coupling of methane (OCM) in comparison with the analogous materials prepared according the convenient wet impregnation method. The OCM reaction was carried out without any dilution of the methane–oxygen mixture. The results of catalytic tests were interpreted in relation to the catalyst silica-matrix phase composition. It was found that two polymorphic phases of SiO2 coexist in each composite material. These phases are cristobalite and quartz in Li- and Na-containing material or cristobalite and tridymite in K-, Rb- and Cs-containing materials. The hypothetical T– x phase diagrams of Me2O–SiO2 (where Me is an alkali metal) systems were constructed to explain the coexistence of two phases of SiO2 in the studied catalysts.
Keywords: Oxidative coupling of methane; Alkali-metal–W–Mn/SiO; 2; catalysts; Solid-phase synthesis technique; SiO; 2; phase composition
Structure and catalytic activity of hosted in mesoporous silicas copper species: Effect of preparation procedure and support pore topology by Tanya Tsoncheva; Vladimiro Dal Santo; Alessandro Gallo; Nicola Scotti; Momtchil Dimitrov; Daniela Kovacheva (pp. 13-21).
.Display Omitted► Copper modified ordered mesoporous silicas with different pore topology. ► “Incipient wetness impregnation” vs “chemisorption–hydrolysis” methods of modification. ► Active catalysts obtained by “chemisorption–hydrolysis” deposition of copper on KIT-6.Copper modifications of ordered mesoporous materials with different pore topology (SBA-15 and KIT-6) were prepared by incipient wetness impregnation and “chemisorption–hydrolysis” methods and further oxidative or consecutive oxidative/reductive treatment. The samples were characterized by nitrogen physisorption, XRD, XPS, FTIR, UV–vis and TPR–TG techniques. The ordered structures and the “chemisorption–hydrolysis” post synthetic method provide the formation of homogeneously dispersed in the mesopores copper species. The “chemisorption–hydrolysis” modification of the silicas with more opened 3D ordered structure (KIT-6) provides the formation of highly active catalysts, but their activity could be easily suppressed after the treatment under the reduction medium.
Keywords: SBA-15; KIT-6; Copper modifications; Pore topology effect; Post-synthesis modification; Methanol decomposition
Surface modification of natural halloysite clay nanotubes with aminosilanes. Application as catalyst supports in the atom transfer radical polymerization of methyl methacrylate by S. Barrientos-Ramírez; G. Montes de Oca-Ramírez; E.V. Ramos-Fernández; A. Sepúlveda-Escribano; M.M. Pastor-Blas; A. González-Montiel (pp. 22-33).
Display Omitted► Surface modification of halloysite nanotubes with aminosilanes has been achieved. ► Modified halloysite nanotubes act as support of CuBr in ATP of methylmethacrylate. ► Catalytic performance depends on both the aminosilane used and the anchoring method. ► The best polymerization control, with the aminosilane physisorbed on halloysite.The grafting of natural halloysite nanotubes (HNT) with aminosilanes exhibiting two (DAS) and three (TAS) amino groups has been investigated and compared to the physisorption of both silanes on halloysite nanotubes. Halloysite nanotubes were used as solid support for the heterogeneous Atom Transfer Polymerization of methyl methacrylate (MMA) into poly(methylmethacrylate) (PMMA) using CuBr as catalyst. Silane grafted on the nanoclay acts both as a ligand that bonds to CuBr and as a catalyst for the heterogeneous MMA polymerization. Grafting of halloysite nanotubes with DAS produced a polymer with polydispersities similar to those produced by the physically adsorbed diaminosilane catalyst, but conversion percentages were lower and a poorer control over the polymerization reaction was achieved. Grafting of halloysite nanotubes with TAS had a detrimental effect on the control of the polymerization reaction and a loss of catalytic activity due to the immobilization of the copper catalyst. The best control over the polymerization of methyl methacrylate is achieved when the catalyst is not immobilized by covalent bond on the surface of halloysite nanotubes. Therefore, physysorption of the CuBr/aminosilane complex on the halloysite nanotubes provided better control on the polymerization reaction compared to the grafting of the aminosilanes on the halloysite nanotubes.
Keywords: ATRP; Halloysite nanotubes; Poly(methylmethacrylate); 3-(2-Aminoethyl)aminopropyltrimethoxysilane; 3-[2-(2-Aminoethyl)aminoethyl]aminopropyltrimethoxysilane
Structural changes occurring at the surface of alumina-supported nanoscaled Mo–V–Nb–(Te)–O catalytic system during the selective oxidation of propane to acrylic acid by Ricardo López-Medina; J.L.G. Fierro; M. Olga Guerrero-Pérez; M.A. Bañares (pp. 34-42).
Display Omitted► Operando Raman-GC study of support-stabilized nanoscaled mixed oxides. ► The nature of entanglement between Mo and V ions determines catalytic activity. ► Reaction temperature transforms from mixed Mo–V–Al oxides (AlVMoO7). ► Mixed Mo–V–Al oxides are active for propane oxidation to acrylic acid. ► V-distorted alpha-MoO3 is not selective, producing CO x.The effect of total coverage on alumina is evaluated for Mo5V4Nb1/Al2O3 catalysts by operando Raman-GC spectroscopy during reaction, demonstrating structural changes during reaction that do not occur during catalyst calcination. XRD detects show no appreciable change but Operando Raman-GC studies are sensitive to changes occurring in the nanometer scale, which modulate the performance during propane oxidation, delivering the structure–activity relationship for deactivation. Raman spectra confirm the formation of nanocrystalline MoO3-type structures during reaction up to 375°C, accompanied by coke deposits, able to block the active sites, being detrimental for the acrylic acid formation. Three new catalysts were preparing by the addition of tellurium as dopant, in this case, the presence of MoO3 is not detected under reaction conditions, since the formation of a distorted rutile structure under reaction conditions is observed, and in this case acrylic acid is obtained as the main reaction product with a yield of ca. 25% at 400°C.
Keywords: Operando; Raman; Mo–V–Te–O; Acrylic acid; Structure–activity relationship; Support-stabilized nanoparticle; Nanostructured catalysts
γ-Fe2O3-supported Pt-Cu nanoparticles synthesized by radiolytic process for catalytic CO preferential oxidation by Junichiro Kugai; Ryota Kitagawa; Satoshi Seino; Takashi Nakagawa; Yuji Ohkubo; Hiroaki Nitani; Hideo Daimon; Takao A. Yamamoto (pp. 43-50).
Display Omitted► Pt-Cu nanoparticles were successfully synthesized on γ-Fe2O3 by radiolytic process. ► Up to 30–50% of Cu can be incorporated in Pt lattice to form Pt-Cu alloy. ► Amorphous CuO layer was also identified on γ-Fe2O3 surface. ► The catalysts that consist of Pt-Cu alloy and amorphous CuO show high PROX activity. ► The high activity was attributed to high O2 transport and lowered H2 chemisorption.Pt-Cu bimetallic nanoparticles immobilized on γ-Fe2O3 support were synthesized by a unique radiolytic process and their physical properties and catalytic activity for CO preferential oxidation were investigated for various Pt/Cu atomic ratios. The chemical composition of the catalysts measured by inductively coupled plasma revealed most of the platinum and copper aqueous precursors were deposited on to the γ-Fe2O3 support after irradiation with electron beam. Crystallographic analysis of the catalysts by X-ray diffraction showed Pt-Cu alloy is formed for wide range of Pt/Cu ratio. From the lattice parameter of this Pt-Cu alloy, it was found that Cu can be incorporated into Pt lattice up to 30at% with the present irradiation condition. The rest of Cu for high-Cu (low-Pt) samples was identified as divalent oxide with poor crystallinity by XANES spectrum. Detailed STEM-EDX analyses further confirmed that Pt-Cu alloy exists as nanoparticles with a few nanometers in diameter and CuO with low crystallinity distributes on entire surface of the γ-Fe2O3 support. The PROX activity showed different trends between high-Pt and high-Cu samples. The CO conversion decreased as the Pt loading was decreased to 50at%, and it monotonically decreased with increasing temperature. However, as the Pt loading was further decreased, the activity increased with temperature by contraries, and reached the maximum conversion at 100°C. Regardless of the low Pt loading, the sample with 10 at% Pt and 90at% Cu exhibited the highest activity at 100°C, which is preferable for low temperature fuel cell applications. This enhanced activity was attributed to oxygen supply via the copper of low crystallinity from the O2-poor atmosphere to Pt-Cu alloy particles that chemisorbs CO molecules.
Keywords: Pt-Cu catalyst; Bimetallic Pt-Cu; Preferential oxidation; PROX; Radiolytic process; Radiation-induced synthesis
Preparation of spindly CuO micro-particles for photodegradation of dye pollutants under a halogen tungsten lamp by Jianpeng Li; Fengqiang Sun; Kaiyuan Gu; Tianxing Wu; Wei Zhai; Weishan Li; Shufang Huang (pp. 51-58).
Display Omitted► Spindly CuO microparticles were prepared for the first time. ► They exhibited excellent photocatalytic activities under the visible-light. ► The particles could be used for the photodegradation of various dye pollutants. ► H2O2 was first introduced to enhance the photocatalytic activity of CuO.Spindly cupric oxide (CuO) micro-particles were synthesized using Cu(NO3)2, hexamethylenetetramine, and NaOH solutions at 95°C. The spindly CuO particles had a shape similar to a carambola of ∼1μm in length and 300nm in width. They were composed of nanosheets with a thickness of ∼5nm. Such particles could be used in the photocatalytic degradation of rhodamine B in the presence of ∼0.01M H2O2. Under irradiation by a 100W halogen tungsten lamp, the CuO showed photocatalytic activities higher than those of P25 and commercially available CuO powder. They were very stable and could be recycled without considerable loss of activity. Other dye and organic pollutants such as methyl orange, methylene blue, erosin B, and p-nitrophenol could also be photodecomposed under identical conditions. These characteristics show the practical applications of the CuO particles in environmental remediation.
Keywords: CuO; Spindly shape; Visible-light photocatalysis; Dye pollutants; Rhodamine B
Influence of framework composition over SAPO-34 and MeAPSO-34 acidity by Fagner Calegario Sena; Bianca Figueirôa de Souza; Núbia Caroline de Almeida; Jonathan Simonace Cardoso; Lindoval Domiciano Fernandes (pp. 59-62).
Display Omitted► SAPO-34 and MeAPSO-34 samples were prepared based on a standard literature procedure. ► Several kinds of transition metal were incorporated into SAPO-34 structure. ► SAPO-34 and MeAPSO-34 presenting similar structures at were obtained. ► Acid sites concentration depended strongly on their metal content and nature.SAPO-34 and MeAPSO-34 samples were prepared based on a standard literature procedure . In fact, several kinds of transition metal were incorporated in the SAPO-34 structure, during the synthesis step, beginning with the same gel. As a result, samples of SAPO-34 and MeAPSO-34, presenting good crystallinity and also having similar surface area and microporosity, were obtained. It was observed that acid sites concentration depended strongly on their metal content. Metal incorporation in the SAPO-34 structure generally increased acid sites concentration but did not affect the acid strength distribution.
Keywords: Silicoaluminophosphates; Low pore size molecular sieves
Ternary composites for glycerol conversion: The influence of structural and textural properties on catalytic activity by Helvio S.A. de Sousa; Francisco de Assis A. Barros; Santiago J.S. Vasconcelos; Josué M. Filho; Cleanio L. Lima; Alcemira C. Oliveira; Alejandro P. Ayala; Manoel C. Junior; Alcineia C. Oliveira (pp. 63-72).
Display Omitted► High surface area ternary composites. ► Phases such as CeO2, ZrO2, NiO, Co3O4, Al2O3 and SiO2 were found. ► Composites mixed CeO2–ZrO2 and Co3O4 nanoparticles. ► Favoured glycerol conversion and acrolein selectivity.Ternary composites were prepared and evaluated regarding their catalytic performance for the glycerol dehydration. The results of XRD and Raman spectroscopy revealed that the nanoparticles that were obtained contained phases such as CeO2–ZrO2, CeO2, NiO, Co3O4, and Al2O3 dispersed on SiO2. The solids possessing elevated textural properties with basic and acidic sites were active in the conversion of glycerol. The mixed CeO2–ZrO2 and Co3O4 nanoparticles of the ternary composite was stabilised by silica and favoured glycerol conversion and selectivity to 1-hydroxyacetone and acrolein due to the stronger resistance to the phase transformations, when compared to other solids that had a high acidity and were quickly deactivated in the reaction media. Variations of the space velocity and the contact time defined the optimal conditions for glycerol conversion and acrolein selectivity.
Keywords: Ternary composites; Characterisations; Activity; Synthesis
Identification of the carbonaceous compounds present on a deactivated cobalt based Fischer–Trospch catalyst resistant to “rejuvenation treatment” by L. Pinard; P. Bichon; A. Popov; J.L. Lemberton; C. Canaff; F. Maugé; P. Bazin; E. Falabella S.-Aguiar; P. Magnoux (pp. 73-80).
GC–MS analysis of the coke species extracted by HF on the 21 days spent catalyst.Display Omitted► FT cobalt catalysts deactivate with the time on-stream. ► Stripped waxes, light waxes and coke are present on the catalytic bed. ► Carbon, n-alcohols, polymeric carbon, carboxylic acids compose the coke. ► Polymeric carbon and carboxylic acids were resistant towards the rejuvenation.The deactivation of a Co–Ru/Al2O3 catalyst during a Fischer–Trospch process was examined under relevant industrial conditions, 220°C and 2MPa. The decline in CO conversion can result from several causes such as oxidation, sintering and carbon deposition. The aim of this work was to identify the carbon compounds deposited on the spent catalyst. At the end of the experiment, the catalyst was first stripped by N2 at the reaction temperature, then the N2-stripped sample was soxhlet-extracted with cyclohexane to recover the “light waxes” trapped in the catalyst pores. Then, the catalyst was dissolved in HF in order to remove the inorganic components and to recover the residual carbon called “coke”.Spent catalyst samples obtained at different points in time on-stream were analyzed using various techniques such as nitrogen adsorption, TPH-MS, TPO-MS and TPH-IR-MS. The coke was constituted of four kinds of carbonaceous compounds: atomic carbon, alcohols, carboxylic acids and polymeric carbon. Only the two last families were resistant to a rejuvenation treatment under hydrogen.
Keywords: Deactivation; Polymeric carbon; Atomic carbon; Carboxylic acids; Regeneration
Enhancement of Pt catalytic activity in the hydrogenation of aldehydes by Yang Tang; Shaojun Miao; Hien N. Pham; Abhaya Datye; Xiaoming Zheng; Brent H. Shanks (pp. 81-88).
Studies were performed to enhance the hydrogenation performance of metal sites on mesoporous silicas catalysts (Pt/SBA15), in order to provide guidance for the further enhancement of bifunctional catalysts (Pt/SBA15-PrSO3H) to be used in one-step hydrogenation/esterification, which is a model reaction for the catalytic upgrading of bio-oil.Display Omitted► Reductive deposition of Pt yields high metal dispersion on SBA15. ► Pt deposited by reductive deposition can be activated at lower temperatures. ► Hydrogen activation can occur at lower temperatures with the activated catalyst. ► High activity for aldehyde hydrogenation was achieved.Bifunctional mesoporous organic–inorganic hybrid silica involving platinum and propylsulfonic acid groups (Pt/SBA15-PrSO3H) have been demonstrated to have potential for catalyzing the combined one-step hydrogenation/esterification (OHE) reaction. This reaction provides a model system for the catalytic upgrading of biomass-derived bio-oil. In this study, efforts were made to improve the catalytic performance of the catalyst for aldehyde hydrogenation, which was determined to be rate limiting in the OHE reaction with the bifunctional catalyst. STEM analysis coupled with hydrogen chemisorption results showed that aqueous reduction–deposition using formaldehyde as the reducing agent produced highly dispersed platinum nanoparticles located within the mesopores of SBA15. XPS and UV–vis demonstrated that the metal sites were not fully activated due to insufficient reducing capability of the formaldehyde. Elevated temperature treatment of the as-prepared materials in either an air or H2 environment was examined. These treatments significantly increased the acetaldehyde hydrogenation activity, especially in the case of H2 treatment. XPS and H2-TPD results demonstrated that Pt species were further reduced and as a result, hydrogen was activated more readily.
Keywords: Dispersion enhancement; Hydrogenation; Platinum; SBA15; Formaldehyde reduction-deposition; Bio-oil; Catalytic upgrading
Gold-catalyzed selective glucose oxidation at high glucose concentrations and oxygen partial pressures by Ulf Prüße; Mirko Herrmann; Christine Baatz; Nadine Decker (pp. 89-93).
.Display Omitted► Gold-catalyzed glucose oxidation at 1–57.5wt% glucose and 1.5–9bar oxygen. ► Apparent activation energy was determined to 54KJmol−1. ► Reaction is likely to follow the Langmuir–Hinshelwood model. ► High long-term stability in ten repeated batches at 20wt% glucose and 9bar oxygen.The aqueous-phase glucose oxidation was studied at initial glucose concentrations of 1–57.5wt% and oxygen partial pressures of 1.5–9bar using a 0.3% Au/Al2O3 catalyst. The highest activity at 40°C (about 5200mmolmin−1gAu−1) was observed at an initial glucose concentration of 20wt% and an oxygen pressure of 9bar. The apparent activation energy was determined to 54kJmol−1. Kinetic analysis revealed that the reaction is likely to follow the Langmuir–Hinshelwood model. The catalyst possessed a high long-term stability in ten repeated batches at 20wt% initial glucose concentration.
Keywords: Gold catalyst; Glucose oxidation; Reaction order; Activation energy
A TEM and UV–visible study of silver reduction by ethanol in Ag–alumina catalysts by Elie Sayah; Dalil Brouri; Yihao Wu; Andrea Musi; Patrick Da Costa; Pascale Massiani (pp. 94-101).
Display Omitted► State and dispersion of silver supported on alumina catalysts. ► Reduction of the highly dispersed cationic silver species by ethanol. ► Active sites transformation in the course of reaction (SCR of NO x). ► Importance of the conditions of grids preparation for transmission electron microscopy (TEM) study of metal supported catalysts.A transmission electron microscopy (TEM) study dedicated to the understanding of dispersion and location of Ag nanospecies in silver–alumina catalysts is reported. A special attention is put on the conditions of powder catalyst deposition on the grids for TEM analysis. When the deposition is conducted through conventional suspension in ethanol (EtOH) then drying, numerous Ag nanoparticles with sizes between 2 and 10nm are observed in the micrographs of calcined Ag/Al2O3. This drastically contrasts with the absence of particle after dry deposition, silver being then well dispersed all over the alumina support, as can be seen by combined STEM/EDS mapping. These distinct observations are straightforwardly attributable to the reducing effect of ethanol towards Ag species that is also identified by UV–visible spectroscopy. The results highlight the importance, for correctness of TEM interpretations, of avoiding any contact between an alcohol solvent and Ag–oxide catalysts in the course of TEM studies, in contrast to experimental conditions that are still often applied nowadays. Finally, the reducing effect of ethanol on silver active sites that is likely to occur during SCR (selective catalytic reduction) of NO x in the presence of EtOH is envisaged and discussed as well.
Keywords: Transmission electron microscopy (TEM); Silver; Nanoparticles; Ethanol; Reduction; UV–visible spectroscopy; Catalysis; SCR of NO; x
IR study of active sites for n-heptane isomerization over MoO3-ZrO2 by Nurun Najwa Ruslan; Nurrulhidayah Ahmad Fadzlillah; Ainul Hakimah Karim; Aishah Abdul Jalil; Sugeng Triwahyono (pp. 102-112).
Display Omitted► MoO3-ZrO2 possesses Brönsted and Lewis acid sites with different acidic strength. ► Bands at 1605 and 1590cm−1 are Lewis acid sites corresponding to monoclinic ZrO2 ► Bands at 1595 and 1580cm−1 are Lewis acid sites corresponding to tetragonal ZrO2. ► Only a doublet bands at 1595 and 1580cm−1 involved in the formation of H+ from H2. ► No activity was observed in the absence of a doublet bands at 1595 and 1580cm−1.The property of acidic sites on MoO3-ZrO2 was studied for n-heptane isomerization. A 2,6-lutidine IR study showed that the introduction of MoO3 on ZrO2 partially eliminated the absorbance band at 1605cm−1 ascribed to Lewis acid sites corresponding to the presence of the monoclinic phase of ZrO2 and developed several Brönsted and Lewis acid sites with different acidic strengths. MoO3-ZrO2 possesses a large number of relatively weak Lewis and Brönsted acid sites as well as strong acid sites. The active protonic acid sites in n-heptane isomerization were formed from molecular hydrogen through a spillover mechanism with the involvement of doublet bands at 1595 and 1580cm−1 ascribed to the Lewis acid sites corresponding to the presence of the tetragonal phase of ZrO2. No catalytic activity of MoO3-ZrO2 for n-heptane isomerization was observed in the absence of the doublet bands at 1595 and 1580cm−1 and hydrogen in the gas phase.
Keywords: MoO; 3; -ZrO; 2; Lewis acid sites; Protonic (Brönsted) acid sites; Monoclinic ZrO; 2; Tetragonal ZrO; 2
Superbasic sodium stannate as catalyst for dehydrogenation, Michael addition and transesterification reactions by Shu-Guo Zhang; Yu-Dan Wei; Shuang-Feng Yin; Sheng-Lian Luo; Chak-Tong Au (pp. 113-118).
Display Omitted► Superbasicity was directly generated on sodium stannate through thermally treating sodium stannate hydrate at 623K. ► The superbasicity was confirmed using a combination of characterization techniques and probe reactions. ► The as-prepared superbase shows wide catalytic applications with high efficiency. ► The catalytic efficiency of the superbase is related to its superbasicity.It has been shown that sodium stannate with superbasic sites generated on its surface can be obtained through simple thermal treatment of sodium stannate hydrate in pure N2. In this study, we analyzed the as-prepared materials using powder X-ray diffraction, X-ray photoelectron spectroscopy, and N2 physisorption methods. The superbasic sites were characterized by techniques of Hammett indicators and temperature-programmed desorption using CO2 as adsorbate. It was shown that after undergoing calcination at 623K, there are ample superbasic sites on sodium stannate: up to 0.254mmol/g. The superbasicity of the materials was further confirmed by employing the 1-hexene as well as cyclohexa-1,4-diene double bond isomerization reactions. The superbasicity is attributed to the higher electron-donating ability of surface O2−. The sodium stannate samples showed excellent catalytic efficiency towards selected reactions, namely the dehydrogenation of propa-2-nol, Michael addition of electron-deficient olefins, and transesterification of cyclic carbonate with methanol. It was observed that with rise of heat-treatment temperature from 573 to 623K, both superbasicity and catalytic activity increased, reaching a maximum at 623K, and then declined. It is deduced that catalytic efficiency is closely related to superbasicity of the sodium stannate catalysts.
Keywords: Superbase sodium stannate; Double bond isomerization; Michael addition; Dehydrogenation; Transesterification
Controlled structure of anatase TiO2 nanoparticles by using organic additives in a microwave process by Victor M. Menéndez-Flores; Misa Nakamura; Tomoki Kida; Zhengyuan Jin; Naoya Murakami; Teruhisa Ohno (pp. 119-123).
Display Omitted► PAAc, the most useful polymer for controlling decahedral anatase structure under microwave. ► Reaction sites separation with high-quality TiO2 faces is more important than surface area. ► Photocatalytic activity of the controlled anatase TiO2 improved by reaction sites separation. ► Microwave process remarkably reduced reaction time and energy, obtaining an efficient and competitive process.Synthesis of anatase nanoparticles was carried out in a microwave system. Crystal morphology was controlled by organic additives including PAAc (polyacrylic acid) and PVP (polyvinylpyrrolidone). Modified TiO2 particles were compared to the bare TiO2 anatase structure. The synthesis of materials via the microwave system has great advantages due to the short reaction period and low energy requirement and is therefore an environmentally friendly process compared to the hydrothermal process. The decomposition of acetaldehyde was studied to determine the photocatalytic activity of the modified anatase TiO2 material.
Keywords: Photocatalysis; Decahedral TiO; 2; anatase; Polyacrylic acid
Pd nanoparticles immobilized on PAMAM-grafted MWCNTs hybrid materials as new recyclable catalyst for Mizoraki–Heck cross-coupling reactions by Mohammad Reza Nabid; Yasamin Bide; Seyed Jamal Tabatabaei Rezaei (pp. 124-132).
Display Omitted► PAMAM dendrimers up to the third generation were grown onto the surface of carbon nanotubes. ► The PAMAM-g-MWCNTs were employed as substrate for in situ generation of Pd nanoparticles. ► This hybrid material was found to be efficient and reusable catalyst in Heck coupling reactions.Polyamidoamine (PAMAM) dendrimers up to the third generation (G) were grown onto the surface of functionalized multiwall carbon nanotubes (MWCNTs-NH2) by a divergent method, the PAMAM-grafted-MWCNTs (PAMAM-g-MWCNTs) hybrid materials were obtained. Because of the surface modification of the multiwall carbon nanotubes with PAMAM dendrimers, these hybrid materials are not only soluble in aqueous medium but also are able to trap water soluble metal ions such as Pd2+ via complex formation of PAMAM dendrimer with metal ions. The reduction of trapped palladium ions in the dendritic shell of PAMAM-g-MWCNTs by sodium borohydride led to immobilized palladium nanoparticles on the surface of MWCNTs. Thus, palladium nanoparticles were immobilized by PAMAM-g-MWCNTs hybrid materials (PdNs-PAMAM-g-MWCNTs) and their application as a new nanocatalyst toward Heck reaction in different conditions was investigated. The G3 and G2 hybrid materials were found to be very active in cross-coupling reactions of aryl iodides, bromides and also chlorides with olefinic compounds in Heck reactions with short reaction time duration and high yields. The catalyst can be recycled several times without loss in activity.
Keywords: Dendrimer; Palladium nanoparticles; Carbon nanotubes; Supported catalysis; Heck reaction