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Applied Catalysis A, General (v.317, #1)
Ce-silica mesoporous SBA-15-type materials for oxidative catalysis: Synthesis, characterization, and catalytic application by M.N. Timofeeva; S.H. Jhung; Y.K. Hwang; D.K. Kim; V.N. Panchenko; M.S. Melgunov; Yu. A. Chesalov; J.-S. Chang (pp. 1-10).
Cerium-containing mesoporous materials have been synthesized by hydrothermal method and characterized by IR, DR-UV–vis and DRIFT spectroscopy, XRD and N2 adsorption methods. Important factors affecting the catalytic activity of Ce-SBA-15, namely the effect of cerium content, the state of cerium ions, the state of silanol groups on the surface of Ce-SBA-15 and stability of the catalyst have been studied in the cyclohexanol and cyclohexene oxidation with hydrogen peroxide. The reaction mechanism was discussed.▪Cerium-containing mesoporous materials have been synthesized by hydrothermal method and characterized by IR, DR-UV–vis and DRIFT spectroscopy, XRD and N2 adsorption methods. It was established that the d100 and unit-cell ( a0) parameter increase with the increase of cerium content up to 2% in SBA-15 and then tend to remain the same. According to DR-UV–vis spectroscopic data, an agglomeration of cerium atoms was observed in the form of fine CeO2 crystallites. Important factors affecting the catalytic activity of Ce-SBA-15, namely the effect of cerium content, the state of cerium ions, the state of silanol groups on the surface of Ce-SBA-15, and stability of the catalyst have been studied in the cyclohexanol and cyclohexene oxidation with hydrogen peroxide.
Keywords: Cerium-containing mesoporous materials; SBA-15; Cyclohexene oxidation; Cyclohexanol oxidation; Hydrogen peroxide
Synthesis and characterization of Cr/Cu/Mg mixed oxides obtained from hydrotalcite-type compounds and their application in the dehydrogenation of isoamylic alcohol by Mónica Crivello; Celso Pérez; Julio Fernández; Griselda Eimer; Eduardo Herrero; Sandra Casuscelli; Enrique RodrÃguez-Castellón (pp. 11-19).
CrCuMg layered double hydroxides (LDH) with hydrotalcite-like structure containing different proportions of Mg2+, Cu2+ and Cr3+ cations have been prepared. The effect of copper for the dehydrogenation reaction of isoamyl alcohol has been examined and high conversions and selectivity to isovaleraldehyde were observed. Experimental data show that the copper is the active specie but the addition of magnesium improves the stability of the catalyst.Conversion versus time on stream using catalysts with different content of copper. HT32 (■); HT70 (*); HT100 (□); HT0 (♦); HT53 (○). ▪CrCuMg layered double hydroxides (LDH) with hydrotalcite-like structure containing different proportions of Mg2+, Cu2+ and Cr3+ cations have been prepared. Thermogravimetry and X-ray diffraction data indicate that the transformation of LDH into mixed oxides is effective after calcination at 450°C. The effect of copper and magnesium for the dehydrogenation reaction of isoamyl alcohol has been examined and high conversions and selectivities to isovaleraldehyde were observed. Experimental data show that the copper is the active specie but the addition of magnesium improves the stability of the catalyst. An exhaustive analysis by XPS allowed us to analyze different copper species in the catalysts. So, Cu2+ was detected as CuO and as CuCr2O4 spinel-like in calcined samples, while Cu0 and Cu2+ were found in the reduced samples, being higher the percentage of the former with the increase of the magnesium content in the sample. Chromium is as Cr3+ in an octahedral coordination in the precursors as found by diffuse reflectance, and it occupies a similar position to that of aluminium in layered double hydroxides. The LDH are poorly crystalline, but the crystallinity degree increases after calcination, as observed by XRD. Moreover, the specific surface area determined by N2 adsorption–desorption and the “memory effect� analyzed by DTA, were related to the content of magnesium.
Keywords: Layered double hydroxides; Hydrotalcites; Isoamyl dehydrogenation; Mixed oxides; Chromium; Copper
Factors influencing the thioresistance of nickel catalysts in aromatics hydrogenation by B. Pawelec; P. Castaño; J.M. Arandes; J. Bilbao; S. Thomas; M.A. Peña; J.L.G. Fierro (pp. 20-33).
Silica–alumina supported nickel catalysts (Ni/ASA) have been modified by the incorporation of electrodonor (Li) or electro acceptor (Pd) elements with the objective of determining the factors controlling the catalyst thioresistance in benzene hydrogenation. The catalysts were tested in benzene hydrogenation (HYD) in the presence of 1-butanethiol (C4H9SH 5ppm of S) and in the hydroconversion of pyrolysis gasoline (PyGas) and compared with zeolite NaY-supported ones. In addition, the catalysts were characterized by variety of techniques (XRD, N2 adsorption–desorption, TPD-H2, TPD-NH3, CO chemisorption, TPR, XPS, FTIR of adsorbed pyridine, TGA–DTA). It was found that the monometallic Ni/ASA catalyst with 24wt.% of Ni was the most active among the catalysts studied in both benzene hydrogenation (+S) and hydroconversion of PyGas. The data of catalyst characterization suggests that the concentration of both metal and acid sites govern catalytic activity in both activity tests being the catalyst ability for hydrogen adsorption one of the most important factors to be taken into account. In general, it was found that the S-poisoning of the catalysts increased with an increase of the catalyst reactivity and diminished when “refractory-type� coke deposited on the metal sites inhibited the S-compound adsorption. For PyGas transformation, the importance of Pd promotion of the nickel catalysts was confirmed for both hydrogenation and ring-opening reactions.Ni/silica–alumina catalysts modified by Li or Pd were tested in benzene hydrogenation in the presence of 1-butanethiol (5ppm of S) and in the hydroconversion of pyrolysis gasoline (PyGas). For PyGas transformation, the importance of Pd promotion of the nickel catalysts was confirmed for both hydrogenation and ring-opening reactions. ▪
Keywords: Benzene hydrogenation; Pyrolysis gasoline; Nickel catalysts; Silica–alumina
Synthesis, characterization and catalytic properties of nanodimensional nickel ferrite/silica composites by E. Manova; T. Tsoncheva; D. Paneva; J.L. Rehspringer; K. Tenchev; I. Mitov; L. Petrov (pp. 34-42).
Nanosized NiFe2O4/silica composites are synthesized using the sol–gel method. The investigated compounds are active in the reaction of catalytic methanol decomposition. Significant differences in their catalytic activity and selectivity to methane, depending on the preparation conditions are observed. In this aspect, nickel ferrites composites opens new prospects for the selectivity control of methanol decomposition to hydrogen, methane or CO. ▪Nanosized nickel ferrite/silica composites are synthesized using the sol–gel method. X-rays diffraction, Mössbauer and infrared spectroscopies, magnetic measurements and thermo-programmed reduction with hydrogen are used for their characterization. Significant differences in their catalytic activity and selectivity in methanol decomposition to CO and methane, depending on the ferrite/silica ratio, the annealing temperature and the phase transformations of the samples by the reaction medium are observed.
Keywords: Nanosized nickel ferrite/silica composites; Sol–gel method; Mössbauer spectroscopy; Methanol decomposition; Magnetic measurements
Pyrazole and trispyrazolylmethane rhenium complexes as catalysts for ethane and cyclohexane oxidations by Elisabete C.B. Alegria; Marina V. Kirillova; LuÃsa M.D.R.S. Martins; Armando J.L. Pombeiro (pp. 43-52).
Conversion of ethane to acetic acid, using K2S2O8 as oxidant and TFA as solvent, and catalytic peroxidative oxidation of cyclohexane, using aqueous H2O2 as oxidant and acetonitrile as solvent, are catalysed by Re complexes with pyrazole or tris(pyrazolyl)methane ligands. The reactions occur via radical mechanisms and the effects of various parameters are reported. ▪The pyrazole complexes [ReCl2{N2C(O)Ph}(Hpz)(PPh3)2]2 (Hpz=pyrazole), [ReCl2{N2C(O)Ph}(Hpz)2(PPh3)]3 and [ReClF{N2C(O)Ph}(Hpz)2(PPh3)]4, and the tris(pyrazolyl)methane compounds [ReCl2(HCpz3)(PPh3)][BF4]5 (pz=pyrazolyl), [ReCl3{HC(pz)3}]7, [ReOCl2{SO3C(pz)3}(PPh3)]8 and [ReO3{SO3C(pz)3}]9, and their precursors [ReCl2{η2- N, O-N2C(O)Ph}(PPh3)2]1 and [ReOCl3(PPh3)2]6, act as selective catalysts (or catalyst precursors), in a single-pot process, for the oxidation of ethane, in the presence of potassium peroxodisulfate K2S2O8, in trifluoroacetic acid (TFA), to give acetic acid, in a remarkable yield (up to ca. 40%) and under mild conditions (in some cases carboxylation can also occur to give propionic acid, but in a much lower yield). The catalytic peroxidative oxidation of ethane to acetaldehyde and of cyclohexane to cyclohexanone and cyclohexanol by an aqueous solution of H2O2 at room temperature is also achieved by using most of those catalyst precursors. The effects of a variety of factors were studied towards the optimization of the processes which are shown to proceed via both C-centered and O-centered radical mechanisms.
Keywords: Alkanes; Functionalization; Rhenium; Homogeneous catalysis; Oxidation; Ethane; Cyclohexane
Catalytic activity of iridium siloxide complexes in cross-linking of silicones by hydrosilylation by Ireneusz Kownacki; Bogdan Marciniec; Anna Macina; SÅ‚awomir Rubinsztajn; David Lamb (pp. 53-57).
A series of catalytic examinations show that monomeric iridium siloxides ([Ir(cod)(PCy3)(OSiMe3)] (II), [Ir(CO)(PPh3)2(OSiMe3)] (III) and [Ir(CO)(PCy3)2(OSiMe3)] (IV)) are effective and selective catalysts for model homogeneous hydrosilylation of vinyltrisiloxane as well as cross-linking of commercial polysiloxane system. ▪A series of catalytic examinations have shown that monomeric iridium siloxides ([Ir(cod)(PCy3)(OSiMe3)] (II), [Ir(CO)(PPh3)2(OSiMe3)] (III) and [Ir(CO)(PCy3)2(OSiMe3)] (IV)) are effective catalysts for model homogeneous hydrosilylation of vinyltris(trimethylsiloxy)silane as well as cross-linking of commercial polysiloxane system. The results of stoichiometric reactions of iridium siloxide with heptamethyltrisiloxane and observed catalytic properties are consistent with the mechanism of catalysis involving a generation of the key-intermediate (16e tetracoordinate Ir–H complex) responsible for the catalytic cycle. Experiments allowed explaining the effect of oxygen on the catalytic activity of phosphine-containing iridium siloxide complexes. The curing process of polysiloxanes catalyzed by iridium siloxideII andIV complexes occurs at a higher temperature (about 200°C) than the same system catalyzed by Karstedt—diallylmaleate system (130°C). The enthalpies of the reaction are comparable (−30 to −38kJ/mol) for both catalysts but the inhibitor is not required for the iridium-catalyzed process.
Keywords: Silicones; Cross-linking; Hydrosilylation; Iridium complexes
Methanolysis of soybean oil in the presence of tin(IV) complexes by Davi A.C. Ferreira; Mario R. Meneghetti; Simoni M.P. Meneghetti; Carlos R. Wolf (pp. 58-61).
In this work, we present the results obtained from the methanolysis of soybean oil using tin(IV)-based commercial compounds as catalysts. In order to characterize the behavior of such catalytic systems in the reaction medium, different reaction times, temperatures and catalyst amounts were used. The efficiency of the catalytic system in terms of yield (% of fatty acid methyl esters formed) varies in the following order: dibutyltin dilaurate>di- n-butyl-oxo-stannane>modified di- n-butyl-oxo-stannane>butylstannoic acid. Parameters as degree of solubility of the catalyst and rate stirring were also investigated.
Keywords: Biodiesel; Catalysts; Tin (IV) complexes; Transesterification; Methanolysis; Catalyst solubility; Soybean oil
Sintering of alumina-supported nickel particles under amination conditions: Support effects by Johan Lif; Ingemar Odenbrand; Magnus Skoglundh (pp. 62-69).
The sintering of alumina-supported nickel particles has been studied after heat-treatment in ammonia+hydrogen at 523K and 250bar. The investigated samples were nickel supported on γ-alumina, transalumina and α-alumina, and co-precipitated nickel oxide-alumina. The sintering process was mainly followed by hydrogen chemisorption. The samples were also characterised by specific surface area measurements, X-ray diffraction, temperature programmed desorption of ammonia, in situ FTIR spectroscopy and temperature programmed reduction. For nickel supported on γ-alumina, up to 40% of the initial metal surface area remained after the heat-treatment in ammonia+hydrogen compared with α-alumina or transalumina where only 10–20% of the initial metal surface area remained after the heat-treatment. The sintering can be correlated to the bond strength between the metal particle and the support. The larger the number of low-coordinated surface aluminium sites is, as for γ-alumina, the stronger the metal–support interaction is and this in turn suppresses diffusion of nickel particles and/or atoms.The sintering of alumina-supported nickel particles has been studied after heat-treatment in ammonia+hydrogen. The stability of nickel against sintering can be significantly enhanced by choosing a support with strong Lewis acid sites, like γ-alumina, which can anchor the nickel particles to the support. These strong Lewis acid sites are most likely low-coordinated surface aluminium sites.▪
Keywords: Sintering; Nickel; Alumina; Lewis acids sites; Coordination number; Amination catalysis
A new kinetic model for heterogeneous (or spatially confined) enzymatic catalysis: Contributions from the fractal and jamming (overcrowding) effects by Feng Xu; Hanshu Ding (pp. 70-81).
A fractal Michaelis kinetics was reformulated for heterogeneous enzymatic reactions, together with a kinetic “jamming� effect caused by the overcrowding in confined space. The new kinetic model was applied to the cellulose hydrolysis by cellobiohydrolase, a heterogeneous system highly fractal due to the strong surface adsorption of the enzyme onto the insoluble substrate and to the one-dimensional “processive� enzymatic mechanism. ▪Heterogeneous catalysis involves catalysts and reactants separated in different phases. In these systems, the interaction between the reactant and catalyst can be quite different from its homogeneous counterpart, because of the peculiarity of the diffusion and molecular collision processes constricted in spaces with dimension less than three. The fractal theory, developed for mathematic, physical, chemical, and biological processes with inherent irregularity and complexity, can be applied to heterogeneous catalysis. To better understand the heterogeneous enzymatic reactions, a fractal Michaelis kinetics was reformulated, after applying the general fractal formalism to the classical model of homogeneous enzymatic reactions. A kinetic “jamming� effect caused by the overcrowding of enzyme/substrate in confined space was also studied. The new kinetic model was applied to the hydrolysis of cellulose by cellobiohydrolase, a representative heterogeneous biocatalytic system highly fractal due to the strong surface adsorption of the enzyme onto the insoluble substrate as well as to the one-dimensional “processive� enzymatic mechanism. The usefulness of the model for the study and application of other enzymatic reactions was discussed.
Keywords: Fractal kinetics; Enzyme; Polymeric substrate; Heterogeneous catalysis
Cobalt molybdenum carbides: Surface properties and reactivity for methane decomposition by Shamsul Izhar; Hiroyuki Kanesugi; Hiroyuki Tominaga; Masatoshi Nagai (pp. 82-90).
The methane decomposition over cobalt molybdenum catalysts carburized at temperatures of 700–973K was performed using a microreactor at 973K. The Co50Mo50C-800 catalyst exhibits a higher conversion and hydrogen production rate. The active species of the cobalt molybdenum carbide catalyst for the CH4 decomposition was the cobalt molybdenum oxycarbide (Co1.0Mo5.6C0.3O0.7 by XPS analysis) on the surface that was formed during the carburization.▪The methane decomposition over cobalt molybdenum catalysts (CoMo100- x; x=0, 25, 50, and 75) carburized at temperatures of 700–973K was performed using a microreactor at 973K. The active species for the production of hydrogen during the methane decomposition was studied on the basis of XRD, TPC, TPR, and XPS. The Co50Mo50C-800 catalyst exhibits a higher conversion and hydrogen production rate compared to the Mo100C-, Co25Mo75C-, and Co75Mo25C-800 catalysts. The XRD measurement showed the presence of β-Mo2C and cobalt molybdenum oxycarbides in the catalyst before and after 6-h reaction. Cobalt molybdenum carburized at 800K produced a surface oxycarbide based on the formation of H2O during the TPC and production of CH4 and H2O during the TPR. The active species of the cobalt molybdenum carbide catalyst for the CH4 decomposition was the cobalt molybdenum oxycarbide (Co1.0Mo5.6C0.3O0.7 by XPS analysis) on the surface that was formed during the carburization. The catalyst also exhibited a longer lifetime during methane decomposition.
Keywords: Co-Mo; Carbide; Methane decomposition; TPC; XRD; TPR; XPS
Synthesis and catalysis of tungsten oxide in hexagonal mesoporous silicas (W-HMS) by Iou-Sheng Ke; Shiuh-Tzung Liu (pp. 91-96).
By using a diblock copolymer containing tungsten complexes as templates, tungsten-hexagonal mesoporous silicas (W-HMS) were synthesized, which could be used as a catalyst for the allylic oxidation of cyclohexene. â–ªHexagonal mesoporous silicas containing tungsten complexes have been synthesized through the condensation of tetraethoxysilane templated by an amphiphilic diblock copolymers modified with tungsten isocyanide complexes under acidic conditions. Upon calcination, the tungsten complex was transformed into its oxide, which was deposited inside the channels. This material is illustrated to be a good catalyst on the allylic oxidation of cyclohexene in the presence of hydrogen peroxide under mild conditions. In addition, this catalyst could be easily recovered after the reaction and re-used without any significant loss of its activity.
Keywords: Silicas; Tungsten; Oxidation; Cyclohexene
Surface structure and Fischer–Tropsch synthesis activity of highly active Co/SiO2 catalysts prepared from the impregnating solution modified with some chelating agents by Takehisa Mochizuki; Takeshi Hara; Naoto Koizumi; Muneyoshi Yamada (pp. 97-104).
The present study investigated the surface structure and Fischer–Tropsch synthesis (FTS) activity of highly active Co/SiO2 catalyst prepared from the aqueous Co nitrate solution modified with chelating agents, i.e. nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA) and/or trans-1,2-diaminocyclohexane- N,N,N′,N′-tetraacetic acid (CyDTA), in order to make clear the origin of their promoting effects reported previously. The catalyst was prepared by impregnating SiO2 support with the aqueous solution containing Co nitrate and the chelating agent followed by drying and calcination. Characterization results of the calcined catalysts by XRD, XPS and TPR showed that modification of the impregnating solution with different chelating agents results in the formation of Co species with different structures after the calcination. On one hand, dispersed Co oxide species was formed on the calcined catalyst modified with NTA, which was in more dispersed state compared with Co3O4-like species on the calcined catalyst without chelating agents. On the other hand, highly dispersed α-Co2SiO4-like species was mainly formed after the calcination when modified with EDTA and/or CyDTA. After H2 reduction, about 90% of Co oxide species over NTA-modified catalyst was reduced to create more metallic Co sites compared with the catalyst without chelating agents, which yielded C10–20 hydrocarbons from syngas at 503K and 1.1MPa ca. three times greater than the catalyst without chelating agents. The catalysts modified with EDTA and/or CyDTA showed relatively lower activities after the reduction because the reduction degree of highly dispersed α-Co2SiO4-like species was much lower than that of Co3O4-like species. Therefore, modification of the impregnating solution with chelating agents increases the number of surface metallic Co sites through modification of the structure of Co species after the calcination, leading to the higher FTS activity. The role of chelating agents during the preparation of the catalyst was also discussed here.Co/SiO2 Fischer–Tropsch synthesis catalysts were prepared from the aqueous Co nitrate solution modified with several chelating agents followed by drying and calcination. Modification with these chelating agents increased the number of surface metallic Co sites through modification of the structure of Co species formed after the calcination, leading to the higher C10–20 hydrocarbon yields. ▪
Keywords: Fischer–Tropsch synthesis; Co/SiO; 2; catalyst; Chelating agents; Co silicates; Catalyst preparation
Promoting effect of fluorine on titania-supported cobalt–molybdenum hydrodesulfurization catalysts by Danhong Wang; Wei Li; Minghui Zhang; Keyi Tao (pp. 105-112).
The species of a series of F–TiO2 support containing various amounts of fluorine (0–4.30wt.%) were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and pyridine-adsorbed IR. The results show that the addition of fluorine has a large effect on titania support and two kinds of fluorides are found to be formed in titania support after titania support is treated by NH4F. The state of the fluoride depends on the fluorine content. With lower fluorine content (≤0.94wt.%) only one kind of fluoride is formed. Further increase in the fluorine content (≥2.07wt.%) results in the formation of two kinds of fluorides. ESR analysis confirmed the formation of Ti3+ species after fluorine-modification, which actually exists as Ti4+ species containing an oxygen vacancy with an electron trapped in. Co–Mo catalysts supported on fluorine-modified titania presented higher HDS activities than Co–Mo catalyst supported on untreated titania. The hydrodesulfurization mechanism on sulfided fluorine-promoted cobalt–molybdenum/titania catalysts was discussed in this report.Two kinds of fluorides are found to be formed in titania support after titania support is treated by NH4F. ESR analysis confirmed the formation of Ti3+ species after fluorine-modification, which actually exists as Ti4+ species containing an oxygen vacancy with an electron trapped in. Co–Mo catalysts supported on fluorine-modified titania presented higher HDS activities than Co–Mo catalyst supported on untreated titania. ▪
Keywords: Fluorine-modification; Titania support; Ti; 3+; Hydrodesulfurization
Preparation of Amberlyst-coated pervaporation membranes and their application in the esterification of acetic acid and butanol by Thijs A. Peters; Nieck E. Benes; Jos T.F. Keurentjes (pp. 113-119).
Catalytic Amberlyst 15 layers have been deposited on composite ceramic/poly(vinyl)alcohol membranes by the dip-coat technique using Aculyn® as a rheology modifier. Tuning of the catalytic layer thickness is possible by varying the number of dip-coat steps. The obtained “dried-mud like� Amberlyst 15 layers are stable during pervaporation and reaction experiments. The catalytic activity of the Amberlyst-coated pervaporation membrane equals the activity of the unsupported catalyst. In the pervaporation-assisted esterification reaction between acetic acid and 1-butanol the catalytic membrane is able to couple catalytic activity and water removal. Due to the high activity of the Amberlyst catalyst the conversion of the esterification reaction is limited by the removal rate of water through the membrane. This is in contrast to zeolite-coated pervaporation membranes, for which the conversion of the esterification reaction between acetic acid and 1-butanol is limited by the catalytic activity.In the manuscript we describe the preparation of composite catalytic membranes by deposition of catalytic Amberlyst 15 layers on top of ceramic supported PVA membranes via the dip-coating technique. We show that this approach allows independent optimisation of both the catalytic and separation functions of the membranes, facilitating efficient integration of reaction and separation. ▪
Keywords: Catalytic membrane; Pervaporation; Esterification; Amberlyst 15; Structured catalyst
Effect of Fe and Ce on Al-pillared bentonite and their performance in catalytic oxidation reactions by J.G. Carriazo; M.A. Centeno; J.A. Odriozola; S. Moreno; R. Molina (pp. 120-128).
A Colombian bentonite was modified by intercalation with polyhydroxocationic solutions of Al3+ containing Fe3+ and Ce3+. Addition of these solutions led to the formation of pillared clays with important catalytic properties in three environmental impact reactions: phenol oxidation in diluted aqueous medium, oxidation of CO and 2-propanol oxidation in gas phase. The catalytic tests revealed the activity of the introduced iron species and the promoter effect of the cerium on the catalytic activity of these species. X-ray diffraction and the transmission electron microscopy results indicated, respectively, the formation of oxide nanoparticles inside and outside of the interlayer spaces of the clay mineral structure. Mössbauer spectroscopy analysis revealed the presence of iron oxides with oxidation state +3 and hematite structure on the solids.A bentonite modified with solutions of Al3+ containing Fe3+ and Ce3+ was obtained with important catalytic properties in three environmental impact reactions. XRD and TEM results indicated the formation of oxide nanoparticles inside and outside of the interlayer spaces of the clay. Mössbauer spectroscopy revealed the presence of iron oxides with oxidation state +3 and hematite structure on the solids. ▪
Keywords: Pillared clay; CWPO reaction; CO oxidation; VOCs oxidation; Environmental catalysis
A comparative study on physicochemical properties and photocatalytic behavior of macroporous TiO2-P25 composite films and macroporous TiO2 films coated on stainless steel substrate by Yongjun Chen; Dionysios D. Dionysiou (pp. 129-137).
A macroporous TiO2-P25 (Degussa) composite film (PPMSGF-PEG) with enhanced photocatalytic activity and excellent adhesion on the stainless steel substrate can be synthesized by optimizing calcination temperature. The PPMSGF-PEG film (500°C) exhibits unique structural properties including high amount of crystalline materials, enhanced BET surface area and pore volume, bimodal pore size distribution, and good structural integrity (without crack formation on its macroporous TiO2 matrix). ▪Two types of photocatalytic films, macroporous TiO2-P25 (Degussa) composite films (PPMSGF-PEG) and macroporous TiO2 films (TiO2-PEG), have been synthesized by a P25-PEG modified sol–gel method and a PEG modified sol–gel method, respectively. The physicochemical properties, including thermal behavior, surface morphology, crystallinity, crystal size, specific surface area (BET), pore volume and adhesion on the stainless steel substrate, of the two types of films were investigated by TGA, SEM, XRD, Raman spectroscopy, HRTEM, N2 adsorption and the tape test. The photocatalytic activities of the films were compared using 4-chlorobenzoic acid (4-CBA) as a model organic contaminant in water. It was found that adding 10g/L P25 in the sol can improve not only the amount of crystalline material immobilized on the support, but also the BET surface area and pore volume of the films calcined at temperatures between 500 and 600°C. N2 adsorption results suggested that the enhanced BET surface area and pore volume were due to the formation of large pores induced by the presence of P25 powders, which could help retain a relatively high pore volume during calcination at higher temperatures. The results on photocatalytic degradation of 4-CBA showed that the increase in photocatalytic activity caused by P25 powders reached maximum for PPMSGF-PEG calcined at 500°C, compared with that of TiO2-PEG film. The tape test showed that adding 10g/L P25 in the sol did not affect the critical calcination temperature (i.e., 500°C) at or above which excellent adhesion between the films and the stainless steel substrate can be maintained. This study proves that optimizing calcination temperature is still an important strategy for the preparation of macroporous TiO2-P25 composite films with enhanced photocatalytic activity and excellent adhesion on the stainless steel substrate.
Keywords: Macroporous; TiO; 2; TiO; 2; -P25; Composite; Films; Photocatalytic; Photocatalysis