Applied Catalysis A, General (v.254, #2)
SPECIAL ISSUE CONTENTS PAGE (iv-v).
Preface by Francesco Di Renzo; François Fajula (171).
Selective synthesis of fatty monoglycerides by using functionalised mesoporous catalysts by Joaquı́n Pérez-Pariente; Isabel Dı́az; Federico Mohino; Enrique Sastre (173-188).
This work describes the performance of “functionalised ordered mesoporous materials” in the esterification of glycerol with fatty acids, such as lauric and oleic acids. The influence of several properties of the catalysts on their activity and monoglyceride selectivity is discussed. For the MCM-41 structure synthesised by the co-condensation method, the influence of the gel composition, hydrophobicity, nature of the functional group and pore size is presented. The catalytic behaviour of structures like SBA-15, SBA-12 and SBA-2 functionalised with mercaptopropyl groups is also discussed.
Keywords: Mesoporous materials; Esterification; Glycerol; Fatty acids; MCM-41; SBA-15; SBA-2; SBA-12; Functionalisation;
Mesoporous Zr and Hf catalysts for chemoselective MPV reductions of unsaturated ketones by Mario De bruyn; Maya Limbourg; Joeri Denayer; Gino V. Baron; Vasile Parvulescu; Piet J. Grobet; Dirk E. De Vos; Pierre A. Jacobs (189-201).
Zr and Hf catalysts were immobilized in mesoporous materials such as MCM-41 or MCM-48; in comparison with the homogeneous catalysts, the resulting materials display strongly increased activity in the Meerwein–Ponndorf–Verley (MPV) reduction of ketones with alcohols as reductants. In the reduction of unsaturated ketones, a very high selectivity for the allylic alcohol is obtained. For efficient reduction, an excess of the reducing alcohol with respect to the enone is required. For the model reduction of benzalacetone with cyclopentanol, the adsorption of reagents and products on the catalytic material is studied. Even complex substrates such as prostaglandin enone precursors can be reduced; in certain cases a substantial diastereomeric excess is observed.
Keywords: Unsaturated ketones; Allylic alcohol; Zr; Hf; Mesoporous materials; MCM-41; MCM-48; Adsorption;
Hydroxylation of 1-naphthol by hydrogen peroxide over UL-TS-1 and TS-1 coated MCF by A Ungureanu; D Trong On; E Dumitriu; S Kaliaguine (203-223).
Two different kinds of titano-silicate zeolite/mesoporous molecular sieves (MMS) materials have been produced following techniques proposed recently in our laboratory. The composite materials designated as UL-TS-1 are obtained by solid phase templated crystallization of a thick walled titanosilicate mesoporous molecular sieves yielding TS-1 nanoparticles in the MMS pore walls. The TS-1 coated mesoporous cellular foams (MCF) are obtained by contacting a clear gel containing protozeolite units of TS-1 with a large pore Ti-MCF. After complete characterization of their textural and surface chemical properties, these solids were used as catalysts in the oxidation of a bulky molecule 1-naphthol by aqueous hydrogen peroxide. Their activities are compared to those of TS-1 and Ti-MMSs as reference materials. UL-TS-1 showed a high specific activity due to their high nanoparticle external surface area whereas successive coatings induced specific activity enhancement of the TS-1 coated Ti-MCF. In both cases, additional activity enhancement was induced by trimethylsilylation of residual OH’s by hexamethyldisilazane (HMDS).
Keywords: TS-1; UL-TS-1; Ti-MCF; TS-1 coated Ti-MCF; Trimethylsilylation; 1-Naphthol oxidation; Hydrogen peroxide;
Catalytic applications of MCM-41 with different pore sizes in selected liquid phase reactions by J.S Choi; D.J Kim; S.H Chang; W.S Ahn (225-237).
A series of MCM-41 with pore diameters in 20–90 Å range was prepared and the effects of pore size on liquid phase reactions of epoxidation, etherification, and esterification were investigated after Ti-grafting, immobilization of Mn–salen complex, and monolayer adsorption of SO3H were performed on the host materials, respectively. Amount of functionalized species increased with the pore diameters of MCM-41, but it leveled off after a thresh hold pore size is attained. MCM-41 with pore diameter of ca. 56 Å was recommended to obtain high concentration of grafted species with good catalytic performances. In cyclohexene epoxidation, conversion showed linear relationship with Ti-contents of the catalyst, which proved to be a primary factor governing the reaction rather than diffusion effect. For MCM-41 immobilized with Mn–salen complexes, active site isolation in high surface coverage was required for good catalytic performances. MCM-41 with enlarged pores was again better for larger amount of thiol group to be attached to the mesopore surfaces, but uniform surface property/shape seems also required to promote the formation of a monolayer-type coated material. Esterification of 1-propanol with hexanoic acid was best catalyzed by the acidity of the sulfone-functionalized MCM-41 materials synthesized after 12 h oxidation treatment of the thiol-grafted MCM-41.
Keywords: MCM-41; Pore-size effect; Ti-grafting; Mn–salen complex; Sulfonic acid immobilization;
Mesoporous H-AlMCM-48: highly efficient solid acid catalyst by S.E. Dapurkar; P. Selvam (239-249).
Mesoporous cubic Na-AlMCM-48 molecular sieve catalyst with a Si/Al (molar) ratio of 60 was synthesized hydrothermally and characterized by various analytical and spectroscopic techniques. 27 Al MAS-NMR results indicate that the presence of aluminum in tetrahedral framework (Brönsted acid site) in both as-synthesized and calcined samples. However, in the case of the latter, a small amount of aluminum was found to be in octahedral coordination. This observation is well supported by NH3-TPD studies over protonated catalyst (H-AlMCM-48), where desorption profile at higher temperature shows features characteristic of Lewis acid sites. Further, these studies also indicate that the presence of high concentration of moderate-to-strong Brönsted acid sites at lower temperature, which are more suitable for the para-selective tertiary-butylation reaction of phenol. Hence, in the present investigation, the reaction was carried out H-AlMCM-48, which however showed much higher activity as compared to the hexagonal H-AlMCM-41. In addition, it was also found that the former does not get deactivated owing to three-dimensional pore system while the latter is susceptible to deactivation on account of one-dimensional pore system.
Keywords: Mesoporous; AlMCM-48; AlMCM-41; Solid acid catalyst; tert-Butyl phenol;
Synthesis of transparent Ti-containing mesoporous silica thin film materials and their unique photocatalytic activity for the reduction of CO2 with H2O by Yasushi Shioya; Keita Ikeue; Makoto Ogawa; Masakazu Anpo (251-259).
The transparent Ti-containing mesoporous silica thin film materials having two different types of hexagonal and cubic pore structures with a thickness of about 50 μm and a lateral size of a few centimeters were successfully synthesized by the solvent evaporation method from tetramethoxysilane (TMOS), vinyltrimethoxysilane (VTMOS), titanium tetra(iso-propoxide) (TIP), and octadecyltrimethylammonium chloride (C18TAC). The films were converted to Ti-containing nanoporous silica thin films by subsequent calcinations in air at 823 K, while the highly ordered mesostructures and macroscopic morphology were retained after the surfactant removal by calcination. The films with hexagonal and cubic symmetry were obtained by changing the composition of the starting mixtures. Various spectroscopic measurements of these films clearly showed that Ti ions are present in the silica networks as a tetrahedrally coordinated Ti-oxide species with a high dispersion state. Thus, developed transparent Ti-containing thin films were used as photocatalysts for the reduction of CO2 with H2O to evaluate their unique and high photocatalytic activity. UV irradiation of these films in the presence of CO2 and H2O led to the formation of CH4 and CH3OH as well as CO and O2 as minor products, their yields increasing linearly against irradiation time, indicating that these films operate as efficient photocatalysts to proceed such a difficult reaction catalytically at 323 K. Furthermore, the films having hexagonal pore structure exhibited higher photocatalytic activity than the Ti-MCM-41 powdered catalyst even with the same pore structure.
Keywords: Ti-containing thin films; Transparent mesoporous thin films; Photocatalysis; Ti-oxide species; Reduction of CO2 with H2O; Mesoporous molecular sieves; XAFS measurements;
Dehydrogenation of ethylbenzene and isobutane over Ga- and Fe-containing mesoporous silicas by N.S Nesterenko; O.A Ponomoreva; V.V Yuschenko; I.I Ivanova; F Testa; F Di Renzo; F Fajula (261-272).
Incorporation of gallium and iron into MCM-41-type silicas leads to creation of active and selective catalysts for the dehydrogenation of hydrocarbons. This catalysts demonstrate remarkable stability with time on stream and do not suffer from repeated reaction–reoxidation cycles. Ga-MCM-41 is particularly efficient for the dehydrogenation of light alkanes. At 550 °C isobutane is converted into a mixture of C2C4 olefins containing 52% of isobutene, which corresponds to 32% of the equilibrium conversion into isobutene at this temperature. Fe-MCM-41 shows the best performance for ethylbenzene dehydrogenation into styrene, in particular, at 600 °C, the yield over this catalyst is 38% per pass and selectivity is 82%, which corresponds to 64% of the equilibrium value. The catalysts have been characterised by XRD, volumetry, infrared spectroscopy, ammonia temperature-programmed desorption (TPD) and temperature-programmed reduction (TPR). Catalytic activity is associated with the presence of nanoparticles of oxides, entrapped in the pores or embedded in the silica network, which generate reducible species able to split CH bonds and allow fast recombinative desorption of hydrogen and olefins.
Keywords: Mesoporous silicas; Ga-MCM-41; Fe-MCM-41; Dehydrogenation; Isobutane; Ethylbenzene;
Fischer–Tropsch synthesis over silica supported cobalt catalysts: mesoporous structure versus cobalt surface density by Andrei Y Khodakov; Rafeh Bechara; Anne Griboval-Constant (273-288).
The effect of support mesoporous structure and cobalt content on cobalt dispersion and reducibility was studied using two series of Fischer–Tropsch (FT) silica supported cobalt catalysts. The first series of the catalysts was supported by an SBA-15 periodic mesoporous silica with narrow pore size distribution, the second series was supported by a commercial mesoporous silica with broader pore size distribution. It was shown that in a wide range of cobalt surface densities (0–50 Co/nm2), cobalt dispersion in silica supported catalysts was largely influenced by support texture. Cobalt dispersion was higher in Co catalysts supported by the SBA-15 silica with a pore diameter of 9.1 nm than in the commercial mesoporous silica with an average pore diameter of 33 nm. A more than 10-fold increase in cobalt surface density did not result in any noticeable sintering of Co3O4 particles in SBA-15 periodic mesoporous silicas; the cobalt dispersion seems to be maintained by catalyst mesoporous structure. The effect of support pore diameter on cobalt dispersion was less significant for the catalysts supported by commercial silicas with broader pore size distribution.At the range of cobalt surface densities from 5 to 15 Co/nm2, higher Fischer–Tropsch reaction rates were observed over cobalt catalysts supported by the SBA-15 periodic mesoporous silica. This effect was attributed to higher cobalt dispersion in these catalysts. An increase in cobalt surface densities did lead to any significant changes in hydrocarbon selectivities and in chain growth probabilities for both series of supported catalysts.
Keywords: Fischer–Tropsch synthesis; Mesoporous materials; Supported catalysts; Mesopores; Texture; Cobalt catalyst; Nanoparticles;
Gold nanoparticles in SBA-15 showing catalytic activity in CO oxidation by Chia-min Yang; Martin Kalwei; Ferdi Schüth; Kuei-jung Chao (289-296).
The preparation of an active gold catalyst for CO oxidation, supported on silica, made by a novel solution technique is reported. The surface of SBA-15 was functionalized with positively charged groups, and [AuCl4]−-species were subsequently incorporated into the channel system via ion exchange. Upon reduction with NaBH4, highly dispersed nanoparticles of gold were formed in the channels of the mesoporous host. A reaction rate of 2.7×10−4 mmol g cat −1 s −1 in CO oxidation was found for this composite material. Compared with a previously reported material obtained by a chemical vapor deposition (CVD) method, this reaction rate is still lower by about one order of magnitude. However, the straightforward preparation method reported here still yields more active catalysts than any other Au/SiO2 system made by a solution technique, which show almost no activity at room temperature. Since the gold particles are essentially isolated from the support by the organic coating of the channels, a support–metal interaction is highly improbable as the source of the catalytic activity of the gold. TEM images of Au/SBA-15 reveal that gold particles start sintering at temperatures higher than 100 °C. Due to this effect, a significant drop in catalytic activity is observed.
Keywords: Gold catalysts; CO oxidation; Mesoporous silica; Functionalization;
Transition metal oxide-doped mesostructured silica films by N Huesing; B Launay; G Kickelbick; S Gross; L Armelao; G Bottaro; M.P Feth; H Bertagnolli; G Kothleitner (297-310).
Mixed metal oxide-doped mesostructured silica films have been prepared by a combination of a ligand-assisted templating (LAT) and solvent evaporation-induced self-assembly (EISA) approach using metal alkoxides as precursors. To overcome the problem of the different hydrolysis and condensation rates of the various alkoxide precursors (silicon alkoxides and transition metal alkoxides), the hydrophilic head group of oligo(ethylene oxide) containing surfactants was coordinated to the M(OR) x groups resulting in metal-containing surfactants. These novel surfactants serve different functions in the EISA process: first, they moderate the hydrolysis and condensation rate of the transition metal alkoxide; second, they allow for a positioning of the transition metal alkoxide within the silica matrix; and third, they act as structure-directing agents. The obtained films are characterized by a high loading of the transition metal oxide species within the silica matrix and a homogeneous distribution throughout the whole film as shown by X-ray photoelectron (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Several transition metal oxides have been incorporated into the silica matrix such as titania, zirconia and tantalum oxide.
Keywords: Sol–gel; Mixed metal oxides; Mesostructured films; Ligand-assisted templating; Evaporation-induced self-assembly;
Lathlike mesostructured γ-alumina as a hydrodesulfurization catalyst support by Randall W. Hicks; Norma B. Castagnola; Zhaorong Zhang; Thomas J. Pinnavaia; Christopher L. Marshall (311-317).
A mesostructured γ-alumina with a lathlike framework morphology, denoted MSU-γ, has been prepared according to previously described methods through the reassembly and crystallization of a mesostructured alumina precursor with initially amorphous framework walls and used as a support for the catalytic hydrodesulfurization (HDS) of dibenzothiophene (DBT). The alumina support was loaded with molybdenum and cobalt ions via incipient wetness impregnation methods and then converted to the active sulfide form by reaction with H2S. HDS reactions of DBT were carried out at 400 °C and 400 psi to achieve a DBT conversion of 69–77% and a biphenyl (BP) product selectivity of 60–64% after a reaction time of 3 h, indicating that most of the DBT could undergo desulfurization while limiting excessive hydrogen consumption through aromatic hydrogenation. Although the dispersion of the active Mo/Co sulfide phase supported on lathlike MSU-γ alumina remained very high after several hours on stream, the conversions most likely were limited by a loss of surface area and porosity under HDS conditions.
Keywords: γ-Alumina; Mesostructured; Hydrodesulfurization; Catalyst support;
Effect of surface proton exchange on hydrodesulfurization performance of MCM-41-supported catalysts by Xiang Li; Anjie Wang; Zhongchao Sun; Chu Li; Jing Ren; Bei Zhao; Yao Wang; Yongying Chen; Yongkang Hu (319-326).
Ni-Mo, Co-Mo, Ni-W and Pt were supported over siliceous MCM-41 (Si-MCM-41) or the proton-exchanged Si-MCM-41 (H+-MCM-41) in order to investigate the effect of support surface modification on the performance of the catalysts. The prepared catalysts were evaluated by the hydrodesulfurization (HDS) of dibenzothiophene (DBT). It is indicated that the supported Ni-Mo sulfides exhibited the highest HDS activity regardless of the support, and that Ni-W sulfides showed the highest hydrogenation activity. The H+-MCM-41-supported Ni-Mo, Ni-W or Pt catalyst performed much better in HDS of DBT than the Si-MCM-41-supported counterpart. From the relative selectivity of cyclohexylbenzene (CHB) to biphenyl (BP) (S CHB/S BP), it could be concluded that the higher HDS performance of H+-MCM-41-supported catalysts may be attributed to the enhanced hydrogenation activity. Nevertheless, a little difference in HDS activity was observed for Co-Mo sulfides supported on Si-MCM-41 or H+-MCM-41. Since the cleavage of sulfur atoms mainly takes the route of hydrogenolysis in HDS of DBT catalyzed by Co-Mo sulfides, the improvement in hydrogenation activity was not significant for Co-Mo sulfides when Si-MCM-41 was ion-exchanged with HNO3. TPR study showed that the profiles of Ni-Mo/Si-MCM-41 and Ni-W/Si-MCM-41 changed markedly after the proton exchange of Si-MCM-41 while the profile of Co-Mo/Si-MCM-41 changed a little. It may be concluded that the removal of sulfur from DBT and hydrogenation take place on separate active sites, and that the spillover of the dissociated hydrogen species over the surface is essential to the hydrogenation pathway. Hydroxyl groups on H+-MCM-41 favors the spillover of the hydrogen species, enhancing the hydrogenation activity of its supported catalysts. On the other hand, Na+ cations on Si-MCM-41 may “trap” the spillover hydrogen species, lowering the hydrogenation activity of its supported catalysts.
Keywords: MCM-41; Ni-Mo; Co-Mo; Ni-W; Pt; Proton exchange; Hydrodesulfurization; Dibenzothiophene;
Organized mesoporous alumina: synthesis, structure and potential in catalysis by Jiři Čejka (327-338).
Organized mesoporous alumina represents a very interesting molecular sieve exhibiting a narrow pore size distribution with higher surface areas compared to conventional aluminas, used as a support for catalytically active species in numerous large-scale industrial processes. This review encompasses various synthesis approaches to organized mesoporous aluminas, description of their structures and properties, and characterization by various experimental techniques. The potential of the mesoporous alumina with respect to use in catalysis is also outlined. Surface areas up to 800 m2/g and pore sizes ranging from 2.0 to more than 10 nm are characteristic for organized mesoporous aluminas prepared by neutral, anionic and cationic synthesis routes. Although utilization of mesoporous aluminas as a support in catalysis has not been reported frequently, they have a certain potential in hydrodesulfurization and metathesis reactions.
Keywords: Organized mesoporous alumina; Mesoporous molecular sieves; Synthesis; Characterization; Catalytic applications;
Al-TUD-1, stable mesoporous aluminas with high surface areas by Z. Shan; J.C. Jansen; W. Zhou; Th. Maschmeyer (339-343).
Very stable, amorphous mesoporous aluminas of the TUD-1 structure type with high surface areas (∼530 m2/g) can be synthesised in a controlled manner using non-surfactant organic molecules. Their porosity as well as pore size can be adjusted either by heating a dried gel in an autoclave or by changing gel ageing procedures. High surface areas can be reached by controlling two important parameters: the water to aluminium ratio in the initial synthesis mixture, and the drying and heating process in the autoclave.
Keywords: Mesoporous; Alumina; Catalyst support; Materials synthesis; Surface area; Stability;
Mesoporous carbon nanotubes for use as support in catalysis and as nanosized reactors for one-dimensional inorganic material synthesis by Jean-Mario Nhut; Laurie Pesant; Jean-Philippe Tessonnier; Gauthier Winé; Jean Guille; Cuong Pham-Huu; Marc-Jacques Ledoux (345-363).
Mesoporous multi-walled carbon nanotubes (MWNTs) with an average inner diameter of about 50 nm were successfully used as a one-dimensional catalyst support either in gas-phase, i.e. selective oxidation of H2S into elemental sulfur in a thrickle-bed configuration, or in liquid-phase reactions, i.e. selective hydrogenation of nitrobenzene into aniline or Friedel-Crafts benzoylation reactions. On one hand, the combination of the small size, i.e. high external surface area, and of the tube structure, i.e. confinement effect, allowed a significant improvement of the catalytic performance when compared to that obtained on traditional grain shaped catalysts as observed in the selective oxidation of H2S and the selective hydrogenation of nitrobenzene reactions. On the other hand, the confinement effect induced by the high aspect ratio of the tubes could, in addition, be effectively used for the synthesis of one-dimensional nanowire zeolitic materials under non-hydrothermal macroscopic conditions. Carbon nanotubes template were removed by combustion leaving behind zeolite nanowires which were made up of zeolite particles of about 10–20 nm. The zeolitic catalysts exhibit a high benzoylation activity compared to that of the commercial one due to its high external surface area.
Keywords: Carbon nanotubes; Zeolite nanowire synthesis; Confinement effect; H2S oxidation; Friedel-Crafts reaction;
AUTHOR INDEX (367-369).
SUBJECT INDEX (371-376).