Catalysis, Volume 26 by Dooley, Han, and Spivey


3657d156713a296.jpeg Author Dooley, Han, and Spivey
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Year 2014
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View Online View Online A Specialist Periodical Report Catalysis Volume 26 A Review of Recent Literature Editors James J. Spivey, Louisiana State University, USA Yi-Fan Han, East China University of Science and Technology, Shanghai, China K. M. Dooley, Louisiana State University, USA Authors Adeyiga Adeyinka, Hampton University, USA C. R. Apesteguı´a, UNL-CONICET, Santa Fe, Argentina Håkon Bergem, SINTEF, Trondheim, Norway Francesca Lønstad Bleken, University of Oslo, Norway Edd A. Blekkan, Norwegian University of Science and Technology, Trondheim, Norway Sara Boullosa-Eiras, Norwegian University of Science and Technology, Trondheim, Norway De Chen, Norwegian University of Science and Technology, Trondheim, Norway J. I. Di Cosimo, UNL-CONICET, Santa Fe, Argentina V. K. Dı´ez, UNL-CONICET, Santa Fe, Argentina Marius Westgård Erichsen, University of Oslo, Norway C. Ferretti, UNL-CONICET, Santa Fe, Argentina Enrique Garcı´a-Bordeje ´, Instituto de Carboquimica, Spain Lenka Hannevold, SINTEF, Trondheim, Norway Simon A. Kondrat, Cardiff University, UK Karl Petter Lillerud, University of Oslo, Norway Rune Lødeng, SINTEF, Trondheim, Norway Xiao-hua Lu, Nanjing University of Technology, China Zhiqiang Ma, ETH Zurich, Switzerland Unni Olsbye, University of Oslo, Norway Xi Pan, Zhejiang University of Technology, China M. F. R. Pereira, Universidade do Porto, Portugal Magnus Ro ¨ nning, Norwegian University of Science and Technology, Trondheim, Norway James J. Spivey, Louisiana State University, Baton Rouge, USA Michael Sto ¨ cker, SINTEF, Trondheim, Norway Nachal Subramanian, Georgia Institute of Technology, Atlanta, USA Stian Svelle, University of Oslo, Norway View Online Stuart H. Taylor, Cardiff University, UK Shewangizaw Teketel, University of Oslo, Norway Jeroen van Bokhoven, ETH Zurich and Paul Scherrer Institute, Switzerland Jian-guo Wang, Zhejiang University of Technology, China Gui-lin Zhuang, Zhejiang University of Technology, China View Online If you buy this title on standing order, you will be given FREE access to the chapters online. Please contact [email protected] with proof of purchase to arrange access to be set up. Thank you ISBN: 978-1-84973-918-4 DOI: 10.1039/9781782620037 ISSN: 0140-0568 A catalogue record for this book is available from the British Library & The Royal Society of Chemistry 2014 All rights reserved Apart from any fair dealing for the purpose of research or private study for non-commercial purposes, or criticism or review, as permitted under the terms of the UK Copyright, Designs and Patents Act, 1988 and the Copyright and Related Rights Regulations 2003, this publication may not be reproduced, stored or transmitted, in any form or by any means, without the prior permission in writing of The Royal Society of Chemistry, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of the licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to The Royal Society of Chemistry at the address printed on this page. Published by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 0WF, UK Registered Charity Number 207890 For further information see our web site at www.rsc.org View Online Preface James J. Spivey,a Kerry Dooleya and Yi-fan Hanb DOI: 10.1039/9781782620037-FP007 We appreciate the efforts by the authors that bring you the current Specialist Periodical Report. These chapters are particularly relevant to the catalysis community in both and fundamental and more applied catalysis. They represent the collective work of a total of 34 researchers in 8 chapters, which are summarized as follows: Chapter 1: Basic catalysis on MgO: generation, characterization and catalytic properties of active sites One of the most studied basic catalysts is MgO and the review by J. I. Di Cosimo, V. K. Dı´ez, C. Ferretti and C. R. Apesteguı´a of INCAPE in Santa Fe, Argentina highlights recent work, especially their own, on both catalytic structure and function. In contrast to other reviews with a more solid state characterization focus, this contribution emphasizes the surface-adsorbate local interactions. A discussion of the range of sites show how they can be discriminated through use of probe molecules is followed by case studies of three characteristic reactions employing the range of sites present in different ways. There is also an extensive description of how DFT based on cluster models can be applied to the study of adsorbate-catalyst interactions in one such reaction, a transesterification. Chapter 2: Potential for metal-carbide, -nitride, and -phosphide as future hydrotreating (HT) catalysts for processing of bio-oils The next review is also from Norway, a joint effort of the Univ. of Science and Technology and Sintef. In this review, Sara Boullosa-Eiras, Rune ¨cker, Lenka Hannevold and Edd Lødeng, Håkon Bergem, Michael Sto Blekkan examine hydrotreating with metal carbides, nitrides and phosphides. While other recent reviews on such catalysts have appeared, this one is different due to its focus on bio-oil upgrading. After a brisk introduction to the various upgrading strategies, there is a detailed review of how these catalysts are properly synthesized. The carbides, phosphides and nitrides are then contrasted with the more traditional oxide-sulfide catalysts both in model compound and real bio-oil reaction studies. A wide range of noble and base transition metals are considered. Chapter 3: Novel carbon materials modified with heteroatoms as metalfree catalyst and metal catalyst support ´, Manuel Fernando R. Pereira, Magnus Here, Enrique Garcı´a-Bordeje ¨nning, De Chen (Instituto de Carboquimica (ICB-CSIC), Spain; Ro a Gordon A. and Mary Cain Dept. Chemical Engineering, Louisiana State University, Baton Rouge, LA 70803. E-mail: [email protected]; [email protected] b East China University of Science and Technology, Shanghai, China. E-mail: [email protected] Catalysis, 2014, 26, vii–ix | vii c The Royal Society of Chemistry 2014 View Online ´rio de Cata ´lise e Materiais (LCM), Laborato ´rio Associado LSRE/ Laborato ´mica, LCM, Departamento de Engenharia Quı Faculdade de Engenharia, Universidade do Porto, Portugal; Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU), Norway) review the discovery of novel carbon materials (carbon nanotubes, graphene) and the application of carbon materials as catalyst and catalyst support. The electronic conductivity, ordered structure and absence of microporosity were pointed to be favorable properties compare with disordered conventional carbon materials. They concluded that the ordered nature of these materials could be precisely functionalized with heteroatoms which have shown good perspectives as metal free catalyst. The more recent catalytic applications of heteroatom doped novel carbon materials both as catalyst and catalyst support were also reviewed. Chapter 4: Computational catalysis in nanotubes Jian-guo Wang, Xi Pan, Gui-lin Zhuang and Xiao-hua Lu (Zhejiang University of Technology, China; State Key Laboratory of MaterialsOriented Chemical Engineering, Nanjing University of Technology, Nanjing, China) review computational catalysis in nanotubes. The applications of computer simulations to the recent area of catalysis in carbon nanotubes and metal oxide nanotubes have been summarized. Specifically, this discusses both density functional theory calculations and molecular dynamics simulations. The authors point out recent research progress in nanotubes and the novel approaches to understand catalytic performance. Particular focus has also been devoted to the formation, structural, and electronic properties of metal oxide nanotubes such as TiO2, ZnO and V2O5 nanotubes. An outlook for computer simulations on catalysis in nanotubes is provided as well. Chapter 5: Catalytic conversion of syngas to i-butanol – Synthesis routes and catalyst developments: A review This contribution is a joint work by Louisiana State University (Nachal Subramanian and James Spivey) and Hampton University (Adeyiga Adeyinka), surveying the possibilities for syngas and related conversions to isobutanol. After a short discussion of the rationale for isobutanol as a fuel additive or alternative fuel, the review proceeds through the various proposed processes, including (1) hydroformylation, (2) direct synthesis from syngas, (3) lower alcohol condensations, and (4) lower alcohol homologations with syngas. For (2) and (3), there are more extensive discussions of both the reaction studies and catalysts employed, while for (4) the agreement between thermodynamic modeling and the limited experimental studies is explored. Chapter 6: Shape selectivity in zeolite catalysis. The Methanol to Hydrocarbons (MTH) reaction The breadth of catalytic research in fuels production is highlighted this review from the Univ. of Oslo, Shewangizaw Teketel, Marius Erichsen, Francesca Bleken, Stian Svelle, Karl Lillerud and Unni Olsbye. They summarize modern work in methanol to hydrocarbons, a process first viii | Catalysis, 2014, 26, vii–ix View Online studied intensively by Mobil in the ‘70s and ‘80s for gasoline production, but now added catalytic reactions to produce other various olefins. Their review takes a fresh look at the wider range of possible zeolite and SAPO catalysts, the roles of topology and zeolite chemistry in shape selectivity, the greater understanding of mechanism now possible based on several isotopic reaction studies, and the role of theoretical studies in deepening this understanding. Chapter 7: Catalyst preparation using supercritical fluid precipitation Simon A. Kondrat and Stuart H. Taylor (Cardiff Catalysis Institute, School of Chemistry, Cardiff University, UK) consider the use of supercritical fluids for the preparation of heterogeneous catalysts, which may offer number of potential advantages. In this chapter the properties of supercritical fluids in the context of catalyst preparation were discussed, and a number of techniques appropriate for the preparation of materials were described in detail. Those techniques are based around precipitation and include supercritical anti-solvent and rapid expansion techniques, and the use of supercritical fluids as solvents and reactants. Examples of the various techniques were given for catalyst preparation and where possible the advantages of using supercritical preparation have been reviewed in the context of catalyst structure and performance. Chapter 8: Thermal conversion of biomass–pyrolysis and hydrotreating Zhiqiang Ma and Jeroen van Bokhoven (Institute for Chemical and Bioengineering, ETH Zurich, Switzerland; Laboratory for Catalysis and Sustainable Chemistry, Paul Scherrer Institute, Switzerland) reviewed the conversion of lignocellulosic biomass into renewable fuels and chemicals by thermal processes, especially pyrolysis. They point out biomassderivative products might serve as feedstock for chemicals and fuels and contribute to a sustainable society. They present progress in producing products by selective pyrolysis, primarily bio-oil. However, bio-oils are often limited in practice by oxygen content, multi-functional types of compounds, and refractory reactivity, all of which it difficult to develop a practical catalytic process. Hydrotreating is considered as a promising route to improve the quality of bio-oil, and this technology has rapidly progressed in the last several years. In this work, state-of-the-art production of bio-oil, with particular focus on hydrotreating, analyzing recent developments and future directions. We appreciate the Royal Society of Chemistry for publication of this volume, particularly Alice Toby-Brant and Merlin Fox, as well as Sarah Salter and Sylvia Pegg in Production. Of course, suggestions and comments are welcome. Catalysis, 2014, 26, vii–ix | ix View Online CONTENTS Cover Image provided courtesy of computational science company Accelrys (www.accelrys.com). An electron density isosurface mapped with the electrostatic potential for an organometallic molecule. This shows the charge distribution across the surface of the molecule with the red area showing the positive charge associated with the central metal atom. Research carried out using Accelrys Materials Studioss. Preface vii James J. Spivey, Kerry Dooley and Yi-fan Han Basic catalysis on MgO: generation, characterization and catalytic properties of active sites J. I. Di Cosimo, V. K. Dı´ez, C. Ferretti and C. R. Apesteguı´a 1 Introduction 2 Experimental 3 Results and discussion 4 Conclusions Acknowledgments References Potential for metal-carbide, -nitride, and -phosphide as future hydrotreating (HT) catalysts for processing of bio-oils Sara Boullosa-Eiras, Rune Lødeng, Håkon Bergem, Michael Sto¨cker, Lenka Hannevold and Edd A. Blekkan 1 Introduction 2 On the nature of metal carbides, nitrides and phosphide materials 3 Catalytic hydrodeoxygation (HDO) applied to Bio-oil (BO) 4 Conclusions Abbreviations and symbols Acknowledgements References 1 1 3 5 25 26 26 29 29 32 42 61 63 63 63 Catalysis, 2014, 26, xi–xiii | xi c The Royal Society of Chemistry 2014 View Online Novel carbon materials modified with heteroatoms as metal-free catalyst and metal catalyst support Enrique Garcı´a-Bordeje´, Manuel Fernando R. Pereira, ¨nning and De Chen Magnus Ro 1 Introduction 2 Heteroatom-modified carbon materials as metal free catalyst 3 Heteroatom-modified carbon materials as catalyst support Conclusions Acknowledgements References 101 102 102 Computational catalysis in nanotubes 109 Jian-guo Wang, Xi Pan, Gui-lin Zhuang and Xiao-hua Lu 1 Introduction 2 Carbon nanotubes 3 TiO2 nanotubes 4 ZnO nanotubes 5 V2O5 nanotubes 6 Conclusions Acknowledgments References 109 110 125 142 149 155 156 156 Catalytic conversion of syngas to i-butanol – Synthesis routes and catalyst developments: A review Nachal Subramanian, Adeyiga Adeyinka and James J. Spivey 1 Rationale for the study 2 Isobutanol 3 Synthesis of isobutanol 4 Scope for further work in this area References Shape selectivity in zeolite catalysis. The Methanol to Hydrocarbons (MTH) reaction Shewangizaw Teketel, Marius Westgård Erichsen, Francesca Lønstad Bleken, Stian Svelle, Karl Petter Lillerud and Unni Olsbye 1 Zeolites 2 The Methanol to Hydrocarbons (MTH) reaction 3 Shape selectivity in the MTH reaction 4 Summary and outlook References xii | Catalysis, 2014, 26, xi–xiii 72 72 73 95 161 161 163 164 174 174 179 179 188 202 211 212 View Online Catalyst preparation using supercritical fluid precipitation Simon A. Kondrat and Stuart H. Taylor 1 Introduction 2 Background into supercritical fluids 3 Supercritical fluid methods for materials preparation 4 Preparation of catalysts using supercritical fluids 5 Conclusion References 218 Thermal conversion of biomass–pyrolysis and hydrotreating 249 Zhiqiang Ma and Jeroen van Bokhoven 1 Introduction 2 General issues and challenges 3 Biomass resources, structure, and its conversion to bio-oil 4 Bio-oil upgrading with hydrotreating catalysts 5 Choice of carrier material 6 Conclusions References 249 250 251 257 266 268 269 218 219 222 227 244 245 Catalysis, 2014, 26, xi–xiii | xiii View Online Basic catalysis on MgO: generation, characterization and catalytic properties of active sites J. I. Di Cosimo,* V. K. Dı´ez, C. Ferretti and C. R. Apesteguı´a* DOI: 10.1039/9781782620037-00001 The generation, characterization and catalytic properties of MgO active sites were studied. MgO samples stabilized at different temperatures were used to control the distribution of surface base sites; specifically, MgO was calcined at 673 K, 773 K and 873 K (samples MgO-673, MgO-773 and MgO-873). The nature, density and strength of MgO base sites were characterized by temperature-programmed desorption of CO2 and infrared spectroscopy after CO2 adsorption at 298 K and sequential evacuation at increasing temperatures. MgO samples contained surface sites of strong (low coordination O2 anions), medium (oxygen in Mg2þ-O2 pairs) and weak (OH groups) basicity. The density of strong basic sites was predominant on MgO-673. The increase of the calcination temperature drastically decreased the density of strong base sites and to a lesser extent that of weak OH groups, while slightly increased that of medium-strength base sites. The catalytic properties of MgO samples were proved for the aldol condensation of citral with acetone to yield pseudoionone, the hydrogen transfer reaction of mesityl oxide with 2-propanol to obtain the unsaturated alcohol 4-methyl-3-penten-2ol, and the synthesis of monoglycerides via the transesterification of methyl oleate with glycerol. The effect of calcination temperature on the MgO catalytic properties depended on the basicity requirements for the rate-limiting step of the base-catalyzed reaction. The activity for both the aldol condensation of citral with acetone and the glycerolysis of methyl oleate diminished with the MgO calcination temperature because these reactions were essentially promoted on strongly basic O2 sites. In contrast, the synthesis of 4-methyl-3-penten-2ol by the hydrogen transfer reduction of mesityl oxide with 2-propanol increased with calcination temperature because the reaction intermediate was formed on medium-strength Mg2þ-O2 pair basic sites. Additional information on the role played by the MgO active sites on the kinetics of base-catalyzed reactions was obtained by performing molecular modeling studies on our MgO catalysts using Density Functional Theory (DFT) for the glycerolysis of methyl oleate, an unsaturated fatty acid methyl ester (FAME). The molecular modeling of glycerol and FAME adsorptions was carried out using terrace, edge and corner sites for representing the MgO (100) surface. In agreement with catalytic results, calculations predicted that dissociative chemisorption of glycerol with O–H bond breaking occurs only on strong base sites (edge sites) whereas nondissociative adsorption takes place on medium-strength base sites such as those of terrace sites. Results also indicated that glycerol was more strongly adsorbed than FAME. The glycerol/FAME reaction would proceed then through a mechanism in which the most relevant adsorption step is that of glycerol. 1 Introduction Alkaline earth metal oxides catalyze a variety of organic reactions requiring the cleavage of a C–H bond step and the formation of carbanion intermediates. In particular, pure and alkali-promoted MgO has Catalysis Science and Engineering Research Group (GICIC), INCAPE, UNL-CONICET. Santiago del Estero 2654. (3000) Santa Fe, Argentina. E-mail: [email protected]; [email protected] Catalysis, 2014, 26, 1–28 | 1 The Royal Society of Chemistry 2014 View Online been shown to promote Cannizzaro and Tischenko reactions [1, 2], Michael, Wittig and Knoevenagel condensations [3, 4], transesterification reactions [5–8], double-bond isomerizations [9], self- and crosscondensation reactions [10–13], Henry reaction [14], alcohol coupling [15–17], and H2 transfer reactions [18]. However, the MgO basicity needed for efficiently promoting these reactions depend on the rate-limiting step requirements. MgO can be synthesized in a variety of presentation formats, including nanosheets [19], nanowires [20] and nanoparticles [21], but its catalytic properties depend greatly on the preparation method. Nevertheless, most of reports on the preparation of magnesia deal with the effect of the synthesis method and conditions on the MgO structural and physical properties [22–24]. Very few papers have attempted to tailor the distribution, density, and strength of surface base sites of MgO upon synthesis in order to design the catalyst surface to reaction requirements [25–27]. More insight on the relationship between the synthesis procedure with the generation and control of MgO surface base sites is then required to improve the efficient use of this oxide in catalysis applications. Detailed characterization of MgO base sites is crucial to establish correlations between the surface basic properties and the catalyst activity and selectivity for a given reaction. The most common methods for characterization of solid basicity are thermal programmed desorption (TPD) and infrared spectroscopy (IR) of preadsorbed probe molecules, and the use of test reactions. TPD studies provide information on the density and strength of base sites while additional insight on the base site nature is often obtained by IR characterization. Carbon dioxide has been largely employed as a probe molecule for evaluating the solid basicity by TPD and IR techniques [28–31] although other acid molecules such as acetic acid have been also used [32]. On the other hand, the test reactions most frequently used for characterizing the catalyst acid-base properties are the decomposition of alcohols, in particular 2-propanol [33–35], 2-butanol [36, 37] and 2-methyl-3-butyn-2-ol [38–40]. In the case of 2-propanol, it is generally accepted that 2-propanol dehydration to propylene occurs on solid acids containing Brønsted acid sites via an E1 mechanism while on amphoteric oxides with acid-base pair sites propylene is obtained through a concerted E2 mechanism [41]. On strong basic catalysts, 2-propanol is dehydrogenated to acetone via an E1cB anionic mechanism [42]. Thus, the catalyst acid-base properties may be related to the propylene/acetone selectivity ratio. In contrast, test reactions have been used only in few cases for characterizing base site strength distributions on solid bases. For example, in a previous work [43], we proposed that on alkali-modified MgO catalysts 2-propanol decomposition to acetone and propylene takes place via an E1cB mechanism in two parallel pathways sharing a common 2-propoxy intermediate; in this mechanism, the intermediate-strength base sites promote acetone formation, whereas high-strength base sites selectively yield propylene. Nevertheless, several studies have shown that the use of test reactions is not sensitive enough to establish a basicity scale of the catalysts [44]. 2 | Catalysis, 2014, 26, 1–28 View Online Theoretical calculations of surface sites have been performed for exploration of MgO catalysis. In general, Density Functional Theory (DFT) calculations have shown to be a powerful tool to characterize the thermal stability of hydrated oxide surfaces [45]. Regarding MgO catalysts, DFT studies on the structure of MgO surface defects have been carried out to establish the stability of surface OH groups for water and methanol adsorptions [46, 47]. Recently, combined IR and DFT studies have been performed in an attempt to specify the actual structure of the CO2 species adsorbed on magnesium oxide surface [48]. Unfortunately, theoretical calculations to predict the relationship between the basic site nature and strength and the reaction mechanism have been done only for limited cases. In this work we study the generation, characterization and catalytic properties of active sites on MgO catalysts. The base properties of MgO samples obtained from Mg(OH)2 decomposition were tuned by modifying the solid calcination temperature. The density and strength of MgO surface base sites were determined by TPD and IR spectroscopy of CO2 adsorbed at 298 K. The activity and selectivity of MgO samples were probed for the liquid-phase cross-aldol condensation of citral with acetone to obtain pseudoionones, the liquid-phase transesterification of methyl oleate with glycerol to yield monoglycerides, and the gas-phase hydrogen transfer reduction of mesityl oxide with 2-propanol toward 4-methyl-3penten-2ol. Besides, we performed DFT calculations to obtain additional information on the role played by the MgO active sites on the kinetics of base-catalyzed reactions. Specifically, we present molecular modeling studies on our MgO catalysts for the glycerolysis of methyl oleate. 2 Experimental 2.1 Catalyst preparation Magnesium oxide samples were prepared by hydration with distilled water of low-surface area commercial MgO (Carlo Erba, 99%, 27 m2/g). 250 ml of distilled water were slowly added to 25 g of commercial MgO and stirred at room temperature. The temperature was then raised to 353 K and stirring was maintained for 4 h. Excess of water was removed by drying the sample in an oven at 358 K overnight. The resulting Mg(OH)2 was decomposed in N2 (30 ml/min STP) to obtain high-surface area MgO which was then treated for 18 h in N2 either at 673, 773 or 873 K to give samples MgO-673, MgO-773 and MgO-873, respectively. 2.2 Catalyst characterization The decomposition of Mg(OH)2 was investigated by differential thermal analysis (DTA) using a Shimadzu DT30 analyzer, by temperature programmed decomposition (TPDe) using a flame ionization detector with a methanation catalyst (Ni/Kieselghur) operating at 673 K and by X-ray diffraction (XRD) in a Shimadzu XD-D1 diffractometer equipped with Cu-Ka radiation source (l = 0.1542 nm) and a high temperature chamber. Samples characterized by X-ray diffraction were heated at 5 K/min until 773 K, taking diffractograms at 298, 373, 573, 673 and 773 K. Catalysis, 2014, 26, 1–28 | 3 View Online Surface areas and pore volumes were measured by N2 physisorption at its boiling point using the BET method and Barret-Joyner-Halender (BJH) calculations, respectively, in an Autosorb Quantochrome 1-C sorptometer. The crystalline structure properties of MgO-x samples were determined by X-ray diffraction (XRD) using the instrument described above. Analysis was carried out using a continuous scan mode at 21/min over a 2y range of 201–801. Scherrer equation was used to calculate the mean crystallite size of the samples. CO2 adsorption site densities and binding energies were determined from temperature-programmed desorption (TPD) of CO2 preadsorbed at room temperature. MgO-x samples were pretreated in situ in a N2 flow at its corresponding stabilization temperature (673, 773 or 873 K), cooled to room temperature, and then exposed to a mixture of 3% CO2/N2 until surface saturation was achieved (10 min). Weakly adsorbed CO2 was removed by flushing in N2 during 1 h. Finally, the temperature was increased to 773 K at 10 K/min. The desorbed CO2 was converted to methane by means of a methanation catalyst (Ni/Kieselghur) operating at 673 K and monitored using a flame ionization detector. The chemical nature of adsorbed surface CO2 species was determined by infrared (IR) spectroscopy after CO2 adsorption at 298 K and sequential evacuation at increasing temperatures. Experiments were carried out using an inverted T-shaped cell containing the sample pellet and fitted with CaF2 windows. Data were collected in a Shimadzu FTIR Prestige-21 spectrometer. The absorbance scales were normalized to 20-mg pellets. Each sample was pretreated in vacuum at its corresponding stabilization temperature and cooled to room temperature, after which the spectrum of the pretreated catalyst was obtained. After admission of 5 kPa of CO2 to the cell at room temperature, the samples were evacuated at increased temperatures, and the resulting spectrum was recorded at room temperature. Spectra of the adsorbed species were obtained by subtracting the catalyst spectrum. 2.3 Catalytic testing 2.3.1 Cross-aldol condensation of citral with acetone. The cross-aldol condensation of citral (Millennium Chemicals, 95% geranial þ neral) with acetone (Merck, p.a.) was carried out at 353 K under autogenous pressure (E250 kPa) in a batch Parr reactor, using acetone/citral = 49 (molar ratio) and catalyst/(citral þ acetone) = 1 wt% ratio. The reactor was assumed to be perfectly mixed and interparticle and intraparticle diffusional limitations were verified to be negligible. Reaction products were analyzed by gas chromatography in a Varian Star 3400 CX chromatograph equipped with a FID and a Carbowax Amine 30 M capillary column. Samples of the reaction mixture were extracted every 30 min and analyzed during the 6-h reaction. The main product of the citral/acetone reaction was pseudoionone, PS (cis- and trans-isomers). Moreover, diacetone alcohol and mesityl oxide were simultaneously produced from self-condensation of acetone. Selectivities (Sj, mol of product j/mol of citral reacted) were calculated as Sj (%) = Cj  100/SCj, where Cj is the 4 | Catalysis, 2014, 26, 1–28 View Online concentration of product j. Yields (Zj, mol of product j/mol of citral fed) were calculated as Zj = SjXCit, where XCit is the citral conversion. 2.3.2 Glycerolysis of methyl oleate. The transesterification of methyl oleate, FAME, (Fluka, W60.0%, with 86% total C18 þ C16 esters as determined by gas chromatography) with glycerol (Aldrich, 99.0%,) was carried out at 493 K in a seven-necked cylindrical glass reactor that allows: separate loading of the two reactants and the catalyst, stirrer, thermocouple, in-out of inert gas to eliminate methanol of the gas phase, and periodical product sampling. Glycerol/FAME molar ratio of 4.5 and a catalyst/FAME ratio (Wcat/n0FAME) of 30 g/mol were used. The reactor was operated in a semibatch regime at atmospheric pressure under N2 (35 cm3/min). Liquid reactants were introduced into the reactor and flushed with nitrogen; then the reactor was heated to reaction temperature under stirring (700 rpm). Reaction products were a- and b-glyceryl monooleates (MG), 1,2- and 1,3-glyceryl dioleates (diglycerides) and glyceryl trioleate (triglyceride). Reactant and products were analyzed by gas chromatography in a SRI 8610C gas chromatograph equipped with a flame ionization detector, on-column injector port and a HP-1 Agilent Technologies 15 meter  0.32 mm  0.1 mm capillary column after silylation to improve compound detectability, as detailed elsewhere [49]. Twelve samples of the reaction mixture were extracted and analyzed during the 8-h catalytic run. 2.3.3 Hydrogen transfer reduction of mesityl oxide with 2-propanol. The gas-phase mesityl oxide/2-propanol reaction was conducted at 573 K and atmospheric pressure in a fixed bed reactor. MgO-x samples sieved at 0.35–0.42 mm were pretreated in N2 at the corresponding calcination temperatures for 1 h before reaction in order to remove adsorbed H2O and CO2. The reactants, mesityl oxide (Acros 99%, isomer mixture of mesityl oxide/isomesityl oxide = 91/9) and 2-propanol (Merck, ACS, 99.5%), were introduced together with the proper molar composition via a syringe pump and vaporized into flowing N2 to give a N2/IPA/MO = 93.4/ 6.6/1.3, kPa ratio. Reaction products were analyzed by on-line gas chromatography in a Varian Star 3400 CX chromatograph equipped with a flame ionization detector and a 0.2% Carbowax 1500/80–100 Carbopack C column. Main reaction products from mesityl oxide conversion were identified as the two unsaturated alcohol isomers (UOL, 4-methyl-3-penten-2ol and 4-methyl-4-penten-2ol), isomesityl oxide, methyl isobutyl ketone, and methyl isobutyl carbinol. 3 Results and discussion 3.1 Generation and characterization of active sites in MgO 3.1.1 Generation of active sites. The base site properties of MgO depend on the preparation method. Usually, MgO is obtained by decomposition of Mg(OH)2 that in turn is produced by different methods such as chemical vapor deposition (CVD), sol-gel, precipitation, and MgO hydration. It has been reported [50] that after Mg(OH)2 decomposition at Catalysis, 2014, 26, 1–28 | 5 View Online high temperature (1023 K), the relative distribution of surface lowcoordination O2 anions is shifted toward the less coordinated ions along the series MgO-CVDoMgO-hydrationEMgO-precipitationoMgOsol-gel. The same order was observed for MgO activity to convert 2-methylbut-3-yn-2-ol into acetone and acetylene, a base-catalyzed reaction [50]. The density and strength of base sites on MgO may also be regulated by controlling both the Mg(OH)2 decomposition and MgO activation conditions. For example, Vidruk et al. [51] reported that densification of Mg(OH)2 before its dehydration to obtain MgO generates a significant increase of surface basicity. We have recently investigated [52] the effect of calcination temperature of MgO obtained by Mg(OH)2 decomposition on its base and catalytic properties. 3.1.1.1 Thermal decomposition of Mg(OH)2. The thermal decomposition of Mg(OH)2 precursor was studied by XRD. The diffractograms in Fig. 1 showed that the Mg(OH)2 brucite structure was stable up to about 573 K, but then, between 573 and 673 K, decomposed to MgO. Figure 1 also shows that the MgO stabilized at 773 K during 18 h is more crystalline than that obtained by dynamic heating up to the same temperature. Consistently, characterization by DTA technique showed that the Mg(OH)2 heating exhibits an endothermic peak between 573 and 673 K arising from the solid decomposition [52]. On the other hand, TPDe experiments revealed the presence of evolved CO2 in the 573–673 K Mg(OH)2 MgO stabilized at 773 K for 18 h Intensity 773 K 673 K 573 K 298 K 30 35 40 2θ (°) 45 50 Fig. 1 XRD diffraction patterns of Mg(OH)2 decomposition. 6 | Catalysis, 2014, 26, 1–28

Author Dooley, Han, and Spivey Isbn 9781849739184 File size 9 Mb Year 2014 Pages 558 Language English File format PDF Category Chemistry Book Description: FacebookTwitterGoogle+TumblrDiggMySpaceShare Over 7000 papers are published in the field of catalysis each year. While the majority appear within a handful publications, keeping up with the literature can be difficult. Now in its 26th volume, the Specialist Periodical Report on Catalysis presents critical and comprehensive reviews of the hottest literature published over the last twelve months.   Industrial and academic scientists face increasing challenges to find cost-effective and environmentally sound methods for converting natural resources into fuels, chemicals and energy. This series is edited by two leading researchers in the field and provides a balanced and in-depth review of the modern approaches to these challenges, covering major areas of heterogeneous and homogenous catalysis, as well as specific applications of catalysis, such as NOx control, kinetics and experimental techniques, such as microcalorimetry.   With chapters detailing specific areas within the field, this series is a comprehensive reference for anyone working in Catalysis and an essential resource for any Library.     Download (9 Mb) Catalysis: Volume 27 Chemical Biology of Glycoproteins Chemical Modelling: Applications and Theory, Volume 10 Petroleum Radiation Processing Carbohydrate Chemistry, Volume 40 Load more posts

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