DOCSLIB.ORG

Ii ION-PAIR BEHAVIOR BETWEEN POLYOXOMETALATES ANION

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Ii ION-PAIR BEHAVIOR BETWEEN POLYOXOMETALATES ANION ION-PAIR BEHAVIOR BETWEEN POLYOXOMETALATES ANION AND ALKALI METAL CATION A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirement for the Degree Master of Science Songtao Ye May 2018 ii ION-PAIR BEHAVIOR BETWEEN POLYOXOMETALATES ANION AND ALKALI METAL CATION Songtao Ye Thesis Approved Accepted: ______________________________ ____________________________ Advisor Dean of the College Dr. Tianbo Liu Dr. Eric Amis ______________________________ ____________________________ Committee Member Dean of the Graduate School Dr. Toshikazu Miyoshi Dr. Chand Midha ______________________________ ____________________________ Department Chair Date Dr. Colleen Pugh iii ABSTRACT Ion-pair behavior describes the partial association of oppositely charged ions in electrolyte solutions. Previous study mainly focused on the ion-pair behavior between simple ions, such as ion pairing in NaCl solution as well as ion-pair interactions in supramolecular complexes and biological associations. However, very few attentions have been placed on the solution system with particle sizes in between. Recently, a group of well-defined, huge anionic cluster named polyoxometalates (POMs) have been synthesized and well characterized. The size of POMs is around nanometer scale, which is exactly between simple ions and large colloids. The solution behavior for POMs is much different form simple electrolyte solutions or large colloids. As a result, it is interesting to study the ion-pair behavior for POMs in solution. Herein, ion-pairs between Lacunary Keggin type POMs and alkali metal cations are investigated. The result showed that ion-pairs are formed between alkali cations and the “pocket” area on the surface of Lacunary Keggin type POMs – K7PW11O39. Electrostatic interaction and the entropy gain during the solvation shell lost were considered major driving forces during the ion-pair formation. Smaller alkali cations (e.g., Li+ and Na+) tended to form contact ion- pair (CIP) which result in an elevated enthalpy change measured by Isothermal Titration Calorimetry (ITC). Larger alkali cations (e.g., Rb+ and Cs+) favored a loose type of ion-pair – solvent separated ion-pair (2SIP) and solvent shared ion-pair (SIP). Size exclusion between the “pocket” area on K7PW11O39 POM surface and alkali cation also played a significant role in determining the ion-pair structure. Results were further confirmed by Nuclear Magnetic Resonance Spectroscopy (NMR). iv ACKNOWLEDGEMENT First, I would like to express my gratitude to my advisor Prof. Tianbo Liu for his patient guidance and strong support for my study at the University of Akron. He brought me this area and offered me great opportunities to study the complex solution behavior. Meanwhile, I also want to thank my committee member Dr. Toshikazu Miyoshi for his advice to my research and constructive feedback to my dissertation. Besides, I would like to appreciate Jiancheng Luo, a senior PhD student in our group. He is so generous to share precious experience and useful methods with me. This dissertation would never be finished without his help. And I also want to all the group members for their assistance during my research. Finally, I would like to extend my appreciation to my family and my friends, especially my parents. I appreciate all your support from both mentally and physically. v TABLE OF CONTENTS LIST OF TABLES .......................................................................................................... vi LIST OF FIGURES ....................................................................................................... vii CHAPTER ...................................................................................................................... 1 I. INTRODUCTION AND BACKGROUND ................................................................. 1 1.1 Introduction of ion-pair behavior ..................................................................... 1 1.2 Experimental methods for studying ion-pair .................................................... 5 1.3 Solution behaviors of macroions ...................................................................... 7 1.4 Study motivation ............................................................................................. 11 II. EXPERIMENT.......................................................................................................... 12 2.1 Sample preparation .............................................................................................. 12 2.1.1 Synthesis of Na3[PW12O40] ·13H2O .......................................................... 12 2.1.2 Synthesis of K7[PW11O39] ·13H2O ............................................................... 12 2.2 Isothermal Titration Calorimetry (ITC) ............................................................... 13 2.3 Nuclear Magnetic Resonance Spectroscopy ........................................................ 15 III. RESULT AND DISCUSSION ................................................................................ 16 vi 3.1 Ion-pair formation monitored by Isothermal titration calorimetry (ITC) ............ 16 3.2 Ion-pair formation monitored by Nuclear Magnetic Resonance Spectroscopy (NMR) ........................................................................................................................... 22 IV. CONCLUSION........................................................................................................ 24 REFERENCE ................................................................................................................. 25 vii LIST OF TABLES Table Page 1. Types of POMs which can form Blackberry in aqueous solution.1 (Reprinted from ref. 34, copyright ACS Publication.) ........................................................................... 8 2. Radius of bare alkali cations and alkali cations in water ............................................. 18 viii LIST OF FIGURES Figure 1 The Eigen–Tamm scheme for stepwise formation from free solvated cations Xx+ and solvated anions Yy− of 2SIP ion pairs, then SIP ion pairs, and finally CIP ion pairs, with elimination of solvent molecules from the solvation shells of the ions.5 (Reproduced from ref. 5, copyright IUPAC 2008) ..................... 1 Figure 2 Dielectric loss (ε") spectrum for 0.37 M NiSO4(aq) at 25 °C. (Reproduced from ref. 1, copyright ACS Publications) ............................................. 6 Figure 3 “Giant Wheel” POMs self-assemble into Blackberry like structure in aqueous solution. (Reprinted with permission from ref. 35, copyright 2003 Nature Publishing Group.) ..................................................................................................... 9 n- Figure 4 Structure of ɑ-Keggin [XM12O40] anion. Red balls represent oxygen atoms, blue balls represent M atoms and green ball represents X atom. The overall POM anion carries n negative charges. (Reprinted from ref. 39, copyright ACS Publications) ............................................................................................................ 10 n- Figure 5 Structure of ɑ-Lacunary Keggin [XM11O39] anion. One tetrahedral unit is removed from ɑ-Keggin type structure ............................................................ 10 Figure 6 Basic configuration of an isothermal titration calorimetry42 .............. 13 n- Figure 7 Structure of ɑ-Lacunary Keggin [XM11O39] anion. ........................... 15 ix 7- Figure 8 Titrating 10 mM KCl solution into 0.5 mM [PW11O39] POM solution. ................................................................................................................................. 16 7- Figure 9 Titrating 10 mM RbCl solution into 0.5 mM [PW11O39] POM solution. ................................................................................................................................. 17 7- Figure 10 Titrating 10 mM RbCl solution into 0.5 mM [PW11O39] POM solution. ................................................................................................................................. 17 x 7- Figure 11 Titrating 10 mM LiCl solution into 0.5 mM [PW11O39] POM solution. ................................................................................................................................. 19 7- Figure 12 Titrating 10 mM NaCl solution into 0.5 mM [PW11O39] POM solution. ................................................................................................................................. 20 Figure 13 Contribution form enthalpy and entropy to the Gibbs free energy during ion- pair formation. ...................................................................................... 21 Figure 14 NMR spectrum for titrating Li+ into K7[PW11O39] POM solution. 22 + Figure 15 NMR spectrum for titrating K into K7[PW11O39] POM solution ...... 23 xi CHAPTER I INTRODUCTION AND BACKGROUND 1.1 Introduction of ion-pair behavior Ion-pair behavior describes the partial association of oppositely charged ions in 2 electrolyte solutions to form distinct chemical species called ion-pairs. Typically, an ion pair can be classified as 3 types, a double solvent-separated ion pair (2SIP), if the primary solvation shells of the both ions remain intact, a solvent-shared ion pair (SIP), if both ions share one solvent layer, or a contact ion pair, which two ions contact directly with each other.3 The development in understanding the relationships between the 4-5 various types of ion pairs was based on ultrasonic absorption data
Load more

Recommended publications
  • The Chemistry of the Carbon-In--Pulp Process
    THE CHEMISTRY OF THE CARBON-IN--PULP PROCESS Michael David Adams A Thesis submitted to the Faculty of Science University of the Witwatersrand, Johannesburg in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg 1989 ABSTRACT Several conflicting theories of the adsorption of aurocyanide onto activated carbon presently exist. To resolve the mechanism, adsorption and elution of aurocyanide are examined by several techniques, including Mossoauer spectroscopy, X-ray photoelectron spectro­ scopy, X-ray diffractometry, Fourier Transform Infrared spectrophotometry, ultraviolet-visible spectrophotometry and scanning electron microscopy. The evidence gathered indicates that, under normal plant conditions, aurocyanide is extracted onto activated carbon in the form of an ion pair M n* [Au(CN) 2 3 n , and eluted by hydroxide or cyanide. The hydroxide or cyanide ions react with the carbon surface, rendering it relatively hydrophilic with a decreased affinity for neutral species. Additional adsorption mechanisms are shown to operate under other conditions of ionic strength, pH, and temperature. The poor agreement in the literature regarding the mechanism of adsorption of aurocyanide onto activated carbon is shown to be due to the fact that different mechanisms operate under different experimental conditions. The AuCN produced on the carbon surface by acid treatment is shown to react with hydroxide ion via the reduction of AuCN to metallic gold with formation of Au (CN) 2 , and the oxidation of cyanide to cyanate. Other species, such as An(CN)5 and Ag(CN)g adsorb onto activated carbon by a similar mechanism to that postulated for Au( C N ) 2 . Ion association of MAu(CN ) 2 salts in aqueous solution is demonstrated by * aans of potentiometric titration and conductivity measurements, and various associated species of KAu(CN), salts are shown to occur in organic solvents by means of infrared spectrophoteaietric and distribution measurements.
    [Show full text]
  • Conversion of Synthesis Gas to Oxygenates by Using Keggin-Type Structure Heteropoly Compound-Based Catalyst Compositions
    (19) TZZ _T (11) EP 2 627 445 B1 (12) EUROPEAN PATENT SPECIFICATION (45) Date of publication and mention (51) Int Cl.: of the grant of the patent: B01J 37/03 (2006.01) B01J 37/08 (2006.01) 07.01.2015 Bulletin 2015/02 B01J 37/02 (2006.01) B01J 27/188 (2006.01) C07C 29/158 (2006.01) C07C 29/157 (2006.01) (2006.01) (2006.01) (21) Application number: 11768222.9 C07C 29/16 C07C 31/04 C07C 31/08 (2006.01) C07C 31/10 (2006.01) (22) Date of filing: 26.09.2011 (86) International application number: PCT/US2011/053202 (87) International publication number: WO 2012/050806 (19.04.2012 Gazette 2012/16) (54) CONVERSION OF SYNTHESIS GAS TO OXYGENATES BY USING KEGGIN- TYPE STRUCTURE HETEROPOLY COMPOUND-BASED CATALYST COMPOSITIONS UMWANDLUNG VON SYNTHESEGAS IN OXYGENATE MITTELS VERWENDUNG VON KATALYSATOREN AUF DER BASIS VON HETEROPOLYVERBINDUNGEN MIT KEGGIN- STRUKTUR CONVERSION DE GAZ DE SYNTHÈSE EN OXYGÉNATS À L’AIDE DE COMPOSITIONS DE CATALYSEUR À BASE D’UN COMPOSÉ HÉTÉROPOLY À STRUCTURE DE TYPE KEGGIN (84) Designated Contracting States: • RAO, Sreenivasa AL AT BE BG CH CY CZ DE DK EE ES FI FR GB Pune 411007 (IN) GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO • BARTON, David, G. PL PT RO RS SE SI SK SM TR Midland, MI 48642 (US) (30) Priority: 11.10.2010 US 391739 P (74) Representative: Beck Greener Fulwood House (43) Date of publication of application: 12 Fulwood Place 21.08.2013 Bulletin 2013/34 London WC1V 6HR (GB) (73) Proprietor: Dow Global Technologies LLC (56) References cited: Midland, MI 48674 (US) US-A- 4 210 597 US-A- 6 127 432 US-B1- 6 278 030 (72) Inventors: • MANIKANDAN, Palanichamy Pune 411014 (IN) Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations.
    [Show full text]
  • Topic2270 Ion Association the Term ' Strong Electrolyte' Has a Long And
    Topic2270 Ion Association The term ‘ strong electrolyte’ has a long and honourable history in the development of an understanding of the properties of salt solutions. This term describes salt solutions where each ion contributes to the properties almost independently of all other ions in a given solution. The word ‘almost’ signals that the properties of a given salt solution are determined in part by charge –charge interactions between ions through the solvent separating ions in solution. Otherwise the ions can be regarded as free. Such is the case for aqueous salt solutions at ambient temperatures and pressures prepared + - + - using 1:1 salts such as Na Cl , Et4N Br … However with decrease in relative permittivity of the solvent, the properties of salt solutions indicate that not all the ions can be regarded as free; a fraction of the ions are associated. For dilute salts solutions in apolar solvents such as propanone a fraction of the salt is described as being present as ion pairs formed by association of cations and anions. With further decrease in the permittivity of the solvent higher clusters are envisaged; e.g. triple ions, quadruple ions…. Here we concentrate attention on ion pair formation building on the model proposed by N. Bjerrum [1,2]. The analysis identifies a given j ion in a salt solution as the reference ion such that at distant r from this ion the electric potential equals ψj whereby the potential energy ⋅ ⋅ ψ of ion i with charge number zi equals z i e j . The solvent is a structureless continuum and each ion is a hard non-polarisable sphere characterised by its charge, ⋅ z j e , and radius rj.
    [Show full text]
  • Ion-Association a Review' Reagents
    ANALYTICAL SCIENCES DECEMBER 1987, VOL. 3 479 Reviews Ion-Association Reagents A Review' Kyoji TBEI Faculty of Liberal Arts and Science, Okayama University of Science, Ridaicho, Okayama 700 Ion-association reagents are widely used for analytical chemistry. The ion-associable cation or anion should be univalent, bulky and charge-dispersed. The reagents are classified by their shape: plane, sphere, chain and polymer types. The ion-associable cation and anion can combine with each other to form the ion-associate in water. This phenomenon has been used for gravimetric and volumetric analyses and for extraction-spectrophoto- metry of a trace component. Several examples of specific and sensitive extraction-spectrophotometries are illustrated. The polymer type reagent can react with the counter-charged poly-electrolyte to form a precipitate quantitatively, and it can be used for colloid titration. Metachromasy phenomenon is based on the formation of the ion-associate of colored ion-associable cation or anion with counter-charged colorless ion-association reagents to show distinguished color changes. Keywords Ion-association reagents, charged quinone theory, extraction-spectrophotometry, colloid titration, metachromasy with ion-associable cations and the cationic one reacts 1 Introduction with ion-associable anions to form the respective ion- associates in an aqueous solution. When the Many kinds of organic reagents have been used for concentration of the ion-associate is relatively high in analytical chemistry. Most of the reagents are water, it is precipitated. This fact is used for chelating reagents. On the other hand, there is an ion- gravimetric or volumetric analysis. When it is diluted, association reagent which does not belong to the it is extracted into an organic solvent which is chelating reagent.
    [Show full text]
  • Equilibrium and Structure Studies of Aqueous Vanadophosphates and Molybdovanadophosphates
    Equilibrium and structure studies of aqueous vanadophosphates and molybdovanadophosphates by Anna Selling <5 °< c/> ■O • V AKADEMISK AVHANDLING som med tillstånd av rektorsämbetet vid Umeå Universitet för erhållande av filosofie doktorsexamen framlägges till offentlig granskning vid Kemiska instutitionen, Sal C, LuO, Naturvetarhuset, fredagen den 7 juni 1996, kl. 13.00. Fakultetsopponent: Dr. Atsushi Yagasaki, Kwansei Gakuin University, Japan. U m eå 1996 Title: Equilibrium and structure studies of aqueous vanadophosphates and molybdovanadophosphates. Author: Anna Selling Address: Department of Inorganic Chemistry, Umeå University, S -901 87 Umeå, Sweden. Abstract: This thesis comprises a summary and discussion of four papers, where heteropolyanions containing phosphorus as heteroatom and molybdenum and/or vanadium as addenda atoms have been studied. The ultimate goal was to study the equilibrium spéciation in the reduced molybdovanadophosphate system. The latter is a good catalyst in the selective oxidation of olefins to carbonyls. The studies were been performed in 0.6 M Na(Cl) medium at 25 °C. The main techniques employed included potentiometry, NMR- and ESR spectrometry, complemented with FTIR, X-ray diffraction and cyclic voltammetry. Experimental data were treated with the computer program LAKE, which is capable of simultaneously handling multimethod data. Before the reduced molybdovanadophosphate system could be studied, the subsystems needed to be known. Since the spéciation in most of the oxidised subsystems has been reported earlier in the same ionic medium, only the binary phosphate and the ternary vanadophosphate systems had to be studied. These are reported in this thesis. All three pXa values for the phosphate system have been determined with high precision. In the vanadophosphate system, equilibrium species with the formula [HzPVi40 42](9 z) and the trans-bicapped Keggin structure were formed.
    [Show full text]
  • Location of Protons in Anhydrous Keggin Heteropolyacids H3pmo12o40 and H3PW12O40 by 1H{31P}/31P{1H} REDOR NMR and DFT Quantum Ch
    Published on Web 06/11/2002 Location of Protons in Anhydrous Keggin Heteropolyacids 1 31 31 1 H3PMo12O40 and H3PW12O40 by H{ P}/ P{ H} REDOR NMR and DFT Quantum Chemical Calculations S. Ganapathy,†,‡ M. Fournier,§ J. F. Paul,§ L. Delevoye,⊥ M. Guelton,§ and J. P. Amoureux*,‡ Contribution from the National Chemical Laboratory, 411 008 Pune, India, LCPS, CNRS-8012, UniVersite´ de Lille1, 59655 VilleneuVe d’Ascq, France, Laboratoire de Catalyse, CNRS-8010, UniVersite´ de Lille1, 59655 VilleneuVe d’Ascq, France, and Bruker-France, 67166 Wissembourg, France Received December 21, 2001 Abstract: HeteroPolyAcids (HPA’s) are a class of solid acids that have broad applications in many fields of science and technology, including catalysis and chemical engineering. The proton locations within the thermally stable and commonly known Keggin unit, which is the primary structure building unit/block, has remained undetermined in anhydrous HPAs, despite numerous theoretical and experimental efforts. However, Rotational Echo DOuble Resonance (REDOR) NMR and Density Functional Theory (DFT) quantum chemical calculations offer a new opportunity to determine the exact locations of protons within the Keggin unit. The crucial experimental evidence is provided for the basic and very extensively studied n+ acidic form of H8-nX M12O40,X) Si, P and M ) Mo, W, belonging to the Keggin structure. While showing that the acidic protons are located in the bridging oxygen positions (RP-H ) 520 ( 20 pm) in H3PMo12O40 and in the terminal oxygen positions (RP-H ) 570 ( 20 pm) in H3PW12O40, REDOR measurements also provide for the first time the structural basis to consistently rank the acid strength for the important class of Keggin solid catalysts.
    [Show full text]
  • Electrostatic and Relativistic Contributions to Ion-Pairing in Polyoxometalate Model Systems
    “This document is the Accepted Manuscript version of a Published Work that appeared in final form in Phys. Chem. Chem. Phys. 2017, 19, 8715, copyright © The Royal Chemistry Society after peer review and technical editing by the publisher. To access the final edited and published work see DOI 10.1039/C6CP08454K. Electrostatic and relativistic contributions to ion-pairing in polyoxometalate model systems Dylan J. Sures, Stefano A. Serapian, Karoly Kozma, Pedro I. Molina, Carles Bo, and May Nyman Abstract Ion pairs and solubility related to ion-pairing in water influence many processes in nature and in synthesis including efficient drug delivery, contaminant transport in the environment, and self-assembly of materials in water. Ion pairs are difficult to observe spectroscopically because they generally do not persist unless extreme solution conditions are applied. Here we demonstrate two advanced techniques coupled with computational studies that quantify the persistence of ion-pairs in simple solutions and offer explanations for observed solubility trends. The system of study, (TMA,Cs)8[M6O19] (M=Nb,Ta), is a set of unique polyoxometalate salts whose water solubility increases with increasing ion-pairing, contrary to + 8- most ionic salts. The techniques employed to characterize Cs association with [M6O19] and related clusters in simple aqueous media are 133Cs NMR (nuclear magnetic resonance) quadrupolar relaxation rate and PDF (pair distribution function) from X-ray scattering. The NMR measurements consistently showed more extensive ion-pairing of Cs+ with the Ta-analogue than the Nb-analogue, although the electrostatics of the ions should be identical. Computational studies also ascertained more persistent Cs+- + [Ta6O19] ion pairs than Cs -[Nb6O19] ion pairs, and bond energy decomposition analyses determined relativistic effects to be the differentiating factor.
    [Show full text]
  • POM@MOF Hybrids: Synthesis and Applications
    catalysts Review POM@MOF Hybrids: Synthesis and Applications Jiamin Sun 1, Sara Abednatanzi 1 , Pascal Van Der Voort 1,* , Ying-Ya Liu 2 and Karen Leus 1 1 COMOC—Center for Ordered Materials, Organometallics and Catalysis, Department of Chemistry, Ghent University, Krijgslaan 281, Building S3, 9000 Ghent, Belgium; [email protected] (J.S.); [email protected] (S.A.); [email protected] (K.L.) 2 State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China; [email protected] * Correspondence: [email protected]; Tel.: +32-(0)9-264-44-42 Received: 4 May 2020; Accepted: 19 May 2020; Published: 21 May 2020 Abstract: The hybrid materials that are created by supporting or incorporating polyoxometalates (POMs) into/onto metal–organic frameworks (MOFs) have a unique set of properties. They combine the strong acidity, oxygen-rich surface, and redox capability of POMs, while overcoming their drawbacks, such as difficult handling, a low surface area, and a high solubility. MOFs are ideal hosts because of their high surface area, long-range ordered structure, and high tunability in terms of the pore size and channels. In some cases, MOFs add an extra dimension to the functionality of hybrids. This review summarizes the recent developments in the field of POM@MOF hybrids. The most common applied synthesis strategies are discussed, together with major applications, such as their use in catalysis (organocatalysis, electrocatalysis, and photocatalysis). The more than 100 papers on this topic have been systematically summarized in a handy table, which covers almost all of the work conducted in this field up to now.
    [Show full text]
  • Ion Association and Solvation in Dichloromethane of Tetrachloro- and Tetrabromoferrates(III) Compared with Simple Halides
    Ion Association and Solvation in Dichloromethane of Tetrachloro- and Tetrabromoferrates(III) Compared with Simple Halides S. Bait, G. du Chattel, W. de Kieviet, and A. Tieleman Department of Inorganic Chemistry Free University, De Lairessestraat 174, Amsterdam, The Netherlands Z. Naturforsch. 33b, 745-749 (1978); received April 26, 1978 Ion Association, Dichloromethane, Tetrachloroferrate(III), Tetrabromoferrate(III), Hydrogen-bridge Formation Conductivity measurements are reported in dichloromethane for tetraethylammonium and tetraphenylarsonium salts of tetrachloro- and tetrabromoferrate(III) and halide ions (chiefly chloride and bromide). Analysis of the data in terms of the recent Fuoss equation has given the ion-pair association constants. The experimental values are close to the ones calculated from the electrostatic Fuoss-Eigen equation. The solvent acts as an acceptor by way of forming hydrogen-bonds to the simple halide ions and to a much less extent to the ferrates. Solvation of chloro- and bromoferrates(III) seems to be comparable, as deduced from the association constants and NMR paramagnetic line broadening. The phenyl groups of the tetraphenylarsonium ion seem to give ^-interaction with the solvent. Introduction proved to be a very good starting point, because it has negligible donor-properties [1, 2], but is a In the study of kinetics and mechanism of co- remarkably good solvent for ion-paired complexes. ordination compounds the emphasis seems to be In addition the symmetrical nature of the anion shifting from aqueous to non-aqueous solvents. In makes it in combination with symmetrical cations this connection a (semi)quantitative knowledge of a model case for treating ion-association with cur- donor and acceptor properties [1] of the various rent conductivity theories.
    [Show full text]
  • The Effect of Cation Type and H+ on the Catalytic Activity of the Keggin Anion [Pmo12o40]3- in the Oxidative Dehydrogenation Of
    Journal of Catalysis 195, 360–375 (2000) doi:10.1006/jcat.2000.2987, available online at http://www.idealibrary.com on The Effect of Cation Type and H+ on the Catalytic Activity 3 of the Keggin Anion [PMo12O40] in the Oxidative Dehydrogenation of Isobutyraldehyde Ji Hu and Robert C. Burns1 School of Biological and Chemical Sciences, The University of Newcastle, Callaghan 2308, Australia Received March 23, 2000; revised July 4, 2000; accepted July 5, 2000 such as the oxidative dehydrogenation of isobutyric acid The oxidative dehydrogenation of isobutyraldehyde to metha- and the oxidation of methacrolein, both of which yield 3 crolein over [PMo12O40] -containing catalysts has been shown to methacrylic acid (1–5). Methacrylic acid is, in turn, reacted proceed through bulk catalysis-type II, which depends on the rates with methanol to yield methyl methacrylate, an extremely + of diffusion of the redox carriers (H and e ) into the catalyst bulk. important acrylic monomer, which is then polymerized to Variations in catalyst behaviour have been shown to change with give poly(methyl methacrylate). Heteropolyoxometalates the countercation and appear to be related to the polarizing abil- are also active acid catalysts, and processes based both on ity of the cation, which can be represented by the ionic potential their redox and acid–base properties have found commer- (charge/ionic radius). This, in turn, may indicate that the active 3 cial applications (3–5). site at the [PMo12O40] ion is close to an attendant countercation. For the alkali metal ions Li+,Na+,K+,Rb+, and Cs+ as well as the The study of heteropolyoxometalates as oxidation– (isoelectronic) ions of the series Cs+,Ba2+,La3+, and Ce4+, the stud- reduction catalysts has involved primarily Keggin-based 3 ies have shown that conversion generally decreases with increasing structures, principally [PMo12O40] , as well as substi- ionic potential, while selectivity to methacrolein is less affected by tuted species involving replacement of one or more changes in this property.
    [Show full text]
  • Electrochemical and Computational Study of Ion Association in the 3− Electroreduction of PW12O40 J
    Article Cite This: J. Phys. Chem. C XXXX, XXX, XXX-XXX pubs.acs.org/JPCC Electrochemical and Computational Study of Ion Association in the 3− Electroreduction of PW12O40 J. M. Gomez-Gil,́ † E. Laborda,† J. Gonzalez,† A. Molina,*,† and R. G. Compton‡ † Departamento de Química Física, Facultad de Química, Regional Campus of International Excellence “Campus Mare Nostrum”, Universidad de Murcia, 30100 Murcia, Spain ‡ Department of Chemistry, Physical & Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, United Kingdom *S Supporting Information ABSTRACT: Insights into ion pairing effects on the redox 3− properties of the Keggin-type polyoxotungstate PW12O40 are gained by combining electrochemical experiments and density functional theory (DFT) calculations. Such effects have been reported to affect the performance of these species as molecular electrocatalysts. Experimental square wave voltam- 3− metry (SWV) of the two-electron reduction of PW12O40 in 4− acetonitrile evidences that the reduced forms PW12O40 and 5− fi PW12O40 can be signi cantly stabilized by ion association. The strength and stoichiometry of the corresponding aggregates are estimated as a function of the nature of the cation (lithium, sodium, and tetramethylammonium) and the oxidation state of the polyoxometalate. The results obtained in combination with DFT enable us to examine the roles of the cation solvation and the charge number and distribution of the polyanions. 1. INTRODUCTION electrochemical and quantum-chemical approach. As will be discussed, the “apparent” relative stability in solution of PW3− Polyoxometalates (POMs) are anionic metal-oxide clusters that 4− 5− show particular electronic properties of great interest in a large and the reduced forms PW and PW can be elucidated from − number of areas,1 5 specifically in electrocatalysis (water voltammetric measurements in an aprotic medium (acetoni- oxidation,6,7 epoxidation of alkenes,8 bromate reduction,9 trile).
    [Show full text]
  • Ion Pair Conductivity Model and Its Application for Predicting Conductivity in Non-Polar Systems
    Ion Pair Conductivity Model and Its Application for Predicting Conductivity in Non-Polar Systems Sean Parlia Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy under the Executive Committee of the Graduate School of Arts and Sciences COLUMBIA UNIVERSITY 2020 © 2020 Sean Parlia All Rights Reserved ABSTRACT Ion-Pair Conductivity Model and Its Application for Predicting Conductivity in Non-Polar Systems By Sean Parlia While the laws of ionization and conductivity in polar systems are well understood and appreciated in the art, theories related to nonpolar systems and their conductivities remain elusive. Currently, multiple conflicting models, with limited experimental verification, exist that aim to explain and predict the mechanisms by which ionization occurs in nonpolar media. A historical overview of the field of nonpolar electrochemistry, dating back to the 1800’s, is presented herein with a focus on the work of prominent scientists such as Fuoss, Bjerrum, and Onsager, who’s pioneering discoveries serve as the scientific foundation for our understanding of ionization in nonpolar systems, from which our knowledge of ion-pairs (i.e. re-associated solvated ions which do not contribute to the overall conductivity of the system) stems. Recent work in the field of nonpolar electrochemistry has focused on ionization models such as the Disproportionation Model and the Fluctuation Model, which ignore ion-pair formation and the existence of these neutral entities altogether. While, the “Ion-Pair Conductivity Model”, the novel conductivity model introduced and explored herein, primarily focuses on the critical role these neutral entities play with regards to the electrochemistry in these systems.
    [Show full text]