DOCSLIB.ORG

Oxidation of Sulfur Dioxide Over Supported Vanadia Catalysts: Molecular Structure ± Reactivity Relationships and Reaction Kinetics

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Oxidation of Sulfur Dioxide Over Supported Vanadia Catalysts: Molecular Structure ± Reactivity Relationships and Reaction Kinetics Catalysis Today 51 (1999) 301±318 Oxidation of sulfur dioxide over supported vanadia catalysts: molecular structure ± reactivity relationships and reaction kinetics Joseph P. Dunna, Harvey G. Stenger Jr.b, Israel E. Wachs*,b aBOC Gases Technology, 100 Mountain Avenue, Murray Hill, NJ 07974, USA bZettlemoyer Center for Surface Studies, Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015, USA Abstract The oxidation of sulfur dioxide to sulfur trioxide over supported vanadium oxide catalysts occurs as both a primary and secondary reaction in many industrial processes, e.g., the manufacture of sulfuric acid, the selective catalytic reduction of NOx with ammonia and the regeneration of petroleum re®nery cracking catalysts. This paper discusses the fundamental information currently available concerning the molecular structure and sulfur dioxide oxidation reactivity of surface vanadia species on oxide supports. Comparison of the molecular structure and reactivity information provides new fundamental insights on the following topics related to the catalytic properties of surface vanadia species during the sulfur dioxide oxidation reaction: 1. role of terminal V=O, bridging V±O±V and bridging V±O-support bonds, 2. number of surface vanadia sites required to perform SO2 oxidation, 3. influence of metal oxide additives, 4. generation and influence of the surface sulfate overlayer, 5. effect of surface acidity on the reaction turnover frequency, 6. competitive adsorption between SO2 and SO3 and 7. reaction kinetics. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Oxidation; Sulfur dioxide; Vanadia catalyst; Sulfur trioxide 1. Introduction ciated sulfur oxide, SOx, emissions. Approximately two-thirds of the 50 billion pounds of sulfur oxides Sulfur dioxide, SO2, is formed from both the oxida- released annually in the United States are emitted from tion of sulfur contained in fossil fuels and industrial coal ®red power plants [1]. Industrial fuel combustion processes that treat and produce sulfur-containing and industrial processes (primarily sulfuric acid man- compounds. The catalytic oxidation of sulfur dioxide ufacture, petroleum re®ning and smelting of non- appears in numerous industrial processes and has a ferrous metals) account for the remainder of the signi®cant environmental impact because of the asso- emissions. Sulfuric acid is the largest volume chemical cur- *Corresponding author. Tel.: +1-610-758-4274; fax: +1-610- rently produced in the world, approximately 95 billion 758-6555; e-mail: [email protected] pounds per year [2], and is manufactured by the 0920-5861/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0920-5861(99)00052-8 302 J.P. Dunn et al. / Catalysis Today 51 (1999) 301±318 contact process, which involves the high temperature 2. savings in operating costs generated by lowering catalytic oxidation of sulfur dioxide to sulfur trioxide SCR temperatures, without the worry of ammo- over a unique supported liquid phase catalyst (silica nium sulfate production and deposition. supported vanadium pyrosulfate with alkali promo- Two new NO /SO removal techniques, SNO (Hal- ters). Under reaction conditions, 450±6108C, the x x x dor Topsoe) and DeSONO (Degussa), combine SCR active vanadia component of the catalyst exists as a x technology with sulfuric acid production [12,13]. Flue molten salt forming a very thin liquid layer on the gas is heated to 3808C and nitrogen oxides are surface of the silica support (only 100±1000 AÊ thick). removed via conventional SCR technology. The pro- Sulfur dioxide oxidation to sulfur trioxide proceeds on ducts are further heated to 4208C and the SO is both the active sites located in the interior of the liquid 2 oxidized to SO over a sulfuric acid contact catalyst. ®lm and on the boundary between the ®lm and the 3 The sulfur trioxide is then contacted with water pro- surface of the silica support [3±5]. Thermodynami- ducing concentrated sulfuric acid. Any unreacted cally controlled equilibrium limitations exist at the ammonia from the SCR reactor is oxidized to NO temperatures necessary for the catalyst to activate, x over the second catalyst bed, consequently, avoiding T>4208C, and the conversion of the sulfur dioxide feed the formation of ammonium sulfates. is incomplete with the very small unreacted portion Sulfur oxide emissions from ¯uid catalytic cracking typically being directly emitted into the environment. (FCC) units account for a sizable fraction of annual In contrast to the sulfuric acid contact process, the SO emissions and are increasingly being targeted by oxidation of SO to SO is undesirable during the x 2 3 the Environmental Protection Agency (EPA). The selective catalytic reduction (SCR) of nitrogen oxides amount of SO emitted from a FCC unit regenerator (NO ) found in the ¯ue gas of power plants. SCR x x is a function of the quantity of sulfur in the feed, coke removes NO in the ¯ue gas by reacting the nitrogen x yield and conversion [14]. Typically, 45±55% of feed oxides with ammonia and oxygen to form nitrogen and sulfur is converted to hydrogen sul®de in the FCC water at approximately 3708C over titania supported reactor, 35±45% remains in the liquid products, and vanadia catalysts (e.g., V O /WO ±MoO /TiO ). 2 5 3 3 2 about 5±10% is deposited on the catalyst in the coke Under typical SCR design and operating conditions, [14,15]. The sulfur in the coke is oxidized to SO NO reduction ef®ciency is directly proportional to the 2 x (90%) and SO (10%) in the FCC regenerator. Tradi- NH :NO ratio up to NO reduction levels of about 3 3 x x tional techniques of SO control such as ¯ue gas 80%. Operating with too high of a NH :NO ratio can x 3 x scrubbing and feedstock hydrodesulfurization are lead to unreacted ammonia bypassing the reactor, effective, but are labor and cost intensive. The least ammonia slip, where it readily combines with SO 3 costly alternative is the use of a SO -reduction catalyst at temperatures below 2508C to form ammonium x as an additive to the FCC catalyst inventory. The sulfates, which can block the catalyst's pores and foul catalyst must be able to: downstream heat exchangers [6]. This problem is so serious that industrial speci®cations for SCR pro- 1. oxidize SO2 to SO3 in the FCC regenerator, cesses include upper limits for the outlet concentration 2. chemisorb the SO3 in the FCC regenerator, and of sulfur trioxide corresponding to approximately 1± then 2% sulfur dioxide conversion. Several studies have 3. release it as hydrogen sulfide in the reducing FCC investigated the development of catalysts capable of reactor. simultaneously suppressing the oxidation of sulfur dioxide to sulfur trioxide while ef®ciently promoting Supported vanadia catalysts, such as Amoco's DeSOx the selective catalytic reduction of nitric oxide [7±11]. catalyst (V2O5/CeO2/Mg2Al2O5), have demonstrated The advantages of such catalysts would be: high activity towards these reactions. In addition, petroleum re®ning operations such as 1. the ability to install more intrinsically active SCR FCC and hydrodesulfurization (HDS) yield hydrogen catalysts (e.g., higher vanadia loadings) without sul®de as an undesired product. The hydrogen sul®de the fear of simultaneously increasing SO3 produc- is typically concentrated and fed to a Claus plant to tion and produce elemental sulfur. However, due to equilibrium J.P. Dunn et al. / Catalysis Today 51 (1999) 301±318 303 limitations only 97% of the sulfur is recovered in the this report due to the limited information available in Claus plant and the tail gas, therefore, needs to be the literature concerning the surface arrangement of treated before being released to the atmosphere. The these catalysts. mobil oil SOx treatment (MOST) process involves combusting the Claus tailgas with air, converting all of the sulfur species to SO2 and SO3.TheSOx is 2. Synthesis of supported vanadia catalysts sorbed onto a V2O5/CeO2/Mg2Al2O5 spinel where it is later regenerated to produce concentrated H2S and Many different synthesis methods have been used in SO2, which is recycled to the Claus plant for further the preparation of supported vanadia catalysts: vapor processing [16]. phase grafting with VOCl3 [19±21], non-aqueous In spite of the industrial importance and environ- impregnation with vanadium alkoxides [22,23] and mental consequences of the above catalytic oxidation vanadium acetate [24], aqueous impregnation of vana- processes involving sulfur dioxide, few fundamental dium oxalate [25], as well as dry impregnation with studies have been performed on the kinetics and crystalline V2O5 [26±29]. However, all the catalysts mechanism of sulfur dioxide oxidation with the excep- were found to contain the same surface vanadia spe- tion of the unique sulfuric acid contact catalyst [3±5]. cies independent of the initial synthesis method after However, the studies on commercial sulfuric acid prolonged calcination [30]. The absence of a ``pre- catalysts are not applicable to the environmental paration memory effect'' is due to the high mobility of oxidation reactions over conventional solid metal V2O5 (Tamman temperature of 3708C) and the strong oxide catalysts since the contact catalyst contains driving force of the mixed oxide system to lower its the active vanadia/alkali/sulfate component as a mol- surface free energy by forming a monolayer of surface ten salt on the silica support. Current research into the vanadia species on the high surface free energy oxide oxidation of SO2 to SO3 over conventional supported support [26±29]. The formation of a monolayer is even vanadia catalysts has focused on establishing the observed during hydrocarbon oxidation reactions over fundamental kinetics and molecular structure-reactiv- physical mixtures of V2O5 and TiO2 [31]. Thus, the ity relationships of the oxidation reaction [17,18]. It is same thermodynamically stable surface metal oxide hoped that the insights generated from these studies species are formed independent of the speci®c synth- will assist in: esis method.
Load more

Recommended publications
  • SULFUR TRIOXIDE -- Chemical Fact Sheet
    OLEUM/SULFUR TRIOXIDE -- Chemical Fact Sheet 1 What is it? Oleum is a cloudy, gray, fuming, oily, corrosive liquid with a sharp, penetrating odor. When Oleum comes into contact with air following a spill, it releases Sulfur Trioxide. Sulfur Trioxide is a white gas having the appearance of fog. It also has a sharp, penetrating odor that is detectable at low concentrations. Because of the tendency to liberate Sulfur Trioxide on contact with air, Oleum is also known as “fuming Sulfuric Acid”. Where does it Oleum is made by dissolving Sulfur Trioxide into Sulfuric Acid. Sulfur come from? Trioxide is made from Sulfur Dioxide in the presence of a catalyst. What are the It is used in the oil refining process to make crude oil distillates into higher quality materials. common uses for it? Manufacture of soap Manufacture of high purity Sulfuric Acid for the electronic industry Manufacture of catalyst used in production of Sulfuric Acid. How is it Oleum is shipped by truck and pipeline. transported in CCC? How is it stored Oleum is stored in covered tanks. in CCC? Health Hazards from Exposure Exposure Route Symptoms First Aid Inhalation Irritates nose, throat and Remove to fresh air. Seek (low concentrations) lungs medical attention if Burning Sensation symptoms persist. Sneezing, coughing Inhalation Burning sensation Remove to fresh air, get (high concentrations & prolonged exposure) Coughing, gagging medical attention including Chest tightness and pain, oxygen administration. Fluid in lungs Initiate CPR if breathing has Suffocation, death stopped. Eyes Severely irritates eyes Rinse eyes with water for at Burning/discomfort least 5 minutes.
    [Show full text]
  • Sulfuric Acid from Sulfur Updates on Contact Process PEP Review 2018-12 February 2018
    ` Sulfuric Acid from Sulfur Updates on Contact Process PEP Review 2018-12 February 2018 Rajiv Narang Director Process Economics Program IHS Markit | PEP Review 2018-12 Sulfuric Acid from Sulfur/Updates on Contact Process PEP Review 2018-12 Sulfuric Acid from Sulfur/Updates on Contact Process Rajiv Narang, Director Abstract Sulfuric acid (H2SO4) is the world’s largest consumed chemical, with consumption of around 260 MMT (million metric tons) on a 100% acid basis and a growth rate of around 2%. Traditionally, consumption of this chemical is considered as a barometer of a nation’s GDP. The majority of sulfuric acid production (59%) is from burning of elemental sulfur, in a contact process. The sulfur is sourced mostly from oil and gas processing facilities, in which the sulfur is removed from various petroleum or natural gas products. IHS Markit’s Process Economics Program (PEP) last addressed this production technology in PEP Report 84A, Sulfuric Acid (June 1985), which covered the manufacture of sulfuric acid from sulfur in new versus old, retrofitted plants, as well as from metallurgical offgases. This review specifically updates the contact process for the production of sulfuric acid by burning of elemental sulfur. The review examines the developments in this production technology, including advances in catalyst, material of construction, and heat recovery. The process is simulated using Aspen Plus™ software. It focuses on technology basis, raw material and utility consumptions, equipment list, capital cost, along with capacity exponents, and production costs for a 2,000 STPD (short ton per day) of (100% basis) sulfuric acid product. This review provides insight into sulfuric acid plant process economics, and can be used as a tool for cost estimation for different plant capacities.
    [Show full text]
  • Source Test Method ST-20 SULFUR DIOXIDE, SULFUR TRIOXIDE
    Source Test Method ST-20 SULFUR DIOXIDE, SULFUR TRIOXIDE, SULFURIC ACID MIST (Adopted January 20, 1982) REF: Regulations 6-320, 6-330, 9-1-302, 9-1-304 thru 310, 10-1-301, 12-6-301 1. APPLICABILITY 1.1 This method is used to quantify emissions of s ulfur dioxide, sulfur trioxide and sulfuric acid mist. It determines compliance with Regulations 6-320 and 6-330 for SULFUR TRIOXIDE and SULFURIC ACID MIST, and 9-1-302, 9- 1-304 thru 310 and 10-1-301 and 12-6-301 for SULFUR DIOXIDE. 1.2 This method, modified with a glass fiber disc filter as the back-up SO 3 filter, has been given alternate status by the EPA to EPA Method 8. It may be used to determine compliance with oxides of sulfur regulations under Regulation 9. 2. PRINCIPLE 2.1 Sulfuric acid mist, sulfur trioxide and sulfur dioxide are collected in a single extractive sampling train. Acid mist is trapped in a quartz wool plug in the sample probe and is subsequently analyzed with an acid-base titration. Sulfur trioxide is absorbed in an 80% isopropyl alcohol (IPA)/water solution with a quartz wool back-up filter and is analyzed using analytical procedure Lab-12. Sulfur dioxide is absorbed in an aqueous hydrogen peroxide solution and is analyzed using analytical procedure Lab-12. 3. RANGE 3.1 The minimum measurable concentration using this method listed below are: 3 3.1.1 Acid mist - 0.0002 gr/ft as H2SO4 3.1.2 Sulfur trioxide - 7 ppm 3.1.3 Sulfur dioxide - 7 ppm 3.2 The maximum measurable concentrations using this method listed below are: 3.2.1 Acid mist - undetermined 3.2.2 Sulfur trioxide - 350 ppm 3.2.3 Sulfur dioxide - 2.5 % 4.
    [Show full text]
  • Catalyst Precursors for Hydrodesulfurization Synthesized in Supercritical Fluids Manuel Théodet
    New generation of ”bulk” catalyst precursors for hydrodesulfurization synthesized in supercritical fluids Manuel Théodet To cite this version: Manuel Théodet. New generation of ”bulk” catalyst precursors for hydrodesulfurization synthesized in supercritical fluids. Material chemistry. Université Sciences et Technologies - Bordeaux I,2010. English. NNT : 2010BOR14092. tel-00559113 HAL Id: tel-00559113 https://tel.archives-ouvertes.fr/tel-00559113 Submitted on 24 Jan 2011 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution - NonCommercial - NoDerivatives| 4.0 International License N° d’ordre : 4092 THÈSE présentée à L’UNIVERSITÉ BORDEAUX I ÉCOLE DOCTORALE DES SCIENCES CHIMIQUES Par Manuel THEODET Ingénieur ENSCPB POUR OBTENIR LE GRADE DE DOCTEUR SPÉCIALITÉ : Physico-Chimie de la Matière Condensée ___________________ NOUVELLE GENERATION DE PRECURSEURS « BULK » DE CATALYSEUR D’HYDRODESULFURATION SYNTHETISES EN MILIEU FLUIDE SUPERCRITIQUE ___________________ NEW GENERATION OF « BULK » CATALYST PRECURSORS FOR HYDRODESULFURIZATION SYNTHESIZED IN SUPERCRITICAL FLUIDS ___________________ Co-superviseurs de recherche : Cristina Martínez & Cyril Aymonier Soutenue le 03 Novembre 2010 Après avis favorable de : M. E. PALOMARES, Professor, UPV, Valencia, Spain Rapporteurs M. M. TÜRK, Professor, KIT, Karlsruhe, Germany Devant la commission d’examen formée de : M.
    [Show full text]
  • PROCESS MODELING and ANALYSIS of CO2 PURIFICATION for OXY-COAL COMBUSTION MASSACHUSETTS INS E by of TECHNOLOGY
    PROCESS MODELING AND ANALYSIS OF CO2 PURIFICATION FOR OXY-COAL COMBUSTION MASSACHUSETTS INS E By OF TECHNOLOGY Chukwunwike Ogbonnia Iloeje MAY 18 2011 B.Eng. Mechanical Engineering LIBRRIES University of Nigeria, Nsukka, 2004 SUBMITTED TO THE DEPARTMENT OF MECHANICAL ENGINEERING IN AR(MES PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN MECHANICAL ENGINEERING AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY JANUARY 2011 0 2011 Massachusetts Institute of Technology. All rights reserved. The author hereby grants to MIT permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part in any medium now known or hereafter created. Signature of Author........... ............................... Department of Mechanical Engineering January 14, 2011 Certified by.............. Ahmed F. Ghoniem Ronald C. Crane Professor Thacic Cunanwicnr Accepted by.................................. .... ................. Dave E.Hardt Chairman, Department Committee on Graduate Students *r PROCESS MODELING AND ANALYSIS OF CO2 PURIFICATION FOR OXY-COAL COMBUSTION By Chukwunwike Ogbonnia Iloeje Submitted to the Department of Mechanical Engineering on January 14, 2011 in Partial Fulfillment of the Requirements for the degree of Master of Science in Mechanical Engineering ABSTRACT Oxy-coal combustion technology has great potential as one of the major CO2 capture technologies for power generation from coal. The distinguishing feature of oxy-coal combustion is that the oxygen source is a high concentration oxygen stream and the product flue gas consists primarily of CO2 and H20 with contaminants like NOx, SOx, and non-condensable gases like argon, oxygen and nitrogen. For carbon sequestration and Enhanced Oil Recovery (EOR) applications, pipeline transport standards as well as storage specifications impose concentration limits on these contaminants.
    [Show full text]
  • (VI) and Chromium (V) Oxide Fluorides
    Portland State University PDXScholar Dissertations and Theses Dissertations and Theses 1976 The chemistry of chromium (VI) and chromium (V) oxide fluorides Patrick Jay Green Portland State University Follow this and additional works at: https://pdxscholar.library.pdx.edu/open_access_etds Part of the Chemistry Commons Let us know how access to this document benefits ou.y Recommended Citation Green, Patrick Jay, "The chemistry of chromium (VI) and chromium (V) oxide fluorides" (1976). Dissertations and Theses. Paper 4039. https://doi.org/10.15760/etd.5923 This Thesis is brought to you for free and open access. It has been accepted for inclusion in Dissertations and Theses by an authorized administrator of PDXScholar. Please contact us if we can make this document more accessible: [email protected]. All ABSTRACT OF THE TllESIS OF Patrick Jay Green for the Master of Science in Chemistry presented April 16, 1976. Title: Chemistry of Chromium(VI) and Chromium(V) Oxide Fluorides. APPROVEO BY MEMBERS OF THE THESIS CO'"o\l TIEE: y . • Ii . ' I : • • • • • New preparative routes to chromyl fluoride were sought. It was found that chlorine ironofluoride reacts with chromium trioxide and chromyl chlo­ ride to produce chromyl fluoride. Attempts were ~ade to define a mechan­ ism for the reaction of ClF and Cr0 in light of by-products observed 3 and previous investigations. Carbonyl fluoride and chromium trioxide react to fom chro·yl fluoride and carbo:i dioxide. A mechanism was also proposed for this react10n. Chromium trioxide 11itl\ l~F6 or WF5 reacts to produce chromyl fluoride and the respective oxide tetrafluoride. 2 Sulfur hexafluoride did not react with Cr03.
    [Show full text]
  • Oxidation of Sulfur Dioxide to Sulfur Trioxide Over Supported Vanadia Catalysts
    Applied Catalysis B: Environmental 19 (1998) 103±117 Oxidation of sulfur dioxide to sulfur trioxide over supported vanadia catalysts Joseph P. Dunn, Prashanth R. Koppula, Harvey G. Stenger, Israel E. Wachs* Zettlemoyer Center for Surface Studies, Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015, USA Accepted 2 June 1998 Abstract The objectives of this research are to establish the fundamental kinetics and mechanism of sulfur dioxide oxidation over supported vanadia catalysts and use these insights to facilitate the design of SCR DeNOx catalysts with minimal sulfur dioxide oxidation activity. A series of supported vanadia catalysts were prepared on various metal-oxide supports: ceria, zirconia, titania, alumina and silica. Raman spectroscopy was used to determine the coordination of surface species. At low vanadia 5 loadings, vanadia preferentially exists on oxide support surfaces as isolated tetrahedrally coordinated (M±O)3V O species. 5 At higher vanadia loadings, the isolated (M±O)3V O species polymerize on the oxide support surface breaking two V±O±M bonds and forming two V±O±V bridging bonds. The turnover frequency for sulfur dioxide oxidation was very low, 104 to 106 s1 at 4008C, and was independent of vanadia coverage suggesting that only one vanadia site is required for the oxidation reaction. As the support was varied, sulfur dioxide oxidation activity of the supported vanadia catalysts varied by one order of magnitude (Ce>Zr, Ti>Al>Si). The basicity of the bridging V±O±M oxygen appears to be responsible for in¯uencing the adsorption and subsequent oxidation of the acidic sulfur dioxide molecule. Over the range of conditions studied, the rate of sulfur dioxide oxidation is zero-order in oxygen, ®rst-order in sulfur dioxide and inhibited by sulfur trioxide.
    [Show full text]
  • Chemical Reactions
    INTRODUCTION:- Sulfuric acid (alternative spelling sulphuric acid) is a highly corrosive strong mineral acid with the molecular formula H2SO4. It is a pungent-ethereal, colorless to slightly yellow viscous liquid which is soluble in water at all concentrations.Sometimes, it is dyed dark brown during production to alert people to its hazards.The historical name of this acid is oil of vitriol. Pure sulfuric acid is not encountered naturally on Earth in anhydrous form, due to its great affinity for water. Dilute sulfuric acid is a constituent of acid rain, which is formed by atmospheric oxidation of sulfur dioxide in the presence of water – i.e., oxidation of sulfurous acid. Sulfur dioxide is the main byproduct produced when sulfur-containing fuels such as coal or oil are burned. Sulfuric acid is formed naturally by the oxidation of sulfide minerals, such as iron sulfide. The resulting water can be highly acidic and is called acid mine drainage (AMD) or acid rock drainage (ARD). This acidic water is capable of dissolving metals present in sulfide ores, which results in brightly colored, toxic streams. Alternative Names:- 1. Oil of vitriol 2. Sulfuric acid 3. Vitriol 4. Battery acid 5. Electrolyte acid PHYSICAL PROPERTIES:- Appearance colourless, oily, corrosive liquid Melting point 10 deg C Molecular Formula H2O4S 337 deg C Boiling point 1mm of Hg at 145.8 deg C Vapor pressure 1.840 g/mL Density <0.3 (25 °C, vs air) vapor density 1.01 pH of 10 % of solution Non flammable Flammability limits 98.07848 g/mol Molar weight CHEMICAL PROPERTIES :- Attacks most metals.
    [Show full text]
  • Oxidation State Slides.Key
    Oxidation States Dr. Sobers’ Lecture Slides The Oxidation State Also known as the oxidation number The oxidation state is used to determine whether an element has been oxidized or reduced. The oxidation state is not always a real, quantitative, physical constant. The oxidation state can be the charge on an atom: 2+ - MgCl2 Mg Cl Oxidation State: +2 -1 2 The Oxidation State For covalently bonded substances, it is not as simple as an ionic charge. A covalent bond is a sharing of electrons. The electrons are associated with more than one atomic nuclei. This holds the nuclei together. The electrons may not be equally shared. This creates a polar bond. The electronegativity of a covalently bonded atom is its ability to attract electrons towards itself. 3 Example: Chlorine Sodium chloride is an ionic compound. In sodium chloride, the chloride ion has a charge and an oxidation state of -1. The oxidation state of sodium is +1. 4 Example: Chlorine In a chlorine molecule, the chlorine atoms are covalently bonded. The two atoms share electrons equally and the oxidation state is 0. 5 Example: Chlorine The two atoms of a hydrogen chloride molecule are covalently bonded. The electrons are not shared equally because chlorine is more electronegative than hydrogen. There are no ions but the oxidation state of chlorine in HCl is -1 and the oxidation state of hydrogen is +1. 6 7 Assigning Oxidation States See the handout for the list of rules. Rule 1: Free Elements Free elements have an oxidation state of zero Example Oxidation State O2(g) 0 Fe(s) 0 O3(g) 0 C(graphite) 0 C(diamond) 0 9 Rule 2: Monatomic Ions The oxidation state of monatomic ions is the charge of the ion Example Oxidation State O2- -2 Fe3+ +3 Na+ +1 I- -1 V4+ +4 10 Rule 3: Fluorine in Compounds Fluorine in a compound always has an oxidation state of -1 Example Comments and Oxidation States NaF These are monatomic ions.
    [Show full text]
  • Structure-Property Relationships of Layered Oxypnictides
    AN ABSTRACT OF THE DISSERTATION OF Sean W. Muir for the degree of Doctor of Philosophy in Chemistry presented on April 17, 2012. Title: Structure-property Relationships of Layered Oxypnictides Abstract approved:______________________________________________________ M. A. Subramanian Investigating the structure-property relationships of solid state materials can help improve many of the materials we use each day in life. It can also lead to the discovery of materials with interesting and unforeseen properties. In this work the structure property relationships of newly discovered layered oxypnictide phases are presented and discussed. There has generally been worldwide interest in layered oxypnictide materials following the discovery of superconductivity up to 55 K for iron arsenides such as LnFeAsO1-xFx (where Ln = Lanthanoid). This work presents efforts to understand the structure and physical property changes which occur to LnFeAsO materials when Fe is replaced with Rh or Ir and when As is replaced with Sb. As part of this work the solid solution between LaFeAsO and LaRhAsO was examined and superconductivity is observed for low Rh content with a maximum critical temperature of 16 K. LnRhAsO and LnIrAsO compositions are found to be metallic; however Ce based compositions display a resistivity temperature dependence which is typical of Kondo lattice materials. At low temperatures a sudden drop in resistivity occurs for both CeRhAsO and CeIrAsO compositions and this drop coincides with an antiferromagnetic transition. The Kondo scattering temperatures and magnetic transition temperatures observed for these materials can be rationalized by considering the expected difference in N(EF)J parameters between them, where N(EF) is the density of states at the Fermi level and J represents the exchange interaction between the Ce 4f1 electrons and the conduction electrons.
    [Show full text]
  • Ruthenium Tetroxide and Perruthenate Chemistry. Recent Advances and Related Transformations Mediated by Other Transition Metal Oxo-Species
    Molecules 2014, 19, 6534-6582; doi:10.3390/molecules19056534 OPEN ACCESS molecules ISSN 1420-3049 www.mdpi.com/journal/molecules Review Ruthenium Tetroxide and Perruthenate Chemistry. Recent Advances and Related Transformations Mediated by Other Transition Metal Oxo-species Vincenzo Piccialli Dipartimento di Scienze Chimiche, Università degli Studi di Napoli ―Federico II‖, Via Cintia 4, 80126, Napoli, Italy; E-Mail: [email protected]; Tel.: +39-081-674111; Fax: +39-081-674393 Received: 24 February 2014; in revised form: 14 May 2014 / Accepted: 16 May 2014 / Published: 21 May 2014 Abstract: In the last years ruthenium tetroxide is increasingly being used in organic synthesis. Thanks to the fine tuning of the reaction conditions, including pH control of the medium and the use of a wider range of co-oxidants, this species has proven to be a reagent able to catalyse useful synthetic transformations which are either a valuable alternative to established methods or even, in some cases, the method of choice. Protocols for oxidation of hydrocarbons, oxidative cleavage of C–C double bonds, even stopping the process at the aldehyde stage, oxidative cleavage of terminal and internal alkynes, oxidation of alcohols to carboxylic acids, dihydroxylation of alkenes, oxidative degradation of phenyl and other heteroaromatic nuclei, oxidative cyclization of dienes, have now reached a good level of improvement and are more and more included into complex synthetic sequences. The perruthenate ion is a ruthenium (VII) oxo-species. Since its introduction in the mid-eighties, tetrapropylammonium perruthenate (TPAP) has reached a great popularity among organic chemists and it is mostly employed in catalytic amounts in conjunction with N-methylmorpholine N-oxide (NMO) for the mild oxidation of primary and secondary alcohols to carbonyl compounds.
    [Show full text]
  • Selective Catalytic Oxidation of Ammonia to Nitrogen on Cuo-Ceo2 Bimetallic Oxide Catalysts
    Hung, Aerosol and Air Quality Research, Vol. 6, No. 2, pp. 150-169, 2006 Selective Catalytic Oxidation of Ammonia to Nitrogen on CuO-CeO2 Bimetallic Oxide Catalysts Chang-Mao Hung* Department of Business Administration, Yung-Ta Institute of Technology & Commerce, 316 Chung-shan Road, Linlo, Pingtung 909, Taiwan, R.O.C. Abstract This study addresses the performance of the selective catalytic oxidation (SCO) of ammonia to N2 over a CuO-CeO2 bimetallic oxide catalyst in a tubular fixed-bed reactor (TFBR) at temperatures from 423 to 673 K in the presence of oxygen. CuO-CeO2 bimetallic oxide catalyst was prepared by co-precipitation with Cu(NO3)2 and Ce(NO3)3 at various molar concentrations. This study tested operational stability and investigated how the influent NH3 concentration (C0 = 500-1000 ppm) influences the capacity to remove NH3. The catalysts were characterized using XRD, FTIR, PSA, SEM and EDX. Ammonia was removed by oxidation in the absence of CuO- CeO2 bimetallic oxide catalyst, and the formation of copper (II) and cerium (IV) oxide active sites was confirmed. Additionally, the effects of the NH3 content of the carrier gas on the catalyst’s reaction rate (r) were observed. The results revealed that the extent of catalytic oxidation of ammonia in the presence of a CuO-CeO2 bimetallic oxide catalyst was a function of the molar ratio Cu:Ce in the bimetallic catalyst. The kinetics of catalyzed NH3 oxidation are described using the rate expression of the Eley-Rideal kinetic model. Also, experimental results indicate a reasonable mechanism for the catalytic oxidation of ammonia.
    [Show full text]