Download or read book Partial Oxidation of Methanol to Formaldehyde Over Isolated Vanadate Species Supported on High Surface Area Metal Oxides written by Jason Lee Bronkema and published by . This book was released on 2007 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book New Concepts in Oxidation Processes written by Eric Genty and published by MDPI. This book was released on 2020-03-06 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Special Issue of Catalysts aims to cover the recent progress and novel trends in the field of catalytic oxidation reaction. Topics addressed in this special issue concern the influence of different parameters on catalytic activity at various scales (atomic, laboratory, pilot, or industrial scales), the development of new catalytic materials of environmental or industrial importance, as well as the development of new methods, both microscopic and spectroscopic, to analyze oxidation processes.

Download or read book Heterogeneous Photocatalysis written by Jennifer Strunk and published by John Wiley & Sons. This book was released on 2021-08-23 with total page 386 pages. Available in PDF, EPUB and Kindle. Book excerpt: Discover the latest research in photocatalysis combined with foundational topics in basic physical and chemical photocatalytic processes In Heterogeneous Photocatalysis: From Fundamentals to Applications in Energy Conversion and Depollution, distinguished researcher and editor Jennifer Strunk delivers a rigorous discussion of the two main topics in her field—energy conversion and depollution reactions. The book covers topics like water splitting, CO2 reduction, NOx abatement and harmful organics degradation. In addition to the latest research on these topics, the reference provides readers with fundamental information about elementary physical and chemical processes in photocatalysis that are extremely practical in this interdisciplinary field. It offers an excellent overview of modern heterogeneous photocatalysis and combines concepts from different viewpoints to allow researchers with backgrounds as varied as electrochemistry, material science, and semiconductor physics to begin developing solutions with photocatalysis. In addition to subjects like metal-free photocatalysts and photocarrier loss pathways in metal oxide absorber materials for photocatalysis explored with time-resolved spectroscopy, readers will also benefit from the inclusion of: Thorough introductions to kinetic and thermodynamic considerations for photocatalyst design and the logic, concepts, and methods of the design of reliable studies on photocatalysis Detailed explorations of in-situ spectroscopy for mechanistic studies in semiconductor photocatalysis and the principles and limitations of photoelectrochemical fuel generation Discussions of photocatalysis, including the heterogeneous catalysis perspective and insights into photocatalysis from computational chemistry Treatments of selected aspects of photoreactor engineering and defects in photocatalysis Perfect for photochemists, physical and catalytic chemists, electrochemists, and materials scientists, Heterogeneous Photocatalysis will also earn a place in the libraries of surface physicists and environmental chemists seeking up-to-date information about energy conversion and depollution reactions.

Download or read book The Partial Oxidation of Methanol to Formaldehyde Over Molybdenum containing Catalysts written by Tsong-Jen Yang and published by . This book was released on 1982 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Understanding the Effect of Modifying Elements in Supported Vanadia Bilayered Catalysts for Methanol Oxidation to Formaldehyde written by William Collins Vining and published by . This book was released on 2011 with total page 330 pages. Available in PDF, EPUB and Kindle. Book excerpt: The field of heterogeneous catalysis has long been interested in understanding the role of site structure on reactivity and selectivity for the rational design of catalysts. Vanadia is of particular interest because of its potential to be highly active and selective for a variety of reactions, such as oxidative dehydrogenation of alkanes to alkenes, or the oxidation of n-butane to maleic anhydride. When supported, vanadia can exist in several environments depending on its surface coverage. At the lowest loadings, below 2 V/nm2, the vanadium exists predominantly in well dispersed, tetrahedral structures with 3 V-O-support bonds and 1 V=O bond. At higher loadings, above 2 V/nm2, V-O-V bonds form on the surface, and at loadings above 7 V/nm2, the vanadia begins to form 3 dimensional domains of V2O5. Methanol oxidation rates over catalysts with varying vanadia loadings have shown no significant effect of the V surface density on the formaldehyde formation rate. However, significant differences in the formaldehyde production rates are observed for different supports. Changing the support from silica to titania or zirconia, will result in increases in the production of formaldehyde from methanol by over an order of magnitude for similar vanadia surface coverages. These differences in rate are observed even though the reaction mechanism is believed to be the same regardless of the support. The mechanism is thought to proceed as follows. First methanol dissociatively adsorbs across a V-O-support bond, producing V-OCH3 and M-OH (M = Si, Ti, Zr, Ce) in a quasi-equilibrated step. Next a surface oxygen abstracts hydrogen from the methoxy group in the rate determining step, and formaldehyde desorbs. The final steps are fast and involve the production of H2O from neighboring hydroxyls and the reoxidation of the catalyst by gas-phase oxygen. When vanadia is supported on bulk TiO2, ZrO2, or CeO2, the support surface area is relatively small (2̃00 m2/g at its highest), and the bulk support causes side reactions which make it difficult to understand the role of the vanadia. Furthermore, by using a bulk support, only the vanadia surface coverage can be varied, such that the effect of different V structures can be elucidated, but not that of V-O-M bonds. Therefore, high surface area silica with a variable coverage of two-dimensional TiO2, ZrO2, and CeO2 layers are used to support isolated vanadate structures to vary the quantity of vanadia bound to the modifying layer. These bilayered catalysts can be used to determine the effect of the V-O-support bonds on the formaldehyde production rate. Three mesoporous silica supports, MCM-48 (1550 m2/g), MCM-41 (1353 m2/g), and SBA-15 (700 m2/g) were used as the high surface area silica. Ti was grafted to the MCM-48 surface using Ti(OiPr)4 and a maximum surface coverage of 2.8 Ti/nm2 was obtained after 3 graftings. The grafting of zirconium was performed using Zr-2-methyl-2-butoxide on MCM-41, and a maximum loading of 2.1 Zr/nm2 was achieved after 3 graftings. The final modifying element, cerium, was grafted onto SBA-15 using Ce(OtBu)4 for a maximum surface coverage of 0.9 Ce nm-2. After treating the MOx/SiO2 (M = Ti, Zr, Ce) samples in air to remove any organic ligands, OV(OiPr)3 was grafted onto the MOx/SiO2 (M = Ti, Zr, Ce) support to achieve the desired V surface coverage of approx. 0.7 V/nm2. The resulting catalysts contain amorphous two-dimensional layers of TiO2, ZrO2, or CeO2 with V existing in a pseudo-tetrahedral structure on the surface. As the surface density of the modifying element layer increases, the quantity of vanadia bound to TiO2, ZrO2, or CeO2 increases. For the VOx/ZrO2/SiO2 catalysts, the fraction of vanadia bound to the zirconia layer was able to be quantified and determined to be 35% of all V for a Zr surface density of 2.8 Zr nm-2. Even for small quantities of modifying elements (0.2 M nm-2), the apparent rate constant for formaldehyde production on VOx/MO2/SiO2 (M = Ti, Zr, Ce) is an order of magnitude higher than for VOx/SiO2 catalysts at the same V surface density. Regardless of the modifying element used, the increase in apparent rate constant is comparable for all catalysts. As the modifying element surface density is increased, the apparent rate constant also increases, which is a result of an increasing fraction of V bound to the MOx layer. Each of these bilayered catalysts can be described using a two-site model of VOx/SiO2 and VOx/MO2 (M = Ti, Zr, Ce) with the latter being responsible for the increased apparent rate constant. This higher activity for the VOx/MO2 site is due to a lower apparent activation energy. For VOx/SiO2, the apparent activation energy is 23 kcal mol-1, but is approximately 17 kcal mol-1 for VOx/MO2 sites. The apparent activation energy can be expressed as the sum of the heat of methanol adsorption and the activation energy for H-abstraction. My results indicate that the lower apparent activation energy observed for the bilayered catalysts is a result of a decrease in the activation energy for H-abstraction. This lower energy pathway occurs because the MOx layer can abstract H from surface methoxy groups. For VOx/SiO2, however, the vanadyl oxygen abstracts H in a higher energy step.

Download or read book Partial Oxidation of Methanol to Formaldehyde Over Sb Mo Oxide Catalysts written by Rafael Alfredo Díaz Real and published by . This book was released on 1991 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The kinetics of the vapor phase air oxidation of methanol to formaldehyde over molybdenum oxide catalysts, antimony oxide catalyst, and their mixtures (both supported and unsupported), at atmospheric pressure and different operating conditions, have been studied in a fixed-bed integral reactor heated by a fluidized sand bath. The effect of various process variables, namely the process temperature (T), the ratio of catalysts to feed flow rate or space time (W/F), and the ratio of methanol fed to air (R), on conversion and yield have been determined. A screening study at varying operating conditions was performed to determine the optimum composition of a Sb$\sb2\rm O\sb4$-MoO$\sb3$ mixture. On the basis of this study a catalyst containing 67% $\rm Sb\sb2O\sb4$-33% MoO$\sb3$ was selected for the detailed kinetic study of oxidation of methanol to formaldehyde. The operating conditions studied were as follows: temperature in the range 623 to 698 K, space times from 5 to 50 $\rm g\sb{cat}/mol\sb{CH\sb3OH}h\sp{-1},$ and methanol to air ratios in the range 0.04 to 0.10 mol$\rm\sb{CH\sb3OH}h\sp{-1}/mol\sb{air}h\sp{-1}.$ This catalyst proved to be highly active and selective to formaldehyde formation. Yields up to $\sim$100% were obtained. Best operating conditions found were obtained at a space time of 27.5 for a methanol/air ratio of 0.06 and a temperature of 698 K. The rate equation for the oxidation of methanol to formaldehyde was derived on the basis of a two-stage redox mechanism$$\eqalign{\rm CH\sb3OH\sb{(g)} + S\sb{ox}\ {\buildrel{k\sb1}\over{\to}}\ &\rm HCHO\sb{(g)} + H\sb2O\sb{(g)} + S\sb{red}\cr\rm O\sb{2\sb{(g)}} + &\rm S\sb{red}\ {\buildrel{k\sb2}\over{\to}}\ S\sb{ox}\cr}$$where S$\rm\sb{ox}$ represents an active site of lattice oxygen and S$\rm\sb{red}$ represents a reduced site of lattice oxygen. The rate equation for the temperature of 648 to 698 K which correlated the data was$$\rm r = {k\sb1P\sb{M}\over 1+{k\sb1P\sb{M}\over 2k\sb2P\sb{O\sb2}}}$$where k$\sb1$ and k$\sb2$ are the temperature dependent rate constants of steps one and two. The equations relating k$\sb1$ and k$\sb2$ with temperature were$$\eqalign{&\rm ln\ k\sb1 = -6.4039-{6.9153\times10\sp3\over T}\cr&\rm ln\ k\sb2 = -3.0154 + {1.8809\times10\sp3\over T}\cr}$$ Several spectroscopic and analytical techniques, viz, electron spin resonance (ESR), x-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), and adsorption studies were used to characterize the catalysts. The surface are of the catalyst used in the kinetic study was 6.1 m$\sp2$/g as determined by the BET method. A preliminary study of the Sb-Mo oxide mixture (load of $\sim$5 wt%) supported on Y zeolite was also carried out. Maximum yield obtained was comparable to that obtained with pure MoO$\sb3.$ A new catalyst has been developed that gave nearly 100% conversion and 100% yield. The industrial potential of this catalyst is very promising.

Download or read book The Function of High Surface Area Mesoporous Metal Oxides in Heterogeneous Catalysis and Partial Oxidation of Methane to Methanol in Near Supercritical Acetonitrile written by Tharindu Madusanka Premalal Kankanam Kapuge and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Nickel incorporated (mol. 30%), high surface area (423 m2 g-1), mesoporous (3.8-4.3 nm) TiO2, bare NiO, and bare TiO2 were synthesized with surfactant-assisted metal dissolution techniques. Ethanol is successfully converted to higher energy density compounds including hexanol (yield 63%), acetic acid (39%), and furan (54%) with bare titanium dioxide (300-500°C), whereas C10 decanoic acid (63%), acetaldehyde (50%) is synthesized on Ni/TiO2 at different temperatures. Meso-microporous hexagonal and monoclinic defective tungsten oxide (WOx) materials were synthesized using a surfactant-assisted metal dissolution methodology. The C(sp2)-C(sp2) cross-coupling of cyclo-pentene, hexane, and heptene with aromatic compounds was achieved with a maximum of 95% yield in 2 hours at 110°C using (max. TOF 7.9 h-1) proton incorporated WOx. When Li+, Na+, and K+ incorporated WOx were used, the reaction was completely stopped. Lower but significant yield (37%) compared to H-WOx (67%) was observed in the presence of cobalt incorporated WOx Mesoporous spinel cobalt oxide (Co3O4) with fine-tuned pore size distributions (9.6-17.6 nm) were synthesized using a series of nonionic surfactants. Tandem synthesis strategy to synthesize amine homo-coupled imine and amine-alcohol cross-coupled imine was introduced. Light-induced singlet oxygen and hydroxyl radical-mediated reaction mechanism was proposed. Metal-free methane conversion with high methanol yield (17% O2 based) at mild temperatures (275°C) was achieved with sub-supercritical acetonitrile cluster assisted boron nitride initiation mechanism. Experimental and theoretical evidence supporting acetonitrile-O2 cluster formation and oxygen activation have been presented. Reaction temperature, dwell time, methane-oxygen and solvent-oxygen molar ratio were identified as other critical factors controlling the methane activation and methanol yield.

Download or read book Partial Oxidation of Methanol to Formaldehyde Over Mo Sn Oxide Catalysts written by Rowaida George Zoumot and published by . This book was released on 1992 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Formaldehyde Synthesis Via the Partial Oxidation of Methane Over Supported Metal Oxide Catalysts written by Aidan William Sexton and published by . This book was released on 1995 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Methanol Oxidation Over Copper and Silver Monometallic and Bimetallic Supported Catalysts written by Luter Leke and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The partial oxidation of methanol to formaldehyde with air as oxidant has been studied with supported monometallic and bimetallic catalysts of copper and silver over a range of temperature and contact times. This was done to investigate the influence the bimetallics could possibly have on either the reaction pathways and/or the product(s) selectivity of the oxidation of methanol. Characterisation of these catalysts was performed by nitrogen adsorption and porosity measurements, XRD, and IR spectroscopy of adsorbed methanol and of adsorbed CO. These results indicated no crystalline phases of the loaded metals to be present. CO adsorption showed the presence of small cluster metal atoms on the surface of the catalysts. The reduction peaks from TPR also revealed the presence of partially oxidised and dispersed metal atoms. Infra-red studies of methanol adsorbed on these sample catalysts revealed the presence of intermediate methoxy and formate species which are believed to be formed in the course of the reactions. Results showed the monometallic copper and silver catalyst to be more active than the bimetallics. Although formaldehyde selectivities and yields were generally low, they were highest for the bimetallics supported on the silica catalyst than the monometalics and alumina supported samples. Copper-silver interaction in the bimetallic was proposed to enhance the reduction of the silver that enhanced the selectivity to formaldehyde. In particular under conditions, low conversions of methanol saw highest selectivities to formaldehyde. There was also a pronounced effect of the supports on product distribution and activities with the alumina based samples being more active than the silica supported ones, with the product distributions on the alumina supported significantly showing high yields of DME while the silica showed high yield for methyl formate with COx and CH4 detected in small quantities on all the catalysts within the parameters investigated.

Download or read book Partial Oxidation of Methanol to Formaldehyde Over Molybdenum tin Oxide Catalysts written by Rowaida George Zoumot and published by . This book was released on 1992 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The vapor phase air oxidation of methanol to formaldehyde was investigated over molybdenum oxide, tin oxide and their mixtures in an integral flow reactor at atmospheric pressure between temperature of 513 and 573 K, a space time of 10-40 hr g-cat/g-mol methanol and a molar ratio of 0.04-0.1 mol CH3OH/mol air. Experiments were done under such conditions that the effects of internal and external heat and mass transfer effects were negligible. The effects of several process variables, temperature, space time and methanol/air ratio on the conversion of methanol and the selectivity of the catalyst for formaldehyde production were determined. The results indicated that the impact of the process variables on the conversion, selectivity and yield of formaldehyde were in the following decreasing order T > W/F > R. A screening study indicated the optimum catalyst composition to be 50% SnO2 and 50% MoO3, while conversion increased with temperature and W/F selectivity decreased. This catalyst proved to be highly active and selective to formaldehyde production. Selectivity and yield of up to about 100% were obtained at 100% conversion at a temperature of 553 K, a space time (W/F) of 40 g-cat/g-mol methanol per hour and a molar ratio (R) of 0.04 mol CH3 OH/mol air. The rate expression r=k1P2M 1+k1P2M2k 2PO2 was deduced assuming a steady-state involving two-stage irreversible oxidation-reduction process. It represented the experimental data satisfactorily. Arrhenius plots of the two rate constants gave activation energies of 31.7 and 18.1 kcal/g-mol.

Download or read book Catalytic Reaction Synthesis for the Partial Oxidation of Methane to Formaldehyde written by Maria-Guadalupe Cardenas-Galindo and published by . This book was released on 1993 with total page 440 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Density Functional Theory Study of the Oxidation of Methanol to Formaldehyde Over Vanadia Supported on Silica Titania and Zirconia written by and published by . This book was released on 2002 with total page 29 pages. Available in PDF, EPUB and Kindle. Book excerpt: Density functional theory was used to investigate the mechanism and kinetics of methanol oxidation to formaldehyde over vanadia supported on silica, titania, and zirconia. The catalytically active site was modeled as an isolated VO4 unit attached to the support. The calculated geometry and vibrational frequencies of the active site are in good agreement with experimental measurements both for model compounds and oxide-supported vanadia. Methanol adsorption is found to occur preferentially with the rupture of a V-O-M bond (M = Si, Ti, Zr) and with preferential attachment of a methoxy group to V. The vibrational frequencies of the methoxy group are in good agreement with those observed experimentally as are the calculated isobars. The formation of formaldehyde is assumed to occur via the transfer of an H atom of a methoxy group to the O atom of the V=O group. The activation energy for this process is found to be in the range of 199-214 kJ/mol and apparent activation energies for the overall oxidation of methanol to formaldehyde are predicted to lie in the range of 112-123 kJ/mol, which is significantly higher than that found experimentally. Moreover, the predicted turnover frequency (TOF) for methanol oxidation is found to be essentially independent of support composition, whereas experiments show that the TOF is 103 greater for titania- and zirconia-supported vanadia than for silica-supported vanadia. Based on these findings, it is proposed that the formation of formaldehyde from methoxy groups may require pairs of adjacent VO4 groups or V2O-- dimer structures.

Download or read book Hydrocarbon Chemistry written by George A. Olah and published by John Wiley & Sons. This book was released on 2017-09-08 with total page 1240 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides an unparalleled contemporary assessment of hydrocarbon chemistry – presenting basic concepts, current research, and future applications. • Comprehensive and updated review and discussion of the field of hydrocarbon chemistry • Includes literature coverage since the publication of the previous edition • Expands or adds coverage of: carboxylation, sustainable hydrocarbons, extraterrestrial hydrocarbons • Addresses a topic of special relevance in contemporary science, since hydrocarbons play a role as a possible replacement for coal, petroleum oil, and natural gas as well as their environmentally safe use • Reviews of prior edition: “...literature coverage is comprehensive and ideal for quickly reviewing specific topics...of most value to industrial chemists...” (Angewandte Chemie) and “...useful for chemical engineers as well as engineers in the chemical and petrochemical industries.” (Petroleum Science and Technology)

Download or read book Investigation of the Partial Oxidation of Methane to Formaldehyde Over Vanadium Oxide Catalysts Supported on Silica written by Benoit J. Kartheuser and published by . This book was released on 1993 with total page 410 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Aqueous Oxidation of Methanol by Vanadium Containing Biocatalysts and Biocatalyst Mimics written by Julie E. Molinari and published by . This book was released on 2012 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: Despite significant structural differences between the active sites of supported vanadium oxide catalysts such as supported VO4/SiO 2, and vanadium bromoperoxidase enzyme mimics such as the vanadium peroxo-oxo compound chelated with N-(2-hydroxyethyl)iminodiacetic acid (heida) or K[VO(O 2)(heida)], both catalysts are capable of conducting similar partial oxidation reactions. The K[VO(O2)(heida)](aq) vanadium enzyme mimic contains a vanadium peroxo-oxo structure, O=VO2, that is not present for vanadia supported on inorganic oxides such as silica. Vanadia dispersed on silica is present as a trigonal pyramidal surface VO4 species possessing one terminal V=O bond and three bridging V-O-Si bonds under dehydrated conditions. The first objective of the studies included in this dissertation was to compare the aqueous methanol oxidation mechanism of K[VO(O 2)(heida)](aq) with that of the vapor-solid methanol oxidation by supported VO4/SiO2. The second objective was then to extend this to the study of Vanadium Haloperoxidases (VHPOs), thereby beginning to bridge the gap between heterogeneous and enzyme catalysis. In this study, we have used in situ Raman, UV-vis and ATR-IR spectroscopy during methanol oxidation to examine the nature of the active sites, most abundant reaction intermediates, rate-determining-step, and oxidation mechanisms of the K[VO(O2)(heida)](aq) mimic compound and inorganic supported vanadia catalyst. In both catalytic systems, methanol chemisorbs at the bridging V-O-ligand and V-O-Si sites. The use of methanol as a molecular probe was employed to provide important information on the active site and mechanism of oxidation by K[VO(O2)(heida)](aq). This study elucidates the K[VO(O2)(heida)](aq) active site, most abundant reaction intermediates, the rate-determining-step, and the important role of the vanadium peroxo structure for aqueous methanol oxidation, bridging the gap between inorganic and protein based vanadate oxidation catalysts. These results were then used as a benchmark for the study of Vanadium Haloperoxidase enzymes.

Download or read book Index to Theses with Abstracts Accepted for Higher Degrees by the Universities of Great Britain and Ireland and the Council for National Academic Awards written by and published by . This book was released on 2000 with total page 786 pages. Available in PDF, EPUB and Kindle. Book excerpt: