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 A Surface Science Approach to Understanding Supported Vandia Catalysts written by Gordon Sek-Yin Wong and published by . This book was released on 2003 with total page 291 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Formaldehyde Yields from Methanol Electrochemical Oxidation on Platinum and Supported Catalysts written by Christina L. Childers and published by . This book was released on 1999 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Technical Study of the Silver catalyzed Methanol Oxidation to Formaldehyde written by Min Qian and published by . This book was released on 2004 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Methanol Oxidation on Transition Elements Oxides written by Abdulmohsen Alshehri and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Methanol oxidation to formaldehyde is one of the most important industries in our lives; the reaction occurs on catalyst surface in heterogeneous catalysis. Iron molybdate is the current selective catalyst. However, molybdenum volatilises during methanol oxidation and leaving the catalyst with a low molybdenum ratio, which deactivates the catalyst, a 2.2 Mo: 1Fe iron molybdate catalyst was used instead the stoichiometric catalyst, while yield of formaldehyde cannot be 100%. The goal of this study is to find more selective and more productive catalyst than iron molybdate catalyst, the first step is to find another transition element as selective as molybdenum, because molybdenum is the selective part, and iron is the active part, the resulting iron molybdate catalyst is a selective catalyst to formaldehyde near molybdenum and active near iron. Experimentally, catalysts were prepared using co-precipitation method, however, some doped catalysts were papered by incipient wetness impregnation, also sol-immobilization was used to prepare nano-gold particles on the surfaces of few supports. Catalysts characterizations were carried out within several techniques for the surface analysis (XPS) and bulk analysis (XRD), also the surface area was measured by BET equipment. Raman too was used in this study, while micro-reactor was the reactor to determine selectivity and activity of each catalyst. When molybdenum replaced by vanadium, the catalyst yielded 100% formaldehyde at 200 oC; moreover, tungsten was selective. Likewise, iron was replaced by other active metals such as manganese, copper and bismuth, which are active. Nano-gold improved activity when doped on molybdenum oxide and iron molybdate supports.

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 The Origin of the Ligand Effect in Supported and Bulk Metal Oxide Catalysis written by Loyd James Burcham and published by . This book was released on 1999 with total page 624 pages. Available in PDF, EPUB and Kindle. Book excerpt: The strong influence of the oxide support upon the turn-over frequency (TOF) of methanol oxidation over supported metal oxide catalysts has been well documented in recent years, but has not yet been completely understood at a fundamental level. The present dissertation probes the mechanistic origin of this interesting phenomenon (e.g., adsorption equilibrium of methanol to surface methoxy species, rate-determining methoxy surface decomposition, and product desorption equilibrium) and also extends the investigation to include similar ligand effects in bulk metal oxide catalysts. Qualitative in situ Raman, IR, and UV-Vis DRS spectroscopy of supported vanadia catalysts during steady-state methanol oxidation demonstrated that the molecular structures of surface vanadia species are very sensitive to the coordination and H-bonding effects of the adsorbed surface methoxy species (the reactive surface intermediates). Hence, spectroscopic monitoring of the surface methoxy intermediates, instead of the surface metal oxide species, provides more reliable information about the surface reaction kinetics responsible for ligand effects in methanol oxidation.

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 Heterogeneous Catalysis of Dimethyl Ether and Methanol written by Patricia Wing-Kee Cheung and published by . This book was released on 2006 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt: Methanol is currently the preferred feedstock to light olefins and oxygenated chemicals because it provides a thermodynamically and kinetically feasible, although indirect, route for methane conversion. Dimethyl ether (DME, CH3OCH3) is an attractive alternate feedstock because its conversion from synthesis gas is more economical and thermodynamically favorable than methanol and its lack of hydroxyl groups lessens its potential to form water by-products. The catalyst site requirements, kinetics, and mechanism of oxidation and carbonylation reactions of methanol and DME are examined here.

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 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 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 Experimental Methods and Instrumentation for Chemical Engineers written by Gregory S. Patience and published by Elsevier. This book was released on 2017-09-08 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experimental Methods and Instrumentation for Chemical Engineers, Second Edition, touches many aspects of engineering practice, research, and statistics. The principles of unit operations, transport phenomena, and plant design constitute the focus of chemical engineering in the latter years of the curricula. Experimental methods and instrumentation is the precursor to these subjects. This resource integrates these concepts with statistics and uncertainty analysis to define what is necessary to measure and to control, how precisely and how often.The completely updated second edition is divided into several themes related to data: metrology, notions of statistics, and design of experiments. The book then covers basic principles of sensing devices, with a brand new chapter covering force and mass, followed by pressure, temperature, flow rate, and physico-chemical properties. It continues with chapters that describe how to measure gas and liquid concentrations, how to characterize solids, and finally a new chapter on spectroscopic techniques such as UV/Vis, IR, XRD, XPS, NMR, and XAS. Throughout the book, the author integrates the concepts of uncertainty, along with a historical context and practical examples.A problem solutions manual is available from the author upon request. - Includes the basics for 1st and 2nd year chemical engineers, providing a foundation for unit operations and transport phenomena - Features many practical examples - Offers exercises for students at the end of each chapter - Includes up-to-date detailed drawings and photos of equipment

Download or read book Supported Metal Single Atom Catalysis written by Philippe Serp and published by Wiley-VCH. This book was released on 2022-02-22 with total page 688 pages. Available in PDF, EPUB and Kindle. Book excerpt: b”Supported Metal Single Atom CatalysisCovers all key aspects of supported metal single atom catalysts, an invaluable resource for academic researchers and industry professionals alike Single atom catalysis is one of the most innovative and dynamic research areas in catalysis science. Supported metal catalysts are used extensively across the chemical industry, ranging from fine and bulk chemical production to petrochemicals. Single atom catalysts (SACs) combine the advantages of both homogeneous and heterogeneous catalysts such as catalyst stability, activity, and high dispersion of the active phase. Supported Metal Single Atom Catalysis provides an authoritative and up-to-date overview of the emerging field, covering the synthesis, preparation, characterization, modeling, and applications of SACs. This comprehensive volume introduces the basic principles of single atom catalysis, describes metal oxide and carbon support materials for SAC preparation, presents characterization techniques and theoretical calculations, and discusses SACs in areas including selective hydrogenation, oxidation reactions, activation of small molecules, C-C bond formation, and biomedical applications. Highlights the activity, selectivity, and stability advantages of supported metal SACs compared to other heterogeneous catalysts Covers applications of SACs in thermal catalysis, electrocatalysis, and photocatalysis Includes chapters on single atom alloys and supported double and triple metal atom catalysts Discusses the prospects, challenges, and potential industrial applications of SACs Supported Metal Single Atom Catalysis is an indispensable reference for all those working in the fields of catalysis, solid-state chemistry, materials science, and spectroscopy, including catalytic chemists, organic chemists, electrochemists, theoretical chemists, and industrial chemists.

Download or read book Strong Metal support Interactions written by R. T. K. Baker and published by . This book was released on 1986 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Classical And Quantum Dynamics In Condensed Phase Simulations Proceedings Of The International School Of Physics written by Bruce J Berne and published by World Scientific. This book was released on 1998-06-17 with total page 881 pages. Available in PDF, EPUB and Kindle. Book excerpt: The school held at Villa Marigola, Lerici, Italy, in July 1997 was very much an educational experiment aimed not just at teaching a new generation of students the latest developments in computer simulation methods and theory, but also at bringing together researchers from the condensed matter computer simulation community, the biophysical chemistry community and the quantum dynamics community to confront the shared problem: the development of methods to treat the dynamics of quantum condensed phase systems.This volume collects the lectures delivered there. Due to the focus of the school, the contributions divide along natural lines into two broad groups: (1) the most sophisticated forms of the art of computer simulation, including biased phase space sampling schemes, methods which address the multiplicity of time scales in condensed phase problems, and static equilibrium methods for treating quantum systems; (2) the contributions on quantum dynamics, including methods for mixing quantum and classical dynamics in condensed phase simulations and methods capable of treating all degrees of freedom quantum-mechanically.

Download or read book Electro Fenton Process written by Minghua Zhou and published by Springer. This book was released on 2017-11-25 with total page 437 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume discusses the theoretical fundamentals and potential applications of the original electro-Fenton (EF) process and its most innovative and promising versions, all of which are classified as electrochemical advanced oxidation processes. It consists of 15 chapters that review the latest advances and trends, material selection, reaction and reactor modeling and EF scale-up. It particularly focuses on the applications of EF process in the treatment of toxic and persistent organic pollutants in water and soil, showing highly efficient removal for both lab-scale and pre-pilot setups. Indeed, the EF technology is now mature enough to be brought to market, and this collection of contributions from leading experts in the field constitutes a timely milestone for scientists and engineers.