Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 204
Book Description
New Insights Into the Oxidative Dehydrogenation of Propane and Ethane on Supported Vanadium Oxide Catalysts
Author: Oxidative Dehydrogenation (ODH) of Ethane to Ethene Over Supported Vanadium Containing Oxide Catalysts
Author: Asad Ahmad KhanOxidative Dehydrogenation of Propane to Propene Over Supported Vanadium Oxide Catalysts
Author: Jordan G. BarrOxygen-free Propane Oxidative Dehydrogenation Over Vanadium Oxide Catalysts
Author: Sameer Ali Al-GhamdiPublisher:
ISBN:
Category :
Languages : en
Pages : 500
Book Description
Propane conversion to propylene has been the subject of intensive researches. This is due to the increasing demand for propylene. Current propylene production processes suffer from several limitations. Oxidative dehydrogenation (ODH) is a promising alternative technology for propylene production overcoming the drawbacks of current processes. However, selectivity control in ODH is still a challenge preventing it from an industrial application. This is due to the formation of undesired carbon oxides. Thus, the development of a selective catalyst is crucial for the commercialization of ODH. Vanadium oxide catalysts have been proposed as the most active and selective catalyst for propane ODH. Moreover, new reactor concepts such as fluidized-bed might also help to make the ODH a feasible alternative for olefins productionas, offering some outstanding advantages in comparison to conventional reactors. This dissertation provides fundamental understanding of structure-reactivity relationship of vanadium oxide catalyst for propane ODH in a fluidized-bed reactor using the lattice oxygen of vanadium oxide catalysts in the absence of gas-phase oxygen. Supported vanadium oxide catalysts with different vanadium loadings (5-10 wt %) supported on?-Al2O3 is used. The prepared catalysts are characterized using several techniques such as BET surface area, H2-TPR, NH3-TPD, O2 Chemisorption, Laser Raman Spectroscopy, Pyridine FTIR and XRD. Characterization of the catalysts reveals that monomeric VOx species are predominant at low vanadium loadings while polymeric VOx species increase with higher loadings until monolayer surface coverage is reached. Moreover, the catalysts display moderated acidity compared to that of the bare alumina due to the relative increase in the number of Brønsted acid sites. Successive-injections propane ODH experiments in the CREC Riser Simulator over partially reduced catalyst show good propane conversions (12%-15%) and promising propylene selectivity (68-86%) at 475-550 0C. Product selectivities are found to augment with the catalyst's degree of reduction suggesting that a certain degree of catalyst reduction is required for better propylene selectivity. Compared to average propylene yields of 5% and 15% obtained in FCC and steam cracking technologies, respectively, promising value of 7% was obtained in the present propane ODH study over vanadium oxide catalyst and under oxygen free conditions. Such result would encourage further investigation of propane ODH in the absence of molecular gas oxygen as promising alternative/supplementary technology for the production of propylene. A kinetic model relating reaction rate to the catalyst's degree of oxidation is proposed. Non- linear regression leads to model parameters with low confidence intervals, suggesting the adequacy of the proposed model in predicting the ODH reaction under the selected reaction conditions.
Springer Handbook of Advanced Catalyst Characterization
Author: Israel E. WachsPublisher: Springer Nature
ISBN: 3031071255
Category : Technology & Engineering
Languages : en
Pages : 1109
Book Description
Co-edited by world-renowned scientists in the field of catalysis, this book contains the cutting-edge in situ and operando spectroscopy characterization techniques operating under reaction conditions to determine a materials’ bulk, surface, and solution complex and their applications in the field of catalysis with emphasis on solid catalysts in powder form since such catalyst are relevant for industrial applications. The handbook covers from widely-used to cutting-edge techniques. The handbook is written for a broad audience of students and professionals who want to pursue the full capabilities available by the current state-of-the-art in characterization to fully understand how their catalysts really operate and guide the rational design of advanced catalysts. Individuals involved in catalysis research will be interested in this handbook because it contains a catalogue of cutting-edge methods employed in characterization of catalysts. These techniques find wide use in applications such as petroleum refining, chemical manufacture, natural gas conversion, pollution control, transportation, power generation, pharmaceuticals and food processing. fdsfds
Oxidative Dehydrogenation of Ethane to Ethylene Over Supported Vanadia and Ni-Nb-M-O Mixed Metal Oxide Catalysts
Author: Ailing QiaoOxidative Dehydrogenation of Ethane to Ethylene Over Supported Vanadia and Ni-Nb-M-O Mided Metal Oxide Catalysts
Author: Ailing QiaoFundamental Studies on the Structure of Surface Oxide Sites on Supported Oxidative Dehydrogenation Catalysts
Author: Alyssa Marie LovePublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
The structure of metal oxide sites on supported metal oxide catalysts has a significant impact on the performance of the catalyst. For example, silica-supported vanadium oxide-a catalyst widely studied for the oxidative dehydrogenation of propane (ODHP) to propene-has a higher selectivity towards propene when the catalyst surface is comprised of primarily dispersed VOx surface species. Conversely, as the loading of vanadium oxide is increased beyond the monolayer coverage threshold, three-dimensional V2O5 particles begin to form which lower the catalyst selectivity towards propene (at higher propane conversions) in favor of COx combustion products. For this catalytic application and for other supported metal oxides, understanding the variables that maximize the dispersion of two-dimensional metal oxide species on a support surface is invaluable information to improve the preparation of these catalysts. This thesis describes the synthesis and detailed characterization of supported oxide catalysts for the oxidative dehydrogenation of catalysts. In this work, vapor-phase grafting techniques were used to investigate the chemical reactions that occur during the synthesis of silica-supported vanadium oxide ODH catalysts. By depositing the neat vanadium precursor, VO(OiPr)3, onto silica dehydrated at 700 degrees C (called V/SiO2(700)), the complexity of variables in the synthesis was significantly decreased (compared to incipient wetness). Key anchoring and restructuring reactions during the formation of vanadium oxide sites on silica were characterized with a combination of infrared (IR), Raman, solid-state nuclear magnetic resonance (NMR), and X-Ray absorption spectroscopic studies, in addition to thermogravimetric analysis-differential scanning calorimetry-mass spectrometry (TGA-DSC-MS), inductively coupled plasma (ICP) elemental analysis, etc. Afterwards, key synthesis variables (i.e., isopropanol solvent, H-bonded silanols and Na+ ions on the support surface) were incorporated into this grafting system to develop a more comprehensive model for the dispersion of vanadium oxide under wet impregnation conditions. Efforts to improve Raman sensitivity towards metal oxide surface sites with shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) are also addressed in this work. The methodology and characterization approach presented for the study of supported vanadium oxide catalysts was also applied to the study of promising new ODHP catalysts, including hexagonal boron nitride and silica-supported boron oxide catalysts.
Mechanistic Insights on the Oxidative Dehydrogenation of Light Alkanes Catalyzed by Boron-based Catalysts
Author: Juan Mauricio VenegasPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Light olefins such as ethylene and propylene form the foundation of the modern chemical industry, with yearly production volumes well into the hundreds of millions of metric tons. Currently, these light olefins are mainly produced via energy-intensive steam cracking. Alternatively, oxidative dehydrogenation (ODH) of light alkanes to produce olefins allows for lower operation temperatures and extended catalyst lifetimes, providing valuable process efficiencies. This route has led to significant research interest due to the wide availability of natural gas from shale deposits. Advances in this area have still not yielded catalysts that are sufficiently selective to olefins for industrial implementation, and ODH still remains a holy grail of selective alkane oxidation research. Research into selective heterogeneous catalysts for the ODH of propane has led to the extensive use of vanadium oxide-based catalysts, and studies on the surface mechanism involved have been used to improve the catalytic activity of the material. Despite decades of research, however, selectivity towards propylene has not proven satisfactory at industrially-relevant conversions. In this thesis, I will present the serendipitous discovery and subsequent development of hexagonal boron nitride (hBN) and other boron-containing catalysts as selective ODH catalysts. Specifically, I will illustrate the evolution of our understanding of the chemical origin of the reactivity of these materials, which until our initial discovery were deemed chemically inert. By combining reactivity studies with spectroscopic characterization highlighted a unique interaction between boron and oxiygen that differs from that of metal oxides. This methodical characterization of catalytic activity and structural changes of hBN during ODH prompted us to zero in on oxidized boron species, not hBN itself, as the true catalyst of alkane oxidation. In turn, this discovery led us to describe a whole class of B-containing materials that share (and often improve upon) the catalytic performance of hBN. At this point, we decided to step away from material studies and instead improve our understanding on how the catalytic performance of hBN is affected by reactor operating parameters. In particular, we investigated the role of heat and mass transfer on catalytic performance. Unexpectedly, we were once again surprised by hBN when various experimental results during these efforts suggested the significance of gas phase chemistry on ODH performance. For example, we observed that upon dilution of hBN with an inert thermal conductor (to mitigate hotspot formation), the observed reactivity scales with total bed volume rather than hBN mass. Up until these studies, we expected all reactivity to stem from oxidized boron species, but these may be only a part of a more complex surface-gas phase reaction network. The final portion of this thesis presents our latest efforts to understand the role of each reactant on surface and gas phase reaction pathways. Within this work, we incorporate water into our reaction feeds to assess its influence as a source of gas phase radical species to carry out propane activation. Indeed, we observe significant rate enhancements by addition of water. This reactivity enhancement likely involves influencing reactive species concentrations primarily in the gas phase and, to a lesser extent, altering the surface composition during ODH. Overall, this thesis expands our understanding of B-based materials as ODH catalysts and highlights the importance of considering gas phase radical chemistry in future process development.
Kinetics of Chemical Processes
Author: Michel BoudartPublisher: Elsevier
ISBN: 1483183971
Category : Science
Languages : en
Pages : 263
Book Description
Kinetics of Chemical Processes details the concepts associated with the kinetic study of the chemical processes. The book is comprised of 10 chapters that present information relevant to applied research. The text first covers the elementary chemical kinetics of elementary steps, and then proceeds to discussing catalysis. The next chapter tackles simplified kinetics of sequences at the steady state. Chapter 5 deals with coupled sequences in reaction networks, while Chapter 6 talks about autocatalysis and inhibition. The seventh chapter describes the irreducible transport phenomena in chemical kinetics. The next two chapters discuss the correlations in homogenous kinetics and heterogeneous catalysis, respectively. The last chapter covers the analysis of reaction networks. The book will be of great use to students, researchers, and practitioners of scientific disciplines that deal with chemical reaction, particularly chemistry and chemical engineering.