Oxidation Stability and Activity of Bulk, Supported and Promoted Molybdenum Carbide Catalysts for Methane Reforming PDF Download

Author: Anna Rini Sekar Darujati
Publisher:
ISBN:
Category : Catalysts
Languages : en
Pages :

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Author: David Charles Lamont
Publisher:
ISBN:
Category : Catalytic reforming
Languages : en
Pages :

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Author: Anna Rini Sekar Darujati
Publisher:
ISBN:
Category : Catalysts
Languages : en
Pages : 0

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The oxidation stability of a low surface area Mo2C catalyst has been studied in the presence of gases associated with the steam and dry (CO2) reforming of methane, at temperatures up to 850°C and pressures to 8 bar. The oxidation onset temperatures were found to be about 600°C when the carbide was exposed to either steam or CO2. There appears to be two distinct mechanisms for Mo2C oxidation: direct oxidation at low temperatures and thermal decomposition followed by oxidation of the Mo metal at temperatures above 750°C. Although onset temperatures were similar, CO2 was a stronger oxidant than steam at the higher temperatures. Both H2 and CO were found to inhibit oxidation and the effect can be explained by their influence on the prevailing kinetics. Trace concentrations of methane were found to completely stabilize the carbide from steam oxidation but significantly higher concentrations were required to stabilize it from CO2 oxidation and this is attributed to the higher rates of CO2 oxidation relative to carburization rates. The effect of pressure on the onset temperature of CO2 oxidation of the carbide was found to be negligible, even when inhibited by CO.

Author: Oscar Gerardo Marin-Flores
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 16

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The objective of this project is to investigate the feasibility of using molybdenum carbide catalysts for the reforming of transportation fuels (gasoline and diesel) in the presence of sulfur. Using trimethyl pentane (TMP) and hexadecane (HD) as model fuels and thiophene and benzothiophene as model sulfur compounds, all of the original objectives of the project were successfully accomplished. We have found that the steam reforming (SR) of sulfur-free TMP can be carried out over bulk Mo2C catalysts at essentially stoichiometric feed conditions without coking, as long as the temperatures are at about 1000 C. However, the stable operating temperature can be lowered to 900 C, by adding molecular oxygen (oxidative-steam reforming (OSR)). The activity of a bulk molybdenum carbide catalyst for the steam (SR) of sulfur free hexadecane was found to be stable under very low steam:carbon ratios at temperatures as low as 885 degrees C under OSR conditions, and at 965 degrees C under SR conditions. For both TMP and HD, the degree of deactivation in the presence of sulfur was dependent on the sulfur concentration but was minimal at concentrations below 100 ppmw. While deactivation was completely reversible in the case of TMP steam reforming, spent catalysts from OSR could only be partially reactivated. However, sulfur poisoning was totally reversible for HD under both SR and OSR conditions.

Author: Dushyant Shekhawat
Publisher: Elsevier
ISBN: 0444535640
Category : Technology & Engineering
Languages : en
Pages : 569

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Fuel Cells: Technologies for Fuel Processing provides an overview of the most important aspects of fuel reforming to the generally interested reader, researcher, technologist, teacher, student, or engineer. The topics covered include all aspects of fuel reforming: fundamental chemistry, different modes of reforming, catalysts, catalyst deactivation, fuel desulfurization, reaction engineering, novel reforming concepts, thermodynamics, heat and mass transfer issues, system design, and recent research and development. While no attempt is made to describe the fuel cell itself, there is sufficient description of the fuel cell to show how it affects the fuel reformer. By focusing on the fundamentals, this book aims to be a source of information now and in the future. By avoiding time-sensitive information/analysis (e.g., economics) it serves as a single source of information for scientists and engineers in fuel processing technology. The material is presented in such a way that this book will serve as a reference for graduate level courses, fuel cell developers, and fuel cell researchers. - Chapters written by experts in each area - Extensive bibliography supporting each chapter - Detailed index - Up-to-date diagrams and full colour illustrations

Author: Robert Lowry McCauley
Publisher:
ISBN:
Category : Carbides
Languages : en
Pages :

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Author: Karthick Murugappan
Publisher:
ISBN:
Category :
Languages : en
Pages : 176

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Growing concerns due to rising CO2 emissions have made biomass an indispensable source of renewable fuels and chemicals. However, biomass inherently has high oxygen content, which translates to low energy density, thereby necessitating a deoxygenation step before being utilized as fuels. Recently, MoO3 and Mo2C have emerged as promising earth-abundant cheap catalysts that perform hydrodeoxygenation (HDO) at relatively low temperatures ( 673 K) and ambient H2 pressures wherein oxygen is selectively removed as water. However, there exists a significant knowledge gap in understanding the stability and the active phases responsible for HDO of these catalysts. Furthermore, their applicability for real biomass conversions has not been largely demonstrated. In this thesis, first, HDO of m-cresol, a biomass-derived model compound, is investigated over bulk and supported MoO 3 catalysts. Detailed reactivity and characterization studies reveal that Mo5+ species plays a critical role during HDO. Specifically, TiO2 and ZrO2 are identified as ideal supports as they feature superior HDO reactivity and stability over bulk MoO3 by stabilizing intermediate Mo oxidation states (i.e. Mo5+) while bulk MoO 3 over-reduces to inactive metallic Mo. Translating from model compound studies, supported MoO3 catalysts are demonstrated to be effective in converting biomass (pine) pyrolysis vapors to hydrocarbons (ca. 30 % yield). In comparison with MoO 3, Mo2C is significantly more stable and selective for HDO of 4-methylanisole to toluene under identical reaction conditions. Mo2C predominantly breaks the stronger phenolic C-0 bond while MoO 3 also breaks the weaker aliphatic C-0 bond, likely due to the presence of Bronsted acid sites. To gain insights into the surface active sites, operando near-ambient XPS is employed during HDO and this technique revealed that HDO seems to operate via distinct active sites over both these materials. Finally, Mo2C is shown to be effective in upgrading real lignin streams to a single product propylbenzene, a precursor for renewable polymer. Overall, this thesis demonstrates the applicability of MoO3 and Mo2C in real biomass conversions and provides insights on the working nature of these catalysts, which will enable the design of more effective HDO catalysts.

Author: Hassana El Zein
Publisher:
ISBN:
Category : Catalysis
Languages : en
Pages : 63

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Author: Sonil Nanda
Publisher: CRC Press
ISBN: 0429952376
Category : Science
Languages : en
Pages : 210

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Book Description
This book provides different aspects on fuel processing and refinery for energy generation. Most updated research findings along with case studies, real scenario examples, and extensive analyses of original research work and literature reviews is included in this book.