Oxidative Dehydrogenation Of Light Alkanes On Metal Oxide Catalysts

Author : Theodore Agbi
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (138 download)

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Download or read book Development and Characterization of Oxyfunctionalized Boron Nitride Catalysts for the Oxidative Dehydrogenation of Light Alkanes to Olefins written by Theodore Agbi and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Light olefins like ethylene and propylene are platform chemicals integral to the chemical industry. Production of polymers, oxygenates, and other important chemical intermediates demand global production volumes that top 100 million metric tons per year. Production of these light olefins, traditionally through steam cracking, is one of the most energy intensive processes in petrochemical sector. Changing refinery feedstocks (i.e. increased availability of natural gas) have created both necessity and opportunity for 'On-Purpose' propylene technologies to meet propylene demands. The oxidative dehydrogenation of propane to propylene (ODHP) is an attractive alternative process to produce propylene. ODHP enables lower process temperatures and avoids coke deactivation of the catalyst, and has the potential to significantly ease energy, capital, and material intensities of industrial propylene production. To-date, metal oxide ODHP catalysts like vanadia-based catalysts-the previous state of the art ODHP catalyst-do not achieve competitive propylene yields to make them industrially viable. The pioneering work of our research group has identified BN-a material renowned for its chemical inertness-as a highly reactive, selective, and stable ODHP catalyst. Since this discovery, we have worked to understand the fundamental reaction mechanisms present and identify structure-performance relationships that may further develop this class of catalyst. To-date, we have developed extensive spectroscopic characterization capabilities to identify the oxyfunctionalized boron layer formed in situ which contains highly dynamic active species responsible for the high reactivity and selectivity observed. Understanding the activation of molecular O2 and functionality of the oxyfunctionalized layer has been a highly collaborative process requiring a myriad of complimentary spectroscopic and reaction studies to develop fundamental insights. As such, I will provide a comprehensive context of our evolving knowledge in this collaborative project that have since been published where possible and will focus mainly on the recent insights made in this work. The work presented in this dissertation characterizes and probes the reactivity of the highly dynamic oxyfunctionalized surface layer that has been correlated with the reactivity and selectivity observed on this catalyst. Herein, the coordination environment of B and extent of oxyfunctionalization were analyzed via X-ray Photoelectron Spectroscopy (XPS), X-ray Absorption Spectroscopy (XAS), and Attenuated Total Reflectance IR (ATR-IR) as a function of the reaction progress. Corresponding reaction studies show direct correlation between the development of tri-coordinated oxygenated B networks and the increasing reactivity and selectivity of the reaction during the catalyst's activation period. The significance of a set of reaction parameters was then examined to identify process levers conducive to oxyfunctionalization quantified by XPS. The acid-base activity of these surface tri-coordnated B networks in the oxyfunctionalized layer are examined via two prototypical reactions: (1) isopropanol decomposition and (2) formic acid decomposition. Catalytic reaction via flow through reactor and temperature programmed decomposition (TPD) studies using Diffuse Reflectance Infrared Fourier Transform IR spectroscopy (DRIFTs) and Mass Spectrometry (MS) are used to extract insights for the adsorption modes of alkoxides and formates their decomposition pathways. Observed surface reactions of isopropoxy intermediates under these conditions are used to understand possible surface reaction pathways available under ODHP conditions. The role of O2 in specific homogeneous pathways of the mixed hetero-homogeneous mechanism previously proposed by us and for supported boron oxide materials are examined. A simplified model for the surface-initiated radical oxidation chemistry pathways, was then used to probe a selectivity descriptor based on the different reactivities of propyl radicals. Using this knowledge, we design, and test model 3D printed BN based monoliths that optimize homogeneous reaction pathways. These catalysts are shown to be highly active and selective and stable for ~2.5wks. The results also suggest that oxygenates may be relevant products from homogeneous reactions. "The Boron Project," as we so lovingly called it, has seen several PhD students matriculate as we contributed diligently to uncovering the behavior of this material. The goal of this work is to highlight new avenues through which we can further understand surface reactivity, new tools through which we can probe gas phase radical chemistries, and new catalyst design approaches.