Application of Transition Metal Coordination for Energy Efficient Processes: Catalysis and Separation

Application of Transition Metal Coordination for Energy Efficient Processes: Catalysis and Separation

Bibliographic Details
Main Author: Shrestha, Sweta
Language:English
Published: The Ohio State University / OhioLINK 2017
Subjects:
Chemistry
transition metals
photochemical water oxidation
olefin paraffin separation
Online Access:http://rave.ohiolink.edu/etdc/view?acc_num=osu1502975499629018
id ndltd-OhioLink-oai-etd.ohiolink.edu-osu1502975499629018
record_format oai_dc
collection NDLTD
language English
sources NDLTD
topic Chemistry
transition metals
photochemical water oxidation
olefin paraffin separation
spellingShingle Chemistry
transition metals
photochemical water oxidation
olefin paraffin separation
Shrestha, Sweta
Application of Transition Metal Coordination for Energy Efficient Processes: Catalysis and Separation
author Shrestha, Sweta
author_facet Shrestha, Sweta
author_sort Shrestha, Sweta
title Application of Transition Metal Coordination for Energy Efficient Processes: Catalysis and Separation
title_short Application of Transition Metal Coordination for Energy Efficient Processes: Catalysis and Separation
title_full Application of Transition Metal Coordination for Energy Efficient Processes: Catalysis and Separation
title_fullStr Application of Transition Metal Coordination for Energy Efficient Processes: Catalysis and Separation
title_full_unstemmed Application of Transition Metal Coordination for Energy Efficient Processes: Catalysis and Separation
title_sort application of transition metal coordination for energy efficient processes: catalysis and separation
publisher The Ohio State University / OhioLINK
publishDate 2017
url http://rave.ohiolink.edu/etdc/view?acc_num=osu1502975499629018
work_keys_str_mv AT shresthasweta applicationoftransitionmetalcoordinationforenergyefficientprocessescatalysisandseparation
_version_ 1719452842721280000
spelling ndltd-OhioLink-oai-etd.ohiolink.edu-osu15029754996290182021-08-03T07:03:57Z Application of Transition Metal Coordination for Energy Efficient Processes: Catalysis and Separation Shrestha, Sweta Chemistry transition metals photochemical water oxidation olefin paraffin separation The goal of this dissertation is to explore the application of transition metals in two energy-intensive processes, photochemical water oxidation and olefin/paraffin separation. Photochemical water splitting is widely studied and involves the exploitation of renewable resources solar energy and water to produce clean hydrogen along with oxygen. Water oxidation process to make oxygen is not thermodynamically and kinetically feasible, thus catalysts which can promote this reaction are needed. With efficient water oxidizing catalysts, the entire water splitting process is promoted. We are focusing on birnessite as catalysts for photochemical water oxidation. Birnessite are layered manganese oxides with intercalated cations and water molecules in the interlayer space. They are known as moderate water oxidizing catalysts. We have developed two strategies to enhance water oxidizing catalytic activity of birnessite.Our first strategy was the deposition of birnessite on zeolite surfaces. The synthesis method involves ion-exchanging Mn2+ cations along with alkaline earth metal co-cations (M2+: Mg2+, Ca2+, Sr2+, Ba2+) into zeolite followed by the precipitation of manganese oxides on zeolite surfaces. M2+ cations control the loading of Mn2+ cations into zeolite, such that the larger cationic size of M2+, the lower the loading of Mn. These samples are amorphous manganese oxides and referred to as M2+MnOx-Y. After treating with high concentration of K+ cations, there was improvement in crystallinity in manganese oxides forming birnessite, and we refer to them as KMnOx-Y(M2+). Photochemical water oxidation was performed in Ru(bpy)32+- persulfate system, and the dissolved oxygen evolution rate (turnover frequency: TOF) was measured. KMnOx-Y(M2+) catalysts were better than the corresponding M2+MnOx-Y. We propose that high concentration of K+ act as structure-directing agents to form disordered birnessite with high Mn3+ content, and the Mn3+ sites are correlated to active sites for water oxidation. The uniform dispersion of birnessite on zeolite also enhanced the catalytic activity of birnessite by immobilizing catalysts on its surface and exposing Mn active sites. This strategy helped to enhance the catalytic activity of birnessite by uniformly dispersing them on the zeolite support by exploiting the zeolite features such as pore size, surface area, and ion-exchange. The second strategy exploited the interlayer space of birnessite. Redox active iron(III) cations were ion-exchanged into the interlayer of birnessite, and referred to as Fe(IE)MnOx. We also adopted an in-situ strategy for doping Fe3+ cations into birnessite, and referred to as Fe(D)MnOx. Fe(IE)MnOx catalysts were better compared to Fe(D)MnOx and KMnOx (K+-birnessite). Fe(D)MnOx samples were hard and gritty large particles. The structure was that of disordered birnessite. The Mn4+ content increased with increasing concentration of Fe3+ doping. Fe(IE)MnOx samples were also disordered birnessite, but the inclusion of Fe3+ cations did not influence the redox state, which was primarily Mn3+. We propose that there are more exposed dilated Mn3+-O bonds and surface adsorbed oxygen/hydroxyl groups in Fe(IE)MnOx, and these characteristics led to efficient water oxidation. By exploiting the ion-exchange property of birnessite, we have synthesized highly active water oxidizing catalysts by intercalating Fe3+ into birnessite. It will be of interest to investigate other transition metals’ influence on the structure-function role of birnessite towards water oxidation.Propylene/propane (PY/PP) separation is of significant industrial importance. PY/PP are separated using highly expensive cryogenic distillation, and membrane-based processes with high flux and selectivity offer an energy-efficient alternative. Thin interconnected continuous layer of zeolite was grown within a porous polyethersulfone (PES) support, and referred to as ZM. The strategy involves modification of ZM by Ag(I) cations by ion-exchanging method, and they are referred to as Ag-ZM. We hypothesize that Ag (I) can enhance PY transport and improve both flux and selectivity, as Ag(I) can bind with unsaturated bonds of olefins via reversible p-complexation. Different concentration of Ag(I) was used followed by coating with a silicone polymer to fix defects, and PY/PP (50:50 mixture) separation was measured as a function of temperature. The PY/PP selectivity of ZM was 1.8, 3.6, and 2.6, and the PY permeance was 211, 1058, and 1712 GPU at 25oC, 50oC, and 75oC respectively. The best Ag-ZM sample had PY/PP selectivity of 3.6, 4.0, and 6.6, with the PY permeance of 260, 357, and 338 GPU at 25oC, 50oC, and 75oC respectively. The PY/PP selectivity performance of Ag-ZM was better compared to ZM, which supports our hypothesis. With high Ag loading in ZM, the steric effect due to blocking of zeolite pores by Ag(I) cations results in low gas permeation through zeolite pores. The significance of this dissertation is two-fold:a)Development of efficient water oxidizing catalysts using earth abundant transition metals manganese and iron b)Development of silver cations fabricated zeolite/PES composite membrane for enhanced propylene/propane separation 2017 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1502975499629018 http://rave.ohiolink.edu/etdc/view?acc_num=osu1502975499629018 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

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