Nanostructured catalytic architectures for CO oxidation and reduction
| dc.contributor.author | Khan, Wasim Ullah | |
| dc.date.accessioned | 2020-02-27T19:54:43Z | |
| dc.date.available | 2020-02-27T19:54:43Z | |
| dc.date.issued | 2019 | en |
| dc.description.abstract | The urbanization and increasing demand of transport vehicles have significant contribution in the emissions of carbon monoxide (CO) which is detrimental to humans, animals and environment. Hence, the conversion of CO either by oxidation or hydrogenation has gained attention in recent years. CO oxidation reaction plays an important role in air purification and vehicle exhaust treatment. CO oxidation also serves as a model reaction for basic studies of more complicated reactions such as methanol synthesis, water gas shift reaction or Fischer-Tropsch Synthesis (FTS). CO hydrogenation or syngas conversion via FTS process was first studied in the early 20th century. Natural gas, biomass, coal and organic wastes are the sources to obtain syngas mixture. The FTS process generates value-added products with wide range of olefins, paraffins and oxygenates. Four types of active metals including ruthenium, nickel, iron and cobalt are mostly reported for the FTS process in the literature. Among these catalysts, iron and cobalt based catalysts are promising and utilized on the industrial scale. In this research work, the copper and cobalt based catalysts were developed with a focus on their utilization for CO oxidation and hydrogenation/reduction via the FTS process. The novel hexameric copper nanoclusters were successfully synthesized and anchored over titanium dioxide (TiO2-P25). The as-synthesized catalysts (with Cu contents varied between 0.15 and 5 wt%) were tested for CO oxidation reaction to find the size- activity threshold. The turnover number results for 8 h time-on-stream revealed that the copper contents up to 0.30 wt% resulted in size-activity threshold above which catalysts showed deactivation due to sintering. The higher dispersion and copper surface area along with strong metal-support interaction were among the factors of the stable performance of lower copper loading (0.15 and 0.30 wt%) catalysts. The oxide support offers unique features to the catalyst including surface area, porosity, and metal dispersion and these parameters later play their role in the catalytic activity. Hence, the next phase was focused on the preparation of titanium dioxide nanotubes/nanorods. The synthesis parameters such as hydrothermal treatment duration (24-72 h) and temperature (130-150℃) were optimized to achieve nanostructures of wide aspect ratio. The hydrothermal temperature of 150℃ for 44 h duration were chosen as optimum operating conditions. The effect of calcination temperature between 400 and 800℃ showed that mixture of nanotubes and nanoparticles were obtained at calcination temperature of 400 and 600℃ while calcination temperature of 800℃ produced uniform titania nanorods (TNRs). In order to demonstrate the role of the catalytically active interfaces between copper and TNRs in CO oxidation reaction, the next phase was planned to anchor copper nanoparticles over TNRs synthesized in the last phase. Copper contents varied from 2.5 to 12.5 wt% showed an optimum of 7.5 wt% and the catalytic activity was assigned to the formation of suitable interface between copper and TNRs and presence of copper in the form of layers over the surface of TNRs. The effect of various oxide supports including TiO2-P25, silica and alumina revealed that TNR supported Cu catalyst had higher rate of reaction as compared with the other oxide supports. Syngas conversion into hydrocarbons via FTS process is reported to utilize cobalt based catalysts which are prone to deactivation. Hence, the addition of small fractions of second metal as promoter and/or to form synergistic bimetallic catalyst influences the catalytic performance and product selectivity. Therefore, the final phase of this project presented the role of base and Cu promoted Co/TNRs catalysts for hydrocarbons production via FTS. The optimum metal loading of 7.5 wt%, found in the last phase, was chosen as basis to synthesize catalysts. The amount of Cu promoter was varied from 1.5 to 6 wt% and the testing of as-synthesized catalysts for the FTS process showed that Cu promotion in smaller fraction (1.5 wt%) presented improved reducibility and CO and H2 adsorption capacities which boosted CO conversion (16.8%) of this catalyst in comparison with base catalyst (9.4%). The increase in reaction temperature over the best catalyst from 240 to 300℃ revealed enhanced CO conversion (25%) but methane and CO2 selectivity was also found to be increased in agreement with previous reports. | en |
| dc.identifier.uri | http://hdl.handle.net/10092/18615 | |
| dc.identifier.uri | http://dx.doi.org/10.26021/2636 | |
| dc.language | English | |
| dc.language.iso | en | |
| dc.publisher | University of Canterbury | en |
| dc.rights | All Right Reserved | en |
| dc.rights.uri | https://canterbury.libguides.com/rights/theses | en |
| dc.title | Nanostructured catalytic architectures for CO oxidation and reduction | en |
| dc.type | Theses / Dissertations | en |
| thesis.degree.discipline | Chemical and Process Engineering | en |
| thesis.degree.grantor | University of Canterbury | en |
| thesis.degree.level | Doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |
| uc.college | Faculty of Engineering | en |