Abstract

Nanomaterials have attracted substantial attention in the area of catalysis due to the unique properties they exhibit such as high surface areas, intricate pore networks and unique morphologies. TiO2 has attracted attention as a catalyst since the discovery of its high photocatalytic activity by Fuishima and Honda in 1972. Given its high thermal stability, low cost, low environmental impact, and versatility, TiO2 is a widely used commercial catalyst and catalyst support. TiO2 is used in many applications such as photocatalysis is also an excellent support material for noble metals in a number of oxidative synthesis and pollution-control reactions. Though TiO2 is a widely used catalyst support, currently available commercial titanias often have low surface area and poor thermal and hydrothermal stability. While several methods reported in literature produce materials of higher surface area and more ideal porosity relative to commercially available titanias, these procedures generally involve inherent drawbacks including time-consuming, complicated, and expensive processes that are not industrially viable. Cost-effective, large-scale preparations of stable, high surface area, mesoporous TiO2 need to be developed. The work in this dissertation focuses on (1) producing high surface area stabilized TiO2 supports of controlled pore diameters and (2) the preparation of well dispersed Pt on these supports using industrially viable processes. The effects of dopants Al, La, Si, and Zr on the stability, surface area, and porosity of anatase TiO2 supports were investigated. Results show that dopants increased the surface area and thermal stability of anatase through structural modifications and grain growth inhibition. Stabilized titanias produced by this method demonstrated equivalent or higher thermal stability and surface area compared with pure anatase and previously reported materials after treatment at 400°C and 700°C including 22 mol% Al-TiO2 calcined at 400°C which had a surface area of 479 ± 39 m2/g, a pore volume of 0.46 ± 0.04 cm3/g, and a pore diameter of 2.9 ± 0.2 nm. Ten synthesis variables were examined and optimized using statistically designed experiments (DOEs). Equations were developed to predict the conditions to obtain the highest surface area and pore volume at the desired pore diameter and predict the pore diameter range that may be obtained for aluminum-modified anatase TiO2. Confirmation trials closely matched predicted surface areas, pore volumes, and pore diameters in all but one trial, demonstrating the power of DOEs in identifying and controlling synthesis variables in relatively few experiments. The structure of Al-modified anatase TiO2 was analyzed to determine the mechanism of Al stabilization. Surface Al stabilized TiO2 by lowering anatase surface energy, stabilizing planes of high surface energy which would otherwise join to achieve stabilization. Al in TiO2 lattice vacancies stabilized TiO2 through increasing lattice strain and limiting mass transport necessary for grain growth. Results demonstrate the importance of structure analysis of doped nanomaterials in the development of stabilized catalysts and catalyst supports. An industrially viable, one-pot synthesis of Pt supported on 22 mol% Al-modified anatase is presented. Pt dispersions as high as 54% (one-pot method) and 59% (DI method) have been obtained. Results show that this one-pot method and the DI method using our Al-modified supports are promising syntheses of highly dispersed Pt catalysts and demonstrate that the alumina-stabilized anatase support is superior to other many available anatase supports.

Degree

PhD

College and Department

Physical and Mathematical Sciences; Chemistry and Biochemistry

Rights

http://lib.byu.edu/about/copyright/

Date Submitted

2013-12-12

Document Type

Dissertation

Handle

http://hdl.lib.byu.edu/1877/etd6632

Keywords

TiO2, anatase, catalyst support, high surface area, thermal stability, statistical design, DOE, synthesis, Pt supported catalyst, controlled porosity

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