Mesoporous γ-alumina is the most extensively used catalysts support in a wide range of catalytic processes. The usefulness of γ-alumina relies on its favorable combination of physical, textural, thermal, and chemical properties. Pore structure properties are among the most important properties, since high surface area and large pore volume enable higher loading of active catalytic phases, while design of pore size and pore size distribution is critical to optimize pore diffusional transport and product selectivity. In addition, accurate determination of surface area (SA), pore volume (PV) and pore size distribution (PSD) of porous supports, catalysts, and nanomaterials is vital to successful design and optimization of these materials and to the development of robust models of pore diffusional resistance and catalyst deactivation.In this dissertation, we report a simple, one-pot, solvent-deficient process to synthesize mesoporous γ-alumina without using external templates or surfactants. XRD, TEM, TGA and N2 adsorption techniques are used to characterize the morphologies and structures of the prepared alumina nanomaterials. By varying the aluminum salts or the water to aluminum molar ratio in the hydrolysis of aluminum alkoxides, γ-alumina with different morphologies and pore structures are synthesized. The obtained alumina nanomaterials have surface areas ranging from 210 m2/g to 340 m2/g, pore volumes ranging from 0.4 cm3/g to 1.7 cm3/g, and average pore widths from 4 to 18 nm. By varying the alcohols used in the rinsing and gelation of boehmite/bayerite precursors derived from a controlled hydrolysis of aluminum alkoxides, the average pore width of the γ-aluminas can be tuned from 7 to 37 nm. We also report improved calculations of PSD based on the Kelvin equation and a proposed Slit Pore Geometry model for slit-shaped mesopores of relatively large pore size (>10 nm). Two structural factors, α and β, are introduced to correct for non-ideal pore geometries. The volume density function for a log normal distribution is used to calculate the geometric mean pore diameter and standard deviation of the PSD. The Comparative Adsorption (αs) Method is also employed to independently assess mesopore surface area and volume.

Nanotechnology is blossoming into one of the premiere technologies of this century, but the key to its progress lies in developing more efficient nanosynthesis methods. Variations in synthetic technique, however, can cause variations in size, structure, and surface characteristics, thereby altering the physical properties and functionality of the particles. Careful structural characterizations are thus essential for understanding the properties and appropriate applications for particles produced by new synthetic techniques.In this work, a new ‘solvent-deficient’ method is presented for the synthesis of an unprecedentedly wide range of metal oxide nanomaterials including at least one metal oxide from each group in Groups 3-4, 6-15, and the Lanthanides. XRD, BET, and TEM structural characterizations as well as chemical purity analyses of the products are given. The intermediates associated with the method are also investigated, allowing the reaction parameters to be rationalized and culminating in a proposed mechanism for the reaction. Several of the reaction intermediates are themselves useful products, expanding the range of this already versatile method. Optimized synthesis parameters as well as structural characterizations are presented for one such intermediate product, the iron oxyhydroxide called ferrihydrite.The Al2O3 nanoparticles produced by the new method show promise in catalyst support applications, and the synthesis and structural analysis (XRD, X-ray PDF, 27Al NMR, TG/DTA-MS) of these nanoparticles is provided. The XRD, PDF, and NMR analyses reveal that the initial boehmite-like phase transforms to the catalytically useful gamma-Al2O3 phase at unusually low temperatures (300-400°C), but boehmite-like local structure defects remain which heal slowly with increasing temperature up to 800°C. The ‘pure’ gamma-Al2O3 may still contain randomized, non-cubic, local structure distortions, and it transforms directly to alpha-Al2O3 at ~1050°C. To rationalize the local structure and the absence of the delta- and theta-Al2O3 phases during the alpha-phase transition, relationships between the many Al2O3 phases are presented via innovative symmetry-mode analyses, revealing a potential quazi-topotactic mechanism for the gamma-to-alpha transition.To stabilize the gamma-Al2O3 phase to higher temperatures for catalyst applications, 3 wt% of a lanthanum dopant was added via a new, 1-pot process based on the new solvent-deficient method. This process is described and X-ray PDF, TEM, 27Al NMR, and EXAFS analyses of the La-doped gamma-Al2O3 nanoparticles reveal that the dopant resides as isolated, adsorbed atoms on the gamma-Al2O3 surface. The first coordination shell of the isolated La is increasingly La2O3-like as calcination temperature increases but changes drastically to be more LaAlO3-like after the alpha-phase transition, which is delayed ~100°C by the La dopant. Combining the EXAFS, PDF, NMR, and symmetry-mode analyses, we provide new insight into the mechanism of stabilization provided by the La dopant.

Mesoporous alumina (Al2O3) in the gamma (γ) phase is widely used as a support in catalytic applications because of its high surface area, large pore volume, acid-base characteristics, and thermal stability. To improve the thermal stability of gamma alumina, dopants such as lanthanum, magnesium, zirconia, and silica are often introduced. Current laboratory-based methods for synthesizing gamma alumina generally involve 10-15 steps and/or use toxic, expensive surfactants and solvents. Industrial methods, while simpler, lack control of pore properties and surface chemistry. In contrast, we have developed an innovative solvent deficient, one-step method that is able to synthesize a wide range of pure and silica-doped aluminas with high surface areas, pore volumes from 0.3 to 1.8 cm3/g, and pore diameters from 5 to 40 nm. More significantly, our silica-doped aluminas are stable up to temperatures as high as 1300<°>C, which is 200<°>C higher than other pure and doped gamma alumina materials.The usefulness of gamma-alumina as a catalyst support is dependent on its favorable combination of textural, thermal, structural, and chemical properties, yet the relationship between structure and these other properties is still not clearly understood due to the poorly crystallized nature of the material. In particular, the mechanism by which the gamma structure is stabilized thermally by so many dopants is still not well understood. Based on our previous PDF experiments on pure and La-doped alumina, we have developed a hypothesis regarding the mechanism by which dopants increase thermal stability. To validate or refute this hypothesis, we collected PDF data on a wider range of laboratory and industrial alumina samples. Herein, we have utilized PDF analysis to study the local to intermediate-range structure of a series of our pure and silica-doped aluminas calcined at 50<°>C intervals between 50 and 1300<°>C as well as pure and silica-doped aluminas from commercial sources and other synthetic methods. This thorough study of alumina local structure will allow us to separate general trends in the local structure from idiosyncrasies based on synthetic method/conditions, and it will help us identify the structural features responsible for improved thermal stability. Having access to these PDF experiments, we have validated our current hypothesis on the nature of stabilization afforded by dopants and, more generally, developed a better understanding of the role structure plays in the properties of aluminas.

Mesoporous γ-Al2O3 is one of the most widely used catalyst supports for commercial catalytic applications. The performance of a catalyst strongly depends on the combination of textural, chemical and physical properties of the support. Pore size is essential since each catalytic system requires a unique pore size for optimal catalyst loading, diffusion and selectivity. In addition, high surface area and large pore volume usually result in higher catalyst loading, which increases the number of catalytic reaction sites and decreases reaction time. Therefore, determination of surface area and porosity of porous supports is critical for the successful design and optimization of a catalyst support. Moreover, it is important to produce supports with good thermal stability since pore collapsing due to sintering at high temperatures often results in catalyst deactivation. In addition, the ability to control the acidity of the catalyst enables us to design desirable acid sites to optimize product selectivity, activity, and stability in different catalytic applications. This dissertation presents a simple, one-pot, solvent-deficient method to synthesize thermally stable silica-doped alumina (SDA) without using templates. The XRD (X-ray diffraction), HTXRD (high temperature X-ray diffraction), SS NMR (solid state nuclear magnetic resonance), TEM (transmission electron microscopy), TGA(thermogravimetric analysis), and N2 adosorption techniques are used to characterize the structures of the synthesized SDAs and understand the origin of increased thermal stability. The obtained SDAs have a surface area of 160 m2/g, pore volume of 0.99 cm3/g, and a bimodal pore size distribution of 23 and 52 nm after calcination at 1100◦C. Compared to a commercial SDA, the surface area, pore volume, and pore diameter of synthesized SDAs are higher by 46%, 155%, and 94%, respectively. A split-plot fractional-factorial experimental design is also used to obtain a useful mathematical model for the control of textural properties of SDAs with a reduced cost and number of experiments. The proposed quantitative models can predict optimal conditions to produce SDAs with high surface areas greater than 250 m2/g, large pore volume greater than 1 cm3/g, and large (40-60 nm) or medium (16-19 nm) pore diameters. In my approach, I control acid sites formation by altering preparation variables in the synthesis method such as Si/Al ratio and calcination temperatures. The total acidity concentration (Brønsted and Lewis) of the synthesized SDAs are determined using ammonia temperatured program, pyridine fourier transform infrared spectroscopy (FTIR), and MAS NMR. The total acidity concentration is increased by introducing a higher mole ratio of Si to Al. In addition, the total acidity concentration is decreased by increasing calcination temperature while maintaining high surface area, large porosity, and thermal stability of γ-alumina support. I also present an optimized synthesis of various aluminum alkoxides (aluminum n-hexyloxide (AH), aluminum phenoxide (APh) and aluminum isopropoxide (AIP)) with high yields (90-95%). One mole of aluminum is reacted with excess alcohol in the presence of 0.1 mole % mercuric chloride catalyst. The synthesized aluminum alkoxides are used as starting materials to produce high surface area alumina catalyst supports. Aluminum alkoxides and nano aluminas are analyzed by 1H NMR, 13C NMR, 27Al NMR, gCOSY (2D nuclear magnetic resonance spectroscopy), IR (infrared spectroscopy), XRD, ICP (induced coupled plasma), and elemental analysis.