Tracy A. Hanna
Research
Our current research involves the synthesis and study of bismuth and molybdenum inorganic and organometallic compounds. Bismuth and molybdenum-containing materials have applications as, for example,
Our approach is synthetic and mechanistic, and we use inorganic, organometallic and organic synthetic methods. Many of the compounds we use are air-sensitive, requiring careful synthetic techniques. We use NMR, FTIR, elemental analysis, and x-ray diffraction as primary characterization techniques. Some current projects in the group are summarized below.
Molybdenum(VI) Oxo Aryloxides: We are synthesizing Mo(VI) compounds that can be used as materials precursors, catalyst model precursors, and molybdoenzyme mimics. Early work has led to the synthesis of an very unusual 4-coordinate complex by the following reaction:
We are exploring further syntheses and reactivity to determine the nature of the ligand control of reactivity and geometry, as well as the synthesis of mixed alkoxide/aryloxide, aryloxide/amide, and aryloxide/halide species.
Bismuth(III) Alkoxides/Aryloxides: Despite their uses in medicine, superconducting materials, and other applications, few homoleptic bismuth(III) alkoxides have been fully characterized. We are synthesizing new bismuth(III) alkoxides and aryloxides such as shown below, and investigating their biological activity, sublimation, and solubility properties for use as pharmaceuticals and/or materials precursors.
Monometallic Models for the SOHIO Process: The selective oxidation and ammoxidation of propylene are important industrial processes to make acrolein and acrylonitrile on large scales. Most industrial catalysts used presently are based on the original Bi2O3.MoO3 catalysts developed by SOHIO (Standard Oil of Ohio Company) workers in 1959-1962, though additives are frequently incorporated to improve performance. Although the process has been used industrially for over thirty years the mechanism of the rate-determining step is not known, and the mechanism of the product-forming steps only partially understood. In our investigations of Bi(III) aryloxides we have found an unusual reaction;
in which BiIII acts as an oxidant under nitrogen atmosphere. The mechanism of this process may parallel the postulated rate-determining step of the industrially important SOHIO process; if so we will be able to use this reaction as a model reaction in order to gain a fundamental understanding of the catalytic cycle.
Discrete Mo-Bi Oxo-bridged Alkoxides: We are also investigating bimetallic models of the SOHIO catalyst active site using bulky alkoxide/aryloxide ligands including calixarene. We will synthesize and study well-defined homogeneous models of the catalyst active site in order to study the mechanism of propylene activation, the role of bismuth in later steps, the role of metal additives, and other aspects of catalytic activity.
Surface Organometallic Catalysts: Heterogeneous catalysts have several key advantages over homogeneous catalysts; they are easier to separate, more durable, and often more active. Most large-scale industrial processes use heterogeneous catalysts, and huge research efforts both within and without industry aim at improving selectivity, versatility, safety, and economy of these processes. Advances in heterogeneous catalysis are severely limited, though, by practical problems of leaching of catalysts from support surfaces, the dearth of mechanistic knowledge about most heterogeneous catalytic reactions, and a lack of understanding of surface effects on supported catalysts. Recent efforts to solve these problems have given rise to the techniques of surface organometallic chemistry and heterogenized homogeneous catalysis.
We will synthesize a new class of heterogenized homogeneous catalysts using a novel technique that can not only ameliorate catalyst leaching but also enable the detailed study of structure-activity relationships and catalyst-support interactions through controlled variation of well-defined catalytic species.
The Research Group
Current Members
Dr. Lihua Liu (postdoctoral associate), Xiaodi (Cindy) Kou (graduate student), Mauricio Quiroz Guzman (graduate student), Anne Bileck (undergraduate research assistant), Daniel Mendoza Espinosa (graduate student), Bernat Martinez Ortega (graduate student)
Former Members
Undergraduate Research Assistants: Brittany Filewood (UTSW Medical School), Gladys Keitany (TCU), Fred Garcia Flores (UDLA), Renu Ouseph (Princeton), Alfredo Angeles (Texas A&M), Mauricio Quiroz Guzman (TCU), Jennifer Knock (U of Houston), Daniel Mendoza Espinoza (TCU), Shin-heui Kim.
Other: Prof. Raul Fonseca Sandoval (UDLA), Dr. Iain Maley, Catalina Ibarra, M.S.(U of Birmingham), Dr. Xiaoyu Wang (UTA), Dr. Shreeyukta Singh (UTA), Dr. Amit Ghosh (TCU), Dr. Charles Gibbs (TCU).