Size and Shape Control in Heterogeneous Catalysis Synthesis

University Of California-Riverside, Riverside CA

Investigators

Abstract

CBET-0752142 Zaera Traditionally, mild catalytic reactions such as double-bond hydrogenations and isomerizations in unsaturated organics have been assumed to not depend on the structure of the surface of the catalyst. However, that conclusion has been based on studies using ill-defined catalysts consisting of metal particles with wide distributions of sizes and shapes; recent catalysis and surface-science experiments indicate that these systems may in fact display some structure sensitivity. Our hypothesis is that selectivity in mild catalytic reactions may be controlled by careful design of catalysts with well-defined structures. This proposal describes research to develop size and shape selected catalysts by using new nanotechnologies in order to test that hypothesis. Specifically, novel colloidal and sol-gel synthetic routes will be developed to produce supported metal (Pt) particles with narrow distributions of sizes and well-defined shapes. This work will be performed in three stages. (1) First, metal particles with well-defined sizes and shapes, including tetrahedral and cubic forms, will be prepared using colloidal procedures deriving from a recent report by the research group of Prof. El-Sayed. Size and shape will be independently controlled in order to individually probe their effect on catalysis. (2) Next, those particles will be dispersed on high-surface-area solids and activated for heterogeneous catalysis. Three approaches will be attempted here at first: impregnation, polymer displacement by easier-to-remove thiol groups, and in-situ sol-gel growth of oxides in the presence of the colloidal particles. (3) Finally, these catalysts will be characterized, and tested for the promotion of two specific reactions: the selective hydrogenation of unsaturated aldehydes to unsaturated alcohols, and the cis-trans isomerization of double bonds in olefins. These reactions have been chosen because it is believed that they may be selectively promoted by the (111) surface facets exposed in tetrahedral particles (in contrast with the (100) planes that terminate the cubic particles). Ultimately, we aim to combine the use of novel synthetic methods with the understanding achieved from studies with model systems to design selective metal supported catalysts for mild catalytic processes based on control of their size and shape. The general basic knowledge generated by our work is also likely to apply to a broader set of synthetic and catalytic issues involving colloidal and sol-gel chemistry and structure sensitivity in catalysis. The value of our approach is that it combines knowledge developed by three separate communities, colloidal chemists, catalyst developers, and surface scientists. If our hypothesis is proven true, it may have great repercussions on the design of new industrial processes, to, for instance, improve fat production in the food industry (where trans olefins are to be avoided because of their adverse health effects), or advance new routes for fine chemical synthesis. Our project will also contribute to the development of a better basic understanding of the chemistry of supported colloidal particles, and of the chemical kinetic factors that affect selectivity on surfaces. New experimental technology with potential broad appeal such as the synthesis of well-defined supported catalysts will be developed. The knowledge deriving from this work may also be of great use for educational purposes by providing data to illustrate basic solid-state synthesis and catalysis principles in undergraduate and graduate classes. Collaborations with Latin American research groups will be forged, and student participation from underrepresented groups in research (Hispanics in particular) will be strongly pursued.