Nanoscience and catalysis
The interface of the fields of catalysis and nanoscale materials is one of the most exciting areas of modern science and is at the forefront of the quest for a sustainable future. Because the field of nanoscience is in its relative infancy and little is known about the size and shape dependent properties of nano-scale materials, potential applications are neither focused nor limited but rather require intensive and comprehensive investigation. The field of nanotechnology has generated a great deal of interest primarily because on this size scale numerous new and potentially useful properties have been observed. These size dependent properties include melting point, specific heat, surface reactivities, catalytic, magnetic, and optical properties.
Catalysis and sustainability
The impact of catalysis in our current everyday lives cannot be understated. It was recently estimated that 35% of global GDP depends on catalysis. In addition, there are major hurdles for mankind that may be overcome with developments in catalysis. In particular, the goal of sustainability with regard to energy and environmental concerns will most certainly require significant contributions from catalysis.
Catalysts are materials that change the rate at which chemical equilibrium is reached without themselves undergoing any change. Through the phenomena of catalysis, very small quantities of a catalytic material can facilitate several thousand transformations. In addition to the remarkable increases in activity observed in the presence of a catalyst, an additional attribute of catalysts is that there is often a selectivity towards certain reaction products that is often of greater importance than activity since a highly selective process eliminates the generation of wasteful by-products.
In addition to the numerous proposed applications, there are also concerns regarding the environmental and health implications associated with the use of these materials. These concerns are however particularly difficult to address because the properties of nanoscale materials are different from both the molecular and bulk forms and can even change as a result of small differences in size and shape. A general understanding of the chemical and physical properties of nanoscale materials as a function of size and shape is necessary to address the concerns about nanomaterials and their applications.
Richards’ group research
A three-fold approach is being pursued in the Richards’ laboratory to establish an understanding of nanoscale materials: 1) preparation of nanomaterials (metals and metal oxides) with a controlled size, shape and composition then combining these materials via the ‘precursor’ concept to form composites; 2) characterization of the physical and chemical properties as a function of size, shape and composition; and 3) examination of the factors that influence the stability of the nanoscale materials and their properties (particularly catalysis).
One of primary obstacles facing scientists working in the field of nanotechnology is the development of an understanding of how particle size and shape (on the nanoscale) influences the physical and chemical properties of the material. For example, nanoscale gold exhibits different colors and UV adsorptions from its bulk and molecular counterparts and furthermore it has been demonstrated that small nanoparticles of gold are excellent catalysts for the oxidation of CO while bulk gold is well known for its inertness.
We are currently exploring the preparation of novel heterogeneous nano-scale catalytic materials utilizing the “precursor” concept. In this way, we independently prepare and characterize the catalyst and support materials then bring the two components together in a final step. This approach allows a comprehensive study of the effects the two components have upon each other in the final material and could ultimately lead to the tailoring of catalytic properties. Further, this approach allows us to study the extent to which the two heterogeneous catalyst components influence each other.
Catalysis and environmental concerns
A focus on catalysis is an important component of these studies because it has been observed that such parameters as catalytic activity and selectivity are dramatically affected by particle size and shape. Thus, the study of catalytic properties provides not only important information about the chemical and physical properties of the nanomaterials but also provides a ‘handle’ by which one can observe how these properties are affected by various conditions. For example, if a material possesses a very high catalytic activity when it is prepared as a nanoparticle which differs from the bulk and molecular forms, then the catalytic activity is a valuable tool to probe the conditions under which the nanoscale properties are demonstrated. Therefore, if a catalytic nanomaterial looses activity under certain conditions (for example with exposure to water) and takes on the properties of the bulk material, then (with proper studies into the exact mechanism) one can begin to develop a set of boundary conditions which can be applied to assess whether the environmental or health risk of the bulk or nanomaterial form is applicable. Finally, catalysis is likely to be one of the primary applications for nanomaterials and therefore among the highest levels of human and environmental exposure with expected products including: fuel cells for cellular telephones, laptop computers and automobiles; air and water purification systems; hydrogen storage materials; and various large scale processes within the chemical and petrochemical industry.