Technology Review

Background Catalysts improve the rate or selectivity of chemical reactions without being consumed in the chemical reaction. “Supported heterogeneous catalysts” consist of catalytic active sites carried on the surfaces of porous solids, known as “supports”. Such catalytic materials are especially important for chemical manufacturing because they minimize the loss of valuable catalytic materials and the need for catalyst separation and recovery. Homogeneous catalysts are distributed throughout the reaction medium on a molecular scale and may be eventually incorporated into the reaction products. Catalysis has been the cornerstone of chemical manufacturing for decades. In 1998, over $3 trillion in goods and services were created worldwide based on chemical processes employing catalysts valued at over $12 billion in several sectors of the chemical industry, including polymers, pharmaceuticals, and petrochemicals. Improvements in catalyst activity and selectivity offer tremendous potential benefits for petrochemical and pharmaceutical manufacturing. Heterogeneous catalysis is also receiving new attention as a critical component of emerging technologies for environmental protection and alternative energy sources. Nanometer-scale features control the activity, selectivity, and lifetime of catalysts. Recent advances in our ability to design, synthesize, characterize, and manipulate nanoscale catalyst features signify the emergence of “catalysis nanoscience” as a distinct research endeavor. Research in catalysis nanoscience seeks fundamental understanding of the relationships among catalyst synthesis procedures, active site structure on the atomic and nano-scales, chemical reaction mechanisms, and catalyst activity, selectivity, and lifetime. Advances in this area may ultimately lead to (1) first-principles design of catalysts for specific chemical reactions, as well as (2) conceptualization and design of novel catalytic reaction schemes that take advantage of selfassembly of “designer” catalytic sites in predetermined twoand three-dimensional configurations. Recent attempts have been also made to bridge different catalysis areas from biocatalysis to homogeneous to heterogeneous processes. Bimetallic clusters represent one such bridging element between homogeneous and heterogeneous catalysis. The ultimate goal of this type of work is to combine the high selectivity of homogeneous cluster catalysts with the stability and versatility of supported heterogeneous catalysts.