Integrated nanocatalysts.

Despite significant advancements in catalysis research, the prevailing catalyst technology remains largely an art rather than a science. Rapid development in the fields of nanotechnology and materials chemistry in the past few decades, however, provides us with a new capacity to re-examine existing catalyst design and processing methods. In recent years, "nanocatalysts" has become a term often used by the materials chemistry and catalysis community. It refers to heterogeneous catalysts at nanoscale dimensions. Similar to homogeneous catalysts, freestanding (unsupported) nanocatalysts are difficult to separate after use. Because of their small sizes, they are also likely to be cytotoxic and pose a threat to the environment and therefore may not be practical for industrial use. On the other hand, if they are supported on ordinary catalyst carriers, the nanocatalysts would then revert to act as conventional heterogeneous catalysts, since chemists have known active metal clusters or oxide particles in the nanoscale regime long before the nanotechnology era. To resolve this problem, we need new research directions and synthetic strategies. Important advancements in catalysis research now allow chemists to prepare catalytic materials with greater precision. By controlling particle composition, structure, shape, and dimension, researchers can move into the next phase of catalyst development if they can bridge these old and new technologies. In this regard, one way seems to be to integrate active nanostructured catalysts with boundary-defined catalyst supports that are "not-so-nano" in dimension. However, these supports still have available hierarchical pores and cavity spaces. In principle, these devices keep the essence of traditional "catalyst-plus-support" type systems. They also have the advantages of nanoscale engineering, which involves both high level design and integration processes in their fabrication. Besides this, the active components in these devices are small and are easy to integrate into other systems. For these reasons, we refer to the final catalytic devices as integrated nanocatalysts (INCs). In this Account, we describe the current status of nanocatalyst research and introduce the various possible forms of design and types of integration for INC fabrication with increasing compositional and structural complexities. In addition, we discuss present difficulties and urgent issues of this research and propose the integration of the INCs into even more complex "supracatalysts" for future research.