Opportunities and challenges of well-defined nanocatalysts
Heterogeneous catalysis has grown from an art to a science. Numerous catalytic materials are being proposed every day in the literature, with surprising and exciting new reactivities being disclosed, and interesting novel concepts being proposed. The study of catalytic processes starting from better defined materials that are tuned in morphology, composition and shape is opening new perspectives for catalyst design. For example, use of nanocrystals in CO oxidation turned out to be crucially dependent on the interfacial contact of the support (ceria) with the metal nanoparticle active sites , while valorization of biomasses were employed as reactants for catalysis by carbon-supported, Pt and PtCo nanocrystals (NCs) with controlled size and composition . A particular type of structure is represented by nanosized core-shell phases, which proved to be superior catalysts in several catalytic reactions, such as methane combustion  as well as photocatalytic hydrogen evolution from biomass-derived substrates  or electrocatalytic water electrolysis  when integrated with multi-walled carbon nanotubes. Every day, nanotechnology applied to heterogeneous catalysts is creating new opportunities for important breakthroughs.