The Nanoscience Revolution: Merging of Colloid Science, Catalysis and Nanoelectronics

Abstract

The incorporation of nanosciences into catalysis studies has become the most powerful approach to understanding reaction mechanisms of industrial catalysts and designing new-generation catalysts with high selectivity. Nanoparticle catalysts were synthesized via controlled colloid chemistry routes. Nanostructured catalysts such as nanodots and nanowires were fabricated with nanolithography techniques. Catalytic selectivity is dominated by several complex factors including the interface between active catalyst phase and oxide support, particle size and surface structure, and selective blocking of surface sites, etc. The advantage of incorporating nanosciences into the studies of catalytic selectivity is the capability of separating these complex factors and studying them one by one in different catalyst systems. The role of oxide-metal interfaces in catalytic reactions was investigated by detection of continuous hot electron flow in catalytic nanodiodes fabricated with shadow mask deposition technique. We found that the generation mechanism of hot electrons detected in Pt/TiO 2 nanodiode is closely correlated with the turnover rate under CO oxidation. The correlation suggests the possibility of promoting catalytic selectivity by precisely controlling hot electron flow at the oxide-metal interface. Catalytic activity of 1.7-7.2 nm monodispersed Pt nanoparticles exhibits particle size dependence, demonstrating the enhancement of catalytic selectivity via controlling the size of catalyst. Pt-Au alloys with different Au coverage grown on Pt(111) single crystal surface have different catalytic selectivity for four conversion channels of n-hexane, showing that selective blocking of catalytic sites is an approach to tuning catalytic selectivity. In addition, presence and absence of excess hydrogen lead to different catalytic selectivity for isomerization and dehydrocyclization of n-hexane on Pt(111) single crystal surface, suggesting that modification of reactive intermediates by the presence of coadsorbed hydrogen is one approach to shaping catalytic selectivity. Several challenges such as imaging the mobility of adsorbed molecules during catalytic reactions by high pressure STM and removing polymeric capping agents from metal nanoparticles remain.

Synthesis, catalysis, surface chemistry and structure of bimetallic nanocatalysts

“…1 Bimetallic materials are important catalysts due to their numerous advantages. [2][3][4][5][6][7] For example, composition (at large scale), coordination environment of the metal atom (on the atomic scale), and electronic state of the parent metal can be tuned systematically due to the spectacular success in the synthesis of bimetallic nanoparticles in the recent decade. [8][9][10][11][12][13] As heterogeneous catalysis is performed on the surface of a catalyst, the surface structure and chemistry of a bimetallic catalyst in term of geometric and electronic structures of metal atoms on the surface are the most important parameters which determine the catalytic performance of a bimetallic catalyst.…”

Nanocrystal bilayer for tandem catalysis

“…Metal nanocrystals with well-controlled shape and size are interesting materials for catalyst design from both electronic structure and surface structure aspects. 3,4,5 From the electronic structure point of view, small metal nanoclusters have size-dependent electronic states, which make them fundamentally different from the bulk. From the surface structure point of view, the shaped nanocrystals have surfaces with well-defined atomic arrangements.…”

Probing Hot Electron Flow Generated on Pt Nanoparticles with Au/TiO2Schottky Diodes during Catalytic CO Oxidation

“…The phenomena associated with reduced size, such as the variation of reaction intermediates with metal nanoparticle size and shape and the role of the oxidemetal interface, are fundamental questions in catalysis. Synthesis of nanoparticles by colloid chemistry has been one of major directions to address these questions 5 .…”