Chemical design and characterization of catalysts and catalysis: an approach to dynamic catalyst design

Premodified Surface Method to Obtain Ultra-Highly Dispersed Metals and their 3D Structure Control on an Oxide Single-Crystal Surface

Precise control of the three-dimensional (3D) structure of highly dispersed metal species such as metal complexes and clusters attached to an oxide surface has been important for the development of next-generation high-performance heterogeneous catalysts. However, this is not easily achieved for the following reasons. (1) Metal species are easily aggregated on an oxide surface, which makes it difficult to control their size and orientation definitely. (2) Determination of the 3D structure of the metal species on an oxide powder surface is hardly possible. To overcome these difficulties, we have developed the premodified surface method, where prior to metal deposition, the oxide surface is premodified with a functional organic molecule that can strongly coordinate to a metal atom. This method has successfully provided a single metal dispersion on an oxide single-crystal surface with the 3D structure precisely determined by polarization-dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS). Here we describe our recent results on ultra-high dispersions of various metal atoms on TiO₂ (110) surfaces premodified with mercapto compounds, and show the possibility of fine tuning and orientation control of the surface metal 3D structures.

Surface molecular engineering in the confined space of templated porous silica

Recent developments in molecular surface engineering inside the confined space of porous materials are surveyed including a new nomenclature proposal.

Advanced chemical design with supported metal complexes for selective catalysis

This review covers several recent topics of novel catalyst design with supported metal complexes on oxide surfaces for selective catalysis such as chiral self-dimerization to create asymmetric oxidative coupling catalysis, surface functionalization with achiral reagents to promote asymmetric catalysis, and molecular imprinting to design shape-selective catalysis. The new concepts and designs find wide applications to a variety of selective catalysts.

Bound Site of Mo Atoms and Its Local Structure in a Mo/HY Catalyst Characterized by Extended X-ray Absorption Fine Structure and Density Functional Calculation

The bound site of Mo atoms and its local structure in a Mo/HY catalyst have been determined by detailed analysis of extended X-ray absorption fine structure (EXAFS). Molybdenum was introduced in the supercage of HY zeolite by cycles of saturated adsorption of Mo(CO)6 at room temperature and subsequent thermal decomposition at 573 K. Two Mo atoms per supercage were immobilized in each CVD-thermal treatment cycle. The Mo loading increased linearly with the cycles up to three cycles at saturation, where six Mo atoms were supported. Temperature-programmed decomposition of the adsorbed Mo(CO)6 was also characterized by GC, QMS, and FT-IR, respectively. The EXAFS analysis including multiple scattering based on theoretical calculations revealed that Mo bound with two oxygen atoms connects to Al, where one of the two oxygen atoms had been associated with a proton. The bound site is called the S(III)' site. The zeolite framework was significantly distorted by the introduction of low-valent Mo, resulting in isolation of the [MoO2Al] unit from the surrounding zeolite framework due to a quasi-disruption of Si-O bonds adjacent to the unit. In the mild oxidation of the low-valent Mo/HY sample two Mo=O bonds were newly formed and the position of Mo was displaced by 0.06 nm so that the distortion of zeolite framework around the Al atom was relieved. The structures were also supported by DFT calculations. This study is the first example that the position of metal cation in zeolite was determined unambiguously by the EXAFS analysis.