Wang-Jae Chun

Kinetic Study of Catalytic Conversion of Cellulose to Sugar Alcohols under Low‐Pressure Hydrogen

Efficient hydrolytic hydrogenation of cellulose to sugar alcohols under low H2 pressures has remained a challenge. This article deals with the conversion of cellulose by using a carbon‐supported Ru catalyst under H2 pressures as low as 0.7–0.9 MPa (absolute pressure at room temperature). Kinetic studies revealed that the Ru catalyst not only enhances the hydrolysis of cellulose to glucose and hydrogenation of glucose to sugar alcohols (sorbitol and mannitol), but also the degradation of sugar alcohols to C2–C6 polyols and gasses. The degradation path limits the total yield of sugar alcohols to less than 40 %. The yield of sugar alcohols is theoretically improved by increasing the ratio of the reaction rates of the cellulose hydrolysis, which is the rate‐determining step in the reaction, to the decomposition. Thus, a mix‐milling pretreatment of cellulose and the Ru catalyst together selectively accelerated the hydrolysis step and raised the yield up to 68 %, whereas the addition of acids in the cellulose conversion was less effective as a result of promotion of side‐reactions. These results demonstrate superior applicability of the mix‐milling treatment in the depolymerization of cellulose to its monomers.

Development of an in situ polarization-dependent total-reflection fluorescence XAFS measurement system

An in situ polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) spectroscopy system has been developed, which enables PTRF-XAFS experiments to be performed in three different orientations at various temperatures (273-600 K) and pressures (10(-10) approximately 760 torr). The system consists of a measurement chamber and a preparation chamber. The measurement chamber has a high-precision six-axis goniometer and a multielement solid-state detector. Using a transfer chamber, also operated under ultra-high-vacuum conditions, the sample can be transferred to the measurement chamber from the preparation chamber, which possesses low-energy electron diffraction, Auger electron spectroscopy and X-ray photoelectron spectroscopy facilities, as well as a sputtering gun and an annealing system. The in situ PTRF-EXAFS for Cu species on TiO2 (110) has been measured in three different orientations, revealing anisotropic growth of Cu under the influence of the TiO2 (110) surface.

Design of a high-temperature and high-pressure liquid flow cell for x-ray absorption fine structure measurements under catalytic reaction conditions

The design and performance of a new high-pressure and high-temperature cell for measurement of x-ray absorption fine structure (XAFS) spectra of solid catalysts working in a flowing liquid are presented. The cell has flat, high-purity sintered cubic boron nitride (c-BN) windows which can tolerate high temperature (900 K) and high pressure (10 MPa). The c-BN is a new material which has the highest tensile strength, second only to diamond, and is also chemically and thermally stable. The use of the cell is demonstrated for measurements of PtPdAl(2)O(3) and Ni(2)PSiO(2) hydrodesulfurization catalysts at reaction conditions. A technique called delta chi (Deltachi), involving determining the difference between XAFS spectra of the sample at reaction conditions and the bare sample, is introduced.

Molecular Catalysts Confined on and Within Molecular Layers Formed on a Si(111) Surface with Direct Si–C Bonds

Two examples of confined molecular catalysts are presented. PtCl(4) (2-) complexes are attached to a thiol-terminated monolayer by ligand exchange of Cl(-) with a thiolate group and incorporated in a multilayer of viologen moieties by ion exchange. All Cl(-) ligands are replaced by OH(-) or H(2) O before HER takes place. Ex situ and in situ XAFS measurements confirm that the Pt complexes accelerate HER without being converted into Pt particles.

Heterogeneous double-activation catalysis: Rh complex and tertiary amine on the same solid surface for the 1,4-addition reaction of aryl- and alkylboronic acids

Double-activation catalysis by a rhodium complex/tertiary amine catalyst for the 1,4-addition of organoboronic acids was investigated. A rhodium complex and a tertiary amine were co-immobilized on the same silica surface by silane-coupling reactions followed by complexation of the Rh species. Structures of the Rh complex and tertiary amine on the silica surface were determined by solid-state 13C and 29Si MAS NMR, XAFS, and XPS measurements. The immobilized tertiary amine accelerated the Rh-catalyzed 1,4-addition of phenylboronic acid to cyclohexenone. The role of the anchored tertiary amine in the 1,4-addition reaction was clarified by solid-state 11B MAS NMR: it activates the arylboronic acid forming a four-coordinate boron species, which then accelerates the transmetallation step in the Rh complex-catalyzed 1,4-addition. The silica-supported Rh complex/tertiary amine catalyst system could be applicable to the reaction of various aryl- and even alkyl-boronic acids.

A scanning tunneling microscopy observation of (√3x√3)R30° reconstructed Ni2P(0001)

A Ni2P(0001) single crystal surface has been studied in the framework of model catalysis with a low temperature scanning tunneling microscope (STM) under ultrahigh vacuum (UHV). We observed a previously unreported (√3×√3) R30° reconstruction and successfully recorded its atomically-resolved STM images. Two types of atomic arrangements have been found for this (√3×√3) R30° structure depending on annealing conditions during preparation. One shows a filled and the other one an empty network of polygons. Upon annealing to 940 K, only the latter empty type of structure has been observed.

Surface structure change of a [Pt4(µ-CH3COO)8]/SiO2 catalyst active for the decomposition of formic acid

Pt4-cluster/SiO2catalyst, prepared from the [Pt4(µ-CH3COO)8] cluster, has shown remarkably high catalytic activity with 100% selectivity to CO2 and H2 for the decomposition of formic acid as compared with the Pt-particle/SiO2 catalyst. In order to elucidate the genesis and the mechanism for catalysis by Pt4-cluster/SiO2, the samples were characterized by kinetics, Pt LIII-edge extended X-ray absorption fine structure (EXAFS), and FTIR spectroscopy. EXAFS and IR data revealed that the surface structure of the catalyst changed from the tetramer to dimers during an induction period, then to monomers which were active for the catalysis. Eventually Pt particles were formed which were of much lower catalytic activity. The structural transformations of the Pt4-cluster/SiO2 catalyst are discussed in relation to the catalytic reaction profiles.

Preparation and structure of a single Au atom on the TiO2(110) surface: control of the Au–metal oxide surface interaction

Three-dimensional Au structures on bare and organic-compound-modified TiO2(110) surfaces were interrogated by Au L3-edge polarization dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) spectroscopy. On the bare TiO2(110) surface, icosahedral Au55 nanoclusters were the main product found. When the surfaces were modified with ortho or meso mercaptobenzoic acid (o-MBA or m-MBA), Au was atomically dispersed. Sulfur atoms in the o- and m- MBA formed strong covalent bonds with Au to produce stable Au-MBA (o- and m- forms) surface complexes. On the other hand, only oxygen atoms on the surface did not make a strong enough interaction to stabilize the Au species. We discuss how the Au species formed on the modified TiO2(110) surface and the possibility to control the Au structure by the surface modification method.

Structures and dynamic behavior of catalyst model surfaces characterized by modern physical techniques

This paper reports the visualization of mobile pyridine on the terraces and site-specific adsorption of pyridine on the particular step sites on a TiO2(110)-(1×1) surface by scanning tunneling microscopy (STM), the anisotropic structure and reactivity of molybdenum oxides dispersed on TiO2(110)-(1×1) characterized by polarization-dependent total-reflection fluorescence x-ray absorption fine structure (PTRF-EXAFS), and the energy dispersive and real-time images of Au mesh on Si(111) recorded by a new x-ray photoemission electron miscroscopy (XPEEM).

A Pd–bisphosphine complex and organic functionalities immobilized on the same SiO2 surface: detailed characterization and its use as an efficient catalyst for allylation

Correction for ‘A Pd–bisphosphine complex and organic functionalities immobilized on the same SiO2 surface: detailed characterization and its use as an efficient catalyst for allylation’ by Ken Motokura et al., Catal. Sci. Technol., 2016, DOI: 10.1039/c6cy00593d.