Tetsutaro Ohmichi

A novel conversion process for waste slag: synthesis of a hydrotalcite-like compound and zeolite from blast furnace slag and evaluation of adsorption capacities

The main components of blast furnace slag (BFS) are CaO, SiO2, A12O3, MgO and slight amounts of transition metals such as Fe, Ti and Mn. We successfully synthesized a hydrotalcite-like compound from BFS via a convenient chemical process: acid-leaching and precipitation. After the HCl acid-leaching process, BFS was separated into hydrated silica with 92 wt% SiO2 content and leaching solution including other components, which afforded a hydrotalcite-like compound after subsequent NaOH addition in high yield (6.2 g from 10.0 g of BFS). By means of XRD and chemical analysis, the product synthesized at 100 °C was identified to be a Ca-Al-based hydrocalumite compound with the stoichiometric molar ratio of Ca : Al : Cl = 2 : 1 : 1, incorporating other metal cations in its structure. The phosphate adsorption capacity of the raw slag was 1.5 mg P/g but increased to over 40 mg P/g when converted into the hydrotalcite-like compound, which was more than three times greater than that of conventional Mg-Al-based hydrotalcite. Furthermore, single-phase A- and X-type zeolites with high crystallinities and excellent water adsorption capacities (247 and 333 mg g−1, respectively) were successfully synthesized using the residual silica through a hydrothermal treatment for 6 h at 100 °C. This conversion process, which enables us to fabricate two different kinds of valuable materials from BFS at low cost and through convenient preparation steps, is surely beneficial from the viewpoint of economical use of BFS.

Transesterifications using a hydrocalumite synthesized from waste slag: an economical and ecological route for biofuel production

Blast furnace slag (BFS), a high volume byproduct resulting from iron-making processes, was used as a low-cost and abundant precursor for preparing a hydrocalumite, and the thus prepared slag-made hydrocalumite and its derivatives were applied for transesterifications of esters including triglycerides. In the transesterification of n-ethyl butyrate, calcined samples provided higher catalytic activities than those of the as-synthesized hydrocalumite due to the interfusion of slag-derived impurity elements, such as Fe and Mn, which act as catalyst promoters. Furthermore, the catalyst calcined at 800 °C in air worked as an efficient catalyst for the transesterification of soybean oil with methanol, affording up to 97% yield of fatty acid methyl esters (FAME) after 6 h under relatively moderate reaction conditions (i.e., methanol/soybean oil = 12, reaction temperature = 60 °C, use of 1 wt% catalyst), and its catalytic performance was reproduced even after air-exposure for 1 day. It is believed that the slag-made hydrocalumite can replace existing solid base catalysts as a low-cost alternative for biodiesel production and potentially contribute to the sustainable chemical processes in an economical and ecological way.

A novel synthetic route to hydroxyapatite–zeolite composite material from steel slag: investigation of synthesis mechanism and evaluation of physicochemical properties

Steel slag is a commercial waste material mainly consisting of SiO2, Al2O3 and CaO, the former two chemicals being major components of zeolites and the latter a major component of hydroxyapatite (HAP). A hydroxyapatite–zeolite composite material (HAP-ZE) was successfully synthesized from steel slag by adding appropriate chemical reagents, H3PO4 and NaOH, viaaging at 363 K for approximately 2 days. The synthesis mechanism and structural properties were clarified by detailed analysis using XRD, FT-IR, SEM, EDX, elemental mapping, and N2 adsorption–desorption measurements. The Ca and Mg components were chemically reacted with phosphate in the early stages of aging, being precipitated as Mg-substituted HAP with (Ca + Mg)/P = 1.67. After 2 days of aging, well-crystallized HAP and faujasite-type zeolite (Na type X-zeolite with SiO2/Al2O3 = 2.4) were separately formed via a non-simultaneous crystallization process. The over-run in aging time led to phase transformation from FAU-zeolite to Pl-zeolite. The minor components in steel slag such as Fe and Mn had little effect on the synthesis of HAP-ZE; however, the inherent SiO2/Al2O3 ratio in steel slag led to a lower yield from the zeolite phase. Furthermore, from the adsorption assessment of volatile organic compounds (VOCs), fatty acid and protein, the HAP-ZE synthesized under optimum conditions was found to have adsorption properties comparable to those of pure zeolite and HAP.

Waste-Slag Hydrocalumite and Derivatives as Heterogeneous Base Catalysts

Blast furnace slag (BFS), a high-volume byproduct resulting from iron-making processes, can be considered as a low-cost and abundant precursor for preparing layered double hydroxide (LDH) compounds. Here we demonstrate that a Ca-based LDH compound (hydrocalumite) synthesized from waste BFS through facile two-step procedures and its derivatives work as useful heterogeneous base catalysts for multiple chemical reactions including the Knoevenagel condensation, oxidation of alkylaromatics with O(2), transesterification, and cycloaddition reaction of epoxides with atmospheric CO(2). Structures were verified by using XRD and thermogravimetric analysis. The surface basicity and coordination geometry of the active metal species that substantially affect the catalytic activity were investigated by CO(2)-temperature programmed desorption (TPD) and X-ray absorption fine structure (XAFS) measurements, respectively. These characterization results revealed that the slag-derived impurity elements, such as Fe, Ti, and Mn, effectively act either as active sites or as catalyst promoters in particular reactions and that the kind of guest counter anion (Cl(-) or NO(3)(-)) also plays a key role for achieving high catalytic efficiencies. In any reaction, the catalyst was easily separated by filtration and recyclable in multiple catalytic runs with retention of its activity and fine selectivity, irrespective of its considerable impurity level. It is believed that the slag-made hydrocalumite can replace existing LDH catalysts as a low-cost alternative and potentially contribute to sustainable chemical processes.

Catalysis of nanosized Pd metal catalyst deposited on Ti-containing zeolite by a photo- assisted deposition (PAD) method*

Using a photo-assisted deposition (PAD) method, nanosized Pd metal can be highly dispersed on Ti-containing silicalite zeolite (TS-1) under UV-light irradiation (PAD-Pd/TS-1). The nanosized Pd metal was deposited directly on the photo-excited tetrahedrally coordinated titanium oxide species (tetra-Ti-oxide) of TS-1 zeolite. Under the flow of H2 and O2 in water solvent, the efficient formation of H2O2 could be observed by the PAD-Pd/TS-1 catalyst under mild reaction conditions (ambient temperature and atmospheric pressure). Furthermore, the presence of phenol in this reaction system led to the formation of the products from the partial oxidation of phenol with the formed H2O2.

Active Skeletal Ni Catalysts Prepared from an Amorphous Ni‐Zr Alloy in the Pre‐Crystallization State

Skeletal Ni catalysts were prepared from an amorphous Ni40Zr60 alloy (a-NiZr) by heating at various temperatures under vacuum, followed by the selective extraction of Zr moieties by an HF treatment. Each sample was characterized by various spectroscopic methods, and the catalytic performance was tested in the hydrogenation of 1-octene. The differences in preparation temperatures of a-NiZr strongly affected the catalytic performance of the obtained catalysts, whereby those prepared from heated a-NiZr in the pre-crystallization state exhibited higher catalytic activity. Especially, moderate thermal treatment of a-NiZr at a temperature slightly lower than that for its crystallization, that is, ~573 K, resulted in a significant enhancement of the catalytic activity. Such prepared skeletal Ni catalyst can also be used efficiently for hydrogen generation from aqueous hydrazine.

Skeletal Ni Catalysts Prepared from Amorphous Ni–Zr Alloys: Enhanced Catalytic Performance for Hydrogen Generation from Ammonia Borane

Skeletal Ni catalysts were prepared from Ni-Zr alloys, which possess different chemical composition and atomic arrangements, by a combination of thermal treatment and treatment with aqueous HF. Hydrogen generation from ammonia borane over the skeletal Ni catalysts proceeded efficiently, whereas the amorphous Ni-Zr alloy was inactive. Skeletal Ni prepared from amorphous Ni30 Zr70 alloy had a higher catalytic activity than that prepared from amorphous Ni40 Zr60 and Ni50 Zr50 alloys. The atomic arrangement of the Ni-Zr alloy also strongly affected the surface structure and catalytic activities. Thermal treatment of the amorphous Ni-Zr alloys at a temperature slightly lower than the crystallization temperature led to an increase of the number of surface-exposed Ni atoms and an enhancement of the catalytic activities for hydrogen generation from ammonia borane. The skeletal Ni catalysts also showed excellent durability and recyclability.

Skeletal Au prepared from Au–Zr amorphous alloys with controlled atomic compositions and arrangement for active oxidation of benzyl alcohol

Skeletal (nanoporous) gold catalysts were prepared from Au–Zr amorphous alloys by immersion in HF solution to extract Zr moieties. The catalytic performance of the skeletal Au catalyst for the oxidation of benzyl alcohol to benzaldehyde was examined using O2 as an oxidant. The amount of benzaldehyde formed over skeletal Au treated with HF solution for 1 h was the highest among the prepared samples, despite the low surface area. Detailed characterization indicated that residual ZrO2 species on the skeletal Au promoted the oxidation reaction. The oxygen storage capacity (OSC) of skeletal Au was measured for the quantitative estimation of active sites and showed a positive correlation with the catalytic activity of skeletal Au, verifying the presence of Au–ZrO2 interfaces. Skeletal Au was also prepared from a Au–Zr crystalline alloy and its catalytic activity was compared with that of the one prepared from the amorphous alloy. The atomic arrangement of the Au–Zr amorphous alloy had a strong effect on the catalytic activity due to the surface structure (coordination number and morphology) of skeletal Au. The unsaturated Au atoms created in the skeletal Au catalysts contributed to the reduction of activation energy for oxidation of benzyl alcohol.

Preparation of nano-sized Pt metal particles by photo-assisted deposition (PAD) on transparent Ti-containing mesoporous silica thin film

We have investigated a novel technique for the preparation of nano-sized Pt metals on Ti-containing mesoporous silica (TMS) thin film by photo-assisted deposition (PAD). The transparent TMS thin film was prepared on a quartz plate through sol—gel/spin coating. XRD, UV-Vis and Ti K-edge XAFS measurements revealed the formation of isolated Ti oxide species with a tetrahedral-coordination geometry in the silica framework. Deposition of Pt metal precursor on TMS thin film under UV-light irradiation, followed by reduction with molecular hydrogen, afforded a transparent thin film (Pt/TMS). The formation of highly dispersed nano-sized Pt metals having narrow size distributions was determined by Pd LIII-edge XANES and TEM analysis. The TMS and Pt/TMS thin films have been demonstrated to exhibit a strong hydrophilic property, even before UV irradiation, compared to the common mesoporous silica and TiO2 thin films. After UV-light irradiation, the contact angle of water droplet on the TMS and Pt/TMS thin films became extremely lower, indicating the appearance of the photo-induced super-hydrophilic property.

PROPERTIES OF Fe-C-Si, Cu-Al, Al-Si ALLOY WIRES PRODUCED BY IN-ROTATING-WATER-SPINNING PROCESS

Fe-C-Si, Cu-Al and Al-Si alloy wires with round cross-section have been spun directly from the alloy melts by the In-Rotating-Water-Spinning Process developed in this Lab. and their structure and mechanical properties have been examined. The cooling rate in the liquid/solid region was estimated to range from 10 3 to 10 5 K/s depending on alloys. Metastable austenite with high strength and fine ductile wires have been obtained.