Masakazu Daté

Microscope Analysis of Au–Pd/TiO2 Glycerol Oxidation Catalysts Prepared by Deposition–Precipitation Method

Gold–palladium bimetallic nanoparticle catalysts prepared by a deposition–precipitation method were effective for aerobic oxidation of glycerol to carboxylic acids. The role of palladium was to suppress C–C bond cleavage that is responsible for the formation of C2 by-product molecules. The nanoparticles were observed by microscope techniques, which further enabled characterizing the respective locations of Au and Pd within the particles.Graphical Abstract

Ultramarine colored: Solid-phase elution of Pt into perovskite oxides

We have found a new route for preparing Pt containing perovskites. Ba containing perovskite powder, (La 0.7 Sr 0.2 Ba 0.1 )ScO 3–δ (LSBS), reacted with Pt foil at 1898 K in air, and formed ultramarine colored Pt containing perovskite, (La 0.7 Sr 0.2 Ba 0.1 )(Sc,Pt)O 3–δ , without changing the GdFeO 3 -type structure. The chemical compositions of the samples before and after firing, measured with inductively coupled plasma (ICP) optical emission spectrometry, were La: Sr: Ba: Sc = 0.70(1): 0.206(4): 0.101(2): 0.98(2) and La: Sr: Ba: Sc: Pt = 0.70(1): 0.197(4): 0.085(2): 0.95(2): 0.0062(2), respectively. The reaction proceeded not only at the interface between perovskite powder and Pt foil, but also over whole powder surface. We name this new preparation method the “solid-phase elution (SE) method”, because the process involves elution of Pt ions from the Pt foil to the LSBS perovskite lattice. It is expected that we can control the amount of Pt introduced into perovskites by using the SE method after optimizing the reaction time and temperature.

Noble Metal Collection through Air: Perovskite Oxide as a Novel Collector

Noble metals, which have a wide range of uses from jewellery to medical and industrial applications, are expensive and can only be obtained from a limited number of sources. 2] Recycling is thus important for the conservation of these limited resources. There are two major recycling methods: pyrometallurgical and hydrometallurgical. In typical processes, the former uses molten metal as a collector (e.g. Cu or Pb) and requires a large-scale plant that often produces air pollution, whereas the latter, in which noble metals are dissolved in strong acid, such as aqua regia, affords low yields of the metals. Here we report a novel noncontact recycling method that involves collection of noble metals by perovskite oxides. Platinum mesh was placed on either side of La0.7Sr0.2Ba0.1ScO3 d perovskite (hereafter denoted as LSBS) powder on a shallow plate, and the plate was covered and heated in air at 1798 K for 10 h. The faint pink LSBS powder turned dark blue during the heating period (Figure 1 a, b), and the Pt content in the LSBS was 0.5 wt %, as indicated by inductively coupled plasma atomic emission spectroscopy (ICP-AES). We recently reported that Pt can be introduced to LSBS by calcining the perovskite on a Pt foil and that Pt cations occupy the Sc sites of the perovskite lattice, while the perovskite structure was preserved after the introduction of Pt. Our current results indicate that the Pt source does not have to be in contact with the perovskite oxide for the incorporation of Pt. We also found that Pt was introduced through air into other perovskite oxides, for example, SrZr0.9Y0.1O3 d, LaSc0.95Zn0.05O3 d, and La0.9Ca0.1AlO3 d. The strong interaction between the noble metals and the perovskite oxides indicate the potential applicability of the oxides for the recycling of the metals. Therefore, we investigated the collection of noble metals from model waste materials. For example, when 0.5 g of Ru/Al2O3 catalyst with a Ru content of 1.0 wt % was heated at 1798 K for 10 h in the presence of 2 g of LSBS powder, the catalyst powder changed from dark green to pure white (Figures 1 c,d), and the amount of Ru remaining on the Al2O3 support was below the detection limit of the X-ray diffraction (XRD) instrument. The LSBS powder turned orange during the heating period, and the Ru content in LSBS after heating was 0.2 wt %. This result indicates that 80 % of the Ru was collected by LSBS from the Ru/Al2O3. The perovskite structures were observed by XRD before and after heating of the LSBS powder (Supporting Information). Similar results were obtained for Pt/Al2O3, Pd/Al2O3, Rh/Al2O3, and Ir/Al2O3. To quantify the ability of the perovskite oxide to absorb noble metals, we calcined LSBS with sources of pure noble metals and then measured the noble metal contents in the LSBS (Table 1). The Rh, Ir, and Ru contents were considerably higher than those of Pt and Pd. Note that the vapor pressures of the noble metal oxides are generally much higher than those of the corresponding noble metals at the calcination temperatures (Table 1), although the vapor pressure of Pd is exceptionally high. 8] Because the vapor pressures of the noble metal oxides were reflected in the relative amounts of the noble metals absorbed by LSBS, we propose that the metals, except for Pd, were evaporated as oxides generated by reaction with oxygen in air. Direct evaporation of Pd metal predominates above 1273 K. Note that in the perovskite oxides we used for our noncontact method for collection of noble metals, one of the components in an ideal ABO3-type perovskite oxide (A or B) was partly replaced with 5–30 mol % of a foreign element with a different valence. This substitution was compensated for by a change in oxygen composition, which resulted in an intrinsically high density of oxygen defects. In fact, perovskite oxides with ideal valence, such as LaScO3, do not absorb Pt even after calcination on a Pt foil at 1898 K for 10 h. This result suggests that a high density of oxygen defects may have played an im[a] Dr. M. Dat , Dr. T. Fujitani Research Institute for Innovation in Sustainable Chemistry National Institute of Advanced Industrial Science and Technology (AIST) 16-1 Onogawa, Tsukuba 305-8569 (Japan) Fax: + 81-29-861-8173 E-mail : m-date@aist.go.jp [b] Dr. K. Nomura, Dr. H. Kageyama Research Institute for Ubiquitous Energy Devices National Institute of Advanced Industrial Science and Technology (AIST) 1-8-31 Midorigaoka, Ikeda 563-8577 (Japan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.201000618. Figure 1. Photographs of LSBS perovskite oxide and noble-metal sources before and after calcination at 1798 K for 10 h on an alumina plate: a) before and b) after calcination with Pt mesh placed on both sides and c) before and d) after calcination with Ru/Al2O3 placed on the left side.

Nanoparticle arrangement by DNA-programmed self-assembly for catalyst applications

To examine the applicability of DNA-programmed self-assembly to preparation of nanoparticle-supported catalysts, the authors performed the arrangement control of Au nanoparticles on powder supports (TiO2 and glass) with this scheme. Scanning electron microscopy and atomic force microscopy observations confirmed that designed arrangement of two kinds of Au nanoparticles is possible on powder and crystal supports. Although catalytic activity of Au-particle/TiO2 systems for CO oxidation was almost inhibited by the presence of DNA, it was successfully recovered by the oxygen plasma treatment. These results indicate that the DNA-programmed self-assembly can be used as a preparation method of novel catalysts with designed nanostructures.