Akifumi Ueno

XPS and TPD characterization of manganese-substituted iron-potassium oxide catalysts which are selective for dehydrogenation of ethylbenzene into styrene

Abstract Manganese-substituted (0–100%) iron–potassium oxide (Mn–Fe–K) catalysts which are selective for dehydrogenation of ethylbenzene to styrene were prepared by the alcoxide sol–gel method. They have been characterized by XPS, BET surface area measurement and TPD studies. The differences of surface properties between the Mn–Fe–K catalysts and unsubstituted iron–potassium oxide (Fe–K) catalyst were reasonably reflected in the XPS spectrum of oxygen (O 1s) and potassium (K 2p). The XPS spectra of Mn–Fe–K catalysts based on the binding energy shifts of O 1s and K 2p bands resembled those of KFeO2 as an active phase for the dehydrogenation of ethylbenzene. On the contrary, the unsubstituted Fe–K catalyst showed the XPS spectra including KOH and Fe3O4 as inactive phases. The presence of Mn ions in the catalyst matrix (γ-Fe2O3, MnFe2O4) results in stabilization of the KFeO2 active phase, and did not affect catalytic behavior of the K-promoted iron based oxide. The maximum enhancement of catalytic activity at the optimum 20% Mn-substitution is owing to the large surface area, the minimization of carbonaceous deposition, and the retardation of pyrolysis of KFeO2 to KOH and Fe3O4.

Thermal and chemical recycle of waste polymers

Abstract Catalytic degradations of polyethylene into fuel oils and of polystyrene into styrene monomer have been studied using solid acids and bases as catalysts. Solid acids such as silica-aluminas and ZSM-5 zeolite were found to be effective to degrade waste polyethylene into fuel oils, and solid bases such as BaO and K 2 O were concluded to be effective to convert waste polystyrene into styrene monomer. A design of recyclable polystyrene films will be briefly mentioned.

Mn-substituted Fe–K mixed oxide catalysts for dehydrogenation of ethylbenzene towards styrene

Abstract K-promoted iron oxide (Fe–K) and partially Mn-substituted Fe–K catalysts prepared by the sol–gel method showed improvement of catalytic activity in the dehydrogenation of ethylbenzene to styrene. Manganese, compared to the other transition metals (Co, Ni, Cu and Zn), was found to be an effective additive element for enhancement of the catalytic activity as well as suppressing of coke deposition. The Mn-substituted Fe–K catalysts with the atomic content of Mn in Mn–Fe mixed oxides: Mn/(Mn+Fe) (between 0 and 100%) were characterized using X-ray diffraction. The largest rate formation of styrene was observed for catalyst with 20% of manganese. On the other hand, no change in activation energy was observed. The lattice strain of the spinel phase between γ-Fe 2 O 3 and MnFe 2 O 4 exhibited the maximum with 20% content of Mn. The experimental data suggest that enhancement of catalytic activity by addition of the Mn is responsible for increasing of the number of active sites in the spinel phase of the catalyst.

Chlorine gas recovery from polyvinyl chloride

Abstract Hydrogen chloride, evolved from polyvinyl chloride by heating at 533 K, was fixed by metal oxides at 533–673 K to form the corresponding metal chlorides. The metal chlorides thus formed were calcined at 623–723 K under an oxygen flow in order to recover chlorine gas and to regenerate the metal oxides. Among the metal oxides employed, cobalt oxide was the most effective both for the fixation and release of chloride ions. With the iterative use of cobalt oxide for HCl fixation at 573 K and subsequent Cl2 release at 673 K, the amount of chloride ions fixed by cobalt oxide powder decreased to one-fifth of those fixed by the fresh cobalt oxide. This is due to the decrease in the BET surface area of cobalt oxide caused by the iterative use.

Effects of Catalyst Heating Rates Upon the Activity of Silica-Supported Silicomolybdic Acid Catalysts for Methane Partial Oxidation

Silica-supported silicomolybdic acid (SMA) catalysts showed a very high activity for partial oxidation of methane into formaldehyde at 873 K in the presence of an excess amount of water vapor in feed. However, the high activity was observed only when the catalysts were heated to 873 K with very high heating rates such as 100 K min-1. In this article, the reason why these high heating rates are necessary to exhibit the higher catalytic activity into formaldehyde will be discussed based on the structural changes in SMA during heating the catalysts to 873 K.

Preparation of spherical and porous SiO2 particles by fume pyrolysis

Abstract Porous SiO 2 spheres were prepared successfully by means of fume pyrolysis using gel solutions derived from Si-alkoxides. Particle sizes in all samples were about 1.5 μm large but surface areas varied from 20 m 2 .g −1 to about 500 m 2 .g −1 with viscosities of source solution. Pores in SiO 2 spheres were formed with almost the same size and the mean pore sizes were controlled in the range of about, 2.2 nm to 0.7 nm in radii. The pore size and surface area were closely connected with the preparation condition and it was, proved that the properties of formed SiO 2 were associated with the gel structures in the fumed droplets and the combustion conditions under O 2 stream.

2.9 – Preparation of UFP Alloy Catalysts by Alkoxide Methods

Publisher Summary This chapter discusses the preparation of catalysts of alloy ultrafine particles (UFPs). Alloy catalysts were examined using electron spectroscopic methods such as XPS and AES. The surface alloy composition is treated as an ensemble of structures where an atom of one element is surrounded by atoms of another element and used the size of such ensembles as a parameter that was indicative of the catalytic activity. The effect of alloying on catalytic activity is chiefly controlled by the geometric arrangement of the metal atoms. The catalytic activity of metal particles changes with the particle size, so a similar effect is expected with alloy catalysts. To examine this behavior, methods for varying the particle size was examined. The preparation must avoid contamination because the catalytic activity is strongly affected by impurities. Aqueous decomposition of metal alkoxides was used, because it was suited for the preparation of high purity oxide powders. Iron-nickel and iron-cobalt catalysts supported on SiO2 were produced. Extended X-rayX-ray absorption fine structure spectroscopy (EXAFS) was used to examine the structure of the alloy fine particles prepared by the alkoxide method. The EXAFS is an effective method for doing structural analyses of fine particles and amorphous samples that are hard to examine using X-rayX-ray diffraction.

Degradation of polyethylene over solid acids and bases

Solid acids (ZSM-5, silica-alimina) and bases (MgO, ZnO) were employed as catalysts for the degradation of polyethylene powder at 673 K. The degradation rate over solid acids were more than two times higher than those over solid bases. The degradation products were gases (C1 to C4), oils (C5 to C20) and wax (higher than C21), analyzed by GC-MS to obtain a product distribution curve as a function of C-atom numbers. A relationship between the acid strength and amount and the product compositions were studied using silica-alumina catalysts with various Si/Al ratios, resulting in an enhancement in the gas production as the acid strength and amount increased.