The relationship between various unsupported molybdenum carbides and their activity toward methane reforming at 973 K and 1 atm was studied. Unsupported molybdenum carbides catalyzed the formation of hydrogen in high selectivity, forming ethylene and ethane rather than benzene as the carbon-containing products. η-Mo3C2, which was nitrided at 973 K and subsequently carbided at 1173 K, was more active than both α-MoC1 - x and β-Mo2C in methane decomposition, forming hydrogen in high selectivity. α-MoC1 - x and γ-Mo2N were transformed to η-Mo3C2 in the bulk structure during methane reforming at 973 K. This transformation caused a significant increase in the turnover frequency of methane reforming. η-molybdenum carbide was also formed during CH4-TPR of γ-Mo2N at 788 K. The linear relationship between the amount of η-carbide determined through H2-TPR of the catalysts and the methane disappearance rate revealed that η-Mo3C2 is the active species for methane reforming. From the XPS analysis, Mo0 was the dominant molybdenum species for the η-Mo3C2 catalysts.

SYNOPSISRelatively uniform polymeric microspheres, the coefficients of variation being close to lo%, were obtained by the BPO-initiated suspension polymerization of styrenic monomers. Unlike the conventional stirred-tank system, a particular microporous glass membrane ( SPG ) provided uniform monomer droplets continuously when monomer was allowed to permeate through the micropores. The monomer droplets were suspended in an aqueous solution containing the stabilizing agents, transferred to a stirred vessel, and polymerized. Up to 10 pm spheres, of a far narrower size distribution than those obtained by conventional microsuspension polymerization spheres, were obtained. The initial droplet size and distribution were retained with the successful suppression of secondary particle nucleation by the addition of hydroquinone in the aueous phase. Crosslinked polystyrene spheres were also synthesized in the presence of various low-molecular-weight diluents. While a good solvent, toluene, was not so effective; poor solvents, n-hexane and n-heptane, easily yielded the microporous structure, the specific surface area being as high as 160 m2/g.

The characteristics of reactions in the monomer phase, aqueous phase, and the interface of monomer/aqueous phase of soap-free emulsion polymerization of 4-vinylpyridine (4VP) and styrene (St) system were evaluated by using the different types of initiators, addition of organic solvents, and changes of agitation rate. The oil-soluble initiators 2,2′-azobis(2,4-dimethylvaleronitrile) (ADVN), benzoyl peroxide (BPO), and 2,2′-azobis(isobutyronitrile) (AIBN), the organic water-soluble initiator, 2,2′-azobis(2amidinopropane) dihydrochloride (V50), and the inorganic water-soluble initiator, potassium persulfate (KPS), were used. 1 H NMR and scanning electronic microscopy (SEM) were employed for the characterizations. As a result, the mechanism of interfacial particle formation was supported. Namely, the minimonomer droplets were generated by the disturbance in the interface of monomer/aqueous phase due to the agitation. The minimonomer droplets were stabilized by the adsorption of surface-active oligomer generated by the reactions in both the aqueous phase and the interface. The monomer transfer from the bulk monomer phase to the growing particles was via the coalescence of minimonomer droplets with particles. The role of reaction in the aqueous phase was proposed to just provide the surface-active oligomer for the stabilization of particles. The rapid reaction in the aqueous phase due to the high concentration of hydrophilic monomer produced longer hydrophilic chains and led to the coagulation of particles by a bridging-coagulation effect. On the basis of this mechanism, the coagulum-free stable latices with high monomer conversion were prepared by using KPS and AIBN and, theoretically, can be prepared by using any type of initiators at a high level of solid content and feed ratio of hydrophilic monomer.

SYNOPSISApplication of the particulate microporous glass membrane (SPG) was extended to the synthesis of fairly monodisperse poly(methy1 methacrylate) (PMMA) microspheres. Hydrophilic monomers have been believed to yield polymer particles of a broad size distribution when the SPG technique was employed. This difficulty was overcome by adopting the droplet swelling technique. The primary uniform emulsion composed of a mixture of hydrophobic diluent (and/or monomer), cosurfactant, and initiator was prepared with an SPG membrane and was allowed to absorb MMA (and diluent) under the principle of the degradative diffusion process from droplets in the secondary emulsion. The coefficient of variation of PMMA spheres was around 10%. Porous PMMA spheres possessing up to 185 m2/g of specific surface area were obtained as well as one-eyed spheres and smooth and solid spheres. 0