Catalyst investigation

As is well known, polyacetylene can be manufactured by various processes using dilTerent catalysts. The most common method is that of Shirakawa [16,17], in which polymerization of acetylene takes place on a Ziegler catalyst. It has been shown in a large number of polymerization tests that the quality of the catalyst depends strongly on the preparation conditions [11]. 

Although a great deal of research has been done on the finished product, polyacetylene film or powder, very little is known about the nature of the catalyst. This led us to carry out an extensive spectroscopic investigation with the object of finding out more about the structure of the active sites, both from measurements on newley prepared, aimealed and aged catalysts as well as on the catalyst during polymerization of (CH)jf. 

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Hardy and Linnett (59) studied the heterogeneous recombination of atomic hydrogen at room temperature on nickel and nickel alloy foils. They did not find any similarity to the behavior of palladium and its alloys with gold studied earlier (35). There was no evidence that, as a result of exposure to atomic hydrogen, hydride was formed in any metal catalyst investigated with a resulting change in the activity of the initial parent metal catalysts. 

There appears to be concentration of rhodium in the surface of the iridium-rhodium clusters, on the basis that the total number of nearest neighbor atoms about rhodium atoms was found to be smaller than the nunber about iridium atoms in both catalysts investigated. This conclusion agrees with that of other workers (35) based on different types of measurements. The results on the average compositions of the first coordination shells of atoms about iridium and rhodium atoms in either catalyst Indicate that rhodium atoms are also incorporated extensively in the interiors of the clusters. In this respect the iridium-rhodium system differs markedly from a system such as ruthenium-copper (8), in which the copper appears to be present exclusively at the surface. 

From the data shown in table 3, it is evident that the effect of Cs promotion on the power law kinetics is twofold First, the reaction order for NH3 is changed to essentially zero, and secondly, the apparent activation energy is higher by more than 20 kJ/mol in the presence of Cs. Contrary to the results obtained by Aika et al. [5], the reaction order for H2 was negative for all catalysts investigated. The positive reaction order for H2 reported by Aika et al. [5] for... 

The Ru/Ti02 catalyst is unique, among many catalysts investigated, in promoting the direct partial oxidation of methane. 

Equimolar amounts of ammonia and isocyanic acid are thus formed. These two endothermic processes, which can be slightly accelerated by catalysts, partially occur already in the gas phase ahead of the SCR catalyst. Investigations of the selective non-catalytic reduction showed that the mixture of ammonia and isocyanic is stable up to 850°C [21]. 

The outcome of this research naturally raised the question whether the catalysts investigated differed also in chemisorptive and catalytic properties. We therefore examined how the adsorption of CO and CO2, and the reaction of benzene with deuterium proceed on these catalysts. This study forms the subject of the present article. 

Goodwin and coworkers have studied the formation of cobalt aluminates.25,26 Jongsomjit et al. studied cobalt aluminate formation by TPR and RAMAN spectroscopy.26 The catalysts investigated were 25% Co/y-Al203 and Ru-promoted (0.5%)-25% Co/y-Al203. The Raman spectra of the samples after various pretreatments are shown in Fig. 3. 

It was found that the reaction conditions which were optimized for the synthesis of poly(arylene siloxanylenes) (43) could be employed for the synthesis of siloxane-modified poly-(arylene carbonates). 2,4,6-Trimethylpyridine (collidine) was selected as the most suitable of all catalysts investigated (43) for the synthesis of the siloxane modified poly(arylene carbonates). Properties of polymers prepared by this method are given in Table I. In comparision to the phosgene-catalyzed homo-polycondensation of bis-silanols, III, the inherent viscosities... 

TABLE 11.1. Ni0-Y203-Zr02 and Ni0-Ce02-Zr02 catalysts investigated in steam reforming reactions ... 

Electron energy-loss spectroscopy (EELS) is nowadays widely used to obtain the information with respect to chemical composition, oxidation state and electronic structure of solids. Since all catalytic processes concern the exchange of electrons between the reactants, EELS is extremely valuable in catalysts investigations [9, 49-57], EELS in an electron microscope exhibits the advantage of high spatial resolution in area of interests with simultaneous structure determination by electron diffraction and imaging. 

The applied electrode potential has been shown to have an effect on both the XANES and EXAFS of PtRu catalysts. The variations of the Pt d band vacancy per atom, (/7j)t,s, with potential over the range 0.0—0.54 V vs RHE for both the poorly mixed 1 1 PtRu/C catalyst investigated by McBreen and Mukerjee ° and a well mixed 1 1 PtRu/C catalyst studied by Russell et al. were less than that for a pure Pt/C catalyst. McBreen and Mukerjee attributed this difference to a reduction in the adsorption of hydrogen on the Pt sites of the alloy catalyst. The results also provide evidence of an electronic effect upon alloying Pt with Ru. The effects on the Ru XANES were much less significant, but some evidence of a change to a higher oxidation state at potentials above 0.8 V was observed. ... 

Some features making X-ray X-edge spectroscopy especially attractive for catalyst investigations are ... 

This encapsulation effect was further characterized by determination of the substrate selectivity using substrates of different sizes. Dienophiles with various tail lengths were applied in a 1 1 molar ratio to react with cyclopentadiene in the presence of a catalyst. The smaller dienophile reacted slightly faster than the bulkier one with each of the catalysts investigated (non-dendritic parent complex, G1. Cu(OTf)2, and G3.Cu(OTf)2). More importantly, G3.Cu(OTf)2 (krei = 1.18) displayed higher substrate selectivity than Gl.Cu(OTf)2 (krei = 1.05). 

In the first part of the chapter, a state-of-the-art review and also a thermodynamic analysis of the autothermal reforming reaction are reported. The former, relevant to both chemical and engineering aspects, refers to the reaction system and the relevant catalysts investigated. The latter discusses the effect of the operating conditions on methane conversion and hydrogen yield. 

Among group 8 transition metal catalysts, iron-based Ziegler-type catalysts such as Fe(acac)3-Et3Al(l 3) (acac = acetylacetonate) have been well known from the early stage of the catalyst investigation, which are readily prepared in situ to polymerize sterically unhindered terminal acetylenes such as -alkyl-, r f-alkyl-, and phenylacetylenes. The formed poly(phenylacetylene) has red color and r-cisoidal structure, and is insoluble and crystalline. 

Metal cluster compounds simulate surface species produced by the interaction of molecules with metal surfaces (Muetterties et al, 1979) and this is of value in understanding heterogeneous catalysis. The development of selective catalysts for the C, chemical industry employing CO (and possibly CO2) as the raw material has resulted in major efforts in metal cluster research. Criteria have been developed to distinguish between cluster catalysis and mononuclear catalysis. Typical of the catalysts investigated hitherto are [Ir4(CO),2. <(PPh3)J where Ph = phenyl and X = 1, 2 or 3. 

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