Unmodified substrates

In blank experiments with the unmodified Pt(l 11) surface, no changes in the IR spectra occurred on the same time scale, even when the step potential was increased to 0.55 V. This is clear evidence that Pt(lll) is not active for the electro-oxidation of COads in this potential range. Hence, the Pt areas in between the Ru islands behave quite differently with respect to CO oxidation than the unmodified substrate. 

In this review we will attempt to highlight the most important contributions toward the realization of a catalytic, enantioselective, vinylogous Mannich reaction and show the current state of the art. This chapter is organized in such a way that vinylogous Mannich reactions of preformed silyl dienolates in Mukaiyama type reactions will be discussed first followed by direct vinylogous Mannich reactions of unmodified substrates. 

Direct Vinylogous Mannich Reactions of Unmodified Substrates... 

Chapter 13 was largely concerned with adsorbed species that are not electroactive. In this chapter we consider electroactive monolayers and thicker films on conductive substrates these are frequently called chemically modified electrodes. This area of electrochemistry has been a very active one in recent years, and a number of reviews discussing the preparation, characterization, and electrochemical behavior of chemically modified electrodes are available (1-14). These electrodes are often prepared by the modification of a conductive substrate to produce an electrode suited to a particular function, whose properties are different from those of the unmodified substrate. Modified electrodes can be prepared in several different ways, as discussed in vSection 14.2, including irreversible adsorption, covalent attachment of a monolayer, and coating the electrode with films of polymers or other materials. 

Molinard pointed out that the ions introduced can serve as specific adsorption sites and that this type of modification allows fine-tuning of the PILC substrate for certain gas adsorption applications [18]. By introducing Sr + in Al-PILC, the gas adsorption isotherms at 273 K and 5 x 10 Pa equilibrium pressure showed that the Nj capacity doubled fi-om 0.06 nunol/g on Al-PILC to 0.12 mmol/g on Sr-Al-PILC. The amoimt of cations in the PILC influences the adsorption properties. A higher cation loading results in a lower capacity but a higher N2/O2 selectivity on Ca-Al-PILC, as was proven by adsorption measurements. For the anion exchanged Cl-Al-PILC, more O2 than N2 was adsorbed (0.09 mmol/g and 0.07 mmol/g, respectively) at 273 K and 5x10 Pa. This affinity for O2 should result from a specific interaction with the Cl"-ions. The CO2 capacity decreased in comparison with the unmodified substrate from 0.5 mmol/g on Al-PILC to 0.2 mmol/g on Cl-Al-PILC at 273 K and 0.5 bar. After modification with other anions, Hke F and PO, the same effect was observed. 

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