Remote control of the activity of a Pt catalyst supported on a mixed ionic electronic conducting membrane

A novel configuration for the in situ control of the catalytic activity of a polycrystalline Pt catalyst supported on a mixed ionic electronic conducting (MIEC) substrate is investigated. The modification of the catalytic activity is achieved by inducing the reverse spillover of oxygen promoting species from the support onto the catalyst surface, thus modifying the chemisorptive bond energy of the gas phase adsorbed reactants. This phenomenon is known as Electrochemical Promotion of Catalysis (EPOC). In this work we investigate the use of a wireless system that takes advantage of the mixed ionic electronic conductivity of the catalyst support (internally short-circuiting the system) in a dual chamber reactor. In this wireless configuration, the reaction takes place in one chamber of the membrane reactor while introduction of the promoting species is achieved by the use of an appropriate sweep gas (and therefore control of the oxygen chemical potential difference across the membrane) on the other chamber. Experimental results have shown that the catalytic rate can be enhanced by using an oxygen sweep, while a hydrogen sweep can reverse the changes. Total rate enhancement ratios of up to 3.5 were measured. © 2008 Elsevier B.V. All rights reserved.

Comparative studies between classic and wireless electrochemical promotion of a Pt catalyst for ethylene oxidation

A comparative study between a classic and a wireless electrochemical promotion experiment was undertaken as a tool towards the better understanding of both systems. The catalytic modification of a platinum catalyst for ethylene oxidation was studied. The catalyst was supported on yttria-stabilised-zirconia (YSZ), a known pure oxide ion conductor, for the classic experiment and La _0.6Sr_0.4Co_0.2Fe_0.8O _3-δ-a mixed oxide ion electronic conductor-was used for the wireless experiment. The two systems showed certain similarities in terms of the reaction classification (in both cases electrophobic behaviour was observed) and the promotion mechanism. Significant difference was observed in the time scales and the reversibility of the induced rate modification. © 2008 Springer Science+Business Media B.V.

In situ modification of a Pt catalyst supported on a mixed ionic-electronic conducting membrane

The electrochemical promotion of a platinum catalyst for ethylene oxidation on a dual chamber membrane reactor was studied. The catalyst was supported on a La_0.6Sr_0.4Co_0.2Fe_0.803 membrane. Due the supporting membrane's electronic conductivity it is possible to promote the reaction by controlling the oxygen chemical potential difference across the membrane. Upon establishment of an oxygen potential difference across the membrane, oxygen species can migrate and spillover onto the catalyst surface, modifying the catalytic activity. Initial experiments showed an overall promotion of approximately one order of magnitude of the reaction rate of ethylene, under an oxygen atmosphere on the sweep side of the membrane reactor, as compared with the rate under an inert sweep gas. The reaction rate can keep its promoted state even after the flow of oxygen on the sweep side was interrupted. This behavior caused further promotion with every experiment cycle. The causes of permanent promotion and on demonstrating controllable promotion of the catalytic activity are presented. This is an abstract of a paper presented at the AIChE Annual Meeting (San Francisco, CA 11/12-17/2006).

Targeting of photooxidative damage on single-stranded DNA representing the bcr-abl chimeric gene using oligonucleotide-conjugates containing [Ru(phen)3](2+)-like photosensitiser groups

Photooxidative damage was induced predominantly at a single guanine base in a target DNA by irradiation (lambda > 330 nm) in the presence of complementary oligodeoxynucleotide conjugates (ODN-5'-linker-[Ru(phen)3]2+) (phen = 1,10-phenanthroline). The target DNA represents the b2a2 variant of the chimeric bcr-abl gene implicated in the pathogenesis of chronic myeloid leukaemia, and the sequence of the 17mer ODN component of the conjugate (3' G G T A G T T A T T C C T T C T T 5') was complementary to the junction region of the sense strand sequence of this oncogene. Two different conjugates were prepared, both of them by reaction of the appropriate succinimide ester with 5'-hexylamino-derivatised 17mer ODN. In Ru-ODN-1 (7) the linker was -(CH2)6-NHCO-bpyMe (-bpyMe = 4'-[4-methyl-2,2'-bipyridyl]), whereas in Ru-ODN-2 (13) it was -(CH2)6-NHCO-(CH2)3-CONH-phen. Photoexcitation of either of the conjugates when hybridised with the 32P-5'-end-labelled target 34mer 5'T G A C C A T C A A T A A G G A A G A A G21 C C C T T C A G C G G C C 3' (ODN binding site underlined) led to an alkali-labile site predominantly (> 90%) at the G21 base, which is at the junction of double-stranded and single-stranded regions of the hybrid. Greater yields were found with Ru-ODN-1 (7) than with Ru ODN-2 (13). In contrast to this specific cleavage with Ru-ODN-1 (7) or Ru-ODN-2 (13), alkali-labile sites were generated at all guanines when the 34mer was photolysed in the presence of the free sensitiser [Ru(phen)3]2+. Since [Ru(phen)3]2+ was shown to react with 2'-deoxyguanosine to form the diastereomers of a spiroiminodihydantoin derivative (the product from 1O2 reaction), 1O2 might also be an oxidizing species in the case of Ru-ODN-1 (7) and Ru-ODN-2 (13). Therefore to determine the range of reaction, a series of 'variant' targets was prepared, in which G21 was replaced with a cytosine and a guanine substituted for a base further towards the 3'-end (e.g. Variant 3; 5'T G A C C A T C A A T A A G G A A G A A C C G23 C T T C A G C G G32 C C3'). While it was noted that efficient reaction took place at distances apparently remote from the photosensitiser (e.g at G32, but not G23 for Variant 3), this effect could be attributed to hairpinning of the single-stranded region of the target. These results are therefore consistent with the photooxidative damage being induced by a reaction close to the photosensitiser rather than by a diffusible species such as 1O2.

Labeled 15NO experiments for the study of NOx reduction over Pt-Ba/Al2O3 LNT catalyst

Labelled 15NO study on N2 and N2O formation over Pt-Ba/Al2O3 LNT catalysts