CO oxidation: Deactivation of Au/TiO2 catalysts during storage

In a study of the phenomenon of catalyst deactivation during storage, Au/TiO₂ catalyst was stored under various conditions, viz. vacuum, nitrogen, air, refrigeration, dark, and light, and tested for CO oxidation activity at regular intervals. The data shows that the catalyst deactivates under all the storage conditions over 12 months and that storage in vacuum significantly enhances the rate and extent of deactivation. Storage in light accelerates the deactivation. The catalyst appears to deactivate through a combination of Au(III) reduction, Au nanoparticle agglomeration, loss of surface hydroxyl groups, loss of surface moisture, and accumulation of surface carbonates and formates. The rate and extent of catalyst deactivation can be limited by storing the catalyst in the dark at sub ambient temperature (refrigerator) and under inert atmosphere.     

On-line deactivation of Au/TiO2 for CO oxidation in H2-rich gas streams

Au-based catalysts, known for ambient temperature CO oxidation, have to provide stable performance of up to 5000 h in order to be commercially applicable in automotive fuel cells. In this report, the on-line deactivation characteristics of Au/TiO₂ in unconventional PROX conditions are discussed. As opposed to CO removal from air, results in this report suggests that carbonates have a minor effect on deactivation of Au/TiO₂ in dry H₂-rich conditions. Also, no conclusive correlation between surface hydration and deactivation was observed. Rather, deactivation appeared to have occurred as a result of an intrinsic transformation in the oxidation state of the active species in the reducing operating conditions; a process which was reversible in an oxidizing atmosphere.     

Observability limits for networked oscillators

Inspired by the neuro-scientific problem of predicting brain dynamics from electroencephalography (EEG) measurements of the brain’s electrical activity, this paper presents limitations on the observability of networked oscillators sensed with quantised measurements. The problem of predicting highly complex brain dynamics sensed with relatively limited amounts of measurement is abstracted to a study of observability in a network of oscillators. It is argued that a low-dimensional quantised measurement is in fact, by itself, an exceptionally poor observer for a large-scale oscillator network, even for the case of a completely connected graph. The main rational is based on (i) an information-theoretic argument based on ideas of entropy in measure preserving maps, (ii) a linear deterministic observability argument, and (iii) a linear stochastic approach using Kalman filtering. For prediction of brain network activity, the findings indicate that the classic EEG signal is just not precise enough to be able to provide reliable prediction and tracking in a clinical setting in view of the complexity of underlying neural dynamics.     

Bioavailability of dietary sodium copper chlorophyllin and its effect on antioxidant defence parameters of Wistar rats

BACKGROUND: There has been growing interest in sodium copper chlorophyllin (Cu‐Chl) as a food colourant and supplement owing to its beneficial biological activities. Studies have revealed that this green pigment inhibits experimental carcinogenesis and interacts with proteins and genotoxic agents. Health‐related activities have also been associated with the prevention of lipid peroxidation. However, intestinal absorption of this pigment has been considered insignificant, raising questions of whether eventual biological properties are related to pre‐ or post‐absorptive actions. In this study, intestinal absorption of Cu‐Chl and its appearance in serum and organs were estimated by high‐performance liquid chromatography analysis in rat feeding experiments. The effect of ingested Cu‐Chl on lipid peroxidation was analysed by measuring thiobarbituric acid‐reactive substances and antioxidant enzyme activities in hepatic and brain tissues of oxidative stress‐induced rats. RESULTS: The two main components of commercial Cu‐Chl, namely Cu‐chlorin e₆ and Cu‐chlorin e₄, showed different digestive behaviours, and only Cu‐chlorin e₄ was found in serum, liver and kidneys. Antioxidant activity in vivo could be observed in brain and seemed to be related to in situ protection but not to antioxidant enzyme modulation. CONCLUSION: As at least one of the major components of Cu‐Chl is effectively absorbed, further pharmacokinetic studies are encouraged to access absorption rates and the role of ingested copper chlorophyllins in mammals. Copyright © 2009 Society of Chemical Industry