Trimethoxymethane as an alternative fuel for a direct oxidation PBI polymer electrolyte fuel cell

The oxidation of trimethoxymethane (TMM) (trimethyl orthoformate) in a direct oxidation PBI fuel cell was examined by on-line mass spectroscopy and on-line FTIR spectroscopy. The results show that TMM was almost completely hydrolyzed in a direct oxidation fuel cell which employs an acid doped polymer electrolyte to form a mixture of methylformate, methanol and formic acid. It also found that TMM was hydrolyzed in the presence of water at 120°C even without acidic catalyst. The anode performance improves in the sequence of methanol, TMM, formic acid/methanol, and methylformate solutions. Since formic acid is electrochemically more active than methanol, these results suggest that formic acid is probably a key factor for the improvement of the anode performance by using TMM instead of methanol under these conditions. © 1998 Elsevier Science Ltd. All rights reserved.

In situ FTIR spectroscopic studies of the oxidation of CO adsorbates on Ru(0 0 0 1) electrodes under open circuit conditions

This paper reports the first observation, using in situ FTIR spectroscopy, of the oxidation of CO adsorbates on the Ru(0001) electrode to CO under open circuit (oc) conditions in both perchloric acid and sulphuric acid solution at 20 and 55 °C. While the significant oc oxidation of the adsorbed CO on the Ru(0001) electrode was observed in perchloric acid solution, much less oc oxidation took place in sulfuric acid solution due to the specific adsorption of bisulfate at the Ru surface which inhibits the surface oxidation and reduces the reactivity of the surface towards the oxidation of CO . The oc oxidation of the CO depends strongly on the oxygen concentration in the solution and the temperature. The data so obtained are compared to those observed at the gas|solid interface, as well as to those obtained from the electro-oxidation of CO , and possible new catalytic oxidation reaction mechanisms are discussed. In addition, it is shown that the C-O frequency of the adsorbed CO may be used as an effective probe of the open circuit potential. © 2003 Elsevier B.V. All rights reserved.

In situ FTIR studies on the effect of temperature on the electro-oxidation of small organic molecules at the Ru(0001) electrode

The adsorption and electro-oxidation of formaldehyde, formic acid and methanol at the Ru(0001) electrode in perchloric acid solution have been studied as a function of temperature, potential and time using in situ FTIR spectroscopy, and the results interpreted in terms of the surface chemistry of the Ru(0001) electrode and compared to those obtained during our previous studies on the adsorption of CO under the same conditions. It was found that no dissociative adsorption or electro-oxidation of methanol takes place at Ru(0001) at potentials 1000 mV, both the oxidation of formic acid to CO and the oxidation of formaldehyde to both CO and formic acid were significantly increased, and the oxidation of methanol to CO and methyl formate was observed, all of which were attributed to the formation of an active RuO phase on the Ru(0001) surface.

Pioglitazone protects HDL(2&3) against oxidation in overweight and obese men

The worldwide epidemic of obesity is a major public health concern and is persuasively linked to the rising prevalence of diabetes and cardiovascular disease. Obesity is often associated with an abnormal lipoprotein profile, which may be partly negated by pioglitazone intervention, as this can influence the composition and oxidation characteristics of low-density lipoprotein (LDL). However, as pioglitazone's impact on these parameters within high-density lipoprotein (HDL), specifically HDL(2&3), is absent from the literature, this study was performed to address this shortcoming.

An investigation of the role of surface nitrate species in the oxidation of propene on a Pt-based diesel oxidation catalyst

Enhancing the low temperature activity of diesel oxidation catalysts is important for cold-start conditions and the possible importance of nitrate species in oxidation reactions has been proposed although definitive evidence has not been reported. To investigate the possible role of surface nitrates, their adsorption and reactivity on a Pt-based diesel oxidation catalyst have been investigated using the Short Time on Stream (STOS) transient kinetic technique. The results provide for the first time definitive evidence for the oxidation of propene by some of these nitrate-type species. © The Royal Society of Chemistry 2013.

Critical role of water in the direct oxidation of CO and hydrocarbons in diesel exhaust after treatment catalysis

CO and C3H6 oxidation have been carried out in the absence and presence of water over a Pd/Al2O3catalyst. It is clear that water promotes CO and, as a consequence, C3H6oxidation takes place at muchlower temperatures compared with the dry feed. The significant increase in the catalyst’s activity withrespect to CO oxidation is not simply associated with changes in surface concentration as a result ofcompetitive adsorption effects. Utilising18O2as the reactant allows the pathways whereby the oxidationdue to gaseous dioxygen and where the water activates the CO and C3H6to be distinguished. In thepresence of water, the predominant pathway is via water activation with C16O2and C16O18O being themajor species formed and oxidation with dioxygen plays a secondary role. The importance of wateractivation is further supported by the significant decrease in its effect when using D2O versus H2O.

Novel ruthenium-terpyridyl complex for direct oxidation of amines to nitriles

High catalytic activity and selectivity has been demonstrated for the oxidation of both aliphatic and aromatic amines to nitriles under benign conditions with dioxygen or air using the Ru2Cl4(az-tpy)(2) complex. The conversion was found to be strongly influenced by the alkyl chain length of the reactant with shorter chain amines found to have lower conversions than those with longer chains. Importantly, by using the ruthenium terpyridine complex functionalized with azulenyl moiety at the 4 position of central pyridine core provided a much higher reactivity catalyst compared with a series of ruthenium terpyridine-based ligand complexes reported. Mechanistic studies using deuterated benzylamine demonstrated the importance of RuOH in this reaction.

Low loading platinum nanoparticles on reduced graphene oxide-supported tungsten carbide crystallites as a highly active electrocatalyst for methanol oxidation

In this study, low loading platinum nanoparticles (Pt NPs) have been highly dispersed on reduced graphene oxide-supported WC nanocrystallites (Pt-WC/RGO) via program-controlled reduction-carburization technique and microwave-assisted method. The scanning electron microscopy and transmission electron microscopy results show that WC nanocrystallites are homogeneously decorated on RGO, and Pt NPs with a size of ca. 3 nm are dispersed on both RGO and WC. The prepared Pt-WC/RGO is used as an electrocatalyst for methanol oxidation reaction (MOR). Compared with the Pt/RGO, commercial carbon-supported Pt (Pt/C) and PtRu alloy (PtRu/C) electrocatalysts, the Pt-WC/RGO composites demonstrate higher electrochemical active surface area and excellent electrocatalytic activity toward the methanol oxidation, such as better tolerance toward CO, higher peak current density, lower onset potential and long-term stability, which could be attributed to the characterized RGO support, highly dispersed Pt NPs and WC nanocrystallites and the valid synergistic effect resulted from the increased interface between WC and Pt. The present work proves that Pt-WC/RGO composites could be a promising alternative catalyst for direct methanol fuel cells where WC plays the important role as a functional additive in preparing Pt-based catalysts because of its CO tolerance and lower price. 

Aerobic oxidation catalysis with stable radicals

Selective oxidation reactions are challenging when carried out on an industrial scale. Many traditional methods are undesirable from an environmental or safety point of view. There is a need to develop sustainable catalytic approaches that use molecular oxygen as the terminal oxidant. This review will discuss the use of stable radicals (primarily nitroxyl radicals) in aerobic oxidation catalysis. We will discuss the important advances that have occurred in recent years, highlighting the catalytic performance, mechanistic insights and the expanding synthetic utility of these catalytic systems.

Molecular mechanism and physiological role of active-deactive transition of mitochondrial complex I

The unique feature ofmitochondrial complex I is the so-called A/D transition (active-deactive transition). The A-form catalyses rapid oxidation of NADH by ubiquinone (k ~10 min) and spontaneously converts into the D-form if the enzyme is idle at physiological temperatures. Such deactivation occurs in vitro in the absence of substrates or in vivo during ischaemia, when the ubiquinone pool is reduced. The D-form can undergo reactivation given both NADH and ubiquinone availability during slow (k ~1-10 min) catalytic turnover(s). We examined known conformational differences between the two forms and suggested a mechanism exerting A/D transition of the enzyme. In addition, we discuss the physiological role of maintaining the enzyme in the D-form during the ischaemic period. Accumulation of the D-form of the enzyme would prevent reverse electron transfer from ubiquinol to FMN which could lead to superoxide anion generation. Deactivation would also decrease the initial burst of respiration after oxygen reintroduction. Therefore the A/D transition could be an intrinsic protective mechanism for lessening oxidative damage during the early phase of reoxygenation. Exposure of Cys of mitochondrially encoded subunit ND3 makes the Dform susceptible for modification by reactive oxygen species and nitric oxide metabolites which arrests the reactivation of the D-form and inhibits the enzyme. The nature of thiol modification defines deactivation reversibility, the reactivation timescale, the status of mitochondrial bioenergetics and therefore the degree of recovery of the ischaemic tissues after reoxygenation.

β-Lapachone alleviates alcoholic fatty liver disease in rats

Alcohol-induced liver injury is the most common liver disease in which fatty acid metabolism is altered. It is thought that altered NAD+/NADH redox potential by alcohol in the liver causes fatty liver by inhibiting fatty acid oxidation and the activity of tricarboxylic acid cycle reactions. β-Lapachone (βL), a naturally occurring quinone, has been shown to stimulate fatty acid oxidation in an obese mouse model by activating adenosine monophosphate-activated protein kinase (AMPK). In this report, we clearly show that βL reduced alcohol-induced hepatic steatosis and induced fatty acid oxidizing capacity in ethanol-fed rats. βL treatment markedly decreased hepatic lipids while serum levels of lipids and lipoproteins were increased in rats fed ethanol-containing liquid diets with βL administration. Furthermore, inhibition of lipolysis, enhancement of lipid mobilization to mitochondria and upregulation of mitochondrial β-oxidation activity in the soleus muscle were observed in ethanol/βL-treated animals compared to the ethanol-fed rats. In addition, the activity of alcohol dehydrogenase, but not aldehyde dehydrogenase, was significantly increased in rats fed βL diets. βL-mediated modulation of NAD+/NADH ratio led to the activation of AMPK signaling in these animals. Conclusion: Our results suggest that improvement of fatty liver by βL administration is mediated by the upregulation of apoB100 synthesis and lipid mobilization from the liver as well as the direct involvement of βL on NAD+/NADH ratio changes, resulting in the activation of AMPK signaling and PPARα-mediated β-oxidation. Therefore, βL-mediated alteration of NAD+/NADH redox potential may be of potential therapeutic benefit in the clinical setting.

Characterisation of the active/de-active transition of mitochondrial complex I

Oxidation of NADH in the mitochondrial matrix of aerobic cells is catalysed by mitochondrial complex I. The regulation of this mitochondrial enzyme is not completely understood. An interesting characteristic of complex I from some organisms is the ability to adopt two distinct states: the so-called catalytically active (A) and the de-active, dormant state (D). The A-form in situ can undergo de-activation when the activity of the respiratory chain is limited (i.e. in the absence of oxygen). The mechanisms and driving force behind the A/D transition of the enzyme are currently unknown, but several subunits are most likely involved in the conformational rearrangements: the accessory subunit 39 kDa (NDUFA9) and the mitochondrially encoded subunits, ND3 and ND1. These three subunits are located in the region of the quinone binding site. The A/D transition could represent an intrinsic mechanism which provides a fast response of the mitochondrial respiratory chain to oxygen deprivation. The physiological role of the accumulation of the D-form in anoxia is most probably to protect mitochondria from ROS generation due to the rapid burst of respiration following reoxygenation. The de-activation rate varies in different tissues and can be modulated by the temperature, the presence of free fatty acids and divalent cations, the NAD/NADH ratio in the matrix, the presence of nitric oxide and oxygen availability. Cysteine-39 of the ND3 subunit, exposed in the D-form, is susceptible to covalent modification by nitrosothiols, ROS and RNS. The D-form in situ could react with natural effectors in mitochondria or with pharmacological agents. Therefore the modulation of the re-activation rate of complex I could be a way to ameliorate the ischaemia/reperfusion damage. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference. Guest Editors: Manuela Pereira and Miguel Teixeira.

Significance of β-dehydrogenation in ethanol electro-oxidation on platinum doped with Ru, Rh, Pd, Os and Ir

In the exploration of highly efficient direct ethanol fuel cells (DEFCs), how to promote the CO₂ selectivity is a key issue which remains to be solved. Some advances have been made, for example, using bimetallic electrocatalysts, Rh has been found to be an efficient additive to platinum to obtain high CO₂ selectivity experimentally. In this work, the mechanism of ethanol electrooxidation is investigated using first principles method. It is found that CH₃CHOH* is the key intermediate during ethanol electrooxidation and the activity of β-dehydrogenation is the rate determining factor that affects the completeness of ethanol oxidation. In addition, a series of transition metals (Ru, Rh, Pd, Os and Ir) are alloyed on the top layer of Pt(111) in order to analyze their effects. The elementary steps, α-, β-C-H bond and C-C bond dissociations are calculated on these bimetallic M/Pt(111) surfaces and the formation potential of OH* from water dissociation is also calculated. We find that the active metals increase the activity of β-dehydrogenation but lower the OH* formation potential resulting in the active site being blocked. By considering both β-dehydrogenation and OH* formation, Ru, Os and Ir are identified to be unsuitable for the promotion of CO₂ selectivity and only Rh is able to increase the selectivity of CO₂ in DEFCs.

Copper(I)/ketoABNO Catalysed Aerobic Alcohol Oxidation

A Cu(I)/9-azabicyclo[3.3.1]nonan-3-one N-oxyl (ketoABNO) aerobic catalyst system is highly effective for the oxidation of secondary alcohols, including unactivated aliphatic substrates. The effects of pressure and gas composition on catalyst performance are examined. The radical can be employed at low loadings and is also amenable to immobilisation on to solid supports.

N,O-Ligated Pd(II) Complexes for Catalytic Alcohol Oxidation

N,O-ligated Pd(II) complexes show considerable promise for the oxidation of challenging secondary aliphatic alcohols. The crystal structures of the highly active complexes containing the 8-hydroxyquinoline-2-carboxylic acid (HCA) and 8-hydroxyquinoline-2-sulfonic acid (HSA) ligands have been obtained. The (HSA)Pd(OAc)2 system can effectively oxidise a range of secondary alcohols, including unactivated alcohols, within 4–6 h using loadings of 0.5 mol%, while lower loadings (0.2 mol%) can be employed with extended reaction times. The influence of reaction conditions on catalyst degradation was also examined in these studies.