Nicolas Donzel

Role of the Organic Feed and the Support Acidity in Hydrotreating Reactions on Pd–Pt on MCM-41 Catalysts

The reactivity of different organic compounds (naphthalene, alkylnaphthalenes, decalins, tetralin and their mixtures) and the roles of the support acidity and of the noble metals were studied in Pd/Pt on MCM-41 (with different Si/Al ratios) catalysts. The catalytic tests showed that the hydrogenolysis/ring-opening reactions mainly occurred on saturated compounds, while cracking took places mainly on unsaturated compounds. The presence of alkyl side chains on the polyaromatic ring inhibited the hydrodearomatization activity, proportionally to their length and number. Mixtures of naphthalene and methylnaphthalenes gave rise to a competition between the substrates, with a decrease in both hydrogenation and hydrogenolysis/ring-opening activities. Increasing support acidity favoured hydrogenolysis/ring-opening and cracking reactions, smoothing the hydrogenation activity. Noble metals are shown to be necessary not only in hydrogenation, but also in hydrogenolysis/ring-opening reactions.

Innovative Membranes for PEMFC with Mixed Sulfonic and Phosphonic Acid Functionality

The technology pull towards simplification of fuel cell systems for automotive applications has driven the need for a high performance membrane that operates under conditions of low relative humidity and temperatures exceeding the boiling point of water. Despite considerable progress, formulating new approaches leading to novel proton conducting membrane systems that have high proton conductivity at high temperature through the full range of relative humidity remains the most difficult challenge at the present time. In the present work, we have associated the properties of a new ether-linked polybenzimidazole that can be directly sulfonated in solution with those of a polymeric phosphonic acid, with the aim of inducing proton conductivity at both lower (-SO3H groups) and higher (-PO3H2 functions) temperatures. As we have described previously [1] poly-[(1-(4,4’-diphenylether)-5oxybenzimidazole)-benzimidazole] (I, PBI-OO), was sulfonated in concentrated sulfuric acid to give polymers having a degree of sulfonation (DoS) of between 100 and 400%, where a DoS of 100% corresponds to the presence of one sulfonic acid function per polymer repeat unit. Vinyl benzyl phosphonic acid (VBPA) was prepared from the corresponding ester. In its polymerised form, p(VBPA) has the advantage of being considerably less soluble in water than poly(vinylphosphonic acid). Various methodologies were investigated to associate the sulfonic and phosphonic acid functionalised systems, including the development of dense, blend and (semi-)interpenetrating network membranes, and the impregnation of VBPA into a microporous s(PBI-OO) membrane prepared using sacrificial porogens. Specific preparation conditions are required in order to develop membranes having no marked phase separation at the micro-scale (transparent membranes). Further, conditions were adjusted so as to maximise the number of phosphonic acid functionalities relative to the sPBI-OO repeat unit in order to favour the aggregation of –PO3H2 groups and ensure percolation of charge carriers. Mixed functionality sPBI-OO/p(VBPA) membranes are mechanically tough. They show no weight loss below 300 °C (5 °C/min heating rate in air), unlike the previously described systems in which poly(vinyl phosphonic acid) is grafted onto PBI, where the membranes started to lose mass above ca. 170 °C [2]. These mixed functionality membranes have a lower water uptake than the corresponding (single functionality) sPBIOO membranes and their dimensional change between the fully hydrated and dry states is significantly less. These observations can be related to hydrogen bonding and/or proton transfer from the sulfonic acid to the phosphonic acid polymer. Phosphonic acid functionalised polymers have a propensity to condensation at intermediate temperatures that is greater than that of sulfonic acid functionalised polymers, and their advantage lies in the fact that the hydration number at which adequate proton conductivity can occur is lower than that of the majority of sulfonic acid systems. Thus while condensation will occur in phosphonic acid functionalised polymers under anhydrous conditions, conductivity is maintained in an atmosphere of low-moderate relative humidity. In a working fuel cell at intermediate temperature, condensation is not expected to be significant. In the present work, conductivity was determined up to 120 °C and at RH values between 25 and 95% on dense interpenetrating network type membranes having 810 phosphonic acid groups/PBI-OO repeat unit. At 90 °C, the conductivity of the mixed functionality membranes is higher than that of the corresponding sulfonic or phosphonic acid functionalised polymers over all the above RH range and, importantly, the dependence of its conductivity on RH is lower. At 120 °C, the mixed functionality (-SO3H/-PO3H2) membrane has higher conductivity than the sulfonic or phosphonic acid functionalised membranes alone at RH values below 80%, and the dependence of its conductivity at this temperature on RH is significantly lower than that of sPBI-OO membranes. This influence of the nature of the protogenic function on RH dependence of the conductivity is important in the context of the search for membrane systems having high conductivity at high temperature and low relative humidity, for both automotive and stationary applications.