Seascape Genomics of the Sugar Kelp Saccharina latissima along the North Eastern Atlantic Latitudinal Gradient

Temperature is one of the most important range-limiting factors for many seaweeds. Driven by the recent climatic changes, rapid northward shifts of species' distribution ranges can potentially modify the phylogeographic signature of Last Glacial Maximum. We explored this question in detail in the cold-tolerant kelp species Saccharina latissima, using microsatellites and double digest restriction site-associated DNA sequencing ( ddRAD-seq) derived single nucleotide polymorphisms (SNPs) to analyze the genetic diversity and structure in 11 sites spanning the entire European Atlantic latitudinal range of this species. In addition, we checked for statistical correlation between genetic marker allele frequencies and three environmental proxies (sea surface temperature, salinity, and water turbidity). Our findings revealed that genetic diversity was significantly higher for the northernmost locality (Spitsbergen) compared to the southern ones (Northern Iberia), which we discuss in light of the current state of knowledge on phylogeography of S. latissima and the potential influence of the recent climatic changes on the population structure of this species. Seven SNPs and 12 microsatellite alleles were found to be significantly associated with at least one of the three environmental variables. We speculate on the putative adaptive functions of the genes associated with the outlier markers and the importance of these markers for successful conservation and aquaculture strategies for S. latissima in this age of rapid global change.

Transient kinetics and in situ spectroscopic techniques for the characterisation of V/Ti-oxide catalysts in toluene partial oxidation

Fabio Rainone

Development of selective oxidation catalysts is a major concern of modern chemical industry. Among several systems, VTi-oxide based catalysts showed the most promising and versatile, able to catalyse key reactions like oxidation of o-xylene to phtalic anhydride and the abatement of NOx for pollution control. Extensive investigation in the past decades concluded that supported vanadia is present as a layer of molecularly-defined surface compounds VxOy, ("monolayer species") on top of the carrier oxide which are the catalytically active sites. Despite all the efforts to correlate the activity of VTi-oxide with its structure, the catalytic role of the different active species in the selective oxidation of hydrocarbons and how to tune their properties are still open questions. The goal of the present thesis is the in situ characterisation of V/Ti-oxide by transient-response chemical (feed step-response, temperature-programmed analyses) and spectroscopic (infrared and Raman) techniques to answer these important questions by using toluene partial oxidation as test reaction. First, the identification and elucidation of the role of the vanadia species was carried out, using Raman spectroscopy and activity tests. The strongly-bound monolayer species which cannot be dissolved by acid treatment were found to have isolated vanadate structure and be catalytically active in toluene partial oxidation. They have redox properties close to more condensed vanadate ("polymeric") species, which are also active. Vanadium present as crystalline V2O5 is not directly active, but plays a role in the surface reduction mechanism. By in situ DRIFTS, it has been shown that V/Ti-oxide active sites work with a coupled mechanism of product desorption and site reoxidation. Re-oxidation can occur either by reaction with gas-phase O2 or by oxygen spillover from bulk V2O5. Acidity associated with V-O-V bridges in monolayer species is likely responsible for the reversible deactivation of the catalysts caused by strongly held surface coke. Second, the modification of the acid/base catalyst properties by K addition and the formation of surface V oxide species were studied. The presence of K modifies the molecular structure of the vanadia surface species and forms new K-containing ones. These species are difficult to reduce in hydrogen and they are not catalytically active. Their presence causes a diminished catalytic activity. At the same time, Lewis and Brønsted acidity is depressed. This eliminates the phenomenon of deactivation. The excessive basicity caused by potassium addition has a detrimental effect on selectivity in benzoic acid, which is strongly held on the surface because of their intrinsic acidity and undergoes overoxidation to CO2. Finally, the VTi-oxide was supported on structured supports based on woven fibreglass. The use of structured beds is interesting in chemical engineering due to their advantages in terms of increased mass and heat trasfer, reduced pressure drop and optimal flow distribution. In order to reach optimum performance, the rather inert silica surface must be modified by adding an alumina layer on top of the fibres. This modification is essential for an optimal support because of insufficient dispersion of the titania layer on silica due to phase repulsion between the two oxides. The structured catalysts possess comparable activity and identical selectivity to the studied non-structured VTi-oxide catalyst with the same content of vanadia layers.

EPFL2004

Transient kinetics and in situ spectroscopic techniques for the characterisation of V/Ti-oxide catalysts in toluene partial oxidation

Fabio Rainone

EPFL2004