FT-IR characterization of the surface acidity of different titanium dioxide anatase preparations

The surface acidity of four different anatase preparations has been studied by FT-IR spectroscopy of adsorbed benzene, ammonia, pyridine, carbon monoxide and dioxide. Our results indicate that surface chemistry of anatase, in particular acidity, greatly depends on the preparation of the sample, both through the resulting morphology and the presence of surface impurities. Different morphologies may result in different types of Lewis acid sites. If pure, anatase does not show Br\uf8nsted acidity. The presence of silica impurities is responsible for an enhancement of Br\uf8nsted acidity on several samples, and may be evaluated by the intensity of an IR band situated near 3730 cm-1. Very strong Br\uf8nsted acidity is generated by the presence of sulfate impurities. \ua9 1985

Energy efficiency and waste reuse: A solution for sustainability in poor West African countries? Case study of the shea butter supply chain in Burkina Faso

National audienceIn West African countries, the objective of producer insertion in competitive markets is often associated with the need to modernize and mechanize production processes, i.e., replace labour by machines. This excludes traditional producers who can barely comply with the economic criteria but who must remain competitive to generate higher incomes. The challenge is to improve the efficiency of traditional methods in supply chains rather than imposing modern technologies that producers hardly adopt. Moreover, West African populations suffer from not having cheap and available energy sources. They, therefore, have to be imaginative for more efficient energy use in order to improve the productivity and quality of their products and support sustainable rural development and incomes. Building on the case study of the shea butter supply chain in Burkina Faso, this article proposes an original approach consisting of improved energy use for a more competitive and sustainable activity. The traditional butter production process consumes a great deal of energy from firewood and generates a lot of organic waste that could be used as an energy source. We examined the feasibility of using alternative energy techniques that could be taken on board as they are simple and designed from local resources, whilst using by-products from the shea butter production chain as biofuels to partially replace firewood. We showed that using alternative energy techniques, taken one by one or combined, can lead to lower energy use and thereby increase women's incomes, whilst helping to conserve forests

Role of Hydroxyl Groups in the Basic Reactivity of MgO: a Theoretical and Experimental Study

Clean (i.e., carbonate- and hydroxyl-free) and hydroxylated MgO surfaces of various morphologies were used to study the correlation between thermodynamic Brønsted basicity (evaluated by the deprotonation of methanol and propyne followed by FTIR) and basic reactivity (evaluated by the conversion of 2-methyl-but-3-yn-2-ol (MBOH)). A correlation is evidenced for clean surfaces, but for hydroxylated surfaces, OH groups, though weak Brønsted bases, are much more active than oxide O2- ions. Some of the hydroxyl groups whose VOH infra-red stretching band is included in the narrow high-frequency OH band were shown to be responsible for such activity. In order to identify them, the irregularities of surfaces involving low coordination (LC) ions were modeled by DFT calculations (mono- and di-atomic steps for 4C ions, corners, kinks and divacancies for 3C ions). All of them dissociate water: except for kinks and divancancies where the OH formed can be considered as isolated, in all the other cases, OH groups are H-bonded. The í OH infra-red frequencies obtained by calculations are consistent with the experimental spectrum which exhibits two domains: the broad low-frequency (${\rm V}_{\rm OH} 3700$ cm-1) corresponds to isolated OH (O2CH, O3CH and O4CH in kinks and divacancies) and H-bond acceptor OH groups (O1CH and O2CH). The latter are inferred to be implied in basic reactivity of hydroxylated surfaces toward MBOH

Etude des procedes susceptibles d'ameliorer l'elaboration de silicium multicristallin a structure basaltique

CNRS RP 400 (686) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Role of Hydroxyl Groups in the Basic Reactivity of MgO : a Theoretical and Experimental Study

International audienceClean (i.e., carbonate- and hydroxyl-free) and hydroxylated MgO surfaces of various morphologies were used to study the correlation between thermodynamic Brønsted basicity (evaluated by the deprotonation of methanol and propyne followed by FTIR) and basic reactivity (evaluated by the conversion of 2-methyl-but-3-yn-2-ol (MBOH)). A correlation is evidenced for clean surfaces, but for hydroxylated surfaces, OH groups, though weak Brønsted bases, are much more active than oxide O2- ions. Some of the hydroxyl groups whose VOH infra-red stretching band is included in the narrow high-frequency OH band were shown to be responsible for such activity. In order to identify them, the irregularities of surfaces involving low coordination (LC) ions were modeled by DFT calculations (mono- and di-atomic steps for 4C ions, corners, kinks and divacancies for 3C ions). All of them dissociate water: except for kinks and divancancies where the OH formed can be considered as isolated, in all the other cases, OH groups are H-bonded. The í OH infra-red frequencies obtained by calculations are consistent with the experimental spectrum which exhibits two domains: the broad low-frequency (${\rm V}_{\rm OH} 3700$ cm-1) corresponds to isolated OH (O2CH, O3CH and O4CH in kinks and divacancies) and H-bond acceptor OH groups (O1CH and O2CH). The latter are inferred to be implied in basic reactivity of hydroxylated surfaces toward MBOH