Mattos L.V.,Federal University of Fluminense |
Jacobs G.,University of Kentucky |
Davis B.H.,University of Kentucky |
Noronha F.B.,Brazilian National Institute of Technology
Chemical Reviews | Year: 2012
Significant progress has been made in gaining insight into the reaction mechanisms of ethanol reforming. To this end, infrared spectroscopy has been a powerful tool in achieving this goal. The dissociation of ethanol to ethoxy species can occur on the support, and those with sufficiently labile O adatoms or OH groups offer a means of accomplishing this step. Dehydrogenation of the ethoxy species to acetaldehyde is very likely assisted by the metal particles added to the support, as well as the presence of labile O adatoms or hydroxyl groups located on the support. A major route to catalyst deactivation is that of carbon formation. Temperature-programmed oxidation, used to characterize the nature of carbon deposits, demonstrated significant amounts of carbon deposited on the catalyst surface. The metal appears to operate across the metal-oxide junction to assist in hydrogen transfer and related reactions such as acetate demethanation.
Neto R.C.R.,Brazilian National Institute of Technology |
Schmal M.,Federal University of Rio de Janeiro
Applied Catalysis A: General | Year: 2013
The different CeO2 oxides and mixed oxide CeZrO2 showed nanosized structures and morphologies in particular distinct structural and surface properties. These catalysts were effective in the iso-synthesis reaction. The flowerlike CeO2 (F) and the mixed oxide (CeZrO 2) showed the highest selectivity toward isobutene and isobutene and low methane formation. The turnover frequency (TOF) related to the total basicity and total acid sites are equal for all catalysts within a factor less than 2 and did not change with the oxygen lattice capacity (OSC), which confirms that the reaction is structure insensitive. The selectivity of total hydrocarbon and of CO2 are independent of the basic sites. However, the selectivity of total iso-C4 exhibits a linear relationship with the basic sites. The mixed oxide (CeZrO2) presented the strongest basic sites and thus the highest selectivity to iso-C4. Significant is the influence of Lewis acid sites on the selectivity of isobutene increasing and isobutane decreasing both linearly with Lewis acid sites. The ratio isobutene/isobutane presented a linear relationship with the Lewis acid sites which are directly related to OSC capacity of reducible oxides. © 2012 Elsevier B.V.
Braga M.D.V.,Brazilian National Institute of Technology
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2013
The genomic distance typically describes the minimum number of large-scale mutations that transform one genome into another. Classical approaches to compute the genomic distance are usually limited to genomes with the same content and take into consideration only rearrangements that change the organization of the genome (i.e., positions and orientation of pieces of DNA, and number of chromosomes). In order to handle genomes with distinct contents, also insertions and deletions of pieces of DNA - named indels - must be allowed. Some extensions of the classical approaches lead to models that allow rearrangements and indels. In this work we introduce a new graph structure that gives a unified view of these approaches, present an overview of their results and point out some open problems related to them. © 2013 Springer-Verlag.
Brazilian National Institute of Technology | Date: 2013-11-22
This invention concerns a process for obtaining lactic acid in a single stage by direct oxidation in an aqueous medium of 1,2-propanediol in the presence of a mixture of heterogeneous catalysts, in conditions of low temperature and low pressure. The reaction takes place in the presence of oxygen and a mixture of heterogeneous catalysts, consisting of a first catalyst of noble metal supported in metallic oxide, and a second basic solid catalyst. The mixture of catalysts is easily recovered by filtration at the end of the process, to be reused. The lactic acid is obtained directly, with selectivity between 50% and 97%.
Brazilian National Institute of Technology and Petrobras | Date: 2011-08-18
Current industrial processes for the production of lactic acid are fermentative, using lactic bacteria which require large volumes and create large quantities of liquid residue which need to be treated. Chemical literature also describes the use of reaction systems with homogeneous catalysis, which also pose problems which in turn impact our costs, owing to the increased requirements in terms of the control of the process and the type of reactor necessary. Therefore, the process used thus far, carried out in hydrogenolysis, isomerisation and oxidation are defective, owing to the significant formation of sub-products, mainly pyruvic acid and acetic acid and the low yield of lactic acid. Lactic acid can also be obtained by the chemical transformation of other sources other than starch, but which are also renewable. The present invention provides a oxidative process for the production of lactic acid, in which the reaction with pure oxygen or oxygen mixed with air takes place below 100 C. and under autogenous pressure, using a noble metal catalyst in a metal oxide. The process uses 1,2-propanediol as primary material, derived from the reaction of hydrogenolysis of the glycerine, and reaches yields of more than 70% of lactic acid and less than 30% in sub-products, pyruvic acid and acetol.