Espalhamento de elétrons por moléculas precursoras da biomassa

Abstract

Replacing fossil fuels with biofuels obtained from renewable sources is an important strategy to minimize greenhouse gas emissions. In this sense, the conversion of lignocellulosic biomass into biofuels is a sustainable source of energy to meet global energy demands. Low-energy electrons in plasmas have the potential to overcome the biomass physicochemical resistance enabling the production of high value chemicals. This happens due to chemical breakdown induced through dissociative electron attachment or electron impact excitation- or ionizationfragmentation processes. In this thesis was investigated the electron scattering by the biomolecules phenol and furfural, that are subunits of the lignocellulosic biomass. Experimental electron-energy loss spectra (EELS) were recorded to phenol and furfural, measured at impact energies of 15, 20, 30, 40 and 250 eV, for angles between 10◦ and 90◦. These spectra were used to derive Cross Sections (CS) and Generalized Oscillator Strengths (GOS) for the dipoleallowed electronic transitions, also allowing the determination of their Optical Oscillator Strengths. Differential cross sections (DCS’s) were measured for the electron-impact excitation of the electronic states as well as of a number of composite unresolved vibrational modes in phenol. These investigations provide the first results published on the literature to singlet and triplet excited electronic states of phenol, up to the first ionization potential and, to the vibrational excitation Cross Sections. In addition, it were obtained integral cross sections (ICS’s) data for electron impact vibrational and electronic excitations in phenol. Triple differential cross sections (TDCS) data for the electron-impact ionization of phenol (e,2e) were generated with coplanar asymmetrical kinematics for an incident electron energy of 250 eV. Regarding to furfural, the experimental data were used along with calculations in order to assign the excited states. The good agreement between the theoretical results and the measurements allows providing the first quantitative assignment of the electronic state spectroscopy of furfural over the energy range studied.