IFEG   20353
INSTITUTO DE FISICA ENRIQUE GAVIOLA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Quantification of silanol groups on mesoporous materials using Solid State Magnetic Resonance
Autor/es:
J. VILLARROEL ROCHA; K. SAPAG; G.A. MONTI; M.C. VALENTINUZZI
Lugar:
Santa Fe
Reunión:
Congreso; III Taller de Resonancia Magnética "NMR and EPR at the Forefront of Research"; 2016
Resumen:
Porous materials have properties which make them suitable for catalytic applications. They are classified according to pore size in: microporous (diameter less than 2 nm), mesoporous (diameter between 2 and 50 nm) and macroporous (greater than 50 nm diameter). In this work, we study mesoporous materials by Solid State Nuclear Magnetic Resonance. Such materials have three-dimensional arrangements of SiO4 and are characterized by an uniform size distribution and narrow pore. Different structures can be obtained according to the synthesis process; in this case we study the M41S and SBA families. From the M41S family we studied the MCM-41 and MCM-48 materials. MCM-41 is the most common and stable, with hexagonal phase. MCM-48 is the most complex phase, with canal systems that interlock to form a network of cubic symmetry. From the SBA Family we studied the SBA-15 materials; they are thermally more stable than the M41S family and have micropores connecting channels together randomly generating a dual porosity.These mesoporous materials have characteristic SiOH arrangements that are identified by a chemical shift in the 29Si-NMR spectrum, with peaks approximately at -90, -100 and -110 ppm which are characteristic of the signals Q2 [(SiO)2(OH)2], Q3 [(SiO)3Si (OH)] and Q4 [(SiO)4] respectively. These signals represent different degrees of condensation of silicon present in these materials. We identified the groups present and calculated their relative proportion in each of the samples to determine the amount of silanol groups.In all the spectra, Q4 is the most intense signal, indicating that among the species of silicon, the tetra coordinated one has the highest proportion. With respect to the total amount of silanol groups (2Q2 + Q3) corresponding to structures SBA-15 synthesized by Soxhlet extraction no significant differences were observed; instead a reduction of approximately 40% was found in calcined samples.