Homogeneous and heterogeneous catalytic behavior of Ni-porphyrines immobilized in SBA-15 for the esterification of DMT Original Research Article

New porphyrin-based hybrids materials, (SBA-15)-O-Si-(CH2)3-NH-CO-(CH2)2-OC-HN-5m-Etio-III-Ni2+ and (SBA-15)-O-Si-(CH2)3-NH-CO-(CH2)2-OC-HN-2-pyrrolic-m-5,10,15,20-TPP-Ni2+, were used as heterogeneous catalysts in the esterification reaction of dimethyl terephthalate (DMT) with ethylene glycol (EG) in semi-batch conditions. These results were compared with those obtained for homogeneous catalysis using pure unsupported porphyrins, Etio-III-Ni2+ and m-5,10,15,20-TPP-Ni2+. The catalytic activity for all systems was determined by measuring the amount of methanol produced during the reaction. The kinetic parameter K was obtained for both processes resulting for the heterogeneous catalyst activation energies of 15.39 kJ/mol for SBA-15-Etio-III-Ni2+ and 23.77 kJ/mol for SBA-15-TPP-Ni2+, while for homogeneous catalysis the activation energies were 10.49 kJ/mol for Etio-III-Ni2+ and 23.45 kJ/mol for TPP-Ni2+. The catalytic efficiencies were determined for both processes resulting that the conversions and the activities were slightly higher for homogeneous processes respect to the heterogeneous ones.