A COMBINED EXPERIMENTAL AND COMPUTATIONAL STUDY OF ACETIC ACID AND METHANOL ADSORPTION ON H-BETA ZEOLITE

LINDINO, CLEBER A.; PERUCHENA, NÉLIDA MARIA; GOMES, GLAUCIO J.; ZALAZAR, M. FERNANDA; SCREMIN, FERNANDO R.; BUDKE COSTA, MICHELLE

BUENOS AIRES

Workshop; PRIMER WORKSHOP LATINOAMERICADO DE MODELADO MOLECULAR Y SIMULACIÓN COMPUTACIONAL; 2016

UBA

Different heterogeneous catalysts have been tested in the esterification of carboxylic acids and alcohols, including zeolites. On solid acids catalyst type zeolites, one might expect a similar esterification behavior than homogeneous catalysis, however little is known about the reaction pathway. Recently, Bedard et al1 studied the kinetic for acetic acid esterification with ethanol on H-zeolites using kinetic measurements, and they proposed a mechanism that proceeds through a surface AcOH/EtOH coadsorbed complex. However, due to the complexity of the reaction path, it is necessary study the elementary steps (including adsorption processes) of this chemical reaction in order to explain at molecular level the complete mechanism. In this work FTIR, FTIR-ATR spectroscopy, TGA and TGA/IR (Thermogravimetric analysis coupled with infrared spectroscopy) together with ab initio calculations at M06-2X/6-31G(D) level are used to study the adsorption of acetic acid and methanol on H-Beta zeolite as a first step of esterification reaction using zeolites. From the theoretical viewpoint, we study different models of adsorption of acetic acid and methanol on the surface of H-Beta zeolite following the mechanisms proposed by Bedard et al1. Frequency modes are also calculated and compared with experimental FTIR spectra. We provide information about the most stable species and their spectroscopic parameters. Our results show that, the acetic acid adsorption (by C=O group) followed by methanol co-adsorption give rise to the more stable complex (-197 kJ mol-1). Moreover, another stable species involved a complex of acetic acid/methanol adsorbed on the Brønsted acid site (-190 kJ mol-1) is found. Spectroscopic analysis of acetic acid adsorption shows the vC=O (1706 and 1668 cm-1), CH3 vibrational band (1487 and 1442 cm-1), and another vibrational band near 3200 cm-1. Theoretical spectrum indicated that the last one is associated with the interaction of hydroxyl group with the basic acid site of the zeolite, showing that the acetic acid is molecularly adsorbed by the carbonyl group on the surface of catalyst.