Effect of ammonia and methylamine as coadsorbates on the adsorption behavior of benzene in NaBeta zeolite studied by FTIR spectroscopy

The single component (benzene, ammonia and methylamine) adsorption and the effect of coadsorbates such as ammonia and methylamine on the adsorption of benzene in NaBeta zeolite have been investigated by FTIR. The changes in the framework upon adsorption of different molecules have been checked and discussed. The benzene location in NaBeta zeolite with or without the presence of coadsorbates has been correlated with the structural and chemical properties of zeolite and with the interaction strength of ammonia, benzene and methylamine with NaBeta zeolite. It reveals that only cations, but not 12R windows of NaBeta are preferentiel adsorption sites for benzene even in the presence of coadsorbates such as ammonia and methylamine. The quantitative analysis on the amount of benzene adsorbed on cations when benzene is present alone suggests that all the cations present in NaBeta zeolite are accessible to benzene molecules. Ammonia and methylamine can interact not only with Na+ ions via the lone pair on nitrogen atoms but also with the large number of silanols present in NaBeta zeolite. The interaction strength of ammonia, methylamine and benzene with NaBeta ranks in the order of methylamine/NaBeta>benzene/NaBeta>ammonia/NaBeta. The interaction of ammonia and methylamine with NaBeta causes an important modification of lattice parameter, indicating the deformation of zeolite framework. However, no significant deformation is observed upon adsorption of benzene alone. In spite of the deformation of zeolite framework, only adsorption of benzene in Na+ ions has been observed and no change in the location of benzene in NaBeta zeolite is detected upon coadsorption of either ammonia or methylamine, being contrary to what we observed in KL zeolite upon coadsorption of methylamine and in NaEMT upon coadsorption of ammonia.