Tailoring the mesopore structure of HZSM-5 to control product distribution in the conversion of propanal

Abstract

Conversion of propanal to gasoline-range molecules was investigated over a series of HZSM-5 catalysts with controlled mesoporosity generated by desilication. Characterization of the structure of the solid by powder X-ray diffraction (XRD), scanning electronic microscopy (SEM), ammonia and isopropylamine temperature programmed desorption (TPD), and n-butane diffusivity measurements confirmed the development of various degrees of mesoporosity in the zeolites. This structural modification seems to have little influence on Bronsted acid density. The catalyst stability was improved upon desilication due to an increase in coke tolerance. The product distribution of the propanal conversion was found to vary with the severity of the desilication. Increasing the extent of desilication gradually reduced the aromatization and cracking reactions, due to a reduction in the fraction of micropores and in the diffusion path length. Mildly desilicated samples were found to exhibit the best stability on stream and inhibited coke formation.