Conversion of Methanol to Hydrocarbons over Nd/B-Modified Dealuminated HZSM-5

Abstract

A series of catalysts were obtained by dealumination of an HZSM-5 zeolite followed by modification with neodymium and/or boron. These samples were tested in the conversion of methanol to hydrocarbons to enhance selectivity towards C₂–C₄ olefins, and especially towards propylene. X-ray diffraction analysis, low-temperature nitrogen adsorption, and ammonia temperature-programmed desorption were employed to characterize the acidic properties and microporous structure of the modified catalysts. The methanol conversion was carried out in a plug-flow fixed-bed reactor at atmospheric pressure and temperatures of 250–550°C in a nitrogen flow. It is shown that dealumination and bimetal modification significantly increase the mesopore volume, facilitate the dispersion of the modifier’s particles on the external surface and in the pores of the zeolite, and markedly reduce the density of strong acid sites. The highest selectivity towards C₂–C₄ olefins (82.3%) and the highest propylene selectivity (52.4%) were achieved at 500°C in the presence of the bimetal-modified dealuminated catalyst (4%Nd-4%B-DHZSM-5). The high selectivity towards light olefins and propylene are attributed to the fact that dealumination and bimetal modification provide a significant increase in the ratio of mesopore volume to total pore volume and a reduction in the density of strong acid sites.