The role of the compositions of HZSM-5 zeolites modified with nanosized anatase in propane and ethanol conversion

Abstract

For the first time catalytic systems based on HZSM-5 zeolites (Si/Al=12, 25, 40) with nanosized anatase (NA) were obtained in situ by a modified hydrothermal method and a sol-gel method. Initial HZSM-5 and NA/HZSM-5 were characterized (XRPD, XAS, FT-IR, DSC, BET, XPS, SEM, TPD) and analyzed in the reactions of propane (liquefied petroleum gas) conversion (РС; temperature range 200–870 °С) with the formation of the main products propylene (C3H6, PP) and ethylene (C2H4, ETH) and liquid ethanol conversion (EC; temperature range 150–360 °C) with the formation of diethyl ether ((C2H5)2O, DEE) and ETH. In the PC reaction the maximum selectivity (SETH = 75%) and conversion (αP = 65%) were obtained on HZSM-5(40) (650 °С). With an increase in the NA content in NA/HZSM-5 SETH value increases up to 85%. In the EC reaction SDEE/ETH~98–99% was reached on HZSM-5(25) (200 °C) and HZSM-5(40) (300 °C); the αE to ETH is comparable (94%) for all HZSM-5 (300 °C). Modification of HZSM-5 with NA leads to a shift in the EC reaction temperature to lower temperature region (αE to ETH ~98% at 280 °C) with SDEE/ETH~94–100% for NA/HZSM-5(25) and NA/HZSM-5(12) obtained by a modified hydrothermal method. It was established the relationship between HZSM-5 and NA/HZSM-5 catalytic activity and their characteristics: Si/Al, NA content and Ti coordination number (NA/HZSM-5), the content of "zeolite water" with OH groups, specific surface area, meso- and micropores volume and spherical particles size (HZSM-5), surface energy of adsorption centers (HZSM-5 and NA/HZSM-5), and hence the content of acid sites, the strength of which is also determined by the temperature of the catalytic reaction. The reaction mechanisms have been presented. The obtained NA/HZSM-5 catalysts have a higher or comparable catalytic activity to commercial ones, but low cost, ease of preparation, and versatility.