Synthesis of efficient bifunctional Pt/PWA-Nb2O5 nanocatalysts for catalytic isomerization of n-hexane: Experimental and optimization studies

Abstract

Herein, high activity/selectivity isomerization nanocatalysts composed of Pt/PWA-Nb2O5 have been synthesized for the first time for n-hexane isomerization. The synthesized catalysts were characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), filed emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), nitrogen adsorption-desorption isotherms, and thermogravimetric Analysis (TGA). The n-hexane isomerization experiments were conducted over synthesized catalyst at different reaction temperatures (Tem. = 120−200 °C), liquid hourly space velocity (LHSV = 1–3 h−1), and H2:n-hexane mixture with a molar ratio (H2/HC = 0.5–1.5). The response surface methodology (RSM) designed by Box-Behnken Design (BBD) was used to optimize the catalytic isomerization. Statistical Analysis of experimental data was accomplished to generate the second-order polynomial model. The optimum reaction parameters were TEM = 160 °C, H2/HC = 1, and LHSV = 2 h−1, in which 51 % isomerization has been obtained. The high isomerization conversion and selectivity were achieved chiefly due to the highly dispersed Pt nanoparticles, appropriate acidity provided by Keggin PWA heteropolyacid with a balanced Brønsted/Lewis acid sites ratio, and highly ordered large mesopores.

Keywords

• Phosphotungstic heteropoly acid
• Niobium oxide
• N-hexane
• Isomerization
• Multifunctional catalyst
• Optimization