Hydrohalogenation of Platinum–Palladium/H-ZSM-5 Catalysts for n-Hexane Hydroconversion

Abstract

Catalysts containing 0.3%Pt-, 0.3%Pd-, and 0.3%Pt-0.3%Pd-/H-ZSM-5 were prepared and modified via hydrochlorination or hydrofluorination and tested for n-hexane hydroconversion throughout a reaction temperature range of 250–500°C. Bifunctionality parameters of the current catalysts were characterized via acid site strength distribution by NH₃-temperature programmed desorption, metal(s) component dispersion by H₂ chemisorption, and temperature programmed reduction. Hydrochlorination was found to leach less structural zeolitic Al in the catalyst than hydrofluorination. HCl modification improved n-hexane hydroisomerization activity, whereas HF treatment was deteriorative via causing pore diffusion restriction by excessively formed debris. Acid sites density and strength were higher on hydrofluorination than on hydrochlorination. Surface area and metals dispersion were higher for hydrochlorinated catalyst but lower for the hydrofluorinated one. Maximum isohexanes production (70%) was realized on hydrochlorinated catalyst at 350°C with 100% selectivity. Crystal unit cell d-spacing, obtained by XRD, was smaller by hydrofluorination than by hydrochlorination, whereas such d-spacing was increased through incorporating Pt and increased more via Pd addition during preparation.

Keywords:

• H-ZSM-5
• hydroisomerization
• Pt
• Pd
• hydrochlorination
• hydrofluorination