Hydrocarbon synthesis over palladium/ZSM-5 bifunctional catalysts

Hydrocarbon synthesis during carbon monoxide hydrogenation over Pd/MZSM-5 (M=H, Na, La) and Pd/SiO2 has been investigated. The turnover frequency depended on the cation-exchanged form of the support, decreasing in the order Pd/NaZSM-5>Pd/LaZSM-5>Pd/HZSM-5>Pd/SiO2. While only methane and oxygenates were formed over Pd/NaZSM-5 and Pd/SiO2, high yields of C2–C3 alkanes and polymethylbenzenes were produced over both Pd/HZSM-5 and Pd/LaZSM-5. Reaction temperature and feed compositions affected product distributions, particularly aromatic yields. Infrared spectroscopy and kinetic evidence indicate that hydrocarbon synthesis over Pd/ZSM-5 occurs via a bifunctional route, consisting of carbon monoxide hydrogenation to methanol, followed by conversion of this oxygenate on zeolite Brønsted acid sites.