Catalytic properties of the graphene oxide / palladium composites as the function of the fabrication method
In this work we used the two step synthetic procedure to prepare palladium nanoparticles (Pd-NP) on graphenic support by impregnating graphene oxide (GO) with Pd(II) ions, and by subsequent thermal or chemical reduction of palladium. The composite materials were prepared with different Pd content: 1.5% and 15.9%. The intermediate and final products were characterized by TGA, XPS, XRD and SEM. The as-prepared materials were tested for the catalysis of the hydrogenation of acetylene to ethylene, the crytical reaction in the industrial production of polyethylene. The catalysts were tested in the pilot scale plant reactor, at conditions, very similar to those used in the real industrial processes. The composite material, prepared by solid phase thermal reduction, exhibited very low catalytic properties, due to the formation of the protective graphene layer on the surface of Pd-NPs, suggesting that the thermal reduction method is not suitable for preparing the palladium-based catalysts on the carbon support. The chemically reduced sample, with 1.5% Pd content, demonstrated good catalytic activity with the conversion factor ranging from 61% through 90% at 40°С and 90°С, respectively, with good selectivity. At 15.9% Pd content, the conversion factor was 100% already at 30°С. The sample performed well even after doubling the flow rate of the feed ethylene mixture, as compared to the standard rate used for testing commercial catalysts. It successfully functioned for three consecutive days of operation, but the catalytic activity partially decreased on the day 3 due to intensive usage.