Strategies for palladium nanoparticles formation on halloysite nanotubes and their performance in acetylene semi‑hydrogenation

Pd nanoparticles are widely applied in catalysis. In this work, the deposition of Pd nanoparticles onto halloysite (Hal) nanotubes from different Pd precursors and solvents has been investigated. The prepared Pd/Hal catalysts have been characterized by low-temperature N2 adsorption, transmission electron microscopy, zeta potential measurement, and tested in the hydrogenation of acetylene. On calcined Hal, the largest nanoparticles are formed in acid media, and the smallest are formed in non-aqueous one. Silanization of halloysite decreases absolute values of its zeta potential significantly and drops PdNPs size twice. Catalytic tests have shown that acetylene conversion and selectivity to ethylene depend on the deposition method, and the most active catalysts were prepared from Pd acetate dissolved in acetone. The lowest activity and highest selectivity to ethylene were demonstrated by the azine-modified halloysite, that could be related to Pd poisoning with nitrogen.