Catalytic Teflon AF-2400 membrane reactor with adsorbed ex situ synthesized Pd-based nanoparticles for nitrobenzene hydrogenation

Abstract

Among the unconventional approaches of supporting catalyst nanoparticles, the layer-by-layer assembly of polyelectrolyte multilayers for nanoparticle adsorption represents an easy and convenient method. It enables the deposition of singularly adsorbed nanoparticles and prevents them from aggregating. In this work, polydopamine was grafted on the internal surface of a Teflon AF-2400 tubular membrane, known for its excellent permeability to light gases and inertness to chemicals. Poly(acrylic acid) and poly(allylamine hydrochloride) were sequentially adsorbed on the modified surface of the membrane. Ex situ synthesised spherical, cubical, truncated octahedral palladium and dendritic platinum-palladium nanoparticles were then incorporated. The catalytic membranes were assembled in a tube-in-tube configuration and tested for 6 h of continuous nitrobenzene hydrogenation with molecular hydrogen. Stable conversion was observed for the truncated octahedral and dendritic nanoparticles, while a progressive deactivation was observed for the other nanoparticles. Due to their small size, the 3.7 nm spherical nanoparticles exhibited the highest reaction rate, 629 molreactant/(molcatalyst⋅h), while the cubical nanoparticles showed the highest turnover frequency, ∼3000 h−1. The reactor concept developed in this work demonstrates how such a tool can serve as platform for conducting continuous multiphase catalytic reactions in flow using singularly adsorbed and finely tuned nanoparticles. The small volume of pressurised gas present in the tube-in-tube reactor offers improved process safety compared to batch, while the Teflon AF-2400 membrane provides control over the gas permeation during reaction