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

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, poly dopamine was grafted onto 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 onto the modified surface of the membrane. Ex situ synthesized spherical, cubical, truncated octahedral palladium or dendritic platinum-palladium nanoparticles were then incorporated. The catalytic membranes were assembled in a tube-in-tube configuration and tested over 6 h of continuous nitrobenzene hydrogenation with molecular hydrogen. Stable conversion was observed for the truncated octahedral and dendritic nanoparticles, while a progressive deactivation occurred for the other nanoparticles. Due to their small size, the 3.7 nm spherical nanoparticles exhibited the highest reaction rate, 629mol(reactant)/(mol(catalyst).h), while the cubical nanoparticles showed the highest turnover frequency, similar to 3000 h(-1). The reactor concept developed in this work demonstrates how such a design can serve as a platform for conducting continuous multiphase catalytic reactions in flow using singularly adsorbed and finely tuned nanoparticles. The small volume of pressurized gas present in the tube-in-tube reactor offers improved process safety compared to a batch process, while the Teflon AF-2400 membrane provides control over the gas permeation during reaction.