Influence of Solvents and Additives on the Pyrophoricity of Palladium on Carbon Catalyst after Hydrogenation

Abstract

We performed a systematic investigation of the conditions causing or preventing self-ignition of spent palladium on a carbon catalyst after hydrogenation reactions. The solvent used for hydrogenation plays a major role. We compared the pyrophoricity of a filtered catalyst, produced with 11 commonly used hydrogenation solvents. Self-ignition was only observed with alcoholic solvents. We also show that self-ignition of spent catalyst can be prevented by an efficient water rinse and/or addition of thiophene. A method is also presented to evaluate the risk of spontaneous ignition of the catalyst cake after hydrogenation with palladium on carbon in a systematic way.

A unified approach to the synthesis of amines through a highly selective and broadly applicable imine reduction using modified Pd-nanoparticles

“…Initially, we considered that under equilibrating conditions, in aqueous solution, the aldehyde may exist as a hydrate, which is less prone to reduction, effectively protecting it. Indeed, incubating a sample of pmethoxybenzaldehyde in a mixture of 18 O-labelled water and ethanol, allowed for the direct detection of 18 Olabelled aldehyde (and the intermediate 18 O-labelled gem-diol hydrate). This result establishes the reversible formation of the gem-diol hydrate under conditions similar to those used in our reaction system.…”

“…The safe handling, disposal and recycling of Pd/C at scale also poses challenges at commercial scale. 18 Finally, the uncontrolled 'dissolution' of presumed-heterogeneous Pd/C adds to variability. A few groups have investigated bespoke metal catalysts to address these concerns, including supported metal catalysts, bimetallic alloys and core shell nanostructures.…”

Shape and Stability Matter: Enhanced Catalytic Reactions via Sol–gel-Entrapped Catalysts

“…Finally, the organosilica-entrapped Pd(0) catalyst is not pyrophoric and does not require excluding air from reactions, as it happens with highly pyrophoric conventional Pd/C catalysts. [27] Self-ignition of spent palladium on a carbon catalyst after hydrogenation reactions is always observed with alcoholic solvents [28]. Hence, the use of a non-pyrophoric catalyst such as SiliaCat Pd(0) eliminates the risk of spontaneous ignition of the catalyst cake after hydrogenation, providing a key technical advantage when considering the industrial upscale of p-nitrophenol hydrogenation en route to paracetamol using pressurized H 2 under flow as reducing agent.…”

Shape and stability matter: enhanced catalytic reactions via sol-gel entrapped catalysts

“…27 Self-ignition of spent palladium on a carbon catalyst after hydrogenation reactions is always observed with alcoholic solvents. 28 Hence, the use of a non-pyrophoric catalyst such as SiliaCat Pd(0) eliminates the risk of spontaneous ignition of the catalyst cake after hydrogenation providing a key technical advantage when considering the industrial upscale of pnitrophenol hydrogenation en route to paracetamol using pressurized H2 under flow as reducing agent.…”