here's a suggestion to deposit metal catalysts on a thin supporting film. The resulting specific area is favourable, one machine can deposit about any metal and works quickly.
The machine resembles the ones that deposit aluminium on polyester film for candy wraps and space blankets. It can be adapted from such a machine, new or second-hand. The machine passes the supporting film between two mandrels and deposits meanwhile the catalyst metal under vacuum. Covering both sides of the film is better, at the same pass even better.
Ptfe, Pe and Pp resist many chemicals and may be the supporting film, but they can't be very thin. Nickel, cobalt and alloys can be electrodeposited as standalone films with 8µm thickness and up. Tantalum and niobium can be laminated but not as thin. Thin tantalum deposited on supporting nickel-cobalt would improve the chemical resistance, and the catalyst metal could come atop.
Ptfe, Pe and Pp need some surface treatment before the catalyst adheres. A supporting metal film probably needs cleaning. Doing it in the same machine (by plasma?) without breaking the vacuum or low pressure thereafter seems better.
Traditionally for semiconductors, an electron gun evaporates the varied metals, even refractory ones. Sputtering is a more recent source, also flexible. A nanosecond pulsed laser should be considered. A machine for candy wraps takes coils over 1m tall, so stacking several souces of catalyst metal seems better.
Measuring off-the-fly the deposited thickness at various heights to control the sources is advantageous with expensive metals. Observing the light reflectance at few short wavelengths may suffice.
To let the reactants, products and solvents through, the plies must be separated, for instance with a thin wire, as they are stacked or rolled. Alternately, a rolling mill can make corrugations or bumps in the films, possibly at every second ply. If the catalyst coil or stack stays loose, being held together by a loop of metal for instance, it's easier to clean and regenerate - advantage over a sintered ceramic.
When seeking compactness, the channels would be thin too, hampering the flow of liquids. An answer is to provide a set of additional wider ways, possibly cut by laser across the stack or coil, to and from the thin channels - possibly as a tree, like animals have arteries, arterioles, capillaries, venules and veins. This applies to sintered materials too.
Marc Schaefer, aka Enthalpy