II International Symposium on Carbon for Catalysis ABSTRACTS

PL-2
The surface of these nanoporous carbons, produced by pyrolysis in either nitrogen or
carbon dioxide, has almost no surface functionality as measured by Boehm titration, TGMS
or surface spectroscopic techniques. This can then be readily enhanced by a variety of
techniques including gas and liquid phase oxidation although some modifications can also be
introduced by modifying the resin precursors. Some preparative conditions can lead to
carbons that function as effective oxidation catalysts in the absence of any added metals 3 .
The resulting functionality also has a major influence on the dispersion and distribution of any
added metals.
The catalytic performance of the carbons and the metal/carbon systems have been
evaluated for use in gas phase reactions (Ruthenium catalysed ammonia synthesis) and
multiphase oxidation and hydrogenation reactions using slurry phase, trickle bed and
monolithic (Taylor flow) reactor geometries. These studies have provided the foundation for
the recent evaluation of the resin derived systems in membrane reactors.
Membrane Systems
The two main driving forces for the development of catalytic membrane reactors have
been either safety, where in oxidation reactors the oxygen and hydrocarbon feeds can be
separated, or equilibrium shifting, where typically one of the products of the reaction is
selectively removed. The earlier studies tended to concentrate on gas phase dehydrogenation
reactions whilst recently there has been greater interest in oxidation and in particular
multiphase oxidation reactions. In the latter case the oxygen is generally in the gas phase on
one side of the membrane whilst the reagent to be oxidised is in the liquid phase on the other
side, with the gas/liquid interface located within the membrane and local to the active catalyst
species. A key requirement in all cases, but most critically in the gas phase applications, has
been the presence of a highly selective surface layer. There has been a significant interest in
for instance dense oxide layers to give very high selectivity for high temperature oxygen
permeation and dense palladium layers for high temperature hydrogen although the majority
of the work has focussed on nanoporous membrane layers which have higher permeabilities
and do not require high temperatures for effective operation. These nanoporous ceramic
systems include zeolites, amorphous oxides and carbon.
To achieve acceptable permeabilities the separating layer must be very thin, typically less
than a few microns and preferably