Asymmetry effects in membrane catalysis

Catalytic processes using porous ceramic where catalytic coatings on the microchannel walls are of current interest for the creation of high speed and compact membrane reactors, especially for the reactions of C1-substrates. Nanoporous ceramic membranes with variation of pore size as a non-linear gradient can play an important role for selective mass-transfer control in membrane catalysis. This paper presents unusual results demonstrating an anisotropy in selective mass transfer in modified catalytic membranes and a related change in C1 reaction route. To create gradient porosity, the directed formation of catalytic walls inside ceramic microchannels for C1 reactions (e.g., methanol decomposition) is achieved by the alkoxo method. Metal-ceramic catalytic membranes with gradient porosity in the range of 2–3000 nm pore size were obtained. The proposed structural design of membranes, including the combination of catalytic coatings inside membrane channels with a top coating of a meso-porous metal oxide layer, exhibits an anisotropy in the catalytic reaction and gas permeation correlating with an improved hydrogen production. Modified high temperature ceramic membranes provide high speed methane conversion into syn-gas and light hydrocarbons at 500–650 °C, showing a good potential for the systematic study of asymmetry effects in membrane catalysis.