in order to provide a wide application of the proton exchange membrane fuel cell (PEMFC) technology, reduce cost and improve characteristics of PEMFC-based power plants, it is necessary to create a compact and economic apparatus for deep cleaning of converted fuel from carbon monoxide. The obstacle of preferential CO hydrogenation is the presence of about 20 vol.% of CO2 and the same amount of H2O along with 1 vol.% of CO. The compact apparatus for deep purification from CO can be only created basing on the highly active (providing 10-20 ppm CO in the outlet gas at GHSV above 6000 h(-1)) and selective catalyst (at least 30% of CH4 and higher hydrocarbons is to be formed by CO hydrogenation). In the present paper, we study the process of preferential CO hydrogenation over the nickel-chromium catalyst, which was found earlier to be efficient in the CO hydrogenation over fine catalyst fraction: outlet CO content below 20 ppm and the selectivity not less than 0.3 at GHSV above 6000 h(-1). We report on the effect of the catalyst grain size on the CO hydrogenation selectivity and consider the possibility of using permeable composite materials for weakening the intraparticle diffusion constrains and for efficient performing the reaction under the study close to the kinetic region. (c) 2007 Elsevier B.V. All rights reserved.