TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Bed: The void content is at least 60%, preferably at least 65%. The specific surface area is at least 20 cm2/cm3, preferably at least 25 cm2/cm3. The packed bed comprises particles with length at least 1 mm, preferably at least 2 mm, and an aspect ratio of at least 10, preferably 20-500, defined as the ratio of the length to the quotient of the volume over the external surface area. The particles fit within boundaries of a hypothetical cylinder with length equal to that of the particles, and the ratio of the length to the diameter of its circular cross section is at least 2, preferably 4-50. The total volume of the support is 5-50 %, preferably 10-40% of the bed volume.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Catalyst: The external surface of the catalyst (precursor) comprises a Group VII metal, preferably cobalt, supported on a support of refractory oxide, preferably silica, alumina, titania, zirconia, or mixed oxides or physical mixtures of these. The metal is at least partly present as metal, and the support exists as particles, extrudates or foam. The supported catalyst are particles of a shell catalyst with an inert core and an outer layer including the metal (precursor). The core is based on metal, preferably aluminum, iron, copper and/or titanium, or the catalyst is in a fixed structure or arranged packing, preferably of metal gauze, woven or non-woven structure, honeycomb or foam. EXAMPLE - A shell metal catalyst precursor was prepared using aluminum shavings (4x1x0.1 mm). These were washed in aqueous phosphoric acid, and coated with zirconia paint ((RTM) ZYP Coatings, type ZO). An aqueous slurry of cobalt hydroxide and ammonium zirconium carbonate ((RTM) BACOTE 20, from MEL Chemicals) was spray coated onto the shavings, dried at 120degreesC for 2 hours and calcined in air at 500degreesC for 2 hours, to form a coating with average thickness 20 micron. These precursors were then used in a microflow reactor at 280degreesC, pressurized with a continuous flow of nitrogen to 1 bar abs. The precursor was reduced in situ for 24 hours with a mixture of nitrogen and hydrogen, the relative ratio of which was gradually increased from 0-100% during reduction. The water concentration in the off gas was kept below 3000 ppmv. Hydrocarbon synthesis involved a mixture of hydrogen and carbon monoxide at ratio of 1.1:1 and a pressure of 32 bar abs. The gas hourly space velocity was 795 Nl /l/h, and the reaction temperature was 213degreesC. After 40 hours, the space time yield as grammes product per liter catalyst particles per hours, methane selectively, C5 hydrocarbon selectivity, and carbon dioxide selectivity were 92 g/l/h; 6.2%w; 84%w: 2.0%w respectively.