There is disclosed a catalyst support for selective gas phase reactions in a tubular fixed bed reactor comprising a metallic monolith having channels the walls of which are adapted to receive a catalytically active phase or an intermediate layer acting as a carrier for a catalytically active phase. The monoliths are coated with catalytically active material and loaded lengthwise into tubular reactors, the channels being parallel to the length of the reactors. The catalysts are particularly useful in the chlorination/oxychlorination of alkenes and alkanes, and the oxidation of alkenes. Compared with the use of conventional catalysts in pellet form or in the form of ceramic monoliths the catalysts of the invention offer greater yields and selectivity, the avoidance of hot spots, greater catalyst life and flexibility in use.