NOVELTY - An apparatus for steam reforming of hydrocarbons comprises steam reformer containing externally-heated vertical tubes (17), each tube having inlet for feed gas mixture containing hydrocarbon and steam, and outlet for reformed gas mixture in which the tubes contain a particulate steam reforming catalyst adjacent the outlet and a structured steam reforming catalyst adjacent the inlet.    USE - An apparatus for steam reforming of hydrocarbons (claimed).    ADVANTAGE - The apparatus maximizes performance and catalyst lifetime without compromising reformer performance or catalyst lifetime; overcomes the need for extensive support structures often required for structured catalysts, particularly at the bottom of the tubes due to high temperature, total weight, and pressure drop; and shortens loading and unloading of the structured catalyst, improving flexibility to provide tailored reforming solutions.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) steam reforming of hydrocarbons which involves passing feed gas mixture containing hydrocarbon and steam through externally-heated vertical tubes disposed within a steam reformer and recovering reformed gas mixture from tubes in which each tube has inlet for feed gas mixture and outlet for reformed gas mixture, and tubes contain a particulate steam reforming catalyst adjacent the outlet and a structured steam reforming catalyst adjacent the inlet so that the feed gas mixture contacts the structured steam reforming catalyst and then the particulate steam reforming catalyst; and    (2) use of apparatus for synthesis of hydrogen, methanol, dimethyl ether, olefins, ammonia, urea, or hydrocarbon liquids.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of a gas-heated steam reformer having externally-heated tubes containing a structured catalyst and a particulate catalyst.    Outer insulated pressure shell (10)    Heat exchange zone (12)    Tube sheet (15)    Process fluid supply conduit (16)    Tubes (17)