TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Component: At least one distributed combustion chamber is provided in a heat transferring relationship with the catalyst bed. The gas separation module is a tube (71, 72). A metal hydride precursor is separated from the reaction chamber by the gas separation module. It is located to react with hydrogen permeating the gas separation module to form a metal hydride. The powder of the intermediate porous layer has a Tamman temperature higher than the Tamman temperature of the hydrogen-selective membrane. The intermediate porous layer further comprises at least one material having a Tamman temperature less than or equal to the Tamman temperature of the hydrogen-selective membrane. The gas separation module comprises a layer of ceramic over the porous substrate and underlying the intermediate porous layer. The porous substrate of the gas separation module is oxidized. The surface of the porous substrate underlying the intermediate porous layer is seeded with nuclei of a hydrogen-selective material. The reactor is a steam reforming reactor and the catalyst bed is steam reforming catalyst bed. It is a dehydrogenation reactor and the catalyst bed is a dehydrogenation catalyst bed.    TECHNOLOGY FOCUS - METALLURGY - Preferred Material: The hydrogen-selective membrane is formed of palladium or its alloy with at least one metal from copper, silver, gold, platinum, ruthenium, rhodium, yttrium, cerium, or indium. The porous substrate is a porous ceramic substrate or a porous metal substrate from stainless steel, and alloy comprising chromium and nickel, a nickel based alloy, and an alloy comprising chromium, nickel, or molybdenum. The powder of the intermediate porous layer comprises a material from metal powders, metal oxide powders, ceramic powders, or zeolite powders. It comprises a material from tungsten, silver, copper oxide, and/or aluminum oxide. Preferred Property: The powder of the intermediate porous layer has an average particle size of 0.5-5 microns. The intermediate porous layer has an average thickness of 1-10 microns. The average pore size of the intermediate porous layer is less than the average pore size of the porous substrate.