Array including a first and a second monolith of a structured catalyst for carrying out an endothermic reaction of a feed gas, wherein: a) the first and second monolith include a macroscopic structure of a first and second electrically conductive material; b) each of said first and second monoliths has a number of flow channels formed therein for conveying feed gas through the monoliths; c) the array includes at least a first and a second conductor electrically connected to said first and second monoliths, respectively, and to an electrical power supply, d) the first and second monolith are electrically connected by a monolith bridge; e) the array is configured to direct an electrical current to run from the first conductor through the first monolith to a second end, then through the bridge, and then through the second monolith to the second conductor.