A hydrogen-producing assembly, comprising: a heat conductive body having a length and defining: a reforming conduit extending longitudinally through the heat conductive body; a feed inlet to the reforming conduit for receiving a feed stream into the reforming conduit; a reformate outlet from the reforming conduit for delivering a reformate gas stream containing hydrogen gas from the reforming conduit; a burner conduit extending through the heat conductive body along a central longitudinal axis therein and adjacent the reforming conduit, wherein the reforming conduit is spaced radially from the burner conduit; a fuel-air inlet to the burner conduit for receiving a fuel-air stream into the burner conduit; and an exhaust outlet from the burner conduit for delivering an exhaust stream from the burner conduit; a reforming catalyst disposed within the reforming conduit and configured to catalyze production of the reformate gas stream from the feed stream via an endothermic reaction within a reforming temperature range; a combustion catalyst disposed within the burner conduit only adjacent to the exhaust outlet, and configured to catalyze ignition of the fuel-air stream via an exothermic reaction; and a fuel-air mixing structure disposed within the burner conduit and configured to support combustion of the fuel-air stream in a combustion region of the burner conduit adjacent the fuel-air inlet; and wherein the heat conductive body extends between the burner conduit and the reforming conduit, surrounds the burner conduit and the reformer conduit and is constructed to conduct heat generated by the exothermic reaction of the combustion of the fuel-air stream in the burner conduit from the burner conduit to the reforming conduit to maintain the reforming catalyst within the reforming temperature range. a heat conductive body having a length and defining: a reforming conduit extending longitudinally through the heat conductive body; a feed inlet to the reforming conduit for receiving a feed stream into the reforming conduit; a reformate outlet from the reforming conduit for delivering a reformate gas stream containing hydrogen gas from the reforming conduit; a burner conduit extending through the heat conductive body along a central longitudinal axis therein and adjacent the reforming conduit, wherein the reforming conduit is spaced radially from the burner conduit; a fuel-air inlet to the burner conduit for receiving a fuel-air stream into the burner conduit; and an exhaust outlet from the burner conduit for delivering an exhaust stream from the burner conduit; a reforming catalyst disposed within the reforming conduit and configured to catalyze production of the reformate gas stream from the feed stream via an endothermic reaction within a reforming temperature range; a combustion catalyst disposed within the burner conduit only adjacent to the exhaust outlet, and configured to catalyze ignition of the fuel-air stream via an exothermic reaction; and a fuel-air mixing structure disposed within the burner conduit and configured to support combustion of the fuel-air stream in a combustion region of the burner conduit adjacent the fuel-air inlet; and wherein the heat conductive body extends between the burner conduit and the reforming conduit, surrounds the burner conduit and the reformer conduit and is constructed to conduct heat generated by the exothermic reaction of the combustion of the fuel-air stream in the burner conduit from the burner conduit to the reforming conduit to maintain the reforming catalyst within the reforming temperature range. a reforming conduit extending longitudinally through the heat conductive body; a feed inlet to the reforming conduit for receiving a feed stream into the reforming conduit; a reformate outlet from the reforming conduit for delivering a reformate gas stream containing hydrogen gas from the reforming conduit; a burner conduit extending through the heat conductive body along a central longitudinal axis therein and adjacent the reforming conduit, wherein the reforming conduit is spaced radially from the burner conduit; a fuel-air inlet to the burner conduit for receiving a fuel-air stream into the burner conduit; and an exhaust outlet from the burner conduit for delivering an exhaust stream from the burner conduit; a reforming catalyst disposed within the reforming conduit and configured to catalyze production of the reformate gas stream from the feed stream via an endothermic reaction within a reforming temperature range; a combustion catalyst disposed within the burner conduit only adjacent to the exhaust outlet, and configured to catalyze ignition of the fuel-air stream via an exothermic reaction; and a fuel-air mixing structure disposed within the burner conduit and configured to support combustion of the fuel-air stream in a combustion region of the burner conduit adjacent the fuel-air inlet; and wherein the heat conductive body extends between the burner conduit and the reforming conduit, surrounds the burner conduit and the reformer conduit and is constructed to conduct heat generated by the exothermic reaction of the combustion of the fuel-air stream in the burner conduit from the burner conduit to the reforming conduit to maintain the reforming catalyst within the reforming temperature range.