A reactor comprising: a plurality of reaction units located within a reaction zone in the reactor, each of the reaction units being adapted to enable carrying out an electrolysis reaction of one or more raw gases; ingress means operative to allow introduction of the one or more raw gases into the reaction zone and to allow distributing the incoming one or more raw gases to the plurality of the reaction units; egress means operative to allow exit of reaction products from the reaction zone; and a heating system; wherein at least one of the reaction units comprises - an active shell having a space defined therein, through which said one or more raw gases flow and in which the reaction occurs, said active shell at its first end having an opening configured for introduction of the one or more raw gases into the reaction unit; and - an inner shell (233, 333) passing through the active shell and being configured to define said space of the active shell around the inner shell for said flow of the one or more raw gases; and wherein the reaction units extend along a longitudinal axis of the reaction zone and are arranged in a spaced-apart relationship along a lateral axis of the reaction zone; and wherein said reaction units are closed-end units; wherein the inner shell (233, 333) is configured either as a feed tube to enable introduction of the one or more raw gases to the at least one of the reaction units, or as a collection tube for reversing flow direction of at least one of the one or more raw gases; and wherein the heating system comprises a plurality of heating sources (120, 222, 223, 326, 327) extending along the reaction zone thereby providing at least a part of energy to carry out the reaction process within the plurality of reaction units. a plurality of reaction units located within a reaction zone in the reactor, each of the reaction units being adapted to enable carrying out an electrolysis reaction of one or more raw gases; ingress means operative to allow introduction of the one or more raw gases into the reaction zone and to allow distributing the incoming one or more raw gases to the plurality of the reaction units; egress means operative to allow exit of reaction products from the reaction zone; and a heating system; wherein at least one of the reaction units comprises - an active shell having a space defined therein, through which said one or more raw gases flow and in which the reaction occurs, said active shell at its first end having an opening configured for introduction of the one or more raw gases into the reaction unit; and - an inner shell (233, 333) passing through the active shell and being configured to define said space of the active shell around the inner shell for said flow of the one or more raw gases; and - an active shell having a space defined therein, through which said one or more raw gases flow and in which the reaction occurs, said active shell at its first end having an opening configured for introduction of the one or more raw gases into the reaction unit; and - an inner shell (233, 333) passing through the active shell and being configured to define said space of the active shell around the inner shell for said flow of the one or more raw gases; and wherein the reaction units extend along a longitudinal axis of the reaction zone and are arranged in a spaced-apart relationship along a lateral axis of the reaction zone; and wherein said reaction units are closed-end units; wherein the inner shell (233, 333) is configured either as a feed tube to enable introduction of the one or more raw gases to the at least one of the reaction units, or as a collection tube for reversing flow direction of at least one of the one or more raw gases; and wherein the heating system comprises a plurality of heating sources (120, 222, 223, 326, 327) extending along the reaction zone thereby providing at least a part of energy to carry out the reaction process within the plurality of reaction units.