A reactor shell suitable for producing synthesis gas and/or carbon dioxide from a fed reactive mixture stream comprising: at least one reactive stream duct formed within said reactor shell and essentially having a reactive stream inlet where said reactive mixture stream is fed, a reactive stream outlet where the reactive mixture stream exits the reactor shell and a catalyst section provided between said reactive stream inlet and reactive stream outlet; an insulation filling at least partly encompassing said reactive stream duct; a structured ceramic catalyst accommodated in said catalyst section, the reactive mixture stream undergoing a catalytic reaction, in particular steam reforming and/or dry reforming and/or partial oxidation and/or reverse water gas shift and/or volatile organic compounds oxidation and combinations thereof, in said structured ceramic catalyst, said structured ceramic catalyst being in monolith or tubular form and having a plurality of hollow flow paths which are configured to allow the reactive mixture stream to pass therethrough by coming in physical contact with the inner walls of the hollow flow paths of the structured ceramic catalyst, the material of the structured ceramic catalyst selected from the group consisting of SiO 2, Al 2 O 3, Y 2 O 3, WO 3, ZrO 2, TiO 2, MgO, CaO, CeO 2, FeO 2, ZnO 2 and combinations thereof supporting a catalytically active material selected from transition metals of the d-block elements; an electrical heating means, powered by at least two electrical feeds connected to an electrical power supply for heating said structured ceramic catalyst up to a predetermined reaction temperature wherein the electrical heating means and electrical power supply are configured to heat the structured ceramic catalyst up to a temperature between 300 and 1300 °C, and the reactor shell has a design pressure between 1 and 150 bar, wherein said electrical heating means is a resistive heating element arranged inside at least some of said hollow flow paths in a manner that there still remains a flowing passage inside the hollow flow paths, and the electrical heating means comprises meandered sections so that it extends in a meandered manner through or along some or all of the hollow flow paths. at least one reactive stream duct formed within said reactor shell and essentially having a reactive stream inlet where said reactive mixture stream is fed, a reactive stream outlet where the reactive mixture stream exits the reactor shell and a catalyst section provided between said reactive stream inlet and reactive stream outlet; an insulation filling at least partly encompassing said reactive stream duct; a structured ceramic catalyst accommodated in said catalyst section, the reactive mixture stream undergoing a catalytic reaction, in particular steam reforming and/or dry reforming and/or partial oxidation and/or reverse water gas shift and/or volatile organic compounds oxidation and combinations thereof, in said structured ceramic catalyst, said structured ceramic catalyst being in monolith or tubular form and having a plurality of hollow flow paths which are configured to allow the reactive mixture stream to pass therethrough by coming in physical contact with the inner walls of the hollow flow paths of the structured ceramic catalyst, the material of the structured ceramic catalyst selected from the group consisting of SiO 2, Al 2 O 3, Y 2 O 3, WO 3, ZrO 2, TiO 2, MgO, CaO, CeO 2, FeO 2, ZnO 2 and combinations thereof supporting a catalytically active material selected from transition metals of the d-block elements; an electrical heating means, powered by at least two electrical feeds connected to an electrical power supply for heating said structured ceramic catalyst up to a predetermined reaction temperature wherein the electrical heating means and electrical power supply are configured to heat the structured ceramic catalyst up to a temperature between 300 and 1300 °C, and the reactor shell has a design pressure between 1 and 150 bar, wherein said electrical heating means is a resistive heating element arranged inside at least some of said hollow flow paths in a manner that there still remains a flowing passage inside the hollow flow paths, and the electrical heating means comprises meandered sections so that it extends in a meandered manner through or along some or all of the hollow flow paths.