NOVELTY - A high temperature steam reformer assembly has catalyst bed housing having walls, zirconia low heat transfer insulation layer provided on internal surfaces of housing walls, catalyst bed provided in the housing, and an unit for introducing a mixture of high temperature steam, air, and fuel, into housing. The catalyst bed is operated to convert a fuel into a hydrogen-enriched fuel gas stream.    USE - For reforming and converting hydrocarbon fuels, such as gasoline, diesel fuel, methane, methanol or ethanol, to hydrogen-rich fuel stream used in fuel cell power plant.    ADVANTAGE - The zirconia insulation layer thermally insulates the walls of the catalyst bed, holds heat in the catalyst bed and protects the catalyst housing against heat-induced degradation up to temperature of 3000 degrees F. The zirconia insulation layer also inhibits carbon deposition on the walls of the catalyst bed and serves as a gas seal for edges of the catalyst bed. The zirconia insulation layer eliminates the need to provide an alumina wash coat and metal oxide coatings on the inner surface of the catalyst housing, for inhibiting carbon deposition in the catalyst bed. The zirconia insulation layer is non-acidic and has carbon gasification properties and does not vaporize in the presence of high temperature stream. Other fuels such as natural gas is also reformed by using the reformer assembly.    DETAILED DESCRIPTION - A high temperature steam reformer assembly (2) has catalyst bed housing (6) having walls, zirconia low heat transfer insulation layer (30) provided on internal surfaces of housing walls, catalyst bed (8) provided in the housing, and an unit for introducing a mixture of high temperature steam, air, and fuel, into housing. The catalyst bed is operated to convert a fuel into a hydrogen-enriched fuel gas stream.    An INDEPENDENT CLAIM is also included for method of minimizing carbon deposition on walls of reformer assembly, which involves covering internal surfaces of the walls of the reformer assembly with a carbon deposition-inhibiting thermal insulating material which will not vaporize at operating temperatures of about 1750 degrees F of the reformer assembly.    DESCRIPTION OF DRAWING(S) - The figure shows fragmented cross-sectional view of the high temperature steam reformer assembly.    Reformer assembly (2)    Catalyst bed housing (6)    Catalyst bed (8)    Zirconia low heat transfer insulation layer (30)