Hydrogen Production via the Catalytic Partial Oxidation of Ethanol on a Platinum–Rhodium Catalyst: Effect of the Oxygen-to-Ethanol Molar Ratio and the Addition of Steam

Abstract

To produce hydrogen for automotive exhaust gas aftertreatment systems, the catalytic partial oxidation of ethanol over a platinum–rhodium catalyst supported on alumina is examined via experimental studies as well as thermodynamic analysis. The research focuses on the effects of the ethanol concentration, oxygen-to-ethanol molar ratio, and water content of ethanol on the ethanol conversion and product yield (e.g., H2, CO, CO2, and CH4). The hot spot temperature and position and the temperature profile along the monolithic catalyst are also analyzed as a function of the inlet gas composition. Different surface chemical reactions (e.g., partial oxidation and steam reforming of ethanol, water–gas shift, and hydrocarbon cracking) are employed to explain the phenomena that take place during ethanol reforming. The process follows the indirect reforming pathway, which involves the exothermic oxidation of ethanol to produce H2O, CO2, and heat, followed by endothermic steam reforming to generate CO and H2. The temperature profile inside the catalyst depends critically on the amount of ethanol supplied and the oxygen-to-ethanol molar ratio. The ethanol conversion, hydrogen production, and selectivity toward hydrogen and methane depend strongly on the operating conditions. The addition of steam has a slightly positive effect on the hydrogen formation and temperature profile.

Heterogeneous Catalysis in (Bio)Ethanol Conversion to Chemicals and Fuels: Thermodynamics, Catalysis, Reaction Paths, Mechanisms and Product Selectivities

“…For example, as unsupported K-doped manganese oxides catalyze the complete oxidation of ethanol to CO 2 at 430 K, alumina-supported catalysts with similar compositions allow full combustion at 473-500 K [46]. Poorly active catalysts indeed produce incomplete combustion with some acetaldehyde coproduction [47] by reaction (9), and due to the much higher toxicity of acetaldehyde with respect to ethanol, this needs to be completely avoided.…”

“…As said, noble metals efficiently catalyze the total oxidation of ethanol usually realized in excess air. However, noble metals can also be applied to produce hydrogen from ethanol using partial oxidation with oxygen, reaction (15) [9,38]. This reaction can have advantages over the strongly endothermic ethanol steam-reforming process (see Section 3.10) because it is only slightly endothermic, because is the result of the strongly exothermic catalytic combustion (reaction (14)) together with the endothermic steam reforming.…”

Overview on the Vital Step toward Addressing Platinum Catalyst Poisoning Mechanisms in Acid Media of Direct Ethanol Fuel Cells (DEFCs)

“…x,ads ads 2 (9) Overall, from the above discussion, it is seen that further oxidation of CH x,ads (reaction 9) and CO ads (reaction 10) to CO 2 required the presence of OH ads . The latter species is formed in significant amounts at higher potentials (ca > 0.4 V vs RHE) from the dissociative adsorption of water on catalyst surfaces, according to reaction 11.…”

Production of Gasolines and Monocyclic Aromatic Hydrocarbons: From Fossil Raw Materials to Green Processes

“…Indeed, hydrogen production is usually limited by the presence of variable amounts of methane, which is at least in part formed by ethanol decomposition [149]. The alternative ethanol partial oxidation [150] and autothermal reforming [151] may help in reducing the amount of methane coproduced and in the reduction in catalyst deactivation by coking, with the drawbacks of the cost of oxygen and a reduction in the H 2 /CO x product ratio.…”