Catalytic partial oxidation and reforming of n-butane over rhodium for syngas production

This work presents an experimental and mechanistic study on the catalytic partial oxidation (CPO) of n -butane for syngas production over a Rh/Al 2 O 3 catalyst. Experiments were conducted in a fixed-bed reactor under fuel-rich conditions (equivalence ratios φ = 1.5, 2.5 and 3.5) within a temperature range of 373–1073 K. The process initiates with total oxidation, seamlessly transitioning to partial oxidation and subsequently to steam/dry reforming regimes as temperature increases, with H 2 emerging as the first syngas product followed by CO and CH 4 . Based on the experimental observations, a reduced global reaction mechanism comprising eight irreversible, lumped steps was developed. Kinetic parameters were extracted from experimental data at φ = 1.5 and validated against independent datasets at φ = 2.5 and 3.5, with the model accurately capturing the major species trends. The Rh catalyst exhibits exceptional performance, achieving H 2 selectivity of 99.1% at φ = 3.5 and 873 K, surpassing reported values for methane and propane CPO systems. In addition, trace C 2-6 hydrocarbons were detected at φ = 3.5 and temperatures above 973 K, indicating the occurrence of hydrocarbon cracking under excessively fuel-rich and high-temperature conditions. XPS analysis further reveals a temperature-induced surface transition from oxidized Rh 3+ to metallic Rh 0 , which is associated with the high catalytic activity. These results provide mechanistic insight and useful kinetic parameters for modeling and optimizing Rh-catalyzed CPO of light hydrocarbons. Novelty and significance statement This work provides the first kinetic analysis and reaction mechanism for the catalytic partial oxidation (CPO) of n -butane over rhodium, addressing a significant gap in the literature, which has predominantly focused on methane and propane. The novelty lies in the elucidation of the unique two-stage reaction pathway for n -C 4 H 10 , beginning with total oxidation, sequentially transitioning through partial oxidation, and finally to reforming. A reduced reaction mechanism comprising eight lumped steps was developed, which successfully captured the species formation and the complex non-monotonic dependence on equivalence ratio and temperature. The significance of this research is that it delivers essential theoretical insights and a practical kinetic model for utilizing n -butane, a major component of LPG and NGL, in efficient syngas production. This directly advances the application of these fuels in solid-oxide fuel cell (SOFC) systems and distributed energy technologies, enhancing energy security and reducing emissions. Ultimately, this work provides guidance for the design and optimization of fuel-flexible catalytic reactors, contributing to the transition towards a more sustainable and diversified energy landscape.