Abstract
The production of solar fuels via the photoreduction of carbon dioxide to methane by titanium oxide is a promising process to control greenhouse gas emissions and provide alternative renewable fuels. Although several reaction mechanisms have been proposed, the detailed steps are still ambiguous, and the limiting factors are not well defined. To improve our understanding of the mechanisms of carbon dioxide photoreduction, a multi-physics model was developed using COMSOL. The novelty of this work is the computational fluid dynamic model combined with the novel carbon dioxide photoreduction intrinsic reaction kinetic model, which was built based on three-steps, namely gas adsorption, surface reactions and desorption, while the ultraviolet light intensity distribution was simulated by the Gaussian distribution model and Beer-Lambert model. The carbon dioxide photoreduction process conducted in a laboratory-scale reactor under different carbon dioxide and water moisture partial pressures was then modeled based on the intrinsic kinetic model. It was found that the simulation results for methane, carbon monoxide and hydrogen yield match the experiments in the concentration range of 10−4 mol·m−3 at the low carbon dioxide and water moisture partial pressure. Finally, the factors of adsorption site concentration, adsorption equilibrium constant, ultraviolet light intensity and temperature were evaluated.
Highlights
Atmospheric carbon dioxide (CO2) mainly from combustion of fossil fuel is one of the major greenhouse gases and contributes about 60% to global warming [1]
The main obstacle for the CO2 photoreduction to CH4 process to be commercialised is its low conversion rate [4]. To address this challenge, understanding the mechanism and reaction kinetics is crucial for the improvement of the reaction efficiency [5]
Most of the kinetic models proposed for CO2 photoreduction were based on the Langmuir-Hinshelwood equation and assumed adsorption and reaction as a one-step process [9]
Summary
Atmospheric carbon dioxide (CO2) mainly from combustion of fossil fuel is one of the major greenhouse gases and contributes about 60% to global warming [1]. The main obstacle for the CO2 photoreduction to CH4 process to be commercialised is its low conversion rate [4]. To address this challenge, understanding the mechanism and reaction kinetics is crucial for the improvement of the reaction efficiency [5]. The heterogeneous CO2 photoreduction process includes the separation and recombination of electron-hole pairs in the semiconductor (photocatalyst), the gas adsorption and desorption on the surface of the photocatalyst, the electron and hole trapping reactions and the radical propagation reactions [6]. Most of the kinetic models proposed for CO2 photoreduction were based on the Langmuir-Hinshelwood equation and assumed adsorption and reaction as a one-step process [9]. Marczewski [12] proposed a simple and easy integrated kinetic Langmuir model to analyze the
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