Photocatalytic oxidation of VOC for cleaning vehicle cabin air DRIFT spectroscopy investigations of surface species

1. Scope The presence of Volatile Organic Compounds (VOCs) in indoor air is a major health issue. The vehicle cabin air is also affected by this problem as being the first mode of transportation [1]. Most of the current depollution systems are based on trapping using adsorption methods, while photocatalytic processes offer the potential to fully and continuously degrade VOCs. n-pentane and its derivatives are present in vehicle cabins [2], and to the best of our knowledge, the photocatalytic-oxidation of this compound has been scarcely studied [3-4]. This study deals with the photocatalytic degradation of n-pentane using a TiO2 DEGUSSA® P25 powder5. The impact of pollutant concentration (17-425 ppmv), relative humidity (r.h.) (0-90%), irradiance power at 365 nm (0.05-2.7 mW/cm²) and oxygen partial pressure (0.02-20%) on the degradation kinetic of n-pentane was investigated at room temperature. Operando DRIFTS experiments were performed under 1200 ppmv of n-pentane and 3.5% O2 in He to study the surface species formed on the photocatalyst and their evolution under UV irradiation. 2. Results and discussion Results show that the n-pentane degradation rate decreases with the relative humidity level, and linearly increases with the irradiance power and the VOC concentration. At 120 mL/min, r.h.=0%, 20% O2 and under an irradiance power of 2.7 mW/cm² at 365 nm, a degradation rate of 0.05 µmol/min is obtained. In addition, the presence of formates surface species under irradiation has been evidenced by DRIFT experiments [6-7]. 3. Conclusions This preliminary study has shown the impact of several parameters in the kinetic of degradation of n-pentane on titanium dioxide. Furthermore, this study highlighted the presence of formates surface species by surface investigation, during the photocatalytic degradation of n-pentane. These results give new insights in the understanding of the VOC photocatalytic degradation mechanism for improving depollution system in vehicle cabins. References 1. D. Muller, D. Klingelhofer, S. Uibel, D. A. Groneberg, J. Occup. Med. Toxicol, 2011, 6, 1-7. 2. J. Faber, K. Brodzik, A. Golda-Kopek, D. Lomankiewicz, Pol. J. Environ. Stud., 2013, 22, 1701-1709. 3. N. Djechri, M. Formenti, F. Juillet, S.J. Teichner, Faraday Discuss. Chem. Soc., 1974, 58, 185-193 4. A. K. Boulamanti, C. J. Philippopoulos, Atmos. Environ, 2009, 43, 3168–3174 5. M. Bouhatmi, F. Dappozze, C. Guillard, P. Vernoux, J. Earth Sci. Geotech. Eng., 2017, 7, 83-88. 6. G. Ya. Popova, T. V. Andrushkevich, Yu. A. Chesalov, E. S. Stoyanov, Kinet. Catal, 2000, 41, 885-891. 7. G. Busca, J. Lamotte, J-C. Lavalley, V. Lorenzelli, J. Am. Chem. Soc. 1987, 109, 5197-5202.