Micro-kinetic modelling of photocatalytic CO2 reduction over undoped and N-doped TiO2

CO2 photoreduction is studied using in-house synthesized undoped and N-doped TiO2 nanoparticle photocatalysts. Comparison with the commercial P25 TiO2 powder shows that the synthesized samples are more effective. P25 produced a negligible amount of CH4, unlike the synthesized samples. N-doping of TiO2 powder caused a higher productivity rate of all products, and provided the best performance for CO2 reduction. The average production rate of CH4 was 0.191 mu mol h(-1) g(-1), whereas that of CO was 0.111 mu mol h(-1) g(-1). The experimental data are used to fit the micro-kinetic modelling parameters. The kinetic constant of H2O dissociation is the lowest for all tested samples, revealing that this is the rate-determining step. The kinetic constants for the H-2, CO, and CH4 formation were of the same order for all catalyst samples, showing that the rates of these reactions are independent of the catalyst type.