Photoreduction of CO2 over heterogeneous modified TiO2 nanoparticles under visible light irradiation: Synthesis, process and kinetic study

Abstract

In this study, Fe-doped, N-doped and Fe-N-codoped TiO2 were synthesized and the effects of dopants, the partial pressure of CO2 and H2O were investigated on the performance of CO2 photoreduction. The synthesized nanoparticles were characterized by XRD, BET, FE-SEM, EDS, TEM, UV–Vis DRS and XPS analysis. A decrease in particle size and an increase in surface area of modified samples were observed by XRD and BET analysis. XPS results have indicated the presence of Fe3+ and substitutional nitrogen in TiO2 lattice. DRS analysis has revealed that absorption spectra of doped samples significantly extended to the visible light region.The partial pressure of CO2 and H2O was systematically varied and investigated in order to indicate the most suitable conditions for achieving high photoreduction activity. The highest production rate of methane and methanol, 28.15 μmol/gcat h and 1.24 μmol/gcat h, respectively, was observed over the 0.12%Fe-0.5%N sample with total flow rate 13 ml/min under 70 w visible light irradiation at optimum partial pressure of reactants (PCO2 = 75.8 kPa, PH2O = 15.5 kPa). The methane rate of the best catalyst (0.12%Fe-0.5%N) under optimum condition was 51 times higher than pure TiO2 at fixed PCO2 = 75.8 kPa, PH2O = 15.5 kPa. A new kinetic model was developed based on Sips isotherm over non-homogenous (heterogeneous) catalyst. The kinetic parameters such as reaction rate constant and affinity coefficients of CO2 and H2O were predicted experimentally. The reaction rate constant as well as CO2 and H2O affinity coefficients were predicted 6.47 μmol/gcat h, 22.74 bar−1 and 145.2 bar−1, respectively.