Photocatalytic Reduction Of CO₂ To Methanol On Nano-TiO₂

This article mainly discussed about photocatalytic reduction of CO₂ to methanol on nano-TiO₂, in which, the TiO₂ was prepared by using the developed sol-gel method, and the TiO₂ was modified through doping a variety of metal ions, including Cu²⁺, Ag⁺, Fe³⁺, Tb³⁺, Eu³⁺, Nd³⁺, and Dy³⁺, the SiO₂/TiO₂ composite catalysts was prepared for photocatalytic reduction of CO₂ to methanol. Meanwhile the impact of ions on the photocatalytic properties of the nano-TiO₂ was studied. In order to obtain the optimum TiO₂ photocatalytic materials, the impact factors were researched, such as the amount of metal added, the time of precursor entered and metal variety. To research on the relations between the preparation condition and the catalytic effective, and on the main catalytic impact factors, the properties of TiO₂ maily including the effectiveness of the catalytic activity, the specific surface area, crystallite size and composition distribution characteristics were examined through XRD, TG/DTG/DSC, BET, SEM, TEM, UV-Vis and PL. In addition, the catalytic activity was evaluated by the yield of methanol. The results showed that TiO₂ without adding metal had taken on certain catalytic activity, in which the catalyst sample was a mixture of anatase(89%) and rutile(11%), the particle size was 10～30nm and the specific surface area was 58.13m²/g. When metal ions were dopped into TiO₂, the particle size was reduced, the specific surface area was increased and the photocatalytic activity was greatly improved. The optimum dopping amount of kinds of substances were as followed: Cu 2.0wt%, Ag 3.0wt%, Eu 0.5M%, Fe 4.0wt%, SiO₂ 3.5wt%.This research adopted a set of self-designed equipments to examine the photocatalytic efficiency in the suspension system, in which a series of catalytic materials were compared with, such as Fe/TiO₂, Cu/TiO₂, Ag/TiO₂, SiO₂/TiO₂, Eu/TiO₂, Tb/TiO₂ and so on. The comparition of catalytic efficiency between different catalytic materials showed Fe/TiO₂>Eu/TiO₂>Cu/TiO₂>SiO₂/TiO₂>Ag/TiO₂>Tb/TiO₂. Fe/TiO₂ catalysis processed the best activity, its methanol yield was 359.79μmol/g·cat.The article comfirmed that the sacrifices of electronic donor in the photocatalytic reduction, the system alkalinity, and the sources of light had significant effects on catalytic efficiency. The optimum conditions were, respectively, the sacrifices of electronic donor in the photocatalytic reduction Na₂SO₃ 0.1mol/L, the system alkalinity: NaOH:0.1mol/L, and the adding amount of catalysis: 1g/L. The comprehensive optimum conditions were selected by orthogonal experiments, which were the amount of catalysis: 1g/L, CO₂ volume flow: 200ml/min, reaction hours: 8h, and reaction temperature: 50℃. Finally, we discussed the reaction kinetics of photocatalytic reduction of CO₂ reaction, and the photocatalytic reaction rate equationwas obtained as follows: r =-dC/dt= 79.515.