Photocatalytic reduction of carbon dioxide can activate chemically inert carbon dioxide by the use of renewable energy. In the present work, the main products of photocatalytic reduction of CO 2 in aqueous TiO 2 suspensions were found to be methane, methanol, formaldehyde, carbon monoxide, and H 2 . Anatase TiO 2 catalysts with various morphologies, such as nanoparticle, nanotube, and nanosheet, were synthesized through a hydrothermal method. The TiO 2 nanosheets were more active than the nanotubes or nanoparticles in the reduction of CO 2 in aqueous solution. This is because the photogenerated carriers prefer to flow to the specific facets. The TiO 2 sheet with high-energy exposed {001} facets facilitates the oxidative dissolution of H 2 O with photogenerated holes, leaving more photogenerated electrons available for the reduction of CO 2 on {101} facets. Moreover, surface fluorination promotes the formation of Ti 3+ species, which is helpful in the reduction of CO 2 to CO 2 − and in extending the lifetime of photogenerated electron−hole pairs. The optimum ratio of exposed {001} to {101} facets for surface-fluorinated TiO 2 nanosheets was found to be ∼72:28, which corresponds to an initial F/Ti ratio of 1. From our analysis of the effect of adding of known intermediates on the photocatalytic reduction of CO 2 , we propose that the photocatalytic reduction of CO 2 with H 2 O on surface-fluorinated TiO 2 nanosheets proceeds via a mechanism involving generation of hydrogen radicals and carbon radicals.

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PtNi alloy nanoparticles supported on carbon (XC-72) are synthesized via a one-pot synthetic approach. This synthesized bimetallic composite offers several advantages, such as reduction of precious Pt along with an increase in activity due to the modified electronic structure. The prepared PtNi/C catalysts were employed as catalysts for NO removal both in a fixed-bed reactor and in a newly designed gas diffusion reactor. The performances of all prepared PtNi/C catalysts were higher than Pt/C at the same conditions and maintained a stable NO removal at a wide temperature window (100–300 °C), especially for Pt65Ni35 (more than 95% from 120 to 300 °C). This is attractive for low temperature SCR technology. According to XPS analysis, the surface layer phase was comprised of Pt contents with Ni being localized beneath the successive layers until Ni content increased to 67% mole ratio. The surface presence of Ni significantly affects the Pt electronic structure and raises the mass specific activity of Pt. Meanwhile, PtNi/C catalysts were introduced in a new gas diffusion reactor to remove NO under quantitatively less catalysts (30 mg), high NO concentration (1000 ppm), and at a high flow rate (resulting in a very short residence time of 0.09 s) condition. NO removal reaches almost 100% below 95 °C for all the PtNi catalysts and among all Pt65Ni35 exhibited the best performance. In addition, the influence of SO2 on the performance of Pt65Ni35 was also investigated, and the catalysts exposed a good antipoisonous property. The excellent performance of PtNi catalysts and a gas diffusion reactor are strongly recommended for their utilization as highly active and economical technology for NO removal.