Photocatalytically Reducing CO2 to Methyl Formate in Methanol Over Ag-SrTiO3 Photocatalysts

Photocatalytically Reducing CO₂ to Methyl formate in Methanol over Ag-SrTiO₃ Photocatalysts

Sui Dandan¹, Yin Xiaohong*[1], Xin Feng², Dong Hongzhi¹, Jiang Wanlin¹

¹School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384, People's Republic of China

²School of Chemistry and Chemical Engineering, Tianjin University,

Tianjin 300072, People's Republic of China

ABSTRACT

The metal-loaded photocatalysts may facilitate the charge separation and transfer because metal site actes as the electron acceptor to avoid the recombination of electrons and holes. For this purpose, Ag-SrTiO₃ nanocrystal photocatalysts were prepared by hydrothermal synthesis method for reducing CO₂ to methyl formate (MF) in methanol via ultraviolet irradiation. CO₂ was reduced to MF by electrons on conduction band of the photocatalyst. In order to obtain a high rate of MF evolution, we researched and optimized the preparation procedure of Ag-SrTiO₃ by changing the Ag dosage, hydrothermal temperature and time. The as-synthesized photocatalysts were characterized for the structural, optical, morphological properties and specific surface area by X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis), high-resolution transmission electron microscope (HRTEM) and N₂ sorption analysis at 77 K. The photocatalytic activity was evaluated in a batch slurry reactor. After ultraviolet light irradiation for 6 h, the product solution was qualitatively analyzed by GC-MS (Agilent 5975C) and quantitatively analyzed by gas chromatograph equipped with a hydrogen flame detector (FID). The as-synthesized photocatalysts were found by XRD to have a perovskite structure. The absorption edge of as-synthesized photocatalyst was evidently shift from 400 nm to 700 nm by Ag-loading. The BET specific surface area of the Ag-loaded SrTiO₃ photocatalyst was much larger than the pristine SrTiO₃ particles. The photocatalytic activities could be further enhanced via extending life-span of the electron-hole pairs by using Ag particle as electron acceptor (Fig. 1). A catalyst of 7 wt% Ag on SrTiO₃ with hydrothermal synthesis at 150 ^oC and 22 h was found to exhibit the highest photocatalytic activity in MF formation rate of 3006 mol/h/g.cat, which was more remarkable than that of pristine SrTiO₃.

Fig. 1  Schematic mechansim of UV photocatalytic reduction of CO₂ over Ag-SrTiO₃

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* Corresponding author: Xiaohong Yin, School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384, China;E-mail:xiaohongyin@hotmail.com