(73d) Photocatalytically Reducing CO2 to Methyl Formate in Methanol Over Ag-SrTiO3 Photocatalysts

Photocatalytically Reducing
CO₂ to Methyl formate in Methanol over Ag-SrTiO₃Photocatalysts

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