Formic acid (chemical formula HCOOH) and methyl formate (HCOOCH3) are the important chemical raw materials, and they are widely used in many fields of organic synthesis, the preparation of dyes, printing and dyeing materials, medicines and so on. Nowadays, the widely used in industry for preparing formic acid is sodium formate method; at the same time, CO and water can also be used in the production, this approach has the lower cost, but it requires a higher temperature and pressure, energy consumption, and higher investment in equipment. Therefore, countries all over the world are seeking the new acid synthesis way.

 

Studies have shown that, CO can be photocatalytic reduction into formic acid, formaldehyde, methanol, methane and other organic compounds in the water. Photocatalytic reduction has mild reaction conditions, low energy consumption, less secondary pollution and other advantages. In recent years, this technology has been widespread concern for it applying in the reduction reaction system of CO which the thermal surface catalysis is hard to realize. Depending on the different photosensitizer and catalyst, the reduction of CO photocatalytic divided into the following four categories:

1. Titanium dioxide as the photosensitizer (or the so called of additives), other metal and metal oxide and so on as a catalyst; the composite of two semiconductors of titanium dioxide and tungsten trioxide is possible to increase its ability to capture protons or electrons, thereby enhancing the photocatalytic property;

2. Porphyrin, Ru (bpy) 32 +, ReX (CO) (bpy) can as a photosensitizer, as well as the catalyst;

3. Ru (bpy) 32+ is as a photosensitizer, and another metal compound to be as a catalyst;

4. Organic as photosensitizer, and the metal composite as a catalyst.

At present, the first class is given priority in the photocatalyst of CO reduction, which the reaction is reacted to the photosensitivity of the titanium dioxide which as a semiconductor.

 

WO₃ as a semiconductor photocatalyst has band gap of 2.4eV ~ 2.8eV, which means the wider absorption band of light, and can respond to visible light, thereby it is considered a good photocatalytic material which is alternative to titanium dioxide photocatalyst. In recent years, the photocatalytic properties of WO₃ are in the ongoing research, especially WO₃ ultrafine powder has broad prospects in catalytic aspect.