In 2005, chemists at the Brookhaven National Laboratory in the United States developed a new type of tungsten based catalyst, which can completely react with several reactants in chemical reactions and convert them into the desired products. This catalyst is easy to recover and can be reused without generating any waste.
A highly active tungsten catalyst consists of tungsten ions and additives. Tungsten ions are one or more of trivalent tungsten ions, tetravalent tungsten ions, or pentavalent tungsten ions. The precursor of tungsten ions is at least one or more of tungsten elemental, tungsten trioxide, tungsten dioxide, or tungsten pentoxide. The promoter is preferably manganese or scandium, and the precursor of additives is the oxide, hydroxide, nitrate of the corresponding additives At least one or more of acetate or carbonate.
According to the percentage composition of tungsten ions and manganese elements at 90% and 10%, the tungsten element is evenly mixed with manganese nitrate, and the catalyst precursor is formed by pressing. 10mL of the catalyst precursor is loaded into a tube reactor made of Monel material with an inner diameter of 1/2 inches and a length of 30cm. Nitrogen is introduced to calcine at 450 ℃ for 8 hours, with a nitrogen space velocity of 200h-1. The temperature is lowered to 300 ℃, and then the tube reactor is sealed. Vacuum is first drawn, and then fluorine gas is introduced, The ventilation capacity of fluorine gas is 3/2 times greater than or equal to the theoretical amount of fluorine gas consumed by tungsten elemental substance and 5/2 times less than or equal to the amount of tungsten elemental substance. After activation for 12 hours, the residual fluorine gas is absorbed with dry alkali lime and purged with nitrogen gas for 2 hours to prepare a tungsten based catalyst.
Chromium catalysts still have defects such as low operating temperature, low catalytic activity, short service life, and difficulty in recycling and reuse. More importantly, chromium is toxic and can cause great harm to humans, especially high valent chromium has strong carcinogenicity. The most direct way to solve this problem is to find new catalysts that can replace chromium, and some scholars have found that tungsten based catalysts can complete this task. Compared with chromium based catalysts, tungsten based catalysts have comparable performance and effectiveness, but have the characteristics of safety, environmental protection, and harmlessness, making them a good choice to replace chromium based catalysts.
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