Tungsten Based Catalyst Preparation

In order to protect the earth's ozone layer, a zero ODP value of HFCs and HFOs has been introduced in the world, and chlorofluorocarbons (CFCs) and hydrogen chlorofluorocarbons (HCFCs) are eliminated with a zero ODP value. HFCs and HFOs have been widely used as refrigerants, cleaning agents, foaming agents, inextinguishing agents and etching agents.

Most of the industrial production of HFCs or HFOs uses halogenated organic compounds to catalyze the fluoro chlorochlorine exchange reaction, which is the core of the fluoro chloroexchange catalyst in the gas-phase catalytic fluorine exchange reaction of halogenated organic compounds. At present, the common fluorine chlorine exchange catalyst is chromium based catalyst,  its main active component is chromium.
Chromium catalyst still has the defects of low temperature, low catalytic activity, short service life, and difficult to recycle and reuse. Chromium is toxic and can cause great damage to artificial. To solve this problem, the most direct way is to find a new type of catalyst that can replace chromium.

The highly active tungsten catalyst consists of tungsten ions and auxiliaries. Tungsten ions are one or several species of tri valent tungsten ions, tetravalent tungsten ions, five valent tungsten ions. The precursors of tungsten ions are at least one or a few of tungsten single, three oxidation tungsten, two tungsten oxide, or five oxidation of two tungsten. The aid is to optimize manganese or scandium. The precursor of the auxiliary is phase. At least one or several kinds of additives, such as oxides, hydroxides, nitrates, acetate or carbonate, should be used.

According to the percentage of tungsten ions and manganese elements, 90% and 10%, the tungsten single substance and manganese nitrate are mixed uniformly, the catalyst precursor is prepared by pressing sheet. The catalyst precursor 10mL is loaded into the tube reactor of Meng Naier material of 1/2 inch and long 30cm. The nitrogen gas is baked for 8 hours at 450°C, the nitrogen air velocity is 200h-1. The temperature is 300°C, then the tube type reactor is closed, the vacuum is extracted first, then the fluorine gas is passed, the amount of fluorine gas is more than equal to 3/2 times the ratio of the theoretical amount of tungsten gas and the quantity of the tungsten material, less than 5/2 times. The residual fluorine gas is absorbed by dry alkali lime and blown with nitrogen. A tungsten based catalyst was prepared for 2 hours.
Compared with the chromium based catalysts, tungsten based catalysts have the same properties and effects, but they are safe, environmentally friendly and harmless, and they are a good choice to replace the chromium based catalysts.

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