Hydrogenation catalyst presulfidation reaction principle

Hydrogenation catalyst presulfidation is a very complex exothermic reaction. The basic research and application of hydrogenation catalyst presulfidation is a very active research field so far. No matter which pre-vulcanization method is used, the most fundamental vulcanizing agent is H2S, so as long as it is easy to provide H2S under pre-vulcanization conditions, such as organic sulfides with low relative molecular weight, they can be used as vulcanizing agents. The pre-vulcanization process is usually divided into two steps: the decomposition of the vulcanizing agent:

CH3SSCH3+3H2→2CH4+2H2S

CS2+4H2→CH4+2H2S

Metal Phase Transformation:

MoO3+H2+2H2S>MoS2+3H2O

3NiO+2H2S+H2>Ni3S2+3H2O

9CoO+8H2S+H2>Co9S8+9H2O

WO3+2H2S+H2>WS2+3H2O

The effect of presulfidation on the hydrogenation catalyst is to change the metal component in the catalyst from an oxidized state to a sulfurized state, such as Co into an active species Co8S9: to make the metal component in the catalyst in the most correct active valence state, with W as Example. W6+ of WO3 is changed into W4+ of active species WS2 after presulfurization. It is generally believed that there are two kinds of radon-adding active centers of catalysts related to sulfur, that is, sulfur vacancies related to Mo and Ni active vacancies related to NiMoS. Sulfurization increases these two active vacancies, which increases the hydrogenation activity. Judging from the surface dispersibility of metal ions, the sulfurized catalyst improves the metal ions of the catalyst, so that the hydrogenation activity is significantly improved. Moreover, the acid density of the catalyst changed after sulfidation, which increased the hydrogenation activity. Practice has proved that with the progress of sulfuration reaction, the activity of the hydrogenation active center increases rapidly, and continuous sulfur supplementation can make the catalyst activity more stable.