Chemisorption hydrogen sulphide

Another method for determination of the nickel area is based on chemisorption of hydrogen sulphide [389], Hydrogen sulphide is the stable sulphur compound at conditions for tubular reforming. It is the most severe poison for the reaction (refer to Section 5.4). The adsorption of hydrogen sulphide on nickel is rapid even below room temperature [376] [381]. At temperatures of industrial interest hydrogen sulphide is chemisorbed dissociatively on nickel. 

Figure 4.5 Nickel surface areas determined by chemisorption of hydrogen and hydrogen sulphide, respectively (using procedures described with test) [415]. Reproduced with the...

A similar behaviour has been observed for other systems including the chemisorption of hydrogen sulphide on other metals (Ag, Fe, Cu, Co, Ru, Pt) [523],... 

Equilibrium constants for Reaction (5.26) are shown in Appendix 2. The equilibrium constant at 700 C is 3.3 10, which means that even a small amount of hydrogen will inhibit the conversion of hydrogen sulphide. Therefore, sulphur removal following this reaction pattern requires a total oxidation of the catalyst. If some part of the nickel surface is still exposed to the gas, hydrogen formed by Equation (5.14) will cause hydrogen sulphide to be retained at the surface by the chemisorption reaction [377] [389]. 

The activation energy in the SPARG reaction in the presence of sulphur in Figure 5.45 is estimated to 227 kJ/mol and the value of the sulphur-free test is 110 kJ/mol. This can be explained by the heat of chemisorption of hydrogen sulphide by comparing the rate expressions for the sulphur-poisoned and the sulphur-free catalysts. 

Y-Alumina supported unpromoted catalyst molybdenum sulphide and promoted catalysts cobalt sulphide - molybdenum sulphide nickel sulphide - molybdenum sulphide were prepared by Precipitation From Homogeneous Solution (PFHS) technique using thioacetamide hydrolysis in a single step. Oxygen chemisorption studies, hydrodesulphurisation (HDS) and hydrogenation (HYD) studies were made for these cat alyst s. These catalysts do not need pre-sulphidation prior to HDS reaction. 

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