CO high-temperature shift catalysts

The concentrations of CO (10%-50%) are different in the synthesis gases produced from different feedstock. CO must be removed because it is a poison for ammonia synthesis catalysts. Generally, CO is converted via reaction with steam to form CO2 and H2 over a catalyst, and then CO2 is removed. The reaction between CO and steam over a catalyst is called CO shift reaction as shown in Eq. (1.16). 

In modern ammonia plant, it commonly adopts two-step shift processes, i.e., high-temperature shift and low-temperature shift. High-temperature shift reaction is run over Fe-Cr catalysts at 350°C-500°C, while low-temperature shift reaction is carried out over Cu-Zn catalysts at 200°C-280°C. The concentration of CO in the synthesis gas is reduced to 2%-3% over the high-temperature shift catalyst, and 

0% over the low-temperature shift catalyst. The residual 0.5%-1.0% CO is further reduced to trace level (below 10 x 10 ) by methanation in the following procedure to meet the requirement for ammonia synthesis catalyst. 

In the late 1960s, with the development of gasification technology which uses heavy oil and coal as raw materials, high sulfur content in synthesis gas led to the deactivation of Fe-Cr high-temperature shift catalyst. Thus, sulfur tolerant Co-Mo shift catalysts have been developed and applied widely since then. The catalysts are active in the temperature range of 160°C-500°C, and also are called wide temperature-range shift catalysts. 

Fes04 is an active component of high-temperature shift catalysts. Iron oxides prepared by different methods have different compositions and crystal phase. Some results show that the catalysts derived from the precursors of 7 — Fe203 and Fe (0H)3 — are the most active ones. 

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