Catalysis 2022 issue

optimising the gas composition to the right H 2 S/SO 2 ratio and space velocity, performance may likely be enhanced further. Recently, Shell Catalysts & Technologies published a paper on effective activation of alumina based low temperature tail gas catalysts. 4 Although the reported sulphiding and test conditions are not identical to what are prac- ticed at Euro Support’s labs, a useful benchmarking of results is provided. Generally speaking, the start-up and test conditions in Euro Support’s tests are somewhat more stringent to the catalyst, when com- pared with Shell’s reported stress test. In Figure 4 , the data, as reported by Shell for a “representative low temperature TGU catalyst”, is com - pared with our own test results for titania- and alumina based catalysts under comparable start-up and operating conditions. Here, activity is represented by the average CO and COS conversion as a fraction of the calculated equilibrium con- version. 5 The data from Shell show a clear decrease in hydrogenation activity when sulphidation temper- ature or hydrogen gas concentration are decreased. Full conversion (99% of equilibrium) is only achieved after activation at 300°C in 10% H 2 , which is not realistic under normal conditions. The best performing alu - mina based catalyst only reached 79% of the equilibrium conversion under optimal sulphiding condi- tions, as applied in our tests. Euro Support’s new generation titania- based CoMo catalysts compare favourably to all the alumina based counterparts. Already at a sulphid- ing temperature of 240°C (meaning no exotherm in the bed), 97% of the equilibrium conversion is reached. If a minor exothermic reaction is experienced, that drives the temper- ature to 260°C, the catalysts reach full (99%) CO and COS conver - sion. Under all circumstances, the TiO 2 -CoMo catalyst performs sig- nificantly better than any alumina- based CoMo catalyst. The dashed line in Figure 4 repre- sents the normalised CO and COS activity for this catalyst after expos- ing the catalyst to standard Claus

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Figure 3 Catalyst performance at T in = 240°C of TiO 2 -CoMo after exposure to the indicated maximum temperature. For the TiO 2 -CoMo catalyst no start-up procedure was applied, while for the Al 2 O 3 -CoMo the performance after best possible in-situ start-up is shown

tail gas at T in = 270°C for four hours its performance roughly matches that of Al 2 O 3 -CoMo after the best possible in-situ start-up. When the temperature was increased slightly, the performance could be enhanced even further. Although more research will be performed in the near future, these results already indicate that it is feasible to be able to start a fresh TiO 2 -CoMo TGTU catalyst without performing a specific start-up procedure. By

240°C when no start-up treatment is performed. Activity is shown as a function of temperature (ΔT) that the catalyst was exposed to for four hours in the same Claus tail gas that was also used for the activity tests. The Al 2 O 3 -CoMo catalyst after best possible in-situ sulphidation at 300°C is included in the figure for comparison. It was found that when Euro Support’s new generation of TiO 2 - CoMo catalyst is exposed to Claus

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Figure 4 Averaged CO and COS conversion activity as percentage of the equilibrium conversion as function of the activation temperature and hydrogen gas concentration during start-up for low temperature TGTU catalysts TiO 2 -CoMo and CoMo-Al 2 O 3 compared to experimental data as reported by Shell 4

38 Catalysis 2022