Preferential catalyst testing

Pore blockage by carbon or heavy products may cause a loss in activity over time. Niemela and Krause39 reported a loss of turnover frequency for Co/Si02 FTS catalysts due to preferential blocking of the narrowest catalyst pores by carbon. Puskas74 found unusually high amounts of wax in the pores on a Co/Mg/ diatomaceous earth catalyst tested in the FTS at 190°C, 1-2 bar, H2/CO = 2.55 for 125 days. In a separate study it was concluded that pore plugging by the waxy products resulted in a fast deactivation of such catalysts.75... 

Dudfield ef al. [328] investigated various catalysts for preferential oxidation in a test reactor that had a design similar to a macroscopic shell and tube heat-exchanger. The catalysts tested are summarised in Table 4.3. The feed, at 10 Lmin , composed of... 

More information on the nature of active sites was obtained using some model catalysts obtained by incipient wetness impregnation of a commercial silica (Si-1803 with surface area = 300 nP g ). A preliminary test performed using the support (Table 39.6) showed a very low selectivity to MDB, with the preferential formation 2-EMP, indicating that acid sites alone are not able to promote the cyclization of the intermediate. 

As an application of Pt nanowires in heterogeneous catalysis, we performed preferential oxidation (PROX) of CO as a test reaction [32]. The PROX reaction is useful for PEM fuel cells for the selective removal of contaminating CO from hydrogen gas, because CO works as a strong catalyst poison for Pt electrode catalysts (Figure 15.24). H2 produced in steam-reforming and the water-gas shift reaction needs further to be purified in the PROX reaction to selectively oxidize a few% CO towards inert CO2 in a H 2-rich atmosphere, to reduce the CO content to <10ppm. Under the PROX conditions, the facile oxidation of H2 to H2O may also occur, thus the catalyst selectivity for CO oxidation over H2 oxidation is an... 

Recent evaluations of S02 oxidation over noble metal catalysts (Pt, Pd, and Rh) have given some information on one particular secondary reaction. It was observed in car tests that S03 formation under the conditions of automobile exhaust is highly vulnerable to catalyst deactivation either by thermal sintering or by poisoning (78, 79). At the same time, the data indicated a lesser sensitivity of CO and hydrocarbon oxidation to catalyst aging. The results were confirmed in laboratory experiments (80). This is one example of preferential suppression of an undesirable side reaction. Obviously, the importance of a given poison on the different secondary reactions will vary widely with catalyst formulation and operating conditions. 

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