The influence of support porosity on the selectivity of home-made 5%Pd-2%In/support (support = SiO 2 , Al 2 O 3 , TiO 2 ) catalysts in nitrate reduction was studied. The main final products of the reaction were N 2 and NH 4? . Together with the decrease in pore diameter, an increase in ammonia concentration in the reaction mixture was observed. It is probably caused by slow diffusion of OH -ions from narrow pores to the solution.
Thermal desorption of H 2 from the surface of Pd/support and Pd-Ag/support (support = Al 2 O 3 , SiO 2 ) catalysts has been investigated. Two wide desorption peaks can be observed for the 5%Pd/support catalyst. The presence of these peaks in the thermogram indicates that several adsorption states exist, which is the result of occurrance of different adsorption centers of specific bond strengths for hydrogen. The addition of silver to the palladium catalysts causes a considerable decrease in the size of the high temperature desorption peak. It is also worth noting that the temperature of the maximum of the desorption rate remains practically constant for all bimetallic catalysts studied. This means that the activation energy of the hydrogen desorption process does not change after the introduction of silver to the palladium catalyst.
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