Study of the interactions of Pd,In with SiO2 and Al2O3 mixed supports as catalysts for the hydrogenation of nitrates in water

This paper shows that the combination of Al2O3 and SiO2 as supports of Pd and In allows the modulation of the catalytic properties of nitrate hydrogenation in water in order to improve nitrate conversion and decrease the formation of ammonia. Mechanical mixtures of monometallic catalysts subjected to reduction in hydrogen at 450 °C are efficient catalysts when Pd is supported on Al2O3 and In is supported on SiO2, thus showing considerably high activity and selectivity to gaseous nitrogen compounds when the proportions are 75 wt.% of Pd/Al2O3 and 25 wt.% of In/SiO2. When these monometallic catalysts are reduced separately and then mixed in situ in the batch reactor, a moderate activity for nitrate reduction is obtained, suggesting that either some migration of In or Pd occurs in solution generating the bimetallic sites that are necessary to activate nitrateions, or that a loose contact between In and Pd is enough to initiate the reaction. This contact could be favored by the opposite pzc of both supports.

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► The combination of Al2O3 and SiO2 allows modulating the catalytic properties.
► Mixtures are efficient when Pd is supported on Al2O3 and In is supported on SiO2.
► Migration of In or Pd occurs in solution generating bimetallic active sites.