The influence of interaction between palladium and indium on the activity of Pd–In/Al2O3 catalysts in reduction of nitrates and nitrites

The influence of indium addition on the catalytic properties of palladium catalysts supported on Al2O3 in the reaction of nitrates reduction to nitrogen was studied. It was found that indium did not show any activity by itself, but acted as a “promoter” for the catalytic activity of monometallic Pd/Al2O3 catalysts. The X-ray diffraction (XRD) and Time-of-flight secondary ion mass spectrometry (ToF-SIMS) studies proved the existence of intermetallic interactions between Pd and In, which probably modified activity and selectivity of bimetallic catalysts in this reaction. The ToF-SIMS technique showed the presence of intermetallic compounds in all the studied bimetallic systems, which could not be proved by XRD measurements in the case of the systems with a small amount of indium.

Graphical abstractBimetallic Pd–In/Al2O3 catalysts are characterized by high activity in the reduction of nitrates and nitrites. However, systems containing the largest amount of indium (5%Pd–5%In/Al2O3) show poorer activity in the studied reactions. On the basis of our investigations, we can say that there are two effects which can influence activity of Pd–In/Al2O3 catalysts in the reduction of nitrates and nitrites: the formation of intermetallic phase and/or the increase in indium surface concentrations in those bimetallic systems.Figure optionsDownload full-size imageDownload as PowerPoint slide