Iron-modified low-percentage alumina-supported rhenium technetium catalysts: Methods for the control of their efficiency in alkane C-H bond activation

The influence of the method of iron introduction into M-Fe/Al2O3 (M = Re, Tc) catalysts, conditions of the treatment of a sample or support Fe(NO3)(3)/Al2O3 (in an air or H-2 atmosphere, time, and temperature), as well as the Fe/M ratio on the efficiency in the process of high paraffin (n-decane and n-dodecane) dehydrogenation, was studied. Three series of M-Fe/Al2O3 catalysts were studied ([M] = 0.05-0.26 at. %, [Fe] = 0.5-10 at. %). These catalysts were prepared by coimpregnation (K-c series) or by the deposition of Re or Tc on iron-modified gamma-Al2O3, which was preliminarily calcined in an air or hydrogen atmosphere (K-o and K-H series, respectively). The activity ranking of the catalysts in the reaction is K-o > K-c > K-H. An increase in the temperature of M-Fe/Al2O3 catalyst reduction with H-2 from 500 to 900 degrees C leads to an increase in the catalyst activity by a factor of 2-4 at [Fe] = 1-2 at. %. For the catalysts with higher iron concentration (greater than or equal to 5 at. %), the activity usually decreases. Only the K-o-series catalysts ([Fe] = 1-2 at. %) are more active than the analogous K-c-series Pt-Fe/Al2O3 catalysts. The introduction of iron leads to an increase in the activity and selectivity toward the dehydrogenation reaction and to a decrease in the temperature of reduction by 100-200 degrees C, which is required to reach the same activity in the reaction of high paraffins as for unmodified M/Al2O3 samples. The catalytic effects can be explained by the formation of bimetallic particles Re-0-Fe-0 or Tc-0-Fe-0 on the surface of gamma-Al2O3.