JNGC 21-2012-29

Negative effect of Ni on PtHY in n-pentane isomerization
evidenced by IR and ESR studies

Ni/PtHY with different Ni loadings was prepared by impregnating HY with hexachloroplatinic acid solution and Ni2+/N,N-dimethylformamide
solution. An increase in the Ni loading decreased the crystallinity, specific surface area and meso-micropores of the catalysts. Ni interacted
with hydroxyl groups to produce IR absorption bands at 3740−3500 cm−1. Increasing Ni loadings resulted in a decrease in the intensities of
the broad bands at 3730−3500 cm−1 and the sharp band at 3740 cm−1 with simultaneous development of new absorbance band at 3700 cm−1
that was attributed to (–OH)Ni. The acidity of the samples did not significantly change with Ni loadings up to 1.0 wt%, which indicated that
Ni mostly interacts with non-acidic silanol groups (terminal- and structural-defect OH groups). The presence of Ni decreased the activity of
PtHY toward the isomerization of n-pentane because of a decrease in the number of active protonic-acid sites that formed from molecular
hydrogen. IR and ESR studies confirmed that Pt facilitated the formation of protonic-acid sites from molecular hydrogen, whereas Ni, even
when combined with Pt, didn’t exhibit such ability. The absence of protonic-acid sites from molecular hydrogen significantly decreased the
yield of iso-pentane and markedly increased the cracking products.