Hydrohalogenation of Pd/H-ZSM-5 Catalysts
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1221
decline faster on the HF-promoted catalyst (more diffusion
restricted) than on the HCl-promoted one, although the
xylenes were higher on the HF-promoted catalyst during
the lower temperature range where the diffusion effect is
not so significant.
valuable liquid yield.
Received December 25, 2006.
3.6. Hydrocracking Reactions
REFERENCES
The hydrocracking reaction includes; (1) a C-C bond
rupture followed by, (2) a hydrogenation step. The first step
requires strong acid sites, whereas the second step requires
active metal sites. The current Pd/H-ZSM-5 catalyst can be
said, with confidence, to acquire one of the most active hy-
drogenating metals (Pd),3,4 together with one of the most
strongly acidic zeolites (H-ZSM-5).1 However, although
the Pd/H-ZSM-5(HCl) and Pd/H-ZSM-5(HF) catalysts ac-
quire higher acid sites number and strength than their un-
treated version (Table 1), it is found that the latter catalyst
is most active for hydrocracking (Fig. 11). Both hydrohalo-
genated catalysts exhibit insignificantly different hydro-
cracking activities; however, the HF treated catalyst seems
slightly less active than the HCl treated one, which may be
attributed to acquiring a somewhat larger amount of AlNF
debris deposited in the zeolitic channels of this catalyst (as
explained above).
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4. CONCLUSION
CHE hydrogenation is a metal-catalysed reaction at
low-temperature; it is somewhat higher on Pd/H-ZSM-
5(HF) than on untreated Pd/H-ZSM-5, whereas Pd/H-
ZSM-5(HCl) is significantly less active. HF improves Pd
dispersion, whereas HCl decreases it. Isomerization, alkyl-
ation and hydrocracking reactions in CHE hydroconver-
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HF-treated Pd/H-ZSM-5 catalysts possess larger acid sites
number and strength than the untreated catalyst, they are
significantly less active for these reactions compared to the
untreated catalyst. HCl and HF doped Pd/H-ZSM-5 contain
amorphous AlNF debris, deposited mostly in the zeolitic
channels, hence, causing significant diffusion resistance
that reduces the rates of the reactions, particularly at higher
temperatures. The amorphous debris is highest in the HF-
treated but lowest in the untreated catalyst. Inhibition of the
hydrocracking activity via hydrohalogenation of Pd/H-
ZSM-5 catalyst can be considered an economic privilege,
since production of lighter gases is considered a loss of the
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