In
this study, we described the synthesis, characterization, and
application of hyperbranched polymer-encapsulated metal nanoparticles
(HEMNs) as integrated catalysts for the supercritical cracking of
hydrocarbon fuels. The metal precursor was extracted into the organic
phase using a hydrocarbon-soluble hyperbranched poly(amidoamine) (CPAMAM)
and then reduced in situ by NaBH4 to produce HEMNs with
virtually a single-size distribution. The monitoring of the preparation
process by UV–vis demonstrated the feasibility of this encapsulation
approach, and the successful synthesis of three different types of
HEMNs, metal (Pd, Pt, Au)@CPAMAM, reflected the universality of this
method. Compared with the existing catalyst octadecylamine-stabilized
Pd nanoparticle, Pd@18N, HEMNs were superior in every aspect. The
new encapsulation method allowed metal NPs to have a smaller particle
size beneficial to their overall specific surface area and a higher
proportion of active surface atoms for a better catalytic activity.
Moreover, the space-limiting effect of the polymer allowed the three
HEMNs to be highly dispersed in decalin and exhibited admirable stability
under storage tests for up to 12 months and high-temperature stability
tests at 180 °C. During the supercritical cracking of decalin,
Pd@CPAMAM possessed a much better catalytic performance than Pd@18N
and CPAMAM (which can also be used as a macroinitiator). To obtain
the same heat sink of 3.02 MJ/kg, the temperature could be lowered
from 725 to 701, 693, and 699 °C for Pd, Pt, and Au HEMNs, respectively.
Pt HEMN turned out to be the best due to its excellent catalytic dehydrogenation/cracking
performance, with the conversion of decalin increasing from 22.3 to
50.7% and the heat sink rising from 2.18 to 2.62 MJ/kg with the existence
of 50 ppm Pt@CPAMAM, at 675 °C. The significant enhancements
were ascribed to the synergistic catalysis through the remarkable
abilities of nanometals to catalyze dehydrogenation/cracking of fuel,
the supercritical stabilization effects from CPAMAM, and the
initiation effects of the hyperbranched polymer CPAMAM.