The production of
carbon-rich hydrocarbons via CO
2
valorization
is essential for the transition to renewable, non-fossil-fuel-based
energy sources. However, most of the recent works in the state of
the art are devoted to the formation of olefins and aromatics, ignoring
the rest of the hydrocarbon commodities that, like propane, are essential
to our economy. Hence, in this work, we have developed a highly active
and selective PdZn/ZrO
2
+SAPO-34 multifunctional catalyst
for the direct conversion of CO
2
to propane. Our multifunctional
system displays a total selectivity to propane higher than 50% (with
20% CO, 6% C
1
, 13% C
2
, 10% C
4
, and
1% C
5
) and a CO
2
conversion close to 40% at
350 °C, 50 bar, and 1500 mL g
–1
h
–1
. We attribute these results to the synergy between the intimately
mixed PdZn/ZrO
2
and SAPO-34 components that shifts the
overall reaction equilibrium, boosting CO
2
conversion and
minimizing CO selectivity. Comparison to a PdZn/ZrO
2
+ZSM-5
system showed that propane selectivity is further boosted by the topology
of SAPO-34. The presence of Pd in the catalyst drives paraffin production
via hydrogenation, with more than 99.9% of the products being saturated
hydrocarbons, offering very important advantages for the purification
of the products.
The tandem process of carbon dioxide hydrogenation to methanol and its conversion to hydrocarbons over mixed metal/metal oxide-zeotype catalysts is a promising path to CO2 valorization.
Zinc-doped zirconia catalytic properties, promising toward CO 2 and CO hydrogenation, are commonly ascribed to the synergic interaction between Zn and Zr, yet an atomic-scale perspective on how this synergy is structurally realized remains elusive. In this work, to address this ongoing challenge, we deeply investigated the structure of three Zndoped ZrO 2 catalysts by combining powder X-ray diffraction (PXRD) and X-ray absorption spectroscopy (XAS). PXRD showed the complete formation of a tetragonal solid solution, undistinguishable by Rietveld refinement from the cubic polymorph. Fit of extended X-ray absorption fine structure (EXAFS) spectra at the Zr and Zn K-edges unveiled the presence of hexagonal/cubic ZnO nanoclusters embedded and chemically bonded to the tetragonal ZrO 2 matrix. The concentration of Zn dopant was evaluated via both PXRD and EXAFS analysis. In situ EXAFS study of the catalyst during activation further confirmed the presence of a chemical interaction at ZnO/ZrO 2 interface, most probably the active site toward CO 2 hydrogenation. The ZnO cluster radius was found to be in the 11−13 Å range, using the Greegor and Lytle spherical model. Taken together, the results demonstrate how the combination of X-ray techniques probing both long-range and local structural properties could unlock an unprecedented level of understanding in mixed metal oxide catalysts.
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