With the successful
preparation of γ-alumina with high-energy
external surfaces such as {111} facets, the crystal-facet effect of
γ-Al2O3 on surface-loaded CrO
x
has been explored for semihydrogenation of acetylene.
Our results indeed demonstrate that the harmonious interaction of
CrO
x
with traditional γ-Al2O3, the external surfaces of which are typically low-energy{110}
facets, has caused a highly efficient performance for semihydrogenation
of acetylene over CrO
x
/(110)γ-Al2O3 catalyst, whereas the activity of the CrO
x
/(111)γ-Al2O3 catalyst for acetylene hydrogenation is suppressed dramatically
due to the limited formation of active Cr species, restrained by the
high-energy {111} facets of γ-Al2O3. Furthermore,
the use of inexpensive CrO
x
as the active
component for semihydrogenation of acetylene is an economically friendly
alternative relative to commercial precious Pd catalysts. This work
sheds light on a strategy for exploiting the crystal-facet effect
of the supports to purposefully tailor the catalytic properties.
Access to aggregated Pt particles on the non-reducing support Al2O3 is essential for selective hydrogenation of chlorinated nitrobenzene to aniline chloride, whereas atomic platinum is nearly inactive.
The crystal-facet
effect of catalytic supports plays a crucial
role in tailoring the physicochemical properties of active sites and
the surface chemically bonded polymer can also regulate the local
environment around active sites for optimizing catalytic performance.
Herein, we report the effect of exposed facets of γ-Al2O3 supports and further modification by surface bonded
long-chain polydimethylsiloxane (PDMS) on the properties of CrO
x
/γ-Al2O3 catalysts
for selective oxidation of propene. The {111} facets of γ-Al2O3 stabilize “non-redox Cr3
+” and promote the overall oxidation rates compared
with catalysts on {110} facets of γ-Al2O3. The surface bonded PDMS, with grafting density being about 0.13
chains/nm2, endows a hydrophobic environment to facilitate
the enrichment of the hydrophobic substrate and the desorption of
hydrophilic products and occupies some acid sites on catalysts to
limit acid-catalyzed side reactions. The inherent liquidlike nature
of bonded PDMS also forms a setting that can regulate the redox ability
of surface Cr species, that lead to modified activation of oxygen
toward more surface adsorbed species. As a result, the modified catalysts
enhance the whole oxidation process with favorable formation of epoxide
product at low reaction temperatures (<225 °C). Our findings
highlight the impact of surface chemically bound polydimethylsiloxane
(PDMS) upon tailoring the surroundings of the catalyst surface, and
that combined with facet-effect of supports can tune the reaction
process toward selective ones.
Nanosheets of nickel doped SAPO‐34 molecular sieves in thickness of ∼10 nm (denoted as NS−Ni‐SAPO‐34) has been successfully prepared through a morphology‐reserved method of synthesis. A special aluminum phosphate in two‐dimensional layered structure is used as precursor and converts to crystallized SAPO‐34 molecular sieve, in nanosheet morphology reserved from the aluminum phosphate precursor, under hydrothermal conditions with tetraethyl orthosilicate and templates of mixed amines added. It is found that adequate amount of nickel, ∼5 wt %, added to the synthetic system is a key factor for the morphology‐reserved synthesis. By characterization, the nickel is proved to be doped in the framework of the molecular sieve, which more likely helps to balance the high surface energy of nanosheet products. The NS−Ni‐SAPO‐34 shows excellent catalytic performance for oxidation of cyclohexanone to adipic acid by gaseous oxygen.
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