We present a comprehensive
mechanistic study on the highly tunable
selectivity over In
x
/ZrO2 catalysts
in CO2 hydrogenation. By variation of the indium loading
between 0.1 and 5 wt %, either an admirable selectivity to methanol
of 70–80% or up to 80% selectivity to CO could be obtained
in the temperature range of 250–280 °C. It is shown that
the shift in the product spectrum is related to the synergy between
indium species and the zirconia substrate through variable interfacial
structures. Zirconia-modulated crystalline In2O3, which prevails for indium loadings between 2.5 and 5 wt %, could
enhance stepwise hydrogenation of *HCOO, leading to *H3CO and finally methanol due to the suitable bonding strengths of
*HCOO and *H3CO. Regarding CO, evidence has been provided
that the synergistic effect between adjacent indium and zirconia sites
is indispensable for the entire catalytic cycle. *HCOO is formed at
the indium–zirconia interfaces and decomposes to CO subsequently.
Highly dispersed InO
x
dominating for loadings
below 0.5 wt % features an enormous indium–zirconia interface
and suppresses hydrogenation ability for *HCOO, thus favoring the
generation of CO. The study provides fundamental insights into the
mechanism of CO2 conversion and reaction pathway tuning
over oxide catalytic systems.
Novel hyperbranched polyselenides with multi-catalytic sites at the branching units have been synthesized which may provide a new approach towards glutathione peroxidase mimics.
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