How Doping Affects the Activity of the Aluminum Oxide Support

Doping may affect both how the H₃C−H bond is broken and where is the destiny of the so-formed methyl group.

Abstract

The performance of heteronuclear clusters [AlXO₃]⁺ (X=Al, AlO₄, AlMg₂O₂, AlZnO, AlAu₂, Mg, Y, VO, NbO, TaO) in activating methane has been explored by a combination of high–level quantum calculations with reported and supplementary gas-phase experiments. With different dopants in [AlXO₃]⁺, the mechanism, reactivity and selectivity towards methane activation varies accordingly. The classic HAT competes with PCET, depending on the composition of intramolecular interactions. Although the existence of terminal oxygen radical is beneficial for classic HAT, the Al_t−C interaction in the [AlXO₃]⁺ clusters as enhanced by the strongly electronegative doping groups (X=Al, AlZnO, Mg, Zn, VO, NbO, TaO) favors the PCET process, facilitating C−H bond breaking. In addition, with different dopants, the destiny of the split methyl group varies accordingly. While strong interaction between Al_t and CH₃ results in the formation of the Al_t−C bond, dopants with variable valance may promote the formation of deep-oxidation products like formaldehyde. It has been discussed in detail how to regulate the activity and selectivity of the active center of the catalyst via rational doping.

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