C-O bond activation and splitting behaviours of CO₂ on a 4H-SiC surface: a DFT study

Conversion of CO2 into valuable chemicals can not only reduce the amount of CO2 in the atmosphere, but also realize the reuse of resources. It's well known that C-O bond activation and splitting are critical steps in the CO2 conversion process and it's crucial to employ an appropriate catalyst. Here, the adsorption and activation behaviors of a CO2 molecule on 4H-SiC surfaces were systematically investigated based on DFT calculations. Calculation results show that the CO2 molecule can anchor on 4H-SiC(0001) and (0001[combining macron]) surfaces. On the 4H-SiC(0001) surface, the adsorbed CO2 molecule prefers to dissociate with an energy barrier of 0.52-0.70 eV, producing an O adatom and a CO molecule on the surface. Further dissociation of the CO is hindered due to a large energy barrier of 2.12 eV. However, if a H atom is introduced, the CO molecule may combine with H into a CHO group and the reaction energy barrier is 1.69 eV. Moreover, the CHO group tends to transform into a CH group and an O adatom, a reaction in which a relatively low energy barrier of 0.09 eV needs to be surmounted. For the 4H-SiC(0001[combining macron]) case, the direct C-O bond dissociation energy barrier for CO2 is only 0.37 eV while further breaking of the C-O bond in CO is energetically unfavorable even with the help of a H atom. So the final products are an O adatom and CO chemisorbed on the 4H-SiC(0001[combining macron]) surface. All the calculation results demonstrate that the inert CO2 molecule can be effectively activated on both the 4H-SiC(0001) and (0001[combining macron]) surfaces and different splitting products could be obtained on the two different surfaces, implying that SiC is an applicable catalyst material for CO2 conversion with high efficiency and product selectivity.