Enhanced catalytic activity for methanol synthesis from CO2 hydrogenation by doping indium into the step edge of Rh(211): A theoretical study

The doping of foreign metals can modify the electronic properties of the original catalyst surfaces, thereby changing the catalytic activity. Realistic surfaces possess many defects, such as step sites. Herein, the first-principles calculation is implemented to research how indium doping on stepped Rh(211) alters the catalytic activity for methanol synthesis. The calculated substitution energy shows that the indium atom tends to be doped at the step edge of Rh(211). Almost all species prefer to adsorb at the step-edge sites because the surface atoms at the step-edge possess the lowest coordination number. The electronic structure analysis demonstrates that the activation degree of CO2* chiefly relies on the charge transfer between CO2* and catalyst. Furthermore, the doped indium atoms make In/Rh(211) expose more H* adsorption sites and promote the relative stability of adsorbed species on In/Rh(211). Besides, the doping of indium significantly inhibits the generation of by-product CO*, and enables the activation barrier to be as low as 0.98 eV for the rate-determining step on In/Rh(211), which is much lower than that of some reported catalysts. The ultrahigh catalytic activity of In/Rh(211) might be attributed to the decrease of the work function induced by the doping of indium, enhancing the relative stability of reaction species and CO2* activation degree.

Automated summary

The electronic properties of catalyst surfaces can be modified by doping with foreign metals, leading to changes in catalytic activity. In this study, first-principles calculations were used to investigate how indium doping affects the catalytic activity of stepped Rh(211) for methanol synthesis. The results showed that indium atoms preferentially dope at the step edge of Rh(211). Adsorption of species was found to occur mainly at the step-edge sites due to the lowest coordination number of surface atoms at the step edge. The activation degree of CO2* was found to depend on the charge transfer between CO2* and the catalyst. The presence of indium atoms increased the number of H* adsorption sites on In/Rh(211) and promoted the relative stability of adsorbed species. Additionally, indium doping significantly inhibited the generation of by-product CO*, resulting in a low activation barrier for the rate-determining step on In/Rh(211). The ultrahigh catalytic activity of In/Rh(211) could be attributed to the decreased work function induced by indium doping, enhancing the relative stability of reaction species and the activation degree of CO2*.