Mechanistic study of Cu-Ni bimetallic catalysts supported by graphene derivatives for hydrogenation of CO2 to methanol

The Cu-Ni bimetallic catalyst supported by graphene derivatives was employed to explore the reaction mechanisms of converting CO2 to methanol. Their properties were analyzed by Raman, XRD, XPS, TG-DSC, TEM and CO2-TPD. Cu or Ni catalyst supported by graphene oxide (GO) tended to combine with defects, leading to less defects of Cu-GO and Ni-GO. So does reduced graphene oxide (rGO). However, ammonia modified graphene (NGO) presented more defects compared to GO and rGO. These changes showed that the functional group and metal ion had been introduced. In addition, more active component (Cu-) could be detected in rGO supported catalyst. In GO and rGO, the addition of Ni could promote the reduction of Cu2+, while Ni showed inhibitory performance in NGO. CuNi-rGO and CuNi-NGO could chemically activate more CO2 at lower temprerature. These catalysts could lower the activation energy of CO2 by 40 %. Most of Ni and Cu dispersed uniformly on supports. In rGO, the size of Cu-Ni was less than 20 nm. In NGO, the size was 50-100 nm. Which means more activation component could been exposed to reactant gas on rGO and it was a better support. Compared with literature, the adsorption capacity of CO2 could increase 76.92 % maximally. In the catalytic test, CuNi-rGO showed a CO2 conversion of 7.87 % and the methanol selectivity of 98.7 % at 498 K and 4.0 MPa, which exhibited a competitive performance compared with other catalysts in literatures.

Automated summary

In this study, Cu-Ni bimetallic catalyst supported by graphene derivatives was used to convert CO2 to methanol. Different graphene derivatives affected the catalyst performance, with Cu-Ni catalyst on rGO showing higher active component. CuNi-rGO and CuNi-NGO could chemically activate more CO2 at lower temperature and reduce its activation energy.