Curbed Reactivity of Co-doped (Nb⁵⁺ and Rh³⁺) Catalyst in the Dry Reformation of Methane

In the dry reforming of methane (DRM), metal doping is used as one of the important methods to modulate the catalyst performance. In this paper, we synthesized two types of catalysts, Rh doped TiO₂ (RTO) and Rh/Nb co-doped TiO₂ (RNTO), and evaluated their performances in DRM. The CH₄ and CO₂ conversion of 79% and 95% in RTO were both higher than that in RNTO (the CH₄ and CO₂ conversion of 73% and 87%) as working for 80 h. The characterizations of XRD, TEM, XPS, EPR, BET, and TPR were carried out to determine the structure of catalysts. We found that the creation of the oxygen vacancies is favorable in Rh solely doped TiO₂ but restricted by Rh/Nb co-doping. The XPS results verified that Rh⁴⁺ and Rh³⁺ were presented in RTO, while only Rh³⁺ can be observed in RNTO. Due to the co-doping of Nb, the Rh induced charge perturbation was balanced by Nb⁵⁺ rather than the deprivation of electrons from O²⁻, therefore the state of Rh³⁺ was stabilized and the content of oxygen vacancies were decreased which resulted in attenuated activity in the DRM reaction.