Preparation of monodispersed NiO particles in SBA-15, and its enhanced selectivity for reverse water gas shift reaction

The preparation of monodispersed NiO particles in SBA-15 using the direct hydrothermal synthesis method with various combinations of metallic salt precursors and acids was investigated in detail. With NiO/SBA-15 containing less than 1 wt% NiO, the NiO particles were monodispersed in the SBA-15 framework using the HCl + Ni(NO₃)₂ combination, whereas when the NiO amount exceeded 2 wt%, the NiO particles aggregated. However, with NiO/SBA-15 containing less than 25 wt% NiO, the NiO particles were monodispersed in the SBA-15 framework using the HCl + NiSO₄ combination, whereas when the NiO amount exceeded 30 wt%, the NiO particles aggregated. In addition, the reverse water gas shift (RWGS) reaction was studied using NiO/SBA-15 obtained by different combinations. Regardless of the combination and temperature, the CO selectivity was 100% using monodispersed NiO particles. In the presence of aggregated NiO particles, the CO selectivity was 100% only at high temperature; by contrast, the CO selectivity was less than 100% at low temperature. To achieve high CO₂ conversion and 100% CO selectivity, the HCl + Ni(NO₃)₂ combination was not desired due to small metal loading, whereas the HCl + NiSO₄ combination was necessary owing to large metal loading. Moreover, NiO/SBA-15 had relatively high thermal stability.