Abstract
A series of Mg doped LaNiO3 nano particles by solids denoted as LaNi1-xMgxO3-δ (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8 and 1) were prepared by the modified citrate sol-gel method and investigated as catalysts for combine reforming of methane (CRM).The resulting oxides were examined by using XRD, BET, ICP, SEM, EDS, TEM, TPR and TGA techniques, under the condition of as-synthesized and used samples. The results showed that highly homogeneous and crystalline oxides with particle sizes in the range of nanometers were obtained through this synthesis method. The XRD patterns of the prepared LaNi1-xMgxO3-δsolids confirmed with increasing Mg amount not only perovskite structure could not form correctly but also the spinel (La2NiO4) and oxide phases (MgO and NiO) are produced on the sample surface. Also according to BET results, the presence of these oxide phases lead to the increase in the surface area of samples .Although, increasing in surface area had not a significant effect in results of activity tests. TPR analysis revealed that the reduction of the prepared samples became more difficult by increasing the degree of substitution (x). The effects of the partial substitution of Ni by Mg and reaction temperatures (600–800 °C) were investigated in CRM process, after reduction of the samples under hydrogen. Although, all catalysts, except LaMgO3, were found to be highly active toward the syngas production during the CRM process but substitution of Ni by Mg could not improve the catalytic activity of the LaNi1-xMgxO3-δ in this process. The catalytic activity in the steady state was found to decrease in the following order:
$${\text{LaNi}}{{\text{O}}_{\text{3}}} \gt {\text{LaN}}{{\text{i}}_{{\text{0}}{\text{.4}}}}{\text{M}}{{\text{g}}_{{\text{0}}{\text{.6}}}}{{\text{O}}_{{\text{3 - }}\delta }} \gt {\text{LaN}}{{\text{i}}_{{\text{0}}{\text{.6}}}}{\text{M}}{{\text{g}}_{{\text{0}}{\text{.4}}}}{{\text{O}}_{{\text{3 - }}\delta }} \gt {\text{LaN}}{{\text{i}}_{{\text{0}}{\text{.9}}}}{\text{M}}{{\text{g}}_{{\text{0}}{\text{.1}}}}{{\text{O}}_{{\text{3 - }}\delta }} \gt {\text{LaN}}{{\text{i}}_{{\text{0}}{\text{.8}}}}{\text{M}}{{\text{g}}_{{\text{0}}{\text{.2}}}}{{\text{O}}_{{\text{3 - }}\delta }} \gt {\text{LaMgO3 - }}\delta$$
Of course, according to the TPR and TGA results, the stability of the samples increased and the coke deposits on the catalyst surface decreased with increasing of x, respectively.
