Effect of NH3 Alkalization and MgO Promotion on the Performance of Ni/SBA-15 Catalyst in Combined Steam and Carbon Dioxide Reforming of Methane

Abstract

In this work, 31.4 wt.% Ni/SBA-15 (Ni/SBA-15) nonpromoted and alkalized with ammonia solution and by MgO promoter catalysts were prepared and used for combined steam and CO2 reforming of CH4 (bireforming). Effect of concentration of ammonia solution (NH3(aq)) (10–25 vol.%) and Mg content (3–12 wt.%) on the properties of the Ni/SBA-15 catalysts was investigated by low-angle and powder X-ray diffraction (XRD), N2-BET isothermal adsorption, SEM, TEM, EDS mapping, H2-TPR, and CO2-TPD methods. The performance of the catalysts in bireforming was assessed in the temperature range of 550–800°C. The enhancement of dispersion of NiO particles, reducibility, and basicity of alkalized Ni/SBA-15 catalysts were responsible for improving the catalytic performance of this catalyst. The results revealed that the Ni/SBA-15 treated with 15-25% NH3(aq) solution and promoted with 3-9% Mg exhibited high activity for CH4 conversion. Meanwhile, Ni6Mg/SBA-15 showed the highest CO2 conversion. Among tested catalysts, Ni/SBA-15-20NH3 and Ni9Mg/SBA-15 samples had an almost equal activity with a CH4 conversion of nearly 97% and a CO2 conversion of about 84% at 700°C thanks to its moderate affinity with both CO2 and CH4. However, the H2/CO ratio of the product mixture remained at 2.02 on the Ni/SBA-15-20NH3 catalyst and almost 1 on the Ni9Mg/SBA-15 sample. These results might be related to the fact that the alkalization of the Ni/SBA-15 catalyst by NH3(aq) solution had an advantage over using MgO because side reactions were unlikely to occur.

Effect of Support on Stability and Coke Resistance of Ni-Based Catalyst in Combined Steam and CO2 Reforming of CH4

“…On all catalysts weak, moderate, and strong basic sites exist, of which the weak basic sites predominate. 20 − 23 Thus, from the obtained results in Table 1 , the decreasing order of the basicity of the catalysts is as follows: Ni/Mg–SBA ≫ Ni/CeO 2 > Ni/SBA > Ni/Mg–Al. The outstanding high basicity of the Ni/Mg–SBA sample can be attributed to the contribution of the alkaline additive MgO and the small particle size caused by the superior specific surface area of the support and the highly ordered channel structure of SBA-15.…”

“…Meanwhile, the silica framework of the SBA-15 support is verified by the broad amorphous silica peak located at 20–30° 25 on the XRD patterns of two SBA-15-supported catalysts. 22 , 23 …”

“…The SEM and TEM images ( Figure S2 ) demonstrate that the rod-shaped structure of CeO 2 still exists in the Ni/CeO 2 sample. 24 The preservation of the ordered hexagonal channels of the SBA-15 support after impregnation of nickel and magnesium precursors and high-temperature treatments 22 , 23 ensures the good stability of the prepared SBA-15 support. However, the shift of the diffraction peak at 2θ = 0.9° to a higher value (2θ = 1.1°) on the narrow-angle XRD pattern of Ni/SBA 22 indicates the grafting of NiO onto SBA-15.…”

“…On the basis of the results obtained in the prior publication, 23 in this report, long-term stability tests of Ni catalysts supported on CeO 2 , SBA-15, MgO-α-Al 2 O 3 , and MgO-SBA-15 in the BRM reaction have been conducted. The carbon deposited and the changes of the catalyst’s characteristics during the reaction have been investigated.…”

“…18 The high activity and stability of Mg-modified Ni/Al 2 O 3 catalysts are due to the beneficial effects of MgO such as enhancement of steam adsorption, basic property, nanosized NiO crystallite, and strong interaction between Ni and the support. 19 In our previous studies, NiO catalysts supported on various supports such as α-Al 2 O 3 promoted by MgO, 20 CeO 2 of different morphologies, 21 mesoporous nanosilica SBA-15, 22 and MgO-promoted SBA-15 23 have been prepared and investigated for dry and bireforming of methane. The results show that the superior activity of NiO supported on CeO 2nanorods (CeO 2 -NR) has been attributed to the stronger interaction of NiO with CeO 2 -NR.…”