Promotional effect of Mg in trimetallic nickel-manganese-magnesium nanocrystalline catalysts in CO2 reforming of methane

In the present paper, the dry reforming reaction was studied over the 10 wt%Ni-3wt.%Mn-x wt.% Mg (x = 2, 4 and 6 wt%) catalysts supported on gamma-Al2O3 with mesoporous structure. The physicochemical characteristics of the samples were determined by XRD, BET, TPO, and SEM techniques. Mesoporous gamma-Al2O3 carrier with the high BET area (186 m(2)/g) was synthesized by a simple sol-gel method and the Ni, Ni-Mn and Mg promoted catalysts possessed nanocrystalline mesoporous structure with the BET area in the range of 127-176 m(2)/g. The average pore radius of the prepared catalysts were smaller than 11 nm. All the synthesized samples exhibited a CH4 conversion in the range of 60-65% at 700 degrees C. The small differences in methane conversion in all catalysts could be related to the same nickel loading. According to the TPR results, the Mg addition caused an increase in the reducibility of the nickel catalyst and the Mg-promoted sample exhibited a higher conversion compared to the monometallic catalyst, due to its higher reducibility. The results showed that the textural characteristics of the catalysts were affected by the content of Mg. The results indicated that the Ni-Mn/Al2O3 catalyst promoted by 4 wt% Mg showed the highest CH4 conversion in all studied reaction temperatures (550-700 degrees C). Furthermore, only one oxidation peak was detected for all catalysts in TPO analysis, which was related to the filamentous form carbon. The 10Ni/Al2O3 and 10Ni3Mn4Mg/Al2O3 catalysts exhibited the highest and the lowest amount of deposited filamentous carbon, respectively. The 10Ni3Mn4Mg/Al2O3 catalyst was stable during the 20 h time on stream without any decline in CH4 conversion. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.