CO2 Reforming of CH4 Using Coke Oven Gas over Ni/MgO-Al2O3 Catalysts: Effect of the MgO:Al2O3 Ratio

Abstract

Research is being actively conducted to improve the carbon deposition and sintering resistance of Ni-based catalysts. Among them, the Al2O3-supported Ni catalyst has been broadly studied for the dry reforming reaction due to its high CH4 activity at the beginning of the reaction. However, there is a problem of deactivation due to carbon deposition of Ni/Al2O3 catalyst and sintering of Ni, which is a catalytically active material. Supplementing MgO in Ni/Al2O3 catalyst can result in an improved MgAl2O4 spinel structure and basicity, which can be helpful for the activation of methane and carbon dioxide molecules. In order to confirm the optimal supports’ ratio in Ni/MgO-Al2O3 catalysts, the catalysts were prepared by supporting Ni after controlling the MgO:Al2O3 ratio stepwise, and the prepared catalysts were used for CO2 reforming of CH4 (CDR) using coke oven gas (COG). The catalytic reaction was conducted at 800 °C and at a high gas hourly space velocity (GHSV = 1,500,000 h−1) to screen the catalytic performance. The Ni/MgO-Al2O3 (MgO:Al2O3 = 3:7) catalyst showed the best catalytic performance between prepared catalysts. From this study, the ratio of MgO:Al2O3 was confirmed to affect not only the basicity of the catalyst but also the dispersion of the catalyst and the reducing property of the catalyst surface.

Effect of Sr Incorporation and Ni Exsolution on Coke Resistance of the Ni/Sr–Al2O3 Catalyst for Dry Reforming of Methane

“…The evident desorption peak in the temperature range of 800–1000 °C is attributed to strong basic sites such as bidentate carbonate species, which react with surface carbon species generated, for example, in the methane decomposition reaction (CH 4 → C + H 2 ), resulting in lower carbon deposition. ,,,, It is noteworthy that Sr promotion resulted in peaks in the range of ≈800 to 900 °C (Figure B,D), which were obviously related to the strong basic site, leading to an increase in the total peak area. ,,,,, The increased peak area signifies a higher amount of CO 2 adsorption, combination, and dissociation, resulting from the enhanced basicity of the catalysts. In addition, strongly basic sites are widely known to have beneficial effects on the activation of CO 2 , ,,− ,, that is, oxygen species generated from CO 2 dissociation and/or bidentate carbonate species on the basic sites are accepted by the surrounding oxygen vacancies . Hence, a large amount of CO 2 adsorption can contribute to the production of a significant amount of oxygen species.…”

“…17,18,20,23,40,55 The increased peak area signifies a higher amount of CO 2 adsorption, combination, and dissociation, resulting from the enhanced basicity of the catalysts. In addition, strongly basic sites are widely known to have beneficial effects on the activation of CO 2 , 16,24,[26][27][28][29][30]39,55 that is, oxygen species generated from CO 2 dissociation and/or bidentate carbonate species on the basic sites are accepted by the surrounding oxygen vacancies. 23 Hence, a large amount of CO 2 adsorption can contribute to the production of a significant amount of oxygen species.…”

“…The characteristics of DRM catalysts significantly affect their performance, such as their activity, stability, and resistance to deactivation. ,,, First, carbon formation, mostly caused by methane cracking, is well-known to be strongly dependent on the number of acidic sites. − Thus, improving the basicity of DRM catalysts strengthens their resistance to carbon formation owing to the promoted adsorption of weakly acidic CO 2 . ,− This leads to the formation of CO and oxygen species that can oxidize the deposited carbon . Our group also conducted research on improving the basicity of Ni/Al 2 O 3 catalysts by adding various alkaline earth metals such as Mg and Ca .…”

Applications of Al2O3‐Based Nano‐Catalysts in Thermocatalytic CO2 Transformations: Impacts of Surface Acidity and Basicity

“…[166][167] 2). [57] Interestingly, regarding the support only, MG70 (MgO : Al 2 O 3 = 7 : 3) possessed a higher amount of CO 2 desorbed than MG30 (154.3 vs. 58.8 cm 3 /g cat ); however, after the Ni deposition, Ni/MG30 turned to be the best in terms of the CO 2 desorption (9.7 cm 3 /g cat ), which could be attributed to the highest reduction degree (96 %) according to the lowest reduction temperature in TPR profiles (Figure 8a) since NiOÀ MgO solid solution possibly formed in the presence of a large content of MgO (Ni/MG70). [168] Different from the coprecipitation and impregnation to dope MgO into Ni/Al 2 O 3 catalyst as above, hydrothermal synthesis was applied to promote the in-situ growth of NiÀ MgÀ Al layered double hydroxides (LDHs) on the Al 2 O 3 substrate with Al 2 O 3 as the Al 3 + source.…”

“…In this scenario, promoters act as a modifier to tune the interaction between metals and Al 2 O 3 , such as the addition of MgO into Ni/Al 2 O 3 to optimize the amount of NiAl 2 O 4 , thus enhancing the Ni dispersion and accelerating the reaction kinetics. [57] More importantly, the intrinsic acidity of Al 2 O 3 retards the CO 2 adsorption but promotes the CÀ H bond breaking; as a result, carbon formation is probably faster than CO 2 dissociation, thus deactivating the catalysts since the metal sites are covered and pores are blocked by the carbon deposits. [58][59] To address this issue, considerable efforts have been dedicated into modifying the Al 2 O 3 supported metal catalysts via adjusting the acidic and basic sites.…”