Oxidative condensation of methane in the presence of modified MnNaW/SiO2 catalysts

Abstract

The effects of cationic (Ce, Zr, and La) and anionic (S, P, and Cl) admixtures on the activity and physicochemical properties of MnNaW/SiO 2 were studied in order to optimize the composition of a catalyst for the oxidative condensation of methane (OCM). It was found that OCM process characteristics can be reg ulated by varying the type (Ce, Zr, La, S, P, and Cl) and concentration (0.5-5 wt %) of a modifying admix ture. For the modified MnNaW/SiO 2 catalysts, the yield of the target reaction products increased in the fol lowing order of modifying admixtures: S < Zr < P < Ce < La < Cl. The addition of lanthanum, cerium, or phosphorus admixtures insignificantly affected the activity of the MnNaW/SiO 2 catalyst, whereas the intro duction of sulfur or zirconium led to a decrease in the yield of C 2 hydrocarbons. Modification with chlorine improved process characteristics and shifted a maximum yield of C 2 hydrocarbons to the low temperature region. It was established that the introduction of lanthanum considerably improved the stability of catalyst operation. The catalyst composition 2Mn-1.6Na-3.1W-2La/SiO 2 was developed to afford a 22% yield of target C 2 hydrocarbons at a 54% conversion of methane after a 24 h reaction performed under optimum conditions (reaction temperature, 800°C; reaction mixture flow rate, 117 mL min -1 and O 2 /CH 4 molar ratio, 0.5).

Silica material variation for the MnxOy-Na2WO4/SiO2

“…100 mg catalyst diluted in 1.5 ml quartz sand and the feed gas composition of CH 4 :O 2 :N 2 = 4:1:4 was used for the experiments. [20,29,31,32,38,43], it has been also presented similar or lower C 2 yield values (5-16%) in some publications [28,33,48,49]. The scattering in catalytic activity results can be clearly seen in Figure 12 However the reason of this fact can be explained that catalytic activity results for the OCM depends strongly on the different factors, e.g.…”

Real-time multi-length scale chemical tomography of fixed bed reactors during the oxidative coupling of methane reaction

“…The multi-length-scale chemical CT experiments presented in this study showed that the La can play this role by trapping the mobile/volatile Na + and WO4 2species by forming this new crystalline phase (NaLa(WO4)2). More importantly, these new results is a major breakthrough in the OCM catalyst design; not only the integrity of catalyst is maintained during the operating conditions but also the catalyst activity is not impaired by the addition of the La components 32,33 . The latter could be attributed to the fact that the OCM reaction process is generally accepted to be based on methane activation at the catalyst surface and gas-phase recombination of methyl radicals.…”

“…Ghose et al achieved 27 % C2 yield, one of the highest reported values for fixed bed reactors in literature, using a 5 % La-10 % Na2WO4-5 % Mn/SiO2 catalyst 32 . More importantly, the presence of La was shown to provide a higher performance of Mn-Na-W/SiO2 catalyst in the OCM reaction as well as improve its stability 32,33 . However, it is still not clear how the La promoter leads to this enhancement in catalyst performance.…”

“…There are only a few studies available where the effects of promoting the Mn-Na-W/SiO2 catalyst with La have been investigated [31][32][33][34] . Wu et al were the first to study the La-Na-W/SiO2 catalysts and it was shown that the catalytic performance is significantly enhanced when compared to the La-free catalyst (i.e.…”

Control of Ni/Ce1-xMxOy Catalyst Properties Via the Selection of Dopant M = Gd, La, Mg. Part 2. Catalytic Activity

“…It was shown that modification of supports is an effective way to control the catalyst performance in reforming of fuels [24][25][26][27][28][29][30]. This study is devoted to the elucidation of the role of support composition in autothermal reforming of ethanol over Ni/Ce 1-x Gd x O y , Ni/Ce 1-x La x O y and Ni/Ce 1-x Mg x O y catalysts.…”