Catalytic combustion of methane over mixed oxides derived from Co–Mg/Al ternary hydrotalcites

Abstract

Co x Mg 3 − x /Al composite oxides (xCoMAO-800) were prepared by calcination of Co x Mg 3 − x /Al hydrotalcites (x = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, respectively) at 800°C. The materials were characterized using XRD, TG-DSC, N 2 adsorption-desorption and TPR. The methane catalytic combustion over the xCoMAO-800 was assessed in a fixed bed micro-reactor. The results revealed that cobalt can be homogenously dispersed into the matrices of the hydrotalcites and determines the structure, specific surface areas and porosity of the derived xCoMAO-800 oxide catalysts. The thermal stability and homogeneity of the hydrotalcites markedly depends on the cobalt concentration in the hydrotalcites. The Co-based hydrotalcite-derived oxides exhibit good activity in the catalytic combustion of methane. The catalytic activity over the xCoMAO-800 oxides enhances with increasing x up to 1.5, but subsequently decreases dramatically as cobalt loadings are further increased. The 1.5CoMAO-800 catalyst shows the best methane combustion activity, igniting methane at 450°C and completing methane combustion around 600°C. The catalytic combustion activity over the xCoMAO-800 oxides are closely related to the strong Co-Mg/Al interaction within the mixed oxides according to the TG-DSC, TPR and activity characteristics.© 2009 Elsevier B.V. All rights reserved.The catalytic combustion of methane has attracted intensive interests in the past few decades, due to its higher energy conversion efficiency and ultra-low emissions of environmental pollutants, such as NO x , CO, and unburned hydrocarbons [1][2][3][4][5][6]. In addition, catalytic combustion of lean methane gas to abate methane emission also has wide-ranging applications [5,7]. For the effective and stable catalytic combustion process, suitable catalysts play a crucial role. Generally, supported noble metal oxides, particularly palladium oxide, are excellent catalysts for lower temperature combustion, but noble metals are expensive and prone to deactivation owing to sintering, decomposition and undesirable interaction with supports under hydrothermal situations encountered in combustion [3,6,[8][9][10]. A variety of inexpensive transition metal oxide catalysts, such as solid solution oxides [11][12][13], perovskites [14][15][16], pyrochlores [17][18][19] and hexaaluminates [7,[20][21][22] have been explored for catalytic combustion of methane. Unfortunately, no single catalyst, so far, can tolerate the stringent hydrothermal conditions existing in methane combustion. Obviously, the further development of new combustion catalysts is indispensable. Currently, multi-staged combustion methodology are used to overcome the drawbacks of the current catalysts for catalytic combustion [2,3], in which the catalysts of high surface area and activity are highly desired to ignite methane at lower temperatures and sustain stable combustion at high temperatures.Among the transition metal oxide catalysts, cobalt-based oxides are ones of the most active catalysts in catalytic methane combustion, and Co...

Catalytic Decomposition of Methane Over M–Co–Al Catalysts (M = Mg, Ni, Zn, Cu)

“…The second weight loss occurred between 250 and 300°C and was related to dehydroxylation of interlayered OH -groups and the decomposition of interlayered hydroxycarbonates. The released gases led to the degradation of the layered structures of the hydrotalcites, and a porous mixed oxide was formed [26,27].…”

Cu/Mn-based mixed oxides derived from hydrotalcite-like precursors as catalysts for methane combustion

“…A number of works address the role of the catalyst preparation method and the nature of the oxide precursor [15,19,20,30,31,33,[40][41][42][43]. In particular, the use of precursors related to the naturally occurring mineral known under the name of hydrotalcite has been indicated as providing particularly active mixed oxide catalysts [24,27,34,35,39,45,46]. Natural hydrotalcite is a layered magnesium aluminium hydroxy carbonate, but the structure can accommodate a number of other cations, in a broad range of ionic radii [48].…”

“…For this reason the materials have been recognized as particularly promising precursors of mixed oxide catalysts [49]. In the case of hydrotalcite-derived catalysts tested for methane combustion the use of Co, Mn, Fe, Ni, or Cu incorporated as main components into the precursor structure has been reported [24,27,34,35,39,45,46]. In the majority of works the investigated catalytic systems contained one transition metal introduced into the Mg-Al hydrotalcite structure.…”

Development of Hydrotalcite Based Cobalt Catalyst by Hydrothermal and Co-precipitation Method for Fischer-Tropsch Synthesis

“…Another weight loss occurs around 280 to 370 °C. The second weight loss is mainly because of elimination of hydroxyl group (OH -) from inlaid water molecules [24,25].…”