Catalytic combustion of methane on novel catalysts derived from Cu-Mg/Al-hydrotalcites
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Catalysis Letters Vol. 99, Nos. 3–4, Feburary 2005 (Ó 2005) DOI: 10.1007/s10562-005-2108-6
Catalytic combustion of methane on novel catalysts derived from Cu–Mg/Al-hydrotalcites Zheng Jiang,1 Zhengping Hao,1,* Junjie Yu,1 Hongxia Hou,1 Chun Hu1 and Jixin Su2 1
Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, P.R. China 2 Environmental Sciences and Engineering School, Shandong University, Ji’nan, 250100, P.R. China
Received 17 May 2004; accepted 5 October 2004
Novel Cu–Mg/Al mixed oxides (designated as i-CMAO-800) were prepared by calcinations of Cu–Mg/Al-hydrotalcites [(Cu2þ +Mg2þ )/Al3þ = 3] at 800 C. Their performance for the catalytic combustion of methane was investigated. The oxides and their precursors were characterized by XRD, TG-DSC, TPR and N2 adsorption/desorption techniques. The results showed that BET surface areas and the stability of the resultant oxides were greatly influenced by the copper contents in hydrotalcite precursors, bringing about difference in their activities for methane catalytic combustion. XRD results indicated that Cu was highly dispersed in hydrotalcite precursors in case of low copper contents, (Cu 40 wt%). For higher Cu contents, Cu(OH)2 was formed, and, consequently, a separate phase of CuO was detected in the oxide catalysts after calcination. As indicated by the TG-DSC results, different decomposition behaviors were observed for various hydrotalcites. Thermal calcination promoted the formation of copper aluminates and segregation of CuO from the bulk phases. TPR results showed 15CMAO-800 has the highest reduction rate, and the catalytic activities of iCMAO-800 mixed oxides depend on both the reduction rates and the amounts of copper ions in mixed oxides. The catalyst 15-CMAO-800 showed the best performance. KEY WORDS: methane catalytic combustion; copper-containing oxides; hydrotalcites.
1. Introduction Hydrotalcite-like compounds (HTLCs), which are also called anionic clays or Layered Double Hydroxides III (LDHs), can be formulated by MII (OH)2 1x Mx n II 2þ 2þ (A )x=n yH2 O, where M = Cu , Ni , Co2þ , Zn2þ , and Mn2þ ; MIII = Al3þ , Fe3þ , Cr3þ , Ga3þ , In3þ , V3þ , Ru3þ , and Rh3þ , and An are anions existing in layers [1–5]. Hydrotalcite-like anionic clays are good function materials used as adsorbents, ion exchangers, base catalysts, and potential precursors of mixed oxides for catalytic application, because these compounds can be easily converted into well-mixed oxides via calcination [1–4] In recent years, some new hydrotalcites with substitution of Mg2þ by Zr4þ , Ti4þ or Sn4þ etc, have been synthesized [1,3,6–8]. The interesting properties of these materials depend on their specific brucite-like octahedral layered structures. Transition metal oxides derived from hydrotalcite anionic clay precursors have been widely used as heterogeneous catalysts because of their highly uniform distribution of cations, their fairly high surface areas and their great potential to be modified to obtain good catalytic properties [1,3].
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