Comparative study of atmospheric and high pressure CO 2 reforming of methane over Ni/MgO-AN catalyst
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Catalysis Letters Vol. 99, Nos. 1–2, January 2005 (Ó 2005)
Comparative study of atmospheric and high pressure CO2 reforming of methane over Ni/MgO-AN catalyst Yu-He Wang and Bo-Qing Xu* Innovative Catalysis Program, Key Lab of Organic Optoelectronics & Molecular Engineering Department of Chemistry, Tsinghua University, Beijing 100084, China
Received 6 July 2004; accepted 16 September 2004
Catalytic activity of Ni/MgO-AN prepared from alcogel derived MgO was studied for the dry reforming of methane under atmospheric as well as high pressure (1.5 MPa). Different catalytic performances are observed in the atmospheric and high-pressure reactions; while the catalyst was highly active and extremely stable under atmospheric pressure it shows a self-stabilization process under high pressure. The self-stabilization process was characterized initially by a decrease in deactivation rate with increasing the reaction time-on-stream (TOS) up to ca. 12 h and then by a thereafter stabilization during the reaction. Characterizations of the coked catalyst with TPO, TEM, SEM, TPH and XRD techniques detected very little carbon deposits (ca. 0.2 wt% of the catalyst charge) on the used catalyst under atmospheric pressure. In contrast, large amount of whisker carbon deposit (ca. 100 wt% of the catalyst charge) were formed on the used catalyst under high pressure. In the high-pressure reaction, the activity decline during the initial stage was closely related to the amount of carbon deposits on the catalyst, which also became stabilized after the catalyst had served the reaction for ca. 12 h. The carbon deposits on the used catalyst in the high-pressure reaction contained two different components (a-carbon and b-carbon) while the carbon deposits in the atmospheric pressure reaction were in the form of a-carbon. No notable sintering of metallic nickel was detected by XRD on the used catalyst in the reaction under atmospheric pressure whereas unavoidable sintering of metallic Ni particles happened within the very first hours of the high-pressure reaction. KEY WORDS: carbon dioxide, deactivation, high pressure reforming of methane, natural gas, Ni catalyst, self-stabilization process.
1. Introduction There has been a great interest in recent years in the more efficient use of natural gas (methane) and the reduction of greenhouse gas (i.e. CO2 ) emission. The production of syngas (CO and H2 ) by CO2 reforming of methane (CH4 + CO2 = 2 H2 + 2 CO) over a heterogeneous catalyst is one of the routes for the utilization methane and CO2 resources [1–11]. The product mixture of this reaction from a stoichiometric (1:1) feed has, in comparison with steam reforming and partial oxidation, a low H2 /CO ratio (1:1) that is preferable for Fischer–Tropsch synthesis because high H2 /CO ratios favor methanation and suppress chain growth [10]. Since some reservoirs of natural gas even contain comparable concentrations of methane, the use of CO2 provides a convenient and cheap oxygen source, for the reforming of methane [11]. Great efforts have been made on
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